Overmodulation Voltage Boundary Adaptation-Based Field Weakening Strategy for High-Speed SPMSM Drives

The overmodulation (OVM) strategy can improve the modulation index (MI) of the output voltage and expand the speed and torque range in the field weakening (FW) region. However, the motor current harmonics would be increased. To solve this issue, this article proposes an OVM voltage boundary adaptation-based FW strategy for high-speed permanent magnet synchronous motor (PMSM) drives. By analyzing the frequency spectrum of the OVM output voltage, an FW current model containing the harmonics is established. The adaptation strategy between different voltage boundaries is adopted in the dynamic state by inserting more continuous voltage vectors. The adaptive regulation of the optimized voltage boundary in the steady state is proposed by increasing the utilization of the dc-bus voltage considering the THD limitation of the phase current. The motor operating state is judged by the speed and current information, and the smooth switching between dynamic and steady states is realized. A contour plot of MIs is constructed to classify the OVM levels, and the boundary initial value curve is fitted to reduce the adaptive time. The proposed strategy can maximize the motor torque and speed satisfying the THD limitation, which is experimentally verified on a 6-kW high-speed PMSM platform.