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Fabio IMMOVILLI

Professore Associato
Dipartimento di Scienze e Metodi dell'Ingegneria

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Pubblicazioni

2023 - A Novel Scalable Digital Data Acquisition System for Industrial Condition Monitoring [Articolo su rivista]
Toscani, A.; Immovilli, F.; Pinardi, D.; Cattani, L.
abstract

This article introduces a novel data acquisition system aimed at condition monitoring (CM) of complex industrial machinery and plants. Current commercial solutions can be divided into two groups: 1) high resolution and 2) data rate rack systems or distributed systems usually at the price of lower performance. The proposed solution aims at filling this gap. It relies on a daisy-chain digital bus architecture, featuring a main node and a series of subordinate nodes, which have been designed to collect data from both analog and digital transducers. It follows that the system is highly scalable and easily reconfigurable: the number and the type of transducers, ranging from low-cost micro electromechanical systems to high quality piezoelectric sensors, can be optimized to match each specific measurement requirements, even after the installation of the system. The proposed technology supports up to 32 channels at 48 kS/s, and guarantees the perfect synchronization of all signals regardless of the transducer type and its position along the bus, allowing to perform advanced data analysis. The system performance is at first evaluated with laboratory tests, then in the scenario of CM of rolling bearing faults, demonstrating good sensitivity and coherence between different accelerometer types.

2023 - Common Architectures and Devices for Current Source Inverter in Motor-Drive Applications: A Comprehensive Review [Articolo su rivista]
Fidone, G. L.; Migliazza, G.; Carfagna, E.; Benatti, D.; Immovilli, F.; Buticchi, G.; Lorenzani, E.
abstract

When compared to the much more common voltage-source inverter (VSI), the current-source inverter (CSI) is rarely used for variable speed drive applications, due to its disadvantages: the need of a constant DC-link current, typically realized with a front-end converter, and the need for reverse-voltage blocking (RVB) devices, typically implemented with in-series diodes. This limits the overall efficiency of the architecture. This paper investigates latest progress of the CSI research, with the aim of demonstrating why CSI could come back in the near future. Different architectures based on modern wide-bandgap (WBG) switches are analyzed, with an emphasis on why CSI can be advantageous compared to VSI.

2023 - Cross-Load Generalization of Bearing Fault Recognition with Decision Trees [Relazione in Atti di Convegno]
Briglia, Giovanni; Immovilli, Fabio; Cocconcelli, Marco; Lippi, Marco
abstract

The literature on condition monitoring is nowadays characterized by a wide variety of machine learning approaches. We argue that, in most of the works, the experimental evaluation is conducted in an oversimplified scenario, where training and test data contain samples obtained under the same radial and torsional load conditions. In this paper, we propose to apply an interpretable machine learning model, namely decision trees, to perform fault detection and recognition across different load configurations, a challenging benchmark that requires general-ization capabilities. The rules extracted from the trees provide explanations of the classification process.

2023 - Novel Single-Stage Current Source Inverter: Extension to Low-Speed Region in Motor Drive Applications [Articolo su rivista]
Benatti, D.; Migliazza, G.; Carfagna, E.; Immovilli, F.; Lorenzani, E.
abstract

In motor drive applications, single-stage current source inverters (CSIs) can manage only a limited speed range when the output voltage is greater than input voltage, due to the intrinsic boost capability. The classical solution adopted in low-speed region to control the input dc current, consists in the insertion of a prestage power converter. This article proposes a single-stage CSI that replaces the input inductance Ldc with coupled inductor. In this way, it is possible to add the needed time interval for the discharge of the magnetic energy of primary inductance Lm when the converter works in low-speed region or at standstill, extending the operating region of the converter. This solution allows to increase the efficiency of traditional CSIs for applications when the motor works most of the time in the high-speed region, thanks to the single-stage power conversion. Experimental and simulation results driving a permanent magnet synchronous machine are shown, confirming the validity of the proposed architecture.

2022 - Design and Optimization of a Magnetic Gear for a Conveyor System Application [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract

Magnetic gears have some advantages when compared to the traditional mechanical ones, especially in terms of maintenance and absence of lubrication. Many types of magnetic gears have been presented in the last years, with the aim of pushing the torque density to very high levels.This paper deals with the design and optimization of a magnetic gear (MG) for an industrial conveyor system. The design was carried out considering the geometrical constraints and the gear ratio imposed by the target application, with the aim of reducing the torque ripple and obtaining a balanced radial attraction force on the segmented ring. Two different internal permanent magnet inner rotor geometries were drafted and optimized by means of finite element simulations. The different designs were compared against each other by means of different figures of merit, including torque ripple, radial force on the segmented ring, power losses and mass of the permanent magnets.

2022 - Hairpin-Wound Rim-Driven Propeller for Electric Boats on Inland Waterways [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract

Electric mobility on water is in the early stage of development but has a great potential, especially when considering inland waterway vessels. Inland waterway vessels are the best candidate to benefit from a battery electric propulsion system, since they typically operate in environments with restrictions on noise and emissions; they have short ranges and are relatively close to charging infrastructures. Rim-driven propellers actuated by large diameter hollow-shaft electrical machines are a promising technology. Rim-driven propellers present a number of advantages when compared to standard propellers, such as increased efficiency and a compact structure that is particularly suitable for small and lightweight boats. The present work details the design and numerical simulation of the electric machine for rim-driven propeller pod applied to a speedboat to be used on lakes and rivers. The electric machine main distinctive features are a high power density, a thin radial section and a hairpin winding construction.

2022 - Performance Analysis of Current Control Strategies for Hybrid Stepper Motors [Articolo su rivista]
Bernardi, F; Carfagna, E; Migliazza, G; Buticchi, G; Immovilli, F; Lorenzani, E
abstract

Hybrid stepper motors are widespread in industrial automation due to their robustness and high torque performance in low speed range, e.g. 3D printers, pick and place, and generally in many low power positioning applications. In order to increase the efficiency and dynamic performance, current/speed/position closed loop controls are implemented for high performance sensored stepper drives. The main challenge comes from the high number of magnetic poles which these motors feature, increasing the ratio between the fundamental and switching frequency. This paper critically evaluates four current control structures based field oriented control: classic PI regulators, sliding mode control, deadbeat predictive current control and model predictive current control. Simulations and experimental results aim to evaluate the dynamic performance, phase current amplitude and distortion in order to support the critical comparison.

2022 - Reconfigurable Multi-Three-Phase Drive for Naval Rim-Driven Propulsion System [Articolo su rivista]
Alosa, C.; Migliazza, G.; Immovilli, F.; Lorenzani, E.
abstract

Multiphase drives are the subject of great interest for the transportation electrification. Multi-three-phase machines are used with modular three-phase converters to obtain a redundant structure and their great advantage is the fault-tolerance capability. Starting from a symmetrical multi-three-phase machine, a reconfigurable architecture drive can be obtained. The main characteristic of a reconfigurable architecture is the ability to change the winding configuration to better match the operating point, specifically the machine speed. The main advantage of this architecture is the capability of reducing the number of active converters when the machine operates at low speed, thus reducing total converter power losses. However, system complexity increases, since reconfiguration cells are needed to interconnect the winding sets. The proposed reconfigurable multi-three-phase drive architecture exhibits two main benefits at low speed operation: increased efficiency and reduced phase current ripple for a given switching frequency. The reconfigurable architecture was assessed by means of analytical as well as numerical simulations, and the benefits obtainable at low speed operation were also demonstrated experimentally on a reduced scale prototype, capable of 'on the fly' reconfiguration without stopping the machine.

