A control method for hydraulic bypass system based on DCS intelligent positioning

Abstract

The present invention discloses a control method for a hydraulic bypass system based on DCS intelligent positioning. The regulating valve positioning system is implemented in DCS software programming, eliminating the need for high-cost hydraulic control servo cards and the need for on-site hardware positioning devices. After comparing the DCS system valve adjustment command with the position feedback, the intelligent control outputs a 4-20mA current signal to the electro-hydraulic proportional valve. A current signal of 4-12mA opens the regulating valve, with 4mA providing the fastest opening rate. A current signal of 12-20mA closes the regulating valve, with 20mA providing the fastest closing rate. 12mA approaches inaction and position retention. To ensure safe and reliable positioning and position retention, each regulating valve system is equipped with a position retention solenoid valve. If the position retention solenoid valve loses power, the corresponding regulating valve remains in place. Only when the position retention solenoid valve is energized and the proportional valve receives a current signal that deviates from 12mA will it open or close at the corresponding rate according to the command value, ensuring that the regulating valve has a better adjustment response rate and positioning accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal automatic control of thermal power generating sets, and in particular relates to a control method for a hydraulic bypass system based on DCS intelligent positioning. Specifically, the pressure regulating valve and the attemperated water regulating valve of the turbine bypass system adopt high-parameter hydraulic power, and the position positioner of the regulating valve is optimized in the DCS software, eliminating the local hardware positioning device. Background Art

[0002] The turbine bypass system is a crucial auxiliary system for large-capacity thermal power generating units, discharging steam that the turbine cannot accommodate under specific operating conditions. During unit startup, it acts as a relief valve to assist with boiler temperature and pressure increase. During rapid load shedding, it also acts as a rapid-acting pressure reducing valve to maintain shutdown without interruption. Therefore, the bypass system valve group, with its reliable and precise positioning and rapid automatic adjustment capabilities, is crucial for the safe and stable operation of the unit.

[0003] A valve positioner is a device mechanically coupled to a valve or actuator that automatically adjusts the pressure output to the actuator to ensure a precisely defined relationship between valve position feedback and the input command signal. For generator sets requiring continuous shutdown without interrupting the flow of the generator, the turbine bypass system requires a large flow capacity, rapid opening and closing capabilities, and precise positioning. The valves are almost always driven by hydraulic high-pressure fire-resistant oil, and positioning control utilizes an electrical hardware solution combining electro-hydraulic servo valves and servo cards. However, electro-hydraulic servo valves have extremely high requirements for hydraulic oil cleanliness and demand stringent manufacturing, processing, and assembly precision for key components, making electro-hydraulic servo systems prohibitively expensive and difficult for power generation companies to adopt. Proportional valves, on the other hand, combine electro-hydraulic control technology using on-off hydraulic and servo elements. Their input is a current signal, and their output is a hydraulic signal. By varying the input current, they can achieve continuous, proportional changes in output flow and pressure. Their control principle is similar to that of servo control valves, but they require less stringent hydraulic oil cleanliness and are significantly less expensive than servo valve-based hydraulic control systems. Therefore, it is very necessary to develop an electro-hydraulic proportional valve group bypass system and its control method with low cost, high reliability, control accuracy and automatic adjustment performance that can meet the needs of power generation production.

[0004] Numerous domestic researchers have studied positioning methods for hydraulic proportional valves, but these applications have primarily been applied to the positioning control of pressurized processing equipment, rotating platforms for wire rod production, hydraulic cylinders for manipulators, and winding carts in the steel industry. No scientific papers or patents have yet identified intelligent positioning control methods for electro-hydraulic proportional valves within DCS software for bypass system valve groups in thermal power plants. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art and to provide a bypass system and its control method with reasonable design, low cost, low requirements on the cleanliness level of hydraulic fire-resistant oil, and intelligent positioning of automatic regulating valve group using DCS software programming.

