Due to high power-transforming capability and excellent fault-tolerant performance, dual three-phase permanent magnet synchronous machines (DT-PMSMs) are widely used in high-reliability applications. Concerning on the remedial strategy for DT-PMSMs under open-phase faults, the conventional method is to reconfigure the controller or the current references in order to obtain optimum postfault performances. Two different control schemes should be separately designed for normal and fault conditions, respectively. Meanwhile, related fault detection measures need to be adopted and the inherent fault detection delay will further result in transient performance deterioration. In order to solve these problems, this article proposes a control strategy, which can achieve natural fault-tolerant capability of DT-PMSMs without additional fault detection algorithm. With the proposed control method adopted, reconfiguration of the control structure and modification of the current command are not required. Thus, the control scheme is simplified. The transition from the healthy to the postfault operation can be improved, meanwhile, the steady-state performances in prefault and postfault situations can be guaranteed. The proposed strategy can be generally applied to single open-phase faults and multiple open-phase faults in DT-PMSMs. Experimental validations are presented on a 1 kW DT-PMSM platform to prove the effectiveness of the proposed strategy.

Open-end winding permanent magnet synchronous machines (OW-PMSMs) supplied by dual inverters have gained increasing research focus due to its advantages in multilevel modulation, flexible control capability, and enhanced fault-tolerant performance. Zero-sequence current is one of the most concerned issues when the common DC bus configuration is adopted. Feedback control of zero-sequence current has been previously proved to be an effective solution to suppress zero-sequence current. However, due to the existence of current measurement errors, DC disturbance and periodic disturbances will inevitably occur in zero-sequence current, which may result in obvious deteriorations of the suppression performance of zero-sequence current. Zero-sequence current circulates in the OW-PMSM, which will lead to unexpected power losses and reduced efficiency. In addition, current measurement errors also cause increased periodic disturbances in the torque and the rotor speed, resulting in torque ripples and speed fluctuations. To address these problems, the exact closed-form hold-equivalent model of OW-PMSMs is derived, and the specific periodic disturbances introduced by current measurement errors are analyzed. Subsequently, zero-sequence current controller and speed controller are designed with enhanced mitigation capability of periodic disturbances resulting from current measurement errors. Its effectiveness under different operation conditions is confirmed experimentally on a 2.3-kW OW-PMSM setup.

Fault-tolerant control is normally required to achieve continuous operation under post-fault modes in some critical fields. Regarding remedial strategies for open-end-winding permanent magnet synchronous machines (OW-PMSMs) in the case of open-phase fault, the typical way is to reconfigure the controller after the fault is detected. Different from those mainstream control strategies which account for the post-fault situations by reconfiguring controllers or modulators, the fault-tolerant predictive control strategy proposed in this paper handles the asymmetry in a different manner. By combining the predictive control strategy with an embedded vector-resonant control scheme, the proposed strategy can achieve effective regulation of OW-PMSMs in both pre- and post-fault operations. Controller reconfiguration and switching between pre- and post-fault control modes based on fault detections are thus avoided. Besides, with the rotor flux harmonics taken into account and benefiting from the proposed zero-sequence controller, the triple-frequency component in the zero-sequence current is successfully suppressed to reduce torque ripples while the fundamental-frequency component is properly retained under post-fault operations, which is required in order to obtain an uninterrupted rotating magnetic field after one phase is open circuited. Experimental validations are conducted to verify the effectiveness of the proposed strategy and its superiority over conventional voltage compensation methods.

This paper deals with the optimal state reference calculation for synchronous motors having a magnetically salient rotor. A lookup table computation method for the maximum torque-per-ampere locus, maximum torque-per-volt limit, and field-weakening operation is presented. The proposed method can be used during the start up of a drive, after the magnetic model identification. It is computationally efficient enough to be implemented directly in the embedded processor of the drive. When combined with an identification method for the magnetic model, the proposed method enables the plug-and-play startup of an unknown motor. Furthermore, a conventional reference calculation scheme is improved by removing the need for one two-dimensional lookup table. A 6.7-kW synchronous reluctance motor drive is used for experimental validation.

In this paper, an observer-based predictive vectorresonant current control strategy for permanent magnet synchronous machines (PMSMs) is proposed, which can effectively improve system performance in case of disturbances caused by converter dead-time effect and model mismatch. Taking the external periodic, nonperiodic disturbances, and system delay into consideration, the system model in discrete-time domain is built. This model is then embedded with vector-resonant scheme with the aim of suppressing periodic disturbances resulting from converter dead-time effect and rotor flux harmonics. An extended-state observer is constructed in order to predict system behavior and to estimate the nonperiodic disturbances caused by parameter variations. The overall control law is then derived on basis of cost function minimization. With the proposed method adopted, the undesired anomalous peak around the resonant frequency in the frequency responses can be avoided. Moreover, enhanced transient performances and wider stability margin can also be obtained. The effectiveness and advantages of the proposed strategy are verified by frequency-domain analysis and comparative experimental studies.

In the control of permanent magnet synchronous machines (PMSMs), predictive controllers have received considerable attention due to the enhanced dynamic responses. However, periodic disturbances caused by dead-time effects and sampling errors deteriorate the performances of PMSMs. In order to suppress periodic disturbances, one typical control structure is to adopt several corresponding resonant controllers connected in parallel with the main controller. Even though excellent steady-state performances can be obtained, coupling effects between reference tracking and periodic disturbance attenuation can be observed, leading to significant transient oscillations under the situation of a reference step change. In order to realize decoupling between reference tracking and disturbance attenuation, this paper proposes a dual-loop predictive control structure, in which the reference tracking is only determined by the primary predictive controller. Periodic-disturbance attenuation is achieved through an embedded disturbance-rejection loop. By applying the proposed controller, periodic disturbances are strongly attenuated while smooth and fast transient performances are simultaneously guaranteed. Furthermore, a wide range of low frequency harmonics can be successfully suppressed, including but not limited to the main periodic harmonics. The steady-state performance, dynamic responses, and robustness against parameter variations of the proposed controller are verified through experiments based on a 2.3-kW PMSM.