JPH05252782A - Speed controller for induction motor - Google Patents

Abstract

PURPOSE:To enhance the precision of a speed control and to stably control a speed. CONSTITUTION:A magnitude of a speed difference of an induction motor 1 with respect to a control precision is judged by drive stopping means 21, and if the difference is smaller than the precision, drive of a liquid resistor 3 is stopped. If the difference is larger than the precision by this judgement, an actual speed is compared with a reference speed by drive stopping means 21. If the actual speed is smaller than the reference speed, the liquid resistor 3 is driven in a direction for accelerating the speed of the motor 1. On the other hand, if the actual speed is larger than the reference speed, the liquid resistor 3 is driven in a direction for decelerating it. After the liquid resistor 3 is driven, drive of the liquid resistor 3 is temporarily stopped by temporary stop means 21, and a magnitude of the difference as to the precision is again judged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to, for example, pump equipment for waterworks and drainage pump equipment in cement factories, and relates to a speed control device for a wire wound induction motor using a liquid resistor (LRH).

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a speed control device for a wound-rotor induction motor (hereinafter referred to as an induction motor). A three-phase AC power supply 2 and a liquid resistor 3 are connected to the induction motor 1. Further, the induction motor 1 is provided with a pulse generator 4, and the pulse generator 4 causes the actual rotation speed of the induction motor 1 (hereinafter referred to as actual speed).
Is detected.

Further, the liquid resistor 3 is constructed so that its resistance value is changed by driving the liquid resistor driving motor 5. The rotation direction of the liquid resistor driving motor 5 changes depending on the direction of the current supplied from the thyristor unit 6.

The actual speed detected by the pulse generator 4 is converted into a voltage signal corresponding to the actual speed by the frequency / voltage (F / V) converter 7 and sent to the speed difference detection circuit 8.

On the other hand, a remote speed reference setter 9 and a local speed reference setter 10 are provided, and the reference speeds set by these speed reference setters 9 and 10 are sent to a speed reference selection circuit 11. In this case, the remote speed reference setter 9 outputs the speed reference as a current signal (4 to 20 mA), and the local speed reference setter 10 outputs the speed reference as a voltage signal.

The speed reference selection circuit 11 receives the switching operation of the remote / local changeover switch 12, selects the speed reference from the remote speed reference setting device 9 or the local speed reference setting device 10, and sends it to the speed difference detection circuit 8. is doing. In this case, the speed reference selection circuit 11 converts the current signal into a voltage signal when selecting the speed reference of the remote speed reference setter 9.

The speed reference and the actual speed are adjusted to a voltage value equivalent to the TOP set value. The speed control is often performed from 70 to 75% of the TOP speed. Therefore, the speed reference selection circuit 11 needs a special adjustment to make the voltage signal sent to the speed difference detection circuit 8 the minimum value of the control range level even if the speed reference is zero.

The speed difference detection circuit 8 compares the speed reference with the actual speed by an operational amplifier and sends the speed difference to the correction direction determination circuit 13. At this time, since the speed reference input to the operational amplifier and the actual speed have opposite polarities, the comparison is made as to which is larger when input to the correction direction determination circuit 13.

The correction direction discriminating circuit 13 discriminates whether or not to correct the speed difference by the relay amplifier and determines the correction direction. In this case, when a speed difference of 4% of the TOP speed appears, the correction is started (pickup) and the correction is ended (dropout) when the speed difference is zero. Then, in the case of correction, the correction direction determination circuit 13 causes each relay 14
Alternatively, 15 is energized to control the firing of the thyristor unit 6. Accordingly, the liquid resistor driving motor 5 is driven, the resistance value of the liquid resistor 3 changes, and the speed of the induction motor 1 is controlled.

By the way, since the correction start value and the correction end value in the correction direction determination circuit 13 are analog adjustments, it takes time to make accurate adjustments. In addition, the speed difference of 4% of the TOP speed is an offset in speed control accuracy. Therefore, although such speed control is simple and inexpensive, the speed characteristic is poor.

Further, as the speed reference approaches the TOP, the curve rises like the motor torque curve shown in FIG. Therefore, the speed control becomes unstable due to the time lag between the corrected speed and the load response (the flow rate of water in the pump facility for waterworks).

[0012]

As described above, since the correction start value and the correction end value are analog adjustments, it takes time to make an accurate adjustment, and a speed difference of 4% of the TOP speed is a speed control accuracy. As an offset. Further, speed control becomes unstable due to the time lag between the correction speed and the load response. Therefore, an object of the present invention is to provide a speed control device for an induction motor, which can improve speed control accuracy and can perform speed control stably.