[0006] The turbine bypass system includes a hydraulic oil station (two hydraulic oil pumps, one in use and one in reserve), a high-pressure bypass pressure regulating valve, a high-pressure bypass water spray cooling regulating valve, a high-pressure bypass water spray cooling stop valve, a low-pressure bypass pressure regulating valve, a low-pressure bypass water spray cooling regulating valve, a low-pressure bypass water spray cooling stop valve and a unit distributed control system DCS. Two of the stop valves use on-off hydraulic components for switch control of full opening or full closing. The four regulating valves use analog control with hydraulic proportional valves, valve position feedback and position-holding solenoid valve hydraulic components. The regulating valve positioning system is implemented in DCS software programming, and there is no local hardware positioning device. The control output of the regulating valve is implemented in the DCS control logic, which is equivalent to the function of a traditional hydraulic servo card. After comparing the DCS valve adjustment instruction with the position feedback, the intelligent control outputs a 4-20mA AO current signal to the electro-hydraulic proportional valve. The current signal is 4-12mA to open the regulating valve, and 4mA has the fastest opening rate. The current signal is 12-20mA to close the regulating valve, and 20mA has the fastest closing rate. 12mA is close to no action to hold the position. In order to ensure the safety and reliability of positioning and holding, each control valve system is equipped with a holding solenoid valve. If the holding solenoid valve loses power, the corresponding control valve will remain in position. Only when the holding solenoid valve is energized and the current signal received by the electro-hydraulic proportional valve deviates from 12mA, the control valve will open or close at the corresponding rate according to the command value.

[0007] The technical solution adopted by the present invention to solve the above-mentioned problem is: a control method of a hydraulic bypass system based on DCS intelligent positioning, characterized by comprising the following steps (the high-pressure bypass valve group is described below, and the low-pressure bypass valve group is described similarly):

[0008] Step 1: Optimize the design of the stop permission conditions of the two backup hydraulic oil pumps to prevent misoperation and ensure the reliable operation of the hydraulic system;

[0009] Step 2: Configure the PID regulator logic of the high-pressure bypass pressure regulating valve, compare the difference between the output command value of the PID regulator and the position feedback value of the pressure regulating valve, and then perform intelligent adjustment and positioning through the variable parameter broken line function F1(X). Configure the PID regulator logic of the high-pressure bypass water spray cooling regulating valve, compare the difference between the output command value of the PID regulator and the position feedback value of the water spray cooling regulating valve, and then perform intelligent adjustment and positioning through the variable parameter broken line function F2(X);

[0010] Step 3: Optimize the design of the energized / de-energized control logic for the holding solenoid valve of the high-pressure bypass pressure regulating valve and the energized / de-energized control logic for the holding solenoid valve of the high-pressure bypass water spray cooling regulating valve;

[0011] Step 4: Optimize the design of the interlock automatic opening / closing control logic of the high-pressure bypass water spray desuperheating stop valve;

[0012] Step 5: After DCS configuration, the bypass system is put into actual operation. Combined with the bypass system steam pressure and water spray cooling regulation characteristics, the adjustment parameters are optimized and set online.

[0013] In the first step, when the boiler is shut down (MFT or BT (circulating fluidized bed boiler)) and the main steam pressure is lower than the set value, or another hydraulic oil pump is running and the oil pressure is normal, the standby hydraulic oil pump is allowed to stop to prevent misoperation and ensure the reliable operation of the hydraulic system. The bypass system can be put into operation normally during the unit startup phase or shutdown without stopping the boiler.

[0014] In the second step, the difference between the output command value of the PID regulator of the control valve and the position feedback value of the control valve is calculated and then intelligently adjusted and positioned through the variable parameter broken line function F(X). The greater the deviation between the command and feedback, the more the output AO command deviates from 12mA, and the smaller the deviation between the command and feedback, the closer the output AO command is to 12mA, which can ensure better adjustment response rate and positioning accuracy of the control valve.

