A method for controlling large fluctuation of rotating speed of bulb tubular unit

Abstract

The application provides a bulb through-flow type unit large fluctuation rotating speed control method, and the control method comprises: a control process comprising an escape speed stage, a real-time control stage and a small fluctuation stage; the escape speed stage comprises: when the unit is thrown off the load, the electromagnetic moment balanced with the hydraulic moment disappears, the unit is forced to produce acceleration, the rotating speed rapidly rises, a guide vane closing law is selected, the rising rate of the unit is controlled, and the rising value of the rotating speed of the unit is limited below the maximum setting value; the real-time control stage comprises: the falling rate of the rotating speed is controlled through the selection of a real-time control stage strategy, so as to ensure that the small fluctuation stage is smoothly entered; and the small fluctuation stage comprises: the guide vane is closed to the no-load opening, and after the rotating speed is stabilized in the small fluctuation range, the small fluctuation stage is entered. The transition process of the rotating speed of the power station is limited between the given maximum rotating speed and the minimum rotating speed, the overshoot is small, the swing times are few, and the regulation precision is high.

Description

Technical Field

[0001] This invention relates to the field of axial-flow turbines, and more particularly to a method for controlling large-fluctuation speed of bulb axial-flow turbine units. Background Technology

[0002] Axial-flow turbines are characterized by low head, high flow rate, and high specific speed. Compared to other conventional units, they exhibit shorter acceleration time, larger transient rate rise, larger inertial constant of the water flow in the intake system, relatively larger water hammer pressure, and greater reverse thrust during large fluctuations. The load shedding transition process in hydropower stations is a typical large fluctuation process. The standards for passing the load shedding test are: the speed at high frequencies should not exceed the set value, the speed at low frequencies should not be lower than 90% of the rated value, and the rise in water hammer pressure should not exceed the specified value. In practical engineering, the guide vanes often use a one- or two-stage closing mechanism during the load shedding transition process. Due to the aforementioned characteristics, this closing mechanism is difficult to meet relevant standards, and there are numerous cases of malfunctions and accidents caused by improper handling of the transition process, resulting in certain economic losses.

[0003] Existing guide vane closing mechanisms are adjusted by controlling the slope of the guide vane closure. Their characteristic is that the closure of the guide vanes and blades proceeds in a straight line or a multi-segment broken line, while the servo motor always moves in the "closing direction." This closing mechanism makes it difficult to simultaneously ensure that the speed does not exceed the maximum speed at high frequencies and does not fall below 90% of the rated speed at low frequencies. In many cases, it fails the load shedding test, causing "overspeed protection and low-frequency protection shutdown," resulting in an emergency shutdown of the unit. The enormous reverse water thrust damages the unit, mainly due to the unidirectional closing direction of the servo motor. Summary of the Invention

[0004] In view of the above problems, the present invention is proposed to provide a method for controlling large fluctuation speed of a bulb turbine generator set to overcome or at least partially solve the above problems.

[0005] According to one aspect of the present invention, a method for controlling large fluctuation speed of a bulb turbine generator unit is provided, the control method comprising a control process including an escape speed stage, a real-time control stage, and a small fluctuation stage;

[0006] The aforementioned speed-up phase includes the disappearance of the electromagnetic torque that balances the hydraulic torque when the unit sheds the load, the unit is subjected to force and accelerates, and the speed rises rapidly. The guide vane closing pattern is selected to control the rate of increase of the unit's speed and limit the increase of the unit's speed to below the maximum set value.

[0007] The real-time control phase includes selecting a strategy to control the rate of decrease of the rotational speed to ensure a smooth transition into the small fluctuation phase.

[0008] The small fluctuation stage includes the process of the guide vane closing to the no-load opening and the rotational speed stabilizing within the small fluctuation range before entering the small fluctuation stage.

[0009] Optionally, the small fluctuation stage is regulated using PID control and a combination of proportional, integral, and derivative control methods.

[0010] Optionally, the real-time control stage specifically includes:

[0011] The control law is determined based on the rotational speed and the rate of change, and the control law includes a first time period, a second time period, and a third time period.

[0012] The first time period is when the movement is directed in the opening direction;

[0013] The second period will remain unchanged for now;

[0014] The third time period is described by changing the closing slope.

[0015] Optionally, the first period of movement in the opening direction specifically includes moving in the opening direction for the first period of time and then closing to the no-load opening degree when the guide vane is closed to the inflection point.

