Research On Control Strategy Of Three-phase Current Source PWM Rectifier

As a current converter,pulse width modulation(PWM)rectifier has been widely used in various fields.PWM rectifier as "green power converter",can make the grid side current sinusoidal,so that the system in the unit power factor operation,to avoid the grid "pollution".PWM rectifiers are generally divided into voltage source PWM rectifiers(VSR)and current source PWM rectifiers(CSR).With the rapid development of superconductivity technology,the problem of energy storage inductance on the DC side of CSR has been solved,and CSR has the characteristics of step-down output,adjustable unit factor,wide range of output voltage regulation,etc.It can be used in data center server,aviation power supply,superconducting energy storage and other applications,and has a broad development prospect in the future.This paper takes three-phase current source PWM rectifier as the research object,and researches the modulation technology,control strategy,and PWM method in discontinuous conduction mode.The main research contents are as follows:Firstly,the working principle of three-phase CSR is introduced from three aspects of topology structure,working mode and SVPWM modulation technology.The mathematical model of three-phase CSR in the coordinate system of three-phase static,two-phase static and two-phase rotation is established,and the equivalent circuit diagram is drawn,which lays a theoretical foundation for the research content in the following paper.Then,it focuses on the study of three-phase CSR under the discontinuous conduction mode(DCM).This paper introduces the traditional PWM method of CSR,analyzes the waveform of the current on the network side,the current on the DC side and the output voltage of CSR under the light load condition,and draws the conclusion that using the traditional PWM method in the discontinuous conduction mode will lead to the current distortion on the network side and the output voltage out of control,and proposes a multi-objective PWM method to solve this problem.By analyzing the current waveform under DCM,this method calculates the actual duty cycle of the vector action to replace the duty cycle expression in the traditional PWM method.The simulation model of three-phase CSR under Matlab/Simulink was established.Through waveform comparison and analysis,it was concluded that the multi-objective PWM method could make the three-phase CSR grid side current sinusoidal under DCM,and the output voltage returned to the reference value.Then,the direct power control strategy of three-phase CSR is studied.Control structure with double closed-loop control structure,the outer ring for the voltage loop,the dc side voltage reference together with controlled by PI controller to adjust the input power inner ring,internal ring will be instantaneous active power and reactive power respectively,together with a reference input controller is adjusted,after adjusting the input SVPWM control module to produce PWM signal control on-off switch tube.Through Matlab/Simulink simulation waveform analysis system input,output performance and dynamic characteristics,verify the feasibility of the control strategy.Finally,an experimental prototype of three-phase CSR is built through the design of main circuit parameters and the internal structure of the prototype.The prototype structure has three layers.The bottom layer consists of power switch tube,sensor and filter capacitor.The middle layer is used for sampling voltage and driving IGBT;The top layer includes sampling conditioning board,DSP control circuit and driver interface.Through the connection and configuration of the software system and the experimental prototype,a three-phase CSR experimental test platform was built to verify the correctness of the proposed multi-objective PWM method and direct power control strategy.