A centrifugal pump performance prediction method based on an improved QP model

Abstract

A centrifugal pump performance prediction method based on improved QP model, comprising the following steps: step 1, obtaining the test sample data of centrifugal pump flow Q, head H, actual working speed n and motor input power P under different input frequencies through centrifugal pump hydraulic performance test; step 2, establishing the flow-head and flow-power polynomial fitting equations of centrifugal pump under different speeds; step 3, dividing the working area of centrifugal pump into multiple working intervals, and converting the power-flow curve of the upper limit speed and the lower limit speed of each interval to obtain two flow-power curves of the current speed; step 4, calculating the predicted flow by the current motor input power, and obtaining the predicted head by the predicted flow; step 5, implanting the improved prediction algorithm into the centrifugal pump controller, and realizing the accurate prediction of the performance of the centrifugal pump based on real-time measurement data. The present application realizes the accurate prediction of the performance of the centrifugal pump without flow sensor.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of centrifugal pump measurement and control method, and particularly relates to a centrifugal pump performance prediction method based on an improved QP model, which is mainly used for quickly and accurately predicting the flow and lift parameters of a centrifugal pump, and real-time monitoring the running state of the centrifugal pump under the condition of no flow and pressure sensors, so as to effectively ensure the safety and reliability of equipment operation. BACKGROUND

[0002] The safe and efficient operation of a centrifugal pump system not only helps to prolong the service life of the equipment, but also effectively reduces energy consumption, and effective state monitoring is the key to guaranteeing the safe and efficient operation. However, due to the limitation of space and cost, it is difficult to monitor the running state of the centrifugal pump through flow and pressure sensors. To solve this problem, some researchers have proposed a centrifugal pump flow prediction method based on power and pressure difference CN201410538240.7, which predicts the flow of the centrifugal pump based on a centrifugal pump flow prediction mathematical model through the calculation and measurement of the torque and pressure difference of the centrifugal pump. However, this method has certain defects in the selection of the prediction model and the accuracy of flow prediction. On this basis, researchers have proposed a pump and fan performance prediction method based on uncertainty analysis CN201910930803.X, which obtains the flow-pressure difference and flow-power performance curves of the pump and fan, adopts a segmented flow-pressure difference prediction model and a flow-power prediction model for the performance curves that are not monotonously changed, and realizes the prediction of the flow by combining uncertainty analysis. However, this method has poor prediction effect for the running data of the centrifugal pump with greater volatility.

[0003] The existing flow sensor-free centrifugal pump performance prediction method has the following shortcomings: 1) the traditional centrifugal pump flow prediction method has no obvious effect in the non-centrifugal pump optimal working area, and it is difficult to form effective prediction; 2) the prediction model is difficult to be implanted into a hardware device. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the application provides a centrifugal pump performance prediction method based on an improved QP model, which improves the traditional polynomial fitting method, selects and predicts a plurality of fitting curves, and weights the prediction values, so as to obtain a centrifugal pump performance prediction model with higher accuracy and wider applicability, thereby realizing accurate prediction of the performance of the centrifugal pump without a flow sensor.

[0005] The technical scheme adopted by the application to solve the technical problems is:

[0006] A centrifugal pump performance prediction method based on an improved QP model, comprising the following steps:

[0007] Step 1. Obtain the test sample data of the centrifugal pump flow rate Q, head H, actual working speed n, and motor input power P at different input frequencies through centrifugal pump hydraulic performance test;

[0008] Step 2. Establish the flow rate-head and flow rate-power polynomial fitting equations of the centrifugal pump at different speeds;

[0009] Step 3. Divide the working area of the centrifugal pump into multiple working intervals, and use the power-flow curves at the upper and lower limit speeds of each interval to obtain two flow rate-power curves at the current speed;

[0010] Step 4. Calculate the predicted flow rate from the current motor input power, and obtain the predicted head using the predicted flow rate;

[0011] Step 5. Plant the improved prediction algorithm into the centrifugal pump controller, and realize accurate prediction of the performance of the centrifugal pump based on real-time measurement data.

