Controller Design Of High Power Modular Multilevel Power Grid Simulator

In the wind power generation system,a large number of energy can be stored in the rotor of the motor.The integration of wind power generation equipment into the grid will cause low-frequency oscillation,sub synchronous resonance and other problems.The equipment in the power grid needs to go through strict grid adaptability test before it is put into use.Therefore,in order to develop a new generation of high reliability offshore wind turbine and shorten the research and development cycle,it is urgent to need a high-performance and widely applicable high-power grid simulation device.Power grid simulator is the core equipment of wind turbine test bench to simulate various operation conditions of power grid.However,due to the equivalent switching frequency of the system,the control bandwidth of the system is difficult to be improved,resulting in the performance of the high-power grid simulator designed is relatively general.Therefore,the modular multilevel converter with high equivalent switching frequency is proposed to be applied in power grid simulator.In this paper,the inverter topology of modular multilevel power grid simulator is studied,and the traditional modular multilevel converter topology is improved according to the demand of power grid simulator.Firstly,the working mechanism of the topology is described in detail,and its equivalent mathematical model is established.The relationship between the capacitor voltage of the sub module,the instantaneous power of the bridge arm and the circulating current in the phase is analyzed.Through the above analysis,the circuit hardware parameters are given.Secondly,the control strategy of modular multilevel converter system is studied,and a sub module capacitor pre charging control strategy of modular multilevel converter is proposed,which is verified by simulation analysis.The two modulation methods of modular multilevel converter are compared and studied,and the differences of their characteristics and application occasions are pointed out,and in order to meet the requirements of power grid In order to speed up the energy exchange between modules under low frequency condition,a closed-loop voltage sharing optimization method based on high-frequency circulating current injection is proposed.In order to verify the research results,a single-phase 3KW modular multilevel power grid simulator prototype is designed.The control architecture and controller composition of the prototype are described in detail,and the conditioning circuit board is introduced.Finally,the modular multilevel converter model is built based on starsim as the simulator,and the controller model of the modular multilevel converter based on FPGA is built as the controller.The controller design is completed through the hardware in the loop experiment,and the single-phase 3KVA sample machine is debugged by using this controller.The control algorithm and the developed controller are verified by experiments.