JPH053235B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to speed control of an induction motor, and in particular to a motor that controls the speed of a shade removal motor by controlling the firing angle.

[Conventional technology]

In general, when the firing angle of a shade removal motor is changed using phase control, there is an angle at which the speed changes rapidly, and when the applied voltage of the shade removal motor changes, the speed of the shade removal motor changes rapidly.
Speed control by changing the firing angle has been considered difficult except for very rough control.

This invention makes it possible to control the speed of a shade removal motor by changing the firing angle.

FIG. 1 shows the relationship between the phase angle for starting an induction motor and its speed. In FIG. 1, in phase angle range 1, the speed of the induction motor hardly changes, and in phase angle range 2, the speed of the induction motor changes rapidly. Therefore, in the phase angle range 2, there is a problem in that a small error in setting the phase angle can cause a large error in the speed of the induction motor.

Figure 2 shows the relationship between the voltage applied to the induction motor and its speed. In Figure 2, the applied voltage range 3
In , the speed of the induction motor hardly changes, and in the applied voltage range 4, the speed of the induction motor changes rapidly. Further, when the cut of the applied voltage by phase angle control and the fluctuation of the applied voltage before the cut overlap, the speed of the induction motor changes rapidly due to the fluctuation of the applied voltage before the cut. In particular, when the speed of the induction motor decreases, there is a problem that it seriously affects equipment using the induction motor.

For example, when an induction motor is used to drive a fan that supplies combustion air for a combustion device,
If the speed of the induction motor decreases too much, even momentarily, the combustion device will stop combustion, and even if the speed of the induction motor increases again, the combustion device will not be able to start combustion, and unburned gas will be released. etc.

In order to compensate the speed of the induction motor for variations in the applied voltage to the induction motor, there is immediate processing using electronic circuitry or by means of computer interrupts. However, when a microcomputer is used as a control means, the interrupt function is limited and immediate processing is difficult.

[Summary of the invention]

This invention has been made to solve these problems, and includes a speed control device for an induction motor that performs speed control by changing the firing angle. Measure the actual speed consisting of the average speed of the induction motor up to the end point, set the firing angle based on the control target speed and the actual speed at the starting point of the next cycle, and set the firing angle based on the control target speed and the actual speed for the next cycle up to the end point. A phase control circuit is provided which controls the drive circuit with the firing angle and repeats the control at a constant cycle, and during the control operation by this phase control circuit, the voltage applied to the induction motor increases during the constant cycle. If the firing angle decreases again, the firing angle of the next cycle should be the same as the firing angle of the previous cycle, or the firing angle should be set by the phase control circuit on the basis of the control target speed and the actual measurement. By setting within the range between the firing angle and the previous firing angle, it is possible to perform speed control that emphasizes speed stability rather than speed responsiveness, and it also prevents power supply voltage fluctuations in which the applied voltage temporarily rises and falls. This prevents the speed from decreasing even if there is a problem.

[Embodiments of the invention]

The principle of speed control of an induction motor according to the present invention will be explained with reference to FIG.

In Figure 3, the time widths T ₁ , T ₂ , and T ₃ are the same time width, that is, the respective time widths are T ₁₁ , T ₁₂ ,
Divide into T ₂₁ and T ₂₂ , T ₃₁ and T ₃₂ . The divided time widths T ₁₁ , T ₂₁ , T ₃₁ are equal, and the time widths T ₁₂ ,
T ₂₂ and T ₃₂ are equal. When the firing angle is set at time t ₁ , the time width T ₁ drives the induction motor at the firing angle set at time t ₁ . Even if a value different from the firing angle before t ₁ is set at time t ₁ , the induction motor cannot reach the speed according to the firing angle set at time t ₁ during time width T ₁₁ . Therefore, the speed of the induction motor in the time span T ₁₁ is not constant, but is fluctuating.

At the time interval T ₁₂ , the induction motor stabilizes at the speed according to the firing angle set at time t ₁ . Therefore,
The actual speed, which is the average speed of the induction motor in the time width T ₁₂ , that is, from the time when a predetermined time has elapsed from the start point of a certain period to the end point of the period, is measured and compared with the control target speed. The firing angle of the time width T ₂ that is a cycle is set to time t ₂ that is the starting point of the next cycle. Similarly, the speed is not measured during time periods T ₂₁ and T ₃₁ when the speed of the induction motor is not constant, that is, when it is not stable, but at times t _{2 and} t 31.
Measure the speed of the induction motor during the time interval T ₂₂ and T ₃₂ when the speed has settled down to the firing angle set at t ₃ ,
The firing angle that approaches the control target speed is set at times _t3 and _t4 .

At this time, if the voltage applied to the induction motor, that is, the power supply voltage, is constant, the speed of the induction motor can be controlled without slowing down too much, but if the power supply voltage fluctuates, the speed of the induction motor cannot be controlled by the above control measurements may vary and the speed of the induction motor may become too slow. In other words, when the power supply voltage decreases, the firing phase angle can be quickly increased to prevent the induction motor from becoming too slow, but when the power supply voltage increases, the induction motor speed becomes too fast, and the , if the firing phase angle is delayed, there is a risk that the speed of the induction motor will become too slow. Therefore, when the power supply voltage increases, it is preferable not to change the ignition phase angle.

