The direct torque control (DTC) method was introduced into the switched reluctance motor (SRM) to reduce its inherent output torque ripple. However, the conventional DTC method produces negative torque more or less, which reduces the torque-ampere ratio of motors. This paper proposes a new DTC method by three improvements. Firstly, the hysteresis-loop control of flux is removed. New selection rule of voltage vectors is established to reduce the torque ripple. Secondly, the sectors divided in electrical space are reorganized by their actual positions according to the inductance profile. The boundaries between certain sectors are calculated and updated according to real-time working conditions. Finally, the alternative voltage vectors for increasing or decreasing torque are distinguished by whether any phase is excited. Therefore, the output torque tracks the reference accurately which reduces the torque ripple. Moreover, the negative torque is avoided by the real-time regulation of turn-off angle, and the torque-ampere ratio is increased accordingly. Simulation and experimental results verify the demonstrated performance of proposed DTC method.

The vibration suppression in the presence of gyroscopic effects is an important issue for safe operations in magnetic bearing levitated varying speed rotor system. This work proposes a synchronous vibration control method with a two-stage notch filter for the magnetically suspended rotor system with strong gyroscopic effects. First, the dynamics of the magnetically suspended rotor system with synchronous vibrations in the rotational motion is modeled. Then the proposed two-stage notch filter is designed and the solution of the two-stage switching point is derived to distinguish low speed and high speed. Stability analysis is also presented in the low-speed region and the high-speed region, respectively. Finally, simulation results demonstrate that the stability can be guaranteed by adjusting the phase shift angle of the notch filter over the entire speed range. Further experimental results confirm the effectiveness of the proposed suppression method.

Magnetically suspended centrifugal compressor (MSCC) is a better energy-saving choice than ordinary centrifugal compressor in industrial applications. However, harmonic currents, which generate from rotor mass unbalance and sensor runout, cause harmonic vibrations which deteriorate the stability of the overall system and lead to higher power consumption. The conventional repetitive controller (CRC) has been used to eliminate harmonic vibrations in magnetic bearing systems, but the CRC method has the drawbacks of frequency shift and shallow notch depth that degrade its performance of harmonic currents suppression. In this paper, a zero-phase odd repetitive controller (ZORC) is proposed. Compared to the CRC, the ZORC has control action only at odd harmonic frequencies and it has no influence on the closed-loop system at even harmonic frequencies. Besides, the conventional first-order low pass filter is replaced with the zero-phase low pass filter and moved outside the internal loop, which dramatically improve its performance of suppressing harmonic currents. The validity and effectiveness of the proposed method are proved both by simulation and experimental results.

Compared with the traditional control method, the direct torque control and direct force control method significantly reduces the torque ripple and the root-mean-square current of the phase winding in the single-winding bearingless switched reluctance motor. However, due to the unreasonable selection of voltage vectors and full cycle control, this method has some problems, such as too many control objects, excessive switching times, and low torque–ampere ratio. This article proposes an improved method for the abovementioned problems. First, the turn- on angle and conduction region of each phase winding are chosen as the control targets, and the operation principle is introduced accordingly. Second, according to the difference of the torque generated by the neighboring phases, the output torque can be distributed more properly to obtain the higher torque–ampere ratio in the commutation region. Finally, the sectors divided in the electrical space are reorganized and the corresponding voltage vectors are optimized. Experimental results show that the proposed method can secure lower torque ripples, fewer switching times, and copper loss. In addition, the torque–ampere ratio is improved as well.

In the active magnetic bearing (AMB)-rotor control system, rotor mass unbalance and displacement sensors runout will bring about harmonic current, which would further result in vibration force transmitted to machine housing. The undesired machine vibration would pose a potential threat to system stability and performance degradation. In order to attenuate harmonic current, this work has proposed a scheme of control system with cascaded mode phase-shift notch filters, and the system stability has been analysed. The harmonic current reduction performances of the system with cascaded mode notch filters are compared with that with parallel mode notch filters. Theoretical analysis has demonstrated that the proposed cascaded mode control system could achieve the same suppression performance as the commonly used parallel mode control system, which is also verified by simulation results. Experiments carried out on a high-speed magnetically suspended centrifugal compressor have validated that the proposed method is effective for harmonic current reduction.