JPS60209694A - Air flow amount control device - Google Patents

Abstract

PURPOSE:To eliminate the output variation of a variable frequency electric source by detecting the abnormality of a frequency commanding signal in the air flow amount control device to preclude the output signal upon detecting the abnormality. CONSTITUTION:When an abnormal signal detecting device 9 has detected an abnormality in the frequency commanding signal, a contact 9b is operated to open a signal line 7 and the output frequency of a variable frequency electric source (electric source V) 6 is controlled by the output signal of an automatic tracking unit 10 so as to be a constant output. Accordingly, the rotating numbers of a motor 4 and the flow amount of a ventillator 5 are not changed since the output of the electric source 6 is constant. According to this method, a normal operation may be continued even when the frequency commanding signal to the V electric source 6 has become abnormal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to air volume control for boilers and the like, and particularly to an air volume control device when a ventilator is driven by an electric motor driven by a variable frequency power source.

[Prior art]

A conventional device of this type is shown in FIG. In the figure, 1 is a commercial power source, 2 and 3 are circuit breakers, 4 is an electric motor, 5 is a ventilator directly connected to the electric motor, 6 is a variable frequency power source (hereinafter referred to as ■ power source), and 8 is a variable frequency power source 6 This is a control device that gives an operating frequency to the controller, and 7 indicates its signal line. FIG. 2 is an explanatory diagram showing the relationship between the frequency command signal, which is the output of the control device 8, and the operating frequency. 3 and 4 are explanatory diagrams of FIG. 1. In the figure, tl indicates the time when the control device 8 commands the output to increase, t indicates the time when the output of the ■power supply 6 has completed increasing, t3 indicates the time when an abnormality occurs in the signal line 7, and t4 indicates the time when the output of the ■power supply after the abnormality occurs. The output of 6 indicates the point at which the change is complete.

Next, the operation will be explained.

In Fig. 1, a commercial power supply 1 connects
A voltage is applied to the power supply 6. (2) Depending on the output frequency F of the power source 6, the rotation speed n of the electric motor 4 is expressed by equation (1).

・-One Sim Ship King! −・・・・・・・・・・・・・・・・・・
. . . Equation (1) Therefore, if the applied power supply frequency F changes, the rotation speed n changes proportionally. That is, (1) If the output frequency F of the power source 6 changes, the rotation speed of the electric motor 4 changes. A ventilator 5 directly connected to the electric motor 4 generates an air volume Q whose output is approximately proportional to the rotational speed n of the electric motor 4, and supplies it to the boiler. In the example of a power generation plant, for example, the power demand from the power grid changes,
If the fuel supply condition changes, the air volume Q required by the boiler changes, and such a command to change the air volume Q is issued by the control device 8.
It is applied to the power source 6 via the signal line 7, and the power source 6 outputs a frequency F corresponding to the required air volume Q.

FIG. 2 is an example showing the frequency command signal value with respect to the operating frequency output from the control device 8. In this figure, in order to change the operating frequency of the V power supply 6 by 10 to 40 Hz,
The control device 8 has a capacity of 4 to 20 m1. It shows that it is controlled by the frequency command signal.

FIG. 3 is a diagram for explaining when the conventional device shown in FIG. 1 operates normally. The control device 8 is 1. At this point, an increase in the air volume Q is requested, and a frequency command signal is given to the power source 6 from the signal line 71. Normally, ■The power supply 6 is designed to change the output at a constant increase/decrease rate in response to a change request. Therefore, ■The output frequency F of the power supply 6 is 1.0 at the time of the change request. The operation for the change request is completed at time point 11 with a slight delay. (2) Depending on the output frequency F of the power source 6, the rotation speed n1 of the electric motor 4 and the output air volume Q of the ventilation fan 5 change.

FIG. 4 shows an example where an abnormality occurs in the signal line 7 shown in FIG. 1, and shows a case where the signal line 7 is disconnected. The output of the control device N8 does not change and requests a constant air volume Q, but the signal line 7 is at time t,
■The input to the power supply 6 becomes zero. As explained in FIG. 3, the output frequency F of the power source 6 decreases to the lower limit value with a slight delay, the rotational speed n of the electric motor 4 also decreases, and the output air volume Q of the ventilation fan 6 decreases. .

Since the conventional device is configured as described above, if the frequency command signal of the control device 8 becomes abnormal, or if the frequency command signal is lost due to a break in the signal line 7, etc.
(2) The power supply 6 drives the electric motor 4 based on the abnormality signal. Therefore, the ventilator 5 directly connected to the electric motor 4 has disadvantages such as being unable to secure the required air volume, extinguishing the boiler fire, and causing the boiler to explode.

