Complex-Vector Power and Cross-Phase Unbalance in Three-Phase Systems

TL;DR

This paper introduces a complex-vector power formulation for three-phase systems that explicitly captures cross-phase unbalance, enhancing the understanding of apparent power beyond traditional scalar representations.

Contribution

It proposes a novel complex-vector power representation that explicitly includes cross-phase unbalance, extending classical apparent power theories for sinusoidal steady-state operation.

Findings

The formulation separates apparent power into intraphase and cross-phase components.

It preserves the apparent power norm under Fortescue transformation.

Numerical examples demonstrate the significance of cross-phase unbalance in power analysis.

Abstract

Unbalanced three-phase systems still lack a compact phasor-domain representation of power that makes phase asymmetry explicit while remaining consistent with established apparent-power definitions. This paper addresses that point through a complex-vector power formulation for sinusoidal steady-state operation. The proposed representation supplements the classical dot-product expression of complex power with the cross product of voltage and current phasors, thereby retaining the usual active and reactive terms while making explicit a cross-phase unbalance vector that captures antisymmetric interphase relations. In this way, apparent power is separated into intraphase and cross-phase contributions, and its norm is preserved under the power-invariant Fortescue transformation. The formulation is extended to three-phase four-wire systems by introducing equivalent coordinates that preserve the effective apparent-power norm for the chosen voltage reference. Only standard complex numbers and matrices are required. Numerical examples show operating conditions in which a non-negligible part of the apparent-power structure is associated with cross-phase unbalance and cannot be inferred from active and reactive power alone. The proposed formulation thus provides a compact phasor-based descriptor of unbalance that complements established apparent-power theories by making explicit a component that is not accessible from scalar apparent-power representations.