When the HVDC transmission system is in low power operation

restricted by the PCC harmonic performance of converters and the AC filter equipment performance

the surplus of reactive power provided by the AC filter may still be tremendous apart from meeting the reactive power consumption of converters. This will lead to the interchange of enormous surplus reactive power between the converter and the AC system

making the voltage of the converter station and nearby substations to become high and then affect safe and stable operation of power grids. By utilizing converter reactive power regulation capability

a kind of reactive power control strategy is proposed

in which the DC voltage is used as control variable and reactive power exchange capacity of converter station as feedback variable. The strategy changes the converter reactive power consumption by changing the reference value of inverter side voltage to effectively suppress the AC system voltage fluctuations without influencing active power transmission. The reactive power control strategy can overcome some disadvantages of low load reactive power optimization function that just cannot accurately control the reactive power because of its open-loop control. The simulation results in PSCAD/EMTDC and RTDS verify the correctness and robustness of the proposed method.