Research on Power Modulation Strategy for MMC-HVDC and LCC-HVDC in Parallel HVDC System

Due to the difference between MMC-HVDC and LCC-HVDC control characteristics and the mutual influence of parallel connection, its power modulation strategy is different from that of LCC-HVDC. Coordinated control strategy of parallel system of MMC-HVDC and LCC-HVDC is analyzed. The methods of power distribution, rate distribution and reactive power control of power limit function are described. Combined with RTDS simulation research of modulation function of Luxi back-to-back HVDC system, the control characteristics of power limitation function of the parallel system under the condition of AC fault at the rectifier side are analyzed in view of the exposed defects. The coordination method of the power limit function, the high voltage crossing control function and the rate distribution optimization is proposed. The simulation results show that the optimized parallel system can perform the power limiting function according to the correct timing and rate.