Research And Implementation Of VIENNA Rectifier Based On The Front Stage Of DC Charging Pile

With the global energy crisis and environmental deterioration worsening,energy conservation and emission reduction have become a global consensus,and new energy electric vehicles are gradually replacing fuel vehicles as a green travel mode.In view of the long charging time and low efficiency of the existing electric vehicle AC charging piles,the high-power DC charging pile technology came into being,especially with the support of national policies,it has developed rapidly.At present,the front-stage rectifier of DC charging piles has the disadvantages such as large DC bus voltage overshoot and high harmonic content of grid-side current.Therefore,it has important theoretical significance and practical value to study a kind of high-power charging pile with low harmonic content and high-power factor.According to the technical indicators of the high-power DC charging pile released by the State Grid,a set of 15kW high-power DC charging pile rectifier system was researched and designed.The thesis took the three-phase three-switch VIENNA rectifier as the research object,established a mathematical model according to the topology and working principle,simplified the mathematical model through abc-dq coordinate transformation,and designed the voltage loop and current loop PI controllers based on it.Aiming at the problems of complicated parameter setting when the PI control strategy was adopted for the voltage outer loop,and the large fluctuation of the DC bus voltage in the case of a sudden load change,which was likely to cause poor system stability,a fuzzy immune PI control strategy for the voltage outer loop based on genetic tuning was proposed.The fuzzy immune controller parameters were optimized by a genetic algorithm,and the best K and η values were substituted into the fuzzy immune PI controller,and then the PI parameters were adjusted online to achieve the purpose of stable bus voltage output under the condition of load mutation.At the same time,aiming at the inherent disadvantage of the imbalance of the neutral point potential of VIENNA rectifier,the fuzzy PI adaptive control strategy was introduced,the PI parameters were modified online,and the balance factor was adjusted to realize the voltage balance of the upper and lower capacitors at the output side.In the MATLAB/Simulink simulation platform,the simulation model of three-phase VIENNA rectifier system with three switches was built.PI control,fuzzy immune PI control and fuzzy immune PI control based on genetic tuning were applied to the voltage outer loop respectively.The simulation results showed that the fuzzy immune control based on genetic tuning can effectively reduce the fluctuation of DC bus voltage.At the same time,the simulation results of the improved neutral point potential balance control and PI control were compared,which showed that the fuzzy PI control can effectively suppress the neutral point potential offset.The experimental results showed that the fluctuation of bus voltage was 3.3%and the deviation of upper and lower capacitor voltage was less than 2.2V under the condition of load mutation.It was verified that the fuzzy immune PI control strategy based on genetic tuning can improve the anti-interference and robustness of VIENNA rectifier system,The improved neutral point control strategy had good control effect on neutral point potential balance of DC side.