Methods and devices for balanced pressure control of circulating pump units in headless continuous casting and rolling production lines

Abstract

This invention proposes a method and device for balanced pressure stabilization control of a circulating pump group in a headless continuous casting and rolling production line. The method includes: performing PID control based on the deviation between a given pressure value and the actual feedback pressure to control the pump operating speed and obtain a first pump speed; performing current balance control on each pump in the pump group to correct the pump operating speed and obtain a second pump speed; and determining the final operating speed of the pumps to be put into operation based on the first pump speed and the second pump speed. This method not only achieves stable and constant pressure water supply from the three pump groups (continuous casting secondary cooling water, low-pressure rolling mill, and high-pressure rolling mill) in the circulating cooling water pool of the production line, but also achieves automatic control of balanced output of each pump and automatic dynamic tracking of user water demand.

Description

Technical Field

[0001] This invention relates to the field of cast steel technology, and in particular to a method and device for balanced pressure control of a circulating pump group in a headless continuous casting and rolling production line. Background Technology

[0002] The continuous casting and rolling production line's turbidity cooling water tank requires stable and constant pressure water supply from three pump sets: the secondary cooling water for continuous casting, the low-pressure water for rolling, and the high-pressure water for rolling. Each pump set consists of multiple pumps, and the water consumption of each pump set is adjusted according to the production line's process, making real-time acquisition difficult. The pump set needs to automatically increase or decrease the number of pumps operating within the set based on the production line's water demand to meet the on-site constant pressure water supply requirements. In addition, the water flow rate varies significantly under different operating modes of the production line, and the system must be able to respond to water demand promptly to ensure stable pressure. Finally, all pumps within the pump set must have the same output, which means that all pumps must have consistent current. If the currents differ significantly, the pumps with lower currents will have poor efficiency, resulting in energy loss and wasted power over long-term operation, while the pumps with higher currents will have higher output, leading to severe wear on the pump blades over long-term operation. Therefore, the pump set control not only needs to achieve constant pressure water supply but also needs to ensure that the operating current of all pumps within the set is consistent.

[0003] Because the pump set needs to achieve both stable constant pressure water supply and consistent output from all pumps, the conventional control algorithm uses a cascade PID control algorithm. The master PID loop acts as a pressure regulating loop to ensure pressure demand, while the slave PID loops act as current regulating loops to achieve current balance. The principle and structure of this control method are shown in [link to relevant documentation]. Figure 1 As shown in the figure. This method adjusts the pump speed according to the current output of the pressure regulation loop of the main PID in the current control loop of the PID, so as to achieve the purpose of consistent current. However, in practical applications, the motor speed cannot be stably controlled by current control. The main reasons include: (1) When the motor speed is increased or decreased, the motor needs to accelerate or decelerate, and the motor current is extremely unstable at this time; (2) When the pump is running at a fixed speed, the current also changes. Therefore, adjusting the speed by feedback current will directly lead to the speed control fluctuating, the motor speed cannot be stabilized, the system is constantly adjusting, and the pressure cannot be stabilized. Therefore, it is necessary to improve the existing pump group pressure stabilization control method. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a method and device for balanced pressure control of the turbidity circulation pump group in a headless continuous casting and rolling production line. By improving the control method of the pump group, this method not only achieves stable and constant pressure water supply from the three pump groups of the continuous casting secondary cooling water, rolling low pressure, and rolling high pressure in the turbidity circulation cooling water pool of the production line, but also realizes automatic control of the balanced output of each pump, and achieves automatic dynamic tracking of user water demand.

[0005] To achieve the above objectives, this invention provides a method for balanced pressure control of a circulating pump group in a headless continuous casting and rolling production line. Each pump group has N pumps, where N is greater than or equal to 2, including:

[0006] PID control is performed based on the deviation between the given pressure value and the actual feedback pressure to control the pump operating speed and obtain the first pump speed;

[0007] The current balance control is performed on each pump in the pump set to correct the pump operating speed and obtain the second pump speed;

[0008] Based on the speed of the first pump and the speed of the second pump, the final operating speed of the pump put into operation is determined.

[0009] Optionally, the PID control employs a dynamic parameter adjustment method, where the proportional and integral parameters of the PID control loop change proportionally to the deviation between the given pressure value and the actual feedback pressure.

