Direct current motor drive

Claim 2

A variable speed motor system comprising an AC source, a DC motor having an armature, a bridge rectifier including thyristors, an inductor between the source and the rectifier, connections from the rectifier to the armature, a capacitor across the armature, said thyristors comprising silicon controlled rectifiers having conduction control gates, means for applying firing potentials to said gates at selected times in successive half-cycles to control the current supplied to the armature, 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, means for obtaining in the reference circuit an error voltage which is the difference between the reference voltage and the speed voltage, a phase control circuit including a capacitor and a variable resistance for determining the times at which the firing potentials are applied to the gates in successive half-cycles, and means for controlling the variable resistance in accordance with the error voltage.

Claim 3

A variable speed motor system comprising an AC source, a DC motor having an armature, a bridge rectifier including thyristors, an inductor between the source and the rectifier, connections from the rectifier to the armature, a capacitor across the armature, said thyristors comprising 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 current supplied to the armature, 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, means for obtaining in the reference circuit an error voltage which is the difference between the reference voltage and the speed voltage, and means controlled by the error voltage for determining times of applying the firing potentials to the gates, a dynamic braking circuit connected across the armature and including a dynamic braking thyristor and a dynamic braking resistor, means for firing the dynamic braking thyristor when the error voltage is of a value to call for a reduction in motor speed, whereby energy is dissipated in thE dynamic braking resistor, a commutating thyristor connected between the AC line and the dynamic braking thyristor to apply a reverse voltage to the dynamic braking thyristor, to commutate the latter off, means controlled by the error voltage arriving at a value corresponding to the desired reduced speed for firing the commutating thyristor, said firing occurring during a positive half-cycle of the source, the commutating thyristor being itself commutated off on a succeeding negative half-cycle.

Claim 4

A variable speed motor system comprising an AC source, a DC motor having an armature, a bridge rectifier including thyristors, an inductor between the source and the rectifier, connections from the rectifier to the armature, a capacitor across the armature, said thyristors comprising 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 current supplied to the armature, 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, means for obtaining in the reference circuit an error voltage which is the difference between the reference voltage and the speed voltage, and means controlled by the error voltage for determining times of applying the firing potentials to the gates, a dynamic braking circuit connected across the armature and including a dynamic braking thyristor and a dynamic braking resistor, means for firing the dynamic braking thyristor when the error voltage is of a value to call for a reduction in motor speed, whereby energy is dissipated in thE dynamic braking resistor, a commutating thyristor connected between the AC line and the dynamic braking thyristor to apply a reverse voltage to the dynamic braking thyristor, to commutate the latter off, means controlled by the error voltage arriving at a value corresponding to the desired reduced speed for firing the commutating thyristor, said firing occurring during a positive half-cycle of the source, the commutating thyristor being itself commutated off on a succeeding negative half-cycle.

Claim 5

A variable speed motor system comprising an AC source, a DC motor having an armature, a bridge rectifier including thyristors, an inductor between the source and the rectifier, connections from the rectifier to the armature, a capacitor across the armature, said thyristors comprising 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 current supplied to the armature, 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, means for obtaining in the reference circuit an error voltage which is the difference between the reference voltage and the speed voltage, and means controlled by the error voltage for determining times of applying the firing potentials to the gates, means controlled only when the error voltage is one polarity to control the times of applying the firing potentials to the gates, the error voltage of the opposite polarity occurring when motor is slowing down and is in a generating condition, a dynamic braking circuit across the armature and including a dynamic braking thyristor and a dynamic braking resistor, firing means for applying a gating potential to the dynamic braking thyristor when the error voltage is of said opposite potential whereby energy is dissipated in the dynamic braking resistor, a commutating thyristor connected between the AC line and the dynamic braking thyristor to apply a reverse voltage to the dynamic braking resistor to commutate the latter off, means controlled by conjoint action of the error voltage resuming its first-named polarity and current flowing in the dynamic braking circuit to fire the commutating thyristor, and thereby to commutate the dynamic braking thyristor, said commutating thyristor being itself commutated on a negative half-cycle of the AC line.

Claim 6

A variable speed motor system comprising an AC source, a DC motor having an armature, a bridge rectifier including thyristors, an inductor between the source and the rectifier, connections from the rectifier to the armature, a capacitor across the armature, said thyristors comprising 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 current supplied to the armature, 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, means for obtaining in the reference circuit an error voltage which is the difference between the reference voltage and the speed voltage, and means controlled by the error voltage for determining times of applying the firing potentials to the gates, means controlled only when the error voltage is one polarity to control the times of applying the firing potentials to the gates, the error voltage of the opposite polarity occurring when motor is slowing down and is in a generating condition, a dynamic braking circuit across the armature and including a dynamic braking thyristor and a dynamic braking resistor, firing means for applying a gating potential to the dynamic braking thyristor when the error voltage is of said opposite potential whereby energy is dissipated in the dynamic braking resistor, a commutating thyristor connected between the AC line and the dynamic braking thyristor to apply a reverse voltage to the dynamic braking resistor to commutate the latter off, means controlled by conjoint action of the error voltage resuming its first-named polarity and current flowing in the dynamic braking circuit to fire the commutating thyristor, and thereby to commutate the dynamic braking thyristor, said commutating thyristor being itself commutated on a negative half-cycle of the AC line.

Claim 7

A system as defined in claim 3, in which the dynamic braking circuit includes a diode in which there is a forward voltage drop when the dynamic braking thyristor is conducting, and means for utilizing said voltage drop to detect the flow of current in the dynamic braking circuit and thus to control the firing of the commutating thyristor when the error voltage changes from its opposite polarity to its first-named polarity.