A Time-Domain Approach to Power Term Definitions under Non-Sinusoidal Conditions

The paper presents a time-domain approach to current and voltage decomposition and power terms definition under periodic, non-sinusoidal conditions. The approach makes reference to basic physical quantities only, like voltages, currents and their integrals and derivatives. Based on these quantities, instantaneous and average power terms are introduced, which are conservative in any electrical networks and naturally extend the definitions used under sinusoidal conditions. Since the defined power terms are additive quantities, the impact of each load connected to the network on total reactive and harmonic absorption can easily be evaluated. Moreover, the reactive power term has a precise physical meaning, being directly related to the energy stored in the network. An orthogonal decomposition of currents (and voltages) is also introduced, where each current component relates to a specific power or energy term and/or to supply voltage and load current distortion. Correspondingly, a decomposition of the apparent power into active, reactive and distortion terms is proposed, where the influence of supply voltage distortion on the distortion power is clearly indicated. Finally, the single-phase approach is extended to poly-phase systems. Relying on conservative quantities, the proposed approach offers a basis for distributed reactive and harmonic compensation under non-sinusoidal conditions