Coordinated and non-coordinated control of energy storage for voltage support in low voltage distribution networks

Abstract

Energy storage is seen as one of a number of crucial technologies if the integration of renewables in distribution networks increases. The work in this thesis considers how to operate energy storage to overcome issues presented by solar photovoltaic (PV) in low voltage (LV) distribution networks. Two control strategies have been developed and applied in a smart grid laboratory to mitigate voltage rise and reverse power flows caused by PV. The first strategy examines the performance of non-coordinated control of energy storage for voltage support. The second strategy involves coordinating the on-load tap changer (OLTC) and energy storage for voltage support and reducing reverse power flows, and it illustrates that coordinated storage unit is a more effective and viable alternative to upgrading network infrastructure. After considering a single storage unit in the network, strategies for controlling multiple storage units are investigated. The main objective of this method is to solve overvoltage with multiple energy storage in LV networks with a proliferation of PV systems. The scheme is based on voltage sensitivity analysis and a battery aging model which influences which storage units are operated to maintain the network voltage within limits. The battery aging model is included to improve to reduce degradation when operated to resolve voltage excursions thus reducing the maintenance and battery replacement costs. To get a better performance of the storage unit for voltage support, a systematic model that includes the PV generator and the energy storage based on linearized differential equations is constructed. The model was used to examine: the dynamic performance of battery storage systems and their active and reactive power voltage regulation feedback controller; small disturbance of active and reactive power exchange with the power system; a methodology to utilise active and reactive power of the energy storage for voltage support. In summary, the study presented by this thesis shows energy storage can be operated in the LV distribution network where significant amounts of PV generators are installed. It allows distribution network operators to have a deeper understanding of how to operate single and multiple energy storage units in future LV distribution networks.