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STEFANO NUZZO

Ricercatore t.d. art. 24 c. 3 lett. B
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

2024 - Multi-physics and multi-objective optimization of a permanent magnet-assisted synchronous reluctance machine for traction applications [Articolo su rivista]
Puglisi, Francesco; Barbieri, SAVERIO GIULIO; Mantovani, Sara; Devito, Giampaolo; Nuzzo, Stefano
abstract

This contribution addresses the rotor design process of a Permanent Magnet-assisted Synchronous Reluctance Machine by adopting a multi-physics and multi-objective optimization algorithm. A Finite Element (FE) approach is employed to determine the electromagnetic and structural responses during the optimization. In particular, a detailed FE structural modeling is used, which often is based on simplifications and inaccuracies in the available literature. A genetic algorithm is adopted, with the objectives being the maximization of the mean torque, the minimization of the torque ripple and the minimization of the stress in the rotor. A parametric analysis of the geometric features precedes the optimization to establish the design variables which mostly affect the machine performance, and thus to reduce the computational cost of the optimization. The presented methodology consists of a useful tool for the final stages of the design process, and provides a rotor with a torque ripple reduced by 15.1% compared to an existing design used as a benchmark, while the mean torque and the maximum stress remain the same as the original configuration.

2023 - AC Losses Analysis and Design Guidelines for Hairpin Windings with Segmented Conductors [Articolo su rivista]
Pastura, Marco; Notari, Riccardo; Nuzzo, Stefano; Barater, Davide; Franceschini, Giovanni
abstract

2023 - Multi-objective Optimizations of Copper and Aluminum Hairpin Windings: a Comparison [Relazione in Atti di Convegno]
Cutuli, Gregorio; Nuzzo, Stefano; Zou, Tianjie; Franceschini, Giovanni; Gerada, Chris; Barater, Davide
abstract

2023 - Optimal Sizing of Hairpin Conductors in highway operation with PWM power supply [Relazione in Atti di Convegno]
Notari, R.; Devito, G.; Bernardi, F.; Pastura, M.; Barater, D.; Nuzzo, S.
abstract

Nowadays, one of the key challenges in the design of electric drives' components is the reduction of high losses at high- frequency operations. The aim of this work is to investigate the AC losses in hairpin windings (HWs) triggered by a space vector pulse width modulation (SVPWM) during both maximum torque per Ampere (MTPA) and flux-weakening (F-W) operations of an interior permanent magnet synchronous motor (PMSM). The ensuing additional losses are evaluated and a fast methodology for the conductor sizing is illustrated. Subsequently, after evaluating the harmonic content of the current feeding the electric motor, estimated considering a standardized highway driving cycle, the losses are assessed using analytical and finite element methods (FEM) and then compared with an HW layout taken as benchmark. The results demonstrate that HWs, when appropriately sized, can significantly reduce AC losses compared to conductors optimised for low-speed extra-urban conditions.

2023 - Performance Analysis of a Permanent Magnet Motor with Continuous Hairpin Winding [Relazione in Atti di Convegno]
Soltani, M.; Nuzzo, S.; Barater, D.; Nardo, M. D.
abstract

The global decarbonization targets require increasingly higher levels of efficiency, torque and power density, reliability, etc. of electrical machines intended for transport applications. Recently, hairpin windings are receiving more and more interest from both industry and academia, as they are a promising solution to achieve the above requirements altogether. However, a number of challenges still need to be addressed, including electromagnetic, thermal and manufacturing aspects. One of these is the reliability of the welding process, where the solution could be adopting continuous hairpin windings. However, these result in open slot designs or special stator arrangements, which can produce undesirable effects in motors, such as ripple torque, increased permanent magnet losses, etc. This paper aims at comparing the main electromagnetic performance metrics for a conventional hairpin winding, wound onto a benchmark stator with a semi-closed slot opening design, and a continuous hairpin winding, where the slot opening is open. Finally, the adoption of semi-magnetic slot wedges is investigated and aimed at improving overall motor performance.

2023 - Potential of Powertrain Electrification in a mid-size Tractor for a more sustainable agriculture [Relazione in Atti di Convegno]
Sassetti, R.; Ferrante, S.; Lenzini, N.; Nuzzo, S.; Fiorati, S.; Barater, D.
abstract

Nowadays, global warming and emission regulations are leading manufacturers and scientific community interests towards off-highway vehicles electrification. This work provides potentials evaluation of powertrain electrification applied to a mid-size tractor. Modelling tools are exploited to perform simulations. Given the lack of standardized working cycles, field data measurements are exploited to build 6 different working cycles representative of specific tractor working conditions. A full hybrid series architecture with a thermostat control logic is investigated as a possible solution for a mid-size tractor. As result, a performance comparison is made between the traditional Internal Combustion Engine and the proposed electrified powertrain. Benefits are evaluated in terms of engine efficiency and fuel consumption.

2023 - Preliminary Sensitivity Analysis and Optimisation of a Wound Field Synchronous Motor for Traction Applications [Relazione in Atti di Convegno]
Petrelli, G.; Nuzzo, S.; Barater, D.; Zou, T.; Franceschini, G.; Gerada, C.
abstract

The automotive field is switching to electric propulsion to guarantee a more efficient and sustainable transportation. Several motor configurations can be adopted for this purpose. Permanent magnet-based motors are usually preferred, but they are the most expensive and the least sustainable, especially when rare-earth materials are employed. Wound Field Synchronous Motors (WFSMs) represent an interesting alternative for their reduced costs, excellent field controllability, acceptable torque performance and inherent fault tolerance. Most importantly, being a rare-earth free technology, they fit with the ever more stringent sustainability demands required by the automotive sector. The aim of this research is to highlight the influence that rotor design parameters of a traction WFSM have on the performance in terms of average torque and torque ripple. To this purpose, multi-objective optimisations are performed. Future study will also focus on cost, weight, efficiency, and sustainability.

2023 - Rare Earth Materials Reduction in a Hypercar Propulsion System [Relazione in Atti di Convegno]
Devito, G.; Puglisi, F.; Barater, D.; Nuzzo, S.; Giacalone, M.; Franceschini, G.
abstract

Low-usage and rare earth free high-performance machines are in high demand, pushed by increasing costs and supply issues of rare earth materials. High torque density and high efficiency are key requirements in traction field. The challenge is designing propulsion systems which achieve such objectives while pursuing a global optimization logic in costs. This paper fits into this context by proposing a solution in which the same interior permanent magnet motor design is used for a four-wheel drive of a hypercar. A proper adaptation in axial length and magnets arrangement of the rear axle motor makes it suitable for the front axle requirements. Electromagnetic finite element analyses are performed to test different solutions with and without ferrite magnets. Torque, torque ripple, base speed, efficiency and rare earth reduction are the outputs under investigation. The best configurations are further studied via finite element structural analyses, as well as they are subjected to vibrational considerations. Different eligible solutions are found out with good performance while achieving a reduction in rare earth usage by 45.5%.

2023 - Refined Structural Design and Thermal Analyses of a High-Speed Wound-Field Generator for the More Electrical Aircraft [Relazione in Atti di Convegno]
Guiducci, A.; Barbieri, S. G.; Nuzzo, S.; Barater, D.; Berni, F.; Cicalese, G.; Fontanesi, S.; Franceschini, G.
abstract

2023 - Review and Future Developments of Wound Field Synchronous Motors in Automotive [Relazione in Atti di Convegno]
Petrelli, G.; Nuzzo, S.; Zou, T.; Barater, D.; Franceschini, G.; Gerada, C.
abstract

Electric motors are increasingly spreading in the automotive sector, following the progressive electrification of transportation aimed to reduce CO2 emissions and increase sustainability. Most of the employed motors are permanent magnets (PM) based and these materials are subjected to price fluctuations. In addition, they are not the key for sustainability, especially when referring to rare earth materials. An alternative to the classic PM motors is the wound field synchronous machine (WFSM) which, thanks to the absence of magnets, represents an inherent more sustainable solution. In addition, this machine presents higher controllability and fault tolerance compared to their PM counterpart, which on the other hand features higher torque density and efficiency values. While WFSMs have been widely adopted and studied as power generators in grid-connected and isolated power plants, their use as traction motors is limited and under investigation. This paper aims to resume the state of the art of WFSMs and to analyze the challenges of its employability in the automotive field. Possible future developments, contextualized considering the authors' vision, will be also discussed.

