E. Levi

Liverpool John Moores University, Liverpool, England, United Kingdom

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Publications (210)358.88 Total impact

  • IET Power Electronics 06/2015; 8(6). DOI:10.1049/iet-pel.2014.0327 · 1.32 Impact Factor
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    ABSTRACT: This paper considers an integrated onboard charger for electric vehicles that incorporates an asymmetrical nine-phase machine and an inverter into the charging process. The charging is from three-phase mains, and it employs exclusively the power electronic components that already exist on board the vehicle and that are mandatory for the propulsion. No new elements are introduced. Moreover, the charging is achieved without any hardware reconfiguration since the existing elements and their connections are not altered during the transfer from propulsion to the charging mode. Instead, the operating principle is based on additional degrees of freedom that exist in nine-phase machines. These degrees of freedom are employed to avoid electromagnetic torque production in the machine during the charging process, although currents flow through its stator windings. The configuration operates with a unity power factor and is capable of vehicle to grid (V2G) operation as well. A detailed theoretical analysis is given, and the control for the charging/V2G and propulsion modes is discussed. Theoretical analysis is validated by experiments for charging, V2G, and propulsion operating regimes.
    IEEE Transactions on Industrial Electronics 05/2015; 62(5):3285-3295. DOI:10.1109/TIE.2014.2345341 · 6.50 Impact Factor
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    ABSTRACT: A four-level five-phase open-end winding (OeW) drive topology is introduced in the paper. The drive comprises a five-phase induction machine with open-end stator windings, supplied using two two-level voltage source inverters with isolated and unequal dc-link voltages, in the ratio 2:1. The topology offers the advantages of a modular structure with fewer semiconductor components and has a greater potential for fault tolerance, compared to an equivalent single-sided fourlevel drive. Due to the large number of switching states, development of a suitable space-vector pulse-width modulation (SVPWM) method can be challenging. Hence, this paper examines the implementation of two level-shifted carrier-based modulation (CBPWM) methods. The effect of dead time on the drive performance is discussed and it is shown that simultaneous PWM switching of both inverters can lead to degraded output phase voltage waveforms. Detailed analysis of this phenomenon is presented, a solution is proposed, and the modified modulation techniques are incorporated in an experimental set-up, at first in conjunction with V/f control. Once when the proof-of-concept has been provided, full field oriented control (FOC) is implemented in this OeW drive topology for the first time; detailed experimental testing is conducted and results are reported.
    IEEE Transactions on Industrial Electronics 04/2015; · 6.50 Impact Factor
  • IEEE Transactions on Industrial Electronics 01/2015; DOI:10.1109/TIE.2015.2418741 · 6.50 Impact Factor
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    ABSTRACT: The analysis and assessment of the pulsewidth modulation (PWM) techniques is commonly based on the comparison of the total harmonic distortion (THD) results. THD is usually calculated by application of the Fourier transformation and by taking a limited number of harmonics into the consideration. In this paper, derivation of analytical formulas for the phase voltage THD is presented. The considered system is a symmetrical multiphase star-connected load, supplied from a multilevel pulsewidth-modulated voltage-source inverter (VSI, three-phase case is also covered). The solution is based on the Parseval's theorem, which links frequency spectrum and time domain through the average power (i.e., root-mean-square (rms) squared value) of the signal. The assumption throughout the derivations is that the ratio of the switching to fundamental frequency is high. Derivations are based on the integration of the power of the PWM signal in a single switching period over the fundamental period of the signal. Only ideal sinusoidal reference voltages are analyzed, and no injection of any type is considered. Formulas for phase voltage THD for any number of phases are derived for two- and three-level cases, for the most commonly used carrier-based methods. Comparison of the analytically obtained curves with simulation and experimental results shows a high level of agreement and validates the analysis and derivations.
    IEEE Transactions on Power Electronics 01/2015; 30(3):1645-1656. DOI:10.1109/TPEL.2014.2316912 · 5.73 Impact Factor
  • IEEE Transactions on Power Electronics 01/2015; DOI:10.1109/TPEL.2015.2424592 · 5.73 Impact Factor
  • IEEE Transactions on Industrial Electronics 01/2015; DOI:10.1109/TIE.2015.2412516 · 6.50 Impact Factor
