Dynamic Voltage Equalization Control of D-STATCOM Under Unbalanced Grid Faults in a Low-Voltage Network

Unbalanced grid faults are very harmful to the network operation. Distributed static synchronous compensator (D-STATCOM) can help to support the grid voltage by injecting the reactive power into the inductive power grid. However, this approach turns to be ineffective for a low-voltage grid, where the network impedance is mainly resistive. In this article, a dynamic voltage equalization control (DVEC) scheme is proposed to suppress the negative sequence voltage, and therefore, reduce the voltage unbalance during the faults in the resistive network. This effect is achieved through transferring proper active power from the negative sequence channel to the positive sequence channel. And the dual-sequence active currents are controlled by DVEC without exchanging extra active power with the grid except the little circuit loss compensation. By flexibly adjusting the control parameter of DVEC, current peak and active power oscillation can be limited within a preset range, respectively, during the process of maximizing the voltage control. As a result, the DVEC scheme can ensure the safe operation of D-STATCOM and the stability of the power grid. Moreover, experimental results are reported to validate the correctness and effectiveness of the proposed scheme.