Subfundamental Cycle Switching Frequency Variation Based on Output Current Ripple Analysis of a Three-Level Inverter

The output current ripple of an inverter shows different variations for sub-fundamental operating cycle and over few fundamental cycles. This paper investigates subfundamental cycle peak-peak current ripple variation of a three-level three-phase inverter over the entire operating modulation index range for the three-level continuous and discontinuous pulsewidth modulation strategies. Furthermore, based on the analytical current ripple variation, a strategy is presented to change the switching frequency within a fundamental cycle while maintaining the peak-peak current ripple similar to the conventional fixed switching frequency strategies. The strategy has been implemented and experimentally validated on a permanent-magnet synchronous motor drive. The results demonstrate that the proposed strategy reduces inverter switching instances and associated losses around 10-30%.