A method for load reduction control due to auxiliary machine failure with variable voltage reduction rate

Abstract

The present invention provides a method for controlling load shedding in response to an auxiliary engine failure with a variable depressurization rate. The method dynamically corrects a depressurization rate baseline setting based on the difference between the main steam temperature upper limit setting and the main steam temperature, the difference between the main steam temperature and the main steam temperature lower limit setting, and the difference between the feedwater flow rate and the feedwater flow rate lower limit setting. The depressurization rate is then limited using the depressurization rate upper and lower limit settings, and the corrected depressurization rate is output for use by the control system. During the auxiliary engine failure load shedding (RB) process, a control logic design with a variable depressurization rate can actively guide changes in the main steam temperature and feedwater flow rate, maintaining them within appropriate ranges and improving the RB success rate.

Description

Technical Field

[0001] The present invention relates to the field of thermal control of thermal power plants, in particular to a load reduction (RB) control method for auxiliary machine failure with variable pressure reduction rate. Background Art

[0002] Coal-fired power plant units often have two or more critical auxiliary units operating in parallel, sharing the load. For example, a 660MW unit is equipped with two forced draft fans, two induced draft fans, two primary fans, six coal mills, and two feedwater pumps. During normal operation, if a single auxiliary unit fails, the unit load cannot be maintained. The control system must quickly reduce the unit load to the level that the remaining auxiliary units can provide. This process is called run back (RB).

[0003] After a RB event occurs, the unit control mode switches to TF (Turbine Follow) mode. At this point, the turbine high-pressure regulating valve will track the main steam pressure setpoint, which is reduced from the current pressure to the target load at a fixed pressure reduction rate. During a short RB event, characterized by significant fluctuations in unit parameters, the pressure reduction rate is a critical control parameter. Its value directly affects the closing speed of the high-pressure regulating valve, which in turn influences the main steam temperature and feedwater flow rate. In conventional RB control logic design, the pressure reduction rate is a fixed value, and the high-pressure regulating valve closes according to a fixed pressure reduction curve. During this process, the main steam temperature and feedwater flow rate fluctuate, but these changes cannot be reflected back to the high-pressure regulating valve. Rapidly changing main steam temperature or feedwater flow that exceeds the limit is often a significant factor in unit tripping and RB failure. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides an auxiliary machine fault load reduction (RB) control method with a variable pressure reduction rate, which can dynamically change the closing speed of the high-pressure regulating valve according to the changing trends of the main steam temperature and feed water flow after the corrected pressure reduction rate, actively maintain the main steam temperature and feed water flow within an appropriate range, and improve the RB success rate.

[0005] A method for controlling load reduction due to auxiliary machine failure with variable pressure reduction rate, the method using a temperature upper limit difference calculation module, a temperature upper limit influence factor calculation module, a temperature lower limit difference calculation module, a temperature lower limit influence factor calculation module, a flow lower limit difference calculation module, a flow lower limit influence factor calculation module, a pressure reduction rate correction module, a small selection module, and a large selection module; the method includes:

[0006] The main steam temperature and the main steam temperature upper limit setting input temperature upper limit difference calculation module, the temperature upper limit difference calculation module is connected to the temperature upper limit influence factor calculation module, and the temperature upper limit influence factor calculation module is connected to the pressure reduction rate correction module;

[0007] The main steam temperature and the main steam temperature lower limit setting input temperature lower limit difference calculation module, the temperature lower limit difference calculation module is connected to the temperature lower limit influence factor calculation module, and the temperature lower limit influence factor calculation module is connected to the pressure reduction rate correction module;

[0008] The water supply flow rate and the water supply flow lower limit setting input flow lower limit difference calculation module, the flow lower limit difference calculation module is connected to the flow lower limit influence factor calculation module, and the flow lower limit influence factor calculation module is connected to the pressure reduction rate correction module;

[0009] The voltage reduction rate reference setting is input into the voltage reduction rate correction module;

[0010] The voltage reduction rate correction module and the voltage reduction rate upper limit setting are connected to the small selection module, the small selection module and the voltage reduction rate lower limit setting are connected to the large selection module, and the large selection module outputs the corrected voltage reduction rate.

