JPH0320993B2 - - 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 VF power supply) that drives rotating bodies such as fans and pumps.
The present invention relates to a VF power supply system, and particularly relates to a VF power supply operating device for when a control signal to the VF power supply is in an abnormal state such as disconnection or short circuit. 2. Description of the Related 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 using a VF power source. 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 VF power source 3; and 8 is a control input to the control device 7. 9 is a signal line connecting the control device 7 and the VF power supply 3, and in FIGS. 2 and 3, t ₁ and t ₃ are the timing start points of the increase and decrease commands of the control signal 8, respectively, and t ₂ and t ₄ are the timing stop points when the output of the V power supply 3 has completed increasing or decreasing, respectively, t ₅ is the point at which an abnormality occurs in the signal line 9, and t ₆ is the timing stop point when the output of the V F power supply 3 has completed changing after the abnormality has occurred. Indicates the point in time. Next, the operation will be explained. In order to make the description more concrete, an example of a power generation plant will be described in which the rotating body 6 is assumed to be a fan, and its output (air volume) is given to a boiler (not shown). That is, in FIG. 1, a VF 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 VF 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 frequency P: Number of poles of the motor Therefore, the rotation speed n and the applied power frequency F are in a proportional relationship. That is, if the output frequency F of the VF power supply 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 output air volume Q 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 power required from the power grid changes or the fuel supply status changes, the air volume Q required by the boiler will also change, so the hourly air volume Q change command is used to control this. The command 8 is given to the control device 7. Then, a command to change the air volume Q is given to the VF power supply 3 via the signal line 9,
VF power supply 3 has a frequency F corresponding to the required air volume Q
Output. FIG. 2 is an explanatory time chart when the conventional VF power supply system shown in FIG. 1 operates normally. In other words, the control command 8 changes the air volume Q at time _t1 .
When an increase is requested and a decrease is requested to return to the original value at time _t3 , the output of the control device 7 becomes the signal line 9 in FIG. 2 and is applied to the VF power supply 3. Normal VF
The power supply 3 is designed to change its output at a constant increase/decrease rate in response to changing demands, and therefore V F
The output frequency F of the power source 3 has a slight delay with respect to the change request times t ₁ and t ₃ and completes its operation at t ₂ and t ₄ , respectively. In other words, if you want to change the output air volume Q of the fan 6, the output frequency F of the VF power supply 3
This is dealt with by changing the rotation speed n of the electric motor 4. Furthermore, Fig. 3 is a time chart when an abnormality occurs in the signal line 9 shown in Fig. 1, and an example of the abnormality is a case where the signal line 9 is disconnected (including loose or disconnected control terminals, etc.). It shows. Here, the control signal 8 naturally does not change, and a constant air volume Q is requested. Therefore, if the wire is disconnected at t ₅ , V F power supply 3
Since the input signal to becomes zero, the output frequency F of the VF power supply 3 is slightly delayed and decreases to the lower limit value as explained in FIG.
and the output air volume Q of the fan 6 also decreases. The conventional operating method of a motor using a VF power supply is as described above, so if an abnormality such as a disconnection occurs in the signal line 9 of the VF power supply 3, the output frequency of the VF power supply 3 will fluctuate unnecessarily. As a result, the electric motor 4,
This has disadvantages such as making the operating state of the rotating body 6 unstable and leading to system accidents. [Summary of the Invention] This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and includes an abnormality detector of the signal line 9 on the side of the VF power supply 3, and when the abnormality detector is activated. It is an object of the present invention to provide an operating device for a variable frequency power supply that prevents the output of the VF power supply 3 from changing when it is not necessary by blocking the output change of the VF power supply 3 from time to time. Embodiments of the Invention An embodiment of the present invention will be described below with reference to the drawings. In the figures, the same parts as in Figures 1 to 3 are designated by the same reference numerals as in Figures 4, 5, and 6.
In the figure, in the case of the present invention, the output signal of the control device 7 shown in FIG. 1 is made into an integral type by an integrating circuit 7A. That is, when the VF power supply system is normal, even if the control signal 8 is a step function input signal, the output signal from the control device 7 increases or decreases at a predetermined ratio. A change rate detector 3A is provided to check whether the change rate of the output signal from the control device 7 is within a predetermined range. Therefore, when the rate of change detector 3A detects that the rate of change is within a predetermined range, the output of the control device 7 is normally transmitted to the VF power supply 3, and the rate of change detector 3A
When it is detected that the change rate has deviated from the predetermined rate of change range, it is determined that an abnormality has occurred due to a disconnection of the signal line 9, etc., and the output change of the VF power supply 3 is blocked by the output of the change rate detector 3A . Try to maintain the status quo. 4 and 5 are explanatory diagrams of the operation of the VF power supply system according to the present invention, and t ₁₂ and t ₃₄ indicate the points at which the output changes of the control device 7 are completed, respectively, when the output signal of the control device 7 is made into an integral type. It shows when it increases and when it decreases. _t5 indicates the point in time when an abnormality such as a disconnection occurs in the signal line 9. FIG. 6 is a block diagram showing an embodiment of the present invention. Figure 7 shows change rate detector 3
FIG. 8 is an explanatory diagram illustrating its operation. In the figure, I _IN is the input signal, G ₁ , G ₂
is a selector switch, PGR is a pulse generator, HLD1 and HLD2 are hold circuits, DTR is a differential voltage detector, and COM is a magnitude judger. Next, the operation of this invention will be explained below. First, FIG. 4 is a time chart when the VF power supply system according to the present invention is operating normally. The control signal 8 has a constant amplitude at time _t1 , and decreases at time _t3 . An example of returning to the original value is shown. Therefore, since the control device 7 is given an integral characteristic, its output exhibits the characteristic shown in the signal line 9 of FIG. This characteristic of the integral rate of change is determined to be normal in the VF power supply 3, and the output of the VF power supply 3 is changed to follow the input signal. Therefore, electric motor 4
The output rotation speed nb and the output air volume Q of fan 6 are also V F
It changes according to the output of the power supply 3. Figure 5 is an example of a case where the signal line 9 becomes abnormal, such as a disconnection, and there is no particular change in the control signal 8, but if the signal line becomes abnormal, such as a disconnection, at time _t5 , the signal on the signal line 9 suddenly changes. The rate of change detector 3 provided in the VF power supply 3
A is activated to prevent the output frequency F of the VF power supply 3 from changing. Therefore, since there is no change in the output frequency F of the VF power source 3, there is no change in the output rotation speed n of the electric motor 4 and the output air volume Q of the fan 6, and the status quo is maintained. The operation of the rate of change detector 3A will be explained with reference to FIG. The pulse generator PGR generates pulses at regular intervals, and the selector switch
G ₁ and G ₂ alternately respond to this pulse and convert the input signal
Hold circuit HLD1, which holds the instantaneous value of I _IN , respectively.
Send to HLD2. If the input signal I _IN changes as shown in FIG. 8, the hold circuits HUD1 and HLD2 output instantaneous values of the input signal I _IN at alternate pulse times as shown in FIG. Above hold circuit HLD1, HLD2
The output difference is detected by the differential voltage detector DTR, and when the differential voltage exceeds a certain value (at time t ₂ + α)
It determines that there is an abnormal change in the input signal I _IN and sends an output signal. Note that α is the pulse generator
This corresponds to the PGR pulse interval. Although the above description has been made using fan speed control in a power generation plant as an example, the same effect can be achieved 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. Further, although the above description has been made using the disconnection of the signal line 9 as an example, other abnormalities such as a short circuit may also occur, and the control device 7
may become abnormal and the output may increase or decrease. Therefore, the rate of change detector described above can be set to be able to detect a rate of change greater than or equal to a predetermined rate of change. As described above, according to the present invention, the output signal of the control device 7 is integrated at a predetermined rate of change and sent to the VF power supply, while the input signal is integrated at a predetermined rate of change on the VF power supply side. A rate-of-change detector 3A is provided to detect when the rate of change is out of a range, and when the rate-of-change detector 3A detects that the rate of change is out of a predetermined range, V F
Since the circuit is configured to prevent changes in the output of the power supply and maintain the current state, there is an effect that normal operation can be continued even if the control signal to the VF power supply becomes abnormal.

