An Active Bypass Pulse Injection-Based Low Switching Frequency PWM Approach for Harmonic Compensation of Current-Source Converters

In this article, a bypass pulse injection-based pulsewidth modulation approach is proposed for mitigating line current harmonics of grid-tied current-source converters (CSCs) operating at a low switching frequency. First, the relationship between the CSC output harmonic current and the format of the bypass pulse is analyzed. Then, through online adjustment of both bypass pulse location and width, the seventh harmonic component of the output current is actively regulated to mitigate the corresponding seventh line harmonic current. Meanwhile, this action may be associated with additional amplification of the fifth output current. To deal with this issue, the unsymmetrical selective harmonic elimination (SHE) modulation with online adjustable switching angles is applied to further mitigate the fifth harmonic line current. It has been experimentally validated that with the application of both the bypass pulse injection and the unsymmetrical SHE-based modulation approaches, both the fifth and the seventh harmonic line currents can be simultaneously suppressed with ultralow switching frequency below 1 kHz.