JPH0446592A - Inverter control method and device - Google Patents

Abstract

PURPOSE:To prevent overload trip of an inverter by increasing the reset speed variation rate under low speed even when the speed of a single pump drops due to switching of control upon occurrence of fault in a control system. CONSTITUTION:Assuming a fault occurs and detected by a control switching detector 35 which changes over a control system switch 25 to a standby side inverter controller 51a. Since the rotational speed of a motor 9 has been dropped through coast down, a frequency detector 42 in the inverter control section 51a judges the rotational speed drop of the motor 9 based on the waveform of a residual voltage and a pull-in frequency setter 43 determines a frequency fp to be reoperated. Upon finish of reoperational preparation, a pull-in control section 34 changes over the switch 24 to side (b) to provide the pull-in frequency fp to an inverter control circuit 18 thus reoperating an inverter. At the same time, the pull-in controller 34 resets the output from a variation rate limiter 17 with the pull-in frequency and turns the switch 24 to side (a).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter control method, and particularly to an inverter control method and apparatus suitable for a system in which flow rate control is performed using a plurality of motor-driven pumps. [Prior Art] In a recirculation pump or the like of a nuclear power plant, the flow rate of water supplied by the pump is controlled by controlling an inverter that supplies power to a motor (induction motor) for driving the pump. A conventional example of such an inverter control device is the one described in Japanese Patent Application Laid-Open No. 61-223596. Operated according to instructions. If the pump cannot be controlled according to the command value due to a momentary power outage, etc., the pump will coast down (the number of revolutions will decrease according to inertia due to the lack of a driving source), so as soon as normal operation is possible, the inverter will Drive the pump motor again and pull it to a certain frequency,
After that, control is performed to return to the speed command of light. If the return speed at this time is too fast, it will cause fluctuations in the process amount, so it is necessary to keep the rate of change at the time of return small.

Furthermore, in the device described in JP-A-59-83578, when the power supply voltage decreases, the motor rotation speed (inverter output frequency) is controlled to decrease in accordance with the coast down of the pump due to the decrease. When power is on, a means for generating a function to control the motor rotation speed to gradually increase is provided to prevent overcurrent from occurring due to the difference between the inverter output frequency and the actual motor rotation speed. Also, JP-A-6
The device described in No. 2-12384 is provided with means for suppressing the overcurrent flowing through the motor when the power is restored according to its magnitude, thereby preventing the inverter from stopping due to the overcurrent.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, one pump, i) or even if there are multiple pumps, is controlled as one control object, and as described below, a plurality of pumps are used, and No consideration was given to the problem that would occur if only one of the machines slowed down.

The above problem is because when multiple pumps are in operation and only one of them slows down, the torque applied to the slowing pump will be affected by the other pumps in operation and will be significantly different from when operating alone. arise.

Figure 3 shows the torque characteristics of the pump ((a) in the same figure) and the coastdown curve during pump trip ((b) in the same figure). As shown in Figure 2, the torque decreases in proportion to the square of the speed. However, if there are other pumps in operation, the torque does not decrease much as shown in characteristic L2, but the speed also decreases. When this becomes low, other pumps cause the pump to operate in forward and reverse flow, so the torque actually increases. Accordingly, as shown in FIG. 3(b), the coast down characteristic of the pump falls faster in characteristic L4 when there is another pump in operation, compared to characteristic L3 when the pump is alone. On the other hand, an event in which the speed of only one of the pumps decreases is when one of the control systems, which are duplicated to improve reliability, breaks down. In other words, if the operating system in a redundant control system (the control system is redundant for each pump) breaks down, the imperter output is stopped and the power to the relevant pump is turned off.
Next, the system switches to the other control system, detects the phase of the pump motor, and pulls in the motor to drive the motor again at a certain speed. When the pump is drawn in this way, the pump coasts down rapidly as described above, so the pump is drawn in at a low speed.There is a risk that the inverter will be overloaded due to backflow from the pump during operation, and the speed If there is a delay in eliminating the overload by recovery, the inverter will trip. Further, since the upper control system controls the pump flow rate to be constant, when the speed of one pump decreases, the speed of the other pumps in operation is increased to restore the process amount. If the speed of the pump that has decreased in this process is suddenly restored, the process control system is usually accompanied by a delay, so the control cannot follow up, resulting in a problem that fluctuations in the process amount become large.

An object of the present invention is to provide an inverter that can prevent tripping due to inverter overload and keep process volume fluctuations stable upon recovery even when the speed of one of the pumps decreases in a system with multiple pumps. The object of the present invention is to provide a control method and device for the.

