A Fixed Operation Frequency Model Predictive Control for LCL-Filter NPC-type Inverter

Three-phase LCL-Filter NPC-type grid-connected inverter has been widely used in the renewable energy generation systems with the advantages of high efficiency, high power and low cost.Finite control set model predictive control (FCS-MPC) has strong robustness and fast dynamic response, so it is widely used in grid-connected inverter control. However,the traditional FCS-MPC bears with irregular switching state,which will reduce the current tracking accuracy, produce current ripple and electromagnetic noise.Aiming at the above shortcomings, an efficient and fixed operation frequency model predictive without weighting factor is presented to ensure fixed operation switching frequency.The voltage vector of different voltage vectors is selected according to the location of the voltage vector reference, and the switching time of the selected are directly calculated by the inversely proportional with cost function value of the vectors. To verify the correctness and effectiveness of the proposed control strategy, a complete simulation model and experimental prototype platform under the digital control is established. The simulation and experimental results show that the steady and the transient performance of the grid current with the proposed control strategy are effectively improved.