The Research On Control Strategy For VSC-HVDC

With the development of high power self-commutated power electronic devices and pulse-width modulation technique, the VSC-HVDC transmission technology which based on the Voltage Source Converter has realized some successful applications in power systems. This transmission technology has advantages such as independent regulation of the active and reactive power and supplying power to the passivity network and so on, and is one of the effective methods to improve the power quality. The control system plays a vital role in the operating performance of VSC-HVDC system. The nonlinear control strategies for the VSC-HVDC system are mainly studied in this thesis.Two control strategies are employed to design the controller of VSC-HVDC system in this thesis. For the first strategy, the passivity-based controller of VSC-HVDC system connected to active network is designed. The EL mathematical model of the VSC-HVDC system which adopts the passivity-based control theory is studied, and the passivity of the system is also verified. The double loop control strategy of the rectifier side is used, designing the inner passive controller which the use of the reference current generated by the outer loop. The passivity-based power controller of the inverter side is designed, so as to realize the control and adjustment of the active and reactive power independently, maintain the stability of the DC voltage. For the second strategy, the variable structure controller of VSC-HVDC system for the passive network is designed. First of all. the approach of state feedback exact linearization is adopted to change the nonlinear mathematical model into the linear one; then, the sliding mode variable structure control theory is adopted to design the controller, realizing the control goals that provide stable three-phase AC voltage for the passive network.In addition, the PI control strategy is also adopted to design the controller of the VSC-HVDC system connected to active network and passive network respectively, Finally, a Matlab-based simulation model is constructed. The simulation results show that, the, control performance of the two control strategies used in this thesis are superior to the PI control strategy, and prove the effectiveness and superiority of the control strategies.