Research On Coordination Control Strategy Of MIDC Transmission System With MMC-HVDC

Multi-infeed direct current(MIDC)with modular multilevel converter high voltage direct current(MMC-HVDC)can achieve the complementary advantages of MMC-HVDC and LCC-HVDC,With the wide application of this parallel hybrid HVDC transmission technology in practical engineering,some new problems have arisen,and new requirements of coordinated control strategy of MMC-HVDC and LCC-HVDC were put forward.The mathematical model and control strategy of LCC-HVDC and MMC-HVDC are introduced firstly in this paper.The method of constant HVDC voltage control and constant HVDC current control of LCC-HVDC are introduced.The decoupling control of active power and reactive power and the current inner loop control logic of MMC-HVDC are introduced.Then the active power and reactive power control of the multi-infeed HVDC transmission system with MMC-HVDC in steady state and transient state are specifically explained.Then the real time digital simulation(RTDS)tests are used to validate the stability control system(SSC)of Luxi back-to-back HVDC.The incoordinated control strategy of MMC-HVDC and LCC-HVDC in Parallel HVDC System and problem is exposed in the existing SSC.The control strategy of MMC-HVDC and LCC-HVDC under fault condition are analyzed.The optimized coordinated control strategy is proposed,and the effectiveness of the method is verified.The influence of the receiving end AC system strength on the commutation failure and recovery of LCC-HVDC is analyzed.Based on the commutation failure immune coefficient and the fault recovery time,the improved of strength of the receiving AC system or reactive power of the MMC-HVDC fed to the receiving end can reduce the occurrence of LCC-HVDC commutation failure and shorten the recovery time.In the last,the follow-up commutation of research on Coordination Control Strategy of MIDC Transmission System with MMC-HVDC is analyzed.The harmonic voltage of the inverter-side converter bus is detecting during the recovery of LCC-HVDC.The harmonic voltage compensation component is added to the link to improve the reactive power support of the MMC-HVDC to the AC system during recovery The reactive power control on the inverter side of the MMC-HVDC can help improve the strength of the AC system and reduce the influence of harmonics,thereby suppressing the occurrence of follow-up commutation,The reliability and stability of MIDC Transmission System with MMC-HVDC is enhanced.The effectiveness of coordinated control strategy is verified on PSCAD/EMTDC.