[Brief explanation of the drawing]

Figure 1 is a schematic system diagram of a motor speed control system using a variable frequency power supply, Figures 2 and 3 are time charts explaining the operation of a conventional variable frequency power supply operating device, and Figures 4 and 5. is a time chart explaining the operation of the variable frequency power supply operating device according to the present invention, FIG. 6 is a block diagram showing an embodiment of the present invention, FIG. 7 is a block diagram of a rate of change detector, and FIG. FIG. 7 is an explanatory diagram illustrating the operation of FIG. 7; 1... Commercial power supply, 2... Switch, 3... VF power supply, 3A... Rate of change detector, 4... Electric motor, 5...
...Coupler, 6...Rotating body, 7...Control device, 7A
...Integrator circuit, 8...Control signal, 9...Signal line.

Claims (1)

[Claims] 1. A variable frequency power supply operating device 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, A frequency control signal that instructs an increase or decrease in the output energy of the rotating body is integrated by an integrating circuit provided in the control device, and the integrated signal is transmitted to a variable frequency power supply having a built-in change rate detector to control the frequency. The rate of change detector detects whether the integrated signal deviates from a predetermined rate of change range, and when the rate of change detector detects the deviation, the change in the output of the variable frequency power supply is prevented. An operating device for a variable frequency power supply characterized by the following.