Characterizing battery behavior for time dependent currents

Batteries connected to the DC grid are exposed to a variety of currents. This paper presents measurements on a Ni-MH battery under different loading conditions and shows how a small signal circuit model can be used to explain the observations, establishing links between physical processes within the battery and elements in the model. At DC currents over 2 C, the impedance of the battery is not influenced by the ripple frequency, but rather by the higher temperatures. Results also show that the impact of the ripple frequency on modulation of the double layer charge is negligible at ripple frequencies exceeding 5 kHz. The amplitude of pulses that can be applied are shown to be governed by diffusion limits and the battery's state of charge.