US 4,230,979 A · Controlled current inverter and motor control system

Abstract

A controlled current inverter system forms the basis of an a.c. motor drive system for furnishing the motor load with a variable frequency, variable magnitude a.c. current from an inverter which is supplied from a variable d.c. current source by way of a d.c. link including an inductor. Torque is the control parameter employed in the system and the motor speed and torque are controlled through the control of motor flux and motor current, by maintaining a controlled ratio between the direct and quadrature motor currents, through separate control paths to the d.c. source and the inverter. A third control path functioning on the difference between the desired and actual motor flux serves as a modifier to the main control paths to improve overall operation and control. Means associated with the basic control paths provide for dynamic braking of the motor.

Claims25

Dependent claims

A control for an a.c. electric motor having a stator and a rotor spaced from the stator by a gap across which gap flux is produced in response to an electrical motor current of variable magnitude and frequency through windings associated with said stator, said control serving to control the electrical torque of said motor and comprising:

(a) means to determine, with respect to the motor, the instantaneous electrical torque and the instantaneous angle between the gap flux and the motor current and to provide signals proportional thereto;
(b) means to establish a torque reference signal proportional to a desired level of electrical torque;
(c) means to compare said torque reference signal with said signal proportional to the instantaneous electrical torque and to generate a current error signal representative of any difference therebetween, said current error signal acting as the primary control parameter serving to vary the magnitude of the motor current;
(d) means responsive substantially solely to said torque reference signal to derive an angle reference signal representative of the desired angle between the gap flux and the motor current;
and,
(e) means to compare said angle reference signal with said signal proportional to the instantaneous angle between the gap flux and motor current and to generate a frequency error signal representative of any difference therebetween and effective to vary the frequency of the motor current.

3 more elements

An a.c. motor drive for use with an a.c. motor having a stator and a rotor spaced from the stator by a gap across which gap flux is produced in response to electrical motor current supplied to said motor comprising:

(a) a variable d.c. current source for providing a d.c. output current which varies in response to a current error input signal;
(b) a source of variable frequency current for supplying current to said motor at a frequency which is a function of a frequency error signal;
(c) link circuit means including an inductor for connecting said d.c. current source to said source of variable frequency current;
(d) means to determine, with respect to the motor, the instantaneous electrical torque and the instantaneous angle between the gap flux and the motor current and to provide signals proportional thereto;
(e) means to establish a torque reference signal proportional to a desired level of electrical torque;
(f) means to compare said torque reference signal with said signal proportional to the instantaneous electrical torque and to generate a current error signal representative of any difference therebetween, said current error signal acting as the primary control parameter serving to vary the magnitude of the motor current;
(g) means responsive substantially solely to said torque reference signal to derive an angle reference signal representative of the desired angle between the gap fluz and the motor current;
and,
(h) means to compare said angle reference signal with said signal proportional to the instantaneous angle between the gap flux and motor current and to generate a frequency error signal representative of any difference therebetween and effective to vary the frequency of the motor current.

6 more elements

In a control for an a.c. induction electric motor having a stator and a rotor spaced from the stator by a gap across which gap flux is produced in response to an electrical motor current of variable magnitude and frequency through windings associated with said stator, said control including first and second electrical power converters and a direct current link connected to, and intermediate, said converters, said control further including means associated with said first converter to control the electrical current in said direct current link, and means associated with said second converter to control the frequency of the electrical motor current, means to effect a dynamic braking mode of motor operation comprising:

(a) command means operative to generate a braking signal to initiate said mode of dynamic braking;
(b) shorting means responsive to said braking signal to short circuit said direct current link at the connection of said link with said first power converter whereby said motor is isolated from said first power converter;
(c) resistive means associated with said direct current link;
(d) switch means responsive to said braking signal to selectively include said resistive means in said direct current link when the dynamic braking mode of motor operation is desired;
and,
(e) frequency control means responsive to said braking signal to control frequency of operation of said second electrical power converter to thereby control said motor.

3 more elements

Dependencies are inferred from the claim text.

Controlled current inverter and motor control system

Life of this patent

Controlled current inverter and motor control system

Life of this patent

Abstract

Claims25