Battery energy storage system for transient stability enhancement and power system damping improvement

Abstract

Battery Energy Storage System (BESS) has emerged as one of the most promising technologies for power system use and is receiving increasing attention from power utilities. BESS is traditionally viewed by utilities as an option to supply peak load through load leveling, but there is now a growing recognition that the fast responses provided by the power electronics and microprocessor control within BESS offer a wide range of additional power system applications, such as back-up supply, power factor correction, energy management, power quality improvement and the ability to provide 'negative load shedding' during emergency operation conditions. This thesis embodies research work on the application of energy storage in general and BESS in particular in two main areas: transient stability enhancement and power system damping improvement. The research aims at developing novel control strategies and investigating the advantages and limitations of BESS for these applications. Two new control strategies based on Fuzzy Logic Control (FLC) and Artificial Neural Networks (ANN) have been investigated, designed and implemented in a time domain simulation environment to rapidly control the output of the BESS to improve first-swing transient stability and to provide additional damping to a weakly damped power system. To ensure an accurate model of the batteries in the BESS during its transient and dynamic mode, a detailed model of the battery cells, both in the charging and discharging mode, has been formulated and implemented in this thesis. The power system model includes the generator D-Q axis model, with its excitation controller and governor representation. Comprehensive simulation studies have been carried out based on a single-machine-to-infinite-bus power system and interconnected multi-machine power systems under a wide range of operating conditions and different types of disturbance. Simulation results confirm the effectiveness and robustness of the two control strategies although, under the novel application of the hysteresis current control on the BESS output current, the rapid charging and discharging of the batteries of the BESS can have the potential of reducing the battery life. To overcome this, the use of the ultra- (or super-) capacitors in parallel with the batteries has been investigated. Results show that this strategy transfers fast oscillation in the battery bank output to the capacitors and hence the batteries only need to cater for the average swing and the ultra-capacitors take care of the rapid change associated with the hysteresis control. It is envisaged that the increase in battery life can justify the additional cost of the ultra-capacitors. The effect of the capacity of the BESS on the effectiveness of system damping has been investigated. Results show that BESS in sufficient quantities could provide considerable advantages for power systems. The impact of using different control signals in controlling the BESS active and/or reactive power outputs on the most appropriate location for system damping enhancement has also been studied.