A sliding pressure rate self-adaptive control method in RB process of thermal power unit

Abstract

The application discloses a sliding pressure rate adaptive control method in RB process of a thermal power unit, and comprises the following steps: step one, whether the condition of triggering the RB function is reached, if yes, entering step two; step two, a new turbine total flow instruction flu' is output by a steam turbine main control PI according to a main steam pressure deviation Δp, so that a target opening of a turbine governing valve is obtained; step three, a sliding pressure target instruction descending rate a is calculated; step four, the sliding pressure target instruction descending rate a after rate limitation is calculated and is transmitted to the turbine and the boiler; and step five, whether the RB mode is exited is judged. limited The sliding pressure target instruction descending rate a is dynamically adjusted and corrected according to the main steam pressure deviation Δp and the turbine total flow instruction flu, so that the sliding pressure target instruction descending rate a is adapted to actual working conditions; and the steam turbine main control adopts the PI closed loop control in the RB working condition, so that the system can maintain various parameters in the safe range while rapidly reducing the load.

Description

Technical Field

[0001] This invention relates to the field of thermal power unit control technology, and more specifically, to an adaptive control method for sliding pressure rate during the RB process of a thermal power unit. Background Technology

[0002] In the boiler-turbine power plant (RB) process, controlling the sliding pressure rate is crucial. When a critical auxiliary machine on one side, such as the induced draft fan or forced draft fan, fails and shuts down, the unit needs to rapidly reduce its load to the capacity of the operating auxiliary machine. During this process, a reasonable decrease in main steam pressure is key to ensuring energy balance between the boiler and turbine: too rapid a pressure drop can lead to a sudden drop in steam temperature and instability in the feedwater system; too slow a drop can prevent the timely release of heat stored in the boiler, causing overpressure risks. Precise sliding pressure control is a core element in maintaining the safe and stable operation of the unit.

[0003] Existing technology employs an open-loop control scheme to regulate the sliding pressure rate: after the RB is triggered, the system generates a sliding pressure target command based on the target load using a fixed function. This command is then processed by a rate limiter and an inertial circuit before being output to the turbine's main control PI controller to control the turbine's total flow rate. This method relies entirely on preset load-pressure curves and empirical values, and is essentially a static feedforward control.

[0004] This traditional control method has significant drawbacks. First, the fixed sliding pressure rate cannot adapt to the dynamic changes in the actual heat load of the boiler, often leading to a mismatch between the pressure setpoint and the actual value, causing problems such as main steam temperature fluctuations and cylinder exhaust overheating. Second, the lack of real-time feedback on the turbine's flow capacity means that when the total flow command is too low, it can easily cause insufficient steam pressure in the feedwater pump or insufficient cooling flow in the high-pressure cylinder. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide an adaptive control method for sliding pressure rate during the RB process of a thermal power unit, which addresses the shortcomings of the prior art. The method has a simple structure and reasonable design. It dynamically adjusts and corrects the sliding pressure target command decrease rate a based on the main steam pressure deviation Δp and the turbine total flow command flu, so that the sliding pressure target command decrease rate a adapts to the actual operating conditions. It adopts PI closed-loop control, which enables the system to maintain all parameters within a safe range while rapidly reducing the load, resulting in good performance.

[0006] To solve the above-mentioned technical problems, the technical solution adopted in this application is: an adaptive control method for sliding pressure rate during the RB process of a thermal power unit, characterized by including the following steps:

[0007] Step 1: Monitor the status of the thermal power unit and determine whether the conditions for triggering the RB function have been met. If so, proceed to Step 2.

[0008] Step 2: Calculate the main steam pressure deviation Δp. The turbine main control outputs the new turbine total flow command flu' based on the main steam pressure deviation Δp. The main steam pressure deviation Δp is the difference between the main steam pressure setpoint and the actual main steam pressure. The target opening degree of the corresponding turbine regulating valve is obtained based on the new turbine total flow command flu'. Drive the turbine regulating valve to the target opening degree.

