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

In this paper, fault diagnosis and fault-tolerant control strategies have been studied comprehensively for dual three-phase permanent-magnet synchronous motor (PMSM) drives to improve the reliability. Based on direct torque control (DTC) with space vector modulation, a series of diagnostic and tolerant control methods have been proposed for five types of faults, namely, speed-sensor fault, dc-link voltage-sensor fault, current-sensor fault, open-phase fault, and open-switch fault. First, diagnosis and tolerant schemes are proposed for speed-sensor fault by estimating the rotor angle speed with the rotating speed of stator flux. Second, diagnosis and tolerant schemes are proposed for dc-link voltage-sensor fault by combining the current model based stator flux observer with the voltage model based stator flux observer. Third, a three-step method is designed to diagnose three types of faults related to current signals, namely, current-sensor fault, open-phase fault, and open-switch fault simultaneously. A vector space decomposition based current estimation method is proposed to achieve fault-tolerant control for the current-sensor fault, and the voltage compensation based fault-tolerant control is presented for both open-phase and open-switch faults. The experiments have been taken on a laboratory prototype to verify the effectiveness of the proposed fault diagnosis and fault-tolerant schemes.

Comprehensive Diagnosis and Tolerance Strategies for Electrical Faults and Sensor Faults in Dual Three-Phase PMSM Drives

Achieving a self-reconfigurable fault-tolerant control in multiphase machines requires a fast fault detection and localization. Most fault detection techniques inherit the three-phase approach by defining fault indices in a per-phase basis. A recent approach suggests an alternative fault detection mechanism based on vector space decomposition (VSD) variables, but the study is limited to open-phase faults (OPFs) for a six-phase drive that is regulated under field-oriented control. It is known, however, that 1) the open-switch faults (OSFs) in the converter are more likely than the OPF in the machine and 2) the drive performance in the event of an open-circuit fault is more critical when model predictive control (MPC) is used. This work extends the study of the VSD fault detection method to multiphase machines with different number of phases (five), control strategy (MPC), and type of faults (OPF and OSF). Although experimental results show that MPC misbehaves after the fault occurrence, the fast detection provided by the VSD approach allows a satisfactory transition to postfault mode of operation.

Open-Switch Fault Detection in Five-Phase Induction Motor Drives Using Model Predictive Control

A large number of factors such as the increasingly stringent pollutant emission policies, fossil fuel scarcity and their price volatility have increased the interest towards the partial or total electrification of current vehicular technologies. These transition of the vehicle fleet into electric is being carried out progressively. In the last decades, several technological milestones have been achieved, which range from the development of basic components to the current integrated electric drives made of silicon (Si) based power modules. In this context, the automotive industry and political and social agents are forcing the current technology of electric drives to its limits. For example, the U.S Department of Energy’s goals for 2020 include the development of power converter technologies with power densities higher than 14.1 kW/kg and efficiencies greater than 98%. Additionally, target price of power converters has been set below $3.3/kW. Thus, these goals could be only achieved by using advanced semiconductor technologies. Wide-bandgap (WBG) semiconductors, and, most notably, silicon carbide (SiC) based power electronic devices, have been proposed as the most promising alternative to Si devices due to their superior material properties. As the power module is one of the most significant component of the traction power converter, this work focuses on an in-deep review of the state of the art concerning such element, identifying the electrical requirements for the modules and the power conversion topologies that will best suit future drives. Additionally, current WBG technology is reviewed and, after a market analysis, the most suitable power semiconductor devices are highlighted. Finally, this work focuses on practical design aspects of the module, such as the layout of the module and optimum WBG based die parallelization, placement and Direct Bonded Copper (DBC) routing.

Power module electronics in HEV/EV applications: New trends in wide-bandgap semiconductor technologies and design aspects

Finite-control set model predictive control (FCS-MPC) has been successfully applied to three-phase electric drives and has proven to bring fast dynamics and high flexibility. The extension of FCS-MPC to regulate machines with more than three phases (i.e., multiphase) presents, however, additional challenges. Leaving aside the higher computational requirements, the appearance of additional degrees of freedom requires a simultaneous current tracking in different subspaces. Hence, the accuracy in the fundamental plane needs to be accomplished with no simultaneous excitement of the secondary planes in order to avoid unacceptable inefficiencies. This paper jointly tackles the performance improvement of fundamental and secondary planes following a two-step procedure: individual virtual voltage vectors (VVs) first ensure low circulating currents and the optimal combination of two VVs provides enhanced current tracking in the fundamental plane. Comparative experimental results confirm the satisfactory performance of the proposed strategy.

Model Predictive Control of Six-Phase Induction Motor Drives Using Two Virtual Voltage Vectors

Fault tolerance is much appreciated at industry in applications with high-reliability requirements. Due to their inherent fault-tolerant capability against open-phase faults (OPFs), drives with multiple three-phase windings are ideal candidates in such applications and for this reason many efforts have been devoted to the development of different fault-tolerant control strategies. Fault detection is, however, a previous and mandatory stage in the creation of fault-tolerant drives, and the study of specific OPF detection methods for six-phase drives is still scarce. Taking advantage of the secondary currents (so called x - y currents) that are unique in multiphase machines, this study proposes new fault indices that detect and locate the OPFs without additional hardware. The method proves to be simple and independent of the operating point, control technique, and drive parameters. Comparative experimental results confirm the capability of the proposed method to achieve fast detection times with good robustness.

A Simple, Fast, and Robust Open-Phase Fault Detection Technique for Six-Phase Induction Motor Drives

Malaga (Spain), 4th to 6th April, 2017
Comunicaciones del Congreso Publicadas en: Renewable Energy and Power Quality Journal (RE&PQJ) ISSN 2172 038X, No.15 April 2017

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An open-phase fault detection method for six-phase induction motor drives

Fault detection is a necessary requirement to exploit one of the most important multiphase drives advantages: the enhanced fault tolerance without additional hardware. Among open-circuit faults, those in power switches of voltage source converters (VSCs) are the most common ones. Nevertheless, in other cases a poor connection or incipient faults may cause an imbalance in the value of the stator resistances. In this case the phase is not open but this anomalous situation requires detection and eventual isolation. This phenomenon is usually called resistance dissymmetry and it leads to current imbalance that in turn reduces efficiency and produces overheating. Moreover, the variation of the machine parameter is an important issue in those control methods based on the machine model, as it is the case in model predictive control (MPC). For this reason, this work presents a resistance dissymmetry detection method based on the vector space decomposition (VSD), implemented together with a MPC-based six-phase induction motor drive. Simulation results are employed to validate the goodness of the proposed method.

Natalia Rios-Garcia

Papers

A Simple, Fast, and Robust Open-Phase Fault Detection Technique for Six-Phase Induction Motor Drives

Open-Switch Fault Detection in Five-Phase Induction Motor Drives Using Model Predictive Control

An open-phase fault detection method for six-phase induction motor drives

Resistance dissymmetry localization method based on vector space decomposition approach for six-phase induction machines