A dynamic load shedding scheme for maintaining system frequency stability with the increasing renewable energy penetration

Abstract

Renewable energy power plants, especially grid connected solar and wind generation units are displacing the conventional generator stations with rotating machines with inertia. In Sri Lanka, renewable energy generation has begun to increase significantly. The total solar and wind energy penetration is 13% for 2020 and according to the least cost long term generation expansion plan 2018 – 2037 of Ceylon Electricity Board, this amount will be 47% by 2030. With the increased penetration of wind and solar energy generations units having no rotational inertia, there would be a variation in operational and dynamic characteristics in the power system. The power generation of solar power plants varies drastically with the cloud cover. The power output of solar and wind energy varies with their intermittent nature and as a result of it, the system frequency deviations become faster and risking the stability of power system as well. This study is focused on evaluating the frequency stability of Sri Lankan power system at major contingencies during the day-peak periods having maximum wind and solar generation. In Sri Lanka, static under frequency load shedding scheme is used to restore the stability of power system after major disturbances. This load shedding scheme is initiated based on the rate of change of frequency and under frequency settings, which shed pre-determined load amounts at frequency set points in six stages. This thesis analyzes the frequency response of Sri Lankan power system with the maximum wind and solar generation for year 2030 to evaluate the performance of the present load shedding scheme in maintaining system stability. A dynamic load shedding scheme can provide quick and optimal solution by using real-time data of operating conditions. Therefore, this research is proposing a new load shedding scheme based on dynamic load shedding method to improve the frequency stability of Sri Lankan power system while absorbing maximum solar and wind power into the system.