Research On Impact Of STATCOM On Operation Performances Of HVDC

High Voltage Direct Current (HVDC) has been widely put into operation due to its specific advantages on technology and economy. With the gradual increase of DC transmission projects in China, it has been paid more attention that how to overcome the shortcomings of the HVDC and reduce the probability of commutation failure. Static Synchronous Compensator (STATCOM) is connected to the AC busbar at the HVDC inverter side. With STATCOM infeed, the AC bus voltage can be regulated effectively, and AC system strength and HVDC stability can also be improved. First, the topology, mathematical model and control strategy for HVDC and STATCOM are presented. The models of single-infeed and dual-infeed HVDC systems with STATCOM are developed in PSCAD/EMTDC. Then, the AC voltage interaction between inverter side AC buses of dual-infeed HVDC system without STATCOM is investigated. With STATCOM infeed, the impact of STATCOM on AC bus voltages and the recovery performance after faults of the dual-infeed HVDC system are analyzed. Based on the index of Critical Short Circuit Ratio (CSCR), the impact of STATCOM with different capacity on operation limits of single-infeed and dual-infeed HVDC systems are studied. Finally, an improved control strategy of HVDC system with STATCOM is proposed. Based on the constant AC voltage control of STATCOM, a regulation function for AC voltage reference value is applied to STATCOM. Meanwhile, additional DC current and extinction angle control functions are further applied to HVDC. The results show that, STATCOM has the ability to effectively improve the operation performances and enhance system stability for HVDC. In addition, the improved control strategy proposed in the paper can reduce the probability of commutation failure.