Developing a smart system to mitigate frequency instability caused by integration of large-scale solar PV systems on the Grid: a case study of UETCL

Abstract

The integration of large-scale solar photovoltaic (PV) systems into the Uganda Electricity Transmission Company Limited (UETCL) grid, driven by Uganda’s renewable energy goals, introduces significant challenges to grid frequency stability. This is due to the intermittent and non-dispatchable nature of solar power and reduced system inertia. This study develops a smart system based on Proportional-Integral-Derivative (PID) Controller to mitigate frequency instability caused by increased solar PV penetration. Using DIgSILENT Powerfactory, a detailed UETCL grid model was developed and validated, incorporating synchronous generators, turbine speed governors, and a PID-based controller for secondary frequency control. Frequency response analyses were conducted for solar PV penetration levels from 4% to 18%, simulating generation loss events to assess grid stability. Results demonstrate that without advanced control, frequency nadirs drop below acceptable limits (49.5 Hz) at penetration levels above 10%, risking under-frequency load shedding. The PID-based controller effectively restores the nominal frequency (50 Hz) within 80 seconds across all scenarios, significantly improving grid stability compared to governor-only responses. Recommendations include limiting solar PV penetration to 10% until advanced control systems and Battery Energy Storage Systems (BESS) are implemented, alongside transmission network expansion in high-solar-potential regions. This smart system enhances the UETCL grid’s resilience, supporting Uganda’s sustainable energy transition.