Determination of Control Requirements to Impose on CIG for Ensuring Frequency Stability of Low Inertia Power Systems

Power systems around the globe are undergoing a transformation characterized by a massive
deployment of converter-interfaced generation (CIG) to effectively combat climate change. However,
achieving a seamless transition from current power systems dominated by synchronous generators (SGs)
to future ones with high levels of CIG requires overcoming several technical challenges. From a frequency
stability perspective, reduced system inertia increases the frequency nadir after a loss of generation thereby
endangering frequency stability. In this context, this paper proposes a novel methodology for determining
control requirements to impose on CIG as their penetration in the network increases. Results of a case study
based on the Chilean grid projected for the year 2046 show that, if only grid-following converters without
frequency control capability are deployed, a maximum CIG penetration level of 75% can be achieved without
threatening frequency stability. The Chilean system can reach a 99% CIG penetration, provided that the
remaining CIGs are deployed in grid-following with frequency support capability. Finally, we show that if
the last SG is replaced with a grid-forming converter, the system can still sustain frequency stability and
exhibits a good dynamic performance. These results demonstrate that, at least from a frequency stability
viewpoint, achieving a 100% based CIG system is technically possible. The proposed methodology can
be used by energy regulators to define the control requirements necessary to impose on CIG for achieving
renewable energy targets in a secure way. Although the obtained results are particular for the Chilean system,
the proposed methodology can be applied to any power system