[0013]

The present invention detects the actual speed of an induction motor and drives a liquid resistance value based on the speed difference between the actual speed and a reference speed to control the speed of the induction motor. In the speed controller of the induction motor,

The magnitude of the speed difference with respect to the control accuracy is judged. If the speed difference is smaller than the control accuracy, the drive stopping means for stopping the driving of the liquid resistor, and if the speed difference is larger than the control accuracy, the actual speed is determined. If the actual speed is lower than the reference speed, the liquid resistor is driven in the direction to accelerate the speed of the induction motor.If the actual speed is higher than the reference speed, the speed of the induction motor is reduced. A speed control device for an induction motor, comprising: a drive unit for driving a liquid resistor; and a temporary stop unit for temporarily stopping the drive of the liquid resistor after acceleration and deceleration by the drive unit. ..

[0015]

By providing such means, the magnitude of the speed difference of the induction motor with respect to the control accuracy is judged by the drive stopping means, and if the speed difference is smaller than the control accuracy, the drive of the liquid resistor is stopped. Further, if the speed difference is larger than the control accuracy by this judgment, the driving means compares the actual speed with the reference speed to judge the speed correction direction. That is,
If the actual speed is lower than the reference speed, the liquid resistor is driven in the direction of accelerating the speed of the induction motor, and if the actual speed is higher than the reference speed, the liquid resistor is driven in the direction of deceleration. After the driving of the liquid resistor, the driving of the liquid resistor is temporarily stopped by the temporary stop means, and the magnitude of the speed difference of the induction motor with respect to the control accuracy is determined again.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The same parts as those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a block diagram of a speed controller for an induction motor. The sequencer 20 includes a CPU arithmetic processing unit 21, a pulse input (PI) board 22, and an analog input (A).
An I) substrate 23, a digital input (DI) substrate 24 and a digital output (DO) substrate 25 are provided.

The pulse generator 4 is connected to the pulse input board 22, and the contacts 26a, 26 of the remote / local changeover switch 26 are connected to the analog input board 23.
The remote speed reference setting device 9 and the local speed reference setting device 10 are connected via b. Of these, the temperature compensation type resistor 27 is connected in parallel to the remote speed reference setting device 9, and the current signal from the remote speed reference setting device 9 is converted into a voltage signal.

One contact 26c of the remote / local changeover switch 26 is connected to the digital input board 24. The thyristor unit 6 is connected to the digital output board 25. The CPU arithmetic processing unit 21 has the following functions.

The magnitude of the speed difference between the actual speed and the reference speed with respect to the control accuracy (hereinafter referred to as a control value) of the induction motor 1 is judged, and if the speed difference is smaller than the control value, the liquid resistor 3 is driven. Drive stop function to stop,

If the speed difference is larger than the control value, a function of comparing the actual speed with the reference speed to correct the speed direction,
That is, if the actual speed is lower than the reference speed, the liquid resistor 3 is driven in the direction to accelerate the speed of the induction motor 1, and if the actual speed is higher than the reference speed, the liquid resistance 3 is decreased in the direction to reduce the speed of the induction motor 1. It has a drive function for driving the resistor 3, and a temporary stop function for temporarily stopping the drive of the liquid resistor 3 after acceleration and deceleration by this drive function. The control value is stored in the register, and 1 RPM of the induction motor 1 is used.
It can be arbitrarily changed up to less than. Next, the operation of the device configured as described above will be described.

The CPU arithmetic processing unit 21 first executes the reading of the speed reference according to the speed reference reading flow chart shown in FIG. In step # 1, the CPU arithmetic processing unit 21 reads the open / closed state of the contact 26c of the remote / local changeover switch 26 through the digital input board 24. If the contact 26c is closed, the speed reference from the remote speed reference setting unit 9 is selected. If it is open, the speed reference from the local speed reference setter 10 is selected. With this choice,
For example, if the contact 26c is open, the CPU arithmetic processing unit 2
1 receives the speed reference from the local speed reference setter 10 through the analog input board 23.

The speed references read from the remote or local speed reference setters 9 and 10 have different values. Therefore, the CPU arithmetic processing unit 21 executes a scaling operation by applying a function generator (FG) to the speed reference taken in the next step # 2.
By this calculation, in step # 3, the speed reference of the same level can be obtained regardless of the speed reference from the remote or local speed reference setters 9 and 10.

Further, the CPU arithmetic processing section 21 executes the reading of the actual speed according to the actual speed reading flow chart shown in FIG. The CPU arithmetic processing unit 21 reads the actual speed from the pulse generator 4 through the pulse input board 22 in step # 10, executes the scaling operation on the actual speed read in the next step 311, and executes the actual speed for control ( The actual control speed) is obtained.

Hereinafter, the CPU arithmetic processing unit 21 executes speed control according to the speed control flowchart shown in FIG. In step # 20, the CPU arithmetic processing unit 21 confirms that the induction motor 1 is in operation, selects the speed reference, and confirms that no failure has occurred. Then, in step # 21, the actual speed and the speed reference are compared. Calculate and find the difference.

