A method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine

Abstract

The present invention discloses a method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine. First, characteristic parameters such as the initial runner diameter, initial speed range, maximum and minimum head, and power range are obtained, and an initial iteration interval is set. Secondly, the bisection method is used to calculate the runner diameter and obtain the maximum rotor-side apparent power in the corresponding super-synchronous and sub-synchronous states. Further, with the goal that the percentage difference in the maximum apparent power is less than 0.05%, the iteration interval is adjusted according to the relationship between the maximum and minimum values and the loop continues until the percentage difference in the maximum apparent power converges within 0.05%, and finally the optimal runner diameter is determined and output. The present invention effectively solves the problems such as low equipment utilization rate and increased cost caused by the decoupling of the runner diameter and the converter capacity in traditional designs, and provides key technical support for the efficient and economic operation of the unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydropower generation, and particularly relates to a method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine. Background Art

[0002] The pump-turbine is the core energy conversion equipment of a pumped-storage power station. In the design of a pump-turbine, the size of the runner diameter affects the energy conversion efficiency of the water flow, torque characteristics, etc., and is a key parameter affecting the hydraulic performance and economy of the unit. Since the variable-speed pumped-storage unit can compensate for the flow loss by increasing the speed when the diameter is reduced, avoiding the unit from entering the hump zone of low flow - high head, appropriately reducing the runner diameter not only helps to optimize the hump zone, make the power reach the rated value, reduce the capacity of the converter, but also can reduce the diameter excavation volume and significantly reduce the construction cost.

[0003] There are significant disciplinary barriers in the current pump-turbine design process, and the design of the runner diameter and the selection of the converter capacity are carried out by personnel in different fields. The traditional selection of the runner diameter is based on the initial parameters to calculate the speed in combination with the specific speed, and the runner parameters are independently determined through hydraulic model optimization and statistical laws. However, this traditional diameter selection method does not establish a connection with the converter capacity. The converter capacity is usually directly determined by the maximum value of the apparent power on the rotor side. Due to the discontinuous change of the synchronous speed of the unit caused by the jump change of the number of motor poles, the difference between the maximum values of the apparent power on the rotor side in the super-synchronous and sub-synchronous states is large, resulting in the idle of the converter power, reducing the operating efficiency of the unit, increasing the manufacturing cost, and being unfavorable to the efficient and economic operation of the variable-speed pumped-storage unit. Therefore, the present invention further optimizes on the basis of the traditional selection of the runner diameter, and provides a method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine that can reduce power idle and construction costs. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine, which solves the problems such as power idle and cost increase caused by the independent design of the runner diameter and the converter capacity in the traditional design; and realizes the economic and efficient design optimization of the unit.

[0005] The technical solution adopted by the present invention is: a method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine, and the specific operation steps are as follows:

[0006] Step 1: Obtain the characteristic parameters of the variable-speed pumped-storage unit under the pump condition: the initial runner diameter D 0, the synchronous speed n r , the initial speed range, the maximum head H max , the minimum headH min and the corresponding power range;

[0007] Step 2: Set the initial iteration interval and calculate the runner diameter using the bisection method D i ;

[0008] Step 3: Calculate the runner diameter D i The corresponding maximum rotational speed n rmax and the minimum rotational speed n rmin ;

[0009] Step 4: Calculate the maximum super-synchronous active power according to the active power calculation formula on the rotor side P rmax and the minimum sub-synchronous active power P rmin ;

[0010] Step 5: Calculate the maximum apparent power on the rotor side in the super-synchronous and sub-synchronous states according to the apparent power calculation formula S rmax , S' rmax ;

[0011] Step 6: Aim for the percentage difference between the maximum apparent powers on the rotor side in the super-synchronous and sub-synchronous states to be less than 0.05%, adjust the iteration interval according to the relationship between the maximum and minimum values and continue the loop; when S rmax and S' rmax the percentage difference converges within 0.05%, finally determine and output the optimal runner diameter D opt .

[0012] The features of the present invention also lie in that

[0013] Furthermore, in Step 1, determine the minimum power H max at the highest head P 1, the maximum power H min at the lowest head P 2, the minimum power H min at the lowest head P 3.