2023 - Upgrade of Exciter for Synchronous Generators basing on the Hybrid Excitation Concept [Relazione in Atti di Convegno]
Nuzzo, S.; Arces, V.; Bolognesi, P.
abstract

In the classical brushless arrangement, the field current of wound-field synchronous generators (SGs) is provided by exciters through rotating diode rectifiers. The control of the SG field current is achieved indirectly by regulating the field current of the exciter, whose excitation winding is stationary. This paper investigates the possibility to equip the exciter with hybrid excitation by adding surface-mounted permanent magnets (PMs). While a hybrid PM-field winding exciter has already been proposed in a recent work, where the selected condition was the rated no-load operation of the SG, in this paper the PMs are designed to sustain the generating set (genset) operation at a suitably selected load condition. This permits to further reduce the excitation losses of the exciter and to operate the genset even in case of full failure in the exciter field system, including the related electronic controller.

2022 - A Simplified Analytical Approach for Hybrid Exciters of Wound-Field Generators [Articolo su rivista]
Devito, Giampaolo; Nuzzo, Stefano; Barater, Davide; Franceschini, Giovanni
abstract

2022 - AC losses reduction in Hairpin Windings produced via Additive Manufacturing [Relazione in Atti di Convegno]
Notari, R.; Pastura, M.; Nuzzo, S.; Barater, D.; Franceschini, G.; Gerada, C.
abstract

2022 - Analysis and Mitigation of AC Losses in High Performance Propulsion Motors [Articolo su rivista]
Hebala, Ahmed; Nuzzo, Stefano; Connor, Peter H.; Volpe, Giuseppe; Gerada, Chris; Galea, Michael
abstract

In this paper, the AC copper losses in classical random windings are investigated and mitigated using several techniques across a range of permanent magnet synchronous motor designs. At high operating frequencies, AC copper losses can represent a substantial share of the total loss in electrical machines, thus, reducing the machine's overall performance, and increasing the thermal loading. Recently, different approaches for modelling AC copper losses have been proposed. This paper utilises simulation software to quantify the expected AC losses in six different propulsion motor designs. The motor designs are then modified to reduce the AC winding losses through the implementation of five different methods. Using two-dimensional finite element analysis, the magnetisation direction, magnet to airgap ratio, copper stranding, magnetic wedges and the motor slot openings are modified to reduce AC losses. The paper considers distributed, fractional, slot and concentrated windings, and the results show promising reductions across these different winding configurations.

2022 - Analysis of Voltage Distribution and Connections within a High-Frequency Hairpin Winding Model [Relazione in Atti di Convegno]
Pastura, Marco; Nuzzo, Stefano; Barater, Davide; Franceschini, Giovanni
abstract

2022 - Combined Magnet Shaping and Asymmetries in Surface-Mounted Permanent Magnet Machines for Improved Torque Performance [Relazione in Atti di Convegno]
Devito, Giampaolo; Nuzzo, Stefano; Barater, Davide; Soltani, Mohammad; Franceschini, Giovanni
abstract

2022 - Investigation of the Temperature Effects on Copper Losses in Hairpin Windings [Articolo su rivista]
Soltani, M.; Nuzzo, S.; Barater, D.; Franceschini, G.
abstract

2022 - Mitigation of AC Winding Losses for Aircraft Propulsion Motors [Relazione in Atti di Convegno]
Hebala, Ahmed; Nuzzo, Stefano; Connor, Peter H.; Volpe, Giuseppe; Gerada, Chris; Galea, Michael
abstract

2022 - On the AC Losses in the End Conductors of Hairpin Windings [Relazione in Atti di Convegno]
Pastura, Marco; Notari, Riccardo; Nuzzo, Stefano; Barater, Davide; Franceschini, Giovanni
abstract

2022 - On the Fault Tolerance and PM Demagnetisation of a High-Performance Aircraft Propulsion Motor [Relazione in Atti di Convegno]
Hebala, Ahmed; Nuzzo, Stefano; Connor, Peter H.; Gerada, Chris; Galea, Michael
abstract

2022 - Output Voltage Overshoot Suppression Control for Multilevel Inverter Architectures [Relazione in Atti di Convegno]
Bernardi, Fabio; Lorenzani, Emilio; Savi, Filippo; Nuzzo, Stefano; Barater, Davide
abstract

2022 - Segmented Hairpin Topology for Reduced Losses at High Frequency Operations [Articolo su rivista]
Preci, Eraldo; Nuzzo, Stefano; Valente, Giorgio; Gerada, David; Barater, Davide; Degano, Michele; Buticchi, Giampaolo; Gerada, Chris
abstract

2021 - 3D lumped parameter thermal network for wound-field synchronous generators [Relazione in Atti di Convegno]
Wang, Y.; Nuzzo, S.; Gerada, C.; Zhao, W.; Zhang, H.; Galea, M.
abstract

This paper proposes a 3D lumped parameter thermal network capable of estimating the temperature distribution in classical, salient-pole wound-field synchronous generators. The developed 3D lumped parameter thermal network can be used for the thermal design and/or analysis of any wound-field synchronous generator geometry, thus offering certain degrees of flexibility.As the accurate estimation of the loss distribution is critical for the accuracy of the proposed 3D lumped parameter thermal network, an electromagnetic finite element model is used in this paper as loss determination tool for an off-the-shelf 400 kVA generator considered as a case study. The simulated losses are validated against experimental measurements to safely include them in the developed network. Finally, the stator and rotor temperatures evaluated through the 3D lumped parameter thermal network are also validated by comparing them against experimental results.

2021 - A Consequent-Pole Hybrid Exciter for Synchronous Generators [Articolo su rivista]
Nuzzo, Stefano; Bolognesi, Paolo; Decuzzi, Giovanni; Giangrande, Paolo; Galea, Michael
abstract

2021 - A Multi-Objective Design Optimization for a Permanent Magnet Synchronous Machine with Hairpin Winding Intended for Transport Applications [Articolo su rivista]
Soltani, Mohammad; Nuzzo, Stefano; Barater, Davide; Franceschini, Giovanni
abstract

2021 - Analytical modelling of harmonics in an exciterless synchronous generator [Relazione in Atti di Convegno]
Fallows, D.; Nuzzo, S.; Galea, M.
abstract

2021 - Considerations on the preliminary sizing of electrical machines with hairpin windings [Relazione in Atti di Convegno]
Soltani, M.; Nuzzo, S.; Barater, D.; Franceschini, G.
abstract

Although the standard preliminary sizing of electrical machines equipping random windings is well consolidated and is worldwide acknowledged to be a good starting point for the design, there is no proof of accuracy and confidence when it comes to hairpin windings. This winding technology is gaining extensive attention due to its inherently high slot fill factor, good heat dissipation, strong rigidity, and short end-windings. These features make hairpin windings a potential candidate for some traction application to enhance power and/or torque densities. In this paper, a comparative design is done using the classical sizing tools available in literature between two surface-mounted permanent magnet synchronous machines, one featuring a random winding and one with a hairpin layout. The study aims at highlighting the hairpin winding challenges at high frequency operations and at showing limits of applicability of these standard approaches when applied to this technology. For verification purposes, finite element evaluations are also performed.

2021 - Design and thermal assessment of a high performance electric motor for racing applications [Relazione in Atti di Convegno]
Rossi, N.; Matteazzi, N.; Petti, G. L.; Fazzini, L.; Nuzzo, S.; Barater, D.; Franceschini, G.
abstract

Recently, an increasing attention in electric and hybrid vehicles is taking place. In order to raise awareness and technical knowledge on vehicles with reduced carbon footprint, several electric car competitions have been launched. Formula SAE is one of these, where talented students from different universities around the globe compete to design a fully electric racing car. This requires the development of high power density drives, with accurate electromagnetic and thermal analyses.This paper presents the design process and the thermal assessment of a high-performance electric motor intended for a FSAE racing car. The starting requirements for the electromagnetic and thermal designs are based on realistic available data from previous competitions and championship regulations.

