Harmonic control strategies of utility-scale photovoltaic inverters

Abstract

Installation of utility-scale photovoltaic power systems (UPVPSs) is continually increasing throughout the world. This leads to increasing number of utility-scale PV inverters (UPVIs) being connected to the grid both at transmission and distribution networks. The amplitudes of harmonics generated by these inverters are becoming important issues of concerns. Manufacturers of these inverters specified 3% current THD. Also, most researches on performance analysis of the current control strategies of these inverters put their current THD at 3%. At utility-scale level, the 3% current THD has large amplitude values which can have significant consequences especially on the distribution networks. This paper statistically relates the percentage current THD of some common industrial UPVIs to their equivalent amplitude current THD. The paper also reviews the existing current control strategies of UPVIs in terms of their performances in optimizing the control of harmonics generated by the UPVIs. Various current control strategies, their mode of operation, advantages, disadvantages and limitations to harmonic reduction are discussed. Several current controllers are compared and evaluated for harmonic emission and control. The current control strategies of the existing inverters are not effective enough to optimize the control of harmonics generated by UPVIs as the amperage magnitude of current THD is high. Further study is necessary to improve on the existing current control strategies or incorporate new ones to optimally control THD of the UPVIs and make them more effective in controlling harmonics at utility-scale level.