ADPSS Based Short-circuit Current Calculation Method of MMC

Modular multilevel converter (MMC) has broad application prospects in new energy transmission. When a MMC is connected to an active AC grid, it is necessary to calculate the three-phase symmetrical short-circuit current contribution of MMC to ensure the safety of power system. The existing method used in actual engineering projects consider MMC as a current source of which the amplitude is the current limiting amplitude of current limiter. It is safe but has too much margin to be accurate. This paper proposes a new method to calculate short-circuit current that can be used in actual engineering project. This paper analyses the characteristics of MMC short-circuit current first, and proposes the key factors affect short-circuit current contributed by MMC during an actual operating condition. On this basis, simulation trials on advanced digital power system simulator (ADPSS) are designed to get the characteristic curves of short-circuit current which can be used to calculate short-circuit current in actual operation of the engineering project. Finally, this paper uses Zhangbei MMC-HVDC project as an example to apply the new method and show the effectiveness and superiority of the method proposed by this paper.

I. Introduction

With the advancement of energy revolution, modular multilevel converter based high voltage direct current (MMC-HVDC) has been widely concerned in the researches of new energy transmission[1],[2],[3]. It is necessary to calculate the three-phase symmetrical short-circuit current contributed by MMC-HVDC when the converter is connected to active AC grid during the calculation and analysis of power system security and stability, which provides support for power system equipment selection, power grid planning and design and operation control.