[Means to solve the problem]

In order to achieve the above object, the present invention provides two speed change rate limiters, one with a larger limit value and the other with a smaller limit value, so that when one of the duplex control systems fails, After switching, first increase the inverter output frequency (corresponding to the speed command value) to the set speed while limiting it with a limiter with a larger speed change rate limit value, then increase it to the set speed with a smaller speed change rate limit value. The speed may be returned slowly while being limited by a limiter, or a speed command compensator may be provided in the inverter controller, and the compensator may be set so that after the above switching, the inverter output frequency increases quickly at first and then gradually increases. The speed change rate is continuously changed by changing the speed change rate, or after the above switching, the pump speed during recovery is kept constant at a large rate of change, and the pump speed during other normal operations is controlled to a speed corresponding to the pump speed during recovery. By doing this, fluctuations in process volume were suppressed.

[For production]

By increasing the speed at a fast rate of change in the initial stage after control switching using a speed change rate limiter or compensator, the low speed range where the inverter becomes overloaded can be overcome within a sufficiently small time considering the inverter's overload capacity. This prevents trips due to inverter overload, and after the inverter escapes from the low speed region where it is overloaded, the speed is increased at a slow speed change rate, thereby minimizing fluctuations in process volume. and stable control can be performed. In addition, by increasing the pump speed that has been switched in the control system at a large speed and controlling other pumps in accordance with this speed increase, inverter overload can be quickly resolved and the process amount can be kept constant as a whole. Since it can be controlled, fluctuations during recovery can be suppressed.

〔Example〕

The present invention will be explained below using examples. Fig. 1 shows an embodiment of the method of the present invention, showing the configuration of an inverter control system and a process control system, and Fig. 2 shows its operation. ! 52
, the power obtained from the power supply bus 1 via the circuit breaker 2 is transformed by the input transformer 3 to a voltage suitable for the thyristor element configuration, and then the rectifier 4 and the DC reactors 1 to 5. After converting the voltage into direct current at a predetermined voltage using a smoothing capacitor 6, it is inversely converted into alternating current at a predetermined frequency using an inverter 7, boosted to motor voltage by an output transformer 8, and supplied to a pump motor 9. Rectifier 4 and inverter 7
The gate signal of the dual inverter controller 5]a
, 51b is selected by the changeover switch 25 and applied via the gate controller 19.

In the process control device i53, the adder 12 calculates the deviation between the output of the main controller 11 and the flow rate signal, and
3 and distributed to the controllers of each pump. This directive is
Since the changeover switches 21 and 22 are normally connected to the a contact side, the frequency command f is outputted to the inverter 52 via the manual/automatic controller 14 and the rate of change limiter 15. This is due to the duplex controller 51 in the inverter 52.
a and 51b. Since the changeover switches 23 and 24 are normally connected to the a contact side, each controller passes through the upper and lower limit limiters 16 and the rate of change limiter 17, and then the inverter control circuit 18 to the rectifier 4 and inverter 7. is converted into a gate command signal.

With such a control system, the inverter control device 5
Ib is in control and a failure does not occur.Figure 2 Time 1
+), the control changeover detector 35 detects this and operates the control system changeover switch 25, and the standby side inverter controller 5
Suppose you switch to 1a. At this time, as explained using FIG. 3, since the rotational speed of the motor 9 has decreased due to coast down, the inverter controller 51a detects the residual voltage waveform from the residual voltage waveform at the frequency detector 42 via the voltage transformer 41. 9 is determined, and the frequency fP at which the re-operation should be determined is determined using the pull-in frequency setter 43. When this restart preparation is completed, the pull-in controller 34 switches the selector switch 24 to the b side, applies the pull-in frequency fp to the inverter control circuit 18, and starts the inverter restart (time t2). At the same time, the pull-in controller 34 resets the output of the rate-of-change limiter 17 at the pull-in frequency, and after a sufficient time has elapsed to complete the pull-in, the changeover switch 24 is returned to the a side (time 1+). On the other hand, the output frequency fO output from the inverter control circuit 8 and the frequency f of the frequency command value 61 from the process control device 53 are compared in the switching controller 33, and if the frequency deviation between the two is large, the switching controller 33 is switched to side b. Selector switch 23b
On the side, the lower value of the command frequency f and the predetermined setting value f1 of the setter 46 is selected by the low value priority gate 45, and the higher value of this and the pull-in frequency fP is selected by the high value priority gate 44. chosen and given. That is, it is operating at a frequency higher than frequency f1, and the pull-in frequency fp is the set value f.

