Research On Control Strategy Of VIENNA Rectifier Under Unbalanced Power Grid

With the development of the electric vehicle industry,the charging power supply as the core device of the energy supply of electric vehicles has been widely concerned by scholars at home and abroad.The front-stage AC/DC rectifier circuit of charging power supply is the core part of charging power supply.Three-phase three-level VIENNA rectifier has been widely used in charging power supply because of its advantages such as small number of switches,simple circuit structure,low harmonic content of input current and so on.However,the actual power grid is unbalanced due to voltage phase and amplitude deviation.At this time,control strategies under balanced conditions will no longer apply.For this reason,the control strategy of VIENNA rectifier under unbalanced power grid is studied in depth in this paper.First of all.the operating modes of the VIENNA rectifier under different input current polarities are analyzed in detail.The mathematical models of VIENNA rectifier under the condition of grid balance and grid unbalanced are established respectively.The VIENNA rectifier based on finite control set model predictive control is studied.According to the features of the limited number of switching states of the rectifier,the current prediction model and the objective function are established.The FCS-MPC control system of the VIENNA rectifier is built.Secondly,under the unbalanced condition of the power grid,the traditional I CS-MPC control will cause the VIENNA rectifier to have the problems of large harmonic distortion of the grid side current and ripple of the DC output voltage.An improved FCS-MPC control algorithm is proposed in this paper.Introducing the constraints of active power and reactive power on the network side into the FCS-MPC algorithm,the power prediction model is established.The stability of DC output voltage can be achieved by predicting and reducing the second harmonic components of active power on the grid side.In order to eliminate one beat delay caused by computing time,two-step predictive control is adopted.A feedback compensation module is added to eliminate the calculation error between the predicted value and the given value of the next cycle.At the same time,considering the disadvantage of unbalanced neutral-point potential in VIENNA rectifier topology,the fundamental cause of unbalanced neutral point of rectifier is analyzed.The neutral point balance prediction model is established and introduced it into the objective function to realize the control of neutral point voltage balance.Finally,using MATLAB/Simulink simulation software to build simulation model and carry out simulation analysis of proposed control strategy.The hardware and software of the rectifier system are designed concretely.An experimental prototype with TMS320F28335 as the main controller is built.Debugging the hardware and software of the experimental platform and completing the experimental verification.The experimental results verify the correctness and effectiveness of the proposed control strategy.