JPS6122157B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pump control device for variable speed operation, and particularly to a pump control device that can perform good operation even when the amount of water demanded decreases.

In variable-speed pump equipment that supplies water to apartment complexes, etc., a pressure holding tank is installed in the middle of the water supply pipe, and when the amount of water supplied becomes extremely low,
The pump is stopped and water is continued to be supplied using the water stored in the pressure holding tank. When the pressure inside the pressure tank drops, this is detected and the pump is restarted. Such an example is shown in FIG. That is, 1 is a suction water tank, and 2 is a pump that performs variable speed operation and is connected to variable speed drive means (not shown). The suction side of this pump 2 is connected to a suction water tank 1 via a stop valve 3. Further, the discharge side is connected to a water pipe 6 via a check valve 4 and a sluice valve 5. 7 is a pressure holding tank connected to 6 in the water pipe, and is equipped with an air supply mechanism 8. That is, this air replenishment mechanism 8 is composed of a drain solenoid valve 10, a water supply solenoid valve 11, an air suction valve 12, and a check valve 13, which operate in opposite directions with respect to the air replenishment tank 9. The sucked air is pushed into the pressure holding tank along with the water supply, and pump 2
Even when the system is stopped, a small amount of water can be continued to be supplied by the action of the compressed air in the pressure holding tank 7. 14 and 15 are a pressure detector and a flow switch attached to the discharge side of the pump 2. 1
6 is a pressure switch attached to the pressure holding tank 7, 1
7 is an orifice connected to the discharge side of the pump 2 to prevent the pump 2 from overheating.

That is, in the pump device configured in this way, in a range where the amount of water demanded is large, the pressure sensor 14 feeds back a pressure signal to the control device,
The variable speed drive means of the pump 2 is controlled so that the discharge pressure becomes equal to the target pressure. In addition, if the flow switch 15 detects that the amount of water demanded has decreased (almost in the range of zero), the pump 2 is stopped and the subsequent water supply is carried out by pushing out the water stored in the pressure holding tank 7. Continuing, when the pressure in the pressure holding tank 7 falls below a predetermined value, this is detected by the pressure switch 16, and the pump 2
I'm trying to restart it.

In this way, when the water demand is low, the pump 2 can be turned on and off by using the pressure holding tank 7.
By repeating the operation, the operating power cost of the pump device is reduced. However, a pump device having such a structure requires a pressure holding tank 7 or an air supply mechanism 8, which not only complicates the structure and increases equipment costs, but also requires a pump room with a large installation area.

Therefore, the present invention provides a pump device that can be constructed with extremely low equipment costs.

In other words, the features of the present invention include a variable speed drive means for the pump, a pressure detection means for detecting the discharge pressure of the pump, and a system for controlling the pump so as to receive a pressure signal from the pressure detection means and maintain the discharge pressure of the pump at a predetermined target pressure. In a pump device that performs speed control operation and is equipped with an arithmetic control means that issues a speed command signal to the variable drive means, a limit flow rate detection means that issues a minimum speed operation command of the pump when the discharge flow rate of the pump reaches a predetermined limit flow rate; ,
limit pressure detection means that issues a pump minimum speed operation cancellation command when the pump discharge pressure reaches a predetermined limit pressure; and a limit pressure detection means that issues a pump minimum speed operation cancellation command after the pump minimum speed operation command is input. The invention also includes arithmetic control means for issuing a minimum speed command signal to the variable speed drive means of the pump for operating the pump at the minimum speed until the pump reaches the minimum speed. Therefore, by combining the signals from the flow rate detector and the pressure detector, the pressure drop on the discharge side is monitored after the pump shifts to the lowest speed operation, and when this discharge pressure reaches a predetermined limit pressure, the pump Since the lowest speed operation is canceled, even if disturbances such as a drop in power supply voltage or deterioration of suction conditions occur,
This effect can be avoided.

