Research On Harmonic Analysis And Suppression Of Electric Vehicle Charger Based On VSR

In recent years,with the rapid development of society,energy and environmental issues have become increasingly prominent.The pollutant gas generated by fuel vehicles accounts for a large proportion of environmental pollution and electric vehicle(EV)can achieve zero emissions of vehicle exhaust and have low energy consumption which has become the focus of external attention.The EV charger is a non-linear device,which will produce harmonic pollution during charging,which will have a certain degree of impact on the safe operation of the vehicle and the power grid.Therefore,the harmonic suppression of the electric vehicle charger is an important direction of current research.Front-end rectifier of the EV charger contains some non-linear components,which is one of the main sources of charger harmonics.Therefore,this thesis studies the AC/DC part of the charger structure.First,it analyzes and compares a variety of charger topologies,and selects the electric vehicle charger grid side based on the three-phase voltage-source PWM rectifier(VSR)structure which has unit power factor characteristics.Compared with uncontrollable rectifier,VSR also has the advantages of low harmonic content and suitable for large-capacity occasions.Secondly,the harmonic characteristics of the charger are analyzed,and the working principle of the three-phase VSR four-quadrant operation is introduced.The basic principles of the traditional SVPWM algorithm are analyzed and based on the above analysis,the mathematical model is established based on the circuit structure of the three-phase VSR.Aiming at the problems of complex coordinate transformation and trigonometric function operation in the traditional SVPWM modulation method,an improved SVPWM modulation method which simplifies the judgment process of the sector,and gives the voltage vector action time is proposed,and the feasibility of the improved algorithm is verified by simulation.Thirdly,the traditional PI control algorithm and nonlinear control algorithm are analyzed,and an improved control strategy is proposed,in which the voltage outer loop adopts sliding mode variable structure control,and the problem of poor robustness and overshoot of the traditional PI voltage loop is solved by designing a reasonable sliding mode controller.The current inner loop introduces fuzzy control technology to improve the traditional PI current loop's poor following performance and poor anti-interference ability in a nonlinear system.The comparison simulation verifies that the improved controller has good robustness,the response speed is fast,the harmonic content of the grid side current is small,and the unit power factor operation can be better realized.Finally,the design of the control system was completed according to the main circuit and control circuit parameters,including the design of hardware and software,and an experimental platform was built to verify the superiority of the improved controller,which has a good suppression effect on the grid-side current harmonics.