2021 - Design of a High-Speed Wound-Field Synchronous Generator for the More Electric Aircraft [Relazione in Atti di Convegno]
Pasquinelli, M. G.; Bolognesi, P.; Guiducci, A.; Nuzzo, S.; Galea, M.
abstract

2021 - Design of the propulsion system for a formula sae racing car based on a brushless motor [Relazione in Atti di Convegno]
Devito, G.; Nuzzo, S.; Barater, D.; Franceschini, G.; Papini, L.; Bolognesi, P.
abstract

Today, an ever-increasing interest in electric propulsion is occurring due to the need of decarbonizing the society in order to avoid a catastrophic climate collapse. To raise awareness on this challenge, Formula SAE, an international university competition in engineering design, has also established an electric propulsion championship. This paper proposes a low budget motor propulsion system for Formula SAE racing cars. The design is based on realistic data available from previous race editions and suitably analyzed for the application at hand. Besides the budget limitation, which constitutes the main design guideline in this work, a set of constraints imposed by the race regulations are considered. Consequently, the performance requirements are defined, and the ensuing propulsion motor design is carried out through a preliminary analytical sizing followed by a finite-element validation and refinement. A good trade-off between cost and performance is achieved in terms of motor design and overall propulsion system architecture.

2021 - Energy Storage System Selection for Optimal Fuel Consumption of Aircraft Hybrid Electric Taxiing Systems [Articolo su rivista]
Recalde, A.; Lukic, M.; Hebala, A.; Giangrande, P.; Klumpner, C.; Nuzzo, S.; Connor, P. H.; Atkin, J.; Bozhko, S.; Galea, M.
abstract

Aircraft taxiing is conventionally performed using the main engines’ inefficient idle thrust. Therefore, in line with greener aviation, the electrification of taxiing is the most viable option to reduce emissions, noise, and fossil fuel consumption during ground operations. This paper studies the potential of hybridising the conventional electric taxiing system, which is currently driven by the Auxiliary Power Unit, with an electrical energy storage system, comprising commercial high-energy and high-power lithium-ion batteries, for the purpose of reducing fuel consumption. Hence, a power distribution optimisation is formulated to minimise fuel consumption over a typical worst-case taxi-out profile. Three different energy management strategies are presented for a narrow-body aeroplane. The optimisation is performed for the selection of off-the-shelf batteries so that their impact on fuel savings can be evaluated in the early design stage. The study showed that a wide range of savings is achievable according to the selected strategy, the added weight allowance, and the battery characteristics. Considering a 180 kg added weight allowance and covering the three investigated strategies, up to 72% of taxiing fuel is saved.

2021 - Evaluation of Inverter Architectures for Output Voltage Overshoot Reduction in WBG Electric Drives [Relazione in Atti di Convegno]
Savi, F.; Barater, D.; Nuzzo, S.; Franceschini, G.
abstract

The electrification of Non Road Mobile Machinery (NRMM) has brought to light several challenges for electrical actuation systems currently in use, above all their low power density. To hit the required targets, a strong increase of the performance, for both machines and drives, will be required. On the power electronic side, wide bandgap devices promise to enable much higher operating frequencies and temperatures, that can drastically cut down on the size of heatsinks and all magnetic components. However, their fast transition times produce an increased electric stress on the stator insulation system, which can experience partial discharges in some cases, thus quickly degrading. This paper strives to thoroughly compare several drive architectures that can mitigate this challenge, guiding the topology choice by analyzing power efficiency, ability to limit or eliminate overvoltages, reliability of the inverter structure and costs.

2021 - Exciterless Wound-Field Medium-Power Synchronous Machines: Their History and Future [Articolo su rivista]
Fallows, D.; Nuzzo, S.; Galea, M.
abstract

2021 - Hairpin Windings: An Opportunity for Next-Generation E-Motors in Transportation [Articolo su rivista]
Nuzzo, Stefano; Barater, Davide; Gerada, Chris; Vai, Pier
abstract

2021 - Hairpin windings: Sensitivity analysis and guidelines to reduce ac losses [Relazione in Atti di Convegno]
Preci, E.; Gerada, D.; Degano, M.; Buticchi, G.; Gerada, C.; Nuzzo, S.; Barater, D.
abstract

Nowadays, electrification in the transportation sector is one of the most viable solutions to reduce CO2 emissions and meet fuel economy requirements. Being the electrical machine one of the most important players in this electrification trend, extensive research is currently being dedicated to the improvement of their efficiency and power density. In automotive applications, hairpin technologies are widely spreading due to their potential in reducing costs and life cycles in a mass production perspective, as well as in increasing the torque capabilities of machines. However, several challenges need to be addressed before the complete replacement of random windings with hairpins can take place. Of these challenges, the loss produced during high frequency operations is one of the most limiting. This paper aims at studying and investigating high frequency (AC) losses for different slot geometries and conductor cross sections, which in turn involve the analysis of different slots-per-pole-per-phase / layers-per-slot combinations. In addition, the effects on the AC losses of reducing the slot fill factor are studied, either by removing the closest conductors to the slot opening or by reducing the hairpin legs' height. Analytical and numerical models are employed to investigate these concepts.

2021 - Improved propulsion motor design for a twelve passenger all-electric aircraft [Relazione in Atti di Convegno]
Hebala, A.; Nuzzo, S.; Connor, P. H.; Giangrande, P.; Gerada, C.; Galea, M.
abstract

This paper investigates the design of a 12-seater aircraft electric propulsion motor (ProMo). The design procedures aim to improve the performance of a previously designed motor, while adding further restrictions to the electrical and thermal boundaries. The main targets are to achieve the required output power of 550 kW, low torque ripple and an efficiency higher than 97%. The proposed procedures include an optimum slot/pole combination study, investigation on the winding configuration and connection, scaling of the airgap thickness and permanent magnet (PM) thicknesses, and finally minimising of the motor volume. The electromagnetic design is performed through a finite element electromagnetic software package, whereas the thermal analysis uses a lumped parameter thermal network-based. The mechanical stress above the rated speed of 2000 rpm is also examined. The final design fulfils the design requirements and meets the electrical and thermal constraints.

2021 - Integrated Damper Cage for THD Improvements of Variable Speed Salient-Pole Synchronous Generators for the More Electric Aircraft [Articolo su rivista]
Wang, Y.; Nuzzo, S.; Gerada, C.; Zhang, H.; Zhao, W.; Galea, M.; Galea, M.
abstract

Wound field synchronous generators have been implemented as aircraft main AC power generation for decades. The trend of moving towards more electric aircraft made DC and variable frequency AC buses favorable for the next generation power systems in aircraft, as opposed to constant frequency AC grid systems. The minimization of the generators’ output voltage total harmonic distortion is an ever-more critical objective, especially for variable frequency power systems where this target has to be met within the whole range of operating speeds. In conventional, constant speed, wound field synchronous generators, a number of consolidated techniques are implemented to meet this requirement. In variable speed synchronous generators intended for the more electric aircraft, these techniques are no longer fully effective and new methodologies are thus necessary. This paper replaces the conventional squirrel-type damper cage with a new integrated damper cage located at the inter-pole regions. The proposed integrated damper cage, while acting as a mechanical structure to retain the field windings at high operating speeds, also achieves very low voltage total harmonic distortion values at different speeds, thus complying with the power quality requirement. A 250 kVA prototype is designed, analyzed, built and tested to prove the proposed concepts and methodologies.

2021 - Investigation of Resistivity Impact on AC Losses in Hairpin Conductors [Relazione in Atti di Convegno]
Pastura, M.; Barater, D.; Nuzzo, S.; Franceschini, G.
abstract

This work provides an analysis of the impact on AC losses in hairpin conductors, provided by different values of resistivity. Starting from some specific stator geometries, the optimal resistivity which minimizes the AC losses is calculated for each configuration through both analytical and finite element (FE) methods, considering a frequency range typical of automotive applications. Possible applications and conditions where a higher resistivity material, such as aluminum, can be adopted, are discussed. The main sources of discrepancies between the analytical and simulative approach are also discussed.

2021 - Modelling of Voltage Distribution within Hairpin Windings [Relazione in Atti di Convegno]
Preci, E.; Nuzzo, S.; Barater, D.; Gerada, D.; Degano, M.; Buticchi, G.; Gerada, C.
abstract

This work discusses the modelling approach adopted for the estimation of the voltage distribution within hairpin windings of electrical machines. The physical phenomena and the major contributors to the occurrence of the uneven voltage distribution are first described. Then, the equivalent circuit used to predict the voltage distribution is presented in detail. The circuital parameters employed in the equivalent circuit are estimated via finite element electrostatic and electromagnetic analyses. Finally, a numerical tool is used to solve the differential equations describing the equivalent circuit above mentioned. Simulation results are illustrated and discussed. The phenomena under investigation are applied to a pre-defined reference system, consisting of slot motorettes.