[0011] Furthermore, the temperature upper limit difference calculation module outputs the difference between the main steam temperature upper limit setting and the main steam temperature, the temperature upper limit influence factor calculation module calculates the difference between the main steam temperature upper limit setting and the main steam temperature to obtain the temperature upper limit influence factor, the temperature lower limit difference calculation module outputs the difference between the main steam temperature and the main steam temperature lower limit setting, the temperature lower limit influence factor calculation module calculates the difference between the main steam temperature and the main steam temperature lower limit setting to obtain the temperature lower limit influence factor, the flow lower limit difference calculation module outputs the difference between the feed water flow and the feed water flow lower limit setting, the flow The quantity lower limit influence factor calculation module calculates the difference between the water supply flow rate and the water supply flow lower limit setting to obtain the flow lower limit influence factor. The pressure reduction rate correction module performs algebraic and operation on the temperature upper limit influence factor, the temperature lower limit influence factor, the flow lower limit influence factor and the pressure reduction rate reference setting. The small selection module performs a small selection calculation on the output of the pressure reduction rate correction module and the pressure reduction rate upper limit setting, selects the minimum value between the two and outputs it. The large selection module performs a large selection calculation on the output of the small selection module and the pressure reduction rate lower limit setting, selects the maximum value between the two and outputs it, and obtains the corrected pressure reduction rate.

[0012] Furthermore, the temperature upper limit influence factor calculation module calculates the difference between the main steam temperature upper limit setting and the main steam temperature to obtain the temperature upper limit influence factor, specifically including: firstly judging the action zone of the temperature upper limit difference; when the temperature upper limit difference is greater than or equal to a certain threshold, it does not enter the action zone; when the temperature upper limit difference is less than a certain threshold, it enters the action zone; the temperature upper limit difference entering the action zone is fitted using the 1 / (exp(x)-1) curve to obtain the temperature upper limit influence factor.

[0013] Furthermore, the temperature lower limit influence factor calculation module calculates the difference between the main steam temperature and the main steam temperature lower limit setting to obtain the temperature lower limit influence factor, specifically including: firstly judging the action zone of the temperature lower limit difference; when the temperature lower limit difference is greater than or equal to a certain threshold, it does not enter the action zone; when the temperature lower limit difference is less than a certain threshold, it enters the action zone; the temperature lower limit difference entering the action zone is fitted using the 1 / (exp(x)-1) curve to obtain the temperature lower limit influence factor.

[0014] Furthermore, the flow lower limit influence factor calculation module calculates the difference between the water supply flow and the water supply flow lower limit setting to obtain the flow lower limit influence factor, specifically including: firstly judging the action zone of the flow lower limit difference; when the flow lower limit difference is greater than or equal to a certain threshold, it does not enter the action zone; when the flow lower limit difference is less than a certain threshold, it enters the action zone; the flow lower limit difference entering the action zone is fitted using the 1 / (exp(x)-1) curve to obtain the flow lower limit influence factor.

[0015] Furthermore, when the depressurization rate correction module performs algebraic and operation on the temperature upper limit influence factor, the temperature lower limit influence factor, the flow lower limit influence factor and the depressurization rate reference setting, the action directions of the temperature upper limit influence factor, the temperature lower limit influence factor and the flow lower limit influence factor are "+", "-" and "+" respectively.

[0016] Furthermore, the upper limit setting of the main steam temperature is the maximum value that the main steam temperature is allowed to reach when the unit is operating normally, and the lower limit setting of the main steam temperature is the minimum value that the main steam temperature is allowed to reach when the unit is operating normally; the lower limit setting of the feed water flow is the minimum value that the feed water flow is allowed to reach when the unit is operating normally.

