Comparison of battery management approaches for energy flow optimization in microgrids

Abstract

The recently emerged approaches to energy flow optimization in microgrids focus on planning how much energy needs to be inserted or exerted from a microgrid energy storage unit in a given fixed time to achieve maximum benefit for the microgrid operation (economical, environmental, etc.). As a result of this planning there is an energy flow command issued from the level of microgrid energy flows optimization towards the management systems of individual energy storages in the microgrid. As the energy flow command can be achieved by different control sequences on the management level of the storage unit, there is a need to assess the optimal control sequence for the energy storage as well as to see how the alternative, simplified approaches to realize the energy flow command perform in comparison. In this work we focus on the battery management system that is subordinated to the microgrid energy flow optimization and compare the approaches of the optimal battery current, constant current and constant power, whereas the optimality is formulated with respect to residual state of charge available after the energy flow command is realized on the battery. On a selected example of valve-regulated lead-acid (VRLA) battery we show that these approaches to battery management yield comparable results which suggests that the mentioned simplified approaches are quite near to the optimal ones with respect to the amount of residual state of charge. We further show how the dynamical model of the optimally managed battery looks like for the case of battery representation via a hybrid electrical model.