[0015] In the third step, the electro-hydraulic proportional valve and the holding solenoid valve cooperate to perform analog control on the control valve: after the holding solenoid valve is energized, the hydraulic control one-way valve opens, and the hydraulic oil enters the control valve cylinder through the proportional valve. After the control valve reaches the required command position, the holding solenoid valve loses power, locking the oil circuit, and the control valve maintains the current position. The current output by the DCS to the proportional valve is 12mA, realizing dual positioning and holding of the control valve, and improving the reliability of the control valve positioning and the adjustment accuracy.

[0016] In the fourth step, when the instruction of the high-pressure bypass water spray cooling control valve is higher than the set value, the pulse action interlock automatically opens the high-pressure bypass water spray cooling stop valve. When the instruction of the high-pressure bypass water spray cooling control valve is lower than the set value, the pulse action interlock automatically closes the high-pressure bypass water spray cooling stop valve. Using the control valve instruction value instead of quoting the position feedback value can avoid the influence of position feedback signal fluctuations and ensure that the stop valve works more reliably.

[0017] In the fifth step, different adjustment parameters need to be set for the electro-hydraulic proportional valve for different working ranges of the control valve. When the deviation between the control valve command and the position feedback is large, it is necessary to give an AO output drive current that deviates from 12mA. That is, the larger the input values ​​of F1(X) and F2(X), the more the output value deviates from the value of 50, to ensure fast and accurate positioning control of the control valve under full stroke conditions; the interlock opening and closing pulse time of the water spray cooling stop valve should be set to only 1 to 2 controller operation cycles, that is, about 0.5 seconds. If the pulse time parameter is too large, it will affect the correct opening and closing action timing of the water spray cooling stop valve.

[0018] The control valve positioning system of the present invention is implemented in DCS software programming, does not require expensive hydraulic servo cards, and has no on-site hardware positioning device. After the DCS system valve adjustment command is compared with the position feedback, the intelligent control outputs a 4-20mA current signal to the electro-hydraulic proportional valve. The current signal of 4-12mA opens the control valve, and 4mA has the fastest opening rate. The current signal of 12-20mA closes the control valve, and 20mA has the fastest closing rate. 12mA is close to being inactive and maintaining the position. In order to ensure the safety and reliability of positioning and maintaining the position, each control valve system is equipped with a position-maintaining solenoid valve. If the position-maintaining solenoid valve loses power, the corresponding control valve will remain in place and will not move. Only when the position-maintaining solenoid valve is energized and the proportional valve receives a current signal that deviates from 12mA can the control valve be opened or closed at the corresponding rate according to the command value, ensuring that the control valve has a better adjustment response rate and positioning accuracy.

[0019] Compared with the prior art, the present invention has the following advantages and effects:

[0020] 1. The cleanliness requirements of the hydraulic oil in the bypass system are reduced, and the regulating valve does not require an on-site hardware positioning device.

[0021] 2. The unit DCS system software programming is used to replace the high-cost servo cards, which greatly reduces the investment cost.

[0022] 3. Optimizing the DCS intelligent positioning control method and adding a holding solenoid valve improves positioning accuracy and adjustment response rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a structural diagram of the control principle of a regulating valve based on DCS intelligent positioning in an embodiment of the present invention.

[0024] Figure 2 This is a logic diagram of the stop permission conditions for the two hydraulic oil pumps in the bypass system in an embodiment of the present invention.

[0025] Figure 3 This is a PID regulator and positioning control logic diagram of the high-pressure bypass pressure regulating valve in an embodiment of the present invention.

[0026] Figure 4 This is a PID regulator and positioning control logic diagram of the high-pressure bypass water spray desuperheating regulating valve in an embodiment of the present invention.

[0027] Figure 5 This is a control logic diagram of the holding solenoid valve of the high-pressure bypass pressure and water spray temperature reduction regulating valve in an embodiment of the present invention.

[0028] Figure 6 This is a logic diagram of the interlock control of the high-pressure bypass water spraying and temperature reduction stop valve in an embodiment of the present invention.

