Electrical-Angle-Partitioned SHEPWM for Field-Oriented Control of Permanent Magnet Synchronous Motor Drives at Low Carrier Ratios

When inverter switching frequency is constrained, PMSM drives operating at relatively high fundamental electrical frequencies may exhibit a low switching-to-fundamental-frequency ratio (low carrier ratio), resulting in fewer voltage vector updates per fundamental cycle and increased current ripple and low-order harmonics. To address the difficulty of synchronizing offline selective harmonic elimination PWM (SHEPWM) switching angles with a field-oriented control (FOC) current loop, this paper proposes an angle-synchronous FOC-SHEPWM implementation based on electrical angle partitioning. A quarter-wave-symmetric SHEPWM model is first established, and the switching angles are solved using Newton iteration and homotopy continuation. A Halton low-discrepancy initial value pool is then constructed. Combined with cumulative interval mapping, admissibility screening, and continuity assessment, it yields switching angle trajectories suitable for closed-loop look-up table implementation and extends the high-modulation-index range toward six-step operation. For online implementation, the ePWM period is updated according to the electrical angular speed, and the offline angles are mapped to intra-partition compare values. Counter-zero sampling, delay angle compensation, dynamic period correction, and fundamental current extraction are integrated to realize synchronized closed-loop pulse generation. The simulation and experimental results demonstrate the stable operation of the SHEPWM-N3, SHEPWM-N5, and SHEPWM-N7 patterns. At equal numbers of switching events, the proposed patterns exhibit lower low-order harmonic content and current total harmonic distortion than ASVPWM, while the fundamental current extraction and dynamic period correction methods reduce d-q-axis current ripple and partition synchronization error, respectively.