Maximum power transfer battery charger for electric vehicles

With the increasing interest in electric vehicles, efficient on-board charging equipment that will operate from a standard household service is needed. This charger should maximize the power flow to the batteries under all conditions in order to reduce the charging time. The input AC voltage can range from 187V (low line) to 264V (high line), and the power that can be transfered to the battery is restricted by the AC line current limit.; In a conventional charger with power factor correction, the power transfer rate is limited to the lowest AC voltage multiplied by the maximum line current. The controller regulates this power level over the entire voltage range. Therefore, as the line voltage rises, the input current will correspondingly drop. These chargers also typically hold the battery current constant throughout the charging cycle. Since the power draw increases as the battery voltage rises with this type of control, the battery current also must be limited so the line current is not exceeded at the maximum battery voltage.; It can be seen that the conventional charger cannot take advantage of favorable operating conditions, namely higher AC line voltages and low battery voltages, to increase the charging current. The maximum power transfer method has been developed to improve this underutilization of the charger. By continually monitoring a set of five voltages and currents in addition to the heat sink temperature, the charger can increase the battery current until either the line current or internal junction temperature of one of the IGBTs is at its maximum limit. This provides the maximum possible transfer of power to the battery.; The IGBT junction temperatures for both stages of the charger must be calculated since there is no known practical method to measure them on-line. The equations for the first stage are very complex due to the modulated waveforms associated with the power factor correction function of this stage. However, these equations coupled with out-of-circuit test data produced loss calculations that were within 4% of in-circuit measurements.; The maximum power transfer charger was constructed and tests conducted on a nickel-iron battery pack to study the performance of the charger over a wide range of conditions. Reductions of 1 to 2{dollar}{lcub}1over 2{rcub}{dollar} hours below the charging time of the conventional charger were recorded over a range of AC line voltages.