JPH0328599B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid supply system that operates by keeping the pressure on the discharge side of a pump constant, and in particular, to suppress pressure fluctuations when starting the pump. The present invention relates to a control device for a liquid supply system that enables the following.

[Conventional technology]

In a liquid supply system using a pump such as a water supply system, it is desirable that the water supply pressure at the demand end is always kept constant.

However, this is extremely difficult in practice, so control is carried out to keep the pressure constant at the water supply end, for example at the discharge part of the pump.For this purpose, the pump is controlled at variable speed and the flow rate is changed. Conventionally, a control device has been used which maintains the discharge pressure constant even when the water is used, and FIG. 1 shows an example of such a water supply system.

In this Figure 1, 1 is a water tank, 2 is a suction pipe, 3 and 7 are gate valves, 4 is a pump, 5 is a motor, 6 is a check valve, 8 is a pressure sensor, 9 is a water supply pipe, and 10 is a control The device 11 is a pressure tank.

The pump 4 is a pump of a spiral type, a turbine type, etc., and is rotationally driven by a motor 5 such as a three-phase induction motor. 6. Functions to feed water into the water supply pipe 9 via the gate valve 7.

The pressure sensor 8 is linked to a water supply pipe 9 connected to the discharge side of the pump 4, detects the pressure on the discharge side of the pump 4, and sends a signal corresponding to the pressure to the control device 1.
It functions to input to 0.

The control device 10 includes a power inverter device for supplying variable frequency AC power to the motor 5;
The motor 5 includes a control circuit consisting of a microcomputer (microcomputer), and the motor 5
control the frequency and voltage of AC power to be supplied to
The rotational speed of the motor 5 is changed according to the discharge pressure of the pump 4, and closed-loop control is performed so that the discharge pressure of the pump 4 converges to a predetermined target value.

The gate valves 3 and 7 are necessary for maintenance, inspection, etc., and the check valve 6 is used to prevent backflow of water when the pump 4 is stopped. The pressure tank 11 is also called an air tank, etc., and is used to maintain the water pressure in the water supply pipe 9 at a predetermined value even when the pump 4 is stopped, and to maintain the pressure in the case of sudden changes in the amount of water supply. It functions to reduce fluctuations.

Next, FIG. 2 shows the operating characteristics of the pump in the system shown in FIG. Q and discharge pressure H are taken on the shaft, respectively. In this figure, curve A shows the Q-H characteristic when the rotational speed N of the pump 4 is the maximum speed N _A (N _MAX ),
Similarly, curves B, C, D, and E show the Q-H characteristics when the rotational speed N of the pump 4 is _NB , _NC , _ND , and _NE , respectively. Also, H _O is pump 4
The discharge target pressure is equivalent to the total head of this system. Furthermore, points A, B, C, D, and H represent the intersections of the target pressure H _O and the Q-H characteristic curves A to E, respectively, and the water supply amounts at these points I to H are Q _{A , Q B} , and Q _B , respectively. Q _C , Q _D , Q _E.

Therefore, if the demand water amount (water supply amount) is now Q _A , as a result of the above-mentioned closed loop control, the pump 4 is brought into an operating state according to the characteristic curve A, and the water amount Q _A is also changed. and the target pressure H _O
It is operated in such a way that it is maintained.

Next, suppose that in this state, the water demand decreases from Q _A and changes as Q _A → Q _B →... → Q _E. Then, the characteristic curve becomes A
If this is done, the water supply pressure H will rise from the target value H _O , so the control device 10 learns of this from the signal from the pressure sensor 8 and lowers the frequency of the AC power being supplied to the motor 5 to reduce the frequency of the AC power supplied to the pump 4. rotation speed of
decrease from N _A to N _B and N _B → N _C → N _D → N _E ,
The characteristic curve is shifted from A to E so that the target pressure H _O is maintained under the new reduced water supply Q _E.

On the other hand, when the amount of water increases from, say, Q _E ,
In contrast to the above, the rotational speed N of the pump 4 is increased from N _E so that the target pressure H _O is similarly maintained.

