A Novel Capacitor-Commutated Converter Based on Submodule-Cascaded STATCOM

To address the challenge of a conventional line-commutated converter (LCC), unable to operate properly in connection with a very weak AC system, the technology of the capacitor-commutated converter (CCC) was widely utilized in 1990s. The topology of the CCC is constructed as a conventional LCC modified with a series capacitor between the converter transformer and the thyristor valves in each phase. Additional phase voltage can be generated on the capacitor to assist the process of the commutation. However, the CCC technology may experience continuous commutation failure due to the uncontrolled charging of the series capacitor. Based on the submodule-cascaded static synchronous compensator (STATCOM), this paper proposes a novel topology called the submodule-cascaded STATCOM-based CCC (SCCC). The SCCC technology enables the function of reactive power compensation and active filtering. It can also improve the transient characteristics of the AC faults via dynamic reactive power injection during the transient process, which helps to reduce the risk of continuous commutation failure in the CCC.