Research on the control method for voltage-current source hybrid-HVDC system

The hybrid-HVDC topology, which consists of line-commutated-converter (LCC) and voltage source converter (VSC) and combines their advantages, has extensive application prospects. A hybrid-HVDC system, adopting VSC on rectifier side and LCC on inverter side, is investigated, and its mathematic model is deduced. The commutation failure issue of the LCC converter in the hybrid-HVDC system is considered, and a novel coordinated control method is proposed to enhance the system commutation failure immunity. A voltage dependent voltage order limiter (VDVOL) is designed based on the constant DC voltage control on the rectifier side, and constant extinction angle backup control is introduced based on the constant DC current control with voltage dependent current order limiter (VDCOL) on the inverter side. The hybrid-HVDC system performances under normal operation state and fault state are simulated in the PSCAD/EMTDC. Then, system transient state performances with or without the proposed control methods under fault condition are further compared and analyzed. It is concluded that the proposed control method has the ability to effectively reduce the probability of commutation failure and improve the fault recovery performance of the hybrid-HVDC system.