Therefore, according to the system shown in Fig. 1, closed-loop control is performed to always maintain the discharge pressure at the target value H _O even if the amount of water supplied by the pump 4 changes, and the pressure is maintained at a nearly constant level. Water can be supplied.

By the way, in such a system, when the water demand Q becomes zero and the water supply pipe pressure H at this time exceeds the target value H _O by a predetermined value, the operation of the pump is stopped, and then the water flow is increased. The pump remains stopped until Q has a finite value and the pressure H falls below the desired value H _O by a predetermined value; therefore, in such a system, if the motor is frequently started, There is.

On the other hand, in such a system, in order to increase the motor's rotational speed at startup, that is, to improve the startup response, the capacity of the inverter device in the control device must be increased, resulting in a large increase in cost. easy.

Therefore, in such systems, the output capacity of the inverter device is generally determined mainly from a cost perspective, ignoring the starting response of the motor, and therefore the rise in motor rotational speed obtained at startup is It is relatively gradual.

[Problem to be solved by the invention]

As a result, this kind of conventional liquid supply system has the disadvantage that a large overshoot occurs in the water supply pressure every time the pump (motor) is started, and large pressure fluctuations are frequently applied to the water supply system. It was hot.

This will be explained with reference to FIG.

Now, when pump 4 is in the stopped state,
Assume that at point A in FIG. 3, a command is given to start operation of the pump, and as a result, a speed command N* called command speed N _IN is input to the inverter device in the control device 10.

Then, the motor 5 starts rotating, but its rotation speed N gradually rises from point A'' and does not immediately reach the command speed N _IN , so the pressure H decreases below the target pressure H _O. As a result, the control device 10 further increases the command speed N*, and finally commands the maximum speed N _MAX .

During this period, the rotational speed N of the pump 4 increases and reaches the speed N' at point B in FIG. 3, and the water pressure H recovers to the target value H _O.

However, even at this time, the command speed N* is still the maximum speed N _MAX , so the rotation speed N of the pump 4 further increases to point C.
This results in a large overshoot in the pressure H.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a stable water supply without the risk of overshooting the water supply pressure even if the responsiveness at pump startup is low. To provide a fluid supply system.

[Means to solve the problem]

To achieve this objective, the present invention provides closed-loop control to converge the pump discharge pressure to a target value when the pump starts rotating and until the operating conditions reach a predetermined state. The system is characterized by stopping its functions and operating the pump under closed-loop control.

[Effect]

The reason why the water supply pressure overshoots when the pump starts is because closed-loop control is applied without providing the necessary responsiveness from a cost perspective. By operating the system, overshoot can be suppressed and water can be supplied stably.

〔Example〕

Hereinafter, the liquid supply system control device according to the present invention will be described as follows.
This will be explained in detail with reference to illustrated embodiments.

FIG. 4 shows an embodiment of the present invention. In FIG. 4, R, S, and T are the power supply, MCB is the wiring disconnector, MCa is the contact of the magnetic contactor MC, and 49 is the overload of the motor 5. Thermal relay for load protection,
INV is an inverter (note that it is obvious that any power converter capable of variable frequency output may be used as a means to drive the motor at variable speed, but this example (The inverter is used as a representative of these.)

Next, μcon is a microcomputer,
Central processing unit cpu, memory M, power supply terminal E,
Input/output port PIA-1, PIA-2, PIA-3,
Consists of PIA-4.

The microcomputer μcon includes interfaces F ₁ , F ₂ , F ₃ , F ₄ and an operation circuit Y as its peripheral devices.

When the switch SS of this operating circuit Y is closed, power is sent to the power terminal E of the microcomputer μcon via the transformer T and the stabilized power supply Z, and operation preparation is completed and control operation is started. . That is, the signal detected by the pressure sensor 8 is sent to the input/output port via the interface _F1 .
It is read from PIA-1 and stored at a designated address in memory M. In addition, the operating speed command signal of the variable speed pump motor is sent from the input/output port PIA-2 via the interface _F2 to the input terminal (not shown) of the inverter INV, and the required operating speed is adjusted according to fluctuations in the water demand. is commanded. Furthermore, the signal that controls the magnetic contactor MC is input/output port PIA−
3 via interface _F3 .
For example, when a signal is output from this port PIA- ₃ to turn on the contact Xa of the interface F3, the coil of the electromagnetic contactor MC is energized.

