Battery chargers for electric vehicles

This article presents a comparative study of the performance of two types of battery chargers being developed for electric vehicles. The first charger is a microprocessor-based ferroresonant battery charger, referred to as the ferroresonant charger. The power delivery section of this charger is a ferroresonant transformer, which exploits the saturation of magnetic materials through its capacitor winding to produce a well-regulated output that resembles a square wave. The control section periodically places a resistive load across the battery under charge that allows this change in resistance to be detected. A microprocessor controls the timing and executes the gating of the needed switches in the circuit and then gathers and analyzes data from the battery charge monitor circuit. The monitor circuit measures the voltage drop across the battery, which is proportional to the battery internal resistance when the load is introduced. The second charger is a multiphase AC-to-DC converter that employs two three-phase transformers to create twelve phases and is called the twelve-phase charger. One transformer primary is in the delta configuration, and the other transformer primary is in the wye configuration. The center-tapped secondaries create the twelve phases. Thyristors are used to control the output voltage of the charger through digital control of the firing angle. A microprocessor controls the charging profile of the battery. A motor-generator set is used to simulate the load to the charger for test conditions.