Effects of Unbalance on Square Wave Inverter Harmonics

The increased usage of inverter-based resources for power generation has brought more attention to standards related to power quality disturbances like harmonics and voltage unbalance. While present standards partially address these issues, the exact effect they have on one another is either unclear or not fully addressed. This work attempts to draw a direct link from the voltage unbalance to the resulting harmonics of a square wave inverter with the goal of gaining a better understanding of this relationship and how it may apply to the harmonics of an inverter-based resource. The connection between unbalance and harmonics is derived by breaking down the unbalanced voltage into balanced positive and negative sequence voltages and then evaluating the switching times of the square wave inverter. After these derivations are completed, several sets of simulation tests are performed to assess the type of impact that different levels of unbalance have on the harmonics and the switching times. It is clear from this work that unbalance has a significant impact on the harmonics and switching times and that a similar approach may help in evaluating the harmonics of inverter-based resources.