[0009] Step 3: Calculate the sliding pressure target command descent rate: the sliding pressure target command descent rate a, a = a3 + a1 × a2, a1 represents the first rate correction coefficient, a1 = f1(Δp), f1(·) represents the first rate correction function, Δp represents the main steam pressure deviation; a2 represents the second rate correction coefficient, a2 = f2(flu'), f2(·) represents the second rate correction function; a3 represents the preset sliding pressure descent rate corresponding to the RB type;

[0010] Step 4: Calculate the descent rate a of the sliding pressure target command after rate limiting. limited ; Sliding target command descent rate a limited This information is transmitted to the steam turbine and boiler to dynamically adjust the main steam pressure setpoint.

[0011] Step 5: Determine if the exit conditions are met. If yes, proceed to Step 6; otherwise, return to Step 2.

[0012] Step 6: Exit RB mode and switch to normal sliding pressure control.

[0013] The above-mentioned adaptive control method for sliding pressure rate during the RB process of a thermal power unit is characterized in that: the first rate correction function f1(·) and the second rate correction function f2(·) are both piecewise linear functions.

[0014] The above-mentioned adaptive control method for sliding pressure rate during the RB process of a thermal power unit is characterized by:

[0015]

[0016] The above-mentioned adaptive control method for sliding pressure rate in the RB process of a thermal power unit is characterized in that: the specific method for "obtaining the target opening degree of the corresponding turbine regulating valve according to the new turbine total flow command flu'" in step two is as follows: according to the new turbine total flow command flu', check the opening degree-flow curve of the turbine regulating valve to obtain the target opening degree of the corresponding turbine regulating valve.

[0017] The aforementioned adaptive control method for sliding pressure rate during the RB process of a thermal power unit is characterized in that: the opening-flow curve of the turbine regulating valve includes the opening-flow curve of the ultra-high pressure regulating valve, the opening-flow curve of the high pressure regulating valve, and the opening-flow curve of the intermediate pressure regulating valve; the turbine regulating valve includes the ultra-high pressure regulating valve, the high pressure regulating valve, and the intermediate pressure regulating valve; the total flow command of the new turbine, flu', is converted into the opening command of the ultra-high pressure regulating valve through the opening-flow curve of the ultra-high pressure regulating valve, the opening-flow curve of the high pressure regulating valve is converted into the opening command of the high pressure regulating valve, and the opening-flow curve of the intermediate pressure regulating valve is converted into the opening command of the intermediate pressure regulating valve.

[0018] The above-mentioned adaptive control method for sliding pressure rate during the RB process of a thermal power unit is characterized in that: the exit conditions in step five include:

[0019] Exit condition 1: Main steam pressure fluctuation < ±0.3MPa for duration t1;

[0020] Exit condition 2: Load fluctuation < ±2% of rated value for duration t2;

[0021] Exit condition 3: Main steam temperature fluctuation < ±5℃ for duration t3;

[0022] Exit condition 4: the duration of the balance between feedwater flow rate and steam flow rate is t4.

[0023] If any exit condition fluctuation exceeds the limit, the timer for other exit conditions is reset to zero, and the process returns to step two.

[0024] The above-mentioned adaptive control method for sliding pressure rate during the RB process of a thermal power unit is characterized in that: in step three, Where a t-k R represents the initial descent rate in the k-th control cycle. max The maximum allowable rate of change is represented by Δt, which represents the control period, and a is the control period. min a represents the minimum rate of descent. max This indicates the maximum rate of descent.

[0025] The above-mentioned adaptive control method for sliding pressure rate in the RB process of a thermal power unit is characterized in that: in step 203, the RB type includes primary air fan RB, forced draft fan RB, induced draft fan RB, feedwater pump RB, coal mill RB, and air preheater RB.

[0026] The above-mentioned adaptive control method for sliding pressure rate during the RB process of a thermal power unit is characterized in that: in step two, the main turbine controller is a PI controller with a proportional gain Kp = 1.4 and an integral time constant Ki = 40s. -1 The rated main steam pressure is 310 bar.

