JPH03139191A - Speed controller for induction motor - Google Patents

Abstract

PURPOSE:Te obtain a speed controller for an induction motor which can deal with abrupt drop of rotary speed due to disturbance by providing an instantaneous speed measuring means in addition to an average speed measuring means and controlling the firing angle immediately upon dropping of the instantaneous speed, measured through the instantaneous speed measuring means, below a predetermined level. CONSTITUTION:Instantaneous speed of an induction motor 2 is measured by the use of interrupting function of a microcomputer 5. The microcomputer 5 counts up the time of interruption every time when an interruption signal is received. If the time of interruption is even, a timer 10 is stopped while when the count of the timer 10 exceeds a predetermined value, judgment is made that the speed of the induction motor 2 has dropped and operation for advancing the firing angle is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a speed control device for an induction motor.

[Prior art] As a prior art to this invention, there is a patent application filed by the same applicant as the applicant of the present application entitled "Speed Control Device for Induction Motor" in 1932.
There is a Japanese Patent Application No. 5926471 (Japanese Unexamined Patent Publication No. 174085/1985) filed on February 15, 1989.

FIG. 1 is a block diagram showing an embodiment of the present invention, and the configuration is the same as that of the prior art except for the timer in the microcomputer.The prior art will be explained below based on FIG. 1.

In Fig. 1, (1) is an AC power supply, (2) is an induction motor to be controlled, (3) is a triac (generally speaking, a firing angle control type switching element), (4) is a photocoupler, ( 5) is a microcomputer, (6) is a zero point detection circuit, (7) is a pulse generator, (8) is a waveform shaping circuit, and (9) is a speed setting device consisting of a volume and the like.

The induction motor (2) shown in Figure 1 is a relatively small induction motor, such as the one used in the blower motor of an oil fan heater, and there is no need to change its speed suddenly (the control response does not need to be very fast). However, stable control must be performed.

FIG. 4 is a front view and a side view showing the configuration of the pulse generator (7) shown in FIG. 1. In each figure, (71) is a rotating shaft connected to the rotating shaft of the induction motor (2), ) is a rotating plate, (73) is a light emitting element, (74) is a light receiving element, (
75) indicates notches provided in the rotary plate (72) at every predetermined rotation angle (90 degrees in the example shown).

As shown in FIG. 4, the pulse generator (7) rotates the induction motor (2) to rotate the rotating shaft (71) and the rotating plate (72), and the light emitting element is generated every 90 degrees of rotation. (73) and the light receiving element (74).
5), the light from the light emitting element (73) is received by the light receiving element (74), and the light receiving element (74) generates a pulse. The generated pulses are passed through a waveform shaping circuit (8
), the waveform is shaped, and the microcomputer (5)
is input to.

The zero point detection circuit (6) is for detecting the zero cross point of the AC power source (1), and this zero cross point is the point where the phase of the AC power source (1) is zero, and the triac (3
) is used as the reference phase when controlling the firing of the

FIG. 5 is a diagram showing a cycle of speed measurement and firing angle control in the prior art, where T is the cycle of controlling the triac (3) at a set firing angle, 1, . 1. ．． 1.
. . . indicates the time point at which a new firing angle is set.

Since the period T1 from the firing angle setting time is a transition period in which the speed of the induction motor (2) is changing, the average speed of the induction motor (2) is measured during the period T2 excluding this period.

This average speed is measured by counting the number of pulses output from the pulse generator (7) during time T2.

The microcomputer (5) compares the measured average speed with the set speed set by the speed setting device (9), calculates the error, determines the firing angle that makes the error zero, and sets this firing. The firing of the triac (3) is controlled at the angular moment.

A photocoupler (4) is inserted to electrically isolate the microcomputer (5) and triac (3).

FIG. 6 is a diagram showing the relationship between the phase angle and the speed of the induction motor (2) when the ignition phase angle is controlled by the apparatus shown in FIG.

[Problems to be Solved by the Invention] Since the conventional speed control device for an induction motor as described above is configured as described above, when the rotational speed of the induction motor suddenly decreases due to some kind of disturbance, , there is no means to deal with this.

For example, even if the voltage of the AC power supply suddenly drops and the rotational speed of the induction motor suddenly drops, the
Since control cannot be performed during this period, there is a problem that the induction motor may stall and lead to a major accident, for example, if it is used as a blower motor for an oil fan heater. .

The present invention was made to solve this problem, and an object of the present invention is to provide a speed control device for an induction motor that can cope with a sudden decrease in rotational speed due to disturbance.

[Means for Solving the Problems] The speed control device for an induction motor according to the present invention includes an instantaneous speed measuring means in addition to the average speed measuring means, and the instantaneous speed measured by the instantaneous speed measuring means is equal to or less than a predetermined value. When this happens, the firing angle is immediately controlled.

