The Improved Overvoltage Suppression Strategy for the Weak Sending-end Renewable Energy HVDC System

Due to the reverse distribution characteristics of power generation system and load consumption in China, many line-commutated converter based high voltage direct current (LCC-HVDC) systems have been built to export the electricity generated by renewable energy. However, commutation failure (CF) or DC blocking easily causes overvoltage on the rectifier side of LCC-HVDC, which can lead to the shutdown of renewable energy grid connected systems in severe cases. To address this issue, the mechanism of overvoltage occurrence in LCC-HVDC was analyzed. An improved Jacobian matrix was proposed based on the characteristics of the weak sending end renewable energy HVDC system. The sensitivity coefficient between the renewable energy grid-connection bus voltage and the LCC-HVDC converter bus reactive power is computed using an improved Jacobian matrix formulation. The sensitivity-based droop coefficients are integrated into the renewable energy grid-connected inverter's reactive power control loop to mitigate excess reactive power from LCC-HVDC systems. To verify the effectiveness of the IOSS, the weak sending end renewable energy HVDC system is built in PSCAD and simulated under different fault scenarios. The results indicate that the IOSS accurately select the appropriate droop coefficients and significantly suppress overvoltage.