[0027] This application has the following advantages compared with the prior art:

[0028] 1. This application has a simple structure, reasonable design, and is easy to implement and use.

[0029] 2. The sliding pressure rate adaptive control method of this application dynamically adjusts and corrects the sliding pressure target command decline rate a based on the main steam pressure deviation Δp and the turbine total flow command flu. This avoids the one-sidedness of single parameter control, prevents pressure runaway caused by delayed release of boiler heat storage, and avoids the risk of overheating caused by insufficient turbine flow. It significantly improves the control accuracy and safety of the RB process, and makes the sliding pressure target command decline rate a adaptable to actual working conditions.

[0030] 3. In the adaptive control of sliding pressure rate in the RB process of thermal power unit, this application adopts PI control. According to the deviation Δa, the new turbine total flow command flu' is output. In the next control cycle, the second rate correction coefficient a2 is calculated based on the new turbine total flow command flu', thereby realizing closed-loop control. This allows the system to maintain all parameters within a safe range while rapidly reducing the load, resulting in good performance.

[0031] In summary, this application dynamically adjusts and corrects the sliding pressure target command reduction rate a based on the main steam pressure deviation Δp and the turbine total flow command flu, so that the sliding pressure target command reduction rate a adapts to the actual working conditions; it adopts PI closed-loop control, which enables the system to maintain all parameters within a safe range while rapidly reducing the load, resulting in good performance.

[0032] The technical solution of this application will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0033] Figure 1 This is a flowchart of the method in this application.

[0034] Figure 2 This is the control logic diagram for the PI in this application.

[0035] Figure 3 A flowchart illustrating the method for calculating the descent rate of the sliding target command in this application. Detailed Implementation

[0036] The present application will now be described in further detail with reference to the accompanying drawings and embodiments thereof.

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0040] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0041] like Figure 1 , Figure 2 and Figure 3 As shown, the adaptive control method for sliding pressure rate in the RB process of a thermal power unit according to this application includes the following steps:

[0042] Step 1: Monitor the status of the thermal power unit and determine whether the conditions for triggering the RB function have been met. If so, proceed to Step 2.

[0043] Step 2: Calculate the main steam pressure deviation Δp. The turbine main controller outputs the new turbine total flow command flu' based on the main steam pressure deviation Δp. The main steam pressure deviation Δp is the difference between the main steam pressure setpoint and the actual main steam pressure. The target opening degree of the corresponding turbine regulating valve is obtained based on the new turbine total flow command flu'. Drive the turbine regulating valve to the target opening degree.

[0044] The turbine main control PI controller performs dynamic PI calculations based on the main steam pressure deviation Δp, outputting the new turbine total flow command flu'. Based on the new turbine total flow command flu', it obtains the target opening degree of the corresponding turbine regulating valve and drives the turbine regulating valve to the target opening degree. Then, in the next control cycle, it calculates the first rate correction coefficient a1 based on the main steam pressure deviation Δp and the second rate correction coefficient a2 based on the new turbine total flow command flu', thus achieving closed-loop control. In step two, the turbine main control is a PI controller with a proportional gain Kp = 1.4 and an integral time constant Ki = 40s. -1 The rated main steam pressure is 310 bar.

[0045] After the main control PI outputs the new turbine total flow command `flu'`, the target opening degree of the turbine regulating valve corresponding to the new turbine total flow command `flu'` is obtained by checking the opening-flow curve of the turbine regulating valve. The opening-flow curve of the turbine regulating valve includes the opening-flow curve of the ultra-high pressure regulating valve, the high pressure regulating valve, and the intermediate pressure regulating valve; the turbine regulating valve includes the ultra-high pressure regulating valve, the high pressure regulating valve, and the intermediate pressure regulating valve; the new turbine total flow command `flu'` is converted into the opening command of the ultra-high pressure regulating valve through the opening-flow curve of the ultra-high pressure regulating valve, the opening-flow curve of the high pressure regulating valve is converted into the opening command of the high pressure regulating valve, and the opening-flow curve of the intermediate pressure regulating valve is converted into the opening command of the intermediate pressure regulating valve.

