JPH02214489A - Overload protecting circuit for induction motor - Google Patents

Abstract

PURPOSE:To control the overcurrent of an inverter by providing an induction motor (IM) overload protecting circuit added to a sensorless vector controller for detecting the torque overcurrent of the IM to feed back it to a speed command to prevent the overload current of the inverter. CONSTITUTION:An overload current of an IM input circuit generated by the overload operation of the IM is detected as the overcurrents of a magnetic flux current Iid' and torque current Iiq' of a circuit 1. A torque current Iiq' is fed back to a speed command as an angular velocity omegaSM of an overtorque element in means 12 via means 10 and 11, and a speed command omegar1* is subtracted by omegaSM to become a new speed command omega<r>*. As a result, primary voltage elements U*, V*, W* to a PWM inverter driver 4 are varied, an inverter 5 is abruptly controlled to prevent the overload current of the inverter, thereby preventing the releasing operation of a thermal relay, an AC breaker.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides an overload protection circuit for an induction motor (hereinafter referred to as IM), specifically, a method for preventing overload of an IM in sensorless vector control. It relates to protection circuits.

[Conventional technology]

In an inverter-controlled motor, an overload current flows through the inverter during overtorque due to motor overload or restart immediately after a momentary power outage.

Generally, instantaneous and time-limited overload protection are used; one type detects overload current using a CT and turns off the inverter, and the other uses a time-limited overload relay to protect against relatively long overloads. There is one that detects this and stops the inverter.

Thermal relays (thermal or electronic) are often used for this time-limited overload detection.

[Problem to be solved by the invention]

I as a driving device by vector control of 1M
The range of application of M is expanding, and along with this, demands on the speed-torque characteristics of IM are also diversifying. For this reason, the frequency of occurrence of inverter overload current due to IM overload is increasing, so rapid control of the inverter prevents IM overload and reduces the number of inverter turn-offs, thermal relays, and AC circuit breakers. It was hoped that it would be restricted.

In order to solve the above-mentioned problems, the present invention provides an IM attached to a sensorless vector control circuit that prevents an overload current of an inverter by detecting an excess torque current of an IM and feeding it back to a speed command. The purpose of this invention is to provide an overload protection circuit.

[Failure to solve the problem]

In order to achieve the above object, the present invention provides means for calculating a torque component from a torque current calculated from a motor primary current and a primary rotation vector in 1M sensorless vector control; means for calculating an overtorque element by comparing the component with a maximum torque specific to the motor, means for calculating an angular velocity of the overtorque element, and a subtracter for correcting a speed command based on the calculated angular velocity. and means for applying the corrected speed command to a circuit for calculating the primary rotation vector via the overload protection circuit for an induction motor.

[Effect]

The motor primary current is converted from 3-phase to 2-phase, and further multiplied by the primary rotation vector to obtain the magnetic flux current 11. ' and torque current 119
′ is calculated, and the secondary magnetic flux φ is calculated from the voltage/current equation of the motor.
2. The slip angular velocity ω5 and torque T are determined as follows.

Here, T2-(f2-11m)/rz, p: differential operator, φ2: secondary magnetic flux, r2: secondary resistance, 12
= secondary leakage inductance, I! m: excitation inductance, PF: pole-logarithm If the motor constant and secondary magnetic flux are known, the torque current can be obtained from equation (3)! 2. Torque T w' can be calculated from °. Therefore, the overtorque ΔT, which is the difference between the maximum torque T a a X specific to the IM and the calculated torque T m', is determined, and the angular velocity ω3. The inverter can be prevented from overload current by calculating it from equations (2) and (3), ΔT, and the occurrence time and feeding it back to the speed command.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram in which an IM overload protection circuit 16 according to the present invention is inserted into a sensorless vector control circuit that vector-controls an IM.

1 is the magnetic flux current I from the motor primary current and primary rotation vector manually supplied via the CT provided in the primary circuit of IM6.
This circuit calculates ld' and torque current 119'.

The IM overload protection circuit 16 according to the present invention includes the circuit 1
Means 10 calculates a torque component from the torque current ■, 9' which is the output of , and an overtorque element △T which is the difference between the calculated torque component M' and the maximum torque T, □ of IM. Means 11 and the overtorque element Δ
Corresponding to T, △1゛.

means 12 for calculating the angular velocity obtained by adding the time element of ω3. The speed command ωr is
and a subtracter 13 for correcting lI.

With the above circuit configuration, the torque current in the motor primary current is detected in the circuit 1, converted into an overtorque element, and then fed back to the speed command as the angular velocity ωsm.

ω"1-ω5ll=ω"Fist - Tsubojizan/Ban...
(4) A primary rotation vector is calculated in circuit 2 based on the speed command ω obtained from equation (4), and this output is given as the primary rotation vector to circuits 1 and 3.

The magnetic flux current command Ild'' is subtracted by the magnetic flux current 11d' output from the circuit l in the subtracter 7, and the difference current IIds is manually input to the circuit 3 together with the torque current 119' output from the circuit 1. .

In circuit 3, primary voltage elements U*, V゜, W
o is calculated and controls the inverter 5 via the PWM inverter drive circuit 4.

Therefore, the overload current of the 1M input circuit caused by overload operation of IM is the magnetic flux current I ld' in circuit 1.
and the torque current 1, , / is detected as an overcurrent,
Torque current 119' is applied via means 10 and 11 to means 12 to determine the angular velocity ω3. of the overtorque element. is fed back to the speed command.

That is, the speed command ωrl. is subtracted by ω to become a new speed command ωr.

As a result, the primary voltage elements U'', V'', and W'' to the PWM inverter drive circuit 4 change, rapidly controlling the inverter 5 to prevent overload current of the inverter, and thereby preventing thermal relays and AC circuit breakers. Prevents release operation.

〔Effect of the invention〕

As explained above, by adding the IM overload protection circuit according to the present invention to the sensorless vector control circuit, the overload current of 1M primary current is detected and converted into the overtorque component of the torque component, and furthermore, the angular velocity change A feedback circuit that corrects the speed command is configured to control the inverter's overcurrent.

Generally, the operating characteristics of thermal relays lack coordination, and the operation of the IM is interrupted each time the inverter is turned off or the AC circuit breaker is opened, but the overload protection circuit according to the present invention Since the load detection accuracy is high and the inverter is rapidly controlled, it has the effect of compensating for the drawbacks of thermal relays and AC circuit breakers, and making it possible to protect the IM from overload by adding a simple circuit. Another advantage is that the control characteristics are sensitive and responsive, allowing maximum torque operation without step-out.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a sensorless vector control circuit including an IM overload protection circuit according to the present invention. 4... PWM inverter drive circuit, 5... Inverter, 6... Induction motor (IM), 16... IM overload protection circuit.

Claims (1)

[Claims] 1. In sensorless vector control of an induction motor,
means for calculating a torque component from a torque current calculated from a motor primary current and a primary rotation vector; means for calculating an overtorque element by comparing the calculated torque component with a maximum torque specific to the motor; means for calculating the angular velocity of the overtorque element; and a subtracter for correcting the speed command based on the calculated angular velocity, the corrected speed command is applied to the
An overload protection circuit for an induction motor, characterized by comprising: means for providing a next rotation vector to a circuit that calculates it;