JPH0870600A - Control apparatus for induction motor - Google Patents

Abstract

PURPOSE: To make it possible to reduce power loss more as compared with a case where required torque is output without intensifying a field system, by issuing a command to correct reference field current to increase it by a required amount when large torque is required. CONSTITUTION: When an induction motor 11 requires large torque, a higher level controller 15 controls the switching circuit 21 in a field reference correcting circuit 19 so that it will select a rate of increase K and add it to a muliplier 22. The multiplier 22 multiplies the reference field current of a field reference circuit 18 by the ratio of increase K, and the reference field current is thereby increased in a preset ratio. The result of increase is added to a vector control unit 24 through a rate circuit 23. The vector control unit 24 vector-synthesizes torque current component and field current component based on reference torque current from a speed control circuit 14 and reference field current from the field reference correcting circuit 19 to obtain resultant current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-phase AC induction motor (hereinafter simply referred to as an induction motor) for driving a hot rolling facility, for example, for carrying materials having greatly different sizes and for use in different operations. The present invention relates to the control of an induction motor that drives mechanical equipment such as a table roller or a pinch roll in which the load fluctuates widely and intermittently, and more particularly to improvement of a control device that vector-controls this induction motor.

[0002]

2. Description of the Related Art In a conventional induction motor control device using vector control, when the base speed is lower than the rated motor speed,
Regardless of the size of the load, the field current component is controlled to a constant value at the base velocity.

Therefore, a large output torque is not required during normal operation, but in the case of mechanical equipment that rarely requires a large output torque in a low speed range depending on the form of operation and the type of material, the equipment has a low speed. Even in the range, it had to be controlled so that a large torque could always be output. That is, even if a large torque is not required in the low speed range, which is almost the case in normal operation, a large, useless field current must always be supplied.

For example, when performing field weakening control in order to output a large torque in a low speed range, which is conventionally performed,
In some motors, the rated current ratio exceeds 40% when the exciting current component is large at a speed lower than the base speed of the induction motor.

[0005]

As described above, although a large torque is not required in the normal operation, the conventional induction motor control device applied to mechanical equipment which should output a large torque rarely outputs a large torque. Even in the rare cases where it should be done, unnecessary current was forced to flow through the electric motor all the time, resulting in a large power loss.

The present invention has been made in order to solve the above-mentioned problems, and the normal operation is performed by controlling the field to be strengthened only when the load requires a large torque below the base speed of the motor. It is an object of the present invention to provide a control device for an induction motor that can reduce the time magnetic field, and thereby can significantly reduce power loss as compared with the case of outputting a required torque without strengthening the field.

[0007]

In order to achieve the above object, the control device for an induction motor according to claim 1 has a field current component determined to be proportional to the field current reference and a torque current reference. And a torque current component determined to be inversely proportional to the field current reference are vector-synthesized, and a phase current corresponding to the combined vector is applied to each phase of the induction motor to control the induction motor at a variable speed. A correction command means for outputting a correction command for the field current reference when the electric motor is operated to output a large torque, and a field magnet for increasing and correcting the field current reference by a predetermined amount when the correction command is output. Reference correction means.

In the induction motor controller according to the second aspect of the present invention, the field current component determined to be proportional to the field current reference and the torque current reference to the field current component are determined to be inversely proportional to the field current reference. When the torque current component is vector-synthesized and a phase current corresponding to the synthesized vector is caused to flow in each phase of the induction motor to control the induction motor at a variable speed, when the induction motor is operated to output a large torque, The correction command means outputs a correction command for a plurality of field current references of different types according to the load state, and a means for setting an increase rate for increasing the field current reference in a plurality of stages, respectively. When a correction command is output from the command means, a field base that selects a larger increase rate for a command corresponding to a heavier load, and increases and corrects the field current reference according to the selected increase rate. And a correction means.

Further, in the control device for the induction motor according to the third aspect, the field reference correction means includes a rate unit for suppressing the time change rate of the field current reference to a predetermined value or less when increasing the field current reference. .

