JPH0353876B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a variable frequency power supply (hereinafter abbreviated as V power supply) that drives a rotating body such as a fan or pump.
The present invention relates to a power supply system, and particularly relates to a variable frequency power supply operation method when a control signal to a V power supply is in an abnormal state such as disconnection or short circuit.

[Prior art]

A conventional device of this type is shown in FIG. In the figure, 1 is a commercial power supply, 2 is a switch,
3 controls the speed of the electric motor 4 with a V power supply. 6 is a rotating body such as a fan or pump; 5 is a connector between the electric motor 4 and the rotating body 6; 7 is a control device that sends a frequency control signal to the V power source 3; 8 is a control signal that is input to the control device 7. , 9 are signal lines connecting the control device 7 and the V power supply 3, and t ₁ in FIGS. 2 and 3.
and t ₃ are the timing start points of the increase and decrease commands of the control signal 8, respectively, t ₂ and t ₄ are the timing stop points when the output of the V power supply 3 completes the increase or decrease, respectively, and t ₅ is the abnormality of the signal line 9. At the time of occurrence,
_t6 indicates the point in time when the output of the V power supply 3 completes the change after the abnormality occurs.

Next, the operation will be explained. In order to make the description concrete, an example of a power generation plant in which the rotating body 6 is assumed to be a fan and its output (air volume) is provided to a boiler (not shown) will be described below.

That is, in FIG. 1, a V power supply 3 receives power from a commercial power supply 1 via a switch 2, and drives a motor 4 by the output of the V power supply 3. Therefore, the rotation speed n of the electric motor 4 is given by equation (1).

n=120×F/P...(1) However, F: Applied power supply frequency P: Number of poles of the motor Therefore, the rotation speed n and the applied power supply frequency F are in a proportional relationship. That is, if the output frequency F of the V power source 3 changes, the rotation speed n of the electric motor 4 changes.

The electric motor 4 is directly connected to a fan 6 by a coupler 5, and the fan 6 supplies an air volume Q whose output is approximately proportional to the rotational speed n of the electric motor 4 to the boiler.

In addition, in the example of a power generation plant, if the required power from the power system changes or the fuel supply status changes, the air volume Q required by the boiler will also change, so in this case, the air volume Q change command is the control command 8. and is given to the control device 7. Then, a command to change the air volume Q is given to the V power supply 3 via the signal line 9, and the V
The power supply 3 outputs a frequency F corresponding to the required air volume Q.

FIG. 2 is an explanatory time chart when the conventional V power supply system shown in FIG. 1 operates normally. That is, when the control command 8 requests an increase in the air volume Q at time t ₁ and requests a decrease to return to the original value at time t ₃ , the output of the control device 7 follows the signal line 9 in FIG.
Therefore, it is applied to the V power supply 3. Normal V power supply 3
is designed to change the output at a constant increase/decrease rate in response to a change request, and therefore the output frequency F of the V power supply 3 is slightly delayed from the change request time points _t1 and _t3 . The operation is completed at time t ₂ and t ₄ respectively. That is, when it is desired to change the output air volume Q of the fan 6, this is done by changing the output frequency F of the V power supply 3 and changing the rotation speed n of the electric motor 4.

In addition, Fig. 3 is a time chart when an abnormality occurs in the signal line 9 in Fig. 1, and shows an example of an abnormality in which the signal line 9 is disconnected (including loose or disconnected connection terminals, etc.). There is. Here, of course, there is no change in the control signal 8, and a constant air volume Q is required. Therefore, if the signal line 9 is disconnected at time t ₅ , the input signal to the V power supply 3 becomes zero, so as explained in Fig. 2, the output frequency F of the V power supply 3 is delayed slightly and decreases to the lower limit value. As a result, the rotational speed n of the electric motor 4 also decreases, and the output air volume Q of the fan 6 also decreases.

The conventional operating method of a motor using a V power source is as described above, so if an abnormality such as a disconnection occurs in the control signal line of the V power source 3, the output frequency of the V power source 3 will fluctuate unnecessarily, resulting in This has disadvantages, such as making the operating conditions of the electric motor 4 and rotating body 6 unstable, leading to system failures.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and uses an intermittent wave of constant amplitude as a frequency control signal to the V power supply, and uses an electric quantity (pulse) other than the amplitude of the intermittent wave. By transmitting the signal width, frequency, digital signal, etc.) to the V power supply, a signal amplitude abnormality detector is provided to deal with the phenomenon in which the amplitude of the intermittent wave changes in the event of an accident (disconnection, short circuit, etc.) on the signal line 9. Provides a variable frequency power supply operation method that can eliminate unnecessary V power output changes even in the event of an accident in the signal line 9 by detecting the abnormality and switching the voltage to the motor from the V power supply to the commercial power supply when an abnormality is detected. It is intended to.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 4, the same parts as in FIG. 1 are designated by the same reference numerals, and 10 and 11 are switches. 7B is a control signal generator, and 3B is a signal abnormality detector.

