I. Introduction
Already in 1865 Maxwell [1] introduced the concept of phase displacement, caused by reactive elements. In 1892 Steinmetz [2] demonstrated, that in case of a nonlinear load non-active currents occur without phase displacement. A historical overview of the development of power theory in the following decades has been published by Skudelny [3] in 1979 at a special ETG
Energy Technology Group of VDE, the German Association for Electrical, Electronic & Information Technologies
conference dedicated to power quantities. At that conference Depenbrock [4] published the main concepts of his extension of the work of Fryze [5], [6] and Buchholz [7] which is the subject of this paper. This so-called FBD method [8] has a firm theoretical base and is applicable to any number of conductors and any kind of current and voltage waveforms. It is also the basis of the German standard on power definition [9], [10].