In this way, the pump 4 and motor 5 continue to operate while maintaining the discharge pressure at H _{2 O} while changing the operating speed in response to changes in the amount of water demand.

Next, FIG. 5 shows the pump 4 in this embodiment.
2, and the same reference numerals as those in FIG. 2 are the same, so their explanation will be omitted.

In this figure, curve A is the Q-H characteristic when the pump operating speed is the maximum speed N _MAX , curve D is the Q-H characteristic when the pump operating speed is the minimum speed N _MIN , and curve C is the speed at startup. The Q-H characteristics at N _IN are shown. Note that H ₁ represents a starting command pressure that is slightly higher than the target pressure H _O.

Next, the operation of this embodiment will be explained in more detail with reference to the flowchart of FIG. It should be noted that this operation is determined by a program pre-stored in the ROM provided in the microcomputer μcon memory M.
As is well known.

Now, when the process shown in FIG. 6 is started, first, in step, various initial values necessary for operation are set as follows.

Memory M ₀ ...Stores the data of the minimum speed N _MIN of the pump motor.

Memory M ₁ ...Stores the data of the initial speed N _IN when starting the pump motor.

Memory M ₂ ...Stores the maximum speed N _MAX data of the pump motor.

Memory M ₃ ... Pump motor operation command speed N _X
Store data.

: : : : Memory _M6 ...Stores target pressure H _O data.

Memory _M7 ...Stores pressure _H1 data at restart.

Memory _M8 ...Stores the magnetic contactor MCON and data.

Note that the memories M ₀ to _{M 8} refer to memory areas set in the memory M in the microcomputer μcon.

After setting these initial values, proceed to the next step and read data representing the pressure in the water supply pipe 9 detected by the pressure sensor 8 from the input/output port PIA- ₁ via the interface F1. , this is loaded into the A register (AccA), and in the following step, data representing the restart pressure _H1 is loaded from the memory _M7 into the B register (AccB).
and then compare these data in steps.

As a result of this comparison, if the pressure in the water supply pipe 9 is higher than the restart pressure _H1 , the commands in steps 1 to ₃ are repeatedly executed until the pressure reaches H1 or less.

On the other hand, if the pressure in the water supply pipe 9 has fallen below the restart pressure _H1 as a result of the judgment in the step, processing with the step is executed, and here the operation signal of the magnetic contactor MC is input/output. The initial speed N IN data is outputted from port PIA-3 via interface _F3 , and then input to input/ _output port PIA-2 as a speed command signal for motor 5 in step.
from the inverter via interface F ₂
Output to the input terminal of INV.

As a result, the motor 5 is started and the pump 4 starts operating.

Therefore, it takes approximately several seconds for the inverter INV to rise to the commanded initial speed N _IN after receiving the start command, depending on the state of the load. For this reason, in the conventional example described above, the problem caused by the overshoot described above occurred, but in the embodiment of the present invention, step standby time processing is provided, in which the inverter INV issues a start command. The system waits for the time t necessary for the speed to rise to the initial speed commanded.

In the following explanation, encircled numbers 11 or more representing the number of steps will be represented by numbers in parentheses.

In this way, the waiting time t has elapsed, and the pump 4
When the operating speed of the motor 5 reaches the commanded speed, the pressure in the water supply pipe 9 is compared with the target pressure H ₀ in the following steps (12). As a result of the comparison,
One of the following processes is performed until these match. In other words, the pressure inside the water supply pipe 9 is the target pressure.
If the pressure inside the water supply pipe 9 is higher than the target pressure H ₀ , then the speed is increased in step 17. If the pressure in the water supply pipe 9 is greater than the target pressure H ₀ , the pressure is decelerated in step (13).

In this way, only when both comparison values become equal, the process proceeds to step (18) without changing gears.
In principle, when the minimum speed N _MIN is reached as the water demand decreases, a signal is generated to stop the pump 4 and motor 5 in step (15), and this causes the pump 4 and motor 5 to stop. , after which the process returns to the step and the subsequent processes are repeated again.