[0012] Further, in step 1, under laboratory conditions, carry out centrifugal pump characteristic test, obtain the centrifugal pump flow rate Q, head H, actual working speed n, and motor input power P measurement values at different specified speed frequencies by means of centrifugal pump hydraulic performance test system, convert the centrifugal pump flow rate Q, head H, and motor input power P at different speeds to specified speed frequencies by similarity theorem as shown in formulas (1)-(3), and draw the centrifugal pump flow rate-head curve and flow rate-power curve after conversion at different standard speed frequencies, Figure 2 is a centrifugal pump flow rate-power performance curve diagram at different standard speed frequencies, Figure 3 is a centrifugal pump head-flow performance curve diagram at different specified speed frequencies;

[0013]

[0014]

[0015]

[0016] In the formula, n is the speed of the centrifugal pump, r / min; n nom is the specified standard speed of the centrifugal pump, r / min; Q is the flow rate of the centrifugal pump, m 3 / h; Q nom is the flow rate of the centrifugal pump at the specified standard speed, m 3 / h; H is the head of the centrifugal pump, m; H nom is the head of the centrifugal pump at the specified standard speed, m; P is the motor input power, kW; P nom is the motor input power at the specified standard speed, kW;

[0017] Furthermore, in step 2, based on the measured values ​​of flow rate Q, head H, motor input power P, and operating speed n at different speeds, a polynomial fitting equation is used to establish an approximate equation for the centrifugal pump head and flow rate, as shown in formula (4); and an approximate equation for the power and flow rate, as shown in formula (5).

[0018] H = a0 + a1Q + a2Q 2 +a3Q 3 (4)

[0019] P = b0 + b1Q + b2Q 2 +b3Q 3 (5)

[0020] In the formula, a0 to a3 are the coefficients of the head approximation equation, and b0 to b3 are the coefficients of the power approximation equation.

[0021] Furthermore, the process of step 3 is as follows:

[0022] First, the working area of ​​the centrifugal pump is divided into multiple working intervals. Each interval has an approximate equation for the motor input power and flow rate at the upper limit speed, as shown in formula (6), and an approximate equation for the head and flow rate at the upper limit speed, as shown in formula (7); an approximate equation for the motor input power and flow rate at the lower limit speed, as shown in formula (8), and an approximate equation for the head and flow rate at the lower limit speed, as shown in formula (9).

[0023] P = a 00 +a 10 Q+a 20 Q 2 +a 30 Q 3 (6)

[0024] H = b 00 +b 10 Q+b 20 Q 2 +b 30 Q 3 (7)

[0025] P = a 01 +a 11 Q+a 21 Q 2 +a 31 Q 3 (8)

[0026] H = b 01 +b 11 Q+b 21 Q 2 +b 31 Q 3 (9)

[0027] where a 00 to a 30 is a coefficient of the approximate equation of the motor input power and flow rate at the upper limit rotational speed, a 01 to a 31 is a coefficient of the approximate equation of the motor input power and flow rate at the lower limit rotational speed, b 00 to b 30 is a coefficient of the approximate equation of the head and flow rate of the centrifugal pump at the upper limit rotational speed, b 01 to b 31 is a coefficient of the approximate equation of the head and flow rate of the centrifugal pump at the lower limit rotational speed;

[0028] According to the equations (1) to (3), the approximate equation of the motor input power and flow rate at the upper limit rotational speed is converted to the current rotational speed as shown in the equation (10), the approximate equation of the head and flow rate at the upper limit rotational speed is converted to the current rotational speed as shown in the equation (11), the approximate equation of the motor input power and flow rate at the lower limit rotational speed is converted to the current rotational speed as shown in the equation (12), and the approximate equation of the head and flow rate at the lower limit rotational speed is converted to the current rotational speed as shown in the equation (13);

[0029] P = a' 00 + a' 10 Q + a' 20 Q 2 + a' 30 Q 3 (10)

[0030] H = b' 00 + b' 10 Q + b' 20 Q 2 + b' 30 Q 3 (11)

[0031] P = a' 01 + a' 11 Q + a' 21 Q 2 + a' 31 Q 3 (12)

[0032] H = b' 01 + b' 11 Q + b' 21 Q 2 + b' 31 Q 3 (13)

[0033] where a' 00 to a' 30 is a coefficient based on the approximate equation of the motor input power and flow rate at the upper limit rotational speed, a' 01a' 31 is the coefficient converted from the approximate equation of the motor input power and flow rate based on the lower limit rotating speed, b' 00 a' 30 is the coefficient converted from the approximate equation of the centrifugal pump head and flow rate based on the upper limit rotating speed, b' 01 a' 31 is the coefficient converted from the approximate equation of the centrifugal pump head and flow rate based on the lower limit rotating speed.

