Research On Control Of NPC Three-level PWM Recifier Based On VDFPI

With the rapid development of power electronics and smart grid,Neutral Point Clamped(NPC)three-level Pulse Width Modulation(PWM)rectifier is widely used in the mine shearer,wind power interface and subway frequency conversion driver due to its advantages of low harmonic distortion and high reliability.However,in the practical application of three-level rectifier,it is inevitable to encounter its own parameter changes and internal and external interference conditions,which will affect the control accuracy and stability of the rectifier.In order to improve dynamic and static performance of three-level rectifier,a control method of Variable Domain Fuzzy Proportion Integral(VDFPI)is proposed in this thesis.Firstly,this thesis takes NPC three-level PWM rectifier as the research object and analyzes the working principle of NPC three-level rectifier and establishes the mathematical model of NPC three-level rectifier.This thesis analyzes the causes of point potential imbalance in the topology of NPC three-level rectifier and puts forward the solution of balancing small vector.Secondly,because the traditional PI control voltage outer loop system is difficult to achieve good dynamic and static performance,this thesis combines PI control and fuzzy control to get FPI controller,and in order to solve the problem of low utilization rate of fuzzy rules in FPI,a variable domain scaling factor is proposed to improve the utilization rate of fuzzy rules.The dynamic and static performance and robustness of the system under PI control,FPI control and VDFPI control are compared by simulation.Compared with the traditional PI control,it is verified that the VDFPI control strategy has better dynamic performance and steady-state accuracy under the conditions of system parameter changes and load disturbance,etc.It is proved that VDFPI is more superior in three-level NPC rectifier control.Thirdly,the hardware and software system of NPC three-level PWM rectifier is designed.Among them,the hardware circuit includes the main circuit and the control circuit.The parameters of the main circuit are calculated.Under the premise of considering the electromagnetic compatibility and signal synchronization,the schematic diagram and parameters of the control circuit such as the power module,the sampling and conditioning circuit,the driver circuit,the communication module and the protection module are designed.Software system design includes Digital Signal Processor(DSP)and Field Programmable Gate Array(FPGA)programming.The main program and interrupt subroutine of DSP,the flow of parallel execution of FPGA and carrier generation program are introduced,and the software program is written.Finally,the hardware part of the power module,sampling and conditioning circuit and driver module were tested respectively.The experiment proved that the hardware circuit can work normally and good stability.Through the test of the FPGA program,the experimental results show that DSP and FPGA can carry out normal communication and output PWM wave to the driver circuit.After each part of the test is completed,the design parameters of the threelevel rectifier are given,and the hardware control circuit is assembled,and the hardware experiment platform is built.Experiments were carried out on NPC three-level rectifier under its own parameter changes and load disturbance.By observing bus voltage and network side current waveforms,it can be found that the improved VDFPI control strategy has faster dynamic response and better robustness than the traditional PI control,which verifies the correctness and effectiveness of the control strategy.