[0010]

As is well known, when two components that are inversely proportional to each other are created and these components are vector-synthesized, the combined vector is small if the two components are similar values, and if the two components are distant values. The combined vector becomes large.
In vector control of an induction motor, when combining a field current component determined to be proportional to the field current reference and a torque current component determined to be proportional to the torque current reference and inversely proportional to the field current reference, It has a similar relationship to this.

Conventionally, since a field current reference having a magnitude capable of outputting a large torque is used even when the output torque is small, a large field current component and a small torque current component are combined, so that the combined vector is large. A large electric current was being sent to the electric motor.

However, in the control device for the induction motor according to the first aspect, when the induction motor is operated so as to output a large torque, the field current reference is increased and corrected by a predetermined amount, but only a small torque is applied. When no output is made, the field current reference is kept small. The torque current component increases by keeping the field current reference small when only a small torque is output, but the torque current component does not increase so much because the output torque is originally small. The values are similar to those of the components. As a result, the field current in the low speed range during the normal operation that does not require a large torque can be reduced, and the power loss can also be suppressed low.

In the control device for the induction motor according to the second aspect, the field current reference is increased and corrected according to the increasing rate of the value as the load increases, so that the fine control can be performed in order to suppress the power loss. Is possible.

In the induction motor control apparatus according to the third aspect of the present invention, when the field current reference is increased and corrected, the rate of change with time is suppressed to a predetermined value or less and correction is performed. Therefore, disturbance is given to the control of the induction motor. Can be prevented.

[0015]

The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of a control device for an induction motor according to the present invention. In the figure, the induction motor 11 drives mechanical equipment which has a low frequency but needs to output a large torque. The main circuit of the induction motor 11 is provided with a converter 13 which is connected to the three-phase AC power source 12 and supplies each phase current corresponding to a combined vector obtained by vector combining the torque current component and the field current component. . Speed control circuit 14
Inputs the speed reference from the host controller 15 which is a computer through the input circuit 16 which performs signal level conversion and the like, and also inputs the speed detection signal of the speed detector 17 which detects the rotation speed of the induction motor 11. Then, the deviation is calculated, and the deviation is amplified and output as a torque current reference. The field reference circuit 18 is the induction motor 1
The speed detection signal of the speed detector 17 for detecting the rotational speed of 1 is input, and the field current reference corresponding to the detected speed is output.

The field reference correction circuit 19 comprises a field reference correction setting circuit 20, a field reference correction switching circuit 21, a multiplier 22 and a rate circuit 23. Among these, the field reference correction setting circuit 20 outputs the field current reference output from the field reference circuit 18 as it is.
And an increase rate K for increasing the field current reference at a preset ratio are set, and the field reference correction switching circuit 21 increases according to the field reference correction command input through the input circuit 16. The rate 1 is switched to the increase rate K and added to the multiplier 22, and the multiplier 22 multiplies the field current reference output from the field reference circuit 18 by the increase rate 1 or K and outputs the result. The rate circuit 23 suppresses the rate of change to a predetermined value or less so as not to disturb the control of the induction motor when the field current reference is switched.

On the other hand, the host controller 15 determines the output torque required for the induction motor 11 according to the operation schedule of the load and outputs a correction command for the field current reference when the load is large and the output torque of the induction motor 11 is increased. The correction command means 151 is provided. The correction command means 151 can be realized by a relatively simple logic. For example, the controller that manages the facility operation schedule receives information that enables the load schedule or the load of the induction motor 11 to be determined, and the host controller 15 can control the induction motor. It is determined whether a large torque is required or a small torque is required, or the signal of the presence detector in the host controller 15 itself is taken in,
Determine whether a large torque is required.If a large torque is required, issue a command to utilize the increase rate that corrects the field reference.In the case where a large torque is not required, an increase rate is issued. This can be realized by the logic of issuing a command that does not utilize.