[0010] Optionally, the output of the PID control loop can be limited based on the frequency converter's response speed. The deviation between the current PID control loop output and the previous PID control loop output cannot exceed the maximum increase or decrease value of the frequency converter.

[0011] If the increase or decrease exceeds the maximum increase or decrease value, the increase or decrease shall be based on the maximum increase or decrease value.

[0012] The maximum increase / decrease value = (maximum motor frequency / frequency converter acceleration / decrease time) * (PID control loop execution cycle / frequency converter acceleration / decrease time).

[0013] Optionally, the step of performing current balance control on each pump in the pump group to correct the pump operating speed and obtain a second pump speed includes:

[0014] Collect the current of all pumps in the pump set.

[0015] When the deviation between the maximum current and the minimum current exceeds the preset deviation adjustment value, the current balance adjustment is performed on the two pumps corresponding to the maximum current and the minimum current until the current deviation between any two pumps in the pump group meets the preset deviation adjustment value.

[0016] Optionally, the current balancing adjustment of the two pumps corresponding to the maximum and minimum currents includes:

[0017] Correct the pump's operating speed corresponding to the maximum current. The correction value for the pump's operating speed corresponding to the maximum current = the current operating speed of the pump corresponding to the maximum current - the current deviation * the adjustment coefficient.

[0018] Correct the pump's operating speed corresponding to the minimum current. The correction value for the pump's operating speed corresponding to the minimum current = the current operating speed of the pump corresponding to the minimum current + the current deviation * the adjustment coefficient.

[0019] Wherein, the current deviation is the deviation between the maximum current and the minimum current, and the adjustment coefficient k = r * (50 / rated current of pump motor), where r represents the adjustment coefficient.

[0020] Optionally, before performing current balance control on each pump in the pump group, when the production line operation mode changes, the pump operation control is performed to increase or decrease the number of pumps required for each pump group. Pumps that meet the operation conditions are put into operation or cut off operation control one by one. After each pump is put into operation or cut off operation, the operation of the next pump is carried out until the number of pumps in operation meets the on-site requirements.

[0021] Optionally, at least one of the following conditions can be used to select whether to start or stop the pump: pump serial number, pump single run time, pump single stop time, pump cumulative run time, and pump cumulative stop time.

[0022] Optionally, the final operating speed of the pump to be put into operation is determined based on the sum of the speeds of the first pump and the second pump.

[0023] In another aspect, the present invention provides a pump balancing and pressure stabilizing control device for a turbid circulation pump group in a headless continuous casting and rolling production line, employing the aforementioned pump balancing and pressure stabilizing control method for a turbid circulation pump group in a headless continuous casting and rolling production line, comprising at least:

[0024] The PID control module is used to perform PID control based on the deviation between the given pressure value and the actual feedback pressure to control the pump speed and obtain the first pump speed.

[0025] The current balance control module is used to perform current balance control on each pump in the pump group, correct the pump control speed, and obtain the second pump speed.

[0026] The pump final operating speed control module is used to determine the final operating speed of the pump to be put into operation based on the speed of the first pump and the speed of the second pump.

[0027] As can be seen from the above solutions, the advantages of the present invention are:

[0028] The present invention provides a pump balancing and pressure stabilization control method for a circulating pump group in a headless continuous casting and rolling production line. This method uses PID control based on the deviation between a given pressure value and the actual feedback pressure to control the pump operating speed, obtaining a first pump speed. Simultaneously, by performing current balancing control on each pump in the pump group, the pump operating speed is corrected to obtain a second pump speed. Then, based on the first and second pump speeds, the final operating speed of the pumps to be put into operation is determined. In a headless continuous casting and rolling production line, this control method automatically controls the number of pumps operating according to the production line's operating mode. Through constant pressure control and current balancing control, it achieves stable pressure control of the pump group while ensuring consistent output of each motor. After the system is put into operation, it achieves automatic control of the pump group with high control accuracy, small pressure deviation, and fast dynamic response, overcoming the drawbacks of high labor intensity and slow real-time response associated with manual control. Attached Figure Description

[0029] Figure 1 This is a logic diagram of the existing balanced pressure control method for the circulating pump group in a headless continuous casting and rolling production line.

