A New Definition of Instantaneous Active-Reactive Current and Power Based on Instantaneous Space Vectors on Polar Coodinates in Three-Phase Circuits.

Abstract

Conventionally, the active, reactive and apparent powers in three-phase circuits have been defined by extending the concept based on the RMS values of voltage and current with respect to time in single-phase circuits. Applying the definition based on single-phase circuits to three-phase systems with non-sinusoidal conditions has resulted in many options in the methods of power properties description, interpretation and compensation, and this has led to a controversy on which method should be chosen, or on how power quantities should be defined. This paper proposes a new definition of the instantaneous active-reactive current and power based on instantaneous space vectors on polar coordinates in three-phase circuits. The instantaneous active-reactive power and current are defined in the voltage-current vector plane without any special fictitious power. The new definition proposed here leads to the same formulas as the conventional ones. The authors claim that this is a great advantage of the new definition. Comparing it to the p-q theory, we discuss the new definition in detail. It is shown that using the new definition one is able to calculate the instantaneous active-reactive power and current directly from the voltage and current space vectors. The new definition, thus, offers a lucid concept of electric power in three-phase circuits. Using digital simulation, an application example is shown to confirm the validity and practicability of the new definition.