[0034] In the step 4, the current motor input power is respectively brought into the formula (10) and the formula (12), a cubic equation is solved, the solution Q1 of the approximate equation of the motor input power and flow rate based on the upper limit rotating speed and the solution Q2 of the approximate equation of the motor input power and flow rate based on the lower limit rotating speed are obtained, and a weighted average of the two is obtained, as shown in the formula (14), that is, the predicted value Q of the flow rate can be obtained. est ;

[0035]

[0036] In the formula, Q est is the predicted flow rate, m 3 / h; n max is the upper limit rotating speed, r / min; n min is the lower limit rotating speed, r / min; Q1 is the predicted flow rate based on the approximate equation of the motor input power and flow rate based on the upper limit rotating speed, m 3 / h; Q2 is the predicted value based on the approximate equation of the motor input power and flow rate based on the lower limit rotating speed, m 3 / h.

[0037] The predicted value Q est of the flow rate is brought into the formula (11) and the formula (13), the predicted head based on the approximate equation of the centrifugal pump head and flow rate based on the upper limit rotating speed and the predicted head based on the approximate equation of the centrifugal pump head and flow rate based on the lower limit rotating speed are obtained, and an average of the two is obtained, as shown in the formula (15), that is, the predicted value H of the head can be obtained. est ;

[0038]

[0039] In the formula, H est is the predicted head of the centrifugal pump, m; H1 is the predicted head based on the approximate equation of the centrifugal pump head and flow rate based on the upper limit rotating speed, m; H2 is the predicted head converted from the approximate equation of the centrifugal pump head and flow rate based on the lower limit rotating speed, m.

[0040] In step 5, the flow and head prediction model of the centrifugal pump at different powers and rotating speeds is finally determined through step 4, the model is implanted into the centrifugal pump controller, the controller can be a standard programmable logic controller (PLC) or a customized single-chip microcomputer controller, the power sensor and the rotating speed sensor are used to measure the motor input power P and the rotating speed n data in real time when the equipment is working, and the improved polynomial fitting prediction model is used to realize the prediction of the flow value in the current state.

[0041] The scheme of the present application is that, for a specific centrifugal pump system, the centrifugal pump related test data is obtained in the laboratory by means of the centrifugal pump hydraulic performance test system, a plurality of flow-power and flow-head performance curves are used to accurately predict the flow and head parameters of the pump under the condition of no flow sensor, the intelligent monitoring and diagnosis of the equipment running state are realized, and the safety and reliability of the equipment running are ensured.

[0042] The beneficial effects of the present application mainly include: 1) by means of the centrifugal pump hydraulic performance test system, the flow-power polynomial equations at different standard rotating speeds are fitted by measuring sample data at different standard rotating speed frequencies, the centrifugal pump performance prediction model is established, the problem of large prediction error existing in the traditional mathematical model is overcome, and the prediction accuracy and applicability are significantly improved; 2) by means of the controller, the flow and efficiency parameters of the pump are accurately predicted under the condition of no flow sensor, the intelligent monitoring and diagnosis of the equipment running state are realized, and the safety and reliability of the equipment running are ensured. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is an improved polynomial fitting method flowchart.

[0044] Figure 2 It is a centrifugal pump head-flow performance curve diagram at different rotating speed frequencies.

[0045] Figure 3 It is a motor input power-flow performance curve diagram at different rotating speed frequencies. DETAILED DESCRIPTION

[0046] The present application will be further described below with reference to the accompanying drawings.

