Sliding mode control of three-phase four-leg shunt active power filter

This paper deals with the application of a sliding mode strategy to control a three-phase shunt active power filter (APF). The APF consists of four-leg voltage source inverter (VSI) bridge. The APF ensures full compensation for harmonic phase currents, harmonic neutral current, and reactive and unbalanced nonlinear load currents. It also regulates its self- sustaining dc bus voltage. The reference currents are obtained from the nonlinear load currents. To control the APF, the selection of the sliding mode switching functions is based on the multivariable state space model in the synchronous dq0 reference frame. The control law has a switching component forcing the system´s trajectory to the sliding surface and a continuous component valid on the sliding surface. The stability of the closed loop system is proved by means of Lyapunov stability criterion. The robustness over a wide range of operation is another property of the control. Simulations are conducted to verify the analytical analysis of the control.