[0030] Figure 2 A schematic diagram of the pump equalization and pressure stabilization control method for the turbid ring pump group in the headless continuous casting and rolling production line provided in the embodiment of the present invention;

[0031] Figure 3 This is a control principle diagram of the pump equalization and pressure stabilization control method for the turbid ring pump group in the headless continuous casting and rolling production line provided in an embodiment of the present invention;

[0032] Figure 4 A framework diagram of the pump equalization and pressure stabilization control device for the turbid ring pump group in the headless continuous casting and rolling production line provided by the present invention;

[0033] in,

[0034] 400-Headless Continuous Casting and Rolling Production Line Turbid Ring Pump Group Pump Balance and Pressure Stabilization Control Device;

[0035] 401-PID control module;

[0036] 402 - Current Balance Control Module;

[0037] 403 - Pump final operating speed control module. Detailed Implementation

[0038] To make the above features and effects of the present invention clearer and easier to understand, specific embodiments are described below, and detailed descriptions are provided in conjunction with the accompanying drawings.

[0039] This invention provides a method for balanced pressure control of a circulating pump group in a headless continuous casting and rolling production line. Specifically, as shown... Figure 2 As shown, Figure 2This diagram illustrates the specific process of the pump balancing and pressure stabilization control method for the circulating pump group in the headless continuous casting and rolling production line. Figure 3 The schematic diagram of this control method is shown.

[0040] In the continuous casting and rolling production line, each pump group has N pumps, where N is greater than or equal to 2. The number of pumps required to operate depends on the production line's operating mode; the greater the water consumption, the more pumps need to be put into operation, and vice versa. When the system is first put into automatic operation, it starts the pumps at the default number to ensure system stability.

[0041] In practical implementation, the pump set control function aims to achieve both stable constant pressure water supply and automatic control of balanced output from each pump. The standard for measuring balanced output is that the difference between the maximum and minimum currents of all operating pumps must be less than or equal to the preset maximum current balance deviation. The pump current magnitude primarily depends on the motor control speed; the higher the speed, the higher the current. Therefore, this embodiment retains the PID speed regulation stage for pressure control in conventional control methods while adding current balance control for each pump. Specifically,

[0042] A method for balanced pressure control of a circulating pump group in a headless continuous casting and rolling production line includes:

[0043] S1. Based on the deviation between the given pressure value and the actual feedback pressure, PID control is performed to control the pump running speed and obtain the first pump speed U(t).

[0044] In practical implementation, the production line has high requirements for water supply, needing to ensure both stable pressure and rapid dynamic response to guarantee stable operation. In conventional PID control, the control parameters are determined and fixed after on-site commissioning. To improve the system's dynamic response speed, this embodiment employs a dynamic parameter adjustment method for PID control. The water supply pressure control adjusts the pump's operating speed based on the deviation between the given pressure value and the actual feedback pressure, thereby improving system response speed to meet the water supply needs of the rolling mill process. Larger proportional and integral parameters in the PID control loop result in faster dynamic response but also lower system stability and a higher risk of overshoot, which is unacceptable. Therefore, this embodiment uses a dynamic parameter adjustment method, where the proportional and integral parameters of the PID control loop are proportional to the deviation between the given pressure value and the actual feedback pressure. That is, the larger the pressure deviation, the larger the proportional and integral parameters are adjusted, and vice versa. This encourages the system pressure to quickly approach the target value. Once close to the target value, the proportional and integral parameters decrease to ensure pressure stability and reduce overshoot. In this embodiment, pressure control adopts dynamic PID control. Compared with conventional PID control, the system has a fast dynamic response, small fluctuations, and stable control.