[0016] Optionally, the second period of temporary inactivity specifically includes:

[0017] When the guide vane closes to the inflection point, it remains stationary until the second period, at which point it closes to the no-load opening.

[0018] Optionally, the third time period of changing the closing slope specifically includes:

[0019] When the guide vane closes to the inflection point, reduce the movement speed to close to the no-load opening.

[0020] The inflection point is the intersection of the runaway speed stage and the real-time control stage.

[0021] Optionally, the process of determining the first closing time and calculating the inflection point includes:

[0022] escape speed time t es The relationship between the maximum increase in rotational speed and the increase in water pressure can be seen in equations (10), (11), and (12). First, assume a set of closing times, and calculate the increase in rotational speed n corresponding to each closing time using the analytical method. max Pressure rise value ζ M Compare the calculation results and select a set of first-stage shut-off time and inflection point values ​​that simultaneously satisfy the requirements of speed and pressure rise;

[0023]

[0024] Where, τ n1 The acceleration time ratio corresponding to the first time period; a0, ax These represent the initial guide vane opening and the no-load opening, respectively; T s1 This is the first closing time; j * The relative value of the additional rotational inertia to the dynamic flow in the runner region; Ω J Let be the rotational inertia constant of the water flow in the runner region; θ and β are the airfoil plane wrap angle and placement angle, respectively; ρ is the hub ratio; ρ is the density of water.

[0025]

[0026] Where, δ cM δ 1M δ M These represent the increase in guide vane lag speed, the maximum increase in speed during the first stage, and the maximum increase in speed during load shedding, respectively, T. c T is the guide vane movement lag time. a T is the acceleration time constant of the rotating parts of the unit. s τ is the guide vane closing time. n For the escape velocity relative to time, σ p Where L1 is the pipe characteristic coefficient, V is the circumference chord length of the water inlet pipe, and V is the pipe characteristic coefficient. 10 V is the average flow velocity in the intake pipe, L2 is the length of the tailrace pipe axis, and V 20 H represents the average flow velocity in the tailrace pipe. Z0 To shed the initial head, n max This represents the maximum rotational speed.

[0027]

[0028] Where, ζ M The maximum relative pressure change is given by σ, where σ is the pipe characteristic coefficient and T is the pipe characteristic coefficient. s T is the guide vane closing time. w Let v0 be the time constant for the acceleration of the water flow in the pipe, v0 be the initial average flow velocity, L be the length of the pipe axis, and H0 be the initial head.

[0029] This invention provides a method for controlling the large fluctuation speed of a bulb turbine generator unit. The control method includes a control process comprising an escape speed stage, a real-time control stage, and a small fluctuation stage. The escape speed stage includes: when the unit sheds its load, the electromagnetic torque balancing the hydraulic torque disappears, the unit experiences acceleration due to force, and the speed rises rapidly. The guide vane closing pattern is selected, and the rate of increase of the unit's speed is controlled to limit the speed increase below the maximum setpoint. The real-time control stage includes: controlling the rate of decrease of the speed through the selection of a real-time control strategy to ensure a smooth transition into the small fluctuation stage. The small fluctuation stage includes: after the guide vanes close to the no-load opening and the speed stabilizes within the small fluctuation range, the unit enters the small fluctuation stage. Through real-time control of the guide vanes, the transient speed is controlled above the rated speed. This ensures that the transient speed of the power plant is confined between the given maximum and minimum speeds, with small overshoot, few oscillations, and high adjustment accuracy.

[0030] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A flowchart of a method for controlling large fluctuation speed of a bulb turbine generator set provided in an embodiment of the present invention. Detailed Implementation

[0033] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0034] The terms "comprising" and "having," and any variations thereof, in the specification, embodiments, claims, and drawings of this invention are intended to cover non-exclusive inclusion, such as including a series of steps or units.

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] like Figure 1 As shown, a method for controlling large fluctuation speed of a bulb turbine generator set is described. The control method includes a control process comprising an escape speed stage, a real-time control stage, and a small fluctuation stage.

[0037] The speed-up phase includes: when the unit sheds the load, the electromagnetic torque that was balanced with the hydraulic torque disappears, the unit is subjected to force and accelerates, and the speed rises rapidly. The guide vane closing law is selected to control the rate of increase of the unit and limit the increase of the unit speed to below the maximum set value.

[0038] The real-time control phase includes: controlling the rate of decrease of the rotational speed by selecting a real-time control phase strategy to ensure smooth entry into the small fluctuation phase;

[0039] The small fluctuation stage includes: from the guide vane closing to the no-load opening, the rotational speed stabilizes within the small fluctuation range, and then enters the small fluctuation stage.