To illustrate with Figure 3, if the power supply voltage increases at time t ₅ , the speed of the induction motor in time interval T ₁₂ increases, and the new firing angle setting value at time t ₂ becomes lower than the previous value. You can gradually reduce the speed of the induction motor. If the power supply voltage rises at time t ₅ and falls at t ₆ , which is within the time T ₁ , the speed of the induction motor in the time span T ₁₂ will increase, and the speed data will be compared with the control target speed to determine the speed at time t 6. t ₂
If a new firing angle is set to delay the firing angle, the power supply voltage has already decreased and the speed has returned to the original speed in the time width T ₂ , so the new firing angle value is too slow and the induction The speed of the electric motor will decrease.

On the other hand, if the power supply voltage rises at time t ₅ and falls at time t ₆ , the voltage after the fall will be at time t ₅ .
If the firing angle is increased when the voltage is higher than the previous voltage, assuming that the power supply voltage has decreased, the speed of the induction motor will be too high. Furthermore, if the power supply voltage rises at time t ₅ and falls at time t ₆ , if the voltage after the drop is lower than the voltage before time t ₅ , it is assumed that the power supply voltage has decreased, and It is also possible to accelerate the firing angle at t ₆ . However, in this invention, since the firing angle is set by comparing the target speed and the actual speed only once every fixed period, the firing angle is set _{only once} every fixed period.
If the supply voltage increases at time t 6 and drops at time t ₆ , if the voltage after the drop is the same or higher than the voltage before time t ₅ , then when setting a new firing angle at time t ₂ , the time width Instead of setting the new firing angle based on the actual speed of the induction motor 11 at T ₁₂ , the new firing angle should be the same as the firing angle determined at t ₁ or different from the firing angle determined at t ₁ . Set the firing angle that minimizes the difference. That is, the firing angle should be the same as that determined in t ₁ , or
Or control when the power supply voltage does not change, that is, the change in firing angle is made smaller than in normal control. By doing this, it is possible to stably control the speed by changing the firing angle of the induction motor,
Moreover, without directly changing the firing angle due to fluctuations in the power supply voltage, even if there is a fluctuation in the power supply voltage that temporarily increases and then decreases, the speed can be controlled without reducing the speed too much.

Note that, as shown in FIG. 3, the power supply voltage changes at time t ₅
When it continues to rise until the time width T ₂ ,
As mentioned above, the measured data of the speed increased due to the rise in power supply voltage is compared with the control target speed to determine the speed at time t ₂ .
Set the new firing angle with .

By the way, there are various methods of measuring the rotational speed of an induction motor, and an example of a method of measuring using a sensor is shown in FIG. 4. Figure a is a side view of the main part, and Figure b is a front view of the main part. In other words, as shown in the figure, a disc 7 with a notch cut into the shaft 6 of the induction motor.
The number of rotations of the induction motor can be measured by attaching the cutout on the disc 7, detecting the cut in the disc 7 with the photo interrupter 8, and counting the number of cuts. The speed of the induction motor can be measured by measuring the rotational speed.

Next, a circuit configuration diagram using a microcomputer according to an embodiment of the present invention is shown in FIG.

In the figure, signal A is a full-wave rectified commercial frequency power supply.The waveform is shaped by the zero point detection circuit, and the microcomputer 5 detects the moment when the voltage is zero, that is, the moment when the phase of the power supply is zero. I'm telling you. The microcomputer 5 accepts this instantaneous signal of zero phase as an interrupt signal. The signal B, which is the rotational speed signal of the induction motor, is shaped into a waveform by a waveform shaping circuit and then transmitted to the microcomputer 5. Note that the signal C is a signal for specifying the speed of the induction motor, and is composed of a volume 9 and the like. Further, in the microcomputer 5, a timer can be constructed using a timer built into the microcomputer or a frequency signal from a power supply.

By the way, the microcomputer 5 receives the signal C
is input, the signal B is counted, the speeds are compared, and the phase is delayed by the phase determined from the timing of the signal A, and the signal D is output. and,
The output signal D is transmitted to a drive circuit for the induction motor 11, which includes a solid state relay 10, and controls the firing angle of the induction motor 11.

Further, the signal E is a signal representing the magnitude of the power supply voltage, and is input to the microcomputer 5. The microcomputer 5 constantly monitors the magnitude of the signal E, and can take measures if the power supply voltage rises and immediately stops.

Note that the counting of signal B is performed by the microcomputer 5, and since the speed is unstable for a certain period of time from the time the firing angle is changed, the counting of signal B is not carried out, but after a certain period of time when the speed becomes stable. The signal B is counted and the speed of the induction motor 11 is detected.

A flowchart of the program of the microcomputer 5 used at this time is shown in FIG.