[0014] Furthermore, Step 2 is specifically as follows:

[0015] Set the initial iteration interval and input the initial value: the lower limit of the initial valuea 1 = αD 0; upper limit of initial value b 1 = βD 0; where, α and β are both variable coefficients, α ranges from 0.98 to 0.99, β ranges from 1.00 to 1.02; α , β are mainly determined by the head and operating characteristics of the variable-speed pumped-storage unit;

[0016] The lower limit of the initial value a 1 and the upper limit of the initial value b 1 are used as the initial inputs for the bisection iteration calculation, and the runner diameter is calculated using the bisection iteration D i : , i is the number of iterations, i = 1, 2, …, k , k = 5000.

[0017] Furthermore, step 3 is specifically as follows:

[0018] The runner diameter D i and the unit speed n 11 and the synchronous speed n r have the following relationship: ;

[0019] The maximum speed ;

[0020] The minimum speed ;

[0021] Where, is the per-unit value of the speed corresponding to the maximum power P 2, is the per-unit value of the speed corresponding to the minimum power P 3, n r is the synchronous speed, is the head.

[0022] Furthermore, step 4 is specifically as follows:

[0023] The maximum super-synchronous active power P rmax and the minimum sub-synchronous active power P rmin are calculated as follows:

[0024]

[0025] Among them, P 2, P 3 are respectively the maximum power and the minimum power at the lowest lift H min Under the condition.

[0026] Furthermore, step 5 is specifically as follows:

[0027] Calculate the maximum value of the apparent power on the rotor side in the super-synchronous and sub-synchronous states S rmax , S' rmax ; The calculation method of the apparent power on the rotor side is as follows:

[0028]

[0029] Among them, is the active power on the rotor side of the variable-speed unit; is the reactive power on the rotor side of the variable-speed unit.

[0030] Furthermore, with the goal that the percentage of the difference between the maximum values of the apparent power on the rotor side in the super-synchronous and sub-synchronous states is less than 0.05%, adjust the iteration interval according to the size relationship of the maximum and minimum values and continue to loop, including:

[0031] (1) If ≥0.05%, adjust the iteration interval according to the size relationship of the apparent power maximum and minimum values and continue to loop, specifically as follows:

[0032] When < , reduce the runner diameter: Let the upper limit of the interval b i = D i , continue the iteration;

[0033] When > , increase the runner diameter: Let the lower limit of the interval a i = D i , continue the iteration;

[0034] Feed the iteration result back to step 2, and continue to use the bisection method to iterate and loop until the percentage is less than 0.05% or the number of loops is greater than 5000. At this time, output the current runner diameter D i as the optimal runner diameter D opt , and end the iteration process;

[0035] If < 0.05%, terminate the iteration and output the current runner diameter D i as the optimal runner diameter D opt .

[0036] Furthermore, when < 0.05%, it is regarded as achieving the goal that the percentage of the difference between the maximum apparent power on the rotor side in the supersynchronous and subsynchronous states is less than 0.05%. At this time, the power redundancy at this diameter is the smallest. Therefore, terminate the iteration and output the current runner diameter D i as the optimal runner diameter D opt .

[0037] The beneficial effects of the present invention are as follows:

[0038] The present invention provides a method for selecting the runner diameter of a variable-speed pumped-storage unit. First, by obtaining characteristic parameters such as the initial runner diameter, synchronous speed, initial speed range, maximum head and minimum head, and corresponding power range under the pump condition, and setting an initial iteration interval; secondly, using the bisection method to calculate the runner diameter, and calculating the corresponding maximum speed and minimum speed at the current runner diameter, and then obtaining the maximum and minimum active power and apparent power on the rotor side in the supersynchronous and subsynchronous states; finally, with the goal that the percentage of the difference between the maximum apparent powers is less than 0.05%, adjust the iteration interval according to the size relationship of the maximum and minimum values and continue to loop until the percentage of the difference between the maximum apparent powers converges within 0.05%, and finally determine and output the optimal runner diameter. In this way, the capacity of the converter is selected as the maximum value of the apparent power on the rotor side, which can effectively reduce the power idle of the unit and improve the equipment utilization rate and the operation efficiency of the unit. In addition, the present invention considers the influence of the runner diameter on the utilization rate and capacity of the converter equipment, breaks the disciplinary barriers between traditional hydraulics and electrical design, and proposes a scientific and reasonable method for optimizing the selection of the runner diameter, which can reduce the converter capacity and construction cost, and provides a reliable theoretical basis for the economic and efficient design of variable-speed pumped-storage units. Description of the Drawings

[0039] In order to more clearly illustrate the embodiments of the present invention, the drawings required for use in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0040] Figure 1Schematic diagram of the implementation process of a method for selecting the runner diameter of a variable-speed pumped-storage unit provided by an embodiment of the present invention. Detailed implementation manners

