JPH0123678B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a pump water supply device driven by a variable speed motor, and particularly to a pump water supply device digitally controlled using a microcomputer.

[Background of the invention]

A conventional pump water supply device driven by a variable speed motor will be described below. Install a pressure sensor in the water supply line of the pump. This pressure sensor measures the discharge pressure, and the deviation between the measured discharge pressure and the target discharge pressure is calculated. The speed of the pump is controlled so that this deviation becomes zero, that is, the measured pressure converges to the target pressure. The above method of convergence to the target pressure is called a negative feedback control method. By changing the discharge target, the pump can be operated continuously and in a variable manner. This method will now be explained using FIGS. 1-4.

Figure 1 is a configuration diagram of the pump device, where 1 is a water tank;
2 is a suction pipe, 3 and 6 are gate valves, 4 is a pump, 5 is a check valve, 7 is a water supply pipe, 8 is a pressure sensor provided in the water supply pipe, and 9 is a variable speed motor. The pressure sensor 8 detects the pressure of the fluid flowing through the water supply pipe and generates a direct current electrical signal (current or voltage) in accordance with the pressure. Figure 2 shows pump 4 of the pump device.
It is an operating characteristic diagram when the system is operated at variable speed, with the horizontal axis representing the water amount Q and the vertical axis representing the pressure H. Curve a shows the Q-H performance when the pump 4 is operating at the maximum rotational speed (100%), and similarly, curve e shows the Q-H performance when the pump rotational speed is operating at the minimum rotational speed. Shows Q-H performance. The rotational speed of the pump is continuously variable, but for convenience, the Q-H performance of the pump at any intermediate rotational speed is shown by curves b, c, and d.

FIG. 3 is a block diagram showing the control flow of the control device for variable speed operation of the pump device, in which the proportional-integral circuit PID includes an error amplifier OP, a proportional circuit P,
It consists of an integrating circuit I and an adder A. Further, CTL indicates a control device for operating the variable speed motor 9 at variable speeds.

FIG. 4 shows a time chart of the proportional-integral circuit PID, and the operation will be explained along this chart. 1st
In Figures ~ 4, when the amount of water used is Q ₀ , the pump 4 is on the pump performance curve C at the rotational speed N ₂ .
O Assume that you are driving at _one point. In this state, the amount of water used changes and when it decreases to Q ₂ , the operating point moves to O ₂ and the pressure inside the water supply pipe 7 increases to H ₁ . At this time, the pressure sensor 8 detects this pressure and generates an electrical signal (direct current or voltage) corresponding to this pressure. _{The difference} ES ₍ E ₀ −
_E1 ) is amplified by the error amplification circuit OP, the amplified signals are applied to the comparator circuit P and the integrator circuit I, respectively, the output signals EP and EI of the proportional circuit P and the integrator circuit I are added by the adder A, and this The signal EP+EI is output as a control signal to the control device CTL of the variable speed motor 9.

That is, as shown in Fig. 4, the electric signal E ₁ emitted from the pressure sensor is larger than the electric signal E ₀ which is the target value corresponding to the target pressure H ₀ , and the deviation between the two is
ES=(E ₀ −E ₁ ) is negative. For this reason, the control signal
EP+EI becomes smaller, and the speeds of the pump 4 and variable speed motor 9 decrease. Said deviation ES=(E ₀
−E ₁ ) becomes 0, the control signal EP + EI becomes stable,
The vehicle will be driven at a speed according to the signal. As a result,
As shown in Fig. 2, the variable speed motor 9 and the pump 4 are decelerated to the rotational speed _N4 , and the pump performance curve is f.
Therefore, the operating point of the pump moves from O ₂ to O ₃ ,
Keep target pressure H ₀ constant. Also, when the amount of water used increases and reaches _Q4 , the operating point moves to O and the pressure in the water supply pipe 7 decreases to _H2 , as described above.
At this time, the pressure sensor 8 detects this pressure, emits an electric signal _E1 , and changes the speed of the variable speed motor 9 so that the deviation ES ( _E0 - _E1 ) from the target value becomes zero.
In this case, the deviation ES is positive, so the speed is increased and the rotational speed becomes _N5 , and the pump performance curve becomes G. This moves the pump operating point from Q ₄ to O ₅ and keeps the target pressure constant at H ₀ . but,
The above conventional techniques have the following problems.