[0047] REFERENCE Figures 1-3A centrifugal pump performance prediction method based on an improved QP model, comprising the following steps: step 1, obtaining test sample data of centrifugal pump flow Q, head H, motor input power P and working speed n under different speeds through centrifugal pump hydraulic performance test; step 2, establishing centrifugal pump flow-head and flow-power polynomial fitting equations under different speeds; step 3, dividing the working area of the centrifugal pump into different working intervals, and using the flow-power curve of the upper and lower limit speeds of each interval to convert two flow-head curves of the current speed; step 4, solving a cubic equation to obtain the solution Q1 of the approximate equation of the centrifugal pump head and flow based on the upper limit speed and the solution Q2 of the approximate equation of the centrifugal pump head and flow based on the lower limit speed, and the weighted average of the two can obtain the predicted value Q of the flow est ; the predicted head value H est is obtained by the predicted flow value Q est ; the details are as follows:

[0048] Step 1. Through centrifugal pump hydraulic performance test, obtain test sample data of centrifugal pump flow Q, head H, actual working speed n and motor input power P under different standard speeds

[0049] In this embodiment, a centrifugal pump with a rated flow of Q n = 15 m 3 / h, a rated head of H n = 70.5 m and a rated speed of n = 2900 r / min is taken as a test object, and centrifugal pump flow Q, head H, actual working speed n and motor input power P measurement values under different standard speeds are obtained by means of a centrifugal pump hydraulic performance test system, and the test data is arranged, wherein the centrifugal pump performance data is shown in Figure 2 and Figure 3 ;

[0050] Step 2. Establishing centrifugal pump flow-head and flow-power polynomial fitting equations under different speeds

[0051] According to the flow Q, head H, motor input power P measurement value under different standard speed, the polynomial fitting equation is used to establish the centrifugal pump flow-power and flow-power approximate equation at different speeds, the flow-power equation at the speed of 3000r / min is shown as formula (1), the flow-power equation at the speed of 3000r / min is shown as formula (2), the flow-power equation at the speed of 2700r / min is shown as formula (3), the flow-power equation at the speed of 2700r / min is shown as formula (4), the flow-power equation at the speed of 2400r / min is shown as formula (5), the flow-power equation at the speed of 2400r / min is shown as formula (6), the flow-power equation at the speed of 2100r / min is shown as formula (7), the flow-power equation at the speed of 2100r / min is shown as formula (8), the flow-power equation at the speed of 1800r / min is shown as formula (9), the flow-power equation at the speed of 1800r / min is shown as formula (10), the flow-power equation at the speed of 1500r / min is shown as formula (11), the flow-power equation at the speed of 1500r / min is shown as formula (12);

[0052] P = 1.39977 + 0.19273Q - 0.000592067Q 2 -0.0000929346Q 3 (1)

[0053] H = 68.74585 + 0.23502Q - 0.050546Q 2 -0.00074927Q 3 (2)

[0054] P = 1.39977 + 0.19273Q - 0.000592067Q 2 -0.0000929346Q 3 (3)

[0055] H = 68.74585 + 0.23502Q - 0.050546Q 2 -0.00074927Q 3 (4)

[0056] P = 1.39977 + 0.19273Q - 0.000592067Q 2 -0.0000929346Q 3 (5)

[0057] H = 68.74585 + 0.23502Q - 0.050546Q 2 -0.00074927Q 3 (6)

[0058] P = 0.73059 + 0.12228Q - 0.00143Q 2 -0.000054026Q 3 (7)

[0059] H = 41.32263 + 0.13896Q - 0.04223Q 2 -0.0013Q 3 (8)

[0060] P = 0.48558 + 0.09389Q - 0.00162Q 2 -0.0000419785Q 3 (9)

[0061] H = 30.35728 + 0.12304Q - 0.04695Q 2 -0.00126Q 3 (10)

[0062] P = 0.30946 + 0.0643Q - 0.000559452Q 2 -0.0000914026Q 3 (11)

[0063] H = 20.98465 + 0.08575Q - 0.04376Q 2 -0.00168Q 3 (12)

[0064] In the formula, Q is the flow rate of the centrifugal pump, m 3 / h; P is the motor input power, kW; H is the head of the centrifugal pump, m;