Then, when the process advances to step (18), a wait time of Δt seconds is executed, after which the process returns to step and the subsequent processing is executed again.

Therefore, when the process shown in the flowchart of FIG. 6 is executed, the operation of the liquid supply system at this time becomes as shown in FIG. 7, and during the waiting time t provided in the step, Open-loop control for the target pressure H ₀ given by the processing after step is not entered, and during this time the command speed N _IN is maintained, and the operating state is maintained by closed-loop control. As a result, by appropriately selecting the waiting time t, it is possible to enter closed-loop control only when the commanded speed N* matches the actual speed, and the target pressure H ₀ can be reached without overshooting. Control can be converged.

By the way, as is clear from the above description, in the above embodiment, it is necessary to adjust the time t in each step to an appropriate value in accordance with the start-up characteristics of the pump drive motor.

Therefore, an embodiment of the present invention that eliminates the need for this adjustment will be described below.

This embodiment differs from the above embodiment only in a part of the control processing operation; specifically,
Adding the configuration shown by the broken line in Figure 4, the inverter
The output of INV, that is, the actual rotational speed N of motor 5, is connected to interface F ₄ and input/output port PIA-4.
In accordance with this, steps (20) to (24) of the process shown in FIG. 6 are replaced with the process consisting of steps (20) to (24) shown in FIG.

Therefore, in this embodiment, the initial speed N _IN commanded to the inverter INV in steps (20) and (21)
is transferred to the B register, and then, in step (23), the actual rotational speed N of the pump 4 and motor 5 is loaded into the A register. Then, in step (24), these are compared, and steps (20) to (24) are repeatedly executed until the two match.
I'm starting to buy time.

Therefore, according to this embodiment, the above-mentioned closed-loop control can be started when the operating speed of the pump matches the initial speed N _IN after the pump is started, and the waiting time t is assumed and set in advance. In addition, there is an advantage in that even if the startup characteristics at startup become different, there is no need for resetting and it can be applied as is.

〔Effect of the invention〕

According to the present invention, even if there is a lot of delay in the start-up characteristics of the pump operating speed at startup, it is possible to prevent the pump discharge pressure from overshooting. In addition to being able to supply water in the current state, the power supply capacity for the pump drive motor is small.
A control device for a liquid supply system that is effective in reducing the cost of the system can be easily provided.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of a liquid supply system, FIG. 2 is a characteristic curve diagram showing an example of the operating characteristics of a pump, and FIG. 3 is a characteristic curve diagram showing an example of the operating characteristics of a conventional liquid supply system. FIG. 4 is a block diagram showing an embodiment of the liquid supply system control device according to the present invention;
Fig. 5 is a characteristic curve diagram showing the operating characteristics of the pump in this embodiment, Fig. 6 is a flowchart showing the operation of an embodiment of the present invention, and Fig. 7 is a characteristic curve diagram showing the operating characteristics. FIG. 8 is a flowchart for explaining the operation of another embodiment of the present invention. 1... Water tank, 2... Suction pipe, 3, 7... Gate valve, 4... Pump, 5... Motor for driving pump, 6... Check valve, 8... Pressure sensor, 9...
Water supply pipe, 10...control device, R, S, T...power supply, MCB...wiring breaker, MC...magnetic contactor, MCa...magnetic contactor MC contact, 49...
Thermal relay, INV...Inverter, μcon...
...Microcomputer, _F1 to _F4 ...Interface, Y...Operation circuit, SS...Switch,
Z...Stabilized power supply.

Claims (1)

[Claims] 1. In a closed-loop control system liquid supply system control device comprising a pump driven by an inverter and controlling the rotational speed of the pump so that the discharge pressure of the pump converges to a target value, starting the pump A start detecting means for detecting a start, and an open loop control means for controlling the rotational speed of the pump by an open loop control method in which a speed command value for the inverter is fixed at a predetermined value, and after the pump starts rotating. , until at least one of the conditions that a predetermined time has elapsed and that the rotational speed of the pump has reached a predetermined value is satisfied, the control function based on the closed loop control method is stopped, and the open loop control means A liquid supply system control device characterized by being configured to switch to control by.