[0046] Table 1 shows the opening-flow curve of the ultra-high pressure regulating valve. As shown in Table 1, under a specific per-unit conversion (0-100 per-unit to 0-1 range) rule, the correspondence between the turbine's total flow demand command flu' and the high-pressure regulating valve's target opening demand CV Dmd is as follows: For example, when flu' = 0.7476, CV Dmd = 0.2231, indicating that the turbine is operating at 74.76% of the rated flow, and the ultra-high pressure regulating valve is opened to 22.31% of the rated opening.

[0047] Table 1. Opening-flow curves of ultra-high pressure regulating valves

[0048]

[0049] In the turbine control system, the turbine main control PI outputs a new turbine total flow command `flu'` based on the main steam pressure deviation Δp. By increasing or decreasing `flu'`, the opening of the regulating valve is adjusted, thereby controlling the rate of change of the main steam pressure. After receiving the ultra-high pressure regulating valve opening commands, high pressure regulating valve opening commands, and intermediate pressure regulating valve opening commands, the servo valve drives the regulating valve to operate. By adjusting the regulating valve opening, the rate of decrease in boiler heat load is matched with the turbine flow rate, thereby stabilizing the main steam temperature, preventing the turbine exhaust steam temperature from exceeding the limit, and maintaining the feedwater pump steam source pressure.

[0050] Step 3: Calculate the sliding pressure target command descent rate: sliding pressure target command descent rate a, a = a3 + a1 × a2, a1 represents the first rate correction coefficient, a1 = f1(Δp), f1(·) represents the first rate correction function, Δp represents the main steam pressure deviation; a2 represents the second rate correction coefficient, a2 = f2(flu'), f2(·) represents the second rate correction function; a3 represents the preset sliding pressure descent rate corresponding to the RB type.

[0051] Regarding the first rate correction factor a1: The boiler heat release Q is mainly due to convective heat transfer Q. dl Heat exchange with radiation Q fs Composition, Q = Q dl +Q fs After the RB triggers load reduction in the thermal power unit, the fuel quantity and air volume in the furnace decrease rapidly, leading to a decrease in convective heat transfer Q. dl The temperature drops rapidly thereafter, but due to a certain delay in the temperature drop of the furnace wall and heat exchange tube wall, the radiative heat transfer rate Q... fs The rate of decrease is relatively slow. Due to differences in the number and location of radiant heat exchange surfaces in different boilers, as well as variations in the type of coal burned and the ash accumulation on the heat exchange tubes before the occurrence of RB (Radiation Reduction), the rate of decrease in boiler heat release varies depending on the boiler type and the time of occurrence of RB. The decrease in boiler heat release Q delays the unit's vaporization process, accelerating the decrease in the actual boiler evaporation rate D. At this time, if the opening of the high-pressure regulating valve and the intermediate-pressure regulating valve of the turbine remains unchanged, the boiler evaporation rate D is approximately proportional to the main steam pressure, and the rate of decrease in boiler evaporation rate is directly reflected in the actual rate of decrease in main steam pressure. The main steam pressure deviation Δp is the difference between the target value and the actual value of the main steam pressure. If the actual value of the main steam pressure is lower than the target value, i.e., the main steam pressure deviation Δp > 0, it indicates that the boiler evaporation rate D is decreasing too quickly, and the preset sliding pressure target command does not match the actual change in boiler heat release. It is necessary to accelerate the current preset sliding pressure decrease rate a3 to match the change in heat load.

[0052] Therefore, it is necessary to modify the current preset sliding pressure drop rate a3 by incorporating the main steam pressure deviation Δp, so that the sliding pressure control is more in line with actual operating conditions and avoids steam temperature fluctuations or turbine exhaust temperature exceeding limits. In actual use, the main steam pressure deviation Δp is mapped to a first rate correction coefficient a1 through the first rate correction function f1(Δp), which is used to correct the preset sliding pressure drop rate a3. f1(Δp) is a piecewise linear function. In one possible embodiment,

[0053] Taking a 1000MW double reheat unit as an example, the relationship between the main steam pressure deviation Δp and the first rate correction coefficient a1 is shown in Table 2:

[0054] Table 2 Comparison of Preset Sliding Pressure Drop Rate and Main Steam Pressure Deviation with First Rate Correction Coefficient

[0055]

[0056] In one possible embodiment, taking a 1000MW unit as an example, the target value of the main steam pressure is 30.0MPa at 100% load; 24.0MPa at 80% load; 18.0MPa at 60% load; and 15.0MPa at 50% load.

