Control of Three-Phase Buck-Type Dynamic Capacitor Using the Model Predictive Control Method for Dynamic Compensation of the Reactive Power and Load Current Harmonics

Abstract

Dynamic capacitor (DCAP) is a shunt power quality device that can simultaneously correct the power factor of the load and reduce the total harmonic distortion (THD) of the source current. In this paper, a novel control method was presented based on the model predictive control (MPC) to control a three-phase three-wire buck-type DCAP. In this method, the injected current of the DCAP was considered as the control variable, which must be controlled by two power electronic switches of the DCAP. The MPC controller minimized the absolute value of the difference between a reference current and a DCAP current in the prediction horizon. The reference current has consisted of two distinct parts, i.e., reactive power compensator (RPC), and harmonic current eliminator (HCE), dynamically based on the fundamental component of the load current. Also, a new prediction model (PM) was proposed to calculate the state variables of the DCAP based on their previous values, the state of the switches, and the prediction values of the grid voltage. The proposed PM was extracted from the linearized differential equations of the DCAP. Since, all the components of the DCAP, such as the capacitor and inductors in the inner and outer filters were modeled in these differential equations system, the proposed PM had excellent performance. The proposed method, unlike the PI controller, has fewer control parameters and can be implemented in extensive operational conditions. The simulation results in MATLAB software showed the superiority of the proposed method in comparison with the even harmonic modulation (EHM) method on a three-phase DCAP