Next, the drive stop function of the CPU arithmetic processing unit 21 obtains the absolute value of the speed difference in step # 22, and compares and judges the magnitude of this speed difference and the control value. As a result of this comparison, if the speed difference is smaller than the control value, the CPU arithmetic processing section 21 moves to step # 23 to stop the driving of the liquid resistor 3.

On the other hand, as a result of the comparison between the speed difference and the control value, if the speed difference is larger than the control value, the CPU arithmetic processing unit 21.
Moves to step # 24 to determine the speed correction direction by comparing the actual speed with the reference speed by the drive function. As a result of this comparison, if the actual speed is lower than the reference speed, the CPU calculation processing section 21 moves to step # 25 and issues a command for driving the liquid resistor 3 in the direction of accelerating the speed of the induction motor 1 for only one second. ..

As a result of the comparison, if the actual speed is higher than the reference speed, the CPU arithmetic processing section 21 moves to step # 26, and the liquid resistor 3 in the direction of decelerating the speed of the induction motor 1.
The command to drive is issued for 1 second only. Each command for acceleration and deceleration is issued for 1 second, and these times are stored in the register in advance.

Next, the temporary stop function of the CPU arithmetic processing unit 21 temporarily stops the driving of the liquid resistor 3 in step # 27. The stop time is also stored in the register. As a result, the load response is absorbed and the load following performance is improved. After that, the CPU arithmetic processing section 21 returns to step # 22 again to compare and judge the magnitude of the speed difference and the control value. Then, the CPU arithmetic processing section 21 starts from step # 22.
When # 27 is repeated and the speed difference becomes larger than the control value, the driving of the liquid resistor 3 is stopped.

As described above, in the above embodiment, if the speed difference between the actual speed and the speed reference is smaller than the control value, the driving of the liquid resistor 3 is stopped, and if the speed difference is larger than the control value, From the comparison result of the actual speed and the reference speed, if the actual speed is smaller than the reference speed, the liquid resistor 3 is driven in a direction to accelerate the speed of the induction motor 1, and if the actual speed is larger than the reference speed, the liquid resistor 3 is decelerated. Since the liquid resistor 3 is driven and then the driving of the liquid resistor 3 is temporarily stopped, the speed control for the induction motor 1 is performed by about 1 compared to the conventional case.
It can be improved to 0 times, and in addition, the instability when the speed reference rises and falls can be eliminated, and the influence of the offset of the speed control due to the LRH temperature change can be eliminated. Further, if there are a plurality of induction motors 1 of the same system, a plurality of programs of the CPU arithmetic processing unit 21 may be copied, whereby the control characteristics of the induction motor 1 of each system can be made uniform and the number of adjustment elements can be reduced. Can also contribute. The present invention is not limited to the above-described embodiment, and may be modified without departing from the scope of the invention.

[0031]

As described above in detail, according to the present invention, it is possible to provide a speed control device for an induction motor, which can increase the accuracy of speed control and can stably control the speed.

[Brief description of drawings]

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

FIG. 2 is a flow chart for reading a speed reference in the apparatus.

FIG. 3 is a flowchart for reading the actual speed in the device.

FIG. 4 is a flowchart of speed control in the device.

FIG. 5 is a configuration diagram of a conventional device.

FIG. 6 is a diagram showing a motor torque curve of the device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Induction motor, 3 ... Liquid resistor, 4 ... Pulse generator, 5 ... Liquid resistor driving motor, 6 ... Thyristor unit, 9 ... Remote speed reference setting device, 10 ... Local speed reference setting device, 20 ... Sequencer, 21 ... CPU arithmetic processing unit, 22 ... Pulse input (PI) substrate, 23 ...
Analog input (AI) board, 24 ... Digital input (D
I) substrate, 25 ... Digital output (DO) substrate, 26 ...
Remote / local changeover switch, 27 ... Temperature compensation resistance.

Claims (1)

[Claims] 1. A speed control device for an induction motor, which detects an actual speed of the induction motor and drives a liquid resistance value based on a speed difference between the actual speed and a reference speed to control the speed of the induction motor. The magnitude of the speed difference with respect to the control accuracy is determined, and if the speed difference is smaller than the control accuracy, drive stopping means for stopping the driving of the liquid resistor, and if the speed difference is larger than the control accuracy, The actual speed is compared with the reference speed, and if the actual speed is smaller than the reference speed, the liquid resistor is driven in a direction to accelerate the speed of the induction motor, and the actual speed is higher than the reference speed. Driving means for driving the liquid resistor in a direction to reduce the speed of the induction motor if it is large, and temporary stopping means for temporarily stopping the driving of the liquid resistor after acceleration and deceleration by the driving means. And a speed control device for an induction motor.