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    ABSTRACT: Independently controlled multimotor drives are typically realized by using a common dc link and independent sets of three-phase inverters and motors. In the case of an open-circuit fault in an inverter leg, one motor becomes single phase. To enable continued controllable operation by eliminating single phasing, the supply for the motor phase with the faulted inverter leg can be paralleled to a healthy leg of another inverter using hardware reconfiguration. Hence, the two motors are now supplied from a five-leg inverter, which has inherent voltage and current limitations. Theoretically, violating the voltage limit leads to inverter overmodulation and large torque oscillations. It is shown here that the finite-control-set model predictive control, designed to control the machines' stator flux and torque, can consider the inherent voltage limit dynamically in the control loop. Apart from preserving the independent control of the two machines, the additional constraint consideration significantly widens the operating speed ranges of the machines. In particular, it is shown that, whenever the voltage limit is entered, the controller reduces the stator flux level automatically, without requiring external flux reference change. The obtained performance is illustrated using experimental results and is also compared to the conventional two-motor field-oriented control scheme. The control concept is thus fully experimentally verified.
    IEEE Transactions on Industrial Electronics 12/2014; 61(12):6603-6614. DOI:10.1109/TIE.2014.2317135 · 6.50 Impact Factor
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    ABSTRACT: The paper studies pulse width modulation (PWM) techniques for a five-phase multilevel open-end winding drive with two inverters supplied with unequal dc-link voltages, which are in the ratio 2:1. It is shown in the paper that application of in-phase disposition modulation (PD-PWM), often used in multiphase multilevel converters, results in overcharging of the capacitor in the dc-link of the converter intended to operate at the lower dc voltage. The voltage space vector combinations which lead to the overcharging are identified and two decoupled modulation techniques which do not activate the troublesome vector combinations are proposed. The performance of the developed modulation techniques is investigated using simulations and an experimental prototype, and the results are presented in the paper.
    Energy Conversion Congress and Exposition (ECCE), Pittsburgh, PA, USA; 09/2014
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    ABSTRACT: A two-motor drive, supplied by a five-leg inverter, is considered in this paper. The independent control of machines with full dc-bus voltage utilization is typically achieved using an existing pulsewidth modulation (PWM) technique in conjunction with field-oriented control, based on PI current control. However, model predictive control (MPC), based on a finite number of control inputs [finite-control-set MPC (FCS-MPC)], does not utilize a pulsewidth modulator. This paper introduces three FCS-MPC schemes for synchronous current control in this drive system. The first scheme uses all of the available switching states. The second and third schemes are aimed at reducing the computational burden and utilize a reduced set of voltage vectors and a duty ratio partitioning principle, respectively. Steady-state and transient performances are analyzed and compared both against each other and with respect to the field-oriented control based on PI controllers and PWM. All analyses are experimental and use the same experimental rig and test conditions. Comparison of the predictive schemes leads to the conclusion that the first two schemes have the fastest transient response. The third scheme has a much smaller current ripple while achieving perfect control decoupling between the machines and is of low computational complexity. Nevertheless, at approximately the same switching loss, the PI-PWM control yields the lowest current ripple but with slower electrical transient response.
    IEEE Transactions on Industrial Electronics 08/2014; 61(8):3867-3878. DOI:10.1109/TIE.2013.2286573 · 6.50 Impact Factor
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    ABSTRACT: Control techniques for electrical machines have been applied for many years to what are called electrical drives (EDs) or adjustable speed drives (ASDs), which are part of almost 25% of applications of electrical machines in the industry. Therefore, this technology has followed the evolution of performances of both power converters and electrical actuators or generators for more than 50 years and the invention of silicon-controlled rectifiers. The aim of this article is not to cover a survey of EDs or ASDs since it has already been covered recently but rather to present trends of the control part related to this technology. Of course, the control part is fully dependent of the power part and cannot be treated as a stand-alone technique.
    IEEE Industrial Electronics Magazine 06/2014; 8(2):43-55. · 5.06 Impact Factor
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    ABSTRACT: Control techniques for electrical machines have been applied for many years to what are called electrical drives (EDs) or adjustable speed drives (ASDs), which are part of almost 25% of applications of electrical machines in the industry. Therefore, this technology has followed the evolution of performances of both power converters and electrical actuators or generators for more than 50 years and the invention of silicon-controlled rectifiers. The aim of this article is not to cover a survey of EDs or ASDs since it has already been covered recently [1] but rather to present trends of the control part related to this technology. Of course, the control part is fully dependent of the power part and cannot be treated as a stand-alone technique.