That is, the microcomputer 5 first sets an initial firing angle 12, determines 13 whether a certain period of time, in this case two seconds, has elapsed, and waits until the two seconds have elapsed. After 2 seconds have elapsed, the number of rotations of the induction motor is counted for the next 4 seconds to measure the speed of the induction motor 14. Next, a signal specifying the speed of the induction motor is read 15. Next, it is determined 16 whether the power supply voltage has increased and decreased during the above 6 seconds, and if the power supply voltage has increased and decreased, the firing angle is not changed 17, that is, the time t ₁ Set the firing angle to be the same as the firing angle determined in _t1 , or set the firing angle with a smaller difference from the firing angle determined in t1. When the power supply voltage increases and does not decrease, a new firing angle is set 18 from the specified induction motor speed and the measured induction motor speed, and again, judgment 1 when 2 seconds have elapsed.
Return to 3.

〔Effect of the invention〕

As explained above, the present invention measures the actual speed, which is the average speed of the induction motor from the time when a predetermined time has elapsed from the start point of a certain period to the end point of the period, and determines the control target speed at the start point of the next period. A phase control circuit is provided which sets the firing angle based on the firing angle and the actual speed, controls the drive circuit at that firing angle until the end point in the next cycle, and repeats this control at regular intervals. During the control operation by the circuit, if the voltage applied to the induction motor increases during the certain period and then decreases again, the firing angle of the next period is made the same as the firing angle of the immediately preceding period, or Since the firing angle is set within the range between the firing angle set by the phase control circuit based on the control target speed and the actual speed and the immediately preceding firing angle, the power supply voltage rises at one point and then falls. This has the effect that even if there is a fluctuation, a decrease in the speed of the induction motor can be prevented and stable speed control can be performed.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the phase angle for starting an induction motor and its speed, Figure 2 is a diagram showing the relationship between the applied voltage of the induction motor and its speed, and Figure 3 is a diagram showing the relationship between the speed and the phase angle of the induction motor according to the present invention. A diagram for explaining the principle of control, FIG. 4 is a side view and a front view of essential parts showing an example of a speed measuring method, and FIG. 5 is a circuit configuration diagram using a microcomputer according to an embodiment of the present invention. , and FIG. 6 is a flowchart of a microcomputer used in an embodiment of the present invention. In the figure, 1 is the phase angle range, 2 is the phase angle range, 3 is the applied voltage range, 4 is the applied voltage range, 5 is the microcomputer, 6 is the shaft of the induction motor, 7 is the disk, and 8 is the photo interrupter,
9 is the volume, 10 is the solid state relay,
11 is the induction motor, 12 is the setting of the initial firing angle, 13 is the determination whether 2 seconds have elapsed, and 14 is the 4
Processing to count the number of revolutions per second, 15 is processing to read a specified speed signal, 16 is determining whether the power supply voltage has increased and decreased during 6 seconds, 17
18 is a process for not changing the firing angle, and 18 is a process for setting a new firing angle. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a speed control device for an induction motor that performs speed control by changing the firing angle, from the average speed of the induction motor from the time when a predetermined period of time has elapsed from the start point of a certain period to the end point of the period. measuring the actual speed, setting a firing angle based on the control target speed and the actual speed at the starting point of the next cycle, and controlling the drive circuit at the firing angle until the end point of the next cycle; A phase control circuit is provided that repeats the control at regular intervals, and when the voltage applied to the induction motor increases during the constant cycle and then decreases again during the control operation by this phase control circuit, the voltage applied to the induction motor increases in the next cycle. A speed control device for an induction motor, characterized in that the firing angle of the current cycle is the same as the firing angle of the immediately preceding cycle. 2. In a speed control device for an induction motor that performs speed control by changing the firing angle, the actual speed is measured, which is the average speed of the induction motor from the time when a predetermined period of time has elapsed from the start point of a certain period to the end point of the period. , at the starting point of the next cycle, a firing angle is set based on the control target speed and the actual speed, and in the next cycle, the drive circuit is controlled at that firing angle until the end point, and the control is carried out at a constant cycle. A phase control circuit is provided which repeats each cycle, and if during the control operation by this phase control circuit, the voltage applied to the induction motor increases during the certain period and then decreases again, the firing angle of the next period is set as above. A speed control device for an induction motor, characterized in that the firing angle is set within a range between the firing angle set by a phase control circuit and the immediately preceding firing angle based on a control target speed and an actual speed. 3. A patent characterized in that the measurement of the speed of the induction motor, the measurement of the applied voltage of the induction motor, the counting of time, the determination of the firing angle of the induction motor, and the signal output timing of the firing angle are performed by a microcomputer. A speed control device for an induction motor according to claim 1. 4. A patent characterized in that the measurement of the speed of the induction motor, the measurement of the applied voltage of the induction motor, the counting of time, the determination of the firing angle of the induction motor, and the signal output timing of the firing angle are performed by a microcomputer. A speed control device for an induction motor according to claim 2.