Predictive Load Voltage Control for Four-leg Inverter with Fixed Switching Frequency

A three-phase four-leg inverter is a common solution to connect distributed generation (DG) to the stand-alone loads as well as providing the neutral wire. Finite Control Set (FCS) model predictive control (MPC) of these inverters suffers from uneven thermal loading due to different switching frequencies of individual legs. Furthermore, the LC filter design becomes more complicated due the variable switching frequencies. In order to overcome these problems, this paper explores a modulated model predictive control scheme which explicitly tracks both the load voltage and filter current references by considering a dual-objective cost-function. Compared with the conventional FCS-MPC, the proposed method has the advantages of enhanced steady-state performance, flexible constraint-handling ability and constant switching frequency. Comparative simulation results with FCS-MPC are provided under different loading conditions, such as unbalanced references and non-linear loads to verify the proposed control strategy.