A chopper converter for electric vehicle propulsion battery charging and propulsion motor field excitation

A dual mode chopper power converter circuit capable of providing the separate functions of on-board propulsion battery charging and propulsion motor field excitation under microcomputer command is described. Normal charge mode delivers 24 A until a predetermined voltage is reached (when connected to an appropriate 115 V service outlet) whereupon current is tapered at constant battery voltage. Underway, the chopper circuitry supplies propulsion motor field current in the range of 2 to 11 A (field weakening). The chopper power circuit employs a fast power Darlington transistor and diode packaged in modular form specifically developed for the electric vehicle application and driven by a special isolated proportional base drive circuit, providing minimum storage time and high efficiency. The power circuit uses two diodes and a field reversing relay to satisfy the topology requirements for both the battery charging and field excitation modes. The selection of modulation schemes and control strategy particular to the present application are discussed.