[0057] Δp = 0 indicates that the target value of the main steam pressure is consistent with the actual value and no correction is needed. At this time, a1 = f1(Δp) = 0, and the sliding pressure rate is dominated by the preset sliding pressure descent rate a3. 0 < Δp ≤ 2 indicates that the actual value of the main steam pressure is too small. At this time, the first rate correction coefficient a1 increases linearly according to 1.1Δp - 0.7. 2 < Δp ≤ 3 indicates that the deviation of the main steam pressure Δp increases, and the correction coefficient is adjusted at an accelerated pace. Δp > 3 indicates that the deviation of the main steam pressure Δp is too large, and the correction coefficient reaches its upper limit.

[0058] Regarding the second rate correction coefficient a2: The turbine total flow command *flu* characterizes the deviation between the preset sliding pressure drop rate a3 and the turbine's required flow capacity. Essentially, *flu* directly reflects the dynamic adjustment effect of the turbine control valve opening on the steam flow. If the turbine total flow command *flu* is too small, on the one hand, it will lead to an excessively low opening of the turbine's high-pressure control valve group, causing excessive exhaust temperature or insufficient steam pressure in the feedwater pump. The throttled steam flow into the turbine will not meet the minimum cooling flow required by the turbine cylinder, resulting in excessive cylinder exhaust temperature. On the other hand, it will lead to a reduced opening of the intermediate-pressure control valve group, which will also cause a decrease in the extraction steam pressure of the turbine's intermediate and low-pressure cylinders, further leading to insufficient steam pressure in the feedwater pump and turbine, reducing the output and sensitivity of the feedwater flow regulation.

[0059] Therefore, it is necessary to correct the current preset sliding pressure decrease rate a3 in combination with the total steam turbine flow command flu, so that the sliding pressure control better fits the actual working conditions, ensure that the steam flow meets the demand, and avoid the exhaust steam temperature exceeding the limit caused by the low opening of the high-pressure control valve and the decrease of the steam source pressure of the feed water pump caused by the insufficient opening of the intermediate-pressure control valve.

[0060] In actual use, the total steam turbine flow command flu is mapped into the second rate correction coefficient a2 through the second rate correction function a2 = f2(flu'), which is used to correct the preset sliding pressure decrease rate a3. a2 = f2(flu') is a piecewise function. In a possible embodiment,

[0061] Taking a certain 1000MW unit with double reheat as an example, the relationship between the total steam turbine flow command flu and the second rate correction coefficient a2 is shown in Table 3:

[0062] Table 3 Comparison table of the preset sliding pressure decrease rate, the total steam turbine flow command and the second rate correction coefficient

[0063]

[0064] When flu = 0, it means that the ultra-high pressure control valve, the high-pressure control valve, and the intermediate-pressure control valve are all closed, cutting off the steam inlet. The second rate correction coefficient a2 takes the maximum value, a2 = 5.0, and the preset sliding pressure decrease rate a3 is forced to accelerate to protect the steam turbine. When 0 < flu ≤ 70%, it means that the opening of the steam turbine control valve is too small, and there is a risk of the exhaust steam temperature exceeding the limit. It is necessary to increase the opening of the steam turbine control valve, and the value of the second rate correction coefficient a2 is greater than 1. When flu > 70%, it means that the flow command is sufficient and no correction is required, a2 = 0, and the sliding pressure rate is dominated by the preset sliding pressure decrease rate a3.

