The Impact of Modular Multilevel Converter Control on DC Short-Circuit Currents of HVDC Systems

In Modular Multilevel Converter (MMC) based DC systems, during the initial stage of a DC fault, the control system operates normally, inserting and bypassing submodules. Consequently, each MMC control technique would provide a different characteristic to the DC short-circuit behavior. Therefore, this paper presents a comparative analysis of MMC control techniques, providing a better understanding on how the control techniques impact the fault currents. The analyses were performed by simulating and applying DC faults to a two-terminal VSC-HVDC system with different groups of control techniques. It was found that the DC fault current was not influenced either by control parameters, modulation or output-current control techniques. The arm-balancing control influenced the DC fault currents as it has an impact on the modulation reference signal.