Front-end low-frequency switched-mode rectifier and its control for permanent-magnet synchronous-motor drive

The low-frequency switching-mode rectifier (LF-SMR) possesses the advantages of lower switching frequency, higher conversion efficiency and simpler control, and thus it is extensively utilised in domestic appliances. However, most of the existing LF-SMRs still lack robust operating performance owing to their open-loop control configuration. The development of an AC-switch based LF-SMR and its closed-loop control for PMSM drives are presented. First, the analysis, design and implementation of the power circuit are carried out. The power-circuit components are properly designed considering the compromise between some key performance parameters. Voltage-control aspects of the uncertain effects of double-frequency voltage ripple on the stable closed-loop control behaviour are first studied. On this basis, the voltage-feedback controller type is determined, and its parameters are designed according to the estimated plant model, the properly specified tracking-response requirements and the limitations of LF-SMR. Independently, to improve further the voltage-regulation conrol, an equivalent load-power disturbance is observed and used to perform the disturbance-feedforward-cancellation control. After the effectiveness of the designed LF-SMR has been confirmed, it is applied to serve as a front-end convertor for two types of permanent-magnet synchronous motor (PMSM) drives further to test its validity experimentally.