Model Predictive Control of Inverters in Microgrid with Constant Switching Frequency for Circulating Current Suppression

The circulating current among the parallel inverter-based distributed generations (DGs) in the microgrid (MG) system causes several negative impacts on the operation of inverters. The suppression of circulating current should be considered in the controller design of the inverter, especially in the case of using finite control set model predictive control (FCS-MPC) in which the switching frequency of the inverter is varied. This paper proposed an MPC with constant switching frequency for the inverter in the MG system. The proposed MPC is based on the use of virtual state vectors in addition to the real state vectors of the inverter. The discrete time model of inverter is used to find the optimal state vector of inverter including virtual states. The modulation voltage is calculated accordingly. The pulse width modulation is used to obtain the constant switching frequency of inverter. The MG system with three inverter-based DGs are used to show the impact of the proposed controller on the circulating current suppression. The effect of different number of virtual state vectors is presented in this study. The feasibility of the proposed controller is validated by the real time simulation using OP5600 of OPAL technologies.