| One of the methods that have been used for the analysis of three phase systems is the rotating fundamental dq frame. Although it was especially used for the analysis of three phase machines, because it is a time domain method is also suitable for the compensating current computation in the active filtering. In fact, it was already been used for the computation of the current fundamental, and if desired, for the computation of some of the upper harmonics. This way the compensator could eliminate from the power grid current all or some of the harmonic content. But this is also, the limitation of this method, because it cannot intrinsically obtain the compensation of reactive power. This is because this method refers to currents and not powers so the reactive power is not defined. At the same time and for the same reasons, it could not obtain the compensated current to have the same shape as the grid voltage. If the compensation goal includes the reactive current compensation, this method must be adapted to compute beside the load current fundamental, 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. |
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