Model Predictive Control–A Simple and Powerful Method to Control UPS Inverter Applications With Output LC Filter Ihab S. Mohamed Electronics and Comm. Dept. Faculty of Engineering Cairo University Email: ehab sami87@yahoo.com Sherif A. Zaid Electrical power Dept. Faculty of Engineering Cairo University Email: sherifzaid3@yahoo.com M. F. Abu-Elyazeed Electronics and Comm. Dept. Faculty of Engineering Cairo University Email: mfathyae@yahoo.com Hany M. Elsayed Electronics and Comm. Dept. Faculty of Engineering Cairo University Email: helsayed@ieee.org Abstract—The total harmonic distortion (THD) plays a major role in determining the quality of the inverter output waveform. The use of an inverter with an output LC filter allows for generation of sinusoidal voltages with low harmonic distortion. Several control schemes have been proposed for the control of three-phase inverter. A Model Predictive Control scheme is used for voltage control of a three-phase inverter with output LC filter. The controller uses a discrete-time model of the system to predict the behavior of the output voltage for all possible switching states generated by the inverter. The voltage vector that minimizes a cost function is chosen and its corresponding switching state is applied during the next sampling instant. The cost function used in this work evaluates the output voltage error at the next sampling time and used as a criterion of system performance. The performance of the proposed predictive control method is compared with hysteresis and pulsewidth modulation control under linear and nonlinear loads, using Matlab/Simulink tools. The results show that the predictive method controls very effectively the output voltage and performs very well compared with the classical solutions. Index Terms—Power conversion, predictive control, uninter- ruptible power systems. I. INTRODUCTION The control of a three-phase inverter is one of the most important and classical subjects in power electronics and has been extensively studied in the last decades [1]. The control of inverters with output LC filter has a special importance in applications where a high quality voltage is needed, such applications include distributed generation and uninterruptible power supplies (UPSs). It is desired, especially for UPS systems, to achieve a good output voltage regulation with any load, typically a nonlinear load [2]. Therefore, low total harmonic distortion (THD) in the output voltage of UPS inverter under various loads and fast dynamic response are the main requirement for high-performance UPS. Several control schemes have been proposed for this con- verter, including nonlinear methods (like hysteresis control), linear methods (like proportional-integral controllers using pulse-width modulation (PWM)) [1], [3], [4], [14], dead- beat control [6]–[8], multiloop feedback control [9]–[11] and repetitive-based controllers [12]. In most of these schemes the output voltage and one of two currents are used by a cascaded control considering outer and inner control loops, with linear or nonlinear controllers and a modulator is needed to generate the drive signals for the inverter switches [2]. Predictive control is a very wide class of controllers that have found rather recent application in power converters due to its fast dynamic response [5]. It presents several advantages that make it suitable for the control of power converters: concepts are easy to understand, it can be applied to a variety of systems, constraints and nonlinearities can be easily in- cluded, multivariable case can be considered, and the resulting controller is easy to implement. It requires a high amount of calculations, compared to a classic control scheme; however, however, the fast microprocessors available today facilitates the possibility of implementation. The main characteristic of predictive control is the use of the model of the system for the prediction of the future behavior of the controlled variables. This information is used by the controller in order to obtain the optimal actuation, according to a predefined optimization criterion. Several control algorithms have been presented under the name of predictive control. A classification of them is presented in [2], [5]. This paper mainly focused on MPC scheme for a three- phase inverter with output LC filter. The controller uses a model of the system to predict, on each sampling interval, the behavior of the output voltage for each possible switch- ing state. Then, a cost function is used as a criterion for selecting the switching state that will be applied during the next sampling interval. There is no need of internal current- control loops and no modulators, compared to a classic control scheme. The gate-drive signals are generated directly by the control. Simulation results comparing the performance of the proposed strategy with well-known hysteresis and PWM control are presented. II. CONVERTER MODEL The three-phase inverter with output LC filter considered in this paper is shown in Fig. 1. The converter and filter models are presented here, and the load is assumed unknown. The