Braking circuit for the mixed regenerative and resistance braking of a d-c series machine operated as a generator

Claim 1

In a braking circuit for the mixed regenerative and resistance braking of a d.c. series machine operating as a generator in which the armature and field windings of said machine are combined with a stabilizing resistor in a series circuit across which is shunted a d.c. control element with a controlled main rectifier and across which is shunted a first braking branch comprising a first braking resistor in series with a first controlled braking rectifier, with the series circuit connected through a return rectifier to a d.c. source which can absorb current at least intermittently, the improvement comprising; a. means to monitor voltage in the circuit and means responsive thereto to generate firing pulses; b. at least a second braking branch comprising a second braking resistor having a resistance different from that of the first braking resistor in series with a controlled braking rectifier, said second braking branch coupled in parallel with said first braking branch; c. a selection circuit having at least three switch positions, selectively closed in response to an input signal and selectively coupling said means generating firing pulses to said first and second controlled braking rectifiers, a first switching position coupling said firing pulses to said first braking rectifier, a second switching position coupling said firing pulses to said second braking rectifier and a third switching position coupling said firing pulses to both said first and second braking rectifiers; d. means to develop a signal proportional to the actual current in said braking circuit; and e. control means for providing a control signal to said selection circuit, said control having as inputs the output of said means providing a signal proportional to actual current and first and second predetermined limit values, said control means providing an output closing said first switch when said actual value exceeds said first predetermined value, an output closing said second switch when said actual value is between said two predetermined values and an output closing said third switch when said actual value is greater than said second predetermined value.