Further, FIG. 5 shows an example of a signal flowing through the signal line 9 in FIG. 4, in which the control signal 8 has two levels F ₁ ,
An example of _F2 is shown. Further, the signal flowing through the signal line 9 shows an intermittent wave whose amplitude is H with pulse widths W ₁ and W ₂ corresponding to the control signal levels F ₁ and F ₂ , respectively.

FIG. 6 is a diagram for supplementary explanation and is an example of boiler air volume control, and 6a and 6b indicate the rotation shaft and impeller of the fan 6. In addition, 12 is a wind path, 12a and 12
13 is the wind direction in which the wind is sent, 14 is a mechanical air volume control mechanism, 14a is a vane, 14b is a drive rod, and 15 is a control input signal to the air volume control mechanism 14. show.

FIG. 7 shows a circuit diagram of the control signal generator, and shows an example of an input-to-frequency converter that forms an output with a pulse width W _P proportional to the magnitude of the input voltage E _I ;
The figure is an explanatory diagram illustrating the operation of FIG. 7. In the figure, E _I is the input voltage, T ₁ to _{T 4} are transistors,
C ₁ and C ₂ are capacitors, R ₁ to R ₇ are resistors, ZD is a zener diode, + _ES is the power supply voltage, E _O is the output signal, and V _C1 is the voltage of the capacitor C ₁ .

Next, the operation of the present invention will be explained below. In Fig. 4, switches 2 and 10 are turned on, and switch 11 is turned on.
Assuming that the motor 4 is operated with the V power supply 3 while the power is kept OFF, the pulse width of the intermittent wave shown in Fig. 5 will be
There is a relationship between Wi and the magnitude Fi of the control signal 8 as shown in equation (2).

Wi=K・Fi ……(2) Here, K: constant, i: any positive integer value Therefore, in the case of Fig. 5, W ₁ =K・F ₁ W ₂ =K・F ₂ … ...(3) The control signal generator 7B for the intermittent waves W ₁ and W ₂ is provided inside the control device 7, and in equation (2), the output frequency for driving the motor 4 of the V power supply 3 is determined by the pulse width Wi of the intermittent waves. It is determined only when

The operation of the control signal generator 7B is as shown in Figure 8, when the transistor _T1 changes from ON to OFF, the voltage
V _C1 rises with a time constant C ₁ R ₁ , and the voltage V _C1 increases with the input voltage
When E exceeds _I , transistor _T2 turns from OFF to ON,
Therefore, the transistor _T3 also changes from OFF to ON.

When this transistor T ₃ is turned ON, the base current of the transistor T ₁ flows through the Zener diode ZD, turning the transistor T ₁ ON, and continuously turning OFF the transistors T ₂ and T ₃ . Capacitor C ₂ is provided to ensure the time necessary to discharge the charge on capacitor C ₁ through transistor T ₁ and return voltage V _C1 to OV.

Considering the input voltage at level E _I1 (small value) and level E _I2 (large value) as shown in Figure 8, the voltage
The time for V _C1 to reach the input voltage E _I is proportional to E _I , and an input-to-frequency converter with a pulse width proportional to the input voltage E _I is obtained, as shown in the output signal E _O in Figure 8. . Therefore, if a disconnection or the like occurs in the signal line 9, the amplitude H of the intermittent wave flowing through the signal line 9 becomes small (including zero) on the input side of the V power supply 3, even if no special change occurs in the control signal 8. . Therefore, by providing a signal abnormality detector 3B on the V power supply 3 side that detects when the amplitude H of the signal line 9 deviates from the normal value, it is possible to determine whether the signal line 9 is in an abnormal state such as a disconnection. As a result, switches 2 and 10 in FIG.
By turning off the switch 11 and turning on the switch 11, the voltage applied to the motor 4 is switched from the V power supply 3 to the commercial power supply 1.

This switching from the V power supply 3 to the commercial power supply 1 is performed by an operation described later. The operation at this time will be explained with reference to FIG.

FIG. 6 explains a mechanical air volume control mechanism as an example. When the fan 6 is operated by the V power source 3, the rotating shaft 6a and impeller 6b of the fan 6 are rotated by the electric motor 4, and this rotation By varying the number, the air volume to the boiler is controlled. Generally, the vane 14a is fixed in a substantially fully open state for energy-saving operation.

