The synchronous fundamental dq frame theory implementation and adaptation for the active filtering

The synchronous fundamental dq frame is a time domain method derived from the space vector transformations of three phase systems. While these methods had been extensively used for the analysis of three phase circuits this particular method is suitable for the active filtering. This is because it obtains the non-sinusoidal current fundamental which can be used for the compensating current computation. The compensation result of this method is a sinusoidal grid current, not in phase with the grid voltage, so only the distortion component of the current is compensated, the reactive component has to be compensated by an external circuit, or absorbed from the power grid. In order to compensate the reactive current this method can be adapted to compute not only the load current fundamental, but also the active component of the load current fundamental. Another adaptation of this method is the unity power factor compensation, which implies that the compensated current has the same shape and phase with the grid voltage, so the active power is transported not only on the voltage fundamental, but also on the voltage harmonics. The implementation of this method and its adaptations on an active filtering system are the objectives of this paper.