On the other hand, the vector control section 24 includes a torque current reference output from the speed control circuit 14, a field current reference output from the field reference correction circuit 19, and a speed detector 17.
The rotational speed detection signal of the induction motor 11 detected by is input, and the field current component proportional to the field current reference and the torque current component proportional to the torque current reference divided by the field current reference, that is, , A torque current component determined to be proportional to the torque current reference and inversely proportional to the field current reference is vector-combined, and has an amplitude corresponding to the composite vector,
Each phase current command is given to the converter 13 by using the detection signal of the speed detector 17 as a phase signal.

Next, the operation of the induction motor controller configured as described above will be described. Now, assuming that the higher-order controller 15 determines that the induction motor 11 does not require a large torque, the switching circuit of the field reference correction circuit 19 from the correction command means 151 in the higher-order controller 15 through the input circuit 16. The logic signal input to 21 is “0” (the increase rate K is not used).

In such a state, the switching circuit 2
The increase rate 1 of the field reference correction setting circuit 6 is selected by 1, and the increase rate 1 and the field current reference output from the field reference circuit 18 are multiplied by the multiplier 22, and vector control is performed through the rate circuit 23. Added to section 24. That is, the field current reference of the field reference circuit 18 is directly applied to the vector control unit 24.

In the vector control unit 24, the speed control circuit 14
Torque current reference and field reference correction circuit 19 input from
As shown in FIG. 2B, based on the field current reference input from the torque current component i proportional to the torque current reference i
and _q, with obtaining a field current component i _d which is inversely proportional to proportional to field磁転flow reference to the torque current reference, determine the combined current i _T These were vector synthesis, further combined current i _T
Is an amplitude signal, and the rotation speed detection signal of the induction motor 11 input from the rotation speed detector 17 is used as a phase signal to give a sine wave phase current command to the converter 13. Controlled according to.

Next, the host controller 15 determines that the induction motor 11 requires a large torque, and the host controller 15 inputs the logic signal "1" (increase rate) to the switching circuit 21 of the field reference correction circuit 19 through the input circuit 16. (Use K) is input, the switching circuit 21 selects the increase rate K and adds it to the multiplier 22.

The multiplier 22 multiplies the field current reference applied from the field reference circuit 18 by the rate of increase K to increase the field current reference at a preset ratio, and the vector control is performed through the rate circuit 23. Added to section 24.

The vector control section 24 is shown in FIG. 2A based on the torque current reference input from the speed control circuit 14 and the field current reference input from the field reference correction circuit 19 as described above. As described above, a torque current component i _q proportional to the torque current reference and a field current component i _d proportional to the torque current reference and inversely proportional to the field current reference are obtained, and these are vector-synthesized to generate a combined current i _T. Then, the combined current i _T is used as an amplitude signal, and the rotation speed detection signal of the induction motor 11 input from the rotation speed detector 17 is used as a phase signal to give a sinusoidal phase current command to the converter 13, The current of the electric motor 11 is controlled according to the size of the load.

[0025] In case of FIG. 2 (c) is small output torque, the field current component i _d in the prior art, the torque current component i
_This shows the relationship with _q, and the field current component i _d corresponds to that when the output torque is large, and the torque current component i _q decreases in inverse proportion to this. When (b) and (c) are compared, in the control of the present embodiment, the combined current i _T is obtained with the small field current component i _d and the relatively large torque current i _q , whereas In the above control, the combined current i _T is obtained by the large field current component i _d and the small torque current component i _q during normal operation. Therefore, when the combined current i _T is compared, the current according to the present embodiment shown in (b) is obviously smaller than that according to the conventional one shown in (c). As a result, the power loss of the induction motor can be suppressed low.

Thus, according to this embodiment, when the induction motor is operated with a large torque output, the input circuit 1
The field current reference is increased according to the command from 6 and this is added to the vector control unit 24 so that a predetermined torque output can be obtained. Therefore, during a normal operation in which a large torque output is not required, a predetermined combined current is used. Therefore, the power loss can be suppressed to a low level as compared with the case where the required torque is output without strengthening the field.