[0040] For existing turbine units operating under load shedding conditions, this invention proposes a method for real-time control of guide vanes and blades based on microcomputer speed governors, employing three closing strategies: ① moving in the opening direction for a period of time; ② remaining stationary for a period of time; ③ changing the closing slope for a period of time.

[0041] This invention divides the control strategy into three stages: the escape velocity stage, the real-time control stage, and the small fluctuation stage.

[0042] Escape speed stage: When the unit sheds the load, the electromagnetic torque that balances the hydraulic torque disappears, the unit is subjected to force and accelerates, and the speed rises rapidly. It is necessary to select a reasonable guide vane closing law to control the rate of increase of the unit and limit the increase of the unit speed to below the maximum set value.

[0043] The speed-out phase is the first important node in the transition process. Improper selection can lead to unsuccessful load shedding tests or, in severe cases, damage to the unit and safety accidents.

[0044] Increasing the guide vane closing speed (shortening the closing time) can suppress the increase in rotational speed, but the pressure rise caused by water hammer also increases, increasing the risk of damage to the unit and hydraulic structures. Slowing down the guide vane closing speed (increasing the closing time) reduces the rise in water hammer pressure, but the increase in rotational speed may exceed the set value, triggering overspeed protection and causing an accidental shutdown, while reverse water thrust can damage the thrust bearing.

[0045] Determining the closing time and inflection point of the first segment requires calculation and verification, specifically including:

[0046] escape speed time t esThe relationship between the maximum increase in rotational speed and the increase in water pressure can be seen in equations (10), (11), and (12). First, assume a set of closing times, and calculate the increase in rotational speed n corresponding to each closing time using the analytical method. max Pressure rise value ζ M Compare the calculation results and select a set of first-stage shut-off time and inflection point values ​​that simultaneously satisfy the requirements of speed and pressure rise;

[0047]

[0048] Where, τ n1 The acceleration time ratio corresponding to the first time period; a0, a x These represent the initial guide vane opening and the no-load opening, respectively; T s1 This is the first closing time; j * The relative value of the additional rotational inertia to the dynamic flow in the runner region; Ω J Let be the rotational inertia constant of the water flow in the runner region; θ and β are the airfoil plane wrap angle and placement angle, respectively; ρ is the hub ratio; ρ is the density of water.

[0049]

[0050] Where, δ cM δ 1M δ M These represent the increase in guide vane lag speed, the maximum increase in speed during the first stage, and the maximum increase in speed during load shedding, respectively, T. c T is the guide vane movement lag time. a T is the acceleration time constant of the rotating parts of the unit. s τ is the guide vane closing time. n For the escape velocity relative to time, σ p Where L1 is the pipe characteristic coefficient, V is the circumference chord length of the water inlet pipe, and V is the pipe characteristic coefficient. 10 V is the average flow velocity in the intake pipe, L2 is the length of the tailrace pipe axis, and V 20 H represents the average flow velocity in the tailrace pipe. Z0 To shed the initial head, n max This represents the maximum rotational speed.

[0051]

[0052] Where, ζ M The maximum relative pressure change is given by σ, where σ is the pipe characteristic coefficient and T is the pipe characteristic coefficient. s T is the guide vane closing time. w Let v0 be the time constant for the acceleration of the water flow in the pipe, v0 be the initial average flow velocity, L be the length of the pipe axis, and H0 be the initial head.

[0053] Based on conventional control principles, the closing times of the first and second stages are selected, and reasonable inflection points are determined to control both the maximum speed and the maximum pressure.

[0054] Real-time control phase: The task of this phase is to control the rate of speed decrease through the selection of a real-time control strategy to ensure a smooth transition into the small fluctuation phase. If a traditional shutdown method is used, the rate of speed decrease may not be properly controlled, and the speed may fall below the minimum setpoint allowed by the power grid. This could even cause low-frequency demagnetization, resulting in power failure or damage to electrical components.

[0055] The three shutdown strategies are methods proposed for controlling the rate of speed decrease, including:

[0056] ① Move in the opening direction for a period of time, that is, when the guide vane is closed to the inflection point, move in the opening direction for a period of time and then close to the no-load opening.

[0057] ② Keep it still for a period of time, that is, when the guide vane is closed to the inflection point, keep it still for a period of time before closing it to the no-load opening.

[0058] ③ Change the closing slope over a period of time; that is, when the guide vane closes to the inflection point, reduce the movement speed to close to the no-load opening. The adjustment is determined by the rotational speed and the changing speed, using one of the three control laws mentioned above.

