Detailed Analysis of Optimized Pulse Patterns Interacting With Salient PMSMs Applying Different Symmetry Conditions

Efficiency and power density of electric vehicle drive systems are important metrics for their performance evaluation. To address these aspects, Optimized Pulse Patterns (OPPs) can be integrated into the modulation strategy. This research investigates the effects of OPPs on the current distortion of salient permanent magnet synchronous motors (PMSMs) applying different symmetry conditions. It places a particular emphasis on three-pulse switching within the overmodulation region. A mathematical model of salient PMSMs is used to demonstrate that the voltage phase angle significantly influences current harmonics. It is revealed that even with a low number of pulses, satisfactory sinusoidal currents can be achieved at high voltage phase angles, thereby reducing the inverter's switching efforts while preserving current waveform quality. Different waveforms such as quarter- and half-wave symmetry (QWS), unrestricted half-wave symmetry (HWS) and restricted HWS are compared, with an innovative approach proposed for unrestricted HWS. The benefits and drawbacks of these waveforms in application to salient PMSMs are investigated, with emphasis on the overmodulation region. It is noted that HWS shows benefits over QWS at medium-load operating points and when zero-vectors are in the waveforms. In contrast, no significant advantages of HWS over QWS could be identified in the overmodulation region. The research proposes a practical OPP implementation strategy that balances effort and efficiency based on this knowledge. Unlike previous studies that used random initial angles to explore solutions, this study methodically examines the solution space for HWS and QWS, selecting initial angles that enhance the chances of finding the global optimum.