Research On DC Microgrid Control Strategy Based On Model Predictive Control

The shortage of energy and the rise of distributed power generation have promoted the development of DC microgrids.Because DC microgrids do not need to consider factors such as frequency and phase,the control method is more flexible,at the same time,the optimized configuration of energy storage devices can reduce the impact of distributed energy grid connection on the stable operation of power systems.Model predictive control has been widely used in various fields due to its fast dynamic response and simple control.This paper applies model predictive control to battery bidirectional DC-DC converter control for the purpose of optimizing the dynamic response of DC microgrid bus voltage,improving the voltage response speed of the bus while optimizing the voltage quality.The main work completed and results achieved are as follows:(1)A strategy for optimizing the dynamic response of bus voltage based on model predictive control is proposed.Firstly,the working principle of the battery measured virtual capacitor is given,and the relationship between the bus voltage and the virtual capacitor current is obtained.Then the optimal virtual capacitor value is obtained by the model predictive control,and it acts on the virtual capacitor control of the bidirectional DC-DC converter.By controlling the change of the virtual capacitor value to optimize the bus voltage dynamics,when the load is abrupt,a larger virtual capacitor is used to slow the change of the DC voltage,and a small virtual capacitor is used in the late dynamic response to make the DC voltage reach a steady state quickly.(2)Because the traditional finite set model predictive control has the problem of insufficient control precision,a multi-step finite set model predictive controller is designed to be applied to the battery current inner loop.Analyze the equivalent circuit model of the bidirectional DC-DC converter under different working modes,and predict the multi-step length of the controlled quantity,at the same time,the DC voltage is added as a secondary evaluation index to the evaluation function to reduce the steady-state error of the DC voltage while ensuring the fastness of the inner loop.(3)A model of current inner loop model prediction control is proposed.The battery current prediction value is obtained by improved model-free prediction.Then the optimal switching state is obtained by the evaluation function and output to the DC-DC converter.Accurate converter inductance and capacitance parameters are not needed in the process,and are not affected by system parameter changes,which greatly improves the accuracy and robustness of the system.(4)According to the above proposed control strategy,the DC microgrid model was built in Matlab/simulink for time domain simulation,and the experimental verification was carried out on RT-LAB real-time simulation platform.The results verify the effectiveness of the optimal control strategy for the dynamic response of the proposed bus voltage.