[0017] The present invention fully considers the influence of the changes of main steam temperature and feed water flow during the RB process on the RB process, that is, the difference between the main steam temperature upper limit setting and the main steam temperature, the difference between the main steam temperature and the main steam temperature lower limit setting, and the difference between the feed water flow and the feed water flow lower limit setting are used to perform dynamic and nonlinear correction on the pressure reduction rate reference setting. The corrected pressure reduction rate will dynamically change the closing speed of the high-pressure regulating valve according to the changing trends of the main steam temperature and feed water flow, actively maintain the main steam temperature and feed water flow within an appropriate range, and improve the RB success rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the control logic design of auxiliary machine failure load reduction (RB) with variable voltage reduction rate of the present invention;

[0019] Figure 2 It is a graph of 1 / (exp(x)-1);

[0020] Figure 3 Schematic diagram of main steam temperature and corrected pressure reduction rate according to an embodiment of the present invention.

[0021] In the figure: 1—main steam temperature, 2—main steam temperature upper limit setting, 3—temperature upper limit difference calculation module, 4—temperature upper limit influencing factor calculation module, 5—main steam temperature lower limit setting, 6—temperature lower limit difference calculation module, 7—temperature lower limit influencing factor calculation module, 8—feed water flow, 9—feed water flow lower limit setting, 10—flow lower limit difference calculation module, 11—flow lower limit influencing factor calculation module, 12—pressure reduction rate benchmark setting, 13—pressure reduction rate correction module, 14—pressure reduction rate upper limit setting, 15—small selection module, 16—pressure reduction rate lower limit setting, 17—large selection module, 18—corrected pressure reduction rate. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention.

[0023] Figure 1 The figure shows a schematic diagram of the control logic design for auxiliary machine fault load reduction (RB) with variable pressure reduction rate. The logic design includes main steam temperature 1, main steam temperature upper limit setting 2, temperature upper limit difference calculation module 3, temperature upper limit influence factor calculation module 4, main steam temperature lower limit setting 5, temperature lower limit difference calculation module 6, temperature lower limit influence factor calculation module 7, feed water flow 8, feed water flow lower limit setting 9, flow lower limit difference calculation module 10, flow lower limit influence factor calculation module 11, pressure reduction rate reference setting 12, pressure reduction rate correction module 13, pressure reduction rate upper limit setting 14, small selection module 15, pressure reduction rate lower limit setting 16, large selection module 17, and corrected pressure reduction rate 18.

[0024] The main steam temperature 1 and the main steam temperature upper limit setting 2 are input into the temperature upper limit difference calculation module 3, the temperature upper limit difference calculation module 3 is connected to the temperature upper limit influence factor calculation module 4, and the temperature upper limit influence factor calculation module 4 is connected to the pressure reduction rate correction module 13;

[0025] The main steam temperature 1 and the main steam temperature lower limit setting 5 are input into the temperature lower limit difference calculation module 6, the temperature lower limit difference calculation module 6 is connected to the temperature lower limit influence factor calculation module 7, and the temperature lower limit influence factor calculation module 7 is connected to the pressure reduction rate correction module 13;

[0026] The water supply flow rate 8 and the water supply flow rate lower limit setting 9 are input into the flow rate lower limit difference calculation module 10, the flow rate lower limit difference calculation module 10 is connected to the flow rate lower limit influence factor calculation module 11, and the flow rate lower limit influence factor calculation module 11 is connected to the pressure reduction rate correction module 13;

[0027] The depressurization rate reference setting 12 is connected to the depressurization rate correction module 13;

[0028] The depressurization rate correction module 13 and the depressurization rate upper limit setting 14 are input to the small selection module 15, and the small selection module 15 and the depressurization rate lower limit setting 16 are input to the large selection module 17. The large selection module 17 processes the data and outputs the corrected depressurization rate 18.

