Double Closed-loop Control Strategy For Three-phase PWM Rectifier

Traditional phase-controlled rectifier and non-controlled rectifier have the disadvantages of large harmonic and low power factor,so they can pollute the power system.The three-phase PWM rectifier has low input harmonic current,relatively stable output voltage,and can effectively ensure that the input side to maintain the unity power factor,three-phase PWM rectifier is widely used in many fields because of its advantages in four-quadrant operation.In this paper,the PWM rectifier system has done a study of related issues.The difference between three-phase PWM rectifier and no-control rectifier is that it has very strong nonlinear characteristics.In view of this,in the process of designing the control system of PWM processor,it is very difficult to achieve the ideal control effect,and the dynamic performance is not ideal,the parameter adjustment is also very complex.So this paper improves the traditional voltage and current double closed-loop control of three-phase PWM rectifier,changing the traditional PI Control Strategy to the double-loop control strategy based on "single neuron + sliding mode change"the traditional space vector control algorithm is improved,and a SVPWM modulation strategy based on NZV is proposed.The research object of this paper is three-phase voltage source PWM rectifier.By studying the basic principle of this rectifier,the mathematical model of three-phase PWM rectifier in different coordinate system is constructed,the coordinate system is divided into two-phase static coordinate system,three-phase static coordinate system and two-phase synchronous rotating coordinate system.Based on the analysis of the traditional space vector control modulation algorithm,the technical improvement is made on the basis of the problems of large computation,complex implementation,low implementation speed and low implementation efficiency,a SVPWM modulation strategy based on NZV is proposed,which divides an AC period into six intervals and synthesizes the DC side voltage of PWM rectifier by using the line voltage with the largest two voltage values and positive polarity in each interval,it not only improves the utilization ratio of DC voltage,but also reduces the switching loss and improves the reliability of PWM rectifier.Based on the double-closed-loop control system,the voltage and current double-closed-loop PI linear control method is studied in this paper.In view of this,this paper proposes a double-loop control strategy based on "single neuron + sliding mode change"for the traditional double-loop control based on PI Controller,which dynamically adjusts the control parameters and responds to the change of load side in real time,the utility model has the advantages of wide voltage regulation range,fast dynamic response and the like.In addition,the sliding mode control structure is introduced into the current inner loop,which greatly simplifies the loop control system of the three-phase PWM rectifier,and has the advantages of improving the steady-state performance,better dynamic performance and Shandong bar performance.The rationality and effectiveness of the improved SVPWM modulation strategy and the new double-loop control strategy are verified by using Matlab/Simlink software.