An Arm Multiplexing Alternate Arm Converter With High Submodule Utilization for HVDC System

Alternate arm converter (AAC) has gained significant popularity in HVDC systems due to the advantages of reduced number and capacitance of submodules (SMs). It has become one of the most promising modular multilevel converter (MMC). This paper proposed a lightweight alternate arm converter (AM-AAC) with high utilization of SMs. The proposed topology focuses on reducing the SMs number to reduce the expensive cost of SMs in converters. A closed-loop energy balance control strategy for AM-AAC is proposed based on the phase-shifted conduction method, which enables AM-AAC to operate even under the grid asymmetrical fault. Compared to MMC, the proposed AM-AAC not only supports AAC operating in high-ratio grid voltage sags but also reduces the SM numbers and capacitance by 58.8% and 44.6%, respectively. The proposed method realizes the multiplexing of arm shaping circuits by alternately conducting arm selection switches, which greatly improves the utilization of SM and effectively achieves the lightweight of the converter. Simulation results demonstrate that AM-AAC exhibits excellent operation performance, thus verifying the correctness of the proposed topology and control strategy.