2022 - Synchronous Reluctance Tubular Machine by Means of Additive Manufacturing [Relazione in Atti di Convegno]
Bianchini, C.; Sala, G.; Torreggiani, A.; Giannotta, N.; Davoli, M.; Macrelli, E.; Immovilli, F.; Bellini, A.
abstract

2021 - Assessment of a Multi-Functional Converter System for Traction Electric Drives [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract

The introduction of strict regulations in terms of air pollution is pushing automotive industry and heavy equipments vehicles manufacturers to integrate electric drives into the powertrain. To overcome the limitations on maximum battery voltage, a DC-DC bidirectional boost converter stage between the battery and the inverter is widely adopted by manufacturers. However, these converters are bulky, expensive and impact on the system efficiency. For this reason, Multi-Functional Converter Systems (MFCS) have been introduced in order to avoid the voltage boost stage and take advantage of the electric motor and the inverter to integrate the boost converter within these two components. This paper carries out a comparison between a traditional architecture, with a DC-DC boost converter stage, and a MFCS, to determine the best solution in terms of efficiency, weight and encumbrance.

2021 - Assessment of master-slave and droop control strategies in multi-three-phase drives [Relazione in Atti di Convegno]
Benatti, D.; Alosa, C.; Carfagna, E.; Immovilli, F.; Lorenzani, E.
abstract

Multi-phase electric drives can be employed in a great variety of applications. Their advantage in terms of fault-tolerance capability is becoming the focus of the work of many research activities, especially in the field of transportation electrification. The main topic is to create redundant and modular multi-three-phase drives to increase the overall system reliability and fault-tolerance. To this aim, distributed control architectures have been assessed. In this paper, a centralized master-slave control is compared against a distributed droop control architecture, in order to identify advantages and drawbacks. Both of the control strategies are applied to a double three-phase drive. The aim of the work is to assess whether the droop control architecture can be a valid alternative to a centralized master-slave control in terms of performances, but with the additional benefit of having a proper full redundant fault-tolerant application.

2021 - Effect of semiconductor parasitic capacitances on ground leakage current in three-phase current source inverters [Articolo su rivista]
Migliazza, G.; Carfagna, E.; Buticchi, G.; Immovilli, F.; Lorenzani, E.
abstract

This paper investigates the influence of power semiconductor parasitic components on the ground leakage current in the three-phase Current Source Inverter topology, in the literature called H7 or CSI7. This topology allows reducing converter conduction losses with respect to the classic CSI, but at the same time makes the topology more susceptible to the parasitic capacitances of the semiconductors devices. In the present work, a grid-connected converter for photovoltaic power systems is considered as a case study, to investigate the equivalent circuit for ground leakage current. The same analysis can be extended to applications regarding electric drives, since the HF model of electric machines is characterized by stray capacitance between windings and the stator slots/motor frame. Simulation results proved the correctness of the proposed simplified common-mode circuit and highlighted the need of an additional common-mode inductor filter in case of resonance frequencies of the common-mode circuit close to harmonics of the power converter switching frequency. Experimental results are in agreement with the theoretical analysis.

2021 - Extended Speed Range Control for a Current Source Inverter Variable Speed Drive [Relazione in Atti di Convegno]
Migliazza, G.; Carfagna, E.; Buticchi, G.; Immovilli, F.; Lorenzani, E.
abstract

Voltage Source Inverters (VSIs) are usually adopted for high-speed motor drive applications due to the topology simplicity and the wide availability of control strategies for this topology. An alternative is the Current Source Inverter (CSI) which allows to achieve high speed range with limited DC voltage due to its intrinsic boost capability, and this is of interest in aerospace applications or electrical vehicles (EV), but a pre-stage is necessary to control the DC input current. In this work an hybrid solution is proposed to extend the speed range of a single stage CSI (i.e. CSI without pre-stage) driving a Permanent Magnet Synchronous Machine (PMSM). In fact using a single stage CSI with DC current control, the machine cannot work properly in low speed region, so the control is composed by two different strategies: one is proposed in this work for low speed operations and the other one is already known for high speed.

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.

2020 - Fault-Tolerant Multi-Three-Phase PMSM Machine for Offroad Vehicle Hybridization [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract

2020 - Multi-three-phase propulsion system for fault-tolerant naval rim-driven propeller [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract

Multi-phase machines are gaining popularity especially in the field of transportation electrification. Multi-three-phase machines used in conjunction with modular three-phase converters result in a redundant structure with the great advantage of fault-tolerance operation capability. The present work reports the study of a multi-three-phase machine for a rim-driven propeller pod, to be employed in yachting boat electrification. The design of the machine, i.e. annular construction with large hollow shaft, was chosen to satisfy the constraints for the integration into the existing propulsion pod and to meet the reference nominal torque and speed for the inner propeller design. Detailed simulation of losses, including the effect of PWM modulation, was performed to assess the machine losses and to define the optimal switching frequency suitable for the drive. The study then focused on the fault operation capability by calculating the radial force acting on the machine rotor under different fault scenarios.

2020 - PMSM-Model-Based Sensorless Control of Hybrid Stepper Motors: Performance and Robustness to Parameters Dispersion [Relazione in Atti di Convegno]
Carfagna, E.; Migliazza, G.; Immovilli, F.; Verrelli, C. M.; Lorenzani, E.
abstract

Extended Kalman Filters (EKFs), Phase Locked Loops (PLLs), and Stator Flux Observers (SFOs) are widely used for sensorless control of Permanent Magnet Synchronous Motors (PMSMs) drives. Their use (in their most advanced version) is here extended, on the basis of model analogies and suitably-guaranteed closed loop stability properties, to the sensorless speed regulation control of Hybrid Stepper Motors (HSMs), in which position and speed sensors are not employed to reduce costs and increase robustness with respect to high temperature and high-vibration environments. Both realistic simulations and experimental results demonstrate the feasibility of the proposed methods in terms of closed-loop performance and robustness to parameters mismatch.

2020 - Reconfigurable Multi-Three-Phase Propulsion System for Naval Rim-Driven Propeller [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract

2020 - Single-phase current source inverter with reduced ground leakage current for photovoltaic applications [Articolo su rivista]
Migliazza, G.; Lorenzani, E.; Immovilli, F.; Buticchi, G.
abstract

Integrated power electronics for photovoltaic applications has attracted increasing interest, due to the possibility of having grid-connected photovoltaic modules with independent maximum power point tracking and high reliability. In this paper, a single-phase Current Source Inverter (CSI) is discussed for a photovoltaic application. The basic CSI topology will be explained for the sake of completeness, highlighting its main features and analyzing the ground leakage current problem, an important benchmark for photovoltaic application. A novel topology, called CSI5, is proposed in this work. The main feature is the presence of additional switches for ground leakage current reduction. The performance of the proposed topology is assessed by numerical simulation, and the experimental results confirm that this solution is able to strongly reduce the ground leakage current and conduction power losses.