[0065] Step 3. Divide the working area of the centrifugal pump into five working intervals, and use the power-flow curve of the upper limit speed and the lower limit speed of each interval to convert two flow-head curves of the current speed

[0066] First, divide the working area of the centrifugal pump with speed 3000-1500 into five working intervals: 3000-2700, 2700-2400, 2400-2100, 2100-1800, 1800-1500, each interval has an upper limit speed centrifugal pump flow-power approximate equation, as shown in formula (13), and a flow-head approximate equation, as shown in formula (14); a lower limit speed centrifugal pump flow-power approximate equation, as shown in formula (15), and a flow-head approximate equation, as shown in formula (16);

[0067] P = a 00 +a 10Q + a 20 Q 2 +a 30 Q 3 (13)

[0068] H = b 00 +b 10 Q + b 20 Q 2 +b 30 Q 3 (14)

[0069] P = a 01 +a 11 Q + a 21 Q 2 +a 31 Q 3 (15)

[0070] H = b 01 +b 11 Q + b 21 Q 2 +b 31 Q 3 (16)

[0071] wherein a 00 to a 30 are coefficients of the approximate flow-rate-power equation at the upper limit rotational speed, a 01 to a 31 are coefficients of the approximate flow-rate-power equation at the lower limit rotational speed, b 00 to b 30 are coefficients of the approximate flow-rate-head equation at the upper limit rotational speed, b 01 to b 31 are coefficients of the approximate flow-rate-head equation at the lower limit rotational speed.

[0072] According to the similarity theorem, the motor input power at the upper limit rotational speed is converted to the current rotational speed by the flow-rate-power approximate equation as shown in equation (17), and the head is converted to the current rotational speed by the flow-rate-head approximate equation as shown in equation (18). The motor input power at the lower limit rotational speed is converted to the current rotational speed by the flow-rate-power approximate equation as shown in equation (19), and the head is converted to the current rotational speed by the flow-rate-head approximate equation as shown in equation (20).

[0073] P = a' 00 +a' 10 Q + a' 20 Q 2 +a' 30 Q 3 (17)

[0074] H = b'00 +b' 10 Q+b' 20 Q 2 +b' 30 Q 3 (18)

[0075] P = a' 01 +a' 11 Q+a' 21 Q 2 +a' 31 Q 3 (19)

[0076] H = b' 01 +b' 11 Q+b' 21 Q 2 +b' 31 Q 3 (20)

[0077] In the formula, a' 00 to a' 30 a' is the coefficient for the transformation based on the flow-power approximation equation of a centrifugal pump at its upper speed limit. 01 to a' 31 b' represents the coefficient of the flow-power approximation equation for a centrifugal pump operating at its lower speed. 00 to b' 30 b' is the coefficient for the transformation based on the approximate equation of flow rate-head for centrifugal pumps at the upper speed limit. 01 to b' 31 These are the coefficients of the approximate equation for the flow rate-head of a centrifugal pump at the lower limit speed.

[0078] Step 4. Substitute the current power into formulas (17) and (19) respectively, solve the cubic equation, and obtain the predicted flow rate based on the approximate equation of flow rate-power for centrifugal pumps with upper speed limit and the approximate equation of flow rate-power for centrifugal pumps with lower speed limit. Take the weighted average of the two, as shown in formula (21), and you can get the predicted flow rate Q. est ;

[0079]

[0080] In the formula, Q est To predict flow, m 3 / h;n max n represents the upper limit of the rotational speed in the range, in r / min. min Q1 is the lower limit speed of the interval, in r / min; Q2 is the predicted flow rate, in m³, based on the centrifugal pump flow-power approximation equation at the upper speed. 3 / h; Q2 is the predicted value based on the approximate equation of flow-power for a centrifugal pump at the lower limit speed, m 3 / h;

[0081] The predicted value of the flow is brought into formula (18) and formula (20), and the predicted head based on the upper limit speed centrifugal pump flow-head approximate equation and the predicted head based on the lower limit speed centrifugal pump flow-head approximate equation are obtained, and the average of the two is taken, as shown in formula (22), that is, the predicted value of the head H est ;