(1) A proportional-integral circuit PID is required to prevent the rotational speed of the variable speed motor and pump from falling below the minimum rotational speed, from running out of control above the maximum speed, and to reduce the offset of automatic control. It was hot.

(2) This proportional-integral circuit PID is analog controlled, and there are many adjustment parts such as target value setting and proportional-integral time setting, which may cause a delay with respect to the target value.

(3) This proportional-integral circuit PID is economically expensive and changes speed so that the deviation between the target pressure and the measured pressure becomes 0, so it is an indirect speed control, which also improves responsiveness. It was contrary to that.

In addition, in recent years, digitalization of control has progressed, and it is being considered to replace the conventional analog configuration with a digital configuration, but according to this, control steps (conventional PID circuit ) is required. In order to realize this control step, it is necessary to calculate a previously stored mathematical formula or to follow a predetermined control pattern in accordance with the control process. However, this requires software development tailored to the pump's discharge characteristics and piping characteristics, or an increase in memory capacity, which is extremely disadvantageous especially when applied to low-priced products.

[Purpose of the invention]

An object of the present invention is to provide a water supply device that can maintain a substantially constant discharge pressure at a low cost.

[Summary of the invention]

The present invention is realized by digital processing using a microcomputer or the like. Specifically, the deviation between the target pressure and the return detection pressure from the pump formulation is calculated, and the command speed difference corresponding to the calculated deviation is calculated based on the function of the deviation and the command speed difference. The speed of the pump is changed by.

To explain in more detail, the present invention continuously changes the rotation speed of the pump according to the amount of water used to maintain the pump discharge pressure almost constant, but the water supply is controlled by a pressure sensor installed in the water supply pipe. Detects the pressure inside the pipe, extracts the corresponding electrical signal, reads this signal into the microcomputer via the interface, stores it in the internal memory, and
Based on arbitrary rotation speed data and a predetermined calculation formula as the initial rotation speed, a command speed difference is calculated from the pressure difference, and this command speed difference data is stored and output from the output device of the microcomputer. After converting the initial rotational speed data into a control signal via the interface and outputting it to the control device of the variable speed motor to operate at the initial speed,
The target pressure data described above is compared with the detection data of the pressure sensor, and the pressure difference is calculated by calculating the command speed difference using a predetermined calculation formula from this pressure difference. If the data is larger, the command speed difference data is added to the initial rotation speed data, and if the target pressure data is smaller, the command speed difference data is subtracted from the initial rotation speed data, and the result is output from the output device. The data is output to the control device of the variable speed motor via the interface, and the data is stored as new rotation speed data.The above process is repeated until the target pressure data and the pressure sensor detection data match, and the target rotation speed is set. I tried to gain speed.

[Embodiments of the invention]

Examples of the present invention will be described below. FIG. 5 shows the control circuit of the pump water supply system according to the embodiment of the present invention, where MCB is the main circuit breaker, MC is the coil of the electric contactor, Mca is the contact point, and INV is the variable speed motor 9. Variable frequency inverter device for changing the rotational speed (In this embodiment, an inverter device is used, but means for changing the rotational speed of the drive motor of the pump 4 include primary voltage control, eddy current coupling, and other variable speed control) (It can also be a device). 49
is a thermal relay for overload prevention, μcon is a microcomputer consisting of a central processing CPU (hereinafter abbreviated as CPU), memory M, current terminal E, input/output ports PIAa, PIAb, PIAc, etc., F ₁ ,
_F2 is an interface for converting a digital signal such as a hexadecimal number into an analog signal, converting an analog signal into a digital signal, and controlling the opening and closing of the electromagnetic contactor.

