| Methods have been developed for internally heating EV/HEV batteries using either low frequency (60 Hz) or high frequency (10–20 kHz) alternating currents (AC) at cold temperatures. The poor performance of these batteries in cold climates is of major concern because they suffer a huge loss in capacity at low temperatures. Another symptom of this low performance is a dramatic increase in the series resistance of the battery, RB, as the temperature drops.; Experimental set-ups were built for both low and high frequencies, and several tests were conducted on both lead acid and NiMH batteries at different AC amplitudes, states of charge (SOCs) and cold temperatures. Low frequency 60 Hz heating was tested on several different lead acid batteries, and the feasibility of using high frequency heating was verified by using a 10–20 kHz inverter to perform tests on a pack of nickel metal hydride (NiMH) batteries. A technique also was developed to determine the internal battery temperature, Tbat, by measuring the series battery resistance, RB. An AeroVironment ABC150 power processing system was used along with the necessary data acquisition hardware and software to measure RB.; The use of 60 Hz is economically attractive because it is relatively simple and inexpensive, as compared to high frequency systems. However, the 60 Hz equipment is much larger and heavier. Therefore it would be a poor choice for on-board purposes, and it is feasible only as an off-board heater. However, a 10–20 kHz heater can be used on-board an HEV, where the power for its inverter would be supplied by the vehicle's generator which is driven by the HEV's heat engine.; The results of this research are described in detail along with experimental data for both low frequency (60 Hz) and high frequency (10–20 kHz) tests. |