2019 - Automated Bearing Fault Detection via Long Short-Term Memory Networks [Relazione in Atti di Convegno]
Immovilli, F.; Lippi, M.; Cocconcelli, M.
abstract

This paper presents a method for automated bearing fault detection via motor current analysis using Long Short-Term Memory networks. Minimal pre-processing is applied to current signals. The proposed approach is experimentally validated on a laboratory trial comprising different test sets for condition monitoring and fault diagnosis of a 6-poles induction motor. Preliminary results confirmed the effectiveness of the proposed method to detect various bearing faults under different operating conditions, such as: shaft radial load and output torque.

2019 - CSI and CSI7 current source inverters for modular transformerless PV inverters [Articolo su rivista]
Lorenzani, E.; Migliazza, G.; Immovilli, F.; Buticchi, G.
abstract

2019 - Critical Aspects and Strategies for Sensorless Control of IPMSM based on Low-Frequency Voltage Injection [Relazione in Atti di Convegno]
Brugioni, R.; Carfagna, E.; Lorenzani, E.; Immovilli, F.
abstract

High-Frequency signal injection is widely adopted for zero and low-speed operating conditions in sensorless control of Interior Permanent Magnet Synchronous Motors (IPMSM) drives. However, the audible noise emissions caused by induced HF current has restricted in some cases its practical application. Low-frequency signal injection solve the noise problem, but it introduces new issues. In particular, the filtering for signal separation is not trivial and affects negatively the current control loop and the dynamic performance of the angle tracking estimator. To overcome these limitations, some new strategies and modifications respect to the traditonal sensorless control are proposed in this paper, using the esteem of specific signal components estimated from known information of the drive. The simulations were carried out considering a discrete-time controller and quantiziers on measured currents and pulsed voltages. The results demonstrated the feasibility of the proposed method.

2019 - Internal Current Return Path for Ground Leakage Current Mitigation in Current Source Inverters [Articolo su rivista]
Lorenzani, E.; Migliazza, G.; Immovilli, F.; Gerada, C.; Zhang, H.; Buticchi, G.
abstract

This paper analyzes in detail the effect of a simple solution for ground leakage current mitigation applicable to transformerless three-phase current source inverter (CSI). The circuit modification solution is assessed for both traditional CSI topology and for CSI with an additional seventh switch, in literature named CSI7 (or H7), in particular with the splitting of the dc input inductance. In the present work, the solution is applied to grid-connected converters for string photovoltaic applications: scope of the circuit modification is to provide an internal return path from the wye connected capacitors of the output CL filter. This additional return path is able to significantly reduce the ground leakage current without adversely affecting THD. The performance of the proposed solution is assessed by the numerical simulations in case of a string of photovoltaic (PV) modules and the different behavior of CSI and CSI7 topologies is thoroughly investigated. Furthermore, the definition of V-cmZC is assessed by applying it to the common mode equivalent circuits for CSI7 with additional return path and their validation by means of a two-step simulation. The simulation results and experimental validation shows good agreement and confirm that the proposed solution is able to strongly reduce the ground leakage current.

2019 - Modular Multi-Three-Phase Electric Drives for Enhanced Reliability and Current Ripple Minimization [Relazione in Atti di Convegno]
Alosa, C.; Immovilli, F.; Lorenzani, E.
abstract

2019 - Wide Voltage Range Dual Active Bridge PV Retrofit Storage System [Relazione in Atti di Convegno]
Fornari, R.; Immovilli, F.; Lorenzani, E.
abstract

This paper presents a storage system integration on the photovoltaic module side of a traditional grid-connected PV plant. The proposed retrofit application is based on a wide voltage range Dual Active Bridge topology, used as bidirectional DC/DC converter. Wide voltage operation capability at PV side is required to allow the integration of the retrofit storage system on a broader range of existing PV plants, characterized by different PV string operating voltage and commercial grid-connected inverters. Dual Active Bridge topology was chosen as a galvanically-insulated bidirectional single stage conversion stage to interface storage batteries to the PV side of the existing photovoltaic plant. The storage battery is charged during the overproduction of the PV plant and the storage system sustains the end-user domestic loads when solar irradiation is insufficient. The proper operation of the commercial inverter, the design and control strategy of the whole system showed the effectiveness of the proposed solution. A full-size 3.2kW converter prototype was manufactured and experimental validation was carried out.

2018 - Critical Aspects of Hybrid PFM-PWM Operation in LLC Converters For Electric Vehicles [Relazione in Atti di Convegno]
Fornari, R; Migliazza, G; Lorenzani, E; Immovilli, F
abstract

In an Electric Vehicle a galvanically insulated auxiliary power module of suitable power size is employed to interface the high-voltage main energy storage battery to the low voltage auxiliary loads. Such converter must be reliable, efficient and compact. Resonant converters have reached widespread application as they are characterized by high efficiency and low Electromagnetic Interference (EMI). Resonant converters are usually operated in Pulse Frequency Modulation (PFM) with fixed duty cycle. In case of high power applications characterized by wide output voltage regulation, Pulse Width Modulation (PWM) can be beneficially adopted to extend the continuous modulation operation at low output voltage / low output power. This work analyses drawbacks and critical aspects of use of PWM along with some modulation strategies able to minimize hard switching commutations in this operating condition. After a first analytical comparison, different PWM strategies are evaluated by means of numerical simulations and experimentally assessed. A Quasi-Resonant control is proposed and assessed by means of simulation, resulting in an effective solution to hard switching commutation.

2018 - Ground Leakage Current Mitigation for Three-Phase Current Source Inverters [Relazione in Atti di Convegno]
Lorenzani, E; Migliazza, G; Immovilli, F
abstract

This paper presents a simple solution for ground leakage current mitigation applicable to transformerless three-phase Current Source Inverter (CSI). The proposed solution is addressed only for CSI topology with an additional seventh switch, in literature named CSI7 (or H7), in particular with the splitting of the DC input inductance. In this paper the solution is applied to grid-connected converters for string photovoltaic applications. The proposed approach is to provide an internal return path from the wye-connected capacitors of the output CL filter. Thanks to CSI7 topology and modulation technique, this additional return path is able to significantly reduce the ground leakage current without adversely affecting power conversion efficiency and THD. The performance of the proposed solution is assessed by numerical simulations in case of strings with a different number of PV modules. Simulation results and preliminary experimental validation show that the proposed solution is able to strongly reduce the ground leakage current.

2017 - CSI7: a Modified Three-phase Current Source Inverter for Modular Photovoltaic Applications [Articolo su rivista]
Lorenzani, Emilio; Immovilli, Fabio; Migliazza, Giovanni; Frigieri, Matteo; Bianchini, Claudio; Davoli, Matteo
abstract

This paper analyzes the performance of a gridtied, wide power range, transformerless, modified threephase Current Source Inverter (CSI), named CSI7. The CSI7 topology is here analyzed along with a suitable Space Vector Modulation (SVM) strategy able to attenuate the excitation of the output CL filter. The theoretical analysis and simple analytic expressions highlighted the performance and limitations of the topology when employed as a singlestage PV inverter, with particular emphasis on injected grid currents distortion and ground leakage current values. The inverter wide input range allows interfacing PV strings of different module count with a simple closed loop control. The principle of operation and control is described, the viability of the CSI7 topology was assessed with simulations and extensive experiments on a full-size laboratory prototype.

