Grid frequency support from inverter connected generation

This paper presents a case study to demonstrate impact of current fleet of inverter connected generation (roof top photovoltaics and utility scale grid following inverters) that have been allowed to connect to power networks with no obligations to respond to system under frequency events. In this study, a grid forming inverter with droop control and grid following inverter connected to a modified IEEE nine-bus test system have been used to show system impact when inverters do not provide system support, and benefits when such inverters provide system support for under frequency events. The case studies performed show that there is potential for inverter connected generation to support transmission grid frequency subject to renewable resource availability or when backed up by energy storage facilities. There is need for grid codes to be reviewed further to put more obligation on intermittent inverter connected generation to provide more grid frequency support functionality, particularly for under frequency events which are the most common in power systems in comparison to over frequency events.