[0029] Main steam temperature upper limit setting 2 is the maximum value allowed for main steam temperature 1 during normal unit operation. Main steam temperature 1 exceeding main steam temperature upper limit setting 2 will endanger safe unit operation. Temperature upper limit difference calculation module 3 calculates the difference between main steam temperature upper limit setting 2 and main steam temperature 1 to obtain the temperature upper limit difference. This value reflects the risk of main steam temperature 1 being too high. The smaller the temperature upper limit difference, the greater the risk of main steam temperature 1 being too high. Temperature upper limit impact factor calculation module 4 calculates the temperature upper limit difference and outputs the temperature upper limit impact factor. Temperature upper limit impact factor calculation module 4 first determines the action zone for the temperature upper limit difference. If the temperature upper limit difference is greater than or equal to a certain threshold, the temperature upper limit impact factor is not calculated and the output is 0. If the temperature upper limit difference is less than the threshold, a 1 / (exp(x)-1) curve fit is performed on the temperature upper limit difference to obtain the temperature upper limit impact factor. The purpose of the action zone judgment is to ensure that the pressure reduction rate is changed only when the main steam temperature 1 is close to the main steam temperature upper limit setting 2, so as to avoid the high pressure regulating valve from fluctuating back and forth when the main steam temperature 1 changes within the acceptable range. The 1 / (exp(x)-1) curve is as follows Figure 2 As shown, when the temperature upper limit difference is closer to 0, the output temperature upper limit influence factor is steeper, and a quick response is made to the abnormal situation that the main steam temperature 1 is close to the main steam temperature upper limit setting 2.

[0030] The main steam temperature lower limit setting 5 is the lowest value allowed for the main steam temperature 1 during normal unit operation. A main steam temperature 1 lower than the main steam temperature lower limit setting 5 will endanger the safe operation of the unit. The temperature lower limit difference calculation module 6 calculates the difference between the main steam temperature 1 and the main steam temperature lower limit setting 5 to obtain the temperature lower limit difference. Its value reflects the risk of the main steam temperature 1 being too low. That is, the smaller the temperature lower limit difference, the greater the risk of the main steam temperature 1 being too low. The temperature lower limit impact factor calculation module 7 calculates the temperature lower limit difference and outputs the temperature lower limit impact factor. The temperature lower limit impact factor calculation module 7 first determines the action zone of the temperature lower limit difference. That is, when the temperature lower limit difference is greater than or equal to a certain threshold, it is not calculated and the temperature lower limit impact factor is output as 0. When the temperature lower limit difference is less than a certain threshold, the temperature lower limit difference is subjected to 1 / (exp(x)-1) curve fitting to obtain the temperature lower limit impact factor. The purpose of the action zone judgment is to ensure that the pressure reduction rate is changed only when the main steam temperature 1 is close to the lower limit setting 5 of the main steam temperature, so as to avoid the high pressure regulating valve from fluctuating back and forth when the main steam temperature 1 changes within the acceptable range. The 1 / (exp(x)-1) curve is as follows Figure 2 As shown, when the lower limit temperature difference is closer to 0, the output lower limit temperature impact factor is steeper, and a quick response is made to the abnormal situation that the main steam temperature 1 is close to the main steam temperature lower limit setting 5.

