Sliding mode control of 3-phase shunt active filter in the d-q frame

In this paper a sliding mode approach is developed to control a three-phase, three-wire voltage source inverter operating as a shunt active filter (AF). The AF has to compensate for harmonics, reactive and unbalanced nonlinear load currents while regulating its self-supporting DC bus voltage. The novelty of the proposed control approach is that the sliding mode switching functions are constructed in such a way that the supply currents shaping and the AF dc voltage regulation are achieved simultaneously. Therefore, there is no need to divide the multivariable state space model in the synchronous d-q reference frame into inner and outer separate loops. The control design is based on Lyapunov stability criterion and the proposed control law has two parts: a switching component forcing the system´s trajectory to the sliding surface and a continuous component valid on the sliding surface. The proposed control strategy allows a better stability and robustness over a wide range of operation. The variable structure controller presented is successfully demonstrated by simulation results.