JPS62104489A - Speed control method for induction motor - Google Patents

Abstract

PURPOSE:To prevent the occurrence, etc. of an overcurrent by controlling the slip of an induction motor, even if the induction motor is forced to accelerate or deccelerate by an external force. CONSTITUTION:To an arithmetic control circuit 11A, a comparator 1, a slip limit arithmetic unit 2 and an output arithmetic unit 3 are provided. An induction motor 4 is driven by the output arithmetic unit 3. The comparator 1 finds out the difference between the command speed and the rotating speed detected by a speed sensor 5 and the difference thus found is inputted to the slip limit arithmetic unit 2. When the induction motor 4 is forced to accelerate under disturbance, the slip limiting value is enlarged and controls the slip of unit. Thus, the overcurrent can be prevented from flowing to the winding.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to the speed of an induction motor used in a power source for a crane, etc., which stably controls the rotation speed to a target rotation speed without being affected by the presence or absence of load swing. Regarding control method.

[Conventional technology]

FIG. 3 is a block connection diagram showing a speed control device for carrying out a conventional speed control method for an induction motor. In the figure, 11 is an arithmetic control circuit.

An acceleration command f or a deceleration command is given to the induction motor 12, and the current rotation speed of the induction motor 12 is compared with the previous rotation speed, and based on this result, either the current rotation speed or the previous rotation speed is determined. It is determined whether to drive the induction motor 12 based on the output corresponding to the output. 13 is a speed sensor that detects the rotational speed of the induction motor 12. Note that the arithmetic control circuit has a memory that stores the rotational speed detected each time.

Next, the operation will be explained according to the flowchart shown in FIG.

First, the current (current) rotational speed of the induction motor 12 is calculated based on the output of the speed sensor 13 (step Q). Next, the rotation speed command value (target rotation speed) t'' is set, and it is determined whether or not the current rotation is acceleration based on this command value. If so, the current and previous rotational speeds are compared (step O).Here, if it is determined that the current rotational speed is higher than the previous rotational speed.

An output corresponding to the current rotational speed is input to the induction motor 12, and its rotational speed is increased compared to the previous rotational speed.

That is, it accelerates (step O). Next, this current rotational speed is stored in the memory, and is used as the previous rotational speed in the same process as above based on the next rotational speed (step O). Further, in step ◎, if it is determined that the current rotational speed is lower than the previous rotational speed, an output corresponding to the previous rotational speed with a higher rotational speed is input to the induction motor 12 (step O),
Prevent the rotation speed from decreasing. This previous rotation speed is then used as the previous rotation speed in the same process as above based on the first rotation speed (step ◎).
0 Furthermore, if it is determined in step O that the rotation speed is not accelerating, and it is further determined in step O that the rotation speed is decelerating, it is then determined whether the current rotation speed is higher than the previous rotation speed (step [ Yes]). If it is judged to be high here,
Since a high rotational speed cannot be adopted during deceleration, an output corresponding to the previous rotational speed is input to the induction motor 12. Step 0) One rotational speed is prevented from increasing. Then, the previous rotational speed is used again as previous rotational speed data (step O). On the other hand, in step ◎, if it is determined that deceleration is not in progress, it is neither acceleration nor deceleration, so the output corresponding to the current rotational speed is sent to the induction motor 1.
2 (step [phase]).

Then, this current rotational speed is used next time as previous rotational speed data.

[Problem that the invention seeks to solve]

The conventional speed control method for an induction motor is as described above, so when this induction motor is used as a power source for a crane, for example, the O induction motor may be forced to accelerate or decelerate due to load swing. At this time, an overcurrent flows through the primary winding, and if left for a long time, the winding may burn out.

This invention was made to solve the above problems, and even when an external force is applied to the induction motor to force it to accelerate or decelerate, it can prevent overcurrent by controlling the slip of the induction motor. The purpose of the present invention is to provide a speed control method for an induction motor that can completely prevent the occurrence of such problems and safely obtain a target rotational speed.

[Means for solving problems]

A speed control method for an induction motor according to the present invention.

During acceleration control of the induction motor, if the current rotational speed is lower than the previous one, the slip of the induction motor is made smaller than the set value, and if the current rotational speed exceeds the previous one during deceleration control, the slip The induction motors are each controlled at full frequency so as to make the speed larger than the set value.

[Effect]

What is the speed control method of the induction motor according to this invention?

A speed sensor detects the rotation speed of the induction motor.

