This article attempts to cover the most recent advancements in multiphase drives (MPDs), which are candidates for replacing three-phase drives in electric vehicle (EV) applications. Multiphase machines have distinctive features that arouse many research directions. This article reviews the recent advancements in several aspects such as topology, control, and performance to evaluate the possibility of exploiting them more in EV applications in future. The six-phase drives are extensively covered here because of their inherent structure as a dual three-phase system, which eases the production process. This article presents different topologies used in dual three-phase drives and the modulation techniques used to operate them as well as the status of using MPDs in traction applications industrially and the upcoming trends toward promoting this technology more.

A Review on Multiphase Drives for Automotive Traction Applications

Multiphase Electric Drives: Introduction

This paper proposes a procedure that is suitable for experimental investigation of real-time open-switch and open-phase faults diagnosis of a five-leg voltage source inverter feeding a five-phase biharmonic permanent magnet synchronous machine (PMSM). The algorithm is based on the specific characteristics of multiphase machines, which allows inverter fault detection with sufficient robustness of the algorithm in the presence of fundamental and third harmonic components. First, the inverter fault effects analysis is achieved in the characteristic subspaces of the five-phase PMSM. Specificities that are interesting for the elaboration of a real-time fault detection and identification (FDI) process are highlighted. Original and particular algorithms are used for an accurate 2-D normalized fault vector extraction in a defined fault reference frame. This frame is dedicated only for FDI. To ensure the high immunity of the FDI process against transient states, a particular normalization procedure is applied. The normalized diagnostic signals are formulated from the defined frame and other variables derived from the reference and measured currents. Simulation and experimental results of open-switch and open-phase faults are provided to validate the proposed algorithm.

https://hal.archives-ouvertes.fr/hal-01560026/document

Experimental Investigation of Inverter Open-Circuit Fault Diagnosis for Biharmonic Five-Phase Permanent Magnet Drive

Torque density of multiphase PMSMs can be enhanced by using current harmonic injection (CHI) techniques that utilize potential torque-producing nonfundamental spatial harmonics of the stator winding function (SWF) to produce an additional average torque. This possibility is ignored in the existing multiphase winding design methods that only aim at maximizing the fundamental spatial SWF harmonic, thus neglecting the remaining torque-producing spatial harmonics. These methods are also restricted by the number of machine phases. Motivated by these drawbacks in the existing methods, this paper proposes a novel heuristic algorithm for designing symmetrical multiphase concentrated windings with maximized average torque by considering all the nonfundamental torque-producing spatial SWF harmonics. The proposed approach is valid for any number of phases. Accordingly, an index is proposed to evaluate the multiphase winding performance in terms of its torque density under the CHI technique. The proposed method is formulated by using analytical treatment of the SWF, based on which, a systematic approach for calculating harmonic winding factors and evaluating the average torque is synthesized. The proposed approach is validated through case studies and experimental tests.

Design of Optimal Winding Configurations for Symmetrical Multiphase Concentrated-Wound Surface-Mount PMSMs to Achieve Maximum Torque Density Under Current Harmonic Injection

Multiphase drives offer enhanced fault-tolerant capabilities compared with conventional three-phase ones. Their phase redundancy makes them able to continue running in the event of faults (e.g., open/short-circuits) in certain phases. Moreover, their greater number of degrees of freedom permits improving diagnosis and performance, not only under faults affecting individual phases, but also under those affecting the machine/drive as a whole. That is the case of failures in the dc link, resolver/encoder, control unit, cooling system, etc. Accordingly, multiphase drives are becoming remarkable contenders for applications where high reliability is required, such as electric vehicles and standalone/off-shore generation. Actually, the literature on the subject has grown exponentially in recent years. Various review papers have been published, but none of them currently cover the state-of-the-art in a comprehensive and up-to-date fashion. This two-part paper presents an overview concerning fault tolerance in multiphase drives. Hundreds of citations are classified and critically discussed. Although the emphasis is put on fault tolerance, fault detection/diagnosis is also considered to some extent, because of its importance in fault-tolerant drives. The most important recent advances, emerging trends and open challenges are also identified. Part 1 provides a comprehensive survey considering numerous kinds of faults, whereas Part 2 is focused on phase/switch open-circuit failures.

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A Comprehensive Survey on Fault Tolerance in Multiphase AC Drives, Part 1: General Overview Considering Multiple Fault Types

In this paper, the study of the torque and power versus speed characteristics for a family of five-phase surface-mounted permanent magnet machine is carried out. With considering hypotheses [linear magnetic modeling, only first and third harmonic terms in the back electromotive force (EMF) and current spectrums], an optimization problem that aims to maximize the torque for given maximum peak voltage and root mean square (RMS) current is formulated: the optimal torque sharing among the two virtual machines (the two dq -axis subspaces) that represent the real five-phase machine is thus calculated for any mechanical speed. For an inverter and a dc voltage sized with only considering the first harmonic of back EMF and current, the problem is solved with changing the virtual machine back EMFs and inductances ratios. With the introduction of the maximum torque/speed point, maximum power/speed point, and maximum reachable speed, it can be shown that, if the inductance ratio is large enough for given Volt–Ampere rating, the machine can produce higher torque without reducing its speed range, thus meaning that the capability of the inverter to work is improved with the use of the third harmonic. This property is all the truer as the base armature reaction is large. A particular five-phase machine is sized and numerically analyzed to check this property.