[0031] The feedwater flow lower limit setting 9 is the minimum value of the feedwater flow 8 allowed during normal operation of the unit. A feedwater flow 8 below the feedwater flow lower limit setting 9 will endanger the unit's safe operation. The flow lower limit difference calculation module 10 calculates the difference between the feedwater flow 8 and the feedwater flow lower limit setting 9 to obtain the flow lower limit difference. This value reflects the risk of the feedwater flow 8 being too low: the smaller the flow lower limit difference, the greater the risk of the feedwater flow 8 being too low. The flow lower limit impact factor calculation module 11 calculates the flow lower limit difference and outputs the flow lower limit impact factor. The flow lower limit impact factor calculation module 11 first determines the action zone of the flow lower limit difference. When the flow lower limit difference is greater than or equal to a certain threshold, it is not calculated and the flow lower limit impact factor is output as 0. When the flow lower limit difference is less than the threshold, a 1 / (exp(x)-1) curve fit is performed on the flow lower limit difference to obtain the flow lower limit impact factor. The purpose of the action zone judgment is to ensure that the pressure reduction rate is changed only when the feed water flow rate 8 is close to the feed water flow lower limit setting 9, so as to avoid the high pressure regulating valve from fluctuating back and forth when the feed water flow rate 8 changes within the acceptable range. Figure 2 As shown, when the flow lower limit difference is closer to 0, the output flow lower limit impact factor is steeper, and a quick response is made to the abnormal situation that the water supply flow 8 is close to the water supply flow lower limit setting 9.

[0032] The depressurization rate correction module 13 performs an algebraic sum calculation on the temperature upper limit influencing factor, the temperature lower limit influencing factor, the flow lower limit influencing factor, and the depressurization rate reference setting 12. During the RB process, if the main steam temperature 1 approaches the main steam temperature upper limit setting 2, increasing the depressurization rate can increase the high-pressure regulating valve opening, allowing more steam to flow through the heat exchanger, thereby reducing the main steam temperature 1. Therefore, the direction of the temperature upper limit influencing factor is "+". If the main steam temperature 1 approaches the main steam temperature lower limit setting 5, reducing the depressurization rate can reduce the high-pressure regulating valve opening, allowing less steam to flow through the heat exchanger, thereby increasing the main steam temperature 1. Therefore, the direction of the temperature lower limit influencing factor is "-". If the feedwater flow rate 8 approaches the feedwater flow rate lower limit setting 9, increasing the depressurization rate can increase the high-pressure regulating valve opening, reduce the steam-water system pressure, reduce the difficulty of the feedwater pump filling water, and increase the feedwater flow rate 8. Therefore, the effect of the feedwater flow rate lower limit influencing factor is "+".

[0033] After the depressurization rate correction module 13 is used to correct the depressurization rate reference setting 12, the output of the depressurization rate correction module 13 may deviate too much from the depressurization rate reference setting 12, thereby endangering the safety of the unit. Therefore, it must be limited to between the depressurization rate lower limit setting 16 and the depressurization rate upper limit setting 14. The small selection module 15 is used to perform a small selection calculation on the output of the depressurization rate correction module 13 and the depressurization rate upper limit setting 14, that is, to select the minimum value between the two and output it. The output of the small selection module 15 will not exceed the depressurization rate upper limit setting 14. The large selection module 17 is then used to perform a large selection calculation on the output of the small selection module and the depressurization rate lower limit setting 16, that is, to select the maximum value between the two and output it. The output of the large selection module 17 will not fall below the depressurization rate lower limit setting 16. Therefore, after correction, the depressurization rate 18 will always remain between the depressurization rate lower limit setting 16 and the depressurization rate upper limit setting 14.

[0034] After the control system uses the corrected pressure reduction rate 18, the main steam pressure setting value will not be a fixed straight line, but will be dynamically affected by the changes in the main steam temperature and feed water flow. Therefore, during the RB process, the high-pressure regulating valve will be able to dynamically adjust the closing speed according to the changing trends of the main steam temperature and feed water flow, preventing the main steam temperature and feed water flow from exceeding the limit and improving the RB success rate.