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] Embodiment 1

[0043] Embodiment 1 of the present invention provides a method for selecting the runner diameter of a variable-speed pumped-storage unit. Considering the influence of the runner diameter on the utilization rate and capacity of the converter equipment, it breaks the disciplinary barriers between traditional hydraulics and electrical design. In the embodiment of the present invention, with the percentage of the difference between the maximum values of the apparent power on the rotor side in the supersynchronous and sub-synchronous states being less than 0.05% as the goal, the dichotomy method is used to iteratively determine the optimal runner diameter. In this way, the capacity of the converter is selected as the maximum value of the apparent power on the rotor side, which can effectively reduce the power idle of the unit, improve the equipment utilization rate and the operation efficiency of the unit. The specific operation steps are as follows:

[0044] Step 1: Obtain the characteristic parameters of the variable-speed pumped-storage unit under the pump condition: the initial runner diameter D 0, synchronous speed n r , initial speed range, maximum head H max , minimum head H min and the corresponding power range;

[0045] Step 2: Set the initial iteration interval and calculate the runner diameter using the dichotomy method D i ;

[0046] Step 3: Calculate the maximum speed D i corresponding to the runner diameter n rmax and the minimum speed n rmin ;

[0047] Step 4: Calculate the maximum supersynchronous active power P rmax and the minimum sub-synchronous active power P rmin according to the formula for calculating the active power on the rotor side;

[0048] Step 5: Calculate the maximum value of the apparent power on the rotor side in the supersynchronous and sub-synchronous states according to the apparent power calculation formula. S rmax 、 S' rmax ;

[0049] Step 6: Take the percentage difference between the maximum values of the apparent power on the rotor side in the supersynchronous and sub-synchronous states being less than 0.05% as the goal, adjust the iteration interval according to the size relationship of the maximum values, and continue to loop;

[0050] When S rmax and S' rmax the percentage difference converges within 0.05%, finally determine and output the optimal runner diameter D opt 。

[0051] Example 2

[0052] On the basis of Example 1, in Step 1, determine the minimum power H max at the highest head P 1, the maximum power H min at the lowest head P 2, the minimum power H min at the lowest head P 3.

[0053] Step 2 is specifically as follows:

[0054] Set the initial iteration interval and input the initial values: the lower limit of the initial value a 1 = αD 0; the upper limit of the initial value b 1 = βD 0; where α and β are both variable coefficients, α the value range is 0.98 - 0.99, β the value range is 1.00 - 1.02; α 、 β are mainly determined by the head and operating characteristics of the variable-speed pumped-storage unit;

[0055] Take the lower limit of the initial value a 1 and the upper limit of the initial value b 1 as the initial input for the bisection method iterative calculation, and use the bisection method to iteratively calculate the runner diameter D i : , i is the number of iterations,i = 1, 2, …, k , k = 5000。

[0056] Example 3

[0057] Based on Example 2, Step 3 is specifically as follows:

[0058] Runner diameter D i and unit speed n 11 and synchronous speed n r relationship: ;

[0059] Maximum speed ;

[0060] Minimum speed ;

[0061] Among them, is the per-unit value of the speed corresponding to the maximum power P 2, is the per-unit value of the speed corresponding to the minimum power P 3, n r is the synchronous speed, is the head.

[0062] Step 4 is specifically as follows:

[0063] Maximum super-synchronous active power P rmax and minimum sub-synchronous active power P rmin are calculated as follows:

[0064]

[0065] Among them, P 2, P 3 are respectively the maximum power and the minimum power at the lowest head H min respectively.

[0066] Example 4

[0067] Based on Example 3, Step 5 is specifically as follows:

[0068] Calculate the maximum values of the apparent power on the rotor side in the super-synchronous and sub-synchronous states S rmax , S' rmax ; The calculation method of the apparent power on the rotor side is as follows:

[0069]

[0070] Among them, is the active power on the rotor side of the variable-speed unit; is the reactive power on the rotor side of the variable-speed unit.

