Research And Development Of Rectifier Module For DC Charging Pile Based On Active Harmonic Suppression

In recent years,China has been vigorously promoting the industrialization and scale development of electric vehicles and their charging facilities in order to achieve the strategic goal of "double carbon" and build a new type of power system.With the gradual increase of the share of electric vehicles in the global market,the performance and reliability of charging piles have raised higher requirements and challenges.Compared with AC charging piles,DC charging piles have higher efficiency and faster charging speed,which is the main development direction of charging piles.At present,the dispersion and randomness of electric vehicle charging load,as well as the dead zone and nonlinearity of switching devices can cause power quality problems such as network-side current harmonics and voltage deviation.At the same time,the large-scale renewable energy generation and distributed power supply are widely and simultaneously scattered into the grid,coupled with the access of long-distance transmission and distribution lines and multi-level transformers,which makes the grid increasingly present the characteristics of a weak grid,and the non-negligible grid equivalent inductance will adversely affect the stability and robustness of the rectifier module,the key component of DC charging pile.Therefore,it is crucial for the rectifier module of DC charging pile to suppress its grid current harmonics,quickly cope with the fluctuation of grid-side inductance,and maintain the stability and robustness of DC bus voltage in high power factor operation and charging process.The main research contents of the paper are as follows:The working principle,mathematical model,topology,switching state and commutation process of three-phase VSR of DC charging pile rectifier module are studied to clarify its advantages as well as the problems.And on this basis,theoretical analysis of the harmonic characteristics during the rectifier module operation is carried out to provide theoretical support for the subsequent design of the rectifier control system.Aiming at the problems of high total harmonic distortion rate of network-side current during charging of rectifier module of DC charging pile and reduced system stability under weak grid,the control strategy of PI+ repetitive control combined with inductorless parameter decoupling is proposed.Firstly,based on the current inner-loop PI control,a PI+ repetitive controller based on parallel structure is designed,and for the compensation link,a second-order low-pass filter is selected to correct the system,which actively suppresses the network-side current harmonics without increasing the filtering device and effectively improves the quality of grid-connected current.In addition,based on the synthetic vector method,the controller parameters are designed to realize the main pole pair elimination by establishing two identical step rotating coordinate system vector differential equations,so as to realize the inductance-free parameter decoupling to cope with the influence of network-side inductance fluctuation on the control system stability under the weak grid.The simulation model of the main circuit of the rectifier module and its control circuit of the DC charging pile is established,and Matlab/Simulink is used to build the simulation and complete the parameter design.The simulation results of the steady-state performance,starting characteristics,and dynamic response of the three-phase VSR rectifier module under the traditional feedforward decoupling PI control and the PI+repetitive control without inductance parameter decoupling proposed in this paper are compared and analyzed to verify the effectiveness of the proposed control strategy.Finally,the hardware circuit and software program are designed and developed to build a DC charging pile rectifier module based on TMS320F28335 as the core controller,and experimental analysis is conducted.The results show that the control strategy can effectively suppress the grid-connected harmonic currents during the rectifier module operation and reduce the influence of the weak grid effect on the charging equipment,so it is suitable to be applied to the control layer of the rectifier module of DC charging pile with weak grid under the high percentage of renewable energy access.