2017 - Experimental Investigation of Shaft Radial Load Effect on Bearing Fault Signatures Detection [Articolo su rivista]
Immovilli, Fabio; Cocconcelli, Marco
abstract

This paper investigates the influence of external radial load applied to the shaft on bearing fault detection based on vibration or current in induction motors operating under different conditions. This paper details the results of a laboratory trial comprising different test sets on the condition monitoring and fault diagnostic of a six-poles induction motor using a design of experiment (DOE) approach. The dedicated test setup comprises a custom-made fixture that allows us to dynamically vary the radial load applied to the output shaft. The aim is to investigate the effects of radial load on the fault diagnosis of shaft bearings and the interactions between other operating parameters, such as output torque. Specific scalar parameters have been proposed for the condition monitoring of the test motor from vibration and current data. The correct choice of the significant parameters is proven by the strong dependence on the damage returned by DOE results.

2017 - Further results on nonlinear tracking control and parameter estimation for induction motors [Articolo su rivista]
Verrelli, C. M; Tomei, P.; Lorenzani, Emilio; Fornari, Raffaele; Immovilli, Fabio
abstract

The original contribution of this paper, which concerns induction motors with uncertain constant load torque and rotor/stator resistances, is twofold. The first innovative contribution relies on the experimental analysis of the latest theoretically-based sensorless/output feedback solutions to the problem of tracking rotor speed and flux modulus reference signals with the simultaneous estimation of the uncertain parameters. The second novel contribution is constituted by the proof of existence for a new adaptive local flux observer from rotor speed and stator currents/voltages, which, in its full-order or reduced-order-like versions, involves neither over-parameterizations nor non-a priori verifiable first order stator resistance identifiability conditions at steady-state.

2017 - Ground leakage current in PV three-phase current source inverter topologies [Relazione in Atti di Convegno]
Lorenzani, E.; Migliazza, G.; Immovilli, F.; Bianchini, C.; Buticchi, G.
abstract

Current source inverter (CSI) is a family of power converters which has been recently investigated for photovoltaic power conversion in grid-tied operation, due to the inherent boost capability and ease of control. This paper assess Photovoltaic three-phase Current Source Inverters by two different CSI topologies and space vector modulation commutation strategies. Different CSI solutions are therefore analyzed by means of numerical simulations and the results are compared in terms of ground leakage current and THD of the injected grid currents. Extensive simulation results show that the CSI7 topology can improve the common mode performance while at the same time increasing the efficiency of the conventional CSI, at the price of a negligible added complexity.

2017 - Investigation on H-8 VSI architecture for bearing currents mitigation in VFD [Relazione in Atti di Convegno]
Barater, D.; Franceschini, G.; Immovilli, F.; Lorenzani, E.
abstract

With the widespread adoption in the industry of variable frequency drives (VFD) for both small and large motor-inverter systems, rolling bearing showed a reduction of lifespan due to inverter-induced bearing currents [1]. Damages include generalized roughness due to pitting and fluting of the bearing races surfaces and rolling elements. These damages are directly related to current flowing between the bearing components and results in vibration, increased friction with associated heat generation and ultimately can lead to bearing seizure or catastrophic failure.

2017 - Multi-stress lifetime model of the winding insulation of electrical machines [Relazione in Atti di Convegno]
Pietrini, G.; Barater, D.; Immovilli, Fabio; Cavallini, A.; Franceschini, G.
abstract

In this paper, a novel multi-stress model which estimates the lifetime of the winding insulation relative to its duty cycle is proposed and investigated. With an adequate implementation of this model, then an electrical machine can be designed not only in terms of its performance requirements, but also considering the associated reliability and lifetime aspects. The determination of the model parameters is based on the results of accelerated thermo-mechanical ageing tests.

2017 - Multistress Characterization of Fault Mechanisms in Aerospace Electric Actuators [Articolo su rivista]
Barater, Davide; Immovilli, Fabio; Soldati, Alessandro; Buticchi, Giampaolo; Franceschini, Giovanni; Gerada, Christopher; Galea, Michael
abstract

The concept behind the more electric aircraft is the progressive electrification of on-board actuators and services. It is a way to reduce or eliminate the dependence on hydraulic, mechanical, and bleed air/pneumatic systems, and pursue efficiency, reliability, and maintainability. This paper presents a specialized test rig whose main objective is to assess insulation lifespan modeling under various stress conditions, especially investigating the interaction between ageing factors. The test setup is able to reproduce a multitude of environmental and operational conditions at which electric drives and motors, used in aerospace applications, are subjected. It is thus possible to tailor the test cycle in order to mimic the working cycle of an electrical motor during real operation in aircraft application. The developed test-rig is aimed at projecting the technology readiness to higher levels of maturity in the context of electrical motors and drives for aerospace applications. Its other objective is to validate and support the development of a comprehensive insulation degradation model.

2017 - Nonlinear tracking control for sensorless permanent magnet synchronous motors with uncertainties [Articolo su rivista]
Verrelli, C. M; Tomei, P.; Lorenzani, Emilio; Migliazza, Giovanni; Immovilli, Fabio
abstract

The recent advanced solution in Marino, Tomei, and Verrelli (2013) to the tracking control problem for sensorless IMs with parameter uncertainties is translated on the basis of letter swap connections between the models of (nonsalient-pole surface) permanent magnet synchronous motors (PMSMs) and induction ones (IMs). The (stability proof-based) nonlinear adaptive position/speed tracking control for sensorless PMSMs (with simultaneous estimation of uncertain constant load torque and stator resistance), which is accordingly obtained by exploring and decoding the design paths in Marino et al. (2013) and which surprisingly represents a simple generalization of the controller in Tomei and Verrelli (2011), constitutes an innovative solution to the related open problem. Illustrative experimental results are included.

2016 - A design method to reduce pulsating torque in PM assisted synchronous reluctance machines with asymmetry of rotor barriers [Relazione in Atti di Convegno]
Davoli, Matteo; Bianchini, Claudio; Torreggiani, Ambra; Immovilli, Fabio
abstract

In this paper a design method for ferrite assisted synchronous reluctance machine is proposed in order to reduce torque ripple and cogging torque. An asymmetrical layout of the rotor flux barriers is proposed in order to reduce the harmonics components of the pulsating torque. The proposed analytical method is validated, employing finite elements simulations, for pure synchronous reluctance (SyR) and permanent magnet assisted synchronous reluctance machines (PMSyR) considering different slot-pole configurations. Simulated machines present a cogging torque and a torque ripple reduction respectively up to 92% and up to 70%. Moreover the electromotive force waveform is improved too. These results are achieved without reducing nominal torque and without increasing machines production costs.

2016 - Ground leakage current reduction in single-phase current source inverter topologies [Relazione in Atti di Convegno]
Migliazza, Giovanni; Lorenzani, Emilio; Immovilli, Fabio; Bianchini, Claudio
abstract

This paper presents a grid-tied single phase photovoltaic microinverter based on Current Source Inverter (CSI) topology. The main topic of this work is related to the identification of a topology and a PWM strategy able to minimize the obvious issues of the basic CSI solution: efficiency and ground leakage current. The strong reduction of this last issue allows the use of the proposed solution in conjunction with Photovoltaic module in building integrated installations. Simulation results and a low voltage experimental validation present the effectiveness of the proposed solution in mitigating ground leakage currents.