    IEEE Industrial Electronics Magazine 06/2014; 8(2):43-55. DOI:10.1109/MIE.2014.2313752 · 5.06 Impact Factor
  • 7th IET International Conference on Power Electronics, Machines and Drives,, Manchester; 05/2014
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    ABSTRACT: Open-end winding three-phase drive topologies have been extensively investigated in the last two decades. In the majority of cases supply of the inverters at the two sides of the winding is provided from isolated dc sources. Recently, studies related to multiphase open-end winding drives have also been conducted, using isolated dc sources at the two winding sides. This paper investigates for the first time a five-phase open-end winding configuration, which is obtained by connecting a two-level five-phase inverter at each side of the stator winding, with both inverters supplied from a common dc source. In such a configuration it is essential to eliminate the common-mode voltage (CMV) that is inevitably created by usual PWM techniques. Based on the vector space decomposition (VSD), the switching states that create zero CMV are identified and plotted. A space vector pattern with large redundancy of switching states is obtained. Suitable space vectors are then selected to realize the required voltage reference at the machine terminals with zero CMV. The large number of redundant states enables some freedom in the choice of switching states to impress these space vectors. Out of numerous possibilities, two particular switching sequences are chosen for further investigation. Both are implemented in an experimental setup, and the results are presented and discussed.
    IEEE Transactions on Industrial Electronics 05/2014; 61(5):2197-2207. DOI:10.1109/TIE.2013.2272273 · 6.50 Impact Factor
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    ABSTRACT: This paper proposes a noninvasive temperature measurement technique of indirect type, applicable in the permanent magnet synchronous motor (PMSM) drives. The motor temperature is required for protection and monitoring purposes, as well as for updating temperature-dependent control parameters. Direct measurement with dedicated sensors requires peripherals and cabling; hence, it is quite involved and often avoided. Temperature estimation based on test signal injection contributes to torque ripple and often relies on other motor parameters. A solution is proposed here, which makes the use of intrinsic pulse-width modulation excitation and does not use electrical or thermal parameters of the considered PMSM. The temperature of the stator winding is estimated from the motor input impedance $bm Z_{bf IN}$(ω) calculated over the range of frequencies starting at and going well beyond $bm f_{bf PWM}$. The paper includes analytical considerations, implementation details and experimental verification obtained with a 4.5-kW PMSM used in battery-supplied propulsion systems.
    IEEE Transactions on Energy Conversion 03/2014; 29(1):215-223. DOI:10.1109/TEC.2013.2292566 · 3.35 Impact Factor
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    ABSTRACT: This paper presents an investigation of the finite-control-set model predictive control (FCS-MPC) of a five-phase induction motor drive. Specifically, performance with regard to different selections of inverter switching states is investigated. The motor is operated under rotor flux orientation, and both flux/torque producing (d-q) and nonflux/torque producing (x-y) currents are included into the quadratic cost function. The performance is evaluated on the basis of the primary plane, secondary plane, and phase (average) current ripples, across the full inverter's linear operating region under constant flux-torque operation. A secondary plane current ripple weighting factor is added in the cost function, and its impact on all the studied schemes is evaluated. Guidelines for the best switching state set and weighting factor selections are thus established. All the considerations are accompanied with both simulation and experimental results, which are further compared with the steady-state and transient performance of a proportional-integral pulsewidth modulation (PI-PWM)-based current control scheme. While a better transient performance is obtained with FCS-MPC, steady-state performance is always superior with PI-PWM control. It is argued that this is inevitable in multiphase drives in general, due to the existence of nonflux/torque producing current components.
    IEEE Transactions on Industrial Electronics 01/2014; 61(1-1):149-163. DOI:10.1109/TIE.2013.2248334 · 6.50 Impact Factor
  • E. Levi, M. Jones, O. Dordevic
