Over‐current protection method for PMSM VSI with small DC‐link capacitor

In this study, an over-current protection method for permanent magnet synchronous motor (PMSM) voltage source inverter (VSI) employing small DC-link capacitor is proposed. Since VSI with small DC-link capacitor has become popular for its long lifetime and compactness. However, the small DC-link capacitor brings the risk of excessive voltage in the DC-link capacitor when the traditional `all-turn-off' over-current protection is utilised. In order to avoid the damage for VSI caused by excessive pumping-up voltage, based on the analysis for the `all-turn-off' method, the proposed method could eliminate reversal current flowing into the DC-link capacitor through switching logic. Consequently, the electro-magnetic energy stored in PMSM windings is converted into mechanical energy and pumping-up voltage is cancelled. Detailed analysis of the proposed method is presented. The effectiveness of the proposed method is verified by simulation and experiments.