Ancillary services provided by photovoltaic inverters: Single and three phase control strategies

Photovoltaic (PV) inverters are power electronic based converters with fast response in the range of milliseconds. Besides, due to solar irradiance variation, these converters have excess capacity that can be used to provide ancillary services to the main grid. Traditionally, ancillary services such as reactive power injection and frequency support are provided by hydro and thermal generation. This work is focused on the analysis of how PV inverters can perform ancillary services and support the grid. Control strategies for reactive power injection and harmonic current compensation are explored. Furthermore, the inverter current saturation plays an important role, once high currents can damage the inverter or reduce its lifetime. Case studies for single and three-phase PV inverters are presented. It is observed that the ancillary service priority must be defined in order to guarantee PV inverter operation under nominal conditions.