An electrical model for energy efficiency evaluation of NiMH batteries

In this work, we propose an electrical model of the battery based on its equivalent circuit for the evaluation of the energy efficiency. The circuit model consists of a current-dependent nonlinear resistance to model the total drop in the battery voltage caused by the activation, concentration, and Ohmic polarizations. The effects of the coulomb losses on the battery run time are also considered in the model. The model targets the state of charge range from 20% to 80% in which best energy efficiency can be achieved, and the total resistance is a function of the battery current magnitude only. The model is intended to be used for real-time management of the battery energy efficiency in grid-connected applications. Through experiments and simulations of two NiMH battery packs, we confirm the effectiveness of the model in evaluating the energy efficiency at different conditions of charge and discharge currents.