Fixed Switching Frequency Model Predictive Switching Sequence Selection for Motor Drives at Low Switching-to-Fundamental Frequency Ratios

This paper addresses the current quality degradation of conventional modulation techniques at high modulation indices and low switching-to-fundamental frequency ratios, in a two-level voltage source inverter motor drive system. The issue is resolved by expanding the allowable switching sequence set and incorporating it into a model predictive control framework. During each sampling interval, the proposed scheme predicts the behavior of the d-axis and q-axis currents for all candidate sequences (including both conventional and newly designed switching sequences), optimizes the initial transition instant, and selects the sequence that minimizes the predicted tracking error. This method simultaneously optimizes both the choice of sequence and the switching times while maintaining a constant switching frequency. Simulations and experiments demonstrate that, at the same switching frequency, the proposed approach significantly reduces current harmonics and enhances current regulation at high modulation indices when compared to space vector pulse width modulation and discontinuous pulse width modulation, resulting in lower current total harmonic distortion.