Examining the Impact of Voltage Unbalance on Power Converter Harmonic Emissions

Abstract

The continuously evolving state of the power grid along with the increased integration of renewable energy sources have put an emphasis on power quality disturbances and the standards that adhere to them. There are multiple standards dedicated to these disturbances, such as harmonic emissions caused by power converters and voltage unbalance. While these standards partially address these disturbances, the exact effect they have on one another is either unclear or not fully addressed. To quantify the relationship between harmonics and voltage unbalance, an extensive set of studies was performed on rectifiers and inverters with the objective of potentially applying the results to power quality standards. The studies on rectifiers consisted of simulations on rectifier circuits with different load characteristics while manipulating the source voltage to different types of unbalance. This ultimately resulted in the development of equations representing the harmonics in terms of the source voltage unbalance percentage, as well as a method for testing the harmonic response to unbalance of similar systems. The studies on inverters consisted of simulations and analytical solutions performed on three-phase pulse-width modulation and square wave inverters while manipulating the AC-side voltage to different types of unbalance. This ultimately resulted in a clear connection between the low-order non-characteristic harmonics of square wave and pulse-width modulation inverters, a concern for standards regarding renewable energy sources. These results are contributions to power quality standards and the overall topic of power quality.