JPS60145488A - Controller for liquid supply system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a liquid supply system that operates while keeping the pressure on the discharge side of a pump constant, and in particular, it relates to a fluid supply system that operates by keeping the pressure on the discharge side of a pump constant, and in particular, a system that can suppress pressure fluctuations at the time of starting the pump. The present invention relates to a control device for a liquid supply system.

[Background of the invention]

In liquid supply systems using pumps such as water supply systems,
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 maintain a constant pressure 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, control devices have been used that keep the discharge pressure constant even when the discharge pressure is constant.
The figure shows an example of such a water supply system.

In this Figure 1, 1 is a water tank, 2 is a suction pipe, 3.7
is a gate valve, 4 is a pump, 5 is a motor, 6 is a check valve,
8 is a pressure sensor, 9 is a water supply pipe, 10 is a control device, and 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. It functions to feed water into the water supply pipe 9 via the gate valve 7.

The pressure sensor 8 is connected to a water supply pipe 9 connected to the discharge side of the pump 4, and functions to detect the pressure on the discharge side of the pump 4 and input a signal corresponding to the pressure to the control device 10.

The control device 10 includes a power inverter device for supplying variable frequency AC power to the motor 5 and a control circuit consisting of a microcomputer, and controls the discharge pressure of the pump 4 taken in from the pressure sensor 8. Frequency J of AC power to be supplied to the motor 5iC according to the signal expressed
Closed loop control is performed by controlling the P relaxation pressure and changing the rotational speed of the motor 50 according to the discharge pressure of the pump 4 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, 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. It functions to reduce pressure fluctuations.

Next, FIG. 2 shows the operating characteristics of the pump in the system shown in FIG. and the discharge pressure H are plotted on the vertical axis. In this figure, curve A is the differential pressure 140
Q when rotational speed N is maximum speed NA (N MAX )
-H characteristics, and similarly below, curves B, C, D, and E indicate that the rotational speed N of the pump 4 is NB, N02ND, and NE, respectively.
It shows the QH characteristics when . Further, Ho indicates the target discharge pressure of the pump 4, and corresponds to the total head in this system. Furthermore, points A22B, H2, and H represent the intersections of the target pressure Ho and the Q-H% characteristic curves A and E, respectively,
The amount of water supplied at these points A to E is Q A +
QB + QO + QD t QK.

Therefore, if the demand water f (water supply amount) is now QA, 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 under the water amount QA. It is operated so that the target pressure HO is maintained.

Next, suppose that in this state, the demand water amount decreases from QA and changes as Q A -+Q B→...→Qm. Then, the characteristic curve becomes A
If left as is, the water supply pressure H will rise from the target value Ho, 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, reducing the rotational speed of the pump 4. from NA to NB and NB-
+N□ -+ ND-+NB, the characteristic curve is moved from A to E, and the new water supply is reduced by 1 tQ]! ! so that the target pressure Ho is maintained under

On the other hand, when the amount of water increases from, for example, QB, the rotational speed N of the differential 140 is increased from NE, contrary to the above, so that the target pressure Ho 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 Ho even if the amount of water supplied by the pump 4 changes, and water is supplied at a nearly constant pressure. can be done.

By the way, in such a system, the water demand Q
becomes zero, and the water supply pipe pressure H at this time is the target value H.
When o exceeds a predetermined value, the pump operation is stopped, the water amount Q reaches a finite value, and the pressure H reaches the target value H.
The pump remains stopped until o is below a predetermined value, and therefore, in such systems, the motor may be activated frequently.

On the other hand, in such a system, the K
In this case, the capacity of the inverter device in the control device must be increased, which tends to result in a large increase in cost.

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. It is relatively gentle.

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. there were.

This will be explained with reference to FIG.

When the pump 4 is in a stopped state, a command is given to start operation of the pump at point A in FIG. do.

Then, the motor 5 starts rotating, but its rotational speed N gradually increases from point A.
Since the commanded speed does not immediately reach the command speed N, the pressure H falls below the target pressure Ho, and as a result, the control device 10
further increases the command speed, and finally reaches the maximum speed NMAX
command.

During this period, the rotational speed N of the pump 4 increases and reaches the fifth speed N at four points in FIG. 3, and the water pressure H recovers to the target value Ho.

However, even at this time, the commanded speed t is still the maximum speed NMAX, so the rotational speed N of the differential gear 140 further increases to the point of failure, causing a large overshoot in the pressure H.