2016 - Test Setup for multistress characterization of insulation degradation mechanisms in electric drives [Relazione in Atti di Convegno]
Barater, Davide; Soldati, Alessandro; Pietrini, Giorgio; Franceschini, Giovanni; Immovilli, Fabio; Galea, Michael; Gerada, Chris
abstract

In this paper a special test setup able to assess lifespan models of electrical motor insulation system under various stress conditions is proposed. The test bed will allow characterizing insulation degradation mechanisms under variable ambient and power supply parameters, from simple models, such as twisted pairs, up to coil form and complete machine operated at rated load.

2015 - Active Rectifier With Integrated System Control for Microwind Power Systems [Articolo su rivista]
Buticchi, Giampaolo; Lorenzani, Emilio; Immovilli, Fabio; Bianchini, Claudio
abstract

This paper presents simple and effective control strategies for the active rectifier stage (AC/DC stage) of a grid-connected low power system for micro wind applications employing Permanent Magnet Synchronous Generator (PMSG). In particular a novel algorithm for the estimation of the rotor angle of the PMSG, based on flux estimators, was implemented using an adaptive low-pass filter coupled with a feed-forward compensator. This enabled a very smooth start-up operation of the PMSG, obtained by pre-loading the values of the flux estimator and using a single voltage transformer (VT) transducer. The solution for the power flow control between the active rectifier and the other(s) power converters connected to the common DC link was implemented without any digital communication between them, in order to obtain a solution suitable for modular architectures (e.g. to be used in conjunction with a grid-connected converter and/or an energy storage system). Simulation and experimental results confirmed the effectiveness of the proposed solutions. The experimental validation was conducted using a grid-connected converter as load for the proposed active rectifier.

2015 - Evaluation of combined reference frame transformation for interturn fault detection in permanent-magnet multiphase machines [Articolo su rivista]
Immovilli, Fabio; Bianchini, Claudio; Lorenzani, Emilio; Bellini, Alberto; Fornasiero, Emanuele
abstract

This paper focuses on modeling and experimental validation of a diagnostic fault classification procedure for interturn fault detection in permanent-magnet (PM) multiphase machines designed for fault-tolerant electric drives. The diagnostic procedure is based on the symmetrical component theory and relies upon the combined space vector D that gathers information from the two original space vectors obtained with different reference frames. The diagnostic index effectiveness and robustness were also investigated against other fault types such as rotor eccentricities and magnet damage to assess its discrimination capability. The proposed procedure was experimentally evaluated for the interturn fault case on a five-phase PM machine. Experiments were carried out at different speed and load levels, with increasing numbers of short-circuited turns. Both simulation and experimental results demonstrated the feasibility of the proposed diagnostic method.

2015 - Low cost PM synchronous servo-applications employing asynchronous-motor frame [Relazione in Atti di Convegno]
Bianchini, Claudio; Davoli, Matteo; Pellegrino, Gianmario; Immovilli, Fabio; Lorenzani, Emilio
abstract

This paper presents a comparison among low cost permanent magnet synchronous machine (PMSM) solutions, employing the frame and the stator laminations of an asynchronous machine. The comparison is carried out by means of finite element simulations. This work aims at obtaining machines with reduced cost, competitive in terms of nominal torque, torque ripple and cogging torque. The baseline for comparison is a surface mounted PMSM with high-strength magnets and non-skewed rotor. In order to reduce torque ripple and cogging torque, magnets with sinusoidal profiles radial wise are first introduced. Second, enhanced hybrid permanent magnets poles are adopted, replacing part of high strength NdFeB material with cheaper ferrite to reduce the production costs of the magnetic pole. Finally these PMSMs are compared to a synchronous reluctance and ferrite-assisted synchronous reluctance machines. The presented results indicate that the hybrid-magnets solution is the best trade-off between performance, cost and manufac-turability and that the ferrite-assisted synchronous reluctance machine is quite competitive and low cost.

2015 - Multistress characterization of insulation aging mechanisms in aerospace electric actuators [Relazione in Atti di Convegno]
Barater, D.; Buticchi, G.; Soldati, A.; Franceschini, G.; Immovilli, Fabio; Galea, Michael; Gerada, Chris
abstract

The concept behind the More Electric Aircraft (MEA) is the progressive electrification of on-board actuators and services. It is a way to reduce or eliminate the dependence on hydraulic, mechanical and the bleed air/pneumatic systems and pursue efficiency, reliability and maintainability. This paper presents a review of the main stress factors affecting the lifespan of insulation materials in aerospace applications. A special test bed is also proposed, to assess insulation lifespan modelling under various stress conditions, especially investigating the interaction between ageing factors. The test bed will allow to characterize insulation degradation under variable ambient and power supply parameters for simple models such as twisted pairs, up to coil form and complete machine operated at rated load. The proposed approach is based on the design of experiments (DOE). The results of the work that will be carried out will allow to identify the most influential factors affecting insulation lifetime and the interactions between them.

2014 - Design optimization for torque ripple minimization and poles cost reduction with hybrid permanent magnets [Relazione in Atti di Convegno]
Bianchini, Claudio; Davoli, Matteo; Immovilli, Fabio; Lorenzani, Emilio
abstract

This paper presents design strategies for the optimized design of the rotor poles in synchronous permanent magnet machines. The strategies are aimed at the reduction of torque ripple and cogging torque. Sinusoidally rounded magnet and rotor step-skewing are investigated, then a new proposal to reduce the cost of magnetic pole made in rare earth is presented. The goal is to introduce into a rotor pole, a fraction of low cost ferrite magnets on either side of the main rare earth NdFeB permanent magnet. The design procedure begins with some analytical consideration that allows to optimize the geometrical design of the magnets. Using Finite Element (FE) simulations, the effectiveness of the analytical model is verified and the results of the various methods are compared.

2013 - Axial Flux Permanent Magnet Machine Desing and Optimization Using Multi Layer 2D Simulation [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; Lorenzani, Emilio; A., Bellini; L., Felici
abstract

This paper presents the design of an axial flux permanent magnet machine for in-wheel application. The machine design and optimization are developed using two-dimensional (2-D) multi-layer finite element analysis approach. The threedimensional model of the machine has been approximated with a set of simulations in which the two-dimensional geometrical parameters were varied appropriately in order to reproduce the actual three-dimensional magnetic behavior. During design optimization, special attention was paid to the reduction of flux linkage harmonic content and to the reduction of cogging torque through the change of the permanent magnet profile and dimensions. Finally, a prototype machine was built to validate the effectiveness of the proposed method.

