In order to expand the modulation index of the single DC-link shunt permanent magnet synchronous motor drive and improve the motor's operating frequency and load capacity, an improved overmodulation strategy is proposed in this paper. A phase current reconstruction strategy based on vector phase shifting is applied to both modulation linear and nonlinear region. To improve the stability of the motor at high speed, an improved flux weakening strategy based on the voltage angle control method is applied, which can effectively reduce the current harmonics. In addition, this paper proposes a dual-mode overmodulation strategy considering the influence of vector phase shift, and the analysis shows that this strategy can effectively improve the modulation index. Finally, the experimental results show the effectiveness of the proposed method in different operation conditions.

The slim film capacitor driving mode can prolong the operating life of the PMSM system and reduce the system volume. However, the small DC-link capacitor and the grid-side filter inductor are prone to LC resonance. Many stability control methods have been investigated, but they cannot work well under the situation of the grid impedance change. An adaptive stability control strategy is proposed to improve the power quality of the grid side for the electrolytic capacitor-less motor drive in this paper. Through the analysis of the phenomenon of the LC resonance on the grid side, the active damping control strategy based on DC-link voltage feedback is designed with the detection of the THD of the grid current. and the control parameters are adaptively changed. Then, the harmonics of the gird currents can be suppressed effectively. Finally, the simulation results verify the feasibility of the strategy.

Permanent magnet linear synchronous motor (PMLSM) has many superior advantages, but the unique structure leads to the large end force. And PMLSM is also affected by other disturbance forces such as the cogging force and friction force. These forces result in the large thrust ripples, which seriously reduce the performance of PMLSM drives. Firstly, the dynamic model and thrust ripple characteristics of PMLSM are analyzed. On this basis, a thrust ripple suppression method based on the Fourier transform compensator cascaded an improved extended state observer (ESO) is proposed. The Fourier transform compensator extracts the amplitude of the 2nd harmonic of the speed ripple, and outputs the feedforward compensation to suppress the detent force in the thrust ripples. The improved ESO observes and compensates other harmonic components. These two parts adopt cascade structure to comprehensively suppress the thrust ripples of PMLSM. Finally, experiments are carried out on a 750W PMLSM drive platform to verify the effectiveness of the proposed suppression method.

Motor drives with reduced DC-link capacitance may face grid current distortion or even instability under weak grid condition. In this paper, the small signal model of reduced DC-link capacitance drive system under weak grid condition is derived and analyzed. On this basis, an impedance reshaping method is proposed to suppress the harmonics of the grid-side current. By extracting DC-link harmonics near the LC resonant frequency and reconstructing the virtual admittance of the drive, the active damping voltage control signal is generated to suppress the harmonic of the grid-side current at the specific frequency. The THD of the grid-side current was reduced from 53% to 39%. The experiment was carried out on a 5.5kW permanent magnet motor drive platform with reduced DC-link capacitance, and the effectiveness of the control strategy was verified by experiments.