A control method for a pumped-storage unit to shed load until it operates under no-load conditions

Abstract

The present invention relates to the technical field of hydro-generator unit control, and particularly to a control method for a pumped-storage unit to shed load until it operates under no-load conditions. The method includes: establishing an analytical model of the external characteristics of the pumped-storage unit; based on the external characteristics model, simulating the load shedding until no-load operation conditions by putting into different numbers of pairs of MGV devices; selecting several additional guide vane openings for load shedding simulation, and taking the minimum of the maximum value of the spiral case inlet pressure and the weighted average of the synchronization time as the optimization objective to obtain the corresponding number of pairs of MGV devices and the pre-opening degree. The present invention determines the preferred number of pairs of MGV devices put into operation and the pre-opening degree suitable for operating under the load shedding until no-load operation conditions through comparison and selection; realizes the calculation of the pumped-storage unit for load shedding until no-load operation conditions, can solve the technical problems of excessive water hammer pressure and difficult synchronization and grid connection after load shedding, and enables the unit to quickly connect to the grid.

Description

Technical Field

[0001] The present invention relates to the technical field of hydro-generator unit control, and particularly to a control method for a pumped-storage unit to shed load until it operates under no-load conditions. Background Art

[0002] Pumped-storage units play a role in peak shaving and frequency modulation in the power grid due to their unique operation mode of bidirectional operation of pumps and turbines. Therefore, pumped-storage units frequently switch operating conditions and often operate under conditions such as turbine startup and pump startup. Under adverse conditions such as load shedding, problems such as excessive water hammer pressure and unstable no-load operation are likely to occur, which may pose a threat to the safe and stable operation of the unit and pipelines. In order to ensure the stable operation of the unit and give full play to the advantages of pumped-storage units, it is urgent to improve the operation quality of pumped-storage units under adverse conditions.

[0003] In practical engineering applications, methods such as optimizing the guide vane closing law, introducing pressure feedback, installing MGV devices, partially closing the ball valve, and optimizing runner design are usually adopted to improve the operation stability of the unit under adverse conditions. For pumped-storage units, the adjustment methods after load shedding can be divided into automatically adjusting the unit to no-load operation and directly acting on the unit to stop. There are many studies on the load shedding until shutdown condition, but the research on the more common load shedding until no-load operation condition is still lacking. The existing solutions cannot solve the technical problems of excessive water hammer pressure and difficult synchronization and grid connection of the unit after load shedding. Summary of the Invention

[0004] The present invention provides a control method for a pumped-storage unit to shed load until it operates under no-load conditions, so as to solve the defects in the prior art that pumped-storage units are prone to excessive water hammer pressure and unstable no-load operation under adverse conditions such as load shedding, solve the technical problems of excessive water hammer pressure and difficult synchronization and grid connection of the unit after load shedding, enable the extreme value of the water system pressure under the load shedding condition to meet the requirements of the regulation and protection calculation, and enable the unit to be quickly connected to the grid.

[0005] The present invention provides a control method for a pumped-storage unit to shed load until it operates under no-load conditions, including:

[0006] S1 Establish an external characteristic analysis model of the pumped-storage unit based on the full characteristic curve of the pump-turbine;

[0007] S2 Based on the external characteristic model, conduct simulations of load shedding until no-load operation conditions by putting into different numbers of pairs of MGV devices according to several preset layout schemes.

[0008] For each of the preset layout schemes, several additional guide vane openings are selected at equal intervals for load rejection simulation, and the maximum value of the spiral case inlet pressure, the minimum value of the draft tube inlet pressure, and the synchronization time corresponding to each value of the additional guide vane opening are obtained when the load is rejected to the no-load operating condition.

[0009] S3 Calculate the weighted average values of the maximum spiral case inlet pressure, the minimum draft tube inlet pressure, and the synchronization time when different additional guide vane openings are taken under each group of preset layout schemes, and obtain the number of MGV devices and the pre-opening degree corresponding to the lowest weighted average value.