[0029] Figure 2 middle:

[0030] 21-Logical "OR"; 22-Logical "AND"; 23-Fixed value (lower limit judgment); 24-Fixed value (upper limit judgment);

[0031] Figure 3 middle:

[0032] 31- set value operator; 32- PID regulator; 33- hand operator (control valve instruction human-machine interface operator); 34- subtraction operator; 35- broken line function operator;

[0033] Figure 4 middle:

[0034] 41-PID regulator; 42-hand operator; 43-broken line function operator;

[0035] Figure 5 middle:

[0036] 51-Absolute value; 52-Bad quality judgment function block (when AI inputs bad quality, the output is logic "1"); 53-Adjusting fixed value (high limit judgment); 54-Adjusting dead zone (low limit judgment); 55-RS trigger;

[0037] Figure 6 middle:

[0038] 61-fixed value (high limit judgment); 62-fixed value (low limit judgment); 63-pulser (rising edge trigger pulse); 64-pulser (rising edge trigger pulse). DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and through examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

[0040] Example

[0041] This embodiment discloses a control method for a hydraulic bypass system based on DCS intelligent positioning. The regulating valve positioning control strategy is implemented in the DCS distributed control system software programming of the generator set. There is no regulating valve positioning device on site, and the system does not require expensive hydraulic servo cards.

[0042] Specifically, the control method includes the following steps in sequence:

[0043] Step 1: Optimize and design the stopping conditions of the two mutual backup hydraulic oil pumps;

[0044] When the boiler is shut down (MFT or BT (circulating fluidized bed boiler)) and the main steam pressure is lower than the set value 23, or another hydraulic oil pump is running and the oil pressure is higher than the set value 24 and is working normally, the standby hydraulic oil pump is allowed to stop.

[0045] Step 2: Configure the logic and process value of the PID regulator 32 of the high-pressure bypass pressure regulating valve as the main steam pressure. The output command value of the PID regulator 32 is subjected to a difference operation between the manual operator 33 of the human-machine interface and the position feedback value of the pressure regulating valve through the subtraction operator 34, and then the parameter-variable broken line function is used by the broken line function operator 35 to perform intelligent adjustment and positioning. Configure the logic and process value of the PID regulator 41 of the high-pressure bypass water spray cooling regulating valve as the steam temperature after the water spray cooling regulating valve. The output command value of the PID regulator 41 is subjected to a difference operation between the manual operator 42 of the human-machine interface and the position feedback value of the water spray cooling regulating valve, and then the parameter-variable broken line function is used by the broken line function operator 43 to perform intelligent adjustment and positioning.

[0046] The difference between the command value output by the PID regulator of the control valve and the position feedback value of the control valve is calculated and then intelligently adjusted and positioned by the variable parameter broken line function F(X). The greater the deviation between the command and the feedback, the more the output AO drive current deviates from 12mA, and the smaller the deviation between the command and the feedback, the closer the output AO drive current is to 12mA, that is, the greater the input value of the broken line function operator 35 and the broken line function operator 43, the more the output value deviates from the value 50 (the DCS AO card component has a 0% to 100% command input, corresponding to an output current of 4mA to 12mA), ensuring rapid and accurate positioning control of the control valve under full stroke conditions.

[0047] Step 3: Optimize the design of the energized / de-energized control logic for the holding solenoid valve of the high-pressure bypass pressure regulating valve and the energized / de-energized control logic for the holding solenoid valve of the high-pressure bypass water spray cooling regulating valve;

[0048] When the absolute value 51 of the deviation between the control valve command and the position feedback is greater than the adjustment set value 53, the holding solenoid valve is energized, the hydraulic control one-way valve opens, and the hydraulic oil enters the control valve cylinder through the proportional valve. The control valve can normally follow the PID regulator output or the command value manually input by the operator to open or close the analog value continuously. When the absolute value 51 of the deviation between the control valve command and the position feedback is less than the adjustment dead zone 54, or the position feedback signal is of poor quality