Model-Based Control for a Three-Phase Shunt Active Power Filter

This paper presents a robust model-based control in natural frame for a three-phase shunt active power filter. For the proposed control method, a linear converter model is deduced. Then, this model is used in a Kalman filter (KF) to estimate the system state-space variables. Even though the states estimation do not match the variables of the real system, it has allowed to design three sliding-mode controllers providing the following features to the closed-loop system: 1) robustness due to the fact that control specifications are met independently of any variation in the system parameters; 2) noise immunity, since a KF is applied; 3) a lower total harmonic distortion (THD) of the current delivered by the grid compared with the standard solution using measured variables; 4) the fundamental component of the voltage at the point of common coupling is estimated even in the case of a distorted grid; and 5) a reduction in the number of sensors. Thanks to this solution, the sliding surfaces for each controller are independent. This decoupling property of the three controllers allows using a fixed switching-frequency algorithm that ensures a perfect current control. Finally, experimental results validate the proposed control strategy and illustrate all its interesting features.