The next big change in various industry applications is associated with power dense motors, such as permanent magnet synchronous motors (PMSMs). Utilization of multiphase PMSM can offer an additional fault-tolerant capability to their applications. Combining both advantages, this paper proposes a simple yet robust current control strategy for a five-phase PMSM under normal operation and in a case of a loss of one phase. Traditional linear current controllers successfully applied to reference tracking of a healthy motor may become less efficient during postfault operation due to additional unmodeled dynamics. This paper proposes a modified angular transformation to a special rotating frame in which the postfault permanent magnet flux linkage remains unchanged and the motor model remains decoupled. Following this, a nonlinear current control scheme based on sliding mode control is proposed, which successfully treats model inaccuracies and provides good dynamic performance and tracking accuracy. Feasibility of the proposed control strategy is experimentally validated on a laboratory scale PMSM motor with a digital signal processor/field programmable gate array based drive.

Fault-tolerant control of a five-phase (5Ph) permanent magnet (PM) motor has been recently widely studied, however decoupled modeling under faulty conditions is discussed in less details. In this paper, decoupled model of the 5Ph PM motor under single-phase open fault is investigated and based on the proposed model field oriented control (FOC) is applied to the motor. The proposed model is based on the concept of preserving values of fundamental magnetic motive force (MMF) and back electromotive force (EMF) under single-phase open fault, the same as in healthy case, along with keeping equal torque equation at fundamental rotating space. Nevertheless, the output torque still presents some noises due to third harmonics of air-gap flux and system uncertainties, and to cope with those disturbances, sliding mode control (SMC) is proposed in the speed loop to improve the speed performance. The proposed SMC contains a PI controller and a chattering term, and thus it can be easily tuned. The decoupled model is verified by transient finite element analysis finite element analysis (FEA) and further experiment results are presented to confirm the effectiveness of the proposed control strategy.

Model-based sensorless field-oriented control (FOC) suffers from overparameterization and can be laborious to use for a five-phase permanent magnet synchronous motor. On the other hand, insulated gate bipolar transistor (IGBT) frequently fails in an electric drive. Under IGBT failure, a freewheeling current is observed, and, above all, it carries the failed phase back electromotive force information. Based on this observation, this article presents the design of a brand new sensorless FOC by exploiting the freewheeling current to accommodate both IGBT and position sensor failures, which is expected to further enhance the drive's fault-tolerant capability. The mathematical model of this current is first established to provide a theoretical basis and a comprehensive understanding of the presented sensorless FOC. By virtue of this model, a second-order generalized integrator with a frequency-locked loop can be used as a simple and elegant way to extract position/speed estimates. Experimental results are provided to validate the proposed sensorless FOC philosophy.

This paper investigates the most elementary phase voltage modulation (PVM) for a more generic Five-phase Permanent Magnet Synchronous Motor (5Ph PMSM) drive under single-phase open fault. Most works on this topic are intended for some specific motor types, and in most cases, it assumes the inverter can still be treated as a linear switching-mode power amplifier. This paper figures out that due to an oscillating neutral the phase voltage is unable to be linearly modulated which is to say the simplest SPWM is problematic to fit a newly developed well-decoupled model under single-phase open fault. To this end, a nonlinear transform incorporating the faulty phase voltage is theoretically proposed which alleviates the influence of oscillating neutral on PVM, and several approaches to cancel the need for phase voltage sensors are comparatively investigated. Accordingly, the PVM with repetitive control and back-EMF compensation is put forward to fix the “faulty inverter” in practice. Plausible PVM approaches are tested experimentally, and the superiority of the proposed PVM is confirmed by experimental results.

Deadbeat direct torque control (DBDTC) calculates the voltage vector based on the motor mathematical model and tracks the torque and flux reference within only one sampling cycle. However, in the traditional DBDTC, the reference torque is generated by a speed PI controller, which presents a low dynamic and poor precision, particularly under external disturbances. To sort out this issue, this article proposes an improved DBDTC control method basing on the sliding mode strategy. First, an antidisturbance sliding mode controller (ASMC) is presented which is superior in offering a fast and accurate reference torque for DBDTC. Along the way, an extended sliding mode disturbance observer is introduced, which estimates total disturbances and compensates the sliding mode controller. To reduce the chattering of sliding mode control, a novel reaching law is proposed. This novel reaching law introduces a system-state variable in the exponential terms of power reaching law and, meanwhile, includes an adaptive exponential reaching action. By this means, it increases system convergence rate to the sliding mode surface while suppressing sliding mode chattering. Finally, both simulation and experimental results show that the proposed control method has a better performance in terms of torque ripple reduction and speed dynamic response.

The decoupled model of Five-Phase Permanent Magnet Synchronous Motors (5Ph PMSMs) under a two-phase open circuit has been developed recently, yet the corresponding PWM has not been fully exploited. The Pulse Width Modulation (PWM), which is straightforward for a balanced system, can be problematic to fit a 5Ph PMSM under faulty conditions. During the open faults, the neutral voltage is drifting over the mid-point of DC bus, thus, the PWM typically designed for a balanced system always fails. In this paper, an affine transformation is first presented to offset the drifting neutral effect, and only then PWMs can be effective. A quasi-sinusoidal PWM, a Space Vector PWM, and a min-max Carrier-based PWM are presented and compared experimentally. Each method has its own merits and demerits, and their effectiveness or rather the proposed affine transformation is validated by the experimental results.