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In recent years, Modular Multilevel Converter based High Voltage Direct Current (MMC-HVDC) transmission system has gradually developed, and the AC short-circuit current contributed by both the converter and AC system needs to be solved urgently. In order to solve this problem, the paper focuses on the transient process of phase current change on the AC side after a unipolar ground fault occurs on the DC side. Then, an equivalent model of the AC system short-circuit current is established. Therefore, a calculation method of the short-circuit current contribution of the AC system based on the arithmetic circuit is given. Finally, a simulation model of two-terminal project built based on PSCAD verifies the correctness of the proposed calculation method.

Synchronized Current Phasor Control (SCPC) is a novel inverter control method proposed recently. This paper investigates the voltage stability of a simple SCPC grid based on the bifurcation theory. Firstly, the expression of the bifurcation point of the simple SCPC grid is derived, and then the variation of voltage stability domain is analysed according to the trajectory of bifurcation point when the inverter droop parameters change. The theoretical analysis results show that the droop parameters have an obvious influence on the voltage stability, which provides guidance for parameter setting.

Synchronized Current Phasor Control (SCPC) is a new control method proposed recently for islanded microgrids. This paper firstly investigates the reactive power compensation characteristics of the SCPC islanded microgrid with I-V droop control, then analyzes the influence of the droop coefficient on it. Through this study, we find that the traditional reactive power compensation strategies are no longer adapted to SCPC islanded microgrids, since their characteristics of reactive power compensation are different from the traditional grid or other islanded microgrids controlled by the typical methods.