Development of State-of-Charge Observers for Lead-Acid Storage Units for Solar-Assisted Autonomous Applications
Abstract
Electric energy storage is a crucial problem for autonomous systems powered by photovoltaic installations. The excess of produced energy under favourable conditions is normally stored into batteries. For large scale applications, where more than one battery is used, the correct utilization of the storing bank plays an important role in order to extend the batteries' lifetime. The context of this work is related to the research on a solar assisted domestic heating application, which includes an autonomous photovoltaic installation and a software-driven resistance load which represents a dwelling heated by a heat pump. The load stands as a sink with time-varying energy consumption. The energy pattern resulting from the climate condition and the user driving behaviour implies a hard float cycling work of the storing bank. Moreover, in such applications, due to the tolerances on the internal parameters, the interactions between the batteries are unavoidable. As a result, some storage units work under constant discharge conditions whereas the others take on the overcharge current and imbalances occur. Therefore, a state-of-charge monitoring scheme of an individual unit can provide an essential information in order to improve energy management.