[0065] Regarding the preset sliding pressure decrease rate a3: The preset sliding pressure decrease rate a3 is set according to different types of RB. It should be noted that different types of RB include primary fan RB, forced draft fan RB, induced draft fan RB, feed water pump RB, coal mill RB, and air preheater RB. In a possible embodiment, taking a 1000MW unit as an example, when it is primary fan RB, the preset sliding pressure decrease rate a3 = 1.8 MPa / min; when it is forced draft fan RB, the preset sliding pressure decrease rate a3 = 1.5 MPa / min; when it is induced draft fan RB, the preset sliding pressure decrease rate a3 = 1.2 MPa / min; when it is feed water pump RB, the preset sliding pressure decrease rate a3 = 2.5 MPa / min; when it is coal mill RB, the preset sliding pressure decrease rate a3 = 3.0 MPa / min; when it is air preheater RB, the preset sliding pressure decrease rate a3 = 1.0 MPa / min.

[0066] The target descent rate a of the sliding pressure is calculated based on the second rate correction coefficient a1, the second rate correction coefficient a2, and the preset sliding pressure descent rate a3, where a = a3 + a1 × a2. Through dynamic correction, the target descent rate a of the sliding pressure is adapted to actual working conditions, avoiding parameter fluctuations.

[0067] Compared to using only the turbine total flow command `flu` for correction, adding correction via the main steam pressure deviation `Δp` can more accurately identify insufficient heat storage release or excessive pressure reduction. This dual-parameter collaborative control achieves synchronous response between boiler-side thermal inertia and turbine-side flow restriction, avoiding the one-sidedness of single-parameter control. It prevents pressure runaway caused by delayed boiler heat storage release and avoids the risk of overheating caused by insufficient turbine flow, significantly improving the control accuracy and safety of the RB process.

[0068] Step 4: Calculate the descent rate a of the sliding pressure target command after rate limiting. limited ; Sliding target command descent rate a limited This information is transmitted to the turbine and boiler to dynamically adjust the main steam pressure setpoint. During the RB control process of a thermal power unit, the sliding pressure target command descent rate 'a' after setting a rate limit is... limited The core significance lies in balancing control response speed and equipment safety. By limiting the rate of change of the sliding pressure target command descent rate 'a', the system can avoid violent valve actions caused by sudden command changes, thereby protecting turbine valves and actuators from mechanical shock, while also preventing thermal stress damage to the boiler drum and pipelines caused by a sudden drop in main steam pressure.

[0069] In one possible embodiment, Where a t-k R represents the initial descent rate in the k-th control cycle. max The maximum allowable rate of change is represented by Δt, which represents the control period, and a is the control period. min a represents the minimum rate of descent. max This represents the maximum rate of descent. Where a... min It is usually set to 0, a max It is usually set to 6 to 10.

[0070] If step three calculates a = 3.0 MPa / min, and the actual pressure drop rate a t =1.0MPa / min. A sudden change in the sliding pressure command from 1.0MPa / min to 3.0MPa / min could cause the turbine regulating valve to open fully instantaneously, resulting in a surge in steam flow and potentially threatening unit safety. Therefore, the maximum permissible rate of change R... max The constraint makes the actual pressure decrease rate a t With the maximum permissible rate of change R maxA smooth transition to a ensures that the pressure change naturally matches the rate of decrease in boiler heat load, thus protecting equipment lifespan and maintaining the stability of the control process.

[0071] Step 5: Determine if the exit conditions are met. If yes, proceed to Step 6; otherwise, return to Step 2. Exit conditions include:

[0072] Exit condition 1: Main steam pressure fluctuation < ±0.3MPa for duration t1;

[0073] Exit condition 2: Load fluctuation < ±2% of rated value for duration t2;

[0074] Exit condition 3: Main steam temperature fluctuation < ±5℃ for duration t3;

[0075] Exit condition 4: the duration of the balance between feedwater flow rate and steam flow rate is t4.

[0076] If exit conditions 1-4 are met simultaneously, proceed to step six and exit RB mode. If any exit condition fluctuation exceeds the limit, the timers for other exit conditions are reset to zero, and the process returns to step two.

