Research On Model Predictive Fixed Frequency Control Strategy Of Vienna Rectifier Based On Duty Cycle Optimization

With the proposal and gradual implementation of the national dual-carbon goal,landscape clean energy power generation and electric vehicle load have developed rapidly.With the advantages of high power factor,few power switching devices and no dead time setting,VIENNA rectifier is widely used in power electronic rectifier power supply such as electric vehicle charger.At the same time,the nonlinear control scheme represented by finite set model predictive control(FCS-MPC)has the advantages of simple design principle,fast dynamic response and strong robustness,and has been gradually applied to the control of power electronic converters.However,the traditional model predictive control itself also has some problems,such as large grid side current ripple,unfixed switching frequency,difficult selection of midpoint balance weight factor and so on.This paper mainly studies the model predictive control of VIENNA rectifier and optimizes it.Firstly,the working principle of VIENNA rectifier is analyzed and the corresponding mathematical model is established,the direct power control scheme of VIENNA rectifier is designed,the next beat power prediction expression is established by using instantaneous power theory,the obj ective function expression of model predictive direct power control is derived,and the unit power factor grid-connected control of rectifier is realized.In order to solve the problem that it is difficult to select the weight coefficient of point potential in the multi-objective expression of model prediction,a method of optimizing redundant small vectors to effectively restrain the fluctuation of midpoint potential is studied.In order to solve the problem of excessive computational burden caused by traditional FCS-MPC ergodic optimization,a fast model predictive control strategy based on sector partition is adopted,which reduces the number of ergodic candidate vector sets from 27 to 3,and reduces the computational complexity of processors in each control cycle.On the basis of the above,in order to solve the problem of large ripple of grid-connected current caused by the action of a single vector in the control period of traditional FCS-MPC,the unweighted weight model predictive double-vector fixed-frequency control strategy based on duty cycle optimization is adopted.On the basis of obtaining the optimal vector,combined with zero vector,the double-vector fixed-frequency control is realized,and the calculation method of vector duty cycle is given.The simulation results show that the double vector synthesis method realizes the fixed switching frequency and achieves better control effect than the single vector,but the double vector fixed frequency control strategy still has some tracking errors.In order to further improve the tracking accuracy and restrain the current ripple on the grid side,referring to the principle of three-vector synthesis of space voltage pulse width modulation(SVPWM),an unweighted factor model predictive three-vector fixed frequency control strategy based on objective function modulation is proposed.By optimizing the adjacent three vectors to synthesize the target vector,the optimal calculation method of the three-vector duty cycle is given.The simulation results show that the three-vector fixed frequency control strategy eliminates the tracking error and reduces the grid-side current ripple and power pulsation.A hardware-in-the-loop experimental platform based on RT-Box is built,and the proposed VIENNA rectifier model predictive fixed frequency control strategy based on duty cycle optimization is verified by experiments.Steady-state and transient experimental results show the effectiveness and superiority of the proposed strategy.