Effects of High Frequency AC Currents on Cold Temperature Battery Performance

A unique method has been developed for internally heating hybrid electric vehicle batteries at cold temperatures using high frequency alternating currents (AC). The poor performance of these batteries in cold climates is of major concern because they suffer a huge loss in capacity. Another symptom of this low performance is a dramatic increase in the series resistance of the battery, RB, as the temperature drops. A high frequency inverter was designed to test the feasibility of AC heating. The inverter was designed for a maximum pack voltage of 200V and minimum operating frequency of 6.67 kHz while operating in the continuous conduction mode. It uses a pair of insulated gate bipolar transistors connected in a half bridge configuration. Tests were conducted on a pack of sixteen series connected nickel metal hydride batteries. Experimental results have shown that at both -20 and -30C, 10-20 kHz AC currents at amplitudes of 60-80 ARMS warmed the pack to about 25 C within a few minutes, and thereby improved the pack discharge capability. Index Terms Hybrid electric vehicle, Alternating current, Nickel metal hydride, High frequency inverter.