Research On Model Predictive Control Of Bidirectional Interface Converter Under Unbalanced Voltage

The bidirectional interface converter is the core device of the AC/DC hybrid microgrid,which can run in inverter and rectifier modes.The bidirectional interface converter plays a vital role in the energy exchange and power balance between the DC microgrid and AC microgrid.Negative sequence current,active and reactive power fluctuations,DC side voltage fluctuation,and increased peak current are generated under unbalanced grid voltage.These phenomena can reduce the operating performance of the interface converter,and then affect the stability of the microgrid.Therefore,it is of great significance to study the control strategy of the bidirectional interface converter under unbalanced grid voltage.Aiming at the phenomenon of negative sequence current,active and reactive power fluctuations under unbalanced grid voltage,a Model Predictive Direct Power Control(MPDPC)based on the power compensation is adopted in the thesis.First of all,deriving the mathematical model in abc,?? and dq coordinates.This mathematical model is used as a theoretical basis to establish the power predictive control model.Secondly,the Second Order Generalized Integrator-Quadrature Signal Generator(SOGI-QSG)is used to separate the positive and negative sequence components of voltage and current.According to the theory of instantaneous power,the power compensation values for suppressing negative sequence current,active and reactive power fluctuations are calculated,and then the traditional power reference value is improved.Then,detailed simulation research and analysis are carried out on the rectifier,inverter and inverter switching to rectifier modes.The traditional dual vector control and current predictive control are used to compare with MPDPC.For the DC side voltage fluctuation phenomenon,the charge and discharge control circuit of super capacitor is designed.Finally,a simulation model is built on the Matlab/Simulink platform to verify the feasibility of the method.The peak value of the output current is also increased under unbalanced grid voltage.For this phenomenon,the model predictive flexible power control strategy with adjustment parameters η is used.By calculating the power reference value that minimizes active and reactive fluctuations,and negative sequence current,the mathematical expression between η and the peak current is established.By adjusting the parameterη,the fluctuations of active and reactive power can be reduced,and the peak value of the output current can also be limited.This control strategy can ensure the stable operation of the bidirectional interface converter.