Assessment of unbalance and distortion components in three-phase systems with harmonics and interharmonics

- An auxiliary reference frequency is introduced to address interharmonics.
- The classical symmetrical component transformation is applied to harmonics and interharmonics.
- Balance, unbalance and distortion components are identified for harmonics and interharmonics.
- Balance, unbalance and distortion indicators are extended from harmonics to interharmonics.

This paper deals with the identification of balance, unbalance and distortion components in unbalanced three-phase systems with distorted waveforms containing harmonics and interharmonics. The analysis starts from the harmonic distortion and unbalance components found through the symmetrical component-based (SCB) approach previously defined by the authors. The SCB approach is extended in this paper by introducing an auxiliary reference frequency and identifying its consistency condition with respect to the fundamental system frequency. After defining the auxiliary reference frequency, the proposed approach directly uses the classical symmetrical component transformation matrix at any harmonic or interharmonic. Various results are presented, for conventional test cases and for measurements gathered from real systems with variable unbalanced and distorted loads. These results show that the extended SCB approach is particularly useful to analyze three-phase systems in unbalanced and distorted conditions with harmonics and interharmonics, because of its simplicity and intuitiveness compared to other approaches.