Power definitions for polyphase systems based on Fortescue's symmetrical components

Power definitions for polyphase power systems with non-sinusoidal and unbalanced voltages and currents are considered in this paper. Based on application of Fortescue's transformation to time-varying voltage and current space vectors, a new approach to power definitions is proposed. Definitions of the complex, apparent, active and non-active powers in terms of the symmetrical components have been proposed. The analysis related to the influence of zero-sequence voltages to power quantities has been performed. The symmetrical components provide calculation of powers by omitting erroneous contribution of the zero-sequence voltages. A significant property of the proposed power definitions in terms of the symmetrical components is that they are invariant to the choice of the voltage reference. Application of the proposed power definitions in terms of the symmetrical components has been demonstrated by the examples of three-phase three-wire and four-wire systems.