2021 - Multi three-phase hairpin windings for high-speed electrical machine: Possible implementations [Relazione in Atti di Convegno]
Pastura, M.; Barater, D.; Nuzzo, S.; Franceschini, G.
abstract

This work provides an in-depth critical analysis related to the feasibility of combining multi three-phase winding layouts with the ever-spreading hairpin technology. After an introduction on the advantages and challenges of both hairpin and multi-phase windings, more details on how these two technologies can be combined are provided. Then two similar stator geometries, with 72 and 96 slots, are analyzed in detail exploiting an 8 poles permanent magnet - assisted synchronous reluctance motor for traction applications. A relevant set of feasible winding configurations are modelled and analyzed through finite element simulations. For every machine, a breakdown of the power losses is provided and compared against that of the same machine topologies having random-wound windings with stranded round conductors. The main results and possible solutions to increase the machine performance are then provided.

2021 - Partial Discharge Phenomena in Electrical Machines for the More Electrical Aircraft. Part II: Impact of Reduced Pressures and Wide Bandgap Devices [Articolo su rivista]
Lusuardi, L.; Rumi, A.; Cavallini, A.; Barater, D.; Nuzzo, S.
abstract

This paper focuses on the inception of partial discharges within the insulation system of electrical actuators used for the More Electrical Aircraft (MEA). Since these machines should operate in the absence of Partial Discharges (PDs), the dependence of the PD Inception Voltage (PDIV) on voltage impulses typical of wide bandgap (SiC) devices is investigated at both 1 bar, reduced pressures close to those typical of aircraft cruising altitudes (150 mbar - 200 mbar) or lower (down to 5 mbar). Propagation issues are not dealt with here as results were obtained working on insulation models consisting of couples of wires twisted together (twisted pairs), thus knowing exactly the potential differences between all points of the insulation model. The results show that the rise times and the switching frequencies associated with wide bandgap devices have little impact on the PDIV. A model able to predict the PDIV of the turn/turn insulation of random wound motors (the most vulnerable part of the insulation) at different pressures is proposed. The model is also able to deal with temperature changes, with limitations that depend on the type on insulation systems.

2021 - Partial Discharges in Electrical Machines for the More Electric Aircraft. Part I: A Comprehensive Modelling Tool for the Characterization of Electric Drives based on fast switching semiconductors [Articolo su rivista]
Pastura, M.; Nuzzo, S.; Immovilli, F.; Toscani, A.; Rumi, A.; Cavallini, A.; Franceschini, G.; Barater, D.
abstract

The arrival on the market of new power devices based on wide bandgap semiconductors has raised a relevant interest due to their superior properties compared to conventional technologies. On the other hand, these devices are inherently characterized by high rates of voltage changes over time, which may result in reliability challenges in electric drives adopting them. In fact, dangerous voltage overshoots at the motor terminals and uneven voltage distributions within the machine windings may occur. These phenomena can trigger a high insulation stress and partial discharges and, as a consequence, they may concur to the premature failure of the dielectric materials. This paper proposes a flexible and comprehensive modelling approach for the accurate analysis and estimation of both voltage overshoots and voltage distributions in a typical converter-cable-motor system intended for more electric aircraft applications. The modelling results are validated against experimental measurements carried out on a physical prototype comprising a wide bandgap-based converter, a connecting cable and an electrical machine stator. The findings are then used in the companion papers (part II and part III) to investigate the dependence of partial discharge phenomena on these voltage waveforms, highlight reliability challenges in modern ±270 V DC bus voltage drives for the more electric aircraft and discuss solutions.

2021 - Partial Discharges in Electrical Machines for the More Electrical Aircraft. Part III: Preventing Partial Discharges [Articolo su rivista]
Rumi, A.; Lusuardi, L.; Cavallini, A.; Pastura, M.; Barater, D.; Nuzzo, S.
abstract

In this paper, the results obtained from lab tests on twisted pairs subjected to different voltage waveforms and atmospheric conditions are used to propose how to modify the IEC Std. 60034-18-41. The goal is to make the standard suitable for the More Electrical Aircraft (MEA). The results show that it is initially necessary to screen out materials through simple tests. The enhancement factors for temperature can be modified to consider reduced pressures and temperatures using a simple model. The aging enhancement factor can be reduced considering the reduced sensitivity of the partial discharge inception voltage (PDIV) at low pressures on the enamel thickness. Eventually, reference will be made to the drive discussed in Part I of this series to draw conclusions about the likelihood of partial discharge inception in a random wound stator and how to reduce it by modifying either the inverter or the stator insulation. Reference to a random wound motor is made throughout the paper.

2021 - Thermal and Electromagnetic Stator Vent Design Optimisation for Synchronous Generators [Articolo su rivista]
Bersch, K.; Nuzzo, S.; Connor, P. H.; Eastwick, C. N.; Rolston, R.; Galea, M.
abstract

This article deals with the stator cooling of an air-cooled, synchronous generator with a power rating of 400 kVA, which has been improved by adding two radial vents to the stator. To ensure an optimal vent design, a novel combined thermal and electromagnetic modelling approach is developed. A parametric 3D Conjugate Heat Transfer Computational Fluid Dynamics (CFD) model is used for the thermal modelling. An electromagnetic 2D Finite Element Analysis determined the impact that venting the stator has on the loss distribution. The models are coupled by deriving analytical correlations between the combined vent width and rotor copper, rotor iron and stator iron losses. These correlations are implemented into the optimisation procedure of the parametric CFD model. Five design parameters are optimised simultaneously with the aim of minimising the peak stator winding temperature. The modeling approach was validated experimentally by thermal, torque and mass flow measurements on the benchmark machine, as well as the newly designed prototype.

2020 - An analytical approach for the design of innovative hairpin winding layouts [Abstract in Atti di Convegno]
Arzillo, A.; Nuzzo, S.; Braglia, P.; Franceschini, G.; Barater, D.; Gerada, D.; Gerada, C.
abstract

This work deals with an analytical approach aimed at accurately predicting Joule losses in innovative hairpin winding layouts. While hairpin windings are seeing an everincreasing use in automotive and aerospace applications due to their inherently high slot fill factor, they also present drawbacks such as the non-uniform current distribution potentially occurring across their cross section. This phenomenon is emphasized at high frequencies, leading to a significant increase of the effective conductor resistance and, consequently, of copper losses. Hence, particular attention has to be given to the design of electrical machines employing hairpin conductors, aiming to reduce the high-frequency losses as much as possible. In this paper, an analytical model based on previous investigations is updated and modified in order to increase the degrees of freedom in the design and analysis of hairpin windings. With the developed analytical model, the copper losses associated to innovative hairpin configurations can be accurately predicted. The findings also confirm that such alternative layouts can effectively reduce the Joule losses when compared to traditional hairpin technologies.

2020 - An evaluation of exciterless topologies for medium power wound-field synchronous generators [Relazione in Atti di Convegno]
Fallows, D.; Nuzzo, S.; Galea, M.
abstract

The wound field synchronous machine has widespread use both as a motor and a generator, due to its low cost, wide power range and its consolidated history built over decades of operation. A critical aspect of these machines is the method of excitation to the field winding. Typically, the choice is between a static excitation system using slip-rings and a rotating excitation system using a brushless exciter. An alternative is that of removing the classical exciter completely and thus feed the field winding through more advanced 'exciterless' solution. The potential to reduce component count and improve power density has resulted in increasing interest in exciterless solutions, over the last couple of decades. This paper thus gives an overview of these methods, assessing and comparing their advantages and disadvantages. A particular focus is on medium power applications, which traditionally have dominated the market of synchronous generators and associated generating sets, and where significant improvements in terms of cost minimisation, power quality, and ease of design are always required.

2020 - Analysis and Modelling of High Frequency Effects on Synchronous Generator's Armature Conductors [Relazione in Atti di Convegno]
Quadri, Q. H.; Nuzzo, S.; Gerada, C.; Galea, M.
abstract

This paper investigates the accuracy of the subdomain modelling technique for high frequency copper loss calculation in stator windings of synchronous generators. The methodology's accuracy is studied at a slot level up to 10 kHz against FE model with realistic conductor dimensions. The analysis demonstrates that improper conductor area representation and eddy current reaction negligence causes increasing error with increasing frequencies. A modified subdomain model is then proposed to address these challenges which has proven to show a good match with a corresponding FE model.

