Research On AC Power Supply Simulator With High Power

In recent years, as the representative of the new-energy power generation technology, the photovoltaic and wind power generation is developing rapidly. The electric energy generated from the new-energy power generation equipments is direct current, which needs to be controlled by the grid-connected converter in order to convert the DC power into AC power and then flow into the power grid. With the increasing capacity of new energy power generation in power grid, the influence which the grid-connected converters have on the power grid is also increasing. In order to conduct analysis on the influence which grid faults have on the grid-connected converters, people needs to simulate the grid faults occur frequently such as voltage sag and frequency mutation and so on. These grid faults will have a great impact on the grid-connected converters. Therefore, the research on the performance of grid-connected converters is becoming a hot spot in academic circles. Because the power grid faults is uncontrollable. When testing the performance of grid-connected converters, it is difficult to reproduce the grid faults directly via the power grid. Therefore, there must be a kind of specialized equipment which can simulate variety of faults occurred in power grid. People name this kind of equipment AC power supply simulator. In this paper, a kind of AC power supply simulator based on power electronic transformation is introduced and the control strategy of the grid-connected side and the output side of the AC power supply simulator are analyzed and discussed in detail. At last, the correctness of the theoretical research results and the practical feasibility of AC power supply simulator are verified through simulation and experiments.First, this paper presents the functions which the AC power supply simulator should have according to the needs of research on the converter. And then the mathematical model of the three-phase PWM rectifier and inverter in different coordinate system is deduced; The operation principle of the grid voltage oriented vector control is analyzed. Finally, the operation principle and control algorithm of the space vector PWM modulation method and the simulation of three-phase unbalanced fault are studied in detail.Secondly, the design method of the hardware parameters of the main circuit of AC power supply simulator is studied. The design method of LCL filter on the grid-connected side and LC filter on the output side is presented, then the effectiveness of the designed parameters are verified through simulations; Finally, the intermediate DC capacitance is designed according to immunity and dynamic performance.At the same time, this paper focus on the research on control strategy of AC power supply simulator. The double closed loop control strategy based on PI controller is introduced and in order to restrain the intermediate DC voltage fluctuation the solution that adding the load current feed forward control strategy is proposed. Also in this part, the operation principle of single voltage closed loop control strategy based on PI controller and double closed loop control strategy based on PR controller is presented and studied. And the virtual impedance control strategy is proposed to improve the quality of the output voltage waveform. Finally, the effectiveness of the control strategy is verified by simulation analysis.To verify the correctness of the theory and simulation analysis, the experimental platform 250KW AC power supply simulator is built in this paper. Through tests on the dynamic performance、steady performance and fault simulation function of AC power supply simulator on the experimental platform, this paper verifies the validity and feasibility of the control strategy of AC power supply simulator, which creates the condition for the scientific research in the field of converter.