Direct current motor drive

Claim 2

A variable speed motor system comprising an AC source, a DC motor having an armature, a bridge rectifier, an inductor between the source and the rectifier to form a substantially constant current source at the rectifier, connections from the rectifier to the armature, a capacitor across the armature, and diverter means comprising thyristors connected across arms of the bridge to divert current from said constant current source to vary the current passing through the rectifier to be supplied to the armature.

Claim 3

A system as defined in claim 1 in which the thyristors are silicon controlled rectifiers having conduction control gates, and means for applying firing potentials to said gates at selected times in successive half-cycles to control the diversion of current from said constant current source.

Claim 4

A system as defined in claim 2, having in addition a reference circuit, means for introducing into the reference circuit a manually sElected reference voltage, means for introducing into the reference circuit a speed voltage dependent on the motor speed, whereby an error voltage which is the difference between the speed voltage and the reference voltage exists in the reference circuit, and means controlled by the error voltage for controlling the diverter means.

Claim 5

A system as defined in claim 2, in which the means for applying firing potentials to the gates comprises a reference circuit, means for introducing into the reference circuit a manually selected reference voltage, means for introducing into the reference circuit a speed voltage dependent on the motor speed, whereby an error voltage which is the difference between the speed voltage and the reference voltage exists in the reference circuit, and means controlled by the error voltage for determining the times at which the firing potentials are applied to the gates in successive half-cycles.

Claim 6

A system as defined in claim 2, in which the means for applying firing potentials to the gates comprises a reference circuit, means for introducing into the reference circuit a manually selected reference voltage, means for introducing into the reference circuit a speed voltage dependent on the motor speed, whereby an error voltage which is the difference between the speed voltage and the reference voltage exists in the reference circuit, a phase control circuit including a variable resistance for determining the times at which the firing potentials are applied to the gates, and means for controlling the variable resistance in dependence on the error voltage.

Claim 7

A system as defined in claim 3 in which the speed voltage is taken from the armature voltage of the motor, and means are provided for compensating for the IR drop in the armature.

Claim 8

A system as defined in claim 6, having in addition a dynamic braking circuit, and means for connecting the dynamic braking circuit across the armature when the error voltage is of a value to call for a reduction of motor speed, whereby kinetic energy of the armature is dissipated in the dynamic braking circuit, said dynamic braking circuit including a dynamic braking thyristor, means controlled by the error voltage for firing the dynamic braking thyristor, and means for commutating the dynamic braking thyristor off when the error voltage is in the range of stable operation, the commutating means including a connection between the dynamic braking circuit and the diverter means to cut off the current through the dynamic braking thyristor when the diverter means becomes non-conducting.