Abstract:
The integration of renewable energy sources into existing power grids is a vital strategy to promote environmentally friendly energy production. Among these sources, solar photovoltaic (PV) systems have seen rapid adoption, with an increase of 25% from the year 2021. However, the transition from conventional synchronous generators (SGs) to utility-scale PV plants can introduce challenges related to grid frequency stability. Unlike SGs, PV plants lack inertia and reserve capabilities, leading to frequency instability in highly PV-enriched grids after significant disturbances. To address this, various storage systems, notably battery energy storage systems (BESS), have been employed in the grid. Yet, relying solely on BESS has drawbacks due to its high installation and operational costs. An alternative mechanism, known as deloaded PV system operation, enables PV plants to contribute to frequency control. However, determining the appropriate size for PV deloading, crucial for effective frequency support, remains unexplored in the literature. Additionally, PV plant reserves may not always suffice due to variability and intermittency. To enhance frequency stability, a combination of BESS and deloaded PV operation is proposed. The optimal pairing of deloaded PV and BESS, considering both frequency response and economic factors, remains an unaddressed research gap.
This thesis aims to develop a methodology to determine the appropriate deloading size of utility-scale PV systems, maintaining frequency stability in PV integrated grids by considering frequency nadir and ROCOF. In addition, a comprehensive methodology is proposed to determine the optimal combination of deloadedutility-scale PV operation with BESS. Moreover, the proposed approaches are validated through performance comparison with existing approaches across different PV power penetration levels. The proposed methods are then tested in a modified IEEE 39 Bus New England test system. The results show that the appropriately sized deloaded PV systems can effectively maintain frequency stability in the grid for all the conducted case studies (20% to 50% PV penetration in the grid). They also outperform BESS and synchronous condenser (SC) in terms of performance. Moreover, the optimal combination of deloaded PV and BESS provides faster frequency response and more efficient performance than similar sized single supporting mechanisms.The outcomes of this thesis comprise a framework for sizing PV deloading to ensure grid frequency response and a technique to optimize the concurrent operation of deloaded PV and BESS, considering technical and economic factors.