If an abnormality occurs in the signal line 9 shown in FIG. 4 in such a state, the signal abnormality detector installed in the V power supply 3 is activated, and the opening degree of the vane 14a is switched from fixed to automatic and the control input signal is activated. The vane 14a is caused to follow the opening degree required in step 15 via the drive rod 14b. In this case, since the rated frequency of the V power supply 3 is usually set below the commercial frequency in order to reduce costs, the output of the V power supply 3 is increased to the rated frequency to bring the rotation speed of the motor 4 close to the rated frequency. At this time, the switching output of the V power supply 3 is increased with a margin. The air volume, which increases as the rotational speed increases, is kept within a safe range by causing the opening degree of the vane 14a to follow the direction in which the air volume decreases. Thus, when the output of the V power supply 3 rises to around the rated frequency, the switches 2 and 10 in Fig. 4 are turned off,
11 to switch the voltage applied to the motor 4 from the V power supply 3 to the commercial power supply 1.

By controlling in this way, the sudden change in the frequency applied to the motor 4 is smaller than simply switching the voltage applied to the motor 4 from the V power supply 3 to the commercial power supply 1 immediately after the signal abnormality detector of the signal line 9 is activated. This reduces the change in air volume when switching.

In this way, even when there is an abnormality in the signal line 9, the driving power source for the motor 4 is safely switched from the V power source 3 to the commercial power source 1, and operation can be continued.

Although the above description has been made using fan speed control in a power generation plant as an example, the same effect can be obtained even if the present invention is applied to a rotating body other than a fan, such as a pump, or a system other than a power generation plant.

Furthermore, although the above embodiment has been described using a disconnection of the signal line 9 as an example, other abnormalities such as a short circuit may also occur. Fifth
Although the intermittent wave in the figure is shown as an example of a minimum value of zero and a maximum value H, the reference amount is not limited to zero.

In addition, in the above explanation, after increasing the output frequency to near the rated output of V power supply 3, switching from V power supply 3 to commercial power supply 1 was performed, but this is not limited to this, and the signal abnormality detector is activated. It goes without saying that other methods such as immediate switching may also be used.

Further, in the above explanation, an example has been described in which the frequency control input is inputted to the V power supply 3 with a pulse width of an intermittent wave, but a digitally coded numerical signal may be used as an intermittent wave.

〔Effect of the invention〕

As described above, according to the present invention, the signal given from the control device to the V power source is an intermittent wave, and the circuit is configured such that the amplitude of the intermittent wave is not used for frequency control, and the amplitude is within a predetermined range. Since the power supply to the motor is switched from the V power supply to the commercial power supply only when the signal line is disconnected, there is an effect that the motor can continue to operate stably even when the signal line becomes abnormal.

Furthermore, by appropriately selecting the amplitude abnormality detection range, V
Just by reducing the amplitude of the control signal to the power source, there are effects such as increasing the chances that the frequency control signal will be correctly applied to the V power source and the operation can continue as it is.

[Brief explanation of drawings]

Fig. 1 is a schematic system diagram of a motor speed control system using a variable frequency power supply, Figs. 2 and 3 are time charts explaining the operation of the conventional variable frequency power supply operation system, and Fig. 4 is a diagram of the motor speed control system using a variable frequency power supply. A schematic system diagram of a motor speed system using a variable frequency power supply for explanation,
FIG. 5 is a time chart explaining the control signal to the variable frequency power supply according to the present invention, FIG. 6 is a supplementary explanatory diagram, FIG. 7 is a circuit diagram of the control signal generator, and FIG.
The figure is an explanatory diagram illustrating the operation of FIG. 7. 1... Commercial power supply, 2, 10, 11... Switch, 3...
V power supply, 3B...Signal abnormality detector, 4...Electric motor, 5
...Coupler, 6...Rotating body, 7...Control device, 7B...Control signal generator, 8...Control signal, 9...Signal line, 1
2... Wind duct, 6b... Impeller of rotating body 6, 14a... Vane.

Claims (1)

[Claims] 1. In a variable frequency power supply operation system comprising an electric motor connected to a variable frequency power supply, and a control device that generates a control signal to be applied to the variable frequency power supply to control the rotation speed of a rotating body coupled to the motor, the A control signal generated from a control signal generator provided in the control device is made into an intermittent wave with a constant amplitude, and it is detected and determined whether the amplitude is outside a predetermined range in the variable frequency power supply. A signal abnormality detector is built in, and when this signal abnormality detector detects that the amplitude of the control signal is outside a predetermined range, the output of the variable frequency power supply is increased to the rated frequency, and then the motor is driven. A variable frequency power supply operation method characterized by comprising a switch for switching the power supply from the variable frequency power supply to the commercial power supply.