Optimal sizing of synchronous condensers to improve system strength under high wind power penetration in a power grid

Abstract

Wind is one of the most economically viable renewable energy sources and hence, its large scale integration is rapidly increasing in many countries. With increasing wind power, conventional fossil fuel based synchronous generators are being replaced from generation fleet. In recent times, wind power plants are mostly based on type 3 (Doubly-Fed Induction Generator: DFIG) and type 4 (Full Scale Converter: FSC) machines. These variable speed wind turbine generators (WTGs) are decoupled from the corresponding grid by power electronics inverters. Due to constrained capacities of these inverters, type 3 and type 4 WTGs usually generate less fault current compared to synchronous generators. As a result, system strength deteriorates under high penetration of wind power. System strength at the Point of Common Coupling (PCC) of a wind power plant is specified by an index called Short-Circuit Ratio (SCR). A minimum value of SCR is essential for fault identification and successful ride through of wind power plants during faults. To improve system strength, synchronous condensers can be utilized because these devices contribute to fault levels. Since the installation of synchronous condensers is expensive, the optimal strategy to allocate them is of major concern. A number of research works have been reported in the literature on the deployment of synchronous condensers to enhance SCR in wind prolific power systems. The existing methods mainly focus on the optimal location of synchronous condensers to maintain satisfactory SCR. However, these techniques do not provide any optimal sizing of synchronous condensers while considering their installation, operational and maintenance costs. Therefore, further investigations are still required to meet this important yet unaddressed research gap. In the above perspective, optimal sizing of synchronous condensers to improve system strength in a wind dominated power grid is determined by considering long-term techno-economic viability. Also, the impact of the selected synchronous condensers on system strength during substantial penetration of wind power in a test network is explored. The outcome of this thesis provides useful guidelines for network operators to maintain adequate system strength under high wind penetration by ensuring long-term technical as well as financial benefits.