Critical evaluation of FBD, PQ and CP J power theories for three-wire power systems

Abstract

Considering unbalanced and non linear three-phase three-wire power systems, this paper discusses the relationship and discrepancies among three modern power theories. The considered approaches were the so called FBD Theory (Fryze-Buchholz-Depenbrock), the pq-Theory and the Conservative Power Theory (CPT). Such theories and related definitions may influence not only the energy control and regulation, mostly in terms of power measurement techniques, revenue metering, instrumentation technology or electronic power conditioning, but also some concepts of power engineering education. The three methods have been summarized, discussed and compared by means of computational simulation. Although the three methods are based on different concepts, the results obtained under ideal conditions are very similar. The main differences appear in the presence of unbalanced and non linear load conditions. Under linear unbalanced conditions, both FBD and pq-Theory suggest that the some current subcomponents contain a third-order harmonic. Besides, neither pq-Theory nor FBD method are able to provide accurate information for reactive current under unbalanced and distorted conditions, what seems to be done by means of the CPT. The paper tries to explain the causes of these differences in terms of the foundations of the power and current's decompositions and the resulting waveforms and spectra.