A new approach to design an observer for load current of UPS based on Fourier series theory in model predictive control system

Abstract

In this paper, the model predictive control (MPC) system based on the state space is designed to generate the appropriate switching pulses for UPS inverters. The fast dynamic response and the capability in assessment of various cost functions are some advantages of the predictive control system. The equations concerning the control system show that the load current should be measured. To eliminate the required sensor for load current measurement a new observer is proposed, so the amount of cost can be reduced and the reliability of the system also enhanced. Ordinary observers like Luenberger in terms of stability and design encounter several difficulties. The proposed observer is developed based on Fourier series and instantaneous power theories. This observer is doing well in estimating the load current and renders superior performance regarding the dynamic behavior, stability and convergence. Furthermore, in this observer there is no need for any parameters adjustment and the load current is accurately observed using the measured output voltage and the filter current. To examine the operation of the system the necessary simulations and laboratory experimental results are provided on a 3-phase 220 V UPS. The obtained results are then compared to those obtained by the Luenberger observer.