A modular protection for grid-connected battery storage systems

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University of New Brunswick


Power systems have been showing a growing interest in utilizing different types of energy storage systems (ESSs), which can be operated as interconnected components. Such ESSs are sought to accommodate high penetration levels of renewable energy, peak-demand management, smart grid functions, and energy markets. Battery units, flywheels, compressed gas, pumped hydro, super capacitors, and superconducting magnetic energy storage (SMES) units are among the popular energy storage systems that have shown potential application for interconnected operation. The design and operation of interconnected ESSs, along with improving the power density, have been subjects for several research works, which recommended the use ESSs with electric energy storage for high power applications. These recommended ESSs include battery units, supper capacitors, SMES units, compressed gas and pumped hydro. The majority of recommended ESSs require the use of power electronic converters (PECs) for charge and discharge operation. Nowadays, battery units, super-capacitors, and SMESs are commercially available with a wide range of power and voltage ratings. Despite the remarkable improvements in the efficiency, reliability, and power density of interconnected battery, super-capacitor, and SMES based ESSs, their protection remains a challenge for their host power systems. In the majority of grid-connected ESSs, the protection is designed using current-based and/or voltage-based protective devices. Several research works have been conducted to address the possible impacts of interconnected ESSs on utility-grade protective devices. The outcomes of these research works have suggested that interconnected ESSs can contribute to fault currents, and adversely impact the responses of upstream non-unit protective devices. Furthermore, these research works have recommended featuring the main controllers of interconnected ESSs with faster responses to changing conditions of the ESSs. However, meeting such a recommendation has to consider the controller characteristics, type of fault, maximum input and output currents, and state-ofcharge of protected ESSs. Other approaches have been developed to address the challenges facing protective devices due to interconnecting ESSs, including the directional relays, adaptive coordination, voltage relays, and communication-assisted relays. These approaches have shown some limited performance due to the impacts of PECs and their controllers on the voltage-current behaviors during and post fault conditions. Moreover, the ability of the relays used demonstrated limited capabilities to detect faults involving grid-connected PECs. The main objective of this research is to develop and test a new digital protection scheme for interconnected ESSs. The proposed digital protection will be designed using multiple digital relays that are located in different parts of the protected ESS. The overall response of the proposed digital protection will be set as a combination of responses by digital relays to maintain a reliable power flow to or from the host power system. The proposed digital protection will be tested for an interconnected battery ESS under different operating and fault conditions.