2020 - Challenges and Future opportunities of Hairpin Technologies [Relazione in Atti di Convegno]
Arzillo, A.; Braglia, P.; Nuzzo, S.; Barater, D.; Franceschini, G.; Gerada, D.; Gerada, C.
abstract

Hairpin windings are seeing an ever-increasing application and development in electrical machines designed for high power and torque densities. In fact, due to their inherently high fill factor, they are very attractive in applications, such as transportation, where these characteristics are considered main design objectives. On the other hand, high operating frequencies also contribute to improve power density of electrical machines. However, at high fundamental frequencies, hairpin windings are characterised by increased Joule losses due to skin and proximity effects. Hence, while these technologies are introducing new opportunities, a number of challenges still need to be addressed. These include manufacturing aspects, contacting processes, thermal management, etc. This paper presents an overview of the current state-of-the-art of hairpin technologies and propose possible future opportunities. The authors' perspective is then finally provided, showing how innovative winding patterns can potentially overcome the above mentioned challenges.

2020 - Challenges and Opportunities for Wound Field Synchronous Generators in Future More Electric Aircraft [Articolo su rivista]
Wang, Y.; Nuzzo, S.; Zhang, H.; Zhao, W.; Gerada, C.; Galea, M.
abstract

Electrical machines and drives keep moving away from traditional technologies such as brushed machines and wound field machines toward lighter, 'easier to maintain' machines. A very interesting aspect is that certain transport applications, especially the aerospace industry, still favor the classical wound field machine for its main generating system such as Boeing 787. This article focuses on investigating this particular trend by presenting a detailed overview of the historical power-generation systems on aircraft. This article compares the current state of the art of wound field machines with other generator families. The results of this analysis are then projected into the needs of the electrical power generation and distribution system on aircraft. Although power density is a major objective for any aerospace application, however, the extra benefits associated with wound field systems are still essential in modern aircraft. This article then focuses on the main challenges for improving the power density of wound field machines. Recommendations, opportunities, and improvements related to wound field machines are discussed. In conclusion, if robust designs for higher speed wound field generators were consolidated, it would be very probable that these classical machines might still be implemented on future More Electric Aircraft (MEA) platforms.

2020 - Feasibility Design Study of High-Performance, High-Power-Density Propulsion Motor for Middle-Range Electric Aircraft [Relazione in Atti di Convegno]
Hebala, A.; Nuzzo, S.; Volpe, G.; Connor, P. H.; Giangrande, P.; Gerada, C.; Galea, M.
abstract

This paper deals with the design of a high power-density, high efficiency and low torque ripple propulsion motor for electric aircraft. The proposed design procedure resulted in a high-performance propulsion motor intended for a direct-drive solution on an 8-12 passenger commercial aircraft with a range up to 1000 miles. The electromagnetic design is firstly addressed and then the thermal management is discussed. A set of design development steps are investigated and validated through finite-element software, involving studies for the optimal selection of the of air gap diameter and the slot/pole combination, followed by improving the efficiency by suitable material selection and methods for losses mitigation. Finally, in order to prove the enhancement of power density and efficiency through this feasibility design study, the designed propulsion motor performance is compared to the state-of-the-art motors of similar direct-drive aircraft propulsion systems.

2020 - Moving Toward a Reliability-Oriented Design Approach of Low-Voltage Electrical Machines by Including Insulation Thermal Aging Considerations [Articolo su rivista]
Giangrande, P.; Madonna, V.; Nuzzo, S.; Galea, M.
abstract

Electrical machines (EMs) are required to consistently perform their intended mission over a specified timeframe. The move toward transportation electrification made the EMs' reliability an even stringent and predominant requirement, since a failure might cause severe economic losses, as well as endanger human lives. Traditionally, the design procedure of motors conceived for safety-critical applications mainly relies on over-engineering approaches. However, a paradigm shift is recently taking place and physics of failure approaches/methodologies are employed to meet the reliability figures, while delivering an optimal design. This article proposes and outlines a reliability-oriented design for low-voltage EMs. Thermal accelerated aging tests are preliminarily carried out on custom-built specimens. Once the aging trend of the turn-to-turn insulation system is assessed, the thermal endurance graph at several percentile values is determined and lifetime models are developed, for both constant and variable temperature operations. Finally, these models are used to predict the turn-to-turn insulation lifetime of motors meant for aerospace and automotive applications.

2020 - Multi-Objective Optimization of Medium-Scale Wound-Field Electric Generators [Relazione in Atti di Convegno]
Bramerdorfer, G.; Marth, E.; Nuzzo, S.; Galea, M.
abstract

This work deals with the optimization of electric generators for multiple performance measures, e.g., the simultaneous maximization of the fundamental harmonic and the minimization of the total harmonic distortion of the Back-EMF. For a given slot/pole-configuration and pole span, the goal is to find the optimal rotor outer contour along the air gap. Different approaches for modeling the rotor contour are followed here, i.e., a Fourier-series based approach and a piecewise discretization of the circumference. The work is about performing optimizations for both approaches and to compare the achieved results (i) when considering similar computational effort, (ii) regarding modeling complexity versus design flexibility, and (iii) the possibility for acquiring additional information, as for instance the sensitivity of the contour regarding manufacturing tolerances.

2020 - On single-phase operation of three-phase synchronous generators [Relazione in Atti di Convegno]
Spagnolo, C.; Nuzzo, S.; Giangrande, P.; Galea, M.; Serra, G.
abstract

Classical synchronous generators have been used for decades in the field of power generation. The traditional manner of operation of these systems is the balanced, three phase configuration. However, recently there has been an interest in re-configuring consolidated, commercial, three phase generators to operate in single phase operation. A main driver for this phenomenon is the aim of manufacturers to extend their range of products for minimum development cost. Such an approach however brings a number of design challenges, especially in terms of the elevated damper cage currents and the negative sequence currents, when a 3-phase machine is 'forced' to operate in 1-phase. This paper therefore investigates and analyses these challenges. Considering a commercial, 3-phase, 400 kVA alternator. Detailed models, validated against experimental validation in 3-phase operation are first obtained. The machine is then re-configured to single phase operation. This paper proposes and shows how a suitable single phase loading can be found for 3-phase generators operating in single phase.

2020 - PM Halbach Arrays in Motors: Loss Reduction and Performance Improvements [Relazione in Atti di Convegno]
Hebala, A.; Nuzzo, S.; Connor, P. H.; Giangrande, P.; Gerada, C.; Galea, M.
abstract

Halbach array configurations represent a common choice in high-performance electrical machines, since a stronger magnetic field is generated for the same Permanent Magnet (PM) volume. Hence, higher torque is developed, and the power density is enhanced. This paper investigates methodologies for reducing the PM losses in Halbach arrangements. A high power density propulsion motor is considered as a case-study and by using Finite Element (FE) software, sensitivity analyses are performed on the main design parameters. Strategies for loss reduction and performance improvements, in terms of torque ripple, total harmonic distortion, efficiency and power density, are investigated and proposed. The effectiveness of axial and radial segmentations, PM edge shape, and semi-magnetic slot wedges are evaluated. Finally, recommendations are made for designing a PM Halbach array.

2020 - Sensitivity analysis on the voltage distribution within windings of electrical machines fed by wide band gap converters [Abstract in Atti di Convegno]
Pastura, M.; Nuzzo, S.; Franceschini, G.; Sala, G.; Barater, D.
abstract

In the last years, Wide Band Gap devices are seeing a significant widespread in electric drives, due to their higher performance compared to conventional semiconductors. However, they also produce higher electric stress due to over-voltages and uneven voltage distributions among winding turns of electrical machines fed by them, which can lead to premature failures and/or reduced lifetimes.This paper presents a sensitivity analysis on the voltage distribution across stator winding turns of an electric motor intended for aerospace applications. The effects of the surge voltage characteristic parameters, such as dv/dt, voltage magnitude and parasitic impedances, are investigated. An equivalent circuit approach, based on the multi-transmission line theory, is developed and implemented in MatLab-Simulink environment, while the relevant circuital parameters are estimated through finite element analysis performed with MagNet and ElecNet software.

2020 - Slot design optimization for copper losses reduction in electric machines for high speed applications [Articolo su rivista]
Bianchini, C.; Vogni, M.; Torreggiani, A.; Nuzzo, S.; Barater, D.; Franceschini, G.
abstract

The need of a wide operating range and a high power density in electric machines for fulland hybrid electric vehicles in traction applications has led to an increase in the operating frequency of the machine. When the electric frequency increases, the additional losses in stator windings become an issue and they have to be taken into account in the design of the electric machine. This issue is more critical when hairpin windings are employed, due to the the skin and proximity effects which produce increased copper losses. In this paper, the relationships between different stator slot parameters (tooth width, slot opening, etc.) and stator winding copper losses have been analysed in order to identify an optimal design of a single stator slot.

