Influence of Inverter Output Filter on Maximum Torque and Speed of PMSM Drives

The paper deals with the maximum torque and speed of permanent magnet synchronous motor (PMSM) drives when the inverter output voltage is filtered by an LC filter whose cut-off frequency is well below the switching frequency. According to steady-state analysis, the filter affects the performance of the motor drive especially at high speeds. The stator current is not equal to the inverter current, and due to the inverter current and inverter voltage limits, the torque-maximizing stator current locus differs from that of a drive without the filter. A field-weakening method is proposed for PMSM drives with an inverter output filter. The method is implemented and tested in a 2.2-kW PMSM drive. The experimental results agree well with the analysis, and validate the high-speed performance of the proposed field-weakening method.