The input/output port PIAa of the microcomputer μcon is connected to the output side of the pressure sensor 8 via an interface _F1 , from which the pressure inside the water supply pipe 7 is detected and read into the internal memory of μcon.
This port PIAa takes in the detected pressure from the pressure sensor 8 at a predetermined sampling period. This detected pressure is a negative feedback amount, and when a deviation is taken from the target pressure and the deviation is 0 or within a threshold value which is a predetermined dead value, it can be considered that the pressure has converged to the target pressure. This convergence to the target pressure takes a minute time, but until this convergence, the detected pressure, which is the amount of negative feedback, is It is necessary to incorporate The detected pressure is taken in one after another at each sampling period of the sample until the sample is collected.
This is the detected pressure for calculating the deviation. Furthermore, the input/output port PIAb of the microcomputer μcon is connected to send a speed change command signal to the variable frequency inverter device INV via the interface _F2 . CTL indicates a control circuit consisting of a transformer, power supply unit Z, start/stop switch SS, magnetic contactor MC, transistor Tr, and relay X. In the control device CTL, the circuit breaker MCB
When the start/stop switch SS is turned on and the start/stop switch SS is closed, stable rectified and smoothed power is sent from the power supply unit Z via the transformer T to the power supply terminal E of the microcomputer μcon, and operation preparation is completed.

FIG. 6 is a characteristic diagram showing pressure changes and speed changes when water is supplied at a constant discharge pressure. To explain in more detail, the target pressure is H ₀ , the operating speed is N, the amount of water used is Q ₀ , and the pump's Q-
Let H performance curve be A.

In this state, if the amount of water used increases from Q ₀ to Q ₁ , the pump operating point moves from O to O ₁ ,
The pressure decreases by −△H ₁ . Also, in order to maintain the discharge pressure at this time at _H0 , the speed increases from N to _N1 . The change at this time is +ΔH ₁ . Similarly,
When the amount of water used changes to Q ₂ , Q ₃ , and Q ₄ , the pressure difference changes to −△H ₂ , +△H ₃ , and +△H _4, respectively, and the speed increases to +△N ₂ and −△N ₃ , respectively. , −△ ₄ .

The above relationship is shown by taking the pressure difference △H between the target pressure H ₀ and the detected pressure on the horizontal axis and the speed difference △N between the current operating speed and the speed after the speed change on the vertical axis. As shown in Figure 7. That is, this speed difference △N
The relationship between and pressure difference △H is curve A (quadratic curve), which is given by △N=f(△H) (1).

Furthermore, equation (1) has a proportional relationship between i and j where the pressure difference ΔH is small. In other words, this means that the pressure difference can be determined and converted into a command speed difference using equation (1).

FIG. 8 is a flowchart showing the control means of the operation control device. To explain in more detail with these drawings, the microcomputer μcon
A program is stored in the memory M so that the pump device can be operated according to the flowchart shown in FIG.

First, in step 1, initial values are set as follows.

Memory _M1 ...Data on the initial rotation speed Nin, Memory _M2 ...Data on the minimum speed Nmin, Memory _M3 ...Data on the maximum speed Nmax, Memory _M4 ...Data on the current operating speed Nx, Memory M ₅ ...Target pressure _H0 data, memory _M6 ...Magnetic contactor MC, ON data In step 2, transfer the ON data of the magnetic contactor MC of _M6 to the accumulator (ACC) A. In step 3, the contents of this ACC-A are transferred to the output port PIAC.
The output port PIAC turns on the transistor Tr shown in FIG. 5 based on this ON data. In other words, only the lowest bit bo of port OUTA is "1".
Therefore, transistor tr becomes conductive and relay X is energized, so that electromagnetic contactor MC is energized and its contact point Mca is closed.

Next, in step 4, the initial rotation speed data stored in _M1 is loaded into ACC-A. In step 6, the data in ACC-A is sent to the input/output port PIAb, and the data is sent to the variable frequency inverter device, which is the control device for the variable speed motor, via the interface _F2 .
Output to INV. At this time, in step 5, ACC
- Store this speed command data in A in memory _M4 . Therefore, the variable speed motor starts operating at the initial speed. After this, in step 8, the signal detected by the pressure sensor 8 is transferred to the interface F ₁
Read ACC to μcon input/output port PIAa through
-Load into A.