[0010] According to a control method for a pumped-storage unit to reject load until the no-load operating condition provided by the present invention, in step S1, an external characteristic analysis model of the pumped-storage unit is established, including:

[0011] Establish a characteristic normal line model of the penstock to obtain the instantaneous head H

[0017] , ,

[0016] , , s , , mt , , s , , t , p , ct ,

[0018] ,

[0012] , mt , ct , , s , , s ,

[0015] , p , ,

[0014] , ,

[0013] , m and the flow rate Q p ;

[0012] Obtain the full characteristic curve of the measured pump-turbine as an interpolation model;

[0013] Establish a first-order model of the generator to obtain the corresponding transfer function;

[0014] Establish a runner flow-through model with the MGV device, and after installing the MGV, obtain the flow rate characteristic Q s and the torque characteristic M s :

[0015]

[0016] wherein, Q s is the total runner flow-through amount, Q mt is the flow rate at the MGV device, Q ct is the flow rate at the conventional guide vane; M s is the total runner torque, M mt is the torque at the MGV device, M ct is the torque at the conventional guide vane; b1, b2, b3, b4 are constants; Z m is the number of pre-opening guide vanes, Z t is the total number of movable guide vanes.

[0017] According to a control method for a pumped-storage unit to reject load until the no-load operating condition provided by the present invention, the pre-opening guide vane opening is the sum of the conventional guide vane opening and the additional opening.

[0018] According to a control method for a pumped-storage unit to reject load until the no-load operating condition provided by the present invention, step S2 includes:

[0019] Without engaging the MGV device, conduct a load rejection simulation until the no-load operating condition is reached. After the load rejection occurs, use a parallel PID control strategy to control the guide vane movement.

[0020] According to a control method for a pumped-storage unit to perform load rejection until the no-load operating condition provided by the present invention, step S2 includes:

[0021] Obtain the iterative initial values of the rotational speed N, head H, and flow rate Q; calculate the conventional guide vane opening and the pre-opening guide vane opening at the guide vane where the MGV device is engaged.

[0022] Calculate the flow rate through the corresponding guide vane based on the guide vane opening; calculate the flow rate through the guide vane where the MGV device is engaged, and calculate the total flow rate at the runner by weighted calculation; calculate the difference between the total flow rate and the iterative initial value of the flow rate Q. If the difference is less than the preset flow rate threshold, proceed to the next step.

[0023] Calculate the torque value at the conventional guide vane based on the conventional guide vane opening; calculate the corresponding torque according to the pre-opening guide vane opening at the guide vane where the MGV device is engaged, and calculate the total torque of the runner.

[0024] Calculate the current rotational speed, and calculate the difference between the current rotational speed and the iterative initial value of the rotational speed N. If the difference is less than the preset rotational speed threshold, proceed to the next step.

[0025] Output the real-time rotational speed N t , the opening y m , the head H t , the flow rate Q t and the torque M t .

[0026] According to a control method for a pumped-storage unit to perform load rejection until the no-load operating condition provided by the present invention, step S3 includes:

[0027] Obtain the simulation results in two cases: without engaging the MGV device and with the MGV device engaged, and compare the rotational speed adjustment Δn, the maximum value of the spiral case inlet pressure H scmax , the minimum value of the draft tube inlet pressure H dtmin , and the synchronization grid connection time T SR .

[0028] On the other hand, the present invention also provides a control system for a pumped-storage unit to perform load rejection until the no-load operating condition, including:

[0029] A model establishment module for establishing an external characteristic analysis model of the pumped-storage unit according to the full characteristic curve of the pump-turbine;

[0030] A simulation module, based on the external characteristic model, performs a load rejection simulation until the no-load operating condition by engaging different numbers of MGV devices according to several preset layout schemes.