[0077] In one possible embodiment, t1 = t2 = t3 = t4 = 30s.

[0078] Taking the primary air turbine RB test as an example, the parameters set before the test are as follows: the target load after the primary air turbine RB is 450MW, the load reduction rate is 2000MW / min, and the preset sliding pressure reduction rate a3 is 1.8MPa / min.

[0079] Before the test, the unit's operating parameters were as follows: Control mode: coordinated mode; Unit load: 912.4MW; Main steam pressure: 30.28MPa; Primary air pressure: 10.15kPa; Furnace negative pressure: -180.5Pa; Coal feed rate: 339.8t / h; Operating coal mills: A, B, C, D, and E coal mills.

[0080] The operator manually stopped the primary air fan on side B, triggering the RB action. The coordination screen displayed "Primary Air Fan RB," and the unit's operating mode switched from coordinated automatic to TF mode. After the RB action, the unit rapidly reduced the load, with a target load value of 450MW. The boiler main control rapidly reduced the air, coal, and water flow to control the boiler load according to the RB target load and rate. During the test, the actual rate of change of the main steam pressure was α. tThe steam pressure ranges from 1.79 to 2.28 MPa / min, with the maximum main steam pressure deviation Δp being 1.55 MPa, corresponding to a first rate correction coefficient a1 = 0.605. The turbine's total flow command, flu, drops to its lowest value of 61.05%. At this point, the ultra-high pressure regulating valve group opening is 21.91%, the high pressure regulating valve group opening is 34.63%, and the intermediate pressure regulating valve group opening is 34.30%, corresponding to a second rate correction coefficient a2 = 3.031. The corrected sliding pressure target command descent rate a = 1.8 + 0.605 × 3.031 = 3.634 MPa / min. PI accelerates the pressure reduction by increasing flu. The ultra-high pressure regulating valve group, high pressure regulating valve group, and medium pressure regulating valve group gradually adjust and open according to the flu' output by PI, after cylinder flow calculation and flow curve conversion. The total turbine flow command gradually increases to 73.44% and eventually remains stable, achieving rapid matching between boiler heat load and turbine inlet steam flow, effectively ensuring the stability of main reheat steam temperature. During the test, the highest exhaust temperature of the ultra-high pressure cylinder of the turbine was 416.41℃, the highest exhaust temperature of the high pressure cylinder was 444.70℃, and the lowest inlet steam pressure of the feedwater pump turbine was 0.8 MPa. The unit did not experience any abnormalities such as high cylinder exhaust temperature alarms or tripping, and the feedwater pump turbine steam source was stable, ensuring the quality of feedwater flow regulation.

[0081] Six minutes and 16 seconds after the primary wind turbine RB was triggered, the actual load of the unit dropped to 592.6MW. The parameters of the unit are shown in Table 3. The parameters are basically stable, and the primary wind turbine RB test is over.

[0082] Table 3. Record of main parameters of the unit under RB operating condition for primary air fan

[0083]

[0084] By real-time correction of the sliding pressure target command decrease rate 'a' and the valve opening, the main steam temperature dropped from an initial 597.5℃ to a minimum of 567.2℃ before recovering to 594.1℃, with fluctuations within ±5℃, far below the trip threshold. The main steam pressure decreased from the preset sliding pressure decrease rate of 30.28 MPa to 21.61 MPa, with an actual rate of 1.79–2.28 MPa / min, without severe oscillations, thus avoiding boiler thermal stress damage. The sliding pressure target command decrease rate 'a' is dynamically adjusted and corrected based on the main steam pressure deviation Δp and the turbine total flow command 'flu,' replacing traditional fixed-rate control and reducing the operational burden on operators.

[0085] The above description is merely an embodiment of this application and does not constitute any limitation on this application. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of this application shall still fall within the protection scope of the technical solution of this application.

