Water pump rotating speed control method for flow stability in water flow standard device

Abstract

The invention discloses a water pump rotating speed control method for flow stability in a water flow standard device, and belongs to the technical field of water pump flow control, the water pump rotating speed control method for flow stability in the water flow standard device comprises the following specific implementation steps: step 1, setting control parameters; 2, adjusting the frequency of an output frequency converter, and outputting the frequency; 3, information in the water pump rotating speed control process is collected; 4, judging a detection signal; and 5, calculating the rotating speed PID, and returning a result. A water pump motor rotating speed closed-loop control method is adopted, so that a pressure head for liquid flowing is constant, and the effect of stabilizing flow is achieved. The flow stability achieves the pressure stabilizing effect of a water tower and is better than the pressure stabilizing effect of a pressure stabilizing tank.

Description

Technical Field

[0001] The invention relates to the technical field of water pump flow control, and more specifically to a water pump speed control method for flow stability in a water flow standard device. Background Art

[0002] Liquid flow meter is a measuring instrument. The standard device for calibration and testing is called liquid flow standard device. Its technical indicators are uncertainty and stability. To ensure the stability of the flow of liquid flow standard device, the traditional method is to "use a constant liquid level high-level container to supply water", that is, the high-level water tower method, see Figure 3 As shown in the figure, it is still generally considered to be the water supply method with the best stability index. It uses a constant liquid level to keep the pressure head of the liquid constant, thus achieving a stable flow rate.

[0003] At present, among the traditional control methods for flow control, the water tower pressure stabilization method has high cost and slow stabilization response, while the pressure stabilization tank method is only suitable for flow control at lower flow rates. When the flow rate is large, the flow control effect is poor.

[0004] Therefore, in view of this, the existing structure is studied and improved, and a water pump speed control method for flow stability in a water flow standard device is provided, in order to achieve a more practical purpose. Summary of the invention

[0005] 1. Technical issues to be solved

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a water pump speed control method for flow stability in a water flow standard device, which uses a closed-loop control method of the water pump motor speed to keep the pressure head of the liquid flow constant and achieve the effect of stabilizing the flow. The flow stability can achieve the effect of water tower pressure stabilization, which is better than the pressure stabilization effect of the pressure stabilizing tank.

[0007] 2. Technical solution

[0008] To solve the above problems, the present invention adopts the following technical solutions.

[0009] A method for controlling the speed of a water pump for flow stability in a water flow standard device. The specific implementation steps of this control method are as follows:

[0010] Step 1: Set the control parameters: Based on the control of the water pump speed control software, set the closed-loop parameters, closed-loop speed and open-loop output frequency in the software;

[0011] Step 2: Adjust the output frequency of the inverter and output: adjust the power supply frequency of the inverter, and the speed of the water pump changes with the power supply frequency of the inverter;

[0012] Step 3: Collect information during the water pump speed control process: When the output inverter frequency changes or stabilizes, detect information about the speed, pressure and flow during the water pump speed control process;

[0013] Step 4: Determine the detection signal: Establish a determination process, and determine whether it is in closed-loop control based on the collected signal. If it is not in closed-loop control, return to step 2;

[0014] Step 5: Calculate the speed PID and return the result: Calculate the speed PID to obtain the output frequency, and return the result to step 2.

[0015] Furthermore, in step one, a main loop and a sub-loop are provided in the water pump speed control software, wherein when the main loop system does not change to set the control parameters, the control variable changed in the sub-loop is the water pump speed.

[0016] Furthermore, in step 1, the closed-loop parameters, closed-loop speed and open-loop output frequency in the software are all set as initial parameters.

[0017] Furthermore, in the step 2, when adjusting the power supply frequency of the frequency converter, the expression of the ratio of the pipeline flow rate to be compared is:

[0018]

[0019] Among them, a is the average value of the average pipeline flow rate;

[0020] n is the number of collected statistics;

[0021] q n It is the value of the flow collected at the corresponding number of times. During the measurement, the change in the power supply frequency between two adjacent measurements is a multiple of 0.01Hz.

[0022] Furthermore, in step 2, the empirical formula for flow rate change before and after the frequency converter is adjusted is:

[0023]

[0024] Among them, Q t It is the flow value expected to be achieved after adjusting the inverter frequency at the current electric control valve opening.

[0025] f0 is the inverter frequency before adjustment.

[0026] Q0 is the flow rate before adjusting the frequency of the inverter at the current electric control valve opening.

[0027] f t is the adjusted inverter frequency.

[0028] Furthermore, in step 2, the speed controller of the water pump adopts a PID controller, and the PID controller is controlled by a PLC.

[0029] Furthermore, in step three, when detecting or measuring the rotation speed of the motor of the water pump, a 1024-line photoelectric encoder is used.

[0030] Furthermore, in step three, pressure feedback is performed after measurement, and the pressure feedback controls the main loop of the system.

[0031] Furthermore, in step 5, when calculating PID, the expression is:

[0032]

[0033] Where u(t) is the output of the controller;

[0034] e(t) is the deviation between the set value and the actual value;

[0035] K p , K i , K d They are proportional, integral and derivative control parameters respectively.