[0045] Furthermore, in practical applications, pressure control often exhibits overshoot. This is because, during the control process, after the output pump speed reaches the variable frequency drive (VFD), the VFD response cannot keep up with the algorithm output; that is, the VFD response lags. This results in a significant difference between the controlled speed and the actual output speed of the VFD. For example, when increasing pressure, once the set pressure is reached, the controlled output speed exceeds the actual speed, and the pump speed continues to increase, leading to pressure overshoot. Conversely, when decreasing pressure, the controlled output speed is less than the actual speed, and the pump speed continues to decrease, resulting in pressure significantly lower than the set pressure. Therefore, in PID control, the change in control output must meet the response speed of the VFD. The response speed of the VFD is determined by the acceleration and deceleration time of the VFD. For example, when the acceleration time of the VFD is 30 seconds, the maximum frequency increase per second is 50 Hz / 30 seconds = 1.66667 Hz / s. Therefore, when using PID control output, it is necessary to limit the increment / decrease range each time. The output of the PID control loop is limited based on the response speed of the frequency converter. The deviation between the current output of the PID control loop and the previous output cannot exceed the maximum increment / decrease range of the frequency converter. Specifically, the output of the PID control loop is limited based on the response speed of the frequency converter. The deviation between the current output of the PID control loop and the previous output cannot exceed the maximum increment / decrease range of the frequency converter. If the deviation exceeds the maximum increment / decrease range, the output is increased or decreased based on the maximum increment / decrease range. The maximum increment / decrease range is calculated as: (maximum motor frequency / frequency converter acceleration / decrease time) * (PID control loop execution cycle / frequency converter acceleration / decrease time).

[0046] S2. Perform current balance control on each pump in the pump set, correct the pump operating speed, and obtain the second pump speed y. i (t).

[0047] In practical implementation, at the same speed, the imbalance of motor current can be caused by factors such as pump efficiency, motor efficiency, and pipeline location. When adjusting the current, the pump needs to increase or decrease its speed. In this case, relying solely on feedback current to control the speed will cause the speed to fluctuate, making it impossible to control the pump speed stably, which in turn leads to unstable pressure control.

[0048] Therefore, to reduce current fluctuations caused by speed regulation, it is crucial to perform current balancing regulation, especially for overall scheduling when multiple pumps are operating. In practical applications, simultaneously performing current balancing regulation on multiple pumps at once yields poor results and leads to significant pressure fluctuations. This embodiment employs a current balancing control strategy. Under stable pressure conditions, by collecting the current of all pumps in the pump group, and comparing only the maximum and minimum currents, current balancing regulation is performed on the two pumps corresponding to the maximum and minimum currents when the deviation between the maximum and minimum currents exceeds a preset deviation adjustment value. This continues until the current deviation between any two pumps in the pump group meets the preset deviation adjustment value. Specifically, the operating speed of the pump corresponding to the maximum current is corrected: the correction value for the operating speed of the pump corresponding to the maximum current = the current operating speed of the pump corresponding to the maximum current - the current deviation * the adjustment coefficient; the operating speed of the pump corresponding to the minimum current is corrected: the correction value for the operating speed of the pump corresponding to the minimum current = the current operating speed of the pump corresponding to the minimum current + the current deviation * the adjustment coefficient. The current deviation is the difference between the maximum and minimum current. The adjustment coefficient k = r * (50 / pump motor rated current), where r represents the adjustment coefficient. The default value of r is 1.0, and its range is 0.7 to 1.0. The adjustment coefficient is obtained as follows: after a current balance adjustment and pressure stabilization, observe the actual current of the two pumps that have been adjusted. If the current of the pump with the maximum current is still greater than the current of the pump with the minimum current by more than 0.3A, the adjustment coefficient is too small; otherwise, the adjustment coefficient is too large. Then, make appropriate adjustments until the current difference is within ±0.3A. After one adjustment, wait for the pressure to stabilize for more than 5 seconds before performing current balance adjustment on the two pumps corresponding to the maximum and minimum currents again until the maximum current deviation in the pump group is: (maximum current - minimum current) ≤ preset deviation adjustment value b. The value of b is determined according to the on-site pump process and is generally 0.8 to 1.5A. In this embodiment, the current balance control adjusts only the pumps corresponding to the maximum and minimum currents at a time to reduce pressure fluctuations. After one current balance control, the pressure must be stabilized before the next adjustment can be performed to ensure constant and stable system pressure control.

[0049] In addition, before implementing current balancing control for each pump in the pump set, pump selection and quantity control are required. Each pump set has N pumps, and the number of pumps required to operate depends on the production line's operating mode. Higher water consumption necessitates more pumps, and vice versa. Upon initial automation, the system starts pumps at the default number. Pump speed control utilizes a PID algorithm based on set and feedback pressures to ensure system stability. When the production line's operating mode changes, pump operation is controlled by increasing or decreasing the required number of pumps for each pump set. Pumps meeting the operating conditions are sequentially put into or removed from operation. After one pump is put into or removed, the next pump is added or removed until the required number of pumps is met. This ensures a stable water supply. To start a pump, the downstream valve is closed, the pump is started, and after 5-10 seconds of operation, the valve is opened. To stop a pump, the downstream valve is closed.

