Accelerated switching function model of hybrid MMCs for HVDC system simulation

An accelerated switching function model (SFM) of the hybrid modular multilevel converter comprising both full-bridge (FB) and half-bridge (HB) submodules (SMs) in each arm is presented for HVDC system simulation, where auxiliary circuits are adopted to represent all possible current paths during normal and fault conditions. The proposed SFM can represent the negative voltage generating capability of the FB SMs and the equivalent switching functions in the blocking states of the FB and HB SMs are also introduced in the proposed model to accurately replicate the potential charging of the SM capacitors, yielding improved simulation accuracy compared to other alternatives. In addition to the faster simulation speed, the proposed model accurately reproduces the converter behaviour during various operating conditions, including normal operation, AC fault, DC fault and so on. The proposed SFMs are assessed in MATLAB/Simulink environment using both down-and full-scale HVDC links and the simulation results confirm the validity of the proposed model in terms of model accuracy and improved simulation speed.