[0059] Small fluctuation stage: After the guide vane closes to the no-load opening and the speed stabilizes within the small fluctuation range, it enters the small fluctuation stage, and is adjusted by PID and proportional, integral and derivative combination control.

[0060] Existing technologies focus on the high-frequency components, aiming to prevent overspeed protection from tripping during load shedding, but neglect the low-frequency components. As a result, the unit often experiences "low-frequency demagnetization" and "loss of plant power" when it trips during an emergency shutdown, generating a huge reverse water thrust that damages the generator's thrust reverser bearings and can even cause serious accidents.

[0061] Beneficial Effects: The three-stage control method proposed in this invention, in addition to controlling overspeed conditions, specifically employs a real-time control method to offer a new solution for excessively rapid speed drops. By controlling the guide vanes in real time, the transient speed is kept above the rated speed. This confines the power plant's speed transient process to between the given maximum and minimum speeds, with small overshoot, few oscillations, and high adjustment accuracy.

[0062] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling large fluctuation speed of a bulb-type turbine generator unit, characterized in that, The control method includes three control stages, namely, a speed-up stage, a real-time control stage, and a small fluctuation stage. The aforementioned speed-up phase includes the process of shedding load from the unit, during which the electromagnetic torque that balances the hydraulic torque disappears, the unit is subjected to force and accelerates, and the speed rises rapidly. The guide vane closing pattern is selected to control the rate of increase of the unit speed and limit the increase of the unit speed to below the maximum set value. The real-time control phase includes controlling the rate of decrease of the rotational speed through the selection of a real-time control phase strategy to ensure smooth entry into the small fluctuation phase; The real-time control phase specifically includes: determining a control law based on the rotational speed value and the changing speed, wherein the control law has three time periods: a first time period, a second time period, and a third time period; moving in the opening direction during the first time period; remaining stationary during the second time period; and changing the closing slope during the third time period. The first time period of moving in the opening direction specifically includes moving in the opening direction for the first time period when the guide vane is closed to the inflection point, and then closing to the no-load opening degree. The second period of temporary immobility specifically includes: when the guide vane is closed to the inflection point, it remains immobile for the second period of time and then closes to the no-load opening. The third time period of changing the closing slope specifically includes: when the guide vane closes to the inflection point, reducing the movement speed to close to the no-load opening; the inflection point is the intersection of the escape speed stage and the real-time control stage; The small fluctuation stage includes the process of the guide vane closing to the no-load opening and the rotational speed stabilizing within the small fluctuation range before entering the small fluctuation stage.

2. The method for controlling large fluctuation speed of a bulb turbine generator unit according to claim 1, characterized in that, The small fluctuation phase is regulated using PID control and a combination of proportional, integral, and derivative control methods.

3. The method for controlling large fluctuation speed of a bulb-type turbine generator unit according to claim 1, characterized in that, The process of determining the first closing time and calculating and demonstrating the inflection point includes: Escape time The relationship between the maximum increase in rotational speed and the increase in water pressure can be seen in the formula. , , First, assume a set of shutdown times, and then calculate the speed increase corresponding to each shutdown time using analytical methods. Pressure rise value Compare the calculation results and select a set of first-stage shut-off time and inflection point values ​​that simultaneously satisfy the requirements of speed and pressure rise; in, The acceleration time ratio corresponding to the first period; These represent the initial guide vane opening and the no-load opening, respectively. This is the first shutdown period; The relative value of the additional rotational inertia to the dynamic water flow in the runner region; Let be the rotational inertia constant of the water flow in the runner region; , These are the airfoil plane wrap angle and the placement angle; The hub ratio; The density of water; in, , , These represent the increase in guide vane lag speed, the maximum increase in speed during the first stage, and the maximum increase in speed during load shedding. The guide vane movement lag time. The acceleration time constant of the rotating parts of the unit. For guide vane closing time, For the escape velocity relative to time, For pipeline characteristic coefficients, For the circumference chord length of the water pipe, The average flow velocity in the water intake pipe, Because of the length of the tailrace pipe axis, The average flow velocity in the tailrace pipe is... To shed the initial head, This represents the maximum rotational speed. in, This represents the maximum relative change in pressure. For pipeline characteristic coefficients, For guide vane closing time, Let be the time constant for the acceleration of water flow in the pipe. Let L be the initial average flow velocity and L be the length of the pipe axis. This is the initial head.

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