Claims

1. A method for adaptive control of sliding pressure rate in a RB process of a thermal power unit, characterized in that: Includes the following steps: Step 1: Monitor the status of the thermal power unit and determine whether the conditions for triggering the RB function have been met. If so, proceed to Step 2. Step 2: Calculate the main steam pressure deviation Δ p The main control unit of the steam turbine calculates the main steam pressure deviation Δ p Output the total flow command of the new steam turbine, flu', where the main steam pressure deviation Δ p The difference between the main steam pressure setpoint and the actual main steam pressure is used to obtain the target opening degree of the corresponding turbine regulating valve based on the new turbine total flow command `flu'`; the turbine regulating valve is then driven to the target opening degree. Step three, calculate the sliding pressure target instruction descending rate: the sliding pressure target instruction descending rate a, a=a3+a1×a2, a1 represents the first rate correction coefficient, , a2 represents the second rate correction coefficient, a3 represents the preset sliding pressure descending rate corresponding to the RB type, p a2 represents the second rate correction coefficient, a3 represents the preset sliding pressure descending rate corresponding to the RB type, , a2 represents the second rate correction coefficient, a3 represents the preset sliding pressure descending rate corresponding to the RB type, First rate correction function f 1(·) and the second rate correction function f 2(·) are all piecewise linear functions; ; ; Step 4: Calculate the descent rate a of the sliding pressure target command after rate limiting. limited ; Sliding target command descent rate a limited This information is transmitted to the steam turbine and boiler to dynamically adjust the main steam pressure setpoint; in step four... ,in R represents the initial descent rate in the k-th control cycle. max This represents the maximum permissible rate of change, and Δt represents the control period. Indicates the minimum rate of descent. Indicates the maximum rate of descent; Step 5: Determine if the exit conditions are met. If yes, proceed to Step 6; otherwise, return to Step 2. Step 6: Exit RB mode and switch to normal sliding pressure control.

2. The adaptive control method for sliding pressure rate during the RB process of a thermal power unit according to claim 1, characterized in that: The specific method for "obtaining the target opening degree of the corresponding turbine regulating valve according to the new turbine total flow command 'flu'" in step two is as follows: based on the new turbine total flow command 'flu', look up the opening degree-flow curve of the turbine regulating valve to obtain the target opening degree of the corresponding turbine regulating valve.

3. The adaptive control method for sliding pressure rate during the RB process of a thermal power unit according to claim 2, characterized in that: The opening-flow curves of the turbine regulating valves include those of the ultra-high pressure regulating valve, the high pressure regulating valve, and the intermediate pressure regulating valve. The turbine regulating valves include ultra-high pressure regulating valves, high pressure regulating valves, and intermediate pressure regulating valves. The total flow command of the new turbine, flu', is converted into the opening command of the ultra-high pressure regulating valve through the opening-flow curve of the ultra-high pressure regulating valve, into the opening command of the high pressure regulating valve through the opening-flow curve of the high pressure regulating valve, and into the opening command of the intermediate pressure regulating valve through the opening-flow curve of the intermediate pressure regulating valve.

4. The adaptive control method for sliding pressure rate during the RB process of a thermal power unit according to claim 1, characterized in that: The exit conditions in step five include: Exit condition 1: Main steam pressure fluctuation < ±0.3MPa for duration t1; Exit condition 2: Load fluctuation < ±2% of rated value for duration t2; Exit condition 3: Main steam temperature fluctuation < ±5℃ for duration t3; Exit condition 4: the duration of the balance between feedwater flow rate and steam flow rate is t4. If any exit condition fluctuation exceeds the limit, the timer for other exit conditions is reset to zero, and the process returns to step two.

5. The adaptive control method for sliding pressure rate during the RB process of a thermal power unit according to claim 1, characterized in that: In step three, the RB types include primary air fan RB, forced draft fan RB, induced draft fan RB, feedwater pump RB, coal mill RB, and air preheater RB.

6. The adaptive control method for sliding pressure rate during the RB process of a thermal power unit according to claim 1, characterized in that: The main control of the steam turbine in step two is a PI controller, with proportional gain Kp = 1.4 and integral time constant Ki = 40 s -1 , and the rated main steam pressure reference value is 310 bar.

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