/pdf/maximum-reachable-torque-power-and-speed-for-five-phase-spm-8s82be7swe.pdf

Maximum Reachable Torque, Power and Speed for Five-Phase SPM Machine With Low Armature Reaction

In the context of traction drives with required torque transient capabilities and a classically wide flux weakening speed range, this paper gives design considerations of a particular double-polarity (DP) five-phase machine. Beyond its intrinsic fault tolerance due to its five phases, its specificity is the ability to develop torques of comparable values under three kinds of supply: with only first, third or both first, and third sinusoidal currents. This property, due to first $(E_{1})$ and third $(E_{3})$ harmonic electromotive forces of comparable values, gives more degrees of freedom for the control of the machine. Unlike three-phase sinusoidal machine, flux weakening is no more the unique solution when maximum voltage is reached. Thanks to the extra degrees of freedom in this kind of machines, more possibilities for the control of the torque and current supply can be applied. At first, elements for the choice of slots/poles combination of such DP machines are given. Then, in the case of an interior permanent magnet synchronous machine, possible adaptations of the rotor are proposed in order to bring the double p/3p polarity property. The last design criterion considered is the level of eddy-current losses, important at high frequencies. For the proof of the concept effectiveness, a prototype with a five-phase fractional-slot concentrated winding of 40 slots and 16/48 poles is presented with results from the experimental setup and finite element modeling. A comparison with the equivalent no-fault-tolerant three-phase 24 slots/16 poles machines is also carried out.

/pdf/design-considerations-of-five-phase-machine-with-double-p-3p-1pajf9t4rs.pdf

Design Considerations of Five-Phase Machine With Double p/3p Polarity

The purpose of the paper is to present the potentialities in terms of the control of a new kind of PM synchronous machine. With five phases and electromotive forces whose first ( E 1 ) and third ( E 3 ) harmonics are of similar amplitude, the studied machine, so-called bi-harmonic, has properties that are interesting for traction machine payload. With three-phase machines, supplied by a mono-harmonic sinusoidal current, the weak number of freedom degrees limits the strategy of control for traction machines especially when voltage saturation occurs at high speeds. As the torque is managed for three-phase machines by a current with only one harmonic, flux weakening is necessary to increase speed when the voltage limitation is reached. The studied five-phase machine, thanks to the increase in the number of freedom degrees for control, aims to alleviate this fact. In this paper, three optimized control strategies are compared in terms of efficiency and associated torque/speed characteristics. These strategies take into account numerous constraints either from the supply (with limited voltage) or from the machine (with limited current densities and maximum acceptable copper, iron and permanent magnet losses). The obtained results prove the wide potentialities of such a kind of five-phase bi-harmonic machine in terms of control under constraints. It is thus shown that the classical Maximum Torque Per Ampere (MTPA) strategy developed for the three-phase machine is clearly not satisfying on the whole range of speed because of the presence of iron losses whose values can no more be neglected at high speeds. Two other strategies have been then proposed to be able to manage the compromises, at high speeds, between the high values of torque and efficiency under the constraints of admissible total losses either in the rotor or in the stator.

Comparison of Optimized Control Strategies of a High-Speed Traction Machine with Five Phases and Bi-Harmonic Electromotive Force

This paper proposes a simple and effective scheme for Direct Torque Control (DTC) of Brushless DC Motor. Unlike the traditional DTC where both the torque and flux must to be employed in order to deliver the switching table for the inverter, the proposed DTC scheme utilizes only the torque information. By considering the particular operating principle of the motor, the instantaneous torque can be estimated only by using back EMF ratio in an unified differential equation. The simulation results have shown the good performance of the proposed scheme. It can be seen thus a very suitable technique for EV drives which need fast and precise torque response.

/pdf/five-phase-version-of-12slots-8poles-three-phase-synchronous-4rj0u0sty7.pdf

Five-Phase Version of 12Slots/8Poles Three-Phase Synchronous Machine for Marine-Propulsion

The paper studies the impact of first and third current-harmonic repartition in a five-phase Permanent Magnet machine whose Electromotive Forces (emfs) have first and third harmonics of the same amplitude. With a five-phase machine, it is possible for the torque production to achieve independent controls of the first and third harmonics of currents by using a vector control in each one of the two characteristic orthogonal sub-spaces of the machine. The same torque quality as obtained with a three-phase machine with sinusoidal emf can be thus obtained with a non-sinusoidal emf and with one more supplementary degree of freedom for the control. Based on the Maximum Torque Per Ampere (MTPA) strategy used for three-phase machines, a comparison of the obtained torque/speed characteristics of the machine is achieved using either one or two harmonics. The voltage limits imposed by the Voltage Source Inverter and two different values of the maximum allowed current densities are taken into account for obtaining the optimum repartition between first and third harmonics of currents: it appears that at first, from the point of view of efficiency, the MTPA is not optimal except for low speeds and secondly that the repartition of currents is not trivial and depends for example on the considered maximum current densities.

/pdf/maximum-torque-per-ampere-strategy-for-a-biharmonic-five-1vy5krssz4.pdf

Hussein Zahr

Papers

Maximum Reachable Torque, Power and Speed for Five-Phase SPM Machine With Low Armature Reaction

Design Considerations of Five-Phase Machine With Double p/3p Polarity

Comparison of Optimized Control Strategies of a High-Speed Traction Machine with Five Phases and Bi-Harmonic Electromotive Force

Five-Phase Version of 12Slots/8Poles Three-Phase Synchronous Machine for Marine-Propulsion

Maximum Torque Per Ampere strategy for a biharmonic five-phase synchronous machine