Research on the Capability of Star-Connected CHB-STATCOM to Compensate the Unbalanced Voltage of Power Grid

For the grid voltage unbalance issue, in this article, the scheme of using star-connected cascaded H-bridge static synchronous compensator (CHB-STATCOM) to suppress the unbalanced voltage at the point of common coupling (PCC) is introduced. However, the capability of star-connected CHB-STATCOM to compensate the unbalanced voltage at the PCC is limited for a certain dc-link voltage. When exceeding the effective compensation range, the star-connected CHB-STATCOM not only fails to achieve the compensation of unbalanced voltage at the PCC, but also further deteriorates the power quality of the grid. In this article, the unbalanced voltage at the PCC caused by load unbalance and power supply unbalance is considered comprehensively, the key influencing factors and quantitative relationship of the maximum output voltage of the star-connected CHB-STATCOM injecting zero-sequence voltage are analyzed in detail, and the effective compensation range of the star-connected CHB-STATCOM for unbalanced voltage at the PCC is given in a quantitative manner. These quantitative analyses provide reference limitation for star-connected CHB-STATCOM to compensate unbalanced voltage at the PCC, which is significant for real-time regulation and selection of the star-connected CHB-STATCOM. Finally, the correctness of the theoretical analysis is verified by simulation and experiment.