[Purpose of the invention]

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

[Summary of the invention]

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. It is characterized by the fact that the system's functions are stopped.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The liquid supply system control device according to the present invention will be described in detail below with reference to illustrated embodiments.

FIG. 4 shows an embodiment of the present invention, in which R
, S, T are power supplies, MCB is a circuit breaker, MCa is a contact of the magnetic contactor MC, 49 is a thermal relay for overload protection of the motor 5, and an INV inverter (the method for variable operation of the motor is Although there are various methods, an inverter is used in this embodiment. However, the present invention is not limited to inverters.) Also, μcon is a microcomputer, and the central processing unit cptt
, memory M, power terminal E, input/output boat P engineering A-1,
It consists of P engineering A-2, P engineering A-3, and P engineering A-4.

The microcomputer μcon is equipped with an interface F1+"2*F3tF4+operation circuit Y as its peripheral device. When the switch SS of this operation circuit Y is closed, power is sent to the power supply terminal EK of the microcomputer μcorL via the transformer T and the stabilized power supply Z. The signal detected by the pressure sensor 8 is read from the input/output boat P A-1 via the interface F1, and is stored in the designated address of the memory M. In addition, the operating speed command signal of the variable speed pump motor is sent from the input/output boat PIA-2 to the interface F2.
The water is sent to an input terminal (not shown) of the inverter INV via the inverter INV, and a required operating speed is commanded in accordance with fluctuations in the amount of water demand.

Furthermore, a signal for controlling the electromagnetic contactor MC is outputted from the input/output boat P A-3 via the interface F3. For example, when the port A-3 outputs a signal that turns on the contact Xα of the interface Fs, the coil of the electromagnetic contactor MC is energized.

In this way, the pump 4 and motor 5 adjust the discharge pressure to HO while changing the operating speed according to the change in the amount of water demanded.
Keep it safe and continue driving.

Next, Figure @5 is an operational characteristic diagram of the pump 4 in this embodiment, and since the same reference numerals as in Figure 2 are the same, the explanation will be omitted.

In this figure, curve A is the Q-H characteristic when the pump operating speed is the maximum speed NMAX, similarly, the curved line is the Q-H characteristic when the pump operating speed is the minimum speed NMIN, and curve B is the Q-H characteristic when the pump operating speed is NB. Curve C shows the Q-H characteristic when the starting speed is NIM.

Note that Hl represents a starting command pressure that is slightly higher than the target pressure Ho.

Next, the operation of this embodiment will be explained in more detail with reference to the flowchart shown in FIG. It is well known that this operation is determined by a program stored in advance in the ROM provided in the memory M of the microcomputer pcon.

When the process shown in FIG. 6 is started, first, in step 1, various initial values necessary for operation are set as follows.

Memory Mo・・・・・・Minimum speed NM of pump motor
Store engineering N data.

Memory M1: Stores the data of the initial speed N/N when starting the pump motor.

Memory M2...Maximum speed NM of pump motor
Store AX data.

Memory M3: Stores the data of pump motor operation command speed Nx.

Memory M6: Stores target pressure Ho data.

Memory M7: Stores pressure H1 data at restart.

Memory M8: Stores the data of the magnetic contactor MCON.

However, the memory MO-M11 refers to a memory area set in the memory M in the microcon beater μcon.

After setting these initial values, proceed to step (2), read data representing the pressure in the water supply pipe 9 detected by the pressure sensor 8 from the input/output boat Pm-1 via the interface F1, and read this data. Load the A register (ACCA) t, and in the following step (2), write down the data representing the restart pressure H1 - Load the B register (ACCB) from υM7, and then compare these data in the step (2).

As a result of this comparison, if the pressure in the water supply pipe 9 is higher than the restart pressure H1, the instructions in steps 1 to 2 are repeatedly executed until the pressure reaches H1 or less.

On the other hand, if the result of the determination in step ■ is that the pressure inside the water supply pipe 9 has decreased below the restart pressure H1, step ■
Execute the processes of and ■, and here output the operation signal of the electromagnetic contactor MC from the input/output boat P engineering A-3 via the interface F3, and then in steps ■ and ■, output it as the speed command signal of the motor 5. Data on the initial speed N is outputted from the input/output boat P A-2 to the input terminal of the inverter INV via the interface F2. In this way, the pump 4 and motor 5 start operating.

