Utilization of energy storage systems and facts devices to improve frequency response in low inertia power systems

Abstract

In recent times, due to prolific wind power penetration in many power systems, synchronous generators (SGs) are being substituted from the generation mix worldwide. Unlike the conventional SGs, variable speed Wind Turbine Generators (WTGs) do not participate in frequency regulation without additional control strategy. During prolific wind generation and interconnection import from an adjacent grid, number of online SGs in a network may reduce. In such situation, a large contingency can cause undesirable Rate of Change of Frequency (ROCOF) and frequency deviation. If ROCOF exceeds 2 Hz/s, steam, hydro and wind turbine generators face difficulties to be in synchronism. Furthermore, if ROCOF is higher than 3 Hz/s, the under frequency load shedding relays may fail to respond quickly to shed loads, which can instigate a system-wide blackout. To overcome this problem, deployment of energy storage systems (ESS), namely, Superconducting Magnetic Energy Storage (SMES) and Battery Energy Storage System (BESS) can be a worthwhile solution. This is due to extremely rapid inertial response capability of SMES and ability of BESS to provide active power support for a fairly long duration. Since these devices are costly, their appropriate sizing is crucial. Although numerous sizing schemes of ESS are already investigated in recent literature, none of the existing works deploy and determine the sizes of the ESS separately for providing inertial support and primary frequency response respectively. Furthermore, when the system inertia is insufficient, a large contingency in the power importing zone may overload an AC interconnection. Consequently, the interconnection could trip due to loss of synchronism, which may lead to system-wide blackout. Although series capacitors can be utilized to solve this problem, they demonstrate several drawbacks such as little controllability and risk of sub-synchronous resonance at high compensation levels. Therefore, further investigations are required to meet these research gaps. In the above perspective, analytical expressions to determine the appropriate sizes of Energy Storage Systems (SMES and BESS)will be formulated in this thesis. Also, a coordinated operational strategy for SMES and BESS to ensure frequency response adequacywill be developed.To avert the risk of cascadingcontingency and subsequent blackout, a frequency responsive Thyristor Controlled Series Capacitor (TCSC)will be modeled.