Research On Intelligent PI Control Method Of Three-phase PWM Rectifier

Electrical energy has always been closely related to people’s life,and good electrical energy quality is a guarantee of a high quality of life.However,the use of non-linear loads injects a large amount of harmonics into the power grid,causing a drop in power quality and even electrical hazards.Therefore,the electrical energy must be strictly processed before it can be used by users.As a kind of "green" power conversion device,the PWM rectifier can ensure the stability of the DC power supply,as well as the power quality of the power grid,thus solving the harmonic pollution problem at the source.Consequently,it is of great significance to research high-performance rectifiers.Firstly,this paper selects topological structure of the three-phase two-level voltage rectifier based on the two main goals of DC voltage stability and unity power factor operation.The working principle of the PWM rectifier and current commutation conditions are analyzed in detail,and its modulation principle has conducted in-depth research.Based on space vector pulse width modulation(SVPWM)theory,a modulation algorithm with simple steps and easy calculation is proposed.The algorithm uses three-phase voltage to determine the position of the sector in the complex plane coordinate system.It directly computes the action time of each vector by simple arithmetical operation,and improves the order of the actions of some sectors.Compared with the traditional SVPWM algorithm,there is no need for complex calculations such as trigonometric functions and irrational numbers,and even harmonics of the voltage are eliminated,providing a certain reference for the system’s rapid response and filter design.Secondly,due to the complex,time-varying and non-linear characteristics of the rectifier system,the parameters of the traditional PI controller are relatively fixed,and it is difficult to meet the unfavorable conditions such as sudden changes in load of the system and voltage pump rise,which affects the operation of the rectifier.Therefore,based on the principle of direct current control,the paper designs the double closed loop control structure of the rectifier voltage outer loop and the current inner loop,and the fuzzy PI controller with adaptive parameters can be added to the voltage outer loop.At the same time,in order to suppress human subjective factors in the fuzzy control design and achieve higher quality control results,the particle swarm optimization algorithm with simple implementation,few parameters,convenient adjustment and strong search ability is used to change the quantization factor and scale factor.Online optimization is performed to complete the intelligent adaptation of the voltage outer loop,which greatly improves the robustness and rapidity of the system.Finally,the whole simulation model of control system for three-phase voltage type PWM rectifier is built in this paper,which verifies that the proposed SVPWM optimization algorithm has the advantages of small harmonic content,simple calculation and fast response.Meanwhile it is proved that the rectifier system based on intelligent PI control can absolutely realize the stability of DC voltage and unit power factor operation under the two conditions of sudden load change and voltage pumping,and it has strong stability and rapidity.