Study on DC Component Suppression of Valve-side Current of Static Synchronous Series Compensator

Synchronous Series Compensator (SSSC), a Flexible Alternating Current Transmission Systems device, is used for the flexible regulation of power system flow, which is of great significance to improve the transmission capacity and stability of the power grid. In engineering applications, system fluctuations, controller accuracy and dynamic adjusting etc. may bring about a slight DC component in the output voltage of SSSC. Since the loop resistance for the DC component is very small, the DC bias of the valve-side current would be significant, which will influence the stability and performance of the control system. Meanwhile, the series transformer and other devices would suffer DC magnetic bias, magnetic saturation of the core, higher loss and even harmonics, threatening the operation of the system. This paper proposes the mechanism that the DC component in the output voltage modulation wave will lead to a DC bias of the current on the SSSC valve-side. The open loop characteristics are simulated. And based on this, a DC component detection and feedback unit is introduced in the original controller to suppress the current DC bias. Finally, according to a SSSC demonstration project, a real-time digital hardware-in-loop simulation model is established and the effectiveness of the suppression strategy is verified.