Complete-independent control strategy of active and reactive power for VSC based HVDC system

The performance of VSC based HVDC system partially depends on its control strategy. Based on the steady state model of VSC-HVDC system, a power control strategy is proposed and a series of mathematical analysis expressions for power delivery are deduced using the coordinate conversion and variables substitution in terms of the original equations. The corresponding power controllers are designed using the PI controller and the nonlinear inverse system. Based on the strategy designed, the transmission limits of active power and reactive power are deduced. According to the circle characteristic of operation represented, it is proved theoretically that the control strategy can independently control the active and reactive power. Case studies are also carried out to testify the control strategy designed using the PSCAD/EMTDC software. Simulation results verify that the power control strategy designed can independently control active power and reactive power and the controllers have rapid responding speed, desirable stability, and highly steady state control accuracy.