Hereinafter, one embodiment of the present invention will be described in detail. That is, the present invention eliminates the need for the pressure holding tank 7, air replenishment mechanism 8, etc. shown in FIG.
FIG. 2 is a block diagram for explaining the configuration of the embodiment, in which reference numeral 18 denotes a variable speed drive means for driving the pump 2, a motor 19 and an eddy current coupling 2.
It is composed from 0. Reference numeral 21 denotes limit flow rate detection means, which inputs flow rate signals from a flow rate detector 22 for detecting the discharge flow rate of the pump 2, a limit flow rate setter 23 set to a value corresponding to a flow rate near zero flow rate to be detected. , a flow rate comparator 24 which issues a minimum speed operation command when the flow rate signal from the flow rate detector 22 becomes less than the value set by the limit flow rate setter 23. Reference numeral 25 denotes a limit pressure detection means, which inputs the pressure signals of the pressure detector 14, the limit pressure setter 26 set to a value corresponding to the minimum pressure to be detected, and the pressure signal from the pressure detector 14 as the limit pressure. It is comprised of a pressure comparator 27 that issues a minimum speed operation cancellation command when the pressure falls below the value set in the setting 26. Reference numeral 28 denotes an arithmetic control means, which sets a target discharge pressure setting device 29 to a value corresponding to the target discharge pressure on the discharge side of the pump 2 and a minimum operating speed of the pump 2 in a normal water supply state. A minimum speed setting device 30 is provided. In normal water supply conditions, this calculation control means also takes in the pressure signal from the pressure detector 14 and compares it with the set value set in the target discharge pressure setting device 29 so that the discharge pressure of the pump 2 becomes equal to the set value. The excitation current of the eddy current joint 20 is controlled. That is,
When the discharge pressure becomes higher than the target pressure, the excitation current is decreased and the pump 2 is decelerated, and when the discharge pressure becomes lower than the target pressure, the excitation current is increased and the pump 2 is accelerated. Further, the calculation control means 28 operates at the lowest speed preset by the lowest speed setting device 30 until the lowest speed operation command signal is input from the flow rate comparator 24 and the lowest speed operation cancellation command signal is input from the pressure comparator 27. pump 2
The excitation current of the eddy current joint 20 is controlled so as to operate the eddy current joint 20.

Further explanation will be added with reference to FIG. Third
In the figure, the horizontal axis shows the discharge flow rate Q of the pump 2, and the vertical axis shows the discharge pressure H. In the figure, L is a pump characteristic curve when pump 2 is operated at full speed, l is a pump characteristic curve when speed control operation is performed, and l ₀ is a pump characteristic curve when pump 2 is operated at minimum speed. Furthermore, H ₁ , H ₂ , and H ₃ represent the actual head, the required end pressure, and the piping loss when water is supplied at the maximum flow rate, respectively. H ₀ is a target pressure determined in advance as a target. Q ₀ is the limit flow rate set near zero water demand, and l ₀ is the limit flow rate Q _0. When supplying the limit flow rate Q 0, pump 2 is operated at the lowest speed to obtain a pressure close to the desired end pressure H ₂ at the pipe end. In _the pump characteristic curve _of pump 2 when

That is, to summarize the operation of the embodiment, in the case of normal operation in which the demand water quantity Q exceeds the limit water quantity _Q0 , the arithmetic control means 28 detects the discharge pressure H of the pump 2 by the pressure detector 14, and adjusts the discharge pressure. A necessary speed command signal is issued to the variable speed drive means 18 so that H becomes equal to the target discharge pressure H ₀ . Further, when the demand water amount Q decreases and reaches the limit flow rate _Q0 , the calculation control means 28 uses the flow rate comparator 24
When the minimum speed operation command signal is received from the variable speed drive means 18, the normal speed control operation for constant discharge pressure is interrupted, and the variable speed drive means 18 is instructed to operate the pump 2 at the minimum speed corresponding to the pump characteristic curve _I0 . Issues minimum speed command signal. This minimum speed command signal causes variable speed drive until the demand water amount Q increases, the discharge pressure amount H decreases to the limit pressure _H4 , and the minimum speed operation cancellation command signal from the pressure comparator 27 is applied to the calculation control means 28. It continues to be output to the means 18. When the minimum speed operation cancellation command signal is issued, the arithmetic control means 28 issues a speed command signal again, and operates under speed control so as to maintain the discharge pressure at the target discharge pressure H ₀ .

