A high frequency inverter for cold temperature battery heating

A high frequency inverter has been designed for internally heating hybrid electric vehicle (HEV) batteries at cold temperatures using alternating current (AC). The inverter was designed for a maximum pack voltage of 200 V and minimum operating frequency of 6.67 kHz while operating in the continuous conduction mode. It uses a pair of insulated gate bipolar transistors (IGBTs) connected in a half bridge configuration. The inverter circuit was first simulated in PSpice for obtaining adequate values for the circuit components and then constructed. A digital circuit was used to control the input signals to the IGBT driver cards. The inverter was tested on a pack of nickel metal hydride (NiMH) batteries at different cold temperatures to verify the feasibility of high frequency AC heating. A sophisticated data acquisition system was used for measuring battery temperature and voltage data for display on a computer. This data was also used to control the inverter operation during the tests. Experimental results have shown that at both -20 and -30 °C, 10-20 kHz AC currents at amplitudes of 60-80 A rms warmed the pack to about 25 °C within a few minutes, and thereby improved the pack discharge capability.