JPS5947155B2 - Pump control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pump control method for keeping a pump discharge flow rate constant.

Conventionally, in order to keep the pump discharge amount constant, a method of controlling the rotation speed of the pump has generally been used.

As shown in FIG. 1, this method compares the flow rate set value given by a flow rate setting device 1 and the flow rate feedback signal detected by a flow meter 2, and determines the P value according to the deviation.
Pump drive motor 5 via I controller 3 and speed controller 4
The rotation speed of the pump 6 is controlled as a condition.
This was based on the assumption that there was a linear relationship between the discharge flow rate of the pump 6 and the rotational speed of the pump 6. However, as shown in FIG. 2, in reality, except for the case where the actual head is zero, the relationship is not linear but nonlinear as a whole, which is extremely inconvenient for control.

In order to eliminate this inconvenience, conventional methods have adopted a method of adding a function generator T to compensate for the nonlinear relationship between pump discharge flow rate and pump rotation speed, as shown in Figure 3, but this method is expensive. The disadvantage is that the pump control device is expensive because it uses a function generator.

Therefore, the present invention provides a rotation speed control method in which a rotation speed corresponding to a desired flow rate setting value is calculated from the Q-H characteristics and load characteristics of the pump 6, and this is used as a rotation speed command for a variable speed pump.
Through this rotation speed control, it is detected that the pump discharge flow rate is close to the flow rate set value, that is, a flow rate control method consisting of a flow rate setting device and a flow rate feedback circuit in a region where a linear relationship between the pump flow rate and the rotation speed holds. The present invention aims to provide a flow rate control method for operating a variable speed pump with high precision by switching to In particular, this method is highly effective when the operating point of the pump changes suddenly, such as during startup and flow rate setting. below,
An embodiment of the present invention will be described below with reference to FIG.

'' This embodiment adds a speed calculator 8 to the conventional circuit shown in FIG.
and two sets of absolute value calculators 9, 9', comparators 10, 10', one minute rotation speed setting device 11, and the comparators 10, 10.
Reed relays 12, 12' that operate according to each output of '
, and the speed calculator 8 calculates the rotational speed Ns based on the following equation in advance.

That is, the pump Q-H characteristic equation H: aN2-bQ2...
......(1) (1), (2) formulas and flow rate setting value Q
The rotation speed Nsvd for obtaining a predetermined flow rate is calculated from s, and the rotation speed of the variable speed pump 6 is first controlled to reach the value Ns.

At the same time, the speed command value Ns from the speed calculator 8 and the signal Ni from the speed detector 5a installed in the variable speed motor 5
The deviation ε1 is input to the comparator 10 by the absolute value calculator 9 as a positive deviation 1ε11.

The comparator 10 uses the set value Ni(5) of the minute rotation speed setting device 11.
1ε,1 is compared, and when 1ε11<NL, the output of the comparator 10 becomes a high level, energizing the reed relay 12 and closing its contact R1a.

By closing this contact R1a, the set value Qs of the flow rate setting device T
is input to the PI controller 6, its output gradually increases, and when the output values NO and Ns match, the deviation ε2 from NO(5Ns) is calculated using the absolute value calculator. 9' is set to 1ε21, and the comparator 10' compares it with NL of the minute rotation speed setting device 11', and when it becomes 1ε2KNL, the above-mentioned coincidence is detected.

In this case, the output of comparator 10' goes high and energizes the subsequent reed relay 12', opening its contacts R2b and closing its contacts R2a.

Therefore, the pump 6 shifts from rotation speed control to flow rate control.
As described above, according to the present invention, it is possible to perform constant pump discharge flow rate control without a function generator, and it is expected to improve control performance in pump transient conditions such as when changing flow rate settings. This invention enables stable flow rate control, and is a useful invention in providing a highly accurate pump control device that is practically cheaper than conventional pump control devices.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional pump control circuit, Fig. 2 is a pump rotation speed-flow characteristic diagram, Fig. 3 is a block diagram of a conventional high-precision pump control circuit, and Fig. 4 is a block diagram of an embodiment of the present invention. It is a block diagram. 1...Flow rate setting device, 2...Flowmeter,
3...PI controller, 4...speed controller, 5...pump drive motor, 6...pump, T...function Generator, 8... Speed calculator, 9 and 9'... Absolute value calculator, 10 and 10'... Ratio generator, 11 and 11'...・
...Minor rotation speed setting device, 12 and 12'...Reed relay.

Claims (1)

[Claims] 1. In a pump discharge flow constant control system based on rotational speed control, a speed calculation device is provided to calculate the rotational speed at which a predetermined flow rate is obtained from the flow rate-total head characteristics, load characteristics, and flow rate set value of the pump, and the calculated value is first converted to the speed. A pump control method characterized by controlling the rotation speed as a command value, and then switching to flow control with a flow rate feedback loop in a region where the flow rate and rotation speed of the pump can be linearized.