Model Predictive Control of Grid-Connected Voltage-Source Converters Operating as STATCOM with Unbalanced Loads

Power systems are rapidly changing to a new model incorporating a wide amount of distributed generation using renewable sources. In this new scenario grid-connected converters, such as compensators for voltage control like STATCOM, are going to play a critical role in its operation. Voltage-source converters (VSCs) are among the most common topology used in grid-connected converters. The VSCs can be also used for connecting alternative renewable energy source to grid as a distributed generation unit. Basically, a grid-connected VSC is a three-phase three-wire converter in which a capacitor is connected to its dc side, while its ac-side voltage is usually controlled based on a pulse-width modulation (PWM) technique. In this paper, we propose a predictive control method, known as finite set model predictive control (FS-MPC), for the ac-side currents. In this case the VSC is utilized as a STATCOM in which the current is controlled to generate reactive power necessary to adjust the grid voltage. The proposed FS-MPC control strategy is easy to implement and is suited for balanced and unbalanced load conditions. The proposed control system is simulated in a VSC STATCOM configuration by using MATLAB SIMULINK. The results show that the proposed method is suitable STATCOMs operating under unbalanced load conditions.