Conditional Sixth-Harmonic Injection to Improve the Linear Modulation Range of Three-Phase Voltage-Source Converters

Overmodulation techniques are used to improve dc bus voltage utilization for three-phase voltage-source converters (VSCs), resulting in significant reduction in fundamental voltage gain. Conventional pulse width modulation (PWM) techniques for three-phase VSCs cannot enhance the linear range of dc bus utilization by more than 15.5%. In this letter, a conditional sixth-harmonic injection technique is introduced, which can theoretically improve the linear modulation range by up to 19.2% for three-phase ac systems without additional hardware components. Experimental validation of the proposed scheme is presented, with its performance compared against the conventional third-harmonic PWM technique.