Research on implementation of compound function based on back-to-back VSC in power grid parallel

This paper introduces the application of back-to-back converter in the power grid synchronization parallel. After converter devices finish the function of power grid parallel and quit running, it may realize many functions besides the power grid parallel by adopting different control strategies to the controllers, such as raising voltage from zero experiments on transmission line in substations, raising current from zero experiments, ice-melting on transmission line, stabilizing the bus bar voltage, reactive power compensation etc. Only by adding one circuit breaker between the bilateral converters and matching corresponding control method without changing its main circuit equipments, the back-to-back converter can be used as two sets of static compensator (STATCOM) when the breaker is open, thus the utilization of back-to-back converter is improved. The specific control method of the STATCOM is presented in this paper. This paper proposes all the schemes to realize the functions stated above and the corresponding control strategies, as well as the control flow charts and implementation of those functions. Meanwhile, it analyzes the key technologies in the charts in detail. The simulations are taken in PSCAD/EMTDC, and the simulation results demonstrate not only the feasibility of back-to-back voltage source converter used in power grid parallel, as a static compensator and the realization of other functions, but also the correctness of control strategies. Thus it improves the utilizations and comprehensive benefits of the back-to-back voltage source converter.