[0071] Taking the percentage of the difference between the maximum values of the apparent power on the rotor side in the supersynchronous and sub-synchronous states to be less than 0.05% as the goal, adjust the iteration interval according to the relationship between the maximum and minimum values and continue the loop, including:

[0072] (1) If ≥0.05%, adjust the iteration interval according to the relationship between the maximum and minimum values of the apparent power and continue the loop, specifically as follows:

[0073] When < , reduce the runner diameter: let the upper limit of the interval b i = D i , continue the iteration;

[0074] When > , increase the runner diameter: let the lower limit of the interval a i = D i , continue the iteration;

[0075] Feed the iteration result back to step 2, and continue to use the bisection method to iterate and loop until the percentage is less than 0.05% or the number of loops is greater than 5000. At this time, output the current runner diameter D i as the optimal runner diameter D opt , and end the iteration process;

[0076] (2) If <0.05%, terminate the iteration and output the current runner diameter D i as the optimal runner diameter D opt .

[0077] Embodiment 5

[0078] Based on Embodiments 1-4, Figure 1 is a schematic flow chart of a method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine provided in Embodiment 5 of the present invention. The above method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine includes:

[0079] S101. Obtain the characteristic parameters of the variable-speed pumped-storage unit under the pump condition: the initial runner diameter D 0, synchronous speed n r , initial speed range, maximum head H max , minimum head H min and the corresponding power range;

[0080] Among them, the initial runner diameter D 0 and synchronous speed n r are determined according to the power station design manual; H max The maximum head H min and the minimum head H max are determined according to the power station head range; P 1, the minimum power H min at the maximum head P 2, the maximum power H min at the minimum head P 3;

[0081] S102. Based on the initial runner diameter D 0 of the pump-turbine, set the initial iteration interval;

[0082] S103. Take the lower limit a 1 of the initial value and the upper limit b 1 of the initial value as the initial input for the bisection method iteration calculation, and use the bisection method to iteratively calculate the runner diameter D i : , i is the number of iterations, i = 1, 2, …, k , k = 5000;

[0083] S104. Based on the runner diameter D i obtained in the above step S103, calculate the maximum speed n rmax and the minimum speed n rmin ;

[0084] S105. Based on the maximum speed n rmax and the minimum speed nrmin , calculate the maximum super-synchronous active power according to the rotor-side active power calculation formula P rmax and the minimum sub-synchronous active power P rmin ;

[0085] S106. Based on the maximum super-synchronous active power obtained in the above step S105 P rmax and the minimum sub-synchronous active power P rmin , calculate the maximum rotor-side apparent power in the super-synchronous and sub-synchronous states according to the apparent power calculation formula S rmax 、 S' rmax ;

[0086] S107. Calculate the percentage of the difference between the maximum rotor-side apparent powers in the super-synchronous and sub-synchronous states, and loop according to whether the percentage is greater than or equal to 0.05%;

[0087] Specifically, it is divided into two cases:

[0088] When the percentage is less than 0.05%, that is <0.05%: The iteration terminates, and the current runner diameter D i is output as the optimal runner diameter D opt ;

[0089] When the percentage is greater than or equal to 0.05%, that is ≥0.05%: Adjust the iteration interval according to the magnitude relationship between the maximum rotor-side apparent powers in the super-synchronous and sub-synchronous states, and continue to loop;

[0090] S108. When the percentage of the difference between the maximum rotor-side apparent powers in the super-synchronous and sub-synchronous states is greater than or equal to 0.05% ( ≥0.05%), adjust the iteration interval according to the magnitude relationship of the rotor-side apparent power extreme values, and continue to loop;

[0091] Specifically, it is divided into two cases:

[0092] When < , reduce the runner diameter: Let the upper limit of the interval b i = D i , and continue the iteration;

[0093] When > When increasing the runner diameter: set the lower limit of the interval a i = D i , and continue the iteration;

[0094] Feed back the assigned iteration interval to step S103, and continue to iterate cyclically using the bisection method until the percentage is less than 0.05% or the number of cycles is greater than 5000. At this time, output the current runner diameter D i as the optimal runner diameter D opt , and end the iteration process.

[0095] The present invention provides a method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine. First, by obtaining characteristic parameters such as the initial runner diameter, synchronous speed, initial speed range, maximum head and minimum head, and corresponding power range under the pump condition, and setting the initial iteration interval; secondly, using the bisection method to calculate the runner diameter, and calculating the corresponding maximum speed and minimum speed under the current runner diameter, and then obtaining the maximum and minimum values of the active power and apparent power on the rotor side in the supersynchronous and sub-synchronous states; finally, aiming at the percentage of the difference in the maximum apparent power being less than 0.05%, adjusting the iteration interval according to the size relationship of the maximum and minimum values and continuing to cycle until the percentage of the difference in the maximum apparent power converges within 0.05%, and finally determining and outputting the optimal runner diameter. In this way, the maximum value of the apparent power on the rotor side is selected for the converter capacity, which can effectively reduce the power idle of the unit and improve the equipment utilization rate and the unit operation efficiency. In addition, the present invention considers the influence of the runner diameter size on the converter equipment utilization rate and capacity, breaks the disciplinary barriers between traditional hydraulics and electrical design, and proposes a scientific and reasonable method for optimizing the selection of the runner diameter, which can reduce the converter capacity and construction cost, and provides a reliable theoretical basis for the economic and efficient design of variable-speed pumped-storage units.

