Open-phase fault is a common failure in PMSM, which would degrade motor performance and increase its loss due to the unbalanced phase currents. However, conventional fault-tolerant strategies suffer from the tracking problem of sinusoidal current references. In this paper, different from previous fault-tolerant strategies, a new fault-tolerant method for open-phase PMSM is proposed by designing a novel transformation matrix for current/voltage references. With the new transformation matrix, the voltage/current references in d-q frame can be transformed to the phase voltage/current references of the two remaining phases. With the proposed method, open-phase fault-tolerant implementation can be much easier (PI controller is enough) and its performance can be much higher. Besides, as the tolerant method is designed based on four-leg inverter, stronger fault-tolerance capability can be obtained compared with the three-phase inverter-based method. Finally, the experimental results confirm the validity of the proposed fault-tolerant method.

Traditional open-switch fault diagnosis methods suffer from poor rapidity or robustness. To solve this issue, a new differential current observer-based fault diagnosis method is proposed in this paper. With the designed differential observer, fault symptoms (residuals) can be generated and adopted for fault diagnosis easily. Considering that the residuals are sensitive to motor operating condition in the conventional model-based method due to model error, an adaptive fault detection threshold is designed. As a result, the false detection and missed detection caused by the change of working condition can be avoided, and stronger robustness against speed, load and parameter variations can be achieved with superior rapidity compared with existing methods. Finally, the rapidity and robustness of the proposed fault diagnosis method are verified sufficiently through experimental results.

Open-phase fault may lead to motor efficiency and performance degradation. Various fault-tolerant methods have been proposed to reconfigure the controller and to track the sinusoidal current references. Unfortunately, the time-varying sinusoidal current commands are difficult to be tracked. In order to improve open-phase permanent magnet synchronous motor (PMSM) performance, a new open-phase PMSM fault-tolerant method is proposed in this paper, which is realized based on a novel reference frame transformation. With the new frame transformation, the position-dependent sinusoidal current commands are transformed to dc variables. Thus, the current controller design becomes very easy (PI controller is enough). The experimental results confirm that with the proposed method the PMSM fault-tolerant performance is enhanced distinctly compared with the conventional fault-tolerant methods.

Due to the phase delay caused by low-pass filter, device retarding, and software retarding, the extracted sensorless motor commutation signal deviation occurs. Unfortunately, the relationship between the phase shift and inactive phase freewheeling has been scarcely referred to through the published papers, and most of the commutation instant shift compensation methods present slow convergence rate. Therefore, a fast commutation instant shift correction method based on analyzing the back-electromotive force (EMF) harmonic information is proposed in this paper. The method is effective both in the steady-speed control and in variable-speed control. Considering that commutation instant shift may induce inactive phase freewheeling and negative torque in motor windings, the freewheeling condition and motor electric operation condition are analyzed as well. Furthermore, to exactly delay the zero-crossing points (ZCPs) of EMF by 30° and compensate the commutation instant shift, the speed detection accuracy and feedback frequency are enhanced by measuring and summing up the 2 × P consecutive half-period of the ZCPs signal. Finally, the validity of the proposed commutation instant shift correction method is verified through experimental results.

Back-EMF zero crossing-based sensorless motor driving method suffers from a starting problem since there is no back-EMF at standstill, while the V/f or I/f based method is parameter sensitive. Without position sensors, smoothly driving a non-salient BLDC motor from standstill is difficult. To solve this problem, the relationship between pre-position current, energizing time, and transient speed in startup process is analyzed. Based on this relationship, starting from standstill and directly switching to self-synchronization stage can be realized without external- synchronization process. In addition, to lower the back-EMF zero-crossing points (ZCPs) detection speed, the line voltages difference ZCPs detection circuit is designed, and a novel phase error correction method based on neuro-fuzzy controller (NFC) is presented to provide accurate commutation point in the high-speed range. The experimental results show that reliable startup and accurate commutation can be guaranteed by the proposed strategy.

Existing methods of compensation of commutation instants are generally developed based on the assumption that the back electromotive force (EMF) is trapezoidal wave and the three-phase windings are symmetrical. But this is not the fact. The actual back EMF waveform and commutation ripple would make the conventional methods disabled. According to the actual back EMF waveforms, the relationship between commutation point shift and the difference of dc-link current, which is sampled at the points before and after commutation, is analyzed. Based on this relationship, a novel self-compensation method of commutation error is proposed, which can be used both in sensorless motor and in hall sensor-based motor. As the shift phase is obtained through analytical method, fast convergence speed can be achieved. Furthermore, the influences caused by the freewheeling of turn-off phase inductance and the unbalanced three-phase windings are analyzed and removed. At last, the validity of the proposed self-compensation method is verified through experimental results.