[Summary of the invention]

The present invention has been made to eliminate the drawbacks of the conventional devices as described above, and includes a device for detecting an abnormal signal and disconnection of the control device 8 when an abnormal signal is generated in the control device 8 and a disconnection of the signal line 7 is performed. When the detection device detects an abnormality, the output signal from the control device 8 is blocked, and ■ the power supply 6
An object of the present invention is to provide an air volume control device that eliminates output changes when unnecessary.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
FIG. 5 shows an embodiment of the present invention, in which the same or corresponding parts as in the figure are given the same reference numerals, and 9 is an abnormal signal detection device (frequency command signal abnormality detection means) connected to the signal line 7; 9
b is a contact that operates when the abnormal signal detection device 9 is activated, 1
0 is an automatic tracking device that follows the frequency command signal that is the output signal of the control device 8. FIG. 6 is an explanatory diagram of FIG. 5.

In the figure, "s" indicates the point in time when a disconnection or the like occurs in the signal line 7. In contrast to the conventional system shown in FIG. 1, FIG. A device 9 is added.

Next, the operation will be explained. The abnormal signal detection device 9 detects that the output signal of the control circuit 8 exceeds the signal range of the signal line 7, that is, the signal range of 4 to 20 m1 from the control device 8 in FIG. 2, and that the signal line 7 itself is disconnected. When a zero signal is detected, the signal line 7 is opened at the contact 9b. The automatic tracking device 10 is a device that follows the output signal of the control device 8 with a slight time delay, and when the output signal is cut off and becomes zero, it holds the signal value immediately before the cutoff. That is, when the abnormal signal detection device 9 opens the signal line 7 due to a disconnection of the signal line 7, etc., the automatic follow-up device 10 controls the power supply 6 to a constant output based on its output signal. Therefore, the rotation speed n of the electric motor 4 and the air volume Q of the ventilation fan 5 do not change due to the constant output of the V power supply 6.

FIG. 6 is an explanatory diagram of the above operation, and shows a case where the output signal of the control device 8 becomes 0 at time t3 due to an abnormality such as a disconnection of the signal line 7 during constant operation. At time t, the abnormality signal detection device 9 detects an abnormality, and the output frequency F of the power supply 6 becomes constant due to the constant output signal of the automatic follow-up device 10. Therefore, even if the signal line 7 becomes abnormal, there is no change in the output frequency F of the power source 6, the operation of the signal line 7 remains at the signal before the abnormality, and the rotation speed n of the electric motor 4 and the air volume Q of the ventilator 5 do not change either. maintained and can continue to operate safely.

Further, to control the air volume Q of the ventilation fan 5, in addition to the control based on the rotation speed n, an inlet vane (or damper) (not shown), which is a mechanical air volume adjustment device, may be used. In this case, when controlling by the rotation speed n, in order to reduce loss,
The artificial vane is fixedly controlled to be almost fully open, but when the abnormality signal detection device 9 detects an abnormality and the rotation speed becomes constant n - as shown above, there is a change in the required air volume of the boiler thereafter. In this case, the fixed control of the artificial vane is canceled and the control is switched to one that can follow the required air volume to safely operate the boiler.

In addition, in the above explanation, the air volume control of a boiler ventilator was explained, but any other target other than the boiler may be used.

Furthermore, although the explanation has been given using a disconnection as an example, other abnormalities such as a short circuit may be used.Furthermore, the output signal may become abnormal due to an abnormality in the control device 8 rather than an abnormality in the signal line 7.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a device for detecting an abnormality in the frequency command signal to the V power source 6, and when this detecting device is activated, (1) the output change of the power source 6 is prevented, and the frequency before the abnormality is changed. Since it is configured to maintain operation using a command signal and to control the air volume using a mechanical air volume adjustment device, ■ Even if the frequency command signal to the power supply 6 becomes abnormal,
This has the effect of providing an air volume control device that can continue normal operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional air volume control device, FIGS. 2, 3, and 4 are explanatory diagrams of FIG. 1, and FIG. 5 is a block diagram showing an embodiment of the air volume control device according to the present invention. FIG. 6 is an explanatory diagram of FIG. 5. 1... Commercial power supply, 2, 3... Breaker, 4... Electric motor, 5... Ventilator, 6... Variable frequency power supply (V power supply), 7... Signal line, 8... ...Control device, 9... Abnormal signal detection device (frequency command signal abnormality detection means), 9b
...Contact, 10...Automatic tracking device. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant: Mitsubishi Electric Corporation Figure 1 Figure 2 Pilgrimage to the capital ★ Bow (mA) Figure 3 tl t2 Figure 4 3 t4 Figure 5 Figure 6

Claims (2)

[Claims] (1) In an air volume control device having a ventilation fan driven by an electric motor, a variable frequency power supply supplying electric power to the electric motor, and a control device generating a frequency command signal giving an operating frequency to the variable frequency power supply, An air volume control system comprising: frequency command signal abnormality detection means for detecting an abnormality in a frequency command signal; and means for fixing the output of the variable frequency power supply to an operating state when the frequency command signal abnormality detection means is activated. Device. (2) The ventilator is equipped with a mechanical air volume adjustment device that controls wind erosion that occurs, and when the operating state of the output of the variable frequency power supply is fixed, the mechanical air volume adjustment device changes from the fixed control to the required air volume. 2. The air volume control device according to claim 1, wherein the air volume control device is configured to switch to automatic control according to the following.