If the value falls below the limit limiter 16, the setter 4
Since the frequency command f1 determined by 6 is given, the input to the inverter control circuit 18 is from the pull-in frequency fP toward the frequency f1 determined by the setting device 46 at the rate of change limited by the rate of change limiter 17. Ascending figure 2 time t
3 to 14), constant frequency operation is performed at the set frequency f1.

The speed change rate during this rising period (times t4 to tS in Figure 2) is limited by the limiter 17, but by setting this value to a large value that eliminates the inverter overload before the inverter trips, Trips due to inverter overload are prevented.

On the other hand, on the process control device 53 side, the switching controller 32 compares the inverter output frequency fO and the frequency command value f, and when the deviation between the two exceeds a certain level, the switching controller 32
2 is set as the b side, and the inverter output frequency fo is given to the rate of change limiter 15 so that the frequency command value f matches the output frequency fO (tieback). When these match, the changeover controller 33 on the inverter 52 side returns the changeover switch 23 to the a side, and the changeover controller 32 on the process control device 53 side returns the changeover switch 22 to the a side. As a result, the inverter operates again according to the frequency command value f from the process controller W53. At this time, the process control device 53
Now, the output of the automatic/manual controller 14 and the frequency command value f
The changeover controller 31 switches the changeover switch 21 to the b side and inserts the rate of change limiter 36 when the deviation becomes larger than a certain value. Since the rate of change limiter 36 is set lower than the rate limiters 15 and 17, after the changeover switch 22 returns to the a side, this rate of change is used to control the frequency command value fs (flow rate) of the system. Controller 138
frequency command value f to the inverter 52 (after time t5 in FIG. 2). When the frequency command value f matches the system frequency command value fs, the switching controller 31
Then, the selector switch 21 is set to the a side again, and the control of the entire system is returned to the normal state (time t6). By performing the speed return at such a small rate of change, the process flow rate is not disturbed.

On the other hand, the controller configurations of other pumps (not shown) in operation also have similar configurations; It is operated according to the frequency command fs. While the control switching of the inverter controllers 51a and 51b in FIG. 1 is occurring, the speed controller 13 increases the speed of the pump in operation and increases the flow rate in accordance with the command from the main controller 11 since the process flow rate decreases. Thus, the system frequency command fs is increased. As the pump driven by the inverter 52 whose control has been switched returns to operation as described above, the process flow rate gradually returns to the original flow rate, and the output fs of the flow rate controller 13 accordingly returns to the original output.

This embodiment has the advantage that the pump speed can be reliably restored after switching the control system by controlling the process control device that monitors the entire process.

FIGS. 4 and 5 are block diagrams and operation diagrams showing another embodiment of the present invention. In FIG. 4, the difference from the first embodiment is that the changeover switch 23 of the inverter 52
On the b side of The point is that the output is directly applied to the inverter 52 via the rate of change limiter 15. When switching of the inverter controller occurs, the changeover switch controller 3
3, the changeover switch 23 is turned to the b side, and the frequency command of the inverter is given from the compensator 47. The compensator 47 determines the deviation between the frequency command value f and the output frequency fO, and provides an output with a rate of change according to the deviation.The larger the deviation, the larger the rate of change, and the smaller the deviation, the smaller the rate of change. do the work.

Therefore, as shown in Figure 5, the return of the pump is initially at a fast rate of change, and the process controller! The rate of change is performed at a slower rate as it approaches the frequency command fs of 53. When the deviation between the output frequency fo of the inverter and the frequency command fs becomes below a certain level, the changeover controller 33 sets the changeover switch 23 to a.
and the return of control is completed.

According to this embodiment, inverter overload trip prevention and stability of process amount control can be achieved in the same way as in the case of FIG. 1, and the advantages of the present invention are that the object of the present invention can be achieved only with a compensator provided in the inverter. There is.

FIGS. 6 and 7 are block diagrams showing a third embodiment of the present invention and diagrams showing its operation. In this embodiment, a special command switching means etc. is not provided on the inverter 52 side, a changeover switch 26 is provided at the outlet of the flow rate controller 13 of the process controller W53, and a speed controller 48 is provided with the inverter output frequency fO as an input. has been established. The speed controller 48 monitors the output frequency of each inverter, and when an imbalance of - room or higher occurs, the changeover switch 26 is set to the b side and the system frequency command fs is switched so that it becomes the output of the speed controller 48. . Speed controller 48 examines the output frequency fo of each inverter and issues an output command that minimizes the total flow rate change in the process. In this way, when the output frequencies of all the inverters fall within a certain deviation, the selector switch 26 is turned to the a side again and the control is returned to the original state. During this period, the inverter in which the control switching occurred returns to normal operation at a rate of change determined by the rate of change controller 17, and the other inverters are operated according to the output command from the speed controller 48.