[0031] For each of the preset layout schemes, several additional guide vane openings are selected at equal intervals for load rejection simulation, and the maximum value of the spiral case inlet pressure, the minimum value of the draft tube inlet pressure, and the synchronization time corresponding to each additional guide vane opening value are obtained under the condition of load rejection to no-load operation.

[0032] A calculation module is used to calculate the weighted average of the maximum value of the spiral case inlet pressure and the synchronization time when different additional guide vane openings are taken under each group of preset layout schemes, and obtain the number of MGV device pairs and the pre-opening degree corresponding to the lowest weighted average.

[0033] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the control method for load rejection of a pumped-storage unit until no-load operation are implemented as described in any one of the above.

[0034] The control method for load rejection of a pumped-storage unit until no-load operation provided by the present invention, compared with the prior art, has at least the following technical effects:

[0035] For the first time, a control strategy for load rejection until no-load operation with an MGV device is proposed; by comparing and selecting the optimal one, the optimal number of MGV device pairs and the pre-opening degree suitable for operation under the condition of load rejection until no-load operation are determined; the calculation of load rejection of a pumped-storage unit until no-load operation is realized, and the additional measures adopted can effectively reduce the rise of water hammer pressure during load rejection and shorten the synchronization grid connection time. Description of the Drawings

[0036] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings 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.

[0037] Figure 1 It is one of the schematic flowcharts of the control method for load rejection of a pumped-storage unit until no-load operation provided by the present invention;

[0038] Figure 2 It is another schematic flowchart of the control method for load rejection of a pumped-storage unit until no-load operation provided by the present invention;

[0039] Figure 3 It is one of the schematic characteristic curve diagrams of the control method for load rejection of a pumped-storage unit until no-load operation provided by the present invention;

[0040] Figure 4 It is the second schematic diagram of the characteristic curve of the control method for the load rejection to no-load operation condition of the pumped-storage unit provided by the present invention;

[0041] Figure 5 It is a comparison diagram of the closing law of the guide vane of the control method for the load rejection to no-load operation condition of the pumped-storage unit provided by the present invention;

[0042] Figure 6 It is a comparison diagram of the effects of the control method for the load rejection to no-load operation condition of the pumped-storage unit provided by the present invention;

[0043] Figure 7 It is a schematic structural diagram of the control system for the load rejection to no-load operation condition of the pumped-storage unit provided by the present invention. Detailed implementation manners

[0044] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative efforts based on the embodiments in the present invention belong to the scope of protection of the present invention.

[0045] The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above accompanying drawings are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or modules is not limited to the listed steps or modules, but optionally further includes steps or modules not listed, or optionally further includes other steps or modules inherent to these processes, methods, products or devices.

[0046] It should be noted that the terms "first" and "second" related to the present invention are only used to distinguish similar objects and do not represent a specific order for the objects. It can be understood that "first" and "second" can be interchanged in a specific order or sequence when permitted. It should be understood that the objects distinguished by "first" and "second" can be interchanged appropriately so that the embodiments of the present invention described here can be implemented in an order other than those described or illustrated here.

[0047] In one embodiment, as Figure 1 shown, the present invention provides a control method for the load rejection to no-load operation condition of a pumped-storage unit, including:

[0048] S1 Establish an external characteristic analysis model of the pumped-storage unit based on the full characteristic curve of the pump-turbine;

[0049] S2 Based on the external characteristic model, perform load rejection simulations until the no-load operating condition by inputting different numbers of pairs of MGV devices according to several preset layout schemes;

[0050] For each of the preset layout schemes, select several additional guide vane openings at equal intervals for load rejection simulations, and obtain the maximum value of the spiral case inlet pressure, the minimum value of the draft tube inlet pressure, and the synchronization time corresponding to each additional guide vane opening value under the load rejection to no-load operating condition;

[0051] S3 Calculate the weighted average values of the maximum value of the spiral case inlet pressure, the minimum value of the draft tube inlet pressure, and the synchronization time when taking different additional guide vane openings under each group of preset layout schemes, and obtain the number of pairs of MGV devices and the pre-opening degree corresponding to the lowest weighted average value.

