A Robust DC-Link Voltage Control Strategy to Enhance the Performance of Shunt Active Power Filters Without Harmonic Detection Schemes

Shunt active power filters $(SAPFs) $ implemented without harmonic detection schemes are susceptible to sudden load variations. This paper proposes a robust control strategy to reduce this drawback. In this strategy, the dc-link voltage is regulated by a hybrid control technique combining a standard proportional–integral $PI$ and a sliding-mode $(SM)$ controllers. The $SM$ scheme continuously determines the gains of the $PI$ controller based on the control loop error and its derivative. The chattering due to the $SM$ scheme is reduced by a transition rule that fixes the controller gains when steady-state condition is reached. This controller is termed as dual-sliding-mode-proportional–integral. The phase currents of the power grid are indirectly regulated by double-sequence controllers with two degrees of freedom, where the internal model principle is employed to avoid reference frame transformation. The proposed control strategy ensures zero steady-state error and improves the performance under hard transients such as load variation. Additionally, it presents robustness when the $SAPF$ is operating under unbalanced conditions. Experimental results demonstrate the performance of the proposed control scheme.