[0036] 3. Beneficial effects

[0037] Compared with the prior art, the advantages of the present invention are:

[0038] This solution establishes a pressure-speed system when controlling the flow rate, and based on this system, uses a closed-loop control method for the speed of the water pump motor to control the pressure. The control loop of the closed-loop control method for the speed of the water pump motor is: photoelectric encoder-frequency converter-water pump speed-photoelectric encoder. The control loop is very short and has a small lag. When the flow rate has not changed, but the speed of the water pump motor has changed slightly, the speed control is performed immediately to achieve the effect of stabilizing the flow rate. This method can quickly reduce the flow rate fluctuation caused by power supply fluctuations, and has low cost, fast response, and a large range of stable flow. The optimization effect is greatly improved compared to the voltage stabilization method of the voltage stabilization tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of the water pump speed control in the present invention;

[0040] Figure 2 It is a system schematic diagram of the pressure-speed control system of the present invention;

[0041] Figure 3 This is a schematic diagram of a liquid flow standard device using a high-level water tower;

[0042] Figure 4This is a schematic diagram of a liquid flow standard device that uses a frequency converter and a pressure-stabilizing tank to form a flow stabilizer. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

[0044] Embodiment 1:

[0045] See also Figure 1 , a water pump speed control method for flow stability in a water flow standard device, the specific implementation steps of this control method are as follows:

[0046] Step 1: Set the control parameters: Based on the control of the water pump speed control software, set the closed-loop parameters, closed-loop speed and open-loop output frequency in the software.

[0047] ① The speed control software is set with a main loop and a sub-loop. When the main loop system does not change and the control parameters are set, the control variable that changes in the sub-loop is the pump speed.

[0048] ②The closed-loop parameters, closed-loop speed and open-loop output frequency in the setting software are all initial parameters.

[0049] Step 2: Adjust the output frequency of the inverter and output: adjust the power supply frequency of the inverter, and the speed of the water pump changes with the power supply frequency of the inverter.

[0050] ① When adjusting the power supply frequency of the inverter, the expression of the ratio of the pipeline flow rate to be compared is:

[0051]

[0052] Among them, a is the average value of the ratio of the average pipeline flow value.

[0053] n is the number of collected statistics.

[0054] q n It is the value of the flow collected at the corresponding number of times. During the measurement, the change in the power supply frequency between two adjacent measurements is a multiple of 0.01Hz.

[0055] ② The empirical formula for flow change before and after the frequency adjustment of the inverter is:

[0056]

[0057] Among them, Qt It is the flow value expected to be achieved after adjusting the inverter frequency at the current electric control valve opening.

[0058] f0 is the inverter frequency before adjustment.

[0059] Q0 is the flow rate before adjusting the frequency of the inverter at the current electric control valve opening.

[0060] f t is the adjusted inverter frequency.

[0061] ③The speed controller of the water pump adopts PID controller, which is controlled by PLC.

[0062] The speed controller is a PID controller, which is implemented by PLC to keep the speed of the water pump constant, which is called "water pump constant speed control method".

[0063] Step 3: Collect information during the water pump speed control process: When the output inverter frequency changes or stabilizes, detect information about the speed, pressure and flow during the water pump speed control process.

[0064] ① When detecting or measuring the speed of the water pump motor, a 1024-line photoelectric encoder is used. That is, the motor can send out 1024 pulse signals for each rotation of the motor. If the motor speed is 1000 rpm, the speed measurement sensitivity is one millionth.

[0065] ②After measurement, pressure feedback is performed, and the pressure feedback is used to control the main circuit of the control system. It can ensure that the pressure remains the same at different test flow points.

[0066] Step 4: Determine the detection signal: Establish a determination process to determine whether it is in closed-loop control based on the collected signal. If it is not in closed-loop control, return to step 2.

[0067] Step 5: Calculate the speed PID and return the result: Calculate the speed PID to obtain the output frequency, and return the result to step 2.

[0068] When calculating PID, the expression is:

[0069]

[0070] Where u(t) is the output of the controller.

[0071] e(t) is the deviation between the set value and the actual value.

[0072] K p , K i , K d They are proportional, integral and derivative control parameters respectively.

[0073] Embodiment 2:

[0074] Based on the above embodiment 1, further description is given.

[0075] See also Figure 2 According to the water pump theory, there are two reasons for the change of flow rate Q in the pipeline:

[0076] First, the performance of the water pump changes;

[0077] Second, the pipeline performance changes.

[0078] When the opening of the regulating valve remains unchanged, the pipeline characteristics can be considered unchanged, that is, when a flow point is calibrated, the opening of the regulating valve remains unchanged. At this time, the working point of the water pump is only related to the performance curve of the water pump.

[0079] The impeller and other mechanical structures of the same water pump are fixed, and its performance curve is only related to the speed of the water pump. At this time, the direct cause of the fluctuation of the pump outlet pressure and pipeline flow is the fluctuation of the water pump speed. Therefore, the speed is selected as the control variable of the secondary loop, and a control system is formed with the pressure loop.

