Thyristor (SCR) Chopper Control System for Transportation Equipment

This paper describes the circuit design used for the application of power semiconductors to the control of dc power in a traction motor system. Type SPM designates a series field traction motor SCR control, providing smooth tractive effort control in motoring and in dynamic braking of 500¿1000 hp (continuously rated) rapid transit car drives. Thyristors are switched by a feedback current control system utilizing a fixed-frequency variable pulse width technique. Armature series reactors and line filter requirements are minimized by a multistage scheme. Both armature and field currents are modulated for full speed range control. Third rail system extreme voltage transients are accommodated by system features. Development and tests of sample equipments on the Chicago Transit Authority system are described. This demonstrator became the first semiconductor chopper propulsion equipment to be placed in revenue service in the United States. Service began in September 1967 on the Chicago Transit Authority´s Skokie Line. A similar 1000-volt equipment was supplied San Francisco Bay Area Rapid Transit for test track evaluation.