2019 - A Methodology to Remove Stator Skew in Small-Medium Size Synchronous Generators via Innovative Damper Cage Designs [Articolo su rivista]
Nuzzo, S.; Galea, M.; Bolognesi, P.; Vakil, G.; Fallows, D.; Gerada, C.; Brown, N.
abstract

This paper proposes and investigates an innovative methodology that can have a significant impact on the market potential of wound field, small-medium size synchronous generators (SGs). The technique proposed here is aimed at removing the need for the traditional stator skewing that is so commonly used in SGs to achieve acceptable values of voltage total harmonic distortion. To do this, a nonstandard damper cage configuration is proposed that comprises modulation of the damper bars' positioning. An off-the-shelf, 400-kVA generator is used as a benchmark machine. Its rotor is optimized and modified according to the proposed technique. The results of the final machine are then compared to the benchmark machine highlighting the excellent advantages that can be achieved through this technique. A full-scale prototype of the modified generator is then built to experimentally validate the concept. Finally, a detailed analysis on all the performance aspects of the prototype is carried out, to guarantee that the proposed technique has no negative impact whatsoever on the generator's performance.

2019 - An Improved Automatic Voltage Regulator for Self-Excited, Small-to-Medium Power Generating Sets equipped with Brushless Excitation Systems [Relazione in Atti di Convegno]
Nuzzo, Stefano; Bolognesi, Paolo; Galea, Michael; Barater, Davide
abstract

The classical, wound-field, synchronous generator is currently enjoying a revamped interest in its design and development, partly due to the ever-increasing requirements in terms of power quality standards, efficiency and power density and partly due to advances in materials and manufacturing techniques. Also, the significant improvements in the computational resources allow the utilization of modern design techniques and tools. Apart from the design of the machine itself, another area of interest is the system-level optimization. The proposed project is aimed at renewing the power electronics and the control logics in power generating sets featuring the popular brushless configuration. An industrial small-to-medium size power generating set is taken as case study. The considered platform is first analyzed at system-level, by modelling in detail all of the components comprised in it. Then, focus is given to the automatic voltage regulator. A faster, more flexible and more efficient system is proposed, based on a 4-quadrant DC-to-DC converter which permits to improve the dynamic response of the excitation system.

2019 - Braking torque compensation strategy and thermal behavior of a dual three-phase winding PMSM during short-circuit fault [Relazione in Atti di Convegno]
Giangrande, P.; Madonna, V.; Nuzzo, S.; Gerada, C.; Galea, M.
abstract

Permanent magnet synchronous machines (PMSMs)employing the dual three-phase winding represent a suitable solution for complying with the reliability requirements typically needed in safety-critical applications. Their inherent fault-tolerant capability allows to operate the system (e.g. electro mechanical actuator or traction drive-train), even after the occurrence of a three-phase short-circuit in one winding set. Nevertheless, an appropriate post-fault control strategy is indispensable for preventing the PMSM performance derating. In this work, the design of a dual three-phase PMSM, intended for aerospace application, is presented. The PMSM performance is evaluated via finite element (FE)analysis, in both healthy and three-phase short-circuit conditions. A post-fault control strategy aimed at balancing the braking torque is then discussed. Since the implemented strategy is based on the current overload of the healthy winding, the temperature rise is experimentally investigated on the PMSM prototype. The thermal analysis verifies the compensation strategy feasibility, by proving that the thermal overload does not have a major effect on the wire insulation lifetime.

2019 - Design of Fault-Tolerant Dual Three-Phase Winding PMSM for Helicopter Landing Gear EMA [Relazione in Atti di Convegno]
Giangrande, P.; Madonna, V.; Nuzzo, S.; Galea, M.
abstract

On modern rotorcraft, electro-mechanical actuators (EMAs) are progressively replacing the bulky and more expensive hydraulic and/or pneumatic systems. Although the migration towards alternative actuation solutions, reliability remains a key requirement for aerospace applications. Fault-tolerant electrical machines are often employed for ensuring the demanded reliability level. In this paper, the design of a dual three-phase winding permanent magnet synchronous machine (PMSM) for helicopter nose landing gear extension/retraction EMA is addressed. Finite element (FE) simulations are used for evaluating the PMSM performance in both healthy and faulty conditions. The compensation strategy implemented on the healthy three-phase winding, while the second one is completely shorted, is also discussed. Finally, a purposely built dual three-phase winding PMSM model is implemented in Dymola environment, where the extension/retraction EMA is simulated. Hence, EMA behaviour under both healthy and faulty conditions is analysed.

2019 - Dv/Dt Filtering Techniques for Electric Drives: Review and Challenges [Relazione in Atti di Convegno]
Pastura, Marco; Nuzzo, Stefano; Kohler, Mario; Barater, Davide
abstract

The use of wide band gap devices in power converters is becoming more and more popular since they enable operations at higher switching frequencies, voltages and temperatures compared to traditional power semiconductors, while also improving the efficiency. However, in electric drives, they also tend to increase voltage overshoots at motor terminals and to produce uneven voltage distributions across stator windings, due to their high rate of voltage change over time (dv/dt). In order to mitigate these issues, passive filters can be employed. The aim of this paper is to give an overview of possible solutions based on passive filters, analyzing the main advantages and drawbacks. A comprehensive, qualitative comparative study is carried out taking into account common mode currents reduction, power losses, costs, dimensions and reliability.

2019 - Excitation system technologies for wound-field synchronous machines: Survey of solutions and evolving trends [Articolo su rivista]
NOland, J. K.; Nuzzo, S.; Tessarolo, A.; Alves, E. F.
abstract

Wound-field synchronous machines (WFSMs) are included in the majority of large power generating units and special high-power motor drives, due to their high efficiency, fiexible field excitation and intrinsic fiux weakening capability. Moreover, they are employed in a wide range of high-end solutions in the low-to-medium power range. This contribution presents a comprehensive survey of classical and modern methods and technologies for excitation systems (ESs) of WFSMs. The work covers the fundamental theory, typical de-excitation methods and all the modern excitation equipment topologies in detail. It also includes a description of the state-of-the-art and the latest trends in the ESs of wound-field synchronous motors and generators. The purpose of the paper is to provide a useful and up-to-date reference for practitioners and researchers in the field.

2019 - Hybrid magnet - Field winding solutions for exciters of synchronous generators [Relazione in Atti di Convegno]
Decuzzi, G.; Nuzzo, S.; Bolognesi, P.; Giangrande, P.; Galea, M.
abstract

For power generation purposes, wound-field synchronous generators are often preferred to permanent magnet machines, due to the need of controlling the field winding voltage and current for guaranteeing a constant voltage at the generator's armature terminals. In a traditional generating set, this function is accomplished by a relatively complex feedback control system which typically comprises an excitation system and an automatic voltage regulator. Due to their excellent and proven performance capability, such classical generating sets have seen only strictly incremental improvements in the last 60 years or so. However, today, there is an interest in revamping their design and development, partly due to the even increasing efficiency and reliability requirements and partly due to advances in material and manufacturing techniques. This work investigates the feasibility of a hybrid permanent magnet - field winding excitation for synchronous generators' exciters. This design solution aims at reducing the losses of the exciter and thus of the whole generating system, while also increasing its reliability.

2019 - Modeling of Classical Synchronous Generators Using Size-Efficient Lookup Tables with Skewing Effect [Articolo su rivista]
Quadri, Q. H.; Nuzzo, S.; Rashed, M.; Gerada, C.; Galea, M.
abstract

In this paper, an analytical model aimed at reducing computational times for the analysis of classical synchronous generators is proposed and validated. While the proposed model's attractiveness comes from its simple and fast nature, however, it also features excellent levels of accuracy. This is achieved by the model's ability to consider aspects like saturation and space harmonics. Such features are usually investigated with computationally-heavy finite element analysis. The proposed method shows that an appropriate flux linkage map of all the machine windings as a function of currents and rotor position can be used to accurately consider these features at no cost of time or accuracy. Furthermore, the integration of the skewing effect within the model has also been proposed by incorporating it within the flux linkage map. The proposed method is investigated through the use of a 72.5kVA, wound field, salient pole synchronous generator. The results are compared with those of a finite element model and also against experimental measurements on a physical prototype. The advantages of the proposed procedure are discussed, where the model's suitability for carrying out lengthy and multiple simulations and its flexibility are highlighted.