[0080] In this pressure loop system, the control loop is: photoelectric encoder - frequency converter - pump speed - photoelectric encoder. The control loop is very short and the lag is very small. That is, the flow rate has not changed, but the speed of the pump motor has changed slightly, and the speed control is performed immediately.

[0081] Embodiment 3:

[0082] Specifically, methods for stabilizing flow also include a water tower pressure stabilization method and a pressure stabilization tank pressure stabilization method.

[0083] See also Figure 3 The operation method of the water pressure stabilization method is simple, but the construction cost of the water tower is high. With the expansion of production scale, the caliber of the flow meter being tested becomes larger and larger, which is not easy to operate.

[0084] See also Figure 4 The pressure stabilization method of the pressure stabilization tank is to use the frequency converter to change the power supply frequency to adjust the flow rate. At the same time, the pressure head of the liquid flow is kept constant through the pressure stabilization of the pressure stabilization tank to achieve the effect of stabilizing the flow rate. However, since the liquid is an incompressible fluid, a large-sized pressure stabilization tank needs to be built to achieve the stability of the flow rate. 5m 3 The surge tank is for 200m 3 A flow rate below 100 / h can achieve a good pressure stabilizing effect, but a larger flow rate will result in a poor pressure stabilizing effect.

[0085] The experimental data comparing the pressure stabilization effects of the water tower pressure stabilization method, the pressure stabilization tank method and the speed closed-loop control method are as follows:

[0086]

[0087]

[0088] As shown in the above table, the performance of the stability within the cumulative time and the stability between the cumulative time of the closed-loop control method of the water pump motor speed is generally higher than that of the water tower voltage stabilization method and the voltage stabilization tank method. Therefore, this closed-loop control method of the water pump motor speed has good practicality.

[0089] The above is only a preferred specific implementation of the present invention; however, the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solution and its improved conception within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for controlling the speed of a water pump for flow stability in a water flow standard device, characterized in that: The specific implementation steps of this control method are as follows: Step 1: Set the control parameters: Based on the control of the water pump speed control software, set the closed-loop parameters, closed-loop speed and open-loop output frequency in the software; Step 2: Adjust the output frequency of the inverter and output: adjust the power supply frequency of the inverter, and the speed of the water pump changes with the power supply frequency of the inverter; Step 3: Collect information during the water pump speed control process: When the output inverter frequency changes or stabilizes, detect information about the speed, pressure and flow during the water pump speed control process; Step 4: Determine the detection signal: Establish a determination process, and determine whether it is in closed-loop control based on the collected signal. If it is not in closed-loop control, return to step 2; Step 5: Calculate the speed PID and return the result: Calculate the speed PID to obtain the output frequency, and return the result to step 2.

2. The method for controlling the speed of a water pump for flow stability in a water flow standard device according to claim 1, characterized in that: In the step 1, a main loop and a sub-loop are provided in the water pump speed control software, wherein when the main loop system does not change to set the control parameters, the control variable changed in the sub-loop is the water pump speed.

3. The method for controlling the speed of a water pump for flow stability in a water flow standard device according to claim 1, characterized in that: In the step 1, the closed-loop parameters, closed-loop speed and open-loop output frequency in the software are all set as initial parameters.

4. The method for controlling the speed of a water pump for flow stability in a water flow standard device according to claim 1, characterized in that: In the step 2, when adjusting the power supply frequency of the frequency converter, the expression of the ratio of the pipeline flow rate to be compared is: Among them, a is the average value of the average pipeline flow rate; n is the number of collected statistics; q n It is the value of the flow collected at the corresponding number of times. During the measurement, the change in the power supply frequency between two adjacent measurements is a multiple of 0.01Hz.

5. The method for controlling the speed of a water pump for flow stability in a water flow standard device according to claim 4, characterized in that: In step 2, the empirical formula for flow rate change before and after the frequency converter is adjusted is: Among them, Q t It is the flow value expected to be achieved after adjusting the inverter frequency at the current electric control valve opening. f0 is the inverter frequency before adjustment. Q0 is the flow rate before adjusting the frequency of the inverter at the current electric control valve opening. f t is the adjusted inverter frequency.

6. The method for controlling the speed of a water pump for flow stability in a water flow standard device according to claim 1, characterized in that: In the step 2, the speed controller of the water pump adopts a PID controller, and the PID controller is controlled by a PLC.

7. The method for controlling the speed of a water pump for flow stability in a water flow standard device according to claim 1, characterized in that: In the step three, when detecting or measuring the rotation speed of the motor of the water pump, a 1024-line photoelectric encoder is used.

8. The method for controlling the speed of a water pump for flow stability in a water flow standard device according to claim 2, characterized in that: In the step three, pressure feedback is performed after measurement, and the pressure feedback is performed on the main loop of the control system.

9. The method for controlling the speed of a water pump for flow stability in a water flow standard device according to claim 1, characterized in that: In step 5, when calculating PID, the expression is: Where u(t) is the output of the controller; e(t) is the deviation between the set value and the actual value; K p , K i , K d They are proportional, integral and derivative control parameters respectively.

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