Practical two phase DC chopper motor drive

During the past ten years the Army has invested a sizable effort into new systems configurations and development programs to improve ground vehicle mobility. USAMERDC, Fort Belvoir, Virginia, has been particularly interested in an improved vehicle mobility for off-highway vehicles, amphibians and engineer equipment through electrical propulsion. Because electrical propulsion drive systems feature individual wheel controls, the supply logistic and construction of such vehicles can be justified in terms of an improved mobility over all types of terrain. Past experience in industry and in the Government has shown that the dc motor propulsion drive is inherently simple to install and to maintain. The dc motor is somewhat heavier than comparable ac motors due to motor speed limitations; however, the dc machine, particularly the series field motor, requires only a simple solid state power processor since the power is processed by the motor´s own commutator. Commercial dc traction motors have an excellent high torque starting characteristic which is mandatory for engineer type vehicle propulsion applications. In the mid-speed range, however, presently available dc motor propulsion drives under consideration for the Army have an unsatisfactory acceleration performance when compared to conventional mechanical drive systems which typically comprise a spark or compression ignition engine and a multispeed transmission. In this context the paper discusses this Center s experimental solid state controller and the method employed to improve the acceleration or peak power propulsion profile of an electric vehicle drive using dc series field motors. A power processor for shunt field motors is also described, also able to provide identical propulsion characteristics through storage of kinetic energy in a high speed flywheel.