Tapered current limit protection for d. c. motor

Claim 2

In a control system for a direct current motor operative with a thyristor power supply, the combination of: a voltage reference regulator having a maximum output, a current regulator, thyristor firing circuit means operative with said thyristor power supply and coupled to the output of said current regulator, an analog multiplier between the output of said voltage reference regulator and the input of said current regulator, and means coupled to said analog multiplier and responsive to the speed of said motor for attenuating the gain of said analog multiplier when the speed of said motor exceeds a predetermined magnitude.

Claim 3

In a control system for a direct current motor operative with a thyristor power supply, the combination of: a voltage reference regulator having a maximum output, a current regulator, thyristor firing circuit means operative with said thyristor power supply and coupled to the output of said current regulator, an analog multiplier between the output of said voltage reference regulator and the input of said current regulator, and means coupled to said analog multiplier and responsive to the speed of said motor for attenuating the gain of said analog multiplier when the speed of said motor exceeds a predetermined magnitude.

Claim 4

In a control system for a direct current motor operative with a thyristor power supply, the combination of: a voltage reference regulator having a maximum output, a current regulator, thyristor firing circuit means operative with said thyristor power supply and coupled to the output of said current regulator, an analog multiplier between the output of said voltage reference regulator and the input of said current regulator, and means coupled to said analog multiplier and responsive to the speed of said motor for attenuating the gain of said analog multiplier when the speed of said motor exceeds a predetermined magnitude.

Claim 5

In a control system in accordance with claim 1 wherein the current carrying ability of said direct current motor tapers off with increase in motor speed along a speed-current characteristic, and said gain attenuating means decreases the gain of said analog multiplier with increase in motor speed above said predetermined magnitude along a curve which approximates said speed-current characteristic.

Claim 6

In a control system in accordance with claim 1 including means for generating a speed feedback signal which is a function of the speed of said motor, and wherein said gain attenuating means includes an absolute value amplifier receiving said speed feedback signal as an input and whose gain is a function of the magnitude but independent of the polarity of said speed feedback signal.

Claim 7

In a control system in accordance with claim 3 wherein said absolute value amplifier includes a summing operational amplifier having said speed feedback signal coupled to the inverting input thereof, and means for applying a direct current bias signal to said inverting input to bias said summing amplifier into saturation, whereby the output of said summing amplifier is constant until said speed feedback signal cancels said bias signal sufficiently to bring said summing amplifier out of saturation.

Claim 8

In a control system in accordance with claim 4 wherein said absolute value amplifier includes a second operational amplifier having said feedback signal coupled to the inverting input thereof and having its output coupled to the inverting input of said summing amplifier, and means for preventing said second operational amplifier from responding to one polarity of said speed feedback signal.

Claim 9

In a control system for a direct current motor energized from a thyristor power supply regulated by gating signals from a firing circuit whose phase angles are a function of an input to said firing circuit, feedback means for generating a speed feedback signal which is a function of the speed of said motor, current feedback means for generating a current feedback signal which is a function of the armature current in said motor, a reference signal source, a speed regulator for comparing said reference and speed feedback signals and having a maximum output, an analog multiplier receiving the output of said speed regulator on one input thereto, a current regulator for comparing the output from said analog multipler with said current feedback signal and for supplying a current error signal to said firing circuit which is a Function of their difference, and modifying circuit means receiving said speed feedback signal as an input for attenuating the gain of said analog amplifier when the speed of said motor exceeds a predetermined magnitude in the forward direction and also when it exceeds a predetermined magnitude in the reverse direction.

Claim 10

In a control system for a direct current motor energized from a thyristor power supply regulated by gating signals from a firing circuit whose phase angles are a function of an input to said firing circuit, feedback means for generating a speed feedback signal which is a function of the speed of said motor, current feedback means for generating a current feedback signal which is a function of the armature current in said motor, a reference signal source, a speed regulator for comparing said reference and speed feedback signals and having a maximum output, an analog multiplier receiving the output of said speed regulator on one input thereto, a current regulator for comparing the output from said analog multipler with said current feedback signal and for supplying a current error signal to said firing circuit which is a Function of their difference, and modifying circuit means receiving said speed feedback signal as an input for attenuating the gain of said analog amplifier when the speed of said motor exceeds a predetermined magnitude in the forward direction and also when it exceeds a predetermined magnitude in the reverse direction.

Claim 11

In a control system in accordance with claim 6 wherein said modifying circuit means includes an absolute value amplifier whose output is a function of the magnitude but independent of the polarity of the speed feedback signal input thereto.

Claim 12

In a control system in accordance with claim 7 wherein said absolute value amplifier includes a summing operational amplifier, means to couple said speed feedback signal to the inverting input of said summing amplifier, and means to apply a direct current bias signal to said inverting input to bias said summing amplifier into saturation when said motor is at standstill, whereby the output of said summing amplifier is constant until said speed feedback signal cancels said bias signal sufficiently to bring said summing amplifier out of saturation.

Claim 13

In a control system in accordance with claim 8 wherein said absolute value amplifier also includes a second operational amplifier having said speed feedback signal coupled to the inverting input thereof and having its output coupled to said inverting input of said summing amplifier, and means for preventing said second operational amplifier from responding to one polarity of said speed feedback signal.

Claim 14

In a control system in accordance with claim 9 wherein said direct current bias signal is of opposite polarity to said speed feedback signal when said motor is rotating in the forward direction and said one polarity of said speed feedback signal to which said second operational amplifier does not respond is generated when said motor is rotating in the forward direction.