Predictive Discontinuous Modulation Strategy With Embedded Inter-Phase Cluster Voltage Control for Cascaded H-Bridge StatComs

The discontinuous pulsewidth modulation (DPWM) in cascaded H-bridge (CHB) static compensators (StatComs) is achieved via adding a common mode voltage to the converter voltage references. Hence, in discontinuously operated CHB StatComs, the common mode voltage has two functions, namely, interphase cluster voltage control and clamping a converter voltage. These two functions are conventionally achieved by two independently designed control stages and interferences between them can cause the loss of cluster voltage control during unbalanced grid conditions, since the fundamental frequency common mode voltage for discontinuous operation is significant. To solve this control issue, this article proposes a DPWM strategy with embedded interphase cluster voltage control using a finite control set model predictive control approach. The proposed predictive DPWM outperforms the conventional DPWM in switching loss reduction while preventing the cluster voltages from diverging during unbalanced grid conditions. The effectiveness of the proposed strategy is verified experimentally considering various grid conditions.