JPH0568199B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Prior Art This invention relates to an induction motor speed control device using an inverter circuit.

(b) Prior Art For example, glass fibers are formed by drawing molten glass from a mold with holes of a certain diameter. The glass fiber is wound onto a drum by driving the drum with an induction motor whose speed is controlled by an inverter circuit. Therefore, since it is required that the variation in the wire diameter of the glass fiber be extremely small, the glass fiber must be wound at a constant linear speed. However, as the winding progresses, the diameter of the package wound on the drum increases.
The rotational speed of the induction motor is changed accordingly.

Conventionally, the speed control of this type of induction motor involves detecting the deviation between the actual rotation speed and the set rotation speed, and giving a speed control command proportional to this deviation to the inverter circuit to control the speed due to load fluctuations, voltage fluctuations, temperature fluctuations, etc. Controls motor speed fluctuations. Furthermore, in recent years, speed control of induction motors is often performed digitally in order to easily change the set rotation speed. So-called PID is used to control the speed of such induction motors.
(Proprotional integral derivative) control is used.

However, when this type of control method is used, there is a problem that the control system becomes complicated because the constants of each element of PID control differ depending on the nature of the load.

Assuming that the reference signal corresponding to the set rotational speed is V1, the detected signal of the measured rotational speed is V2, and the speed command signal issued one step before is V3', V3 = V3' +
When the speed command signal V3 calculated by (V1 - V2) or V3 = (V3'/V2) x V1 is given to the inverter circuit, the speed command signal V3 becomes the rotation speed detection signal as shown in Fig. Since a large phase delay occurs with respect to V2, if there is a large difference between the reference signal V1 and the detection signal V2, a problem arises in that the so-called hunting phenomenon, in which the rotational speed changes periodically, increases.

On the other hand, the speed control command V3 is set to V3=V1+(V1
−V2). However, this method has the problem that only half the rotation speed can be guaranteed against the rotation speed difference caused by motor slippage. This will be explained in detail below. Now, the reference rotation speed is 3600 rpm, and the actual rotation speed is
Suppose that the motor is 3550 rpm and the speed control command V3 is 3650 rpm, so the motor slips at 100 rpm. In this case, according to the above equation, a speed command signal of 3650 rpm is output. As a result, the rotation speed of the induction motor becomes stable at 3550 rpm. In other words, for a slippage of 100rpm, half of the slippage, 50rpm, is guaranteed.

(C) Purpose The purpose of the present invention is to provide a speed control device for an induction motor that uses a relatively simple control method, has excellent transient response, and can accurately guarantee against motor slippage. .

(d) Configuration The induction motor control device according to the first invention calculates V3=V3 based on the reference signal V1 corresponding to the reference rotation speed of the motor and the detection signal V2 obtained by detecting the rotation speed of the motor. V1+(V1−V2)×2
The present invention is characterized in that the speed command signal V3 calculated by is given to an inverter circuit that controls the speed of the induction motor.

On the other hand, when the difference between the reference signal V1 and the detection signal V2 is larger than a predetermined reference value, the induction motor control device according to the second invention calculates the speed calculated in the same manner as in the first invention. A command signal V3 is given to the inverter circuit. When the difference between the reference signal V1 and the detection signal V2 is smaller than the reference value, a speed command signal V3 calculated based on the previously given speed command V3' is given to the inverter circuit.

(e) Embodiment FIG. 1 is a block diagram schematically showing the configuration of an induction motor speed control device according to an embodiment of the first invention.

Reference numeral 1 indicates an induction motor whose speed is controlled by an inverter circuit 2. 3 is a rotation speed detector for detecting the rotation speed of the induction motor 1; 4 is a pulse counter to which the output of the rotation speed detector 3 is applied. 5 is a reference signal V corresponding to the reference rotation speed of the induction motor 1;
This is a reference rotation speed generator that generates 1.

6 receives the reference signal V1 from the reference rotation speed generator 5;
These are arithmetic units that are each given a rotational speed detection signal V2 from the pulse counter 4 and output a speed command signal V3. This arithmetic unit 6 receives the applied signal V
1 and V2, V3=V1+(V1−V2)×
The arithmetic unit 6 that calculates the speed command signal V3 from the relational expression 2 is composed of, for example, a microcomputer.

Reference numeral 7 denotes a D/A converter that converts the speed command signal V3 as a digital signal given from the computing unit 6 into an analog signal and supplies it to the inverter circuit 2.

Next, the operation of the induction motor speed control device shown in FIG. 1 will be explained.

Now, suppose that the measured rotational speed becomes 3500rpm due to a slip of 100rpm with respect to the reference rotational speed of 3600rpm as described above, and these rotational speeds are given to the calculator 6 as signals V1 and V2. Since the arithmetic unit 6 uses twice the deviation between the signals V1 and V2 as the correction value, the slip is accurately guaranteed. In addition, the speed command signal V3
is calculated by adding the correction value to the reference signal V1, so the speed command signal V
There is no time delay between V.3 and the detection signal V2.

Next, a speed control device for an induction motor according to a second invention will be explained.

As mentioned above, since the control device according to the first invention uses twice the deviation between the reference signal V1 and the detection signal V2 as the correction value, the rotation speed may be affected by causes other than the decrease in rotation speed due to motor slip, such as rotation due to an increase in the temperature of the inverter. If the number decreases, there is a risk that hunting may occur in the motor.