In the embodiment described above, the pressure H and flow rate Q on the discharge side of the pump 2 are detected using the pressure detector 14 and the flow rate detector 22, and are passed through the pressure comparator 27 and the flow rate comparator 24, respectively. According to
The minimum speed operation cancellation command and the minimum speed operation cancellation command are obtained, but these are ON or ON at the limit flow rate Q ₀ or less.
Flow switch turned OFF, also limit pressure H ₄
You can also use a pressure switch that turns on or off as follows. Furthermore, it is desirable that the minimum speed be set in the relationship shown in the example, but it _is not limited to this _.
It is a good operating speed if the above discharge pressure H is obtained. Naturally, the minimum speed at this time is
The operating speed must be slower than the operating speed required to generate the target discharge pressure amount H ₀ at the critical flow rate Q ₀ , and moreover, the operating speed must be capable of supplying the discharge pressure H exceeding the actual head H ₁ . In addition, when the critical pressure H ₄ exceeds the critical flow rate Q ₀ and the water demand increases,
It is possible to set an appropriate pressure that exceeds the actual head H ₁ and intersects the pump characteristic curve l ₀ . Further, in the embodiment, the variable drive means 18 of the pump is constituted by the motor 19 and the eddy current coupling 20, but this can also be done by controlling the voltage of the motor, or by using static cerbium control.

In this way, the present invention decelerates the pump to the minimum speed and continues operating the pump when the water demand decreases to around zero, and when the zero water demand increases and the pressure on the discharge side decreases, the normal discharge pressure is reduced. This returns to constant control. Therefore, according to the present invention, there is no need for a pressure holding tank and an air supply mechanism, and the initial equipment cost can be reduced.Furthermore, the floor area of the pump room can be reduced, so civil engineering and construction costs can be reduced. can be reduced. Furthermore, according to the present invention, the frequency of starting the pump is extremely reduced, thereby extending the life of the equipment and reducing the shock to the power supply. In addition, since the operating power cost of a pump is proportional to the cube of the number of revolutions, compared to conventional pumps that turn on and off when the water demand is low, the present invention operates at low speed when the water demand is near zero. A pump device that continues to do so would be advantageous.

Furthermore, in the present invention, normal operation of the pump is resumed by a signal from a pressure detector, so even if a disturbance such as a drop in power supply voltage or deterioration of pump suction conditions occurs during minimum speed operation, this will not occur. This allows for stable operation at all times by avoiding any negative effects.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a pump for explaining the configuration of a conventional pump device, FIG. 2 is a block diagram for explaining one embodiment of the present invention, and FIG.
FIG. 3 is a pump characteristic curve diagram for explaining the operation of the embodiment shown in the figure. 2...Pump, 14...Pressure detector, 18...Variable speed drive means, 21...Limit flow rate detection means, 25...Limit pressure detection means, 28...Calculation control means, _H0 ...Target pressure, _H4 ...Limit pressure, Q ₀ ...Limit flow rate.

Claims (1)

[Claims] 1. A variable speed drive means for the pump, a pressure detection means for detecting the discharge pressure of the pump, and a pressure signal received from the pressure detection means to control the speed to the variable speed drive means for the pump so as to maintain the discharge pressure of the pump at a predetermined target pressure. In a pump device that performs speed control operation and is equipped with arithmetic control means that issues a command signal, the pump device includes a limit flow rate detection device that issues a minimum speed operation command for the pump when the discharge flow rate of the pump reaches a predetermined limit flow rate, and a pump discharge pressure limit pressure detection means that issues a minimum speed operation cancellation command for the pump when the pump reaches a predetermined limit pressure; 1. A control device for a pump, comprising: arithmetic control means for issuing a minimum speed command signal for driving the speed command signal to a variable speed drive means of the pump.