[0096] Example 6

[0097] Suppose the characteristic parameters of a pumped-storage power station under the pump condition are as follows: the initial runner diameter D 0 = 4.1576 m, the synchronous speed n r = 428.6 r / min, the maximum head H max The adjustment range of the unit input power is 274.3~321 MW, and its minimum power P 1 = 274.3 MW, the minimum head H min The adjustment range of the unit input power is 228.5~321 MW, and its maximum power P 2 = 321 MW, the minimum power P3 = 228.5 MW.

[0098] (1) Based on the initial runner diameter of the pump-turbine D 0, set the initial iteration interval:

[0099] Lower limit of the initial value: a 1 = αD 0 = 0.99 D 0 = 0.99 × 4.1576 = 4.116 (m)

[0100] Upper limit of the initial value: b 1 = βD 0 = D 0 = 4.1576 (m)

[0101] Among them, according to the head and operation characteristics analysis of this pumped-storage power station in this embodiment, the variable coefficient α is taken as 0.99, β is taken as 1.

[0102] (2) First calculate the runner diameter using the bisection method:

[0103]

[0104] (3) Calculate the maximum rotational speed n rmax and the minimum rotational speed n rmin :

[0105]

[0106]

[0107] (4) According to the active power calculation formula on the rotor side, calculate the maximum super-synchronous active power P rmax and the minimum sub-synchronous active power P rmin :

[0108]

[0109]

[0110] (5) According to the apparent power calculation formula, calculate the maximum apparent power on the rotor side in the super-synchronous and sub-synchronous states S rmax , S' rmax :

[0111]

[0112] (6) Determine whether the percentage of the difference between the maximum apparent power on the rotor side in supersynchronous and sub-synchronous states meets the convergence condition: < 0.05%; if the convergence condition is not met, adjust the iteration interval according to the relationship between the maximum and minimum apparent powers on the rotor side, and continue the loop:

[0113] = 40.63% > 0.05%

[0114] It can be seen that at this diameter, the convergence condition is not met. The maximum apparent power on the rotor side in the sub-synchronous state is much larger than that in the supersynchronous state, and the difference between the two is large. If the converter capacity is selected according to the maximum apparent power on the rotor side in the sub-synchronous state (15.09 MW), it will cause a large amount of power idle and reduce the efficiency of the unit. Therefore, the iteration interval will be adjusted according to the relationship between the two, and the loop will continue.

[0115] Since < , the runner diameter will be reduced and the upper limit of the adjustment interval b 1 = D 1 = 4.1368 m, and continue the iterative calculation.

[0116] (7) After multiple iterative calculations, output the final optimal runner diameter:

[0117] Using Figure 1 the schematic flow chart of the embodiment of a method for selecting the runner diameter of a variable-speed pumped-storage unit shown in D for multiple iterative calculations, when the runner diameter D = 4.1356 m, the maximum apparent powers on the rotor side in supersynchronous and sub-synchronous states are nearly equal. At this time, the maximum speed of the unit at this runner diameter is 1.04 × 428.6 r / min, the minimum speed is 0.947 × 428.6 r / min, and the speed change range is -5.3% ~ 4%; the maximum apparent power on the rotor side in the sub-synchronous state is 13.239 MW, and the maximum apparent power on the rotor side in the supersynchronous state is 13.237 MW, meeting the convergence condition:

[0118] = 0.015% < 0.05%

[0119] Therefore, output the runner diameter at this time as the optimal runner diameter D opt= 4.1356 m, the converter capacity is taken as an approximate value of 13.24 MW, which is the maximum value of the apparent power on the rotor side. It can be seen that through the optimization of the embodiments of the present invention, the converter capacity is reduced from 15.09 MW under the initial runner diameter (4.1576 m) to 13.24 MW under the optimal runner diameter (4.1356 m), greatly reducing the converter capacity and construction cost, effectively reducing the idle power of the unit, and improving the equipment utilization rate and the operating efficiency of the unit.

