Present point of view about the instantaneous reactive power theory

The instantaneous reactive power theory has been the most used in nonlinear load compensation with active power filters (APF). Its application to APF control allows constant source power to be obtained after compensation in a simple way. It works optimally with balanced and sinusoidal source voltage, but not so good with unbalanced or non-sinusoidal source voltage. Although the p-q theory obtains constant source power in all the cases, in the second one the source current obtained is not balanced and sinusoidal. On the other hand, some researches argue that it is not a complete power theory because it does not assign a physical meaning to the power terms. Necessary modifications in the original formulation to treat compensation under any condition of voltage supply are discussed. Moreover, here, it is reformulated in phase coordinates, which allows a simpler treatment for analysing the different compensation strategies. On the other hand, from the power point of view, it is proved that the introduction of instantaneous imaginary power makes p-q formulation a formal theory of electric power in three-phase system. Finally, compensation strategies are applied to a practical power system and the results are presented.