[0052] According to a control method for a pumped-storage unit to perform load rejection until the no-load operating condition provided by the present invention, in step S1, establish an external characteristic analysis model of the pumped-storage unit, including:

[0053] Establish a characteristic normal model of the penstock to obtain the instantaneous head H of the pipeline p and the flow rate Q p , where the transient head H of the pipeline p and the flow rate Q p are solved by the following formulas:

[0054]

[0055] In the formula, C P , B R , C M , B S are constants, which can be obtained from the known parameters of the previous moment;

[0056] Obtain the full characteristic curve of the measured pump-turbine as an interpolation model; to avoid the influence of the S characteristic on the interpolation calculation, use an improved Suter transformation method to process and interpolate and extend it;

[0057] Establish a first-order model of the generator to obtain the corresponding transfer function:

[0058]

[0059] where, T a is the inertia time constant of the unit; e n is the self-regulation coefficient of the generator;

[0060] Establish a runner flow model with the MGV device, and after installing the MGV, obtain the flow rate characteristic Q s and the torque characteristic M s :

[0061]

[0062] Among them, Q s is the total flow through the runner, and Q mt is the flow through the MGV device, and Q ct is the flow through the conventional guide vane; M s is the total torque of the runner, and M mt is the torque at the MGV device, and M ct is the torque at the conventional guide vane;

[0063] b1, b2, b3, b4 are constants, and preferably the values of the constants are 1.0;

[0064] Z m is the number of pre-opening guide vanes, and Z t is the total number of movable guide vanes.

[0065] According to a control method for a pumped-storage unit to shed load until it operates under no-load conditions provided by the present invention, the pre-opening guide vane opening is the sum of the conventional guide vane opening and the additional opening:

[0066] y m,MGV = m + y m ;

[0067] An improved Suter transformation method is used to process the full characteristic curve and perform interpolation and extension, and the formula is as follows:

[0068]

[0069]

[0070] In the formula, WH and WM respectively represent the head and torque characteristics of the pump-turbine; n, q, h, and m respectively represent the relative values of rotational speed, flow rate, head, and torque; in this embodiment, C y = 0.2, C h = 0.5, k1 = 1.0, k2 = 10.

[0071] According to a control method for a pumped-storage unit to shed load until it operates under no-load conditions provided by the present invention, step S2 includes:

[0072] Do not put into the MGV device, conduct a simulation of shedding load until it operates under no-load conditions, and use a parallel PID control strategy to control the guide vane action after the load shedding occurs.

[0073] Furthermore, as Figure 2 shown, step S2 includes:

[0074] Obtain the iterative initial values N0, H0, and Q0 of the rotational speed N, head H, and flow rate Q; calculate the conventional guide vane opening y m and the pre-opening guide vane opening y at the guide vane where the MGV device is put into operation m,MGV , Δy m represents the difference between y m,MGV and y m , that is, the additional opening;

[0075] According to the guide vane opening y m calculate the flow rate Q corresponding to the guide vane ct ; based on y m,MGV calculate the flow rate Q at the guide vane where the MGV device is put into operation mt , and calculate the total flow rate at the runner by weighted calculation; calculate the difference between the total flow rate and the iterative initial value of the flow rate Q. If the difference is less than the preset flow rate threshold, proceed to the next step; otherwise, determine the initial value and calculate again;

[0076] According to the conventional guide vane opening y m calculate the torque value M at the conventional guide vane ct ; calculate the corresponding torque M according to the pre-opening guide vane opening at the guide vane of the MGV device mt , and calculate the total torque of the runner;

[0077] Calculate the current unit rotational speed according to the generator equation, and calculate the difference between the current unit rotational speed and the iterative initial value N0 of the rotational speed. If the difference is less than the preset rotational speed threshold, proceed to the next step; otherwise, determine the initial value and calculate again;

[0078] Output the real-time rotational speed N t , opening y m , head H t , flow rate Q t and torque M t .