[0120] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, reference can be made to each other. The key point of each embodiment is to illustrate the differences from other embodiments.

[0121] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine, characterized in that, The specific operation steps are as follows: Step 1: Obtain the characteristic parameters of the variable-speed pumped-storage unit under the water pump condition: the initial runner diameter D 0, synchronous speed n r , initial speed range, maximum head H max , minimum head H min and the corresponding power range; Step 2: Set the initial iteration interval and calculate the runner diameter using the bisection method D i ; Step 3: Calculate the runner diameter D i The corresponding maximum rotational speed n rmax And the minimum rotational speed n rmin ; Step 4: Calculate the maximum super-synchronous active power according to the rotor-side active power calculation formula P rmax and the minimum sub-synchronous active power P rmin ; Step 5: Calculate the maximum values of the apparent power on the rotor side in the supersynchronous and subsynchronous states according to the apparent power calculation formula S rmax 、 S' rmax ; Step 6: Aim at the percentage of the difference between the maximum apparent power on the rotor side in supersynchronous and subsynchronous states being less than 0.05%, adjust the iteration interval according to the relationship between the maximum values and continue to loop; when S rmax and S' rmax the percentage of the difference converges within 0.05%, finally determine and output the optimal runner diameter D opt； Specifically as follows: Taking the percentage of the difference between the maximum values of the rotor-side apparent power in the supersynchronous and subsynchronous states being less than 0.05% as the target, adjust the iteration interval according to the relationship between the maximum values and continue the loop, including: If (1) ≥ 0.05%, adjust the iteration interval according to the relationship between the maximum and minimum apparent power values and continue to loop as follows: When < , reduce the runner diameter: Let the upper limit of the interval b i = D i , and continue the iteration; When > , increase the diameter of the runner: set the lower limit of the interval a i = D i , and continue the iteration; Feed the iteration result back to Step 2, and continue to use the bisection method for iterative loop until the percentage is less than 0.05% or the number of loops is greater than 5000. At this time, output the current runner diameter D i as the optimal runner diameter D opt , and end the iterative process; If <0.05%, the iteration terminates and the current runner diameter is output D i as the optimal runner diameter D opt .

2. The method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine, as claimed in claim 1, is characterized in that In Step 1, determine the maximum head according to the initial speed range H max The minimum power under P 1. The minimum head H min The maximum power under P 2. The minimum head H min The minimum power under P 3.

3. The method for selecting the runner diameter of a variable-speed pumped storage unit's pump-turbine, as claimed in claim 2, is characterized in that Step 2 is specifically as follows: Set the initial iteration interval and input the initial values: lower limit of the initial value a 1 = αD 0; upper limit of the initial value b 1 = βD 0; Among them, α and β are both variable coefficients, α with a value range of 0.98 to 0.99, β and the value range of is 1.00 to 1.02; Lower limit of the initial value a 1 and the upper limit of the initial value b 1 are used as the initial inputs for bisection iteration calculation, and the runner diameter is calculated by bisection iteration D i : , i is the number of iterations, i = 1, 2, …, k , k = 5000.

4. The method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine, as claimed in claim 3, is characterized in that Step 3 is specifically as follows: Runner diameter D i With unit speed n 11 And synchronous speed n r Relationship: ; Maximum rotational speed ; Minimum rotational speed ; Among them, is the maximum power P the per-unit value of the rotational speed corresponding to 2, is the minimum power P the per-unit value of the rotational speed corresponding to 3, n r is the synchronous speed, is the head.

5. The method for selecting the runner diameter of a variable-speed pumped-storage unit's pump-turbine, as described in claim 4, is characterized in that Step 4 is specifically as follows: Maximum super-synchronous active power P rmax and minimum sub-synchronous active power P rmin are calculated as follows: Among them, P 2、 P 3 are respectively the maximum power and the minimum power under the lowest lift head H min ​ 6. The method for selecting the runner diameter of a variable-speed pumped storage unit's pump-turbine, as described in claim 5, is characterized in that Step 5 is specifically as follows: Calculate the maximum value of the apparent power on the rotor side in the supersynchronous and subsynchronous states S rmax 、 S' rmax ; The calculation method of the apparent power on the rotor side is as follows: Among them, is the active power on the rotor side of the variable speed unit; is the reactive power on the rotor side of the variable speed unit.

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