Research on Modelling and Control of Three-level PWM Rectifier System

In order to solve the problem that there is coupling among neutral current and three phase current in the model of three-level PWM rectifier, this thesis has introduced the idea of coordinate transformation to transform the model from three-phase stationary coordinate system to two-phase rotating coordinate system, which reduces the order of the system to four-order linear compact model, according to the principles of grid voltage vector orientation. Based on strategy analysis of the control of three-level rectifier, we have made the solution that design the structure of the rectifier system into the double closed-loop which is consist of voltage loop and current loop, realizing the purpose that the power factor of AC side keeps 1 and the voltage of DC side keeps stability. With completing the decoupling of the state feedback of current, this thesis has designed the inner current controller and the outer voltage controller respectively, according to the engineering design methods of making atypical system typical. For dealing with the problems of DC bus voltage disturbance caused by load current, we have introduced the feed-forward compensator to improve the anti-jamming performance of the system. Finally, the results of Matlab simulation have proved that the designed three-level PWM rectifier system has good dynamic indicators and anti-interference ability.