2013 - Bearing fault model for induction motor with externally induced vibration [Articolo su rivista]
Immovilli, Fabio; Bianchini, C.; Cocconcelli, Marco; Bellini, Alberto; Rubini, Riccardo
abstract

This paper investigates the relationship between vibration and current in induction motors operated under external vibrations. Two approaches are usually available to define this relationship. The former is based on airgap variations, the latter on torque perturbation. This paper is focused on the airgap variations model. The ball bearing fault is modeled by contact mechanics. External vibrations often occur in many industrial applications where external induced vibrations of suitable amplitude cause cyclic radial loading on the machine shaft. The model is validated by experiments, thanks to a dedicated test setup, where an external vibration source (shaker) was employed, together with ball bearing alterations in order to decrease the stiffness of the support along radial direction. To maximize the effects of externally induced vibrations, the frequency chosen was near the flexural resonance of the rotor (determined by FEM analysis). The direction of the external vibration is radial with respect to the axis of the electric machine under test. During tests, both stator phase currents and vibration of the machine were sampled. The test setup allowed to vary machine speed and load, vibration amplitude and bearing stiffness (damage level). Radial effects are usually visible only in case of large failures that result in significant airgap variations, as confirmed by experiments

2013 - Experimental Evaluation of Combined Reference Frames Transformation for Stator Fault Detection in Multi-Phase Machines [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; Lorenzani, Emilio; Bellini, Alberto; E., Fornasiero
abstract

This paper focuses on the modeling and experimental validation of a diagnostic index for fault detection in multiphase machines. Experiments are carried out on of a five-phase permanent-magnet machine designed for fault tolerant applications. The diagnostic index is aimed at stator faults detection and is based upon the combination of information from two different reference frames. The diagnostic index effectiveness and robustness are assessed by Finite Element analysis and experiments.

2013 - Performance Analysis of a Modified Current Source Inverter for Photovoltaic Microinverter Applications [Relazione in Atti di Convegno]
Lorenzani, Emilio; Immovilli, Fabio; Bianchini, Claudio; A., Bellini
abstract

This paper analyzes the performance of a grid-tied photovoltaic module integrated, transformerless, three-phase Current Source Inverter (CSI). The design exploits CSI inherent step-up capability to obtain a single stage power interfacing between the low voltage PV input and the high AC voltage output, to be fed into the distribution grid. A modified CSI converter topology is proposed along with a suitable PWM strategy and a simple closed loop control. The theoretical analysis and simple analytic expressions highlighted the performance and limitations of the topology when employed in single-stage PV microinverter supplied by a single low voltage PV panel. The principle of operation and control is described, and the traditional CSI topology has been simulated numerically in Matlab/Simulink environment. Results obtained with the proposed topology are presented and evaluated in order to validate the theoretical assumptions.

2013 - Power Losses Analysis in Interleaved Flyback Based PV Grid Connected Micro-Inverters [Relazione in Atti di Convegno]
Causo, Alberto; Salati, Andrea; Lorenzani, Emilio; Immovilli, Fabio; Bianchini, Claudio
abstract

This paper analyzes the power losses of photovoltaic micro-inverters based on flyback topology. A double secondary winding flyback converter topology was considered to inject alternating current into the grid. The purpose of this work is the identification and quantification of the different power losses present in a simple flyback topology and in the interleaved version with two different control strategies. The power losses comparison was carried out after designing a 250 W power converter using commercial, low cost components. Simulations in Matlab/Simulink environment highlighted the effectiveness of the interleaved architecture.

2012 - Dynamic Modeling of Double Cage Induction Machines for Diagnosis of Rotor Faults [Relazione in Atti di Convegno]
Lorenzani, Emilio; Salati, Andrea; Bianchini, Claudio; Immovilli, Fabio; Bellini, Alberto; Lee, S. B.; Yoo, J.; Kwon, C.
abstract

Double cage induction motors are typically employed in applications that require high starting torque for frequent, loaded starts. This makes the starting (outer) cage susceptible to fatigue failure since it must withstand the large thermo-mechanical stress associated with the high starting current and long acceleration time. Conventional FFT-based spectrum analysis techniques are insensitive to outer cage faults due to the small outer cage current under steady state operation, and the fault indicators and thresholds applied to single cage rotors cannot be used. Therefore, there is a strong industrial need for research and development of analysis techniques and advanced fault detection algorithms for double cage machines. However, there are only a few publications that investigate double cage rotor faults. In this paper, a dynamic model for rotor cage faults in double cage motors, which is the first step towards double cage rotor fault research, is derived. A 7.5 Hp separate end ring fabricated copper double cage rotor is built for experimental verification of the proposed fault model (copper inner cage/brass outer cage). The tests performed under startup and steady state operation show that the proposed fault model can provide sufficient accuracy and can be used as the basis for interpretation of FFT results and development of advanced fault detection algorithms.

2012 - Micro Wind Turbine System Integration Guidelines PMSG and Inverter Front End Choices [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; Lorenzani, Emilio; Bellini, Alberto; G., Buticchi
abstract

This paper is aimed at the modeling and simulation of wind power system, with particular emphasis on small wind turbines employing surface permanent magnet synchronous gen- erators (SPMSGs). Generator and inverter front-end interaction is analytically and numerically modeled, in order to evaluate the generator’s efficiency depending on its electric parameters, both during normal and power limited operation. Passive and active rectifier front-end are taken into account to assess the influence of power electronics front-end over system performances. The final target of this work is to determine design guidelines for small wind turbine system optimization. The analysis is carried out through simulations which take into account the interactions of the SPMSG’s electrical parameters and through the evaluation of the generator’s efficiency at different operating conditions and inverter front-end architectures. The data obtained was further validated with experimental characterization of two different system architectures.

2012 - Review of Design Solutions for Internal Permanent Magnet Machines Cogging Torque Reduction [Articolo su rivista]
Bianchini, Claudio; Immovilli, Fabio; Lorenzani, Emilio; Bellini, Alberto; Davoli, M.
abstract

Internal permanent magnet synchronous machinesare spreading in industrial production.They feature high torque density and extended speed rangethat are key issues in many fields of applications, however theircogging torque is typically quite high.Many methods and design guidelines for cogging torquereduction exist in literature and this paper compares them. Forthis purpose, the different design guidelines are applied to acommon reference machine in order to assess their effectiveness.Computer Finite Element Analysis (FEA) are carried out for eachcase in order to compare the cogging torque reduction capabilityof the different techniques. The side effects of these techniques,such as back-emf and rated torque profile distortions, willbe taken into account. The paper contribution is to comparethe various cogging torque reduction techniques and magneticgeometries on a common reference machine to identify the mosteffective ones.

2011 - A test bench for accelerated thermal ageing of III–V concentration solar cells using forward bias injection [Relazione in Atti di Convegno]
Immovilli, Fabio; Bianchini, Claudio; Bellini, Alberto; Sala, A.
abstract

Power production from solar photovoltaic systems is constantly increasing. In the last few years concentration photovoltaic (CPV) system using III-V multijunction cells appeared on the market, promising doubled efficiencies compared to traditional silicon PV solar panels. For CPV systems to be competitive on the market, they must be reliable to assure long-term operation. This paper presents the design and construction of a test bench for thermal cycling characterization of dense array receivers employing III-V multijunction cells mounted on a microchannel heat sink. Instead of a climatic chamber, the proposed test bench employs forward bias injection (FBI) to heat the cells, in order to better mimic on-field operating conditions. The experimental results of the accelerated ageing test are coherent with preliminary on-field trials, with a good agreement on the fault mechanism.