Therefore, the inverter INV takes approximately several seconds after receiving the start command until its output reaches the commanded initial speed Nk NK, although it depends on the load condition.

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, in the next step Waiting time processing is executed for the time t required for the signal to rise. In this way, pump 4 and motor 5
When the operating speed reaches the commanded speed, the pressure in the water supply pipe 9 and the target pressure Ho are compared in the following steps ① to ①. As a result of comparison, one of the following processes is performed until they match. That is, when the pressure inside the water supply pipe 9 is lower than the target pressure Ho, speed increasing processing is performed in step 0, and when the pressure inside the water supply pipe 9 is higher than the target pressure Ho, deceleration processing is performed in step O.

In this way, only when the two comparison values become equal, does the gear shift proceed directly to step [share]. Note that the speed is decelerated as the demand water volume decreases, and when the minimum speed NMIN is reached, a signal is generated to stop the pump 4 and motor 5 in step O, thereby stopping the pump 4 and motor 5, and then in step O. Return to step (2) and repeat the subsequent processing.

In step [share], Δ is executed for a waiting time of seconds, after which the process returns to step [share] 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. The closed loop control for the target pressure HoK given by the subsequent processing is not entered 5c, and the command speed NIN is maintained as it is during this time.As a result, by appropriately selecting the waiting time t, the command speed f
It is possible to enter closed-loop control only when the speed coincides with the actual speed, and control can be converged to the target pressure Ho without overshooting.

By the way, as is clear from the above description, in the above embodiment, it is necessary to adjust the time t in step (2) to an appropriate value in accordance with the start-up characteristics of the pump drive motor.

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, a configuration shown in broken lines in FIG. 4 is added, and the output of the inverter INV, that is, the actual The rotational speed N is taken in through the interface F4 and the input/output boat P A-4, and accordingly, steps 1 to 2 of the process shown in FIG. 6 are changed to steps Φ to 1 shown in FIG. This is replaced by a process consisting of the following.

In this embodiment, at the end of the step, the initial speed N, which is commanded to the inverter INV, is transferred to the B register, and then, at the end of the step, the actual rotational speed N of the pump 4 and motor 5 is loaded into the A register.

Then, these steps are compared, and the processes of steps Φ to Φ are repeatedly executed until the two match, thereby buying time.

Therefore, according to this embodiment, it is possible to shift to the above-described closed-loop control when the operating speed of the pump matches the initial speed N after the pump is started. There is no need to set it in advance, and even if the startup characteristics at startup become different, there is no need to set it again and it can be applied as is.

〔Effect of the invention〕

As explained above, according to the present invention, even if there is a lot of delay in the rise characteristics of the pump operating speed at startup, it is possible to prevent overshoot from occurring in the pump discharge pressure, which is a disadvantage of the conventional technology. In addition to being able to supply water in a stable state except for can.

[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, and FIG. 6 is a block diagram showing an embodiment of the liquid supply system control device according to the present invention. FIG. 7 is a characteristic curve diagram showing its operating characteristics, and FIG. 8 is a flow chart for explaining the operation of another embodiment of the present invention. 1...Water tank, 2...Suction pipe, 3,7
...Gate valve, 4...Pump, 5...
...Pump drive motor, 6...Check valve, 8...Pressure sensor, 9.Old...Water supply pipe, 1
0...Control device, R, S, T...Group/power supply, M
CB...Wiring breaker, MC...Magnetic contactor, MCα...Contact of electromagnetic contactor MC,
49... Thermal relay, INV..., Inverter, μco1'6... Micro Combiator, F
1-F4・Old-・Interface, Y・・・Operation circuit, SS・・Switch, Z・・・Stabilized power supply. -Seal of Seal, Figure 5, Figure 6

Claims (1)

[Claims] 1. A liquid supply system control device equipped with a closed-loop control system that detects the discharge pressure of a pump and controls the rotational speed of the pump so that the discharge pressure converges to a target value. The method is characterized in that means is provided for detecting the start of the pump, and the function of the closed loop control system is maintained in a standby state until a predetermined condition is satisfied after the pump starts rotating. Liquid supply system control device. 2. The liquid supply system according to claim 1, wherein the predetermined condition is whether or not the elapsed time after the pump starts rotating reaches a predetermined value. Control device. 3. The liquid supply system control device according to claim 1, wherein the predetermined condition is whether the rotational speed of the pump reaches a predetermined value.