2019 - Reduced order lumped parameter thermal network for dual three-phase permanent magnet machines [Relazione in Atti di Convegno]
Giangrande, P.; Madonna, V.; Nuzzo, S.; Spagnolo, C.; Gerada, C.; Galea, M.
abstract

In recent years, electrical machines are employed in an ever-increasing number of safety-critical applications, which require high power density, along with a demanding level of reliability and/or fault-tolerance capability. Multi-phase machines are generally considered a suitable option for satisfying these constraints. Among them, the dual three-phase configuration claims the additional benefit of being operated through conventional power electronics converters and control strategies. Despite the undeniable advantages and their wide diffusion, the thermal modelling of dual three-phase machines still represents an open research topic. Thus, this paper proposes the thermal analysis of a dual three-phase permanent magnet synchronous machine, highlighting the thermal coupling between the two winding sets. An experimentally fine-tuned lumped parameter thermal network is initially presented. Then, due to its relatively high number of nodes, a reduced order thermal network using only 3 nodes is developed. Finally, both thermal networks are examined and compared under several load conditions, in terms of accuracy and computational burden.

2019 - Review, Challenges, and Future Developments of Electric Taxiing Systems [Articolo su rivista]
Lukic, M.; Giangrande, P.; Hebala, A.; Nuzzo, S.; Galea, M.
abstract

The ever-increasing demand for passenger air traffic results in larger airline fleets every year. The aircraft market forecast reveals an unprecedented growth for the coming decades, leading to serious environmental and economic concerns among airlines and regulatory bodies. Different approaches, for both airborne and ground operations, have been proposed to reduce and control emissions without compromising profit margin. For on-ground activities, the electric taxiing (ET) methodology is one of the suggested solutions for reducing the emissions and the acoustic noise in the airport, and for lowering the fuel consumption and operating costs. This article, thus, aims to review and collate the more important literature related to ET systems, in order to draw an inclusive picture regarding the current state-of-the-art of a moving and growing sector that just started its first steps toward an ambitious target. After introducing the general concept of ET, elaborations on the benefits and challenges of available technologies are done with a detailed comparison of the different systems. Finally, recommendations for future research and outlook on ET are presented.

2019 - Simplified Damper Cage Circuital Model and Fast Analytical-Numerical Approach for the Analysis of Synchronous Generators [Articolo su rivista]
Nuzzo, S.; Bolognesi, P.; Gerada, C.; Galea, M.
abstract

The long and enduring history of utilization of the wound-field synchronous generator in a large number of applications makes it one of the most known and consolidated electrical machine technologies. Thus, its design, modeling, and analysis processes have been widely exploited and implemented through various and different methods, including the equivalent circuit approach. When a damper cage is embedded within the rotor of the synchronous generator, its theoretical analysis becomes quite complicated. Thus, today numerical tools are being used. In this paper, an alternative way of modeling symmetric damper cages of salient-pole synchronous generators is presented. The proposed approach is embedded in the circuital model of the generator. A hybrid analytical-numerical model is implemented, permitting to accurately predict the voltage waveforms of the generator with excellent accuracy, however, at a lower cost of computational resources than the pure numerical method. A case study of an off-the-shelf 400 kVA machine is considered to develop and validate the proposed technique. The results are compared with the corresponding finite-element and experimental evaluations for validation purposes.

2019 - The potential of exploiting non-symmetric structures in electrical machines [Relazione in Atti di Convegno]
Nuzzo, S.; Marfoli, A.; Papini, L.; Bolognesi, P.; Gerada, C.; Galea, M.
abstract

Typically, electrical machines feature rotor and stator winding configurations and core structures which comply with both simplicity and cost requirements. Such constraints limit the design search space and degrees of freedom, thus leading to exploit and implement only standard symmetrical layouts which therefore represent by far the most common choice. In this paper, the potential of adopting non-symmetrical windings and geometries in electrical machines is discussed. The perceived benefits are first detailed and then proven by applying the concepts to two case studies, namely a squirrel-cage induction machine and a salient-pole synchronous machine.

2018 - Analysis, Modeling, and Design Considerations for the Excitation Systems of Synchronous Generators [Articolo su rivista]
Nuzzo, S.; Galea, M.; Gerada, C.; Brown, N.
abstract

The traditional generating set is usually comprised of a classical, wound-field, salient-pole, or cylindrical rotor synchronous generator, excited by a separate smaller machine, via a rotating, uncontrolled diode rectifier. The effects of the commutation processes of the diode bridge are often overlooked and neglected. However, due to the uncontrolled nature of this process, the rectified voltage available at the main generator's rotor terminals can be significantly lower than the expected value. This is especially true for low-to-medium power rated systems. In this paper, a detailed investigation of these aspects is done and an accurate voltage drop prediction model is then proposed. The model is validated with finite-element analysis and with experimental results for a particular low-medium rated generating system in the 400 kVA power range. The validated tool is then integrated into an innovative design tool, which first performs an analytical presizing procedure and then utilizes a genetic algorithm approach to identify an optimal excitation system design, aimed at minimizing the voltage drop ensuing from the diode commutations, with minimum impact on the overall efficiency.

2018 - Combined Thermofluid and Electromagnetic Optimisation of Stator Vent Cooling [Relazione in Atti di Convegno]
Bersch, K.; Nuzzo, S.; Connor, P. H.; Eastwick, C. N.; Galea, M.; Rolston, R.; Vakil, G.
abstract

A combined electromagnetic and thermal modelling approach has been developed to optimise the design of multiple radial stator vents in an air-cooled, synchronous generator with a power rating of several hundred kVA. An experimentally validated 3-D Conjugate Heat Transfer Computational Fluid Dynamics model has been created and coupled with 2-D Electromagnetic Finite Element Analysis. Correlations between the combined vent width and rotor copper, rotor iron and stator iron losses were derived from the electromagnetic analysis. These correlations were implemented into the optimisation procedure of the parametric thermofluid model. Five parameters: vent locations, widths and the height of a baffle, were optimised simultaneously with the aim of minimising the peak stator winding temperature. The peak stator winding temperature was reduced by 11.1 %. The average stator winding temperature decreased by 6.3 %. To maintain the machine's power output, the removal of active stator material was compensated by increasing the rotor current.

2018 - Harmonic reduction methods for electrical generation: A review [Articolo su rivista]
Fallows, D.; Nuzzo, S.; Costabeber, A.; Galea, M.
abstract

This study provides a comprehensive literature review of techniques for harmonic related power quality improvement of electrical generation systems. Increasing interest in these aspects is due to ever more stringent power quality requirements, deriving from new grid codes and compliance standards, aimed at limiting waveform harmonic distortion at all points of the distribution network. Although a wealth of literature is available for such techniques, it has never been compiled into a handbook incorporating all the solutions aimed at both electrical machine and power system engineers.

2018 - Simplified Analytical Circuital Model of Damper Windings Exploiting Symmetries [Relazione in Atti di Convegno]
Nuzzo, S.; Bolognesi, P.; Galea, M.
abstract

The damper windings of salient-pole, wound-field synchronous generators are currently attracting a renewed interest due to their impact on the machine efficiency and power quality, which was somewhat overlooked in the past. This paper focuses on the equivalent circuital modeling of damper windings. After recalling its main physical features, the general approach is first presented, permitting to define an equivalent circuit and to derive the related resistance and inductance matrixes whatever is the pattern of the cage bars. Further assumptions deriving from common or advanced features of damper windings are then analyzed, such as symmetrical, antisymmetrical, shifted and modulated position patterns. It is then shown how such assumptions can be exploited to simplify and shrink the equivalent circuital model of damper windings when analyzing realistic operating conditions.

2018 - State of the Art of Electric Taxiing Systems [Relazione in Atti di Convegno]
Lukic, M.; Hebala, A.; Giangrande, P.; Klumpner, C.; Nuzzo, S.; Chen, G.; Gerada, C.; Eastwick, C.; Galea, M.
abstract

The aviation industry represents an ever-expanding economy and the aircraft market forecast reveals an optimistic growth for the coming decades. New requirements and guidelines call for a more efficient, reliable, and environment friendly aircraft operations during both airborne and ground phases. Considering on-ground operations, the electric taxiing is one of the suggested solutions for reducing the emissions and the acoustic noise in the airport, and for lowering the fuel consumption and the flight costs. This paper provides an overview of the most important existing electric taxiing systems and also presents the basic concepts related to it. Finally, detailed comparison of the different systems is given with recommendations for the future research.

