Abstract

Conventionally, the active, reactive, and apparent power in three-phase circuits has 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 nonsinusoidal conditions has resulted in many options in the description of power properties, as well as their interpretation and compensation, and this has led to a controversy as to which method should be chosen, and 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 in polar coordinates for 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, which 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. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(2): 83–91, 1997

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