This paper presents a new method to evaluate the unbalance in the presence of harmonic distortion. The balanced, the first unbalanced, and the second unbalanced components are obtained from the original three-phase current and voltage phasors of each harmonic component. The equivalent rms value of three-phase voltage and current is then decomposed into the balanced fundamental, the unbalanced fundamental, the balanced harmonic, and the unbalanced harmonic components. The same decomposition is applied to the apparent power, and the system unbalance can then be evaluated through the proposed system total unbalance distortion factor. The unbalanced fundamental, the balanced harmonic, and the unbalanced harmonic distortion factors are defined. These distortion factors clarify the interleaving between the unbalance and harmonic distortion and are suitable for unbalance evaluation in the presence of harmonics. Numerical examples are also presented to illustrate the application of the proposed method on the study and characterization of unbalance in power systems.
[1]
Ward Jewell,et al.
Pitfalls of electric power quality indices
,
1998
.
[2]
A. E. Emanuel,et al.
Practical definitions for powers in systems with nonsinusoidal waveforms and unbalanced loads: a discussion
,
1996
.
[3]
A. E. Emanuel.
Powers in nonsinusoidal situations-a review of definitions and physical meaning
,
1990
.
[4]
Yahia Baghzouz,et al.
Discussion of power definitions contained in the IEEE Dictionary
,
1994
.
[5]
L. Czarnecki.
Reactive and unbalanced currents compensation in three-phase asymmetrical circuits under nonsinusoidal conditions
,
1989
.
[6]
A. E. Emanuel,et al.
On the definition of power factor and apparent power in unbalanced polyphase circuits with sinusoidal voltage and currents
,
1993
.
[7]
L. Czarnecki.
Orthogonal decomposition of the currents in a 3-phase nonlinear asymmetrical circuit with a nonsinusoidal voltage source
,
1988
.