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    ABSTRACT: In this paper derivation of an analytical formula for the leg voltage THD is presented. The considered system is a leg of a multilevel pulse width modulated (PWM) voltage source inverter (VSI). The solution is based on the Parseval's theorem. The assumption throughout the derivations is that the ratio of the switching to the fundamental frequency is high. Derivations are based on the integration of the power of the PWM signal in a single switching period over the fundamental period of the signal. Only an ideal sinusoidal reference leg voltage is analysed. Analytical expression for the leg voltage THD is given for any number of levels. Validity of the derived analytical equations is confirmed by simulations and experiments.
    7th IET International Conference on Power Electronics, Machines and Drives (PEMD 2014); 01/2014
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    ABSTRACT: Using the vector space decomposition approach, the currents in a multiphase machine with distributed winding can be decoupled into the flux and torque producing α-β components, and the loss-producing x-y and zero-sequence components. While the control of α-β currents is crucial for flux and torque regulation, control of x-y currents is important for machine/converter asymmetry and dead-time effect compensation. In this paper, an attempt is made to provide a physically meaningful insight into current control of a six-phase machine, by showing that the fictitious x-y currents can be physically interpreted as the circulating currents between the two three-phase windings. Using this interpretation, the characteristics of x-y currents due to the machine/converter asymmetry can be analyzed. The use of different types of x-y current controllers for asymmetry compensation and suppression of dead-time-induced harmonics is then discussed. Experimental results are provided throughout the paper, to underpin the theoretical considerations, using tests on a prototype asymmetrical six-phase induction machine.
    IEEE Transactions on Power Electronics 01/2014; 29(1):407-417. DOI:10.1109/TPEL.2013.2248170 · 5.73 Impact Factor
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    ABSTRACT: This paper discusses the operation of a multiphase system, which is aimed at both variable-speed drive and generating (e.g., wind energy) applications, using back-to-back converter structure with dual three-phase machine-side converters. In the studied topology, an asymmetrical six-phase induction machine is controlled using two three-phase two-level voltage source converters connected in series to form a cascaded dc link. The suggested configuration is analyzed, and a method for dc-link midpoint voltage balancing is developed. Voltage balancing is based on the use of additional degrees of freedom that exist in multiphase machines and represents entirely new utilization of these degrees. The validity of the topology and its control is verified by simulation and experimental results on a laboratory-scale prototype, thus proving that it is possible to achieve satisfactory dc-link voltage control under various operating scenarios.
    IEEE Transactions on Industrial Electronics 01/2014; 61(1):164-176. DOI:10.1109/TIE.2013.2248338 · 6.50 Impact Factor
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    ABSTRACT: Multiphase electric drives have been recently proposed for applications where the highest overall system reliability and a reduction in the total power per phase are required. Strategies derived from the conventional field-oriented control have been traditionally used in high-performance speed-control applications of multiphase drives. The well-known direct torque control (DTC) technique has been also applied in the multiphase case, but the achieved performance with a hysteresis-control-based approach is far from that obtainable with the three-phase drive, although the control structure is actually more complex. In this paper, a predictive-torque-control method is introduced as an alternative to the DTC technique for the high-performance variable-speed operation of multiphase drives. Simulation and experimental results are provided to illustrate the properties of the developed method.
    IEEE Transactions on Industrial Electronics 08/2013; 60(8):2957-2968. DOI:10.1109/TIE.2012.2198034 · 6.50 Impact Factor

Publication Stats

4k Citations
358.88 Total Impact Points

Institutions

  • 1994–2014
    • Liverpool John Moores University
      • • School of Engineering, Technology and Maritime Operations
      • • Electrical Electronic Engineering Research Centre
      Liverpool, England, United Kingdom
  • 1994–2013
    • University of Liverpool
      • • School of Engineering
      • • Department of Electrical Engineering and Electronics
      Liverpool, England, United Kingdom
  • 2011
    • University of Vigo
      • Department of Electronics Technology
      Vigo, Galicia, Spain
  • 2003–2008
    • University of Belgrade
      • School of Electrical Engineering
      Belgrade, SE, Serbia
  • 2006
    • Politecnico di Torino
      • DET - Department of Electronics and Telecommunications
      Torino, Piedmont, Italy
  • 2004
    • Northumbria University
      • School of Computing, Engineering and Information Sciences
      Newcastle-on-Tyne, England, United Kingdom
  • 1999–2004
    • University of Novi Sad
      • Faculty of Technical Sciences
      Varadinum Petri, Autonomna Pokrajina Vojvodina, Serbia
  • 2002
    • Chongqing University
      Ch’ung-ch’ing-shih, Chongqing Shi, China