The second invention has been made to prevent such hunting phenomenon. The configuration of this embodiment will be explained below with reference to FIG.

FIG. 3 shows the flow of processing in the microcomputer constituting the arithmetic unit 6 mentioned above. That is, after sampling the rotation speed in step S1, the difference between the reference signal V1 and the detection signal V2 and the reference value are determined in step S2.
A comparison with V0 is made.

If V1-V2 is larger than the reference value V0, the process moves to step S3, where V3=V1+
An arithmetic process of (V1-V2)×2 is performed. After step 3 is completed, the process returns to step S1.

On the other hand, if it is determined in step S2 that V1-V2 is smaller than the reference value V0, the process moves from step S2 to step S4. Step S
4, the speed command V3 calculated by V3=V3'+(V1-V2) is obtained. Here V
3' indicates the speed command signal output in the previous step. After step S4 is completed, the process returns to step S1.

In this way, when the deviation between the reference signal V1 and the detection signal V2 is small, the next speed command signal V3 is generated based on the speed command signal V3' given in the previous step.
Since the motor is calculated, hunting phenomenon of the motor can be prevented.

In the above embodiment, the number of revolutions of the induction motor 1 is counted by the number of revolutions detector 3, and this is supplied to the calculator 6 via the pulse counter 4. However, the means for detecting the number of revolutions of the motor is not limited to the above-mentioned one, and for example, the number of revolutions of the motor can be determined by measuring the time required for one revolution of the motor and taking the reciprocal of this time. Of course it's a good thing.

Furthermore, in the explanation of FIG. 1, it has been explained that the arithmetic unit 6 performs digital processing using a microcomputer. However, this arithmetic processing may be performed by analog processing.

Further, in the second invention, for example, when the motor is started or when the speed setting of the motor is changed, the process may unconditionally proceed to step S4 shown in FIG. This is because in such a case, there is no need to determine the deviation between the reference signal V1 and the detection signal V2, and the difference is already larger than the reference value V0.

Furthermore, in the description of the second invention, the reference signal V
1 and the detection signal V2 becomes smaller than the reference value, the speed command signal V3 is changed to V3=V3'+
It has been explained that it is calculated by (V1-V2). However, the present invention is not limited to this, and the speed command signal V3 may be calculated from V3=(V3'/V2)×V1. Further, the speed command signal V3 may be a value proportional to the results calculated by each of the above equations.

(f) Effect The speed control device for an induction motor according to the first aspect of the invention uses the reference signal V1 corresponding to the reference rotational speed of the motor and the detection signal V2 obtained by detecting the rotational speed of the motor to =V1+(V1−V2)
The speed of the induction motor is controlled by giving the speed command signal V3 calculated by x2 to the inverter circuit.

Therefore, according to the present invention, speed control can be performed using a relatively simple method. In addition, unlike conventional control, hunting does not occur when the deviation between the reference signal V1 and the detection signal V2 becomes large, so the motor rotation speed can be adjusted to the reference rotation speed more quickly than with conventional devices. It can be reinstated.

Further, in the induction motor speed control device according to the second invention, when the difference between the reference signal V1 and the detection signal V2 is larger than a predetermined reference value, V3=V1+(V1−V2)×2. The calculated speed command signal V3 is given to the inverter circuit, and if the difference between the two signals is smaller than the reference value, the speed command signal V3 calculated based on the previously given speed command V3' is given to the inverter circuit. giving.

Therefore, according to the present invention, the hunting phenomenon of the motor can be prevented even when the difference between the reference signal V1 and the detection signal V2 is small, so speed control with fast transient response can be performed regardless of the magnitude of the deviation. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing the configuration of a speed control device for an induction motor according to an embodiment of the first invention, FIG. 2 is an explanatory diagram of the operation of the speed control device shown in FIG. 1, and FIG. FIG. 4 is an explanatory diagram of the operation of the embodiment according to the second invention, and FIG. 4 is an explanatory diagram of the operation of the conventional speed control device. DESCRIPTION OF SYMBOLS 1...Induction motor, 2...Inverter circuit, 3...Rotation speed detector, 5...Reference rotation speed generator, 6...Arithmetic unit.

Claims (1)

[Claims] 1. An inverter circuit that drives an induction motor, and a reference signal V corresponding to a reference rotation speed of the motor.
1; a rotational speed detection means that detects the rotational speed of the motor and provides a detection signal V2; and given the reference signal V1 and the detection signal V2, V3=V1+(V1-V2). 1. A speed control device for an induction motor, comprising: arithmetic means for supplying a speed command signal V3 calculated by x2 to the inverter circuit. 2. An inverter circuit that drives an induction motor, and a reference signal V corresponding to the reference rotation speed of the motor.
1; a rotational speed detection means that detects the rotational speed of the motor and provides a detection signal V2; and compares the difference between the reference signal V1 and the detection signal V2 with a predetermined reference value. a comparison means, when the difference between the reference signal V1 and the detection signal V2 is larger than the reference value, V3=V1+(V1−
V2)×2 is given to the inverter circuit, and when the difference between the reference signal V1 and the detection signal V2 is smaller than the reference value, the speed command signal V3 calculated by A speed control device for an induction motor, comprising: arithmetic means for providing a speed command signal V3 calculated by the inverter circuit to the inverter circuit.