[0050] In addition, each pump has an automatic / manual switching function, and this selection is only possible for pumps in automatic mode. In automatic mode, choosing which pump to use for increasing or decreasing the number of pumps is also a crucial consideration. During the configuration process, at least one of the following conditions can be used to select whether to start or stop the pump: pump number, single run time, single stop time, cumulative run time, or cumulative stop time. When selecting by pump number, the pump can be selected from largest to smallest or smallest to largest. When selecting by single run / stop time, the pump can be selected based on the longest single run time, shortest single run time, longest single stop time, or shortest single stop time. When selecting by cumulative run / stop time, the pump can be selected based on the longest cumulative run time, shortest cumulative run time, longest cumulative stop time, or shortest cumulative stop time. If the pump start-up selection criteria are chosen from smallest to largest sequence number, when adding a pump, the pump with the smallest sequence number among the remaining non-operating pumps in automatic mode is selected as the added pump. Similarly, if the longest single-run time is selected as the pump stop rule, when removing an operating pump, the pump with the longest single-run time among all operating pumps is selected as the stopped pump. In this embodiment, the number of pumps is automatically increased or decreased based on the production line's operating mode. Users can choose from multiple control options according to their needs.

[0051] S3. Determine the final operating speed of the pump to be put into operation based on the speed of the first pump and the speed of the second pump.

[0052] Based on the sum of the speeds of the first pump and the second pump, the final operating speed of the pump put into operation is determined, i.e., the final operating speed of the pump put into operation = U(t) + yi (t), where i is the pump number.

[0053] Therefore, the pump balancing and pressure stabilization control method for the circulating pump group in the headless continuous casting and rolling production line provided by this invention performs PID control based on the deviation between the given pressure value and the actual feedback pressure to control the pump operating speed and obtain a first pump speed; simultaneously, by performing current balancing control on each pump in the pump group, the pump operating speed is corrected to obtain a second pump speed; then, based on the first pump speed and the second pump speed, the final operating speed of the pumps to be put into operation is determined. In the headless continuous casting and rolling production line, this control method automatically controls the number of pumps in operation according to the production line operation mode, and through constant pressure control and current balancing control, it achieves stable pressure control of the pump group while ensuring the control problem of consistent output of each motor. After the system is put into operation, it realizes automatic control of the pump group with high control accuracy, small pressure deviation, and fast dynamic response, thus overcoming the drawbacks of high labor intensity and slow real-time response of manual control.

[0054] In another aspect, the present invention provides a pump equalization and pressure stabilization control device 400 for a turbid circulation pump group in a headless continuous casting and rolling production line. This pump equalization and pressure stabilization control device for a turbid circulation pump group in a blast furnace headless continuous casting and rolling production line can realize each process of the above-mentioned pump equalization and pressure stabilization control method for a turbid circulation pump group in a headless continuous casting and rolling production line.

[0055] like Figure 4 As shown, Figure 4 The diagram shows the architecture of the pump balancing and pressure stabilizing control device 400 for the circulating pump group in the headless continuous casting and rolling production line.

[0056] A pump balancing and pressure stabilizing control device 400 for a headless continuous casting and rolling production line's circulating pump group includes at least:

[0057] The PID control module 401 is used to perform PID control based on the deviation between the given pressure value and the actual feedback pressure to control the pump speed and obtain the first pump speed.

[0058] The current balance control module 402 is used to perform current balance control on each pump in the pump group, correct the pump control speed, and obtain the second pump speed.

[0059] The pump final operating speed control module 403 is used to determine the final operating speed of the pump to be put into operation based on the speed of the first pump and the speed of the second pump.

