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

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

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

With the increasing demand for electric vehicles, reliability in motor drives is an issue of growing importance. Over the years, various fault-tolerant three-phase motor drive topologies have been introduced and their performances have been investigated. Evaluation of the postfault power of a fault-tolerant drive should take into account both the postfault torque and speed, which depend on both the postfault current and voltage limits. Nevertheless, the postfault motor voltage limits are usually omitted from discussion. Furthermore, current limit in induction motor drive is not as direct as that in permanent magnet motor drive, due to the presence of the flux current. In this paper, the performances of available fault-tolerant three-phase induction motor drives have been reinvestigated, taking into account the impact of not just currents, but also voltage limits for both the inverter and machine. By deriving the postfault machine voltage equations, the effects of machine parameters and operating point on the voltage limit and hence the speed limit are explained. Depending on the topology, the motor may be able to run above the rated speed to gain extra power. The analysis is verified through experiment results on a 1 kW induction machine for four different fault-tolerant drive topologies.

Performance Comparison of Fault-Tolerant Three-Phase Induction Motor Drives Considering Current and Voltage Limits

The fault tolerance of electric drives is highly appreciated at industry for security and economic reasons, and the inherent redundancy of six-phase machines provides the desired fault-tolerant capability with no extra hardware. For this reason some recent research efforts have been focused on the fault-tolerant design, modeling, and control of six-phase machines. Nevertheless, a unified and conclusive analysis of the postfault capability of six-phase machine is still missing. This paper provides a full picture of the postfault derating in generic six-phase machines and a specific analysis of the fault-tolerant capability of the three mainstream six-phase induction machines (asymmetrical, symmetrical, and dual three phase). Experimental results confirm the theoretical post fault current limits and allow concluding, which is the best six-phase machine for each fault scenario and neutral arrangement.

A Unified Analysis of the Fault Tolerance Capability in Six-Phase Induction Motor Drives

Pico-hydro generation system is the effective way to help the remote communities by generates electricity using water as a main source. The main objective of this project is to introduce the green technology for the society in order to reduce the cost of fuel consumption. Green technology is an alternative energy whereas it is cheap, effective and reliable. It can reduce sources of fuel, capital costs and pollution. Furthermore, the idea of this project is to generate electricity by develop a prototype of pico-hydro generation system that produce low capacity to be used in rural communities. Generally, this project focused on designing and producing a pico-hydro system that can be used for small capacity equipments such as motor and bulb. Besides, this project able to analyze the output of generator based on the rotation of turbine. Water flow in the high-pressure PVC pipe has potential to drive the turbine where it is connected with a generator to convert mechanical energy to electrical energy. In this project, it can be found that the pulley system can increase the efficiency of the turbine. The turbine that connected to the pulley system required lower speed compared to the turbine that connected directly to the generator.

Pico-hydro power generation using dual pelton turbines and single generator

This paper presents a fault-tolerant investigation of symmetrical multi-phase induction machines (five-phase, sixphase, seven-phase and nine-phase) in terms of minimum loss and maximum torque with single isolated neutral point under open-circuit fault at one of the phases. Minimum reconfiguration of the controller attainable for the post-fault control by using normal decoupling transformation. The postfault performance is carried out based on derating factor, minimum stator copper loss and minimum peak current. The simulation results confirm the validity of the theoretical postfault current limits for symmetrical multi-phase induction machines under one open-phase fault.

Fault tolerant capability of symmetrical multiphase machines under one open-circuit fault

Effects of flux derating methods on torque production of fault-tolerant polyphase induction drives

This paper presents the comparison between two switching techniques for a multi-phase voltage source inverter (VSI) using Space Vector Modulation (SVPWM). Two different techniques which based on large vectors and the combination of large and medium vectors have been examined under a two-level five-phase inverter. The performance of these techniques are observed and evaluated in terms of harmonic contents for voltage waveform by employing MATLAB/Simulink software. It can be observed that the unwanted harmonic contents is produced in the auxiliary subspace (d3-q3) and embedded in the fundamental subspace (d1-q1). It can also be observed that the switching technique using combination of large and medium vectors has rapidly reduced the harmonic contents produced by d3-q3 subspace especially the 3rd and 7th harmonics order.

Wan Noraishah Wan Abdul Munim

Papers

A Unified Analysis of the Fault Tolerance Capability in Six-Phase Induction Motor Drives

Pico-hydro power generation using dual pelton turbines and single generator

Fault tolerant capability of symmetrical multiphase machines under one open-circuit fault

Effects of flux derating methods on torque production of fault-tolerant polyphase induction drives

Multi-phase inverter Space Vector Modulation