[Function] In the present invention, the instantaneous speed measuring means is constituted by a second counter that counts how many basic clocks of the microcomputer are included between the periods of pulses generated by the pulse generator, and the instantaneous speed measuring means is If the instantaneous speed measured by the means falls below a predetermined value, the firing angle is immediately controlled and the rotational speed of the induction motor is increased, thereby preventing the induction motor from stalling even in such cases. It becomes possible to do so.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a block diagram showing an embodiment of the present invention. In the figure, <10) indicates a timer in the microcomputer (5), and except for this timer (10), it is the same as the prior art and has already been explained. Although redundant explanation will be omitted here, in this embodiment, the second counter is configured by using the reference clock pulse of the microcomputer (5) or the reference clock pulse and the timer (10). It differs from the prior art in that

FIG. 2 is a waveform diagram for explaining the operation of this embodiment. In FIG. 2, waveform (a) is the output waveform from the waveform shaping circuit (8), and waveform (b) is the gate waveform of the T2 period. (c
) is a waveform obtained by expanding the time of waveform (a), waveform (d) is a gate of time τ according to waveform (c), and waveform (e) is a reference clock pulse of the microcomputer (5).

Similar to the conventional device, the average speed can be measured by counting the number of pulses of waveform (a) that pass through the gate of waveform (b) with the first counter, and the microcomputer (5) can measure the number of pulses of waveform (a) that pass through the gate of waveform (b). By performing the operation, an average speed measuring means can be constructed.

Furthermore, by counting the number of pulses of waveform (e) that pass through the gate of waveform (d), a numerical value corresponding to the reciprocal of the instantaneous velocity can be obtained, and this operation is performed by the microcomputer (5). By this, instantaneous speed measuring means can be constructed.

The average speed obtained by the average speed measuring means is used for feedback control of the rotational speed of the induction motor in the same manner as in the prior art. Further, if the instantaneous speed obtained by the instantaneous speed measuring means falls below a predetermined value, the firing angle is immediately controlled to increase the rotational speed of the induction motor.

Figure 3 shows the above-mentioned operation performed by a microcomputer (5
), 81 to S12 indicate each step, respectively.

For example, in FIG. 5, if T1=2 seconds and T2=4 seconds, an initial firing angle is set in step S1. Then, in step S2, wait until 2 seconds have elapsed, and in the next step S3, pulses output from the pulse generator 7) for 4 seconds are counted to measure the average speed of the induction motor (2). Then, in step S4, the speed setting device (9
), the error between this set speed and the average speed is determined, a new firing angle is set in step S5, and the process returns to step S2.

Meanwhile, the instantaneous speed of the induction motor (2) is measured using the interrupt function of the microcomputer (5).

The microcomputer (5) performs step S6. In step S7, the number of interrupts is counted up each time an interrupt signal is received, and in step S7 it is determined whether the number of interrupts is an odd number or an even number. In step S9, a timer (10) is newly started.

If the number of interrupts is an even number, the timer (lO) is stopped in step S10, and if the count value of the timer (10) exceeds a predetermined value in step S11, the induction motor (2) is stopped. It is determined that the speed of
In step 81.2, the firing angle is accelerated.

Note that the timer (10
) is the same as the count value of the second counter described with reference to FIG.

In the above embodiment, the average velocity and instantaneous velocity are obtained from the output pulses of the pulse generator (7), but the average velocity and instantaneous velocity may be obtained by other methods.

[Effects of the Invention] As described above, according to the present invention, the speed of the induction motor can be controlled stably, and disturbances can be quickly responded to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the invention, FIG. 2 is a waveform diagram explaining the invention in detail, and FIG. 3 is a flowchart when the control of the invention is executed by a microprogram. Fig. 4 is a diagram showing the configuration of the pulse generator shown in Fig. 1, Fig. 5 is a diagram showing the speed measurement and firing angle control cycle, and Fig. 6 is a diagram showing the phase angle when controlling the firing phase angle. FIG. 3 is a diagram showing the relationship with the speed of an induction motor. In the figure, (1) is an AC power supply, (2) is an induction motor, (
3) is a triac, (4) is a photocoupler, (5) is a microcomputer, (6) is a zero point detection circuit, (7)
is a pulse generator, (8) is a waveform shaping circuit, and (9) is a speed setting device. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (2)

[Claims] (1) A speed control device for an induction motor that inserts a firing angle control type switching element between an AC power source and an induction motor, and controls the speed of the induction motor by controlling the firing angle of this switching element. In, the period T for controlling the firing angle is determined, the firing angle during the period is set at the start point of each period, and the time from this setting point to the end of the period after a predetermined time T_1 has elapsed. an average speed measuring means for measuring the average rotational speed of the induction motor during T_2 (T-T_1); comparing the average rotational speed measured by the average speed measuring means with a set speed to detect an error; firing angle calculating means for calculating the firing angle in the next cycle of the cycle; instantaneous speed measuring means for measuring the instantaneous rotational speed of the induction motor within a time sufficiently shorter than the period T; this instantaneous speed measurement A control means for controlling the induction motor to immediately set a new firing angle and increase the speed of the induction motor when the instantaneous rotational speed measured by the means becomes less than a predetermined limit value. Speed control device for induction motor. (2) The induction motor is equipped with a pulse generator that outputs one pulse every predetermined rotation angle, and the average speed measuring means includes a first counter that counts the number of pulses output from the pulse generator within the T_2 time period. 2. The induction motor according to claim 1, wherein said instantaneous speed measuring means comprises a second counter that counts the number of clock pulses included in a pulse period outputted by said pulse generator. Speed control device.