In this paper, fault diagnosis and tolerant control strategies have been studied comprehensively for dual-three phase PMSM drives to improve the reliability. Based on direct torque control (DTC) with space vector modulation (SVM), 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. Firstly, diagnosis and tolerant schemes are proposed for speed-sensor fault by estimating the rotor angle speed with the rotating speed of stator flux. Secondly, 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. Thirdly, 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 (VSD) 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 fault and open-switch fault. The experiments have been taken on a laboratory prototype to verify the effectiveness of the proposed fault diagnosis and tolerance schemes.

In this article, a minimum-copper-loss fault-tolerant control scheme is proposed for open-phase fault and open-switch fault of dual three-phase permanent magnet synchronous motor (DT-PMSM) drives. Both the winding configurations of isolated neutral points and connected neutral points are studied in this article. In conventional minimum-copper-loss fault-tolerant control schemes, the constraints of sinusoidal phase currents result in insufficient copper-loss reduction. Different from them, the current references with the theoretically lowest copper losses are first derived and applied for different fault cases of DT-PMSM drives without using any unnecessary constraints in the proposed fault-tolerant control scheme. Thus, all phase currents in the proposed minimum-copper-loss fault-tolerant control scheme are optimized to be nonsinusoidal waveforms. Besides, the copper losses are further reduced by fully utilizing the remaining healthy switch in the faulty inverter leg for the open-switch fault of DT-PMSM drives with the proposed scheme. It has been theoretically and experimentally proved that the proposed fault-tolerant control scheme can reduce copper losses than all existing fault-tolerant schemes for both open-phase fault and open-switch fault in typical two-level voltage-source-inverter-fed DT-PMSM drives.

The traditional fault-tolerant procedure usually comprises fault detection and fault tolerance. Fault detection is adopted to locate the specific fault, which increases the complexity and misdiagnosis risk of fault-tolerant systems. This article introduced an adaptive fault-tolerant control for open-phase faults and open-switch faults in dual three-phase permanent magnetic synchronous machine (PMSM) drives. The proposed fault-tolerant scheme is fulfilled by going through three operation states: healthy operation, transient xy open-loop faulty operation, and fault-tolerant operation. The angle of fault-tolerant reference currents on xy plane is obtained from the transient xy open-loop faulty operation. Unified fault-tolerant reference currents of open-circuit faults are built up by using the above reference angle. After the open-circuit faults occur, the unified fault-tolerant reference currents are directly applied to the drive system without fault localization. Experimental results demonstrate a very smooth switching capability of the developed adaptive fault-tolerant control from the faulty operation to the fault-tolerant operation without extra hardware.

Aiming at tolerating common electric faults of multiphase motor drives comprehensively and minimizing the adverse impacts from the remedial scheme itself, a diagnosis-free self-healing scheme is put forward for the open-circuit faults of dual three-phase permanent-magnet synchronous motor (PMSM) drives. Firstly, the self-healing mechanisms of dual three-phase PMSM drives are analyzed in detail. On the basis of theoretical analysis, the repressed self-healing capability of the dual three-phase PMSM drives is fully released by optimizing the current references on harmonic subspace. Since the diagnosis process is not required in the proposed self-healing scheme, the misdiagnosis problem and the prolonged damage caused by the additional time cost of diagnosis can be fundamentally avoided. The proposed self-healing scheme can be generally applied to open-switch faults, single open-phase faults and multiple open-phase faults in the multiphase motor drives. No change is required for the machine model, modulation strategy or control framework under different open-circuit faults. Thus, the complex transition strategies among different fault-tolerant control methods for different faults can be avoided, and the adverse impacts from the remedial scheme itself can be minimized. Experimental verification is presented to prove the validity of the proposed self-healing scheme.

The utilization of power converters in a distribution network could give rise to stability problems, especially when the penetration is high. The existing literature studies the modeling and stability of converters with specific control or synchronization methods. However, the types or the control schemes of converters are normally different in an actual grid, and moreover the line impedance plays an important role on the network stability. In this regard, this paper aims at studying the modeling and stability issues of a two-bus electric network with both grid-forming and grid-following converters. The main purpose is to provide design guidelines and solution of two-bus system with converters for stable operation. The interactions between the converters in various scenarios will be investigated by considering the effect of line impedance. More importantly, a filter-based stabilized control strategy will be proposed for the grid-forming converters to mitigate the oscillation in the network. Simulation and experimental results are provided to validate the effectiveness of the theoretical analysis and control strategy.

The direct torque control (DTC) has been widely used in motion control of electric drives, especially for the switching table based direct torque control (ST-DTC) and the space vector modulation (SVM) based direct torque control (SVM-DTC). The classical ST-DTC schemes can achieve fast dynamic response but may suffer from distinct torque and flux ripples in steady-state operation. On the other hand, the classical SVM-DTC schemes have lower ripples in torque and flux, but the methods slow down dynamic response of DTC. Different from them, a novel hybrid DTC scheme is proposed for dual three-phase PMSM drives in this paper, which can achieve fast dynamic response of classical ST-DTC scheme and good steady-state performance of classical SVM-DTC scheme simultaneously. The key is to implement different torque control methods under dynamic operation mode and steady-state operation mode. A switching method has been proposed to guarantee smooth transition between the two operation modes. The decoupling control of torque and stator flux is achieved with the proposed control scheme, and the stator flux is controlled stably all along. The experiments have been provided to verify the validity and the superior operation performance of the proposed scheme.