Research On Model Predictive Direct Power Control Of Three Phase Grid-connected Inverter

II The traditional energy sources are gradually exhausted and the development of new energy sources is in line with the development trend of today's world.Inverter plays an important role in the new energy generation grid-connected system.Three-phase gridconnected inverters have received extensive attention from researchers because of many advantages.The control strategy of three-phase grid-connected inverter is related to the stable operation of the new energy generation grid-connected system.Switching frequency of the traditional model predictive direct power control strategy is high,which results in large switching loss.The general low-frequency strategy reduces system performance.This paper aims to ensure the stable and efficient operation of three-phase grid-connected inverters while reducing the switching loss.Firstly,the working principle of the three-phase grid-connected inverter is analyzed,and the corresponding mathematical model is established.Then the instantaneous power theory is studied and the principle of direct power control is elaborated.The model predictive control is outlined.The existing model predictive direct power control is described.The working principle of the current frequency-reduction model predictive direct power control strategy is described.Based on the existing theories,the multi-cost function frequency-reduction and variable coefficient frequency-reduction model predictive direct power control are proposed.The working principle of these two kinds of control strategy is analyzed.The multi-cost function frequency-reduction strategy increases the number of cost functions based on the existing frequency-reduction strategy,allowing the system to follow the power deviation to determine an appropriate cost function.This strategy is suitable for a steady-state system and has poor performance under dynamic conditions.The variable coefficient frequencyreduction strategy transforms the fixed switching function coefficient in the original lowfrequency strategy into adaptive coefficients to adapt to system power variation.The system follows the power deviation to select the switching function coefficient.The simulation verifies that this strategy can achieve better control effect under steady state and dynamic conditions.Finally,on the basis of the previous theory,the experimental hardware circuit was designed and the experimental platform was set up.The experimental results are analyzed and the effectiveness of the proposed multi-cost function frequency-reduction and variable coefficient frequency-reduction model predictive direct power control strategies are verified.