US 4,051,419 A · Control system of an alternating-current motor

Abstract

An alternating-current motor is used as an actuator of a positioning control system. The control variable to control the torque of the motor is the load angle .theta..sub.d of a synchronous motor or the slip frequency f.sub.s of an induction motor. The highest and the lowest limit values of the control variable are respectively predetermined from the characteristics between the torque and the control variable and from other design considerations. The preparatory value E for the control variable is synthesized in accordance with an equation E=G.sub.1 (.theta..sub.c -.theta..sub.a)-G.sub.2 p.theta..sub.a, where .theta..sub.c is the reference position, .theta..sub.a is the controlled position, G.sub.1 and G.sub.2 are respectively amplification constants, and p denotes the differential operator d/dt. When E is within the predetermined highest and the lowest limit values of the control variable, E is used as the control variable; when E is larger than the predetermined highest limit value, the highest limit value is used as the control variable; and when E is smaller than the predetermined lowest limit value, the lowest limit value is used as the control variable. After the control variable is thus determined, the instantaneous phase angle signal is synthesized in accordance with an equation .theta..sub.p =.theta..sub.a + .theta..sub.d or .theta..sub.p =.theta..sub.a + 2 .pi.f.sub.s /p where the instantaneous electrical angular position of the rotor of the motor is also denoted by .theta..sub.a. The instantaneous phase angle of the power supply to the motor is controlled with this synthesized .theta..sub.p as the reference signal. The voltage amplitude V.sub.1 of the power supply is controlled as a constrained variable to control the torque of the motor. The reference signal of the voltage amplitude V.sub.1 is determined as a function of the frequency of the power supply, or in one embodiment for a synchronous motor, as a function of the frequency and the load angle.

Claims23

Dependent claims

A control system of a polyphase alternating-current motor comprising:

a polyphase alternating-current motor;
power supply means for generating a polyphase alternating-current voltage to be supplied to said motor, the amplitude and the instantaneous phase angle of said alternating-current voltage being controllable;
position detector means for detecting the instantaneous electrical angular position of the rotor of said motor with respect to a stator reference;
means for producing an initial value for the control variable to control the torque generated by said motor;
phase signal generator means for generating an instantaneous phase angle signal from said initial value for the control variable and said detected instantaneous electrical angular position of said rotor;
phase angle control means for controlling said instantaneous phase angle of said alternating-current voltage with said generated instantaneous phase angle signal as the reference signal;
voltage signal generator means for generating a voltage signal in accordance with a predetermined voltage control law;
and
voltage control means for controlling said amplitude of said alternating-current voltage with said generated voltage signal as the reference signal.

6 more elements

A velocity control system of an electric motor in which the velocity error between a reference velocity and the controlled velocity of said motor is integrated by digital adder means to produce the position error in digital register means, the improvement comprising:

a positive overflow memory, a sign digit memory, and a negative overflow memory;
a first gate for transmitting the overflow digit signal at the resultant output terminal of said adder means to the set terminal of said positive overflow memory when said sign digit memory is in a reset state;
a second gate for transmitting said overflow digit signal to the reset terminal of said sign digit memory when said sign digit memory is in a set state and said negative overflow memory is in a reset state;
a third gate for transmitting said overflow digit signal to the reset terminal of said negative overflow memory when said negative overflow memory is in a set state;
a fourth gate for transmitting the sign digit signal at the resultant output terminal of said adder means to the reset terminal of said positive overflow memory when said positive overflow memory is in a set state;
a fifth gate for transmitting said sign digit signal to the set terminal of said sign digit memory when both said sign digit memory and said negative overflow memory are in reset states;
a sixth gate for transmitting said sign digit signal to the set terminal of said negative overflow memory when said sign digit memory is in a set state;
when both said positive overflow memory and said negative overflow memory are in reset states, said position error being represented by the contents of said register means and the state of said sign digit memory;
when said positive overflow memory is in a set state, said position error being assumed to be M irrespective of the contents of said register means where M-1 is the maximum capacity of said register means;
and
when said negative overflow memory is in a set state, said position error being assumed to be -M irrespective of the contents of said register means.

8 more elements

Dependencies are inferred from the claim text.

Control system of an alternating-current motor

Life of this patent

Control system of an alternating-current motor

Life of this patent

Abstract

Claims23