According to this embodiment, the pump in which switching has occurred is the restrictor 1
Since the recovery occurs at a large rate of change determined by 7, inverter overload trips are prevented, and by directly using the pump speed with few delay factors to control unbalanced conditions, the process volume can be reduced even if the inverter recovery speed remains high. This has the advantage that fluctuations in can be kept small.

〔Effect of the invention〕

According to the present invention, even if the speed of one pump decreases due to control switching after a control system failure, the inverter overload trip can be prevented by increasing the return speed change rate at low speeds. In addition, it has the effect of suppressing fluctuations in process volume by adjusting the speed of other pumps in operation at a slow rate of change, or by controlling the speed of the pump in operation according to the speed of the pump during recovery. There is.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams showing one embodiment of the present invention and diagrams showing its operation, Figure 3 is a diagram showing torque characteristics and coastdown characteristics when using a single pump and when using multiple pumps, and Figure 4 5 and 5 are block diagrams showing a second embodiment of the present invention and diagrams showing its operation, and FIGS. 6 and 7 are block diagrams showing a third embodiment of the present invention and diagrams showing its operation. It is a diagram. 4... Rectifier, 7... Inverter, 9... Pump motor, 17, 36... Rate of change limiter, 32.33...
- Changeover switch controller, 21 to 26... Changeover switch, 44.45... Gate, 46... Speed setting device, 4
7...Compensator, 48...Speed controller, 51a, 5
1b... Inverter controller, 53... Process control device. Figure Jr.

Claims (1)

[Claims] 1. A control signal for the total flow rate is given to a plurality of pump systems consisting of an inverter controlled by a duplicated control means and a motor-driven pump driven by the inverter to calculate the total flow rate of each pump. In a method for controlling an inverter in a system that controls flow rate, one of the pump systems described above is
If the control means in the control system fails and the speed of the pump in the pump system decreases while switching to the control means in the standby system, the control means in the standby system will switch to the control means in the standby system. A method for controlling an inverter, characterized in that the inverter is controlled so that the pump speed recovered is faster when the speed is lower and slower when the speed is higher. 2. To control the total flow rate of each pump by giving a control signal for the total flow rate to a plurality of pump systems consisting of an inverter controlled by a duplicated control means and a motor-driven pump driven by the inverter. In the inverter control device in the system, one of the pump systems is
If the control means in the control system fails and the speed of the pump in the pump system decreases while switching to the control means in the standby system, the control means in the standby system will switch to the control means in the standby system. An inverter control device characterized in that the inverter is controlled so that the pump speed recovered is faster when the pump speed is low and slower when the speed is high. 3. a speed setting means, a first control means for limiting the speed to a first rate of change or less, and a second limiting means for limiting the speed at a second rate of change smaller than the first rate of change; In addition, the control means of the standby system controls the first limiting means when the reduced speed of the pump is smaller than the speed set in the speed setting means, and the second limiting means when the reduced speed of the pump is higher than the speed set in the speed setting means. 3. The inverter control device according to claim 2, wherein the speed recovery is performed by limiting the speed increase rate of the pump. 4. Provide an auxiliary command means that outputs a speed command value that changes continuously at a rate of change that increases as the difference between the speed target value in normal conditions and the speed command value at that point increases, and controls the backup system. 3. The inverter control device according to claim 2, wherein the means controls the inverter of the pump by the output of the auxiliary command means until the speed of the pump whose speed has decreased returns to a normal value. 5. To control the total flow rate of each pump by giving a control signal for the total flow rate to a plurality of pump systems consisting of an inverter controlled by a redundant control means and a motor-driven pump driven by the inverter. In the inverter control device in the system, a control signal adjustment means for the total flow rate is provided, and if the control means in execution of control in one of the pump systems breaks down, switching to the control means in the standby system is performed. If the speed of the pump in the pump system decreases while the pump is running, the control means of the standby system controls the inverter so that the speed of the pump whose speed has decreased increases at a predetermined constant rate of change, and the control signal adjustment means adjusts the control signal for the total flow rate so that the total flow rate of each pump is constant based on the speed command output from the control means of each pump system to the inverter. An inverter control device characterized by: