The Research On Control Strategy For VSC-HVDC

With the development of full-controlled power semiconductor devices, which were extensively used in power system, the HVDC based on voltage source converter has become the development trend of future power network, not only it has the advantages of traditional HVDC, but also make the power flow reversed and achieves independently controlling of active and reactive power. These unique advantages attract more and more home and abroad scholars to engage in the research on VSC-HVDC.The article introduced the basic principle and control methods of the VSC-HVDC, established transient mathematical model of VSC-HVDC based on synchronous rotating frame. According to the model, introduced direct feedback control strategy, designed dual-loop controller of inner power and external voltage, achieve decoupling for active and reactive power of VSC-HVDC. Mainly analyzed the nonlinear control strategy of the VSC-HVDC transmission system, as the VSC-HVDC system model is a multi-input multi-output and strongly coupled nonlinear system, achieve linearization and decoupling of VSC-HVDC transmission making use of inverse theory, and structure pseudo-linear system for the controller designed of rectifier side and inverter side. Finally, design the controllers by means of sliding mode control system, reach independently controlled of active power and reactive power, ensure the system dynamic stability under large disturbance.The paper analyzes the two ways of power supply for active network or passive network based on the transient mathematical model of VSC-HVDC and verify the system dynamic stability under perturbations using of variable structure controller based on inverse system method, it has obvious advantage compared with direct feedback decoupling, and in the power supply mode of passive network, set constant AC voltage controller in the inverter side, reflects the dynamic stability of VSC-HVDC for passive load power supply.