Brushless DC Motor Propulsion Using Synchronous Motors for Transit Systems

In this paper, a brushless dc motor propulsion system using synchronous motors is described which is suitable for transit applications. The propulsion system consists of two-quadrant transistorized front-end chopper and a three-phase transistorized inverter (forming the electronic commutator for the synchronous machine phase currents) to provide both controlled propulsion and regenerative braking. The control scheme makes the system operate stably at all speeds and avoids loss of synchronization. Performance characteristics of the drive are derived and compared with those of a dc motor propulsion drive. Improved low-speed performance and reduced torque pulsation are achieved by proper switching of the electronic commutators. A prototype model using a 5-hp synchronous motor is built and tested.