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Multiphase machines are gaining increasing popularity because of their distinct advantages over three-phase counterparts, such as reduced per phase power rating, improved reliability and increased degrees of freedom. This paper overviews the development history of multiphase machines and drive techniques in Section II. Three kinds of drive algorithms, including Field-Oriented Control (FOC), Direct Torque Control (DTC) and Model Predictive Control (MPC), are introduced in Section III. Then two types of fault-tolerant methods are compared in Section IV, which are the Vector Space Decomposition (VSD) strategy and Optimal Current Control (OCC) method. Furthermore, different types of existing multiphase converter topologies are listed in Section V, and various kinds of multiphase PWM methods are discussed in Section VI. Finally, based on the review, developing trends of multiphase drive techniques are forecasted.

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Electric propulsion is widely used in ship propulsion systems, and multiphase machines are gaining increasing popularity because of their fault-tolerant ability, high power density, and reduced torque ripple. This study concentrates on the tandem ship propulsion configuration with two 15-phase induction machines (IMs) fixed on the same shaft. Based on fieldoriented control and reconfiguration fault-tolerant control for the single 15-phase IM, the master-slave coordinated control strategy is designed for the tandem motors, which can not only achieve power allocation between two motors during normal operation, but also minimise the total stator copper loss of the two motors and maximise the propulsion output power ability during fault-tolerant operation. Experiment results from a ship propulsion experimental platform verify the effectiveness of the proposed control strategies.

This paper proposes optimized control methods for global minimum backflow power based on a triple-phase-shift (TPS) control strategy. Three global optimized methods are derived to minimize the backflow power on the primary side, on the secondary side and on both sides, respectively. Backflow power transmission is just a portion of non-active power transmission in a dual active bridge (DAB) converter. Non-active power transmission time is proposed in this paper, which unifies zero power transmission and backflow power transmission. Based on the proposed index, an optimized control method is derived to achieve both the maximum effective power transmission time and minimum current stress of DAB at the same time. A comparative analysis is performed to show the limitations of the minimum backflow power optimization method. Finally, a prototype is built to verify the effectiveness of our theoretical analysis and the proposed control methods by experimental results.

The current imbalance between stator phase windings could shorten the motor life and affect the drive performance, whereas in case of multiphase drive applications, there is not a general current balance control strategy that can apply to symmetrical inverters with any phase number m. Based on the generalized Symmetrical Component Theory, this letter analyzed the values of relative symmetrical components of multiphase systems in balanced and unbalanced cases. Then developed from the conventional Rotor-flux Oriented Control (RFOC), the current-balance RFOC is proposed to compensate the current imbalance for symmetrical m-phase inverters. Finally, experiment results from the five-phase and nine-phase drive systems confirm the validity of the control strategy in eliminating current imbalance. Index Terms-Multiphase, voltage source inverter (VSI), current imbalance.ɶ I can be called positive and negative k th

Fault-tolerant capability greatly promoted the application of multiphase machines on safety-critical occasions, and fault-tolerant control strategies are required to suppress the torque ripples. Based on the generalised symmetrical components (SCs) theory, a general expression of the independent SCs is derived during the fault-tolerant operation of symmetrical multiphase machines in this study, and coefficients of the four basic rotating components in the general expressions are calculated for specific open-circuit conditions. Then the bidirectional rotating proportional-integral controllers are designed to control all the rotating components in each SC. Considering control loops for all the independent SCs, an enhanced rotor fieldoriented control fault-tolerant strategy is proposed for symmetrical multiphase induction machines (IMs) with any phase number m. Furthermore, additional rotating current controllers in the first SC control loop are added to reduce the low-order current harmonics during the fault-tolerant operation. Experimental evaluations in terms of the transient, dynamic and harmonic performances on both five-phase and nine-phase IM drive platforms are provided to verify the effectiveness of the proposed fault-tolerant strategy.