Research on starting-up control strategy of VSC-HVDC system

The starting-up control strategy is an important issue for voltage source convert-high voltage direct current (VSC-HVDC) system. If a VSC-HVDC system starts up without any auxiliary starting-up control strategy, the overcurrent will occur both in AC and in DC sides. Such overcurrent rises rapidly, and its value is several times as the normal operating current. It endangers the convert equipment seriously and may cause mal-operation of the overcurrent and differential under-voltage protection. A simple but effective starting-up control strategy is proposed. It consists of a current limiting resistance (R-in) and three improved controllers. R-in is supplemented into AC side of converter to suppress the overcurrent during uncontrolled rectifier stage, and the design method of R-in is performed in detail. Then, three improved controllers, including DC voltage slope controller, active power adaptive droop controller and reactive power deviation correction controller, are designed to restrain the overcurrent during controlled voltage stage. By introducing this starting-up control strategy, the overcurrent in the VSC-HVDC system is restrained effectively and the system can start up steadily. Substantial simulations conducted on PSCAD/EMTDC platform have demonstrated the outperformance of the proposed strategy in mitigating overcurrent in VSC-HVDC system.