[0079] According to a control method for a pumped-storage unit to shed load until it operates under no-load conditions provided by the present invention, step S3 includes:

[0080] Obtain the simulation results in two cases of not putting the MGV device into operation and putting the MGV device into operation, and compare the rotational speed adjustment Δn, the maximum value H scmax of the inlet pressure of the volute, the minimum value H dtmin of the inlet pressure of the draft tube, and the synchronization grid connection time T SR ;

[0081] In a specific embodiment, a simulation of shedding load until it operates under no-load conditions is carried out in the case of putting the MGV device into operation. The shedding load conditions under three schemes of putting 1, 2, and 3 pairs of MGV devices into operation are respectively tested, and several additional openings Δy m are selected at equal intervals, and a shedding load simulation is carried out so that the additional opening Δym Open to a certain value Δy according to a linear rule c ;

[0082] Step S3 includes the following sub-steps:

[0083] (3.1) Set Scenarios 1-3 as the cases of putting 1, 2, and 3 pairs of MGV devices respectively;

[0084] (3.2) In the case of Scenario 1, let Δy c be a series of values, and conduct load rejection simulations until the no-load operating condition;

[0085] (3.3) In the case of Scenario 2, let Δy c be a series of values, and conduct load rejection simulations until the no-load operating condition;

[0086] (3.4) In the case of Scenario 3, let Δy c be a series of values, and conduct load rejection simulations until the no-load operating condition;

[0087] (3.5) With the goal of minimizing the maximum value of the spiral case inlet pressure and the shortest synchronization time, select the corresponding number of MGV pairs put in and the pre-opening degree (Δy c ) as the optimal solution.

[0088] The test results of the maximum value of the spiral case inlet pressure (H scmax ) and the synchronization time (T SR ) are shown in Table 1 below;

[0089] From the following table and Figure 5 as shown, it can be obtained that Δy c in Scenario 1 is larger, followed by Scenario 2 and then Scenario 3. And H scmax in Scenario 1 is larger, and the synchronization time decreases with the increase of Δy c . Among them, the effect is the best when the pre-opening is 30%, but a larger opening degree will cause greater interference to the water flow in the runner area, resulting in the vibration of the unit main shaft;

[0090] Compared with Scenario 1, the control effect of Scenario 2 is better, the reduction of the maximum value of the spiral case inlet pressure is greater, and the synchronization time is also better. Among them, the control effect is the best when the pre-opening is 21%;

[0091] H scmax in Scenario 3 first decreases and then increases, and the synchronization time continuously increases. When the additional opening degree increases to 12%, its evaluation index is the best;

[0092] Therefore, combining Table 1 and Figure 6 as shown, select Scenario 3 as the optimal layout plan, where Δy c = 12% is the optimal additional opening degree.

[0093] Table 1 Load rejection results of different layout modes of MGV device and pre-opening degrees

[0094]

[0095] Simulations are carried out respectively in two cases of not putting into and putting into the MGV device, the process curves are compared, and the improvement effect of the MGV device is clarified;

[0096] The comparison diagram of the closing laws of the guide vanes where the MGV device is located and the conventional guide vanes when the load is rejected until the MGV device is put into the no-load operation condition is as Figure 5 shown;

[0097] Compare the process curves when no additional measures are put into and when the MGV device is put into, and compare the rotational speed overshoot Δn, the maximum value of the spiral case inlet pressure H scmax , the minimum value of the draft tube inlet pressure H dtmin , the synchronization grid connection time T SR and other equivalent values; The results are as Figure 6 shown (the subscript m represents the situation of putting into the MGV device) and Table 2 (the extreme value occurrence time is in parentheses);

[0098] Table 2 Comparison of results of adopting different control strategies in the load rejection condition

