ANALYSIS OF FREQUENCY CONTROL AND GRID STORAGE EFFECTIVENESS FOR A WEST AFRICAN INTERCONNECTED TRANSMISSION SYSTEM

Abstract

The West Africa Power Pool (WAPP) Interconnected Transmission System (WAPPITS) has faced challenges with frequency control due to limited primary frequency control reserves (PFR). Battery Energy Storage Systems (BESS) have been identified as a possible solution to address frequency control challenges and to support growing levels of variable renewable energy in the WAPPITS.This dissertation examines existing frequency control challenges in the West African Power Pool Interconnected Transmission System and evaluates the effectiveness of Battery Energy Storage Systems (BESS) as a solution to enhance grid stability and resilience amid growing ambitions to increase variable renewable energy (VRE) penetration. To carry out this assessment, three studies were conducted - the first study assesses the effectiveness of BESS in providing primary frequency reserves (PFR) using open-loop simulations based on real WAPPITS frequency data. Results from this study suggest that droop-based BESS control strategies can mitigate fast frequency variations. In addition, it demonstrates that integrating BESS alone into the grid will not solve the frequency control challenges in WAPPITS, requiring the need for a revision of frequency control provision, including mandatory participation of traditional power plants in the provision of the service. The second study investigates primary and secondary frequency control challenges in WAPPITS using surveys from Transmission System Operators, field tests on power plants as well as analysis of events in the grid. Results reveal critical challenges: inadequate PFR reserves, reliance on under-frequency load shedding, and a lack of automatic secondary frequency control via automatic generation control (AGC). The study recommends (1) enforcing mandatory PFR compliance and (2) establishing an ancillary services market to incentivize reserve provision. The third study uses PSS/E dynamic simulations to assess primary frequency response provision using different mixes of BESS and conventional generation in responding to the maximum N-1 contingency (400MW loss). Simulation results suggest that BESS -only PFR provision outperforms conventional generation-only PFR in fast frequency response across the frequency metrics analyzed. However, a hybrid mix of BESS and conventional reserves achieves adequate performance on all metrics and is more cost effective. The research demonstrates that BESS can significantly improve frequency stability in WAPPITS, but to successfully achieve this, there is need for technical and regulatory reforms, including: • Mandatory PFR participation for conventional plants, • Ancillary services markets to mobilize reserves, and • Implementation of hybrid PFR provision by BESS and conventional power plants. This research provides policy makers and technical experts with insights to guide the implementation of frequency control service provision, underscoring the need for institutional and market reforms coupled with technological innovations to solve the existing frequency control challenges in WAPPITS.