Robust Discrete Time Disturbance Observer with Finite Control Set Model Predictive Control in UPS System

In this paper, output voltage of a three phase uninterrupted power supply is controlled using finite control set model predictive control. A discrete time disturbance observer is used to estimate the disturbance load current. A robust method is proposed to determine gain matrix of the observer. This optimal gain matrix was computed using linear matrix inequality method. The control system is designed in alpha-beta reference frame and implemented in Matlab environment. The comparative simulation results are given for three different observers in order to see performance of the proposed robust method. The results show that the proposed LMI matrix can be used to calculate the optimal observer gain matrix. Furthermore, an additional integration term can be included in the disturbance observer to improve FCS-MPC performance. The effect of the sampling period on FCS-MPC is evaluated under different sampling frequency. The results show that a small sampling frequency can be used with proposed observer in FCS-MPC.