2011 - Currents and Vibrations in Asynchronous Motor with Externally Induced Vibration [Relazione in Atti di Convegno]
Immovilli, Fabio; Bianchini, C.; Cocconcelli, Marco; Bellini, Alberto; Rubini, Riccardo
abstract

This paper presents an experimental investigation ofthe airgap variation model for vibration and current harmonicsrelationship in induction motors. To this aim, an external vibrationsource was employed, together with ball bearing alterationsin order to decrease stiffness. The direction of the externalvibration is radial with respect to the axis of the electricmachine under test. To maximize the effect of externally inducedvibrations, the frequency chosen was near the flexural resonanceof the rotor, determined by FEM analysis.During tests both currents and vibration of the machine wereacquired. The test rig allowed to vary speed, vibration level andbearing stiffness. An electromagnetic brake provided a variableoutput load for the electric machine. The focus of the paper isthe review of fault models used in literature. Radial effects areusually visible only in case of large failures that result in air-gapvariations, as the experiments confirmed

2011 - Fault Detection of Linear Bearings in Brushless AC Linear Motors by Vibration Analysis [Articolo su rivista]
Bianchini, C.; Immovilli, F.; Cocconcelli, M.; Rubini, R.; Bellini, A.
abstract

Electric linear motors are spreading in industrial automation because they allow for direct drive applications with very high dynamic performances, high reliability, and high flexibility in trajectory generation. The moving part of the motor is linked to the fixed part by means of linear bearings. As in many other electric machines, bearings represent one of the most vulnerable parts because they are prone to wear and contamination. In the case of linear roller bearings, this issue is even more critical as the rail cannot be easily fully enclosed and protected from environmental contamination, unlike the radial rotating bearing counterpart. This paper presents a diagnostic method based on vibration analysis to identify which signature is related to a specific fault

2011 - Homopolar Generators: an Overview [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; Bellini, Alberto; Lorenzani, Emilio; C., Concari; M., Scolari
abstract

Homopolar generators are a particular class of electrical machines capable of generating DC current without the use of mechanical commutators or electronic rectifiers. This paper presents an overview of the typical configurations of homopolar DC machines. The paper focuses on generating operation, trying to assess the optimal configuration for a high efficiency generator. Among the possible solutions, a specific configuration which uses permanent magnets for the excitation field was chosen and built to perform a set of experiments.

2010 - Cogging torque reduction methods for internal permanent magnet motors: Review and comparison [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; Bellini, Alberto; Davoli, Matteo
abstract

Internal permanent magnet synchronous machines are spreading in industrial production. High torque density and extended speed operation range are key issues in many fields of applications. Many methods and design guidelines for cogging torque reduction exist in literature and this paper compares them. To this aim, the different design guidelines are applied to a reference machine to assess their effectiveness. Computer FEA analysis are carried out for each case in order to compare the cogging torque reduction potential of the different techniques. Other side effects, such as b.e.m.f and torque quality will be taken into account. The paper contribution is to compare various techniques on a common ground (the reference machine) to identify the most effective ones. ©2010 IEEE.

2010 - Diagnosis of Bearing Faults in Induction Machines by Vibration or Current Signals: a Critical Comparison [Articolo su rivista]
Immovilli, Fabio; Bellini, Alberto; Rubini, Riccardo; C., Tassoni
abstract

Mechanical imbalances and bearing faults account for a large majority of faults in a machine, especially for smallmedium size machines. Therefore their diagnosis is an intensively investigated field of research. Recently many research activities were focused on the diagnosis of bearing faults by current signal. This paper compares the bearing fault detection capability obtained with vibration and current signals. The paper contribution is the use of a simple and effective signal processing technique for both current and vibration signals, and a theoretical analysis of the physical link between faults, modeled as a torque disturbance, and current components. The focus of the paper is on the theoretical development between torsional torque and current component amplitudes and a review of fault models used in literature. Another contribution is the realization of realistic incipient faults and their experimental validation. Radial effects are visible only in case of large failures that result in air-gap variations. Experiments are reported that confirm the proposed approach.

2009 - Design of linear alternators for thermoacoustic machines [Relazione in Atti di Convegno]
Rossi, Andrea; Immovilli, Fabio; Bianchini, Claudio; Bellini, Alberto; Serra, Giovanni
abstract

This paper compares the available technologies for linear electromagnetic alternators and categorizes them in order to find the best solutions for the thermoacoustic based CHCP. Tubular oscillating permanent magnet actuator featuring SMC stator with a quasi-Halbach PM slider is analyzed and modeled theoretically. Here, a similar configuration is compared to other moving magnet structure but employing open modular construction with laminated magnetic steel winding cores and a critical comparison is made relying on electromagnetic and mechanical simulations to retrieve the best solution for the thermoacoustic application. © 2009 IEEE.

2009 - Detection of Generalized Roughness Bearing Fault by Spectral Kurtosis Energy by Vibration or Current Signals [Articolo su rivista]
Immovilli, Fabio; Cocconcelli, Marco; Bellini, Alberto; Rubini, Riccardo
abstract

Generalized roughness is the most common damage occurring to rolling bearing. It produces a frequency spreading of the characteristics fault frequencies, thus being difficult to detect with spectral or envelope analysis. A statistical analysis of typical bearing faults is here proposed in order to identify the spreading bandwidth related to specific conditions, relying on current or vibration measurements only. Then a diagnostic index based on the computation of the energy in the above defined bandwidth is used to diagnose bearing faults. The proposed method was validated experimentally with vibration signals, with robust and reliable results. The same procedure can be extended to current signals.

2009 - Fault Diagnosis of Linear Bearings in Brushless AC Linear Motors [Relazione in Atti di Convegno]
Bianchini, C.; Immovilli, Fabio; Cocconcelli, Marco; Rubini, Riccardo; Bellini, Alberto
abstract

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2009 - Fault diagnosis of linear electric generators for thermoacoustic machines [Relazione in Atti di Convegno]
Rossi, Andrea; Immovilli, Fabio; Bianchini, Claudio; Bellini, Alberto; Serra, Giovanni
abstract

Energy generation and its optimal use are key issues nowadays. In this framework the use of cogeneration (CHP) or trigeneration (CHCP) is an attractive solution towards higher system efficiency. Traditional thermal machines are used as a prime mover in a CHP/CHCP plant. Recently novel technologies were investigated for prime mover and cooler. Among them thermoacoustics is attractive as it allows to embed a prime mover, a cooler and an alternator in a single machine. Moreover, it features reduced maintenance cost as it requires no moving parts but the electric alternator. The design of an efficient electric alternator is one of the major challenge, as it must convert into electricity a small linear displacement of the mover at high frequency. The latter is a critical item in terms of diagnostics also. Here the fault diagnosis of a thermoacoustic generator is investigated, where the major defects are ageing or fatigue of the spring used to center and sustain the mover of electric generator. The fault diagnosis is based on the non invasive analysis of electric signals at the generator terminal. The paper also deals with post fault strategies. © 2009 IEEE.

2009 - On the Detection of Distributed Roughness on Ball Bearings Via Stator Current Energy: Experimental Results [Articolo su rivista]
G., Curcuru'; Cocconcelli, Marco; Immovilli, Fabio; Rubini, Riccardo
abstract

This paper deals with the detection of distributed roughness on ball-bearings mounted on electric motors. Ball bearings allows the rotation of the motor’s shaft and moreover they are intensively used in industrial applications, so a failure of those components produces unexpected downtime of the line-production. Most of the literature techniques focus on the early detection of localized faults on bearing (eg. on the outer ring) in order to determine the bearing life and to plan the bearing replacing. Localized faults can be detected because they have characteristic signatures which is revealed in the frequency spectrum of the vibration signal acquired by an external sensor, eg. accelerometer. Unfortunately other faults exist which do not have a characteristic signatures and then they could not be foreseen accurately: eg. the distributed roughness. In this paper the motor stator current energy is proposed as a fault indicator to identify the presence of the distributed roughness on the bearing. Moreover an orthogonal experiment is set to analyse, through a General Linear Model (GLM), the dependencies of the current energy to the roughness level, but also to other two environmental conditions: the motor velocity and the loads applied externally. ANOVA investigates the statistical significance of the considered factors.