[0035] Using the auxiliary machine fault load reduction (RB) control method with variable depressurization rate of the present invention, taking the temperature lower limit influence factor calculation module as an example, the main steam temperature curve of the RB process of the coal mill of a 660MW coal-fired unit is calculated. During the calculation process, the depressurization rate base setting is set to 1.0MPa / min, the depressurization rate upper limit setting is set to 1.3MPa / min, the depressurization rate lower limit setting is set to 0.7MPa / min, the main steam temperature lower limit setting is set to 560℃, and the action zone judgment threshold of the temperature lower limit influence factor calculation module is set to 18℃. The final calculated corrected depressurization rate is as follows: Figure 3 shown. Figure 3 It shows that after the coal mill RB occurs, the main steam temperature gradually decreases from 590℃ to 569℃, approaching the lower limit setting of the main steam temperature. In the interval where the main steam temperature is greater than or equal to 578℃, the difference between the main steam temperature and the lower limit setting of the main steam temperature is greater than or equal to 18℃, and it has not yet entered the action zone. The lower limit influence factor of the temperature is 0, and the corrected pressure reduction rate is equal to the pressure reduction rate benchmark setting, that is, 1.0MPa / min. In the interval where the main steam temperature is less than 578℃, the difference between the main steam temperature and the lower limit setting of the main steam temperature is less than 18℃, entering the action zone, and starting to calculate the lower limit influence factor of the temperature by fitting the 1 / (exp(x)-1) curve. The corrected pressure reduction rate corrected by the lower limit influence factor of the temperature gradually decreases and eventually reaches the lower limit value of 0.7MPa / min. It can be seen that Figure 1 The calculation model can respond to abnormal low main steam temperature conditions during the RB process by adjusting the pressure reduction rate downward, thereby suppressing further drops in main steam temperature. The calculation principles and processes of upper temperature limit influence factor calculation module 4 and lower flow rate limit influence factor calculation module 11 are similar to those of lower temperature limit influence factor calculation module 6, and similar conclusions can be drawn.

[0036] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by technicians in this technical field within the technical scope disclosed in the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for controlling load reduction due to auxiliary machine failure with variable voltage reduction rate, characterized by: The method uses a temperature upper limit difference calculation module (3), a temperature upper limit influence factor calculation module (4), a temperature lower limit difference calculation module (6), a temperature lower limit influence factor calculation module (7), a flow lower limit difference calculation module (10), a flow lower limit influence factor calculation module (11), a pressure reduction rate correction module (13), a small selection module (15), and a large selection module (17); the method includes: The main steam temperature (1) and the main steam temperature upper limit setting (2) are input into the temperature upper limit difference calculation module (3), the temperature upper limit difference calculation module (3) is connected to the temperature upper limit influence factor calculation module (4), and the temperature upper limit influence factor calculation module (4) is connected to the pressure reduction rate correction module (13); The main steam temperature (1) and the main steam temperature lower limit setting (5) are input into a temperature lower limit difference calculation module (6), the temperature lower limit difference calculation module (6) is connected to a temperature lower limit influence factor calculation module (7), and the temperature lower limit influence factor calculation module (7) is connected to a pressure reduction rate correction module (13); The water supply flow rate (8) and the water supply flow rate lower limit setting (9) are input into the flow rate lower limit difference calculation module (10), the flow rate lower limit difference calculation module (10) is connected to the flow rate lower limit influence factor calculation module (11), and the flow rate lower limit influence factor calculation module (11) is connected to the pressure reduction rate correction module (13); The depressurization rate reference setting (12) is input into the depressurization rate correction module (13); The depressurization rate correction module (13) and the depressurization rate upper limit setting (14) are connected to the small selection module (15), the small selection module (15) and the depressurization rate lower limit setting (16) are connected to the large selection module (17), and the large selection module (17) outputs the corrected depressurization rate (18).