[0082]

[0083] In the formula, H est is the predicted head of the centrifugal pump, m; H1 is the predicted head based on the upper limit speed centrifugal pump flow-head approximate equation, m; H2 is the predicted head converted based on the lower limit speed centrifugal pump flow-head approximate equation, m;

[0084] Step 5. The improved prediction algorithm is implanted into the centrifugal pump controller, and the accurate prediction of the performance of the centrifugal pump is realized based on real-time measurement data

[0085] The QP improved algorithm is implanted into the centrifugal pump control, the measured speed and motor input power values are taken as the input of the prediction model, the corresponding flow prediction value and head prediction value are obtained, and the measured flow value and head value are compared and analyzed, the flow prediction error is less than 0.4 m 3 / h, the head prediction error is less than 0.2 m, and the prediction accuracy is good.

[0086] Finally, through the centrifugal pump performance prediction model, the real-time flow and head measurement values are obtained, and under the condition of no flow sensor, the performance prediction of the centrifugal pump and the real-time monitoring of the equipment running state can be realized, and the safety and reliability of the equipment running are ensured.

[0087] The content described in the embodiments of the present specification is only a list of implementation forms of the inventive concept, and is only for illustrative purposes. The protection scope of the present application should not be regarded as being limited to the specific forms described in the embodiments, and the protection scope of the present application also extends to the equivalent technical means that can be thought of by those skilled in the art according to the inventive concept.