[0060] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be applied, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0061] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for balanced pressure control of circulating pump groups in a headless continuous casting and rolling production line, wherein each pump group has N pumps, where N is greater than or equal to 2, characterized in that... include: PID control is performed based on the deviation between the given pressure value and the actual feedback pressure to control the pump operating speed and obtain the first pump speed. The PID control adopts a dynamic parameter adjustment method, and the proportional and integral parameters of the PID control loop are proportional to the deviation between the given pressure value and the actual feedback pressure. Perform current balance control on each pump in the pump set to correct the pump operating speed and obtain the second pump speed, including: Collect the current of all pumps in the pump set. When the deviation between the maximum current and the minimum current exceeds the preset deviation adjustment value, current balance adjustment is performed on the two pumps corresponding to the maximum current and the minimum current to correct the operating speed of the pump corresponding to the maximum current and the pump corresponding to the minimum current, until the current deviation between any two pumps in the pump group meets the preset deviation adjustment value; wherein, the second pump speed includes the operating speed correction value of the pump corresponding to the maximum current and the operating speed correction value of the pump corresponding to the minimum current. The operating speed correction value of the pump corresponding to the maximum current = the current operating speed of the pump corresponding to the maximum current - the current deviation * the adjustment coefficient, and the operating speed correction value of the pump corresponding to the minimum current = the current operating speed of the pump corresponding to the minimum current + the current deviation * the adjustment coefficient. The current deviation is the deviation value between the maximum current and the minimum current, and the adjustment coefficient is r * (50 / rated current of pump motor), where the value of r ranges from 0.7 to 1.

0. The final operating speed of the pumps put into operation is determined based on the sum of the speeds of the first and second pumps.

2. The method according to claim 1, characterized in that, The output of the PID control loop is limited based on the frequency converter's response speed. The deviation between the current output of the PID control loop and the previous output must not exceed the maximum increase or decrease value of the frequency converter. If the increase or decrease exceeds the maximum increase or decrease value, the increase or decrease shall be based on the maximum increase or decrease value. The maximum increase / decrease value = (maximum motor frequency / frequency converter acceleration / decrease time) * (PID control loop execution cycle / frequency converter acceleration / decrease time).

3. The method according to claim 1, characterized in that, Before performing current balance control on each pump in the pump set, the following steps are also included: When the production line operation mode changes, the pump operation is controlled to increase or decrease based on the required number of pumps to be operated by each pump group. Pumps that meet the operating conditions are put into operation or cut off operation one by one. After one pump is put into operation or cut off operation, the operation of the next pump is carried out until the number of pumps in operation meets the on-site requirements.

4. The method according to claim 1, characterized in that, The pump can be started or stopped based on at least one of the following conditions: pump serial number, pump single run time, pump single stop time, pump cumulative run time, and pump cumulative stop time.

5. A pump balancing and pressure stabilizing control device for a circulating pump group in a headless continuous casting and rolling production line, characterized in that, The method for balanced pressure control of the circulating pump group in a headless continuous casting and rolling production line according to any one of claims 1-4 includes at least the following: The PID control module is used to perform PID control based on the deviation between the given pressure value and the actual feedback pressure to control the pump speed and obtain the first pump speed. The PID control adopts a dynamic parameter adjustment method, and the proportional and integral parameters of the PID control loop are proportional to the deviation between the given pressure value and the actual feedback pressure. The current balance control module is used to perform current balance control on each pump in the pump set, correct the pump control speed, and obtain the second pump speed. It includes: Collect the current of all pumps in the pump set. When the deviation between the maximum current and the minimum current exceeds the preset deviation adjustment value, current balance adjustment is performed on the two pumps corresponding to the maximum current and the minimum current to correct the operating speed of the pump corresponding to the maximum current and the pump corresponding to the minimum current, until the current deviation between any two pumps in the pump group meets the preset deviation adjustment value; wherein, the second pump speed includes the operating speed correction value of the pump corresponding to the maximum current and the operating speed correction value of the pump corresponding to the minimum current. The operating speed correction value of the pump corresponding to the maximum current = the current operating speed of the pump corresponding to the maximum current - the current deviation * the adjustment coefficient, and the operating speed correction value of the pump corresponding to the minimum current = the current operating speed of the pump corresponding to the minimum current + the current deviation * the adjustment coefficient. The current deviation is the deviation value between the maximum current and the minimum current, and the adjustment coefficient is r * (50 / rated current of pump motor), where the value of r ranges from 0.7 to 1.

0. The pump final operating speed control module is used to determine the final operating speed of the pump in operation based on the sum of the speeds of the first pump and the second pump.

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