In step 7, the data of the target pressure _H0 stored in _M5 is transferred to ACC-B, and in step 9, the two pressures are compared. As a result of the comparison, if the pressure H in the water supply pipe is greater than the target pressure _H0 by more than a, the process proceeds to step 10, where the stored value is _M4 . Transfer the current driving speed Nx to ACC-A.
In step 11, the minimum pump speed Nmin, which is the value stored in _M2 , is transferred to ACC-B. In step 12, it is determined whether the current driving speed Nx has reached the minimum speed Mmin, and if it has, the process proceeds to step 26 without changing gears, and as a result of the determination, the current driving speed is If the speed is higher than the minimum speed Nmin, the pressure in the water supply pipe is re-ported in the next 13 steps.
read into memory in μcon via PIAa, and
In step 14, the deviation between this read pressure data and the target pressure _H0 is determined, and based on this deviation, the above-mentioned
Calculate and find the command speed difference using equation (1). Furthermore, a
is a dead value, that is, a dead band.
When there is a deviation within this threshold value a, it is assumed that the pressure has converged to the target pressure, and the shift command is not issued and the process moves to step 26.

Next, in 15 steps, the command speed difference data obtained in 14 steps is subtracted from the current operating speed data, and then transferred to ACC-A, and then in 16 steps, the ACC
- The result after the subtraction latched to A is stored in the memory _M4 as updated speed data, and in 17 steps this updated (corrected) speed data is output from the input/output port PIAb of μcon to the variable speed control means INV and decelerated. Issue a command. After this, the time △t required to reach the command speed is processed in 26 steps, and the process is repeated at 7 steps.
Returning to the step, the subsequent processes are repeated so that the target pressure and the measured pressure are within ±a.
Here, a is the hysteresis of the target pressure.

I will continue to explain further, but now, variable speed motor 9
It is assumed that the rotational speed of the pump 4 is N as shown in FIG. 6, and the pump 4 is operating at a pressure H ₀ at the 0 point on the characteristic curve A. Under these conditions, the amount of water used decreases.
At Q ₃ , the pressure increases. The pressure increases and the operating point moves from O to _O3 , and the pressure in the water supply pipe 7 decreases.
When H ₃ is reached, the pressure sensor 8 detects this and generates an electrical signal. The difference between this pressure H ₃ and the target pressure H ₀ is +△H ₃ , and when the speed difference △N is calculated from equation (1) mentioned above, it becomes -△N ₃ , which is △N from the current operating speed N. Subtract ₃ and issue a speed command of N-△N ₃ . As a result, the speed is N ₃ (=N−△
N ₃ ), the operating point moves from O ₃ to O ₅ , and operation continues around this point.

Also, as a result of the comparison in 9 steps, the data of the internal pressure H of the water supply pipe 7 is more a than the data of the target pressure _H0 .
If it is smaller than 18, proceed to step 18 and
The speed at which you are currently driving on the step is the maximum speed.
It is determined whether Nmax has been reached. If Nmax has been reached, proceed to step 26 without changing gears; if not, the process from step 21 onward is executed. In this process, the operation is completely opposite to that described above. That is, the pressure difference is determined, the command speed difference is calculated using equation (1), and from now on, this value is added to the current operating speed and given as the new speed.

Furthermore, if the pressure difference is within ±a, the process proceeds to step 26 without changing gears, and then returns to step 26 and repeats the subsequent steps until the measured pressure and target pressure substantially match.

By the way, the formula used in steps 14 and 22 is
Instead of formula (1), as mentioned above, when the pressure difference is within the range of i and j, △N=K・△H (2) where K: proportionality constant (slope of the straight line).

By using this, the μcon software can be made even simpler.

Incidentally, although the instruction system of the microcomputer in FIG. 8 of this embodiment is shown as an example using an "8080" or equivalent, the present invention is not limited to this.