Claims

1. A method for predicting performance of a centrifugal pump based on an improved QP model, characterized in that, The method comprises the following steps: Step 1. Obtain the test sample data of the centrifugal pump flow Q, head H, actual working speed n and motor input power P under different input frequencies through centrifugal pump hydraulic performance test; Step 2. Establish the centrifugal pump flow-head and flow-power polynomial fitting equations under different speeds; Step 3. Divide the working area of the centrifugal pump into multiple working intervals, and convert the power-flow curves of the upper and lower limit speeds of each interval to obtain two flow-power curves of the current speed; Step 4. Calculate the predicted flow by the current motor input power, and obtain the predicted head by the predicted flow; Step 5. Plant the improved prediction model into the centrifugal pump controller, and realize accurate prediction of the performance of the centrifugal pump based on real-time measurement data; In step 1, under laboratory conditions, centrifugal pump characteristic test is carried out, and the centrifugal pump flow Q, head H, actual working speed n and motor input power P measurement values under different specified speed frequencies are obtained by means of a centrifugal pump hydraulic performance test system. The centrifugal pump flow Q, head H and motor input power P under different speeds are converted to specified speed frequencies by similarity theorem as shown in formulas (1)-(3), and the centrifugal pump flow-head curve and flow-power curve under different standard speed frequencies after conversion are drawn; In the formula, n is the rotating speed of the centrifugal pump, r / min; n nom is the specified standard rotating speed of the centrifugal pump, r / min; Q is the flow of the centrifugal pump, m 3 / h; Q nom is the flow of the centrifugal pump at the specified standard rotating speed, m 3 / h; H is the head of the centrifugal pump, m; H nom is the head of the centrifugal pump at the specified standard rotating speed, m; P is the input power of the motor, kW; P nom is the input power of the motor at the specified standard rotating speed, kW; In step 2, according to the measurement values of flow Q, head H, motor input power P and working speed n under different speeds, the polynomial fitting equation is used to establish the approximate equation of centrifugal pump head and flow as shown in formula (4), and the approximate equation of power and flow as shown in formula (5); H = a0+ a1Q + a2Q + a3Q 2 3 (4)​ P = b0+ b1Q + b2Q + b3Q 2 + b4Q 3 (5) In the formula, a0 to a3 are the coefficients of the head approximation equation, and b0 to b3 are the coefficients of the power approximation equation; The process of step 3 is as follows: Firstly, the working area of the centrifugal pump is divided into multiple working intervals, and each interval has a motor input power and flow approximation equation of the upper limit speed as shown in formula (6), a head and flow approximation equation of the upper limit speed as shown in formula (7), a motor input power and flow approximation equation of the lower limit speed as shown in formula (8), and a head and flow approximation equation of the lower limit speed as shown in formula (9); P = a 00 + a 10 Q + a 20 Q 2 + a 30 Q 3 (6) H = b 00 + b 10 Q + b 20 Q 2 + b 30 Q 3 (7) P = a 01 + a 11 Q + a 21 Q 2 + a 31 Q 3 (8) H = b 01 + b 11 Q + b 21 Q 2 + b 31 Q 3 (9) where a 00 to a 30 is the coefficient of the approximate equation of the motor input power versus flow at the lower limit speed, a 01 to a 31 is the coefficient of the approximate equation of the motor input power versus flow at the lower limit speed, b 00 to b 30 is the coefficient of the approximate equation of the centrifugal pump head versus flow at the upper limit speed, b 01 to b 31 is the coefficient of the approximate equation of the centrifugal pump head versus flow at the lower limit speed; According to formulas (1)-(3), the motor input power and flow approximation equation under the upper limit speed is converted to the current speed as shown in formula (10), the head and flow approximation equation under the upper limit speed is converted to the current speed as shown in formula (11), the motor input power and flow approximation equation under the lower limit speed is converted to the current speed as shown in formula (12), and the head and flow approximation equation under the lower limit speed is converted to the current speed as shown in formula (13); P = a' 00 + a' 10 Q + a' 20 Q 2 + a' 30 Q 3 (10) H = b' 00 + b' 10 Q + b' 20 Q 2 + b' 30 Q 3 (11) P = a' 01 + a' 11 Q + a' 21 Q 2 + a' 31 Q 3 (12) H = b' 01 + b' 11 Q + b' 21 Q 2 + b' 31 Q 3 (13) In the formula, a' 00 to a' 30 is a coefficient converted based on the upper limit rotational speed centrifugal pump power and flow rate approximate equation, a' 01 to a' 31 is a coefficient converted based on the lower limit rotational speed centrifugal pump power and flow rate approximate equation, b' 00 to b' 30 is a coefficient converted based on the upper limit rotational speed centrifugal pump head and flow rate approximate equation, b' 01 to b' 31 is a coefficient converted based on the lower limit rotational speed centrifugal pump head and flow rate approximate equation. In step 4, the current power is brought into formula (10) and formula (12) respectively, a cubic equation is solved, and solutions Q1 based on the upper limit speed centrifugal pump power and flow approximate equation and Q2 based on the lower limit speed centrifugal pump power and flow approximate equation are obtained. The two are weighted and averaged as shown in formula (14), and the predicted value Q of the flow is obtained est ; wherein Q est is the predicted flow rate, m 3 / h; n max is the upper interval speed, r / min; n min is the lower interval speed, r / min; Q1 is the predicted flow rate based on the upper interval speed motor input power and flow rate approximation equation, m 3 / h; Q2 is the predicted value based on the lower interval speed motor input power and flow rate approximation equation, m 3 / h; The predicted value Q of the flow rate is calculated by the following equation (10) using the predicted value H of the head and the predicted value N of the rotation speed. est The predicted value H of the head is calculated by the following equation (15) using the predicted value Q of the flow rate and the predicted value N of the rotation speed. est ; where H is the head of the centrifugal pump, m; H1 is the predicted head based on the upper limit of the interval, m; H2 is the predicted head based on the lower limit of the interval, m. est where H is the head of the centrifugal pump, m; H1 is the predicted head based on the upper limit of the interval, m; H2 is the predicted head based on the lower limit of the interval, m.

2. A method for performance prediction of a centrifugal pump based on an improved QP model as claimed in claim 1, wherein, In step 5, the flow and head prediction model of the centrifugal pump at different power and rotating speed is finally determined in step 4, and the model is implanted into the centrifugal pump controller, which is a standard programmable logic controller (PLC) or a customized single-chip microcomputer controller. The power sensor and the rotating speed sensor are used to measure the input power P and the rotating speed n of the motor in real time when the equipment is working. The improved polynomial fitting prediction model is used to realize the prediction of the flow value under the current state.

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