Efficient braking control for variable speed electric motor - uses electronic frequency changer for control of speed and regenerative braking torque using smaller ballast resistor

摘要

The electric motor speed control is supplied with rectified DC from the power network (1) and a rotating field is generated in known fashion by a combination of electrically timed switches (7). A regenerative braking circuit comprising switch (6) and ballast resistor (5) is connected in parallel with the DC output of the sources and provides the necessary heat sink for energy dissipation during braking. Generation during braking is arranged to produce a higher frequency component in the motor windings by the electronic switching unit (7) and losses in the motor are thereby increased with corresponding reduction in the ballast (5) rating requirement for effective retardation. ADVANTAGE - Minimises dimensioning of ballast resistor and its switch up to limits imposed by thermal capacity of motor windings.