Model Predictive Control Of Three-Phase Grid Connected Inverter Based On Virtual Vector Design

The three-phase grid connected inverter is the core equipment of the new energy power generation grid connected system and the link between the new energy power generation system and the power grid.The performance index of the grid connected inverter directly affects the new energy grid connected power quality.The output current of the traditional finite control set model predictive control algorithm(FCS-MPC)has large ripple and serious distortion.In order to improve the power quality of grid connected inverter,this paper studies the model predictive control strategy.The main research contents are as follows:Aiming at the problem of large output current ripple of traditional 8-vector model predictive control algorithm,an improved model predictive algorithm based on virtual vector is proposed.The cause of current ripple is analyzed by vector space diagram.A new voltage vector is synthesized by using adjacent voltage vectors to expand the set of alternative vectors,and the calculation method of duty cycle of alternative vectors is analyzed.The simulation results show that the model predictive control algorithm with fixed duty cycle virtual vector can effectively reduce the harmonic of three-phase grid connected current compared with the traditional model predictive control algorithm.Aiming at the problem of 14 times value function optimization in the improved model predictive control algorithm system based on virtual vector,a fast voltage vector positioning algorithm is proposed.Firstly,the vector space is partitioned twice,and the vector of each sector is allocated.The mathematical model of the boundary of each sector of the vector is solved by coordinate operation and linear programming.Finally,the prediction model of the sector at k+1 time is established.Simulation results show that this strategy only needs one sector judgment and three value function optimization,and can effectively reduce the amount of calculation in the system operation process.Aiming at the problem of system performance degradation caused by parameter perturbation during the operation of three-phase grid connected inverter system,a compensation model of inverter parameter error is proposed.Firstly,the nominal and actual value models of delay compensation link,current prediction link and vector time action link are established respectively.Secondly,the error sources,primary and secondary factors and error transmission relationship of each link are analyzed.Finally,the parameter error compensation model of each link is established.The simulation results show that the parameter error compensation model can effectively improve the steady-state performance of the system.Finally,a three-phase grid connected inverter experimental platform based on DSP28335 is built to verify the proposed virtual vector based improved model predictive control algorithm.The experimental results show that the virtual vector based model predictive control algorithm can effectively reduce the output ripple of three-phase grid connected current compared with the traditional model predictive control algorithm.