Power Exchange Control Of Back-to-Back Four-Quadrant Voltage Source Converter

Back-to-back four-quadrant VSC(voltage source converter) that has the advantages of controlled flexibly and supplying power with small harmonic amount have been widely applied in the field of HVDC Light, FACTS (Flexible AC Transmission Systems) ,Wind Power and so on. The object of back-to-back four-quadrant VSC is to realize power's exchange of both sides AC system. The performance of it bases on the stability, speed and accuracy of adjusting any reactive and active power between VSC and power grid. This dissertation analyzes the working principle of back-to-back four-quadrant VSC and studies its modulation and control principle, and designs it's nonlinear decouple controller.This dissertation elaborates the state space model of back-to-back four-quadrant VSC system in the abc coordination and synchronous orthogonal dq frame and analyzes the power exchange principle of back-to-back VSC system. Then, this dissertation introduces the basic principles and the characteristics of the space vector PWM (SVPWM) and designs a two-level SVPWM algorithm. In addition, this dissertation studies the equivalent relationship between SVPWM and SPWM, and through simulation to give an explanation.Power exchange control strategy is the core algorithm of control system. So, it is the focus of this dissertation. First, according to multiple-input multiple-output linear theory of nonlinear systems, the feedback control law is derived based on the one side VSC's model in dq frame and a nonlinear decoupled controller with proportional controller is proposed in this dissertation. Further, this dissertation analyzes the problem of controller's control static error generated by system's parameter estimation inaccuracy and proposes two methods to eliminate control static error. At last, extensive simulations are conducted using PSCAD/EMTDC under various operations of back-to-back VSC system to verify the validity of the established modeland the designed control method.Moreover, a physical prototype of 30kVA/380V was developed for research. Experiments are conducted combining the contents of simulation. Experimental results are consistent with the theoretical analysis and simulation results, and verified the conclusion of this dissertation study. In addition, phsyical prototype will provide physical analogue's experimental platform of large interconnected power systems and HVDC light system for dynamic simulation laboratory.