Multi-Objective Pulse Pattern Optimization for Synchronous Machine Drives Considering Different Symmetry Properties

Abstract

This research investigates the effects of optimized pulse patterns (OPPs) on the switching losses of two-level voltage-source inverters (VSIs) and current total harmonic distortion (THD) of permanent magnet synchronous machines (PMSMs) with magnetic anisotropy, considering different symmetry properties. Based on a mathematical model of the VSI and PMSM, a multi-objective optimization framework is derived that balances these two competing goals. By extending the common analytical formulations of the optimization problem for current THD, it considers the influence of switching pulse positions on switching losses during design. All possible waveform symmetry properties, such as quarter-wave symmetry (QWS), restricted half-wave symmetry (HWS), and non-restricted HWS, are compared. The resulting Pareto curve in the two-dimensional solution space provides OPPs with low current THD, low switching losses, or a compromise between the two. An experimental evaluation is conducted, indicating for the most part a good agreement between the predicted and measurement-based Pareto curves. Furthermore, this study conducts an extensive parameter analysis, varying the operational conditions in terms of pulse number, modulation index, power factor, anisotropic factor, and voltage phase angle. Significant differences are observed between non-restricted HWS and QWS, as either lower switching losses at the same current THD or vice versa can be achieved. In contrast, only minor differences exist between non-restricted and restricted HWS. This study proposes utilizing non-restricted HWS for future OPP designs, as it achieves reductions under all varying operating conditions.