Improved Three-Vector Model Predictive Current Control Strategy for Fixed Switching Frequency on a Grid-Connected Inverter

When the three-phase grid-connected inverter system is in operation, there are problems of significant switching losses and power losses. At the same time, if the switching frequency is not fixed, it will lead to problems such as a high content of low-order harmonics in the current on the grid side. This paper takes the three-phase grid-connected inverter as the research object and proposes a solution. Establish a mathematical model for the inverter system and analyze the transformation relationships of relevant electrical quantities across different coordinate systems. First, the paper proposes an improved three-vector model predictive current control algorithm. It employs an orthogonal-axis current zero-crossing method to calculate vector action times, enabling rapid and efficient determination of the desired sector. Then, based on this, an optimized switching sequence method is proposed. It fixes the switching frequency by adding a constraint term to the objective function. Finally, the effectiveness of the proposed method was validated through simulation and experimental results. The results demonstrate that the proposed control strategy optimizes the switching sequence and achieves fixed switching frequency control. It can effectively reduce switching losses and power losses, thereby lowering the harmonic content in the grid-connected side current. At the same time, the grid-connected current exhibits low harmonic content and minimal current ripple. Concurrently, the grid-connected current exhibits low harmonic content and minimal current ripple. Under dynamic conditions, it maintains high current tracking accuracy and demonstrates strong system robustness.