2009 - On the Detection of Distributed Roughness on Ball Bearings Via Stator Current Energy: Experimental Results [Relazione in Atti di Convegno]
G., Curcurù; Cocconcelli, Marco; Immovilli, Fabio; Rubini, Riccardo
abstract

This paper deals with the detection of distributed roughness on ball-bearings mounted on electric motors. Ball bearings allows the rotation of the motor’s shaft and moreover they are intensively used in industrial applications, so a failure of those components produces unexpected downtime of the line-production. Most of the literature techniques focus on the early detection of localized faults on bearing (e.g. on the outer ring) in order to determine the bearing life and to plan the bearing replacing. Localized faults can be detected because they have characteristic signatures which is revealed in the frequency spectrum of the vibration signal acquired by an external sensor, e.g. accelerometer. Unfortunately other faults exist which do not have a characteristic signatures and then they could not be foreseen accurately: e.g. the distributed roughness. In this paper the motor stator current energy is proposed as a fault indicator to identify the presence of the distributed roughness on the bearing. Moreover an orthogonal experiment is set to analyse, through a General Linear Model (GLM), the dependencies of the current energy to the roughness level, and two environmental conditions: the motor velocity and the loads applied externally. ANOVA investigates the statistical significance of the considered factors

2008 - Arc Linear Motors for Direct Drive Robots: Galileo Sphere [Relazione in Atti di Convegno]
Bianchini, Claudio; Immovilli, Fabio; P., Mignano; Bellini, Alberto
abstract

This paper presents the design of an arc linear motor for a new type of robot, named Galileo Sphere, based on direct drive technology for pick and place operations. Pick and place robots require high dynamics and position accuracy and repeatability. A classical implementation is based on rotating electric machines with reduction gearboxes and kinematic mechanisms that convert the rotating motion to linear where necessary.The direct drive technology reduce mechanical losses, backlash, MTBF and a number of components. This technology also achieves higher dynamic and accuracy.The robot has a polar-like configuration with 5 degree of freedom.A dynamical simulator was used to assess motors, that satisfies a typical pick and place trajectory with the different payload. The proposed solution resulted feasible, even at high working frequencies and with payloads up to 4 kg. The precisionand repeatability remained high, within 100 micron.The working is a spherical sector with 1870 mm maximum diameter, and 450mm vertical reach.

2008 - Comparative analysis of CHCP systems based on solar energy [Relazione in Atti di Convegno]
Immovilli, Fabio; Bellini, Alberto; Bianchini, Claudio; Rossi, Andrea; Franceschini, G.
abstract

The combined production of heating, cooling and electricity (CHCP) or trigeneration in a grid-connected energy market may become profitable with respect to traditional systems, where electricity, heat, and cooling are produced or purchased separately. Namely, the use ofsolar energy as a primary energy source can lead to a substantial improvement, overcoming many of the traditional drawback associated with micro-cogeneration and trigeneration.So doing a CHCP system with renewable energy sources is realized, that is an attractivesolution for domestic needs, provided that a cost-effective technical solution is available.This paper reviews and compares CHCP system and technologies based on solar energy.

2008 - Diagnosis of bearing faults of induction machines by vibration or current signals: a critical comparison [Relazione in Atti di Convegno]
Bellini, Alberto; Immovilli, Fabio; Rubini, Riccardo; C., Tassoni
abstract

Early diagnosis of faults in induction machines is an extensively investigated field, for cost and maintenance savings.Mechanical imbalances and bearing faults account for a large majority of faults in a machine,especially for small-medium size machines. Therefore their diagnosis is an intensively investigatedfield or research.Recently many research activities were focused on the diagnosis of bearing faults by currentsignal. Stator current components are generated at predictablefrequencies related to the electrical supply and mechanical frequenciesof bearing faults. However their detection is not always reliable, since the amplitude of fault signaturesin the current signal is very low.This paper compares the bearing fault detection capabilityobtained with vibration and current signals.To this aim a testbed is realized that allows to testvibration and current signal on a machine with healthyor faulty bearings. Signal processing techniquesfor both cases are reviewed and compared in order toshow which procedure is best suited to the differenttype of bearing faults. The paper contribution is the use of a simple and effectivesignal processing technique for both current and vibrationsignals, and a theoretical analysis of the physical link betweenfaults and current components including torque ripple effects. As expected becauseof the different nature of vibration and current, bearingfault diagnosis is effective only for those fault whose mechanicalfrequency rate is quite low.Experiments are reported that confirm the proposed approach.

2008 - Diagnosis of mechanical faults by Spectral Kurtosis Energy [Relazione in Atti di Convegno]
Bellini, Alberto; Cocconcelli, Marco; Immovilli, Fabio; Rubini, Riccardo
abstract

Generalized roughness is the most common damage occouring to roller bearing. It produces a frequency spreading of the characteristics fault frequencies, thus being difficult to detect with spectral or envelope analysis. A statistical analysis of typical bearing faults is here proposed in order to identify the spreading bandwidth related to a specific conditions, relying on current measurements only. Then a diagnostic index based on the computation of the energy in the above defined bandwidth is used to diagnose bearing faults. The proposed method was validated experimentally with vibration signals, with robust and reliable results. Subsequently it has been applied to stator currents monitoring.

2008 - Solar trigeneration for residential applications, a feasible alternative to traditional micro-cogeneration and trigeneration plant [Relazione in Atti di Convegno]
Immovilli, Fabio; Bellini, Alberto; Bianchini, Claudio; Franceschini, G.
abstract

Trigeneration stands for the combined production of electricity, heat, and cooling (CHCP).This paper reviews and compares CHCP system based on solar energy with respect to traditional CHCP ones.A further comparison is made among the possible technologies for solar CHCP to assess the technical solutions more suited to residential applications. Beyond photovoltaic based systems, two other solutions are proposed: a concentrated sunlight all-thermoacoustic system and an hybrid thermo-photovoltaic system.In a grid-connected energy market, the adoption of CHCP plants may become profitable with respect to traditional systems, where the single energies are produced or purchased separately. Specifically, the onset of solar trigeneration can lead to a substantial improvement, overcoming many of the traditional drawback associated with micro-cogeneration and trigeneration.The result is a trigeneration system based totally on renewable energy. This is especially attractive for the residential demand, provided that a cost-effective technical solution is available.

2007 - A DEVICE FOR HANDLING AND/OR PERFORMING WORK OPERATIONS ON OBJECTS [Brevetto]
Immovilli, Fabio
abstract

A device for handling and/or performing work operations on objects comprises: at least a first arm (2) comprising a first end (2a) for supporting a tool (3) for picking or working; means for supporting and moving (4) the first arm (2); a first linear electric motor (5) connected to the first arm (2) for promoting a translation of the first arm (2) along a straight trajectory (X), preferably horizontal, and a second linear electric motor (6), associated to the first linear electric motor (5), developing along a closed path (P), which sets in rotation the first arm (2) about at least a circular trajectory (9).