Research on coordinated reactive power control strategy of hybrid-HVDC

Based on the hybrid HVDC transmission system, which is composed by line-commutated converter (LCC) in parallel with voltage source converter (VSC), a coordinated reactive power control strategy of hybrid-HVDC in both steady and transient states is proposed. The operation characteristics in situations like low load operation, filter switching, and de-locking process are analysed. Influence of the method to AC bus voltage and system power factor is taken into account. Three kinds of reactive control methods of VSC and LCC are studied, and the logical relationship between the filter and VSC reactive power controller is also given. Considering both the system voltage drop and the risk of commutation failure caused by AC faults, the VSC in voltage control mode is utilised to maintain AC bus voltage stability by providing emergency power support. Simulation results show the feasibility and effectiveness of presented control strategy, then the proposed strategy is applied in practical DC project, whose results achieve the desired effect by engineering field test.