Research Of Control Method For Power Electronic Transformer

With the development of advanced power electronic technology, high bandwidth communication technology and internet technology, the concept of smart grid is put forward. Intelligent substation is an important part of the smart grid, the main development direction of the future substation is to optimize and improve the conventional substation by the use of automatic control, detection technology, power electronic technology, advanced system monitoring and management technology. Conventional transformer is important equipment in intelligent substation. Because of its large size, large weight, no fault isolation and no self-protection function, it is possible to use smart power electronic transformer to replace the conventional power transformer. Intelligent power electronic transformer has a small size, controllable power factor and reactive power compensation, which can realize the function of detection, diagnosis and protection. In order to ensure the safe and reliable operation of power electronic transformer, this paper mainly studies the power electronic transformer based on double PWM converter.The working principle of the high voltage input level, the intermediate isolation level and the low voltage output level is analyzed, and the mathematical model of each part is established. According to the control target of the high voltage input level, the middle isolation level and the low voltage output level, the control strategy is formulated, the control strategy diagram is given, and the detailed analysis is carried out. Through the frequency domain mathematical model and the typical I and II- type correction principle, the outer and inner loop parameters of the system are designed, and the selection principle of the controller parameters is given. The simulation model of intelligent power electronic transformer is built by Matlab/Simulink simulation software, and the simulation of the system operation is carried out in normal grid, load switching,and short circuit fault and voltage distortion conditions.In order to improve the robustness of the system, internal model controlstrategy of power electronic transformer is proposed. The basic principle,topology structure and properties of the internal model controller are analyzed,internal model controller and filter are designed for high-voltage side and low-voltage side, and selection principle of PID parameters is given. In order to overcome the shortcomings of the traditional PI control, the fuzzy PI control strategy is proposed, and the membership function, the domain and the fuzzy rules are designed. The simulation is carried out in case of the same simulation conditions with the traditional PI control. The simulation results show that the internal model control and fuzzy PI control have better robustness, dynamic performance and disturbance rejection capability in load switching and power grid anomaly conditions.