[0099]

[0100]

[0101] (3.6) Clarify the improvement effect of the measure of putting into the MGV device on the load rejection until the no-load operation condition;

[0102] It can be seen from Figure 6 that when the load is rejected until the no-load operation condition occurs, adopting the MGV device can better improve the operation quality of the unit. In the early stage of load rejection, putting into the MGV device can effectively reduce the maximum value of the spiral case inlet pressure, increase the minimum value of the draft tube inlet pressure, reduce the reverse over-current peak value and shorten the synchronization time; in the later no-load operation, putting into the MGV device makes the fluctuation ranges of parameters such as rotational speed, spiral case inlet pressure, draft tube inlet pressure and flow rate continuously decrease, and the unit can enter the no-load steady state. Therefore, putting into the MGV device in the embodiment of the present invention can better improve the operation effect of the unit during the load rejection until the no-load operation condition.

[0103] On the other hand, as Figure 7 shown, the present invention also provides a control system for a pumped-storage unit during the load rejection until the no-load operation condition. The system described below can be correspondingly referred to the method described above, and specifically includes:

[0104] A model establishment module, configured to establish an external characteristic analysis model of the pumped-storage unit according to the full characteristic curve of the pump-turbine;

[0105] A simulation module, based on the external characteristic model, performs a simulation of load rejection until no-load operation conditions by putting into different numbers of MGV devices according to several preset layout schemes;

[0106] For each of the preset layout schemes, several additional guide vane openings are selected at equal intervals to perform a load rejection simulation, and the maximum value of the spiral case inlet pressure, the minimum value of the draft tube inlet pressure, and the synchronization time corresponding to each additional guide vane opening value are obtained under the condition of load rejection until no-load operation;

[0107] A calculation module, configured to calculate the weighted average of the maximum value of the spiral case inlet pressure and the synchronization time when different additional guide vane openings are taken under each preset layout scheme, and obtain the number of MGV device pairs and the pre-opening degree corresponding to the lowest weighted average.

[0108] The present invention also provides an electronic device, which may include: a processor, a communication interface, a memory, and a communication bus. Among them, the processor, the communication interface, and the memory complete communication with each other through the communication bus. The processor can call the logical instructions in the memory to execute the steps of the control method for load rejection of the pumped-storage unit until no-load operation conditions provided by the above-mentioned various methods.

[0109] In addition, when the logical instructions in the above-mentioned memory are implemented in the form of a software functional unit and sold or used as an independent product, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: various media such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc that can store program codes.

[0110] On the other hand, the present invention also provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the steps of the control method for the pumped-storage unit to unload until it operates under no-load conditions provided by the above-mentioned various methods.

[0111] In another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it realizes the steps of the control method for the pumped-storage unit to unload until it operates under no-load conditions provided by the above-mentioned various methods.

[0112] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative labor.

[0113] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the essence of the above technical solution, or the part that contributes to the prior art, can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; 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 of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for a pumped-storage unit to shed load until it operates under no-load conditions, characterized in that Including: S1 Establish an external characteristic analysis model of the pumped-storage unit based on the full characteristic curve of the pump-turbine; S2 Based on the external characteristic analysis model, conduct load rejection simulations until the no-load operation condition by putting into different numbers of pairs of MGV devices according to several preset layout schemes; For each of the preset layout schemes, select several additional guide vane openings at equal intervals to conduct load rejection simulations, and obtain the maximum value of the spiral case inlet pressure, the minimum value of the draft tube inlet pressure, and the synchronization time corresponding to each additional guide vane opening value under the load rejection to no-load operation condition; S3 Calculate the weighted average values of the maximum value of the spiral case inlet pressure, the minimum value of the draft tube inlet pressure, and the synchronization time when taking different additional guide vane openings under each group of preset layout schemes, and obtain the number of pairs of MGV devices and the pre-opening degree corresponding to the lowest weighted average value; Among them, in step S1, establishing the external characteristic analysis model of the pumped-storage unit includes: Establish the characteristic normal model of the pressure pipeline to obtain the instantaneous water head of the pipeline and flow rate ; Obtain the full characteristic curve of the measured pump-turbine as an interpolation model; Establish a first-order model of the generator and obtain the corresponding transfer function; Establish a flow-through model of the runner with the MGV device. After installing the MGV, obtain the flow characteristics of the runner and torque characteristics : ； wherein, is the total flow rate through the runner, is the flow rate at the MGV device, is the flow rate at the conventional guide vane; is the total torque of the runner, is the torque at the MGV device, is the torque at the conventional guide vane; , , , are constants; is the number of pre - opening guide vanes, is the total number of movable guide vanes.

