Research On Performance Of Three-Phase PWM Rectifier With Sliding Mode Variable Structure Control

The PWM rectifier is a multi-variable,strongly coupled nonlinear system.In order to achieve the control goal of current decoupling when the system parameters and load are stable,a double closed-loop control strategy based on PI linear controller is often used.However,uncertain factors such as load abrupt changes and system parameter changes and disturbances may occur during the actual operation of the system.PI linear control has not been able to make the system adapt quickly.In order to overcome these uncertainties and the impact of disturbances on system performance,nonlinear control strategies must be applied to improve system performance.Sliding mode variable structure control is a nonlinear control strategy.The parameter accuracy is not high when modeling.Therefore,when the system parameters change and the load is disturbed,it has strong robustness and can improve the performance of the PWM rectifier.In this paper,the three-phase voltage type PWM rectifier has been taken as the research object.The structure and working principle of the rectifier have been analyzed.The mathematical model of the two-phase rotating coordinate system of the rectifier has been established.The feedback decoupling control strategy of the three-phase PWM rectifier has been studied and simulated.The principle and design method of sliding mode variable structure control have been studied.The conditions of precise feedback linearization of nonlinear systems and the sliding mode variable structure control method of nonlinear systems have been analyzed.The affine nonlinear system model of two-input and two-output of three-phase PWM rectifier was derived.The current inner loop decoupling of threephase PWM rectifier has been realized by feedback linearization.Based on this,a double closed-loop control scheme of current inner loop and voltage outer loop based on sliding mode variable structure control has been designed.The simulation experiment and feedback decoupling were adopted.The control strategy has been compared and analyzed.The simulation results showed that the sliding mode variable structure control strategy can improve the dynamic performance of the three-phase PWM rectifier.The system design of the three-phase PWM rectifier was completed,including the hardware design of the main circuit and the control circuit.Based on the sliding mode variable structure control strategy,the system software design was completed and the experimental verification analysis was carried out.The experimental results show that the sliding mode variable structure control strategy can effectively improve the dynamic response capability and load disturbance resistance of the system,and make the system more robust when the parameters are disturbed.