As described above, according to this embodiment, the proportional-integral circuit PID for the speed command of the variable speed motor is no longer required.
Not only is it economically inexpensive, but by appropriately determining the shift control width △N and waiting time t according to the pressure difference between the target pressure and the measured pressure, the offset with respect to the target pressure can be reduced and the responsiveness can be improved. Not only can speed commands be improved, but direct speed commands can be provided in contrast to conventional indirect speed commands. Furthermore, it has the advantage that the convergence time to the target pressure is quick.

In addition, to prevent runaway, a minimum rotational speed Nmin and a maximum rotational speed Nmax are set, and operation is required between these limits, so there is no pressure drop and pressure changes are small, which adversely affects the control device of the variable speed motor. Never.

In this embodiment, the pressure sensor 8
The microcomputer μcon calculates and converts the difference between the measured pressure and the target pressure into a direct speed command difference, so if the pressure change is small, a small speed command signal is issued, and if it is large, a large speed command signal is issued. Therefore, the response is good and the overshoot with respect to the target value is small.

Furthermore, in a water supply system like this embodiment, if the pump capacity is to be changed due to an increase or decrease in the number of customers, or if the discharge pressure is to be changed, etc., the data is stored in the memory M of the microcomputer μcon prior to pump operation. New target discharge pressure, speed change control range for increasing or decreasing pump operating speed, pump operating limit speed (maximum rotation speed and minimum rotation speed),
Furthermore, it is convenient to add a control step for inputting data such as the initial rotational speed of the pump, which is provisionally determined at the initial stage of starting the water supply system.

〔Effect of the invention〕

The present invention is characterized in that pump water supply control is performed not by an analog system but by a digital system, in particular by a microcomputer, and that pressure is controlled based on the functional relationship between pressure deviation and command speed difference without performing PID processing. Obtaining a command speed difference corresponding to the deviation,
Since the variable speed pump was operated based on this command speed difference, it was possible to improve the response.

[Brief explanation of drawings]

Fig. 1 is a block diagram for explaining the configuration of one embodiment of the present invention, Fig. 2 is a characteristic curve diagram for explaining the operation of a conventional water supply device, and Fig. 3 is a control system of the conventional device. 4 is a timing diagram for explaining the control characteristics of the conventional device, FIG. 5 is a block diagram for explaining the configuration of the operation control device of the embodiment, and FIGS. FIG. 7 is a characteristic diagram showing the relationship between pressure difference and speed difference, and FIG. 8 is a flowchart for explaining the control procedure of the embodiment apparatus. 4... Pump, 7... Water supply pipe, 8... Pressure sensor, INV... Variable frequency inverter device, H ₀
...Target pressure.

Claims (1)

[Claims] 1. A pump that receives operating speed control corresponding to a target pressure, and a pump that is provided in a water supply pipe connected to the pump,
A pressure sensor detects a pressure corresponding to the pump operating speed, and the detected pressure of the pressure sensor is negatively fed back at a predetermined sampling period in order to converge to the operating speed of the pump to the operating speed corresponding to the target pressure, and the pressure detected by the pressure sensor is negatively fed back to the operating speed corresponding to the target pressure. means for calculating the deviation from the detected pressure at each sampling time; and pressure deviation-command speed difference conversion means for calculating the command speed difference corresponding to the pressure deviation from the relationship between the pressure deviation obtained from the characteristics of the pump and the command speed difference. ,
A pump water supply device comprising: a pump variable speed drive means that takes in the command speed difference, corrects the previous command speed according to the speed difference, and operates the pump at the corrected command speed. 2. When the pressure deviation is below a threshold value, the pump operating speed is considered to have converged to correspond to the target pressure, so zero is output as the command speed difference, and the pump speed is not changed. pump water supply device. 3 The above function is a negative command speed difference when the pressure deviation is positive, a positive command speed difference when the pressure deviation is negative, and the absolute value of each speed difference is the magnitude of the absolute value of the pressure deviation at that time. A pump water supply device according to claim 1 having a corresponding size. 4. The pump water supply device according to claim 1, wherein the command speed difference is not output and speed change is not performed when the current operating speed is either the pump minimum speed or the pump maximum speed.