2. The control method of a pumped-storage unit for load rejection until no-load operation condition according to claim 1, characterized in that, The pre-opening guide vane opening is the sum of the normal guide vane opening and the additional opening.

3. The control method of a pumped-storage unit for load rejection until no-load operation condition according to claim 2, characterized in that, Step S2 includes: Without putting into the MGV device, conduct load rejection simulations until the no-load operation condition, and adopt a parallel PID control strategy to control the guide vane action after the load rejection occurs.

4. The control method for a pumped-storage unit to unload until it operates under no-load conditions according to claim 2, characterized in that, Step S2 includes: Obtain the rotational speed and water head and flow rate for the initial iteration values; calculate the normal guide vane opening and the pre-opening guide vane opening at the guide vane where the MGV device is put into operation; Calculate the flow rate at the guide vane corresponding to the guide vane opening; calculate the flow rate at the guide vane where the MGV device is put into operation, and calculate the total flow rate at the runner by weighted calculation; calculate the difference between the total flow rate and the initial iteration value of the flow rate If the difference is less than the preset flow rate threshold, proceed to the next step; Calculate the torque value at the normal guide vane according to the normal guide vane opening; calculate the corresponding torque according to the pre-opening guide vane opening at the MGV device guide vane, and calculate the total torque of the runner; Calculate the current rotational speed and calculate the difference between the current rotational speed and the initial value of the iterative rotational speed If the difference is less than the preset rotational speed threshold, proceed to the next step; Output the real-time rotational speed , opening degree , water head , flow rate and torque .

5. The control method of a pumped-storage unit for load rejection until no-load operation condition according to claim 3, characterized in that Step S3 includes: Obtain the simulation results under two conditions: without the MGV device being put into operation and with the MGV device being put into operation, and compare the rotational speed adjustment , the maximum value of the volute inlet pressure , the minimum value of the draft tube inlet pressure , the synchronization grid connection time .

6. A control system for a pumped-storage unit during load rejection until no-load operation condition, characterized in that, The system is used to implement the steps of the control method for the pumped-storage unit to reject load until the no-load operation condition as described in any one of claims 1 to 5, including: A model establishment module for establishing an external characteristic analysis model of the pumped-storage unit based on the full characteristic curve of the pump-turbine; A simulation module, based on the external characteristic analysis model, conducts load rejection simulations until the no-load operation condition by putting into different numbers of pairs of MGV devices according to several preset layout schemes; For each of the preset layout schemes, select several additional guide vane openings at equal intervals to conduct load rejection simulations, and obtain the maximum value of the spiral case inlet pressure, the minimum value of the draft tube inlet pressure, and the synchronization time corresponding to each additional guide vane opening value under the load rejection to no-load operation condition; A calculation module for calculating the weighted average values of the maximum value of the spiral case inlet pressure and the synchronization time when taking different additional guide vane openings under each group of preset layout schemes, and obtaining the number of pairs of MGV devices and the pre-opening degree corresponding to the lowest weighted average value.

7. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the control method for the pumped-storage unit to reject load until the no-load operation condition as described in any one of claims 1 to 5.

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