A Direct Carried-Based PWM Scheme With Reduced Switching Harmonics and Common-Mode Voltage for Current Source Converter

The performance of a current source converter (CSC) is greatly affected by its adopted modulation schemes. Among various modulation schemes, the carrier-based pulsewidth modulation (CB-PWM) has gained increasing attention owing to its inherent autosequencing process. However, existing CB-PWM schemes suffer from either high switching harmonics in ac current or high low-order common-mode voltage (CMV), and sometimes, both, which restrains the application of this promising scheme. To address this issue, this article explores the modulation mechanism of CB-PWM for a CSC. Based on that, this article proposes a direct CB-PWM scheme. Its implementation, mechanism, and characteristics have been developed and presented in detail. It is shown that the proposed scheme enjoys inherent low switching frequency, easy implementation, as well as high dc current utilization. More importantly, compared with existing CB-PWMs, the proposed scheme can simultaneously reduce the switching harmonics of ac current and the low-order CMV for a CSC. These superior performances can bring potential benefits to scale down the ac filter and common-mode choke for practical CSC applications. Effectiveness of the proposed scheme is verified experimentally with a CSC operating as an inverter.