Research On Model Predictive Control Strategy Of Power Conversion System Under Unbalanced Conditions

To solve the problems of unbalanced voltage and power fluctuations caused by various factors,energy storage systems have been utilized in new energy power generation systems,and the research of control strategies for inverters under various working conditions has become a hot issue.An improved model predictive control for the control strategy of power conversion system under unbalanced conditions is proposed in this dissertation,which solves the power quality problems under various operating conditions.At first,the dissertation adopts the model predictive control with flexible control mode and fast transient response and the control strategy of virtual synchronous generator commonly used in off-grid inverters.In combination,an improved VSG-MPC control strategy is proposed,which retains the advantages of virtual synchronous generators with the inertia and damping required by the power system,and also combines the advantages of model predictive control.The cost function in the model predictive control has also been improved and designed to improve the accuracy of current control,and the Luenberger observer used can reduce the current sensors used in the hardware,which is more economical.Secondly,for unbalanced load conditions,this dissertation utilizes an unbalanced voltage compensation mechanism in the improved VSG-MPC proposed under balanced conditions,and further improves the cost function,fully taking into account the voltage control accuracy and the switching loss.The proposed improved VSG-MPC can well cope with the complex conditions of asymmetry of three-phase load parameters and single-phase open circuits.Then,for unbalanced grid conditions,an improved model predictive direct power control(MP-DPC)based on the traditional look-up table direct power control is proposed in this dissertation,which solves the shortcoming of direct power control that the switching frequency isn’t fixed.Through the power analysis of the unbalanced grid,three kinds of control objectives are introduced to combine with MP-DPC,which can realize the control objective of the system under unbalanced grid conditions.Finally,the dissertation verifies the above-mentioned control strategy through the Matlab/Simulink simulation platform,and builds the corresponding hardware-in-the-loop experiment platform,completes the software and hardware design,and further develops the proposed control strategy under unbalanced conditions.The sufficient verification proves the correctness and superiority of the proposed control strategy.