2017 - A Fast Method for Modeling Skew and Its Effects in Salient-Pole Synchronous Generators [Articolo su rivista]
Nuzzo, S.; Galea, M.; Gerada, C.; Brown, N.
abstract

The general effects of implementing skewing techniques in electrical machines are well known and have been extensively studied over the years. An important aspect of such techniques is related to the identification of optimal methods for analyzing and modeling any skewed components. This paper presents a fast, finite-element-based method, able to accurately analyze the effects of skew on wound-field, salient-pole synchronous generators in a relatively shorter time than the more traditional methods. As a vessel for studying the proposed technique, a 400 kVA alternator is considered. Analytical and theoretical considerations on the benefits of skewing the stator in the generator under analysis are preliminary carried out. A finite-element model of the machine is built and the proposed method is then implemented to investigate the effects of the skewed stator. Comparisons against more traditional techniques are presented, with focus on the analysis of the voltage total harmonic distortion and the damper bars' currents. Finally, experimental tests are performed at no-load and on-load operations for validation purposes, with excellent results being achieved.

2017 - A hybrid analytical-numerical approach for the analysis of salient-pole synchronous generators with a symmetrical damper cage [Relazione in Atti di Convegno]
Nuzzo, S.; Bolognesi, P.; Galea, M.; Gerada, C.
abstract

The equivalent circuit approach has been widely exploited for the theoretical analysis of electromagnetic devices. However, in the field of classical wound-field synchronous generators, the presence of the damper cage complicates the analysis of such devices and the accurate prediction of the inherent induced currents is still matter of ongoing research. 12Focus is given to the accurate prediction of the no-load voltage waveform, by implementing a hybrid analytical-numerical model for a specific alternator.

2017 - An analytical and genetic-algorithm-based design tool for brushless excitation systems of low-medium rated synchronous generators [Relazione in Atti di Convegno]
Nuzzo, S.; Galea, M.; Gerada, C.; Brown, N. L.
abstract

The sizing procedures adopted for the everyday design of electrical machines are well known and consolidated. However, for brushless exciters of field wound, synchronous generators, there is significant room for improvement as the impact of the diodes' commutations in the rotating bridge rectifier are often neglected. This paper deals with the development of a fast analytical, genetic-algorithm-based design tool for the excitation systems of salient-pole, field wound synchronous generators. As vessel for this study, the exciter of a particular 400kVA is considered. The proposed tool is focused on achieving exciter designs that minimize the voltage drop due to the commutation processes in the rotating diode rectifier, with minimum impact on the overall efficiency.

2017 - Analysis of salient-pole synchronous generators operating in single-phase condition [Relazione in Atti di Convegno]
Spagnolo, C.; Nuzzo, S.; Serra, G.; Gerada, C.; Galea, M.
abstract

The power generation industry has recently started to invest interest and focus on the single-phase operation of traditional three-phase, wound-field, synchronous generators. This is partially due to a combination of customer requirements and the need to understand the extent of flexibility in their current products. This paper deals with an in-detail analysis of a salient-pole, wound-field, three-phase synchronous generator operating in single-phase condition, at unity power factor. The particular 400kVA alternator is first analysed via the classical analytical equations and the results compared with finite-element and available experimental measurements for validation purposes. The tools developed in this stage are then used to analyse the generator under study when it operates in single-phase condition with different values of load. In this work, it can be observed how single-phase operation of synchronous generators can result in an increase of the power-per-phase performance and that, with the appropriate winding configuration, the machine can be used in single-phase operation with a reduced loading.

2017 - Improved Damper Cage Design for Salient-Pole Synchronous Generators [Articolo su rivista]
Nuzzo, S.; Degano, M.; Galea, M.; Gerada, C.; Gerada, D.; Brown, N.
abstract

The benefits of implementing a damper winding in salient-pole synchronous generators are widely known and well consolidated. It is also well known that such a winding incurs extra losses in the machine due to a number of reasons. In order to improve the overall efficiency and performance of classical salient-pole, wound field synchronous generators that employ the traditional damper cage, an improved amortisseur winding topology that reduces the inherent loss is proposed and investigated in this paper. This is essential in order to meet modern power quality requirements and to improve the overall performance of such "classical" machines. The new topology addresses the requirements for lower loss components without compromising the acceptable values of the output voltage total harmonic distortion and achieves this by having a modulated damper bar pitch. As vessel for studying the proposed concept, a 4-MVA salient-pole synchronous generator is considered. A finite element model of this machine is first built and then validated against experimental results. The validated model is then used to investigate the proposed concept with an optimal solution being achieved via the implementation of a genetic algorithm optimization tool. Finally, the performance of the optimized machine is compared to the original design both at a steady state and transient operating conditions.

2017 - Power quality improvement by pre-computed modulated field current for synchronous generators [Relazione in Atti di Convegno]
Fallows, D.; Nuzzo, S.; Costabeber, A.; Galea, M.
abstract

Although power quality aspects of electrical machines have been extensively studied and investigated for a large number of years, room for improvement still exists in the field of classic, wound-field, synchronous generators. This paper proposes an innovative method of power quality improvement for single-phase synchronous generators in which the usual DC field current is replaced by a calculated current waveform. The optimised field current waveform is designed in such a way that harmonics created by the machine geometry and the winding configuration are significantly reduced.

2017 - Prediction of the voltage drop due to the diode commutation process in the excitation system of salient-pole synchronous generators [Relazione in Atti di Convegno]
Nuzzo, S.; Galea, M.; Gerada, C.; Brown, N. L.
abstract

The commutation processes in uncontrolled diode rectifiers have been extensively studied and modelled. However, in some applications, such as electrical power generation, the effects of these processes are often neglected. In low to medium rated, field wound, synchronous generators, the excitation system makes up a significant percentage of the whole generating set. Thus, the voltage drop due to the diode commutations can be quite significant. It is therefore of critical importance that these are considered during all the design stages of the brushless excitation system of synchronous generators. In this paper, a detailed analysis of the commutation aspects related to the diode rectifier of a brushless exciter of a 400kVA synchronous generator is presented and an accurate voltage drop prediction model is proposed and validated.

2017 - Sensitivity analysis for performance and power density improvements in salient-pole synchronous generators [Relazione in Atti di Convegno]
Wang, Y.; Vakil, G.; Nuzzo, S.; Degano, M.; Galea, M.; Gerada, C.; Zhang, H.; Brown, N.
abstract

Objective of this paper is to provide design recommendations to improve the performance and power density of a 400kVA salient-pole synchronous generator, without exceeding the limitations due to critical parameters such as total harmonic distortion of the no-load voltage. Preliminarily, a finite-element analysis of the considered machine is carried out, aiming at validating the inherent model against experiment measurements. An in-detailed sensitivity analysis of the machine's design parameters that mostly affect the performance of the platform under investigation is performed. It has been found that the position and the shape of axial ventilation ducts, as well as the stator slot shape do not affect the electromagnetic performance in a significant way and it can be highly beneficial from a thermal point of view, resulting in reduced rotor temperatures. Additionally, the shape of the salient poles and the damper winding arrangement can produce positive effects on the general performance, particularly allowing for an improved voltage THD and power density of the machine being studied in this paper.

2016 - Damper cage loss reduction and no-load voltage thd improvements in salient-pole synchronous generators [Relazione in Atti di Convegno]
Nuzzo, S.; Galea, M.; Gerada, C.; Gerada, D.; Mebarki, A.; Brown, N. L.
abstract

Salient-pole synchronous generators (SG) have a long history of utilization as reliable power generation systems. Important aspects of such generators include a high power-to-weight ratio, high efficiency and a low cost per kVA output [1]. Another critical aspect is the requirement for very low harmonic content in the output voltage. Hence, it is very important to be able to model and predict the no-load voltage waveform in an accurate manner in order to be able to satisfy standards requirements, such as the permissible total harmonic distortion (THD). Also, at steady-state conditions, parasitic voltages are induced in the damper bars which lead to a current flow with associated power losses and an increase in temperatures. This paper deals with an in-detail analysis of a 4 MVA SG, whose operation is studied and compared with experimental results for validation purposes. The same platform is then used to propose innovative solutions to the existing design and operational challenges of the machine aimed at reducing ohmic loss in the damper cage and improving the output voltage THD, without reverting to disruptive techniques such as rotor and/or stator skewing.