In the above embodiment, the field reference correction circuit 1 is used.
9 is provided with the field reference correction circuit 20 capable of switching from the increase rate 1 to the increase rate K. However, a plurality of increase rates having different values are provided, and the increase rate to be used according to a command from the host controller 15 is set. It is also possible to adopt a configuration of selection.

With such a structure, the load is large,
When it is necessary to increase the output torque of the induction motor, the combined current flowing in the main circuit of the induction motor 11 can be reduced in a plurality of steps and reduced, and fine control can be performed.

Further, the field reference correction circuit 19 is provided with a plurality of different field reference correction values without providing the field reference correction setting circuit 20, the switching circuit 21 and the multiplier 22, and the induction motor 1
When the output torque of No. 1 is increased, these field reference correction values may be selected to control the combined current flowing in the main circuit of the induction motor 11 in a plurality of patterns.

With this structure, fine control can be performed in the same manner as described above, and the field reference correction circuit 19 can be used.
The configuration of can be simplified.

Further, in the above embodiment, the field reference correction setting circuit 20 having a preset increase rate is provided and switching is performed by the switching command signal from the correction command means 151. Even if the host controller 15 gives the increase rate itself to the output field current reference value as a digital or analog signal, fine control can be performed. In this case, it is needless to say that it is necessary to take measures such as having a limit value of the highest field reference in the control device so that the field reference does not become excessive and to prevent the field reference from changing abruptly. .

[0032]

As described above, according to the present invention, in the low speed region of the induction motor, a large torque is not required during normal operation, but the field current of the induction motor is rarely output under a load condition in which a large torque is output. Since it has a function that can be dealt with by increasing the power consumption, it is possible to reduce power loss during normal operation and contribute to energy saving of power.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a control device for an induction motor according to the present invention.

FIG. 2 is a vector diagram showing a main circuit current component of the induction motor for explaining the operation of the embodiment.

[Explanation of symbols]

 11 Three-Phase AC Induction Motor 12 Three-Phase AC Power Supply 13 Converter 14 Speed Control Circuit 15 Upper Controller 16 Input Circuit 17 Speed Detector 18 Field Reference Circuit 19 Field Reference Correction Circuit 20 Field Reference Correction Setting Circuit 21 Switching Circuit 22 Multiplier 23 Rate circuit 24 Vector control unit 151 Correction command means

Claims (3)

[Claims] 1. A vector combination of a field current component determined to be proportional to a field current reference and a torque current component determined to be proportional to a torque current reference and inversely proportional to a field current reference, and a combined vector. In a control device for an induction motor, in which a phase current corresponding to is passed through each phase of the induction motor to control the induction motor at a variable speed, when the induction motor is operated to output a large torque, a field current reference Control of an induction motor, comprising: a correction command unit that outputs a correction command; and a field reference correction unit that corrects the field current reference by a predetermined amount when the correction command is output. apparatus. 2. A field current component determined to be proportional to the field current reference and a torque current component determined to be proportional to the torque current reference and inversely proportional to the field current reference are vector-combined to obtain a combined vector. In a control device for an induction motor, in which a phase current corresponding to is passed through each phase of the induction motor to control the induction motor at a variable speed, when the induction motor is operated to output a large torque, depending on the load state. The correction command means includes a correction command means for outputting a correction command for a plurality of different field current references, and a means for setting an increase rate for increasing and correcting the field current reference in a plurality of stages. When a correction command is output, a field reference that increases the value of the command corresponding to a heavier load, and increases and corrects the field current reference according to the selected increase rate. Control for an induction motor for a positive means, comprising the. 3. The field reference correction means comprises a rate section for suppressing a time change rate of the field current reference to a predetermined value or less when increasing the field current reference.
The control device for the induction motor according to [1].