2. The auxiliary machine fault load reduction control method with variable voltage reduction rate according to claim 1, characterized in that: The temperature upper limit difference calculation module (3) outputs the difference between the main steam temperature upper limit setting and the main steam temperature. The temperature upper limit influence factor calculation module (4) calculates the difference between the main steam temperature upper limit setting and the main steam temperature to obtain the temperature upper limit influence factor. The temperature lower limit difference calculation module (6) outputs the difference between the main steam temperature and the main steam temperature lower limit setting. The temperature lower limit influence factor calculation module (7) calculates the difference between the main steam temperature and the main steam temperature lower limit setting to obtain the temperature lower limit influence factor. The flow lower limit difference calculation module (10) outputs the difference between the feed water flow and the feed water flow lower limit setting. The flow lower limit influence factor calculation module (11 ) calculates the difference between the water supply flow rate and the water supply flow rate lower limit setting to obtain the flow rate lower limit influence factor, the pressure reduction rate correction module (13) performs algebraic sum operation on the temperature upper limit influence factor, the temperature lower limit influence factor, the flow rate lower limit influence factor and the pressure reduction rate reference setting (12), the small selection module (15) performs a small selection calculation on the output of the pressure reduction rate correction module (13) and the pressure reduction rate upper limit setting (14), selects the minimum value between the two and outputs it, the large selection module (17) performs a large selection calculation on the output of the small selection module (15) and the pressure reduction rate lower limit setting (16), selects the maximum value between the two and outputs it, and obtains the corrected pressure reduction rate (18).

3. The auxiliary machine fault load reduction control method with variable voltage reduction rate according to claim 2, characterized in that: The temperature upper limit influence factor calculation module calculates the difference between the main steam temperature upper limit setting and the main steam temperature to obtain the temperature upper limit influence factor, specifically including: firstly, judging the action zone of the temperature upper limit difference; when the temperature upper limit difference is greater than or equal to a certain threshold, it does not enter the action zone; when the temperature upper limit difference is less than a certain threshold, it enters the action zone; the temperature upper limit difference entering the action zone is fitted using a 1 / (exp(x)-1) curve to obtain the temperature upper limit influence factor.

4. The auxiliary machine fault load reduction control method with variable voltage reduction rate according to claim 2, characterized in that: The temperature lower limit influence factor calculation module calculates the difference between the main steam temperature and the main steam temperature lower limit setting to obtain the temperature lower limit influence factor, specifically including: firstly, judging the action zone of the temperature lower limit difference; when the temperature lower limit difference is greater than or equal to a certain threshold, the action zone is not entered; when the temperature lower limit difference is less than a certain threshold, the action zone is entered; the temperature lower limit difference entering the action zone is fitted using a 1 / (exp(x)-1) curve to obtain the temperature lower limit influence factor.

5. The auxiliary machine fault load reduction control method with variable voltage reduction rate according to claim 2, characterized in that: The flow lower limit influence factor calculation module calculates the difference between the water supply flow and the water supply flow lower limit setting to obtain the flow lower limit influence factor, specifically including: firstly judging the action zone of the flow lower limit difference; when the flow lower limit difference is greater than or equal to a certain threshold, it does not enter the action zone; when the flow lower limit difference is less than a certain threshold, it enters the action zone; the flow lower limit difference entering the action zone is fitted using the 1 / (exp(x)-1) curve to obtain the flow lower limit influence factor.

6. The auxiliary machine fault load reduction control method with variable voltage reduction rate according to claim 2, characterized in that: When the pressure reduction rate correction module (13) performs an algebraic sum operation on the temperature upper limit influence factor, the temperature lower limit influence factor, the flow rate lower limit influence factor and the pressure reduction rate reference setting (12), the action directions of the temperature upper limit influence factor, the temperature lower limit influence factor and the flow rate lower limit influence factor are "+", "-" and "+", respectively.

7. The auxiliary machine fault load reduction control method with variable voltage reduction rate according to claim 2, characterized in that: The main steam temperature upper limit setting (2) is the maximum value that the main steam temperature (1) is allowed to reach when the unit is operating normally. The main steam temperature lower limit setting (5) is the minimum value that the main steam temperature (1) is allowed to reach when the unit is operating normally. The feed water flow lower limit setting (9) is the minimum value that the feed water flow (8) is allowed to reach when the unit is operating normally.

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