An extension to definition of apparent power for multiphase systems in non-sinusoidal conditions

Abstract

SUMMARYThe generalized definition of apparent power for multiphase systems in non-sinusoidal conditions is extended in this paper. The meaning of apparent power is still a matter of discussion. The apparent power definition for unbalanced three-phase systems is in two schools of thought. The first school is based on a pure theoretical approach and the second is related to the IEEE 1459-2000 standard, which is based on practical concept. Both approaches define the apparent power as the maximum active power that can be delivered to the load for unchanged load equivalent voltages and currents. This paper at first, reviews the theoretical approach of apparent power definition for three-phase unbalanced systems. Then this definition is extended using a vector space for multiphase power systems. This extension of the generalized definition considers a system which not only could be unbalanced but also could include non-sinusoidal voltage and current waveforms. It also considers unequal line resistances. An example is presented which compares the results obtained using this method with the results of the IEEE approach. A three-phase unbalanced non-sinusoidal system in which a rectifying diode is employed in one of the phases is also used to further evaluate performance of different power definitions under study. By using an exact model to define the apparent power, the proposed extended definition provides accurate results.