The difference in rotational speed between the current and previous rotational speed detected in this way is determined, and according to this difference, the rotational speed of the induction motor is controlled so as to reach the target value, thereby effectively preventing the occurrence of overcurrent. .

〔Example〕

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

In FIG. 1, 11 is an arithmetic control circuit as a microprocessor, which is provided with a comparator 1, a limit arithmetic device 2, and an output arithmetic device 3. 4 is an induction motor driven by the output calculation device 3; 5 is a speed sensor for detecting the rotational speed of the induction motor 4; Note that the comparator 1 calculates the difference between the command speed and the rotational speed detected by the speed sensor 5, and inputs the difference to the total υ limit calculation device 2.

Next, the operation will be sequentially explained according to the flowchart shown in FIG.

First, the arithmetic and control circuit 11A reads the rotational speed of the induction motor 4 from the speed sensor 5 each time according to a certain program, and stores it in a memory (not shown) while updating it (step 1). Next, the comparator 1 compares the command speed with the current (current) speed obtained from the speed sensor 5, and determines whether the vehicle is accelerating or decelerating (step 2). If it is accelerating, it is determined whether the current rotational speed is higher than the previous rotational speed (step (step)), and if the current rotational speed is lower than the previous rotational speed, it is forced to It is determined that the vehicle has been decelerated, and the slip limit calculation device 2 makes the slip limit value smaller than a predetermined value (step ■).

If the current rotational speed is higher than the previous one in the step, it is assumed that there is no disturbance, and the besilimint value is held at the set value (step ■).

- 10,000, if it is determined in step (2) that the vehicle is not accelerating, it is determined in step (2) whether or not the vehicle is decelerating.

At this point, it is determined that the vehicle is decelerating.

Furthermore, during this deceleration, it is determined whether or not the current rotational speed is higher than the previous one (step ■).If it is determined that it is higher here, it is determined that the acceleration was forcibly caused by a disturbance. Increase the total 9 limit value (step ■).

However, if the current rotational speed is υ lower than the previous time, it is assumed that there is no disturbance and the vesi limit value is maintained at the set value (step 1).Then, based on this vesi limit value, the output calculation device 3 outputs the The frequency is determined and supplied to the induction motor 4, and the frequency is controlled to a target rotation speed (step 2).

When the induction motor 4 is subjected to a disturbance in this way, it is possible to suppress overcurrent from flowing to the first winding by using the slip rate as an example, and when the disturbance is small, a predetermined slip is maintained and the motor is applied. It is possible to obtain sufficient torque during deceleration.

〔Effect of the invention〕

As described above, according to the present invention, even when the induction motor is forced to accelerate or decelerate due to external factors, the induction motor can be controlled according to the difference between the current rotation speed and the previous rotation speed. As a result, it is possible to stably obtain the target rotation speed without causing overcurrent in the windings, and when external factors are small, sufficient torque can be obtained through normal control. There is an effect that you can get what you can.

[Brief explanation of drawings]

Figure WJ1 is a block connection diagram for carrying out the speed control method for an induction motor according to an embodiment of the present invention, Figure 2 is a flow diagram showing the same speed control operation, and Figure 3 is a conventional speed control method for an induction motor. FIG. 4 is a block connection diagram for implementing the same, and is a flow diagram showing the speed control operation. 1 is a comparator, 2 is a υ limit calculation device, 3 is an output calculation device, 4 is an induction motor, and 5 is a speed controller. Patent Applicant: Mitsubishi Electric Corporation (2 others) Procedural Supplement (Volunteer) 61.9. -5 Showa 1゛, Month 1-1 Special Ba'
40601 No. 2, Name of the invention, Speed control method for induction motor 3, Name of the person making the correction (601) King Electric Machine Ceremony (1 representative R Shiki Mamoru -1k 5, Subject of correction (2) Attachment 6. Contents of the amendment (1) The description will be corrected as follows. 1. 7. A document containing the amended catalog of attached documents in Figure 2. 1 or more copies of Figure 2.

Claims (1)

[Claims] In an induction motor speed control method that performs acceleration control or deceleration control to bring the induction motor to a target rotation speed while comparing the current rotation speed of the induction motor with the previous rotation speed, during the acceleration control If the current rotation speed is lower than the previous rotation speed, the slip of the induction motor is made smaller than the set value, and if the current rotation speed exceeds the previous rotation speed during the deceleration control, the induction motor A method for controlling the speed of an induction motor, characterized in that the frequency of each of the induction motors is controlled so that the slip of the motor is made larger than a set value.