A Generic Two-Stage Carried-Based PWM Scheme With Adjustable Switching Patterns for Current Source Converter

Modulation schemes play a key role in effectively driving the current source converter (CSC). Among various modulation schemes, the carrier-based pulse width modulation (CB-PWM) has gained much attention owing to its inherent auto-sequencing process. However, the fixed switching patterns in the existing CB-PWM methods reduce the available degrees of freedom, which imposes underlying restrictions on the performance of a CSC (e.g., to minimize the switching frequency or to reduce the current ripple). To address this issue, an innovative concept of two-stage modulation, which modulates the active and zero current vectors in a switching sequence, respectively, in two stages, is explored in this article. Based on that, this article proposes a generic CB-PWM scheme with adjustable switching patterns for flexibly modulating the CSC. Its mechanism is presented to develop its modulation characteristics. It shows that the proposed PWM scheme can flexibly achieve different modulation objectives by only adjusting the offset voltage in the second stage. Three derivations of the proposed scheme have then been discussed in detail, which can achieve a minimized switching frequency, a reduced dc-link current ripple, or a compromise between them. Representative experimental results have been provided to verify the effectiveness of the proposed modulation scheme.