A controller to compensate voltage sags, unbalance and harmonic distortion using a series active filter

In this paper we present an adaptive controller for the series active filter to guarantee a sinusoidal balanced voltage on the load side despite of the presence of perturbations in the source voltage such as unbalance, harmonic distortion, sags and swells, as well as disturbances in the current load such as step changes, unbalance and distortion by higher order harmonics. To accomplish this objective, the series active filter is forced to inject the appropriate voltage to the line through a series connected transformer. This task is performed by the proposed controller in three stages (loops). First, an inner control loop forces the injected voltage to track a periodic reference. Second, an outer control loop regulates the voltage level in the capacitor (the storage element) making possible the construction of such a periodic reference. Third, the power flow between the line and the DC capacitor is handled by an outer (higher level) loop that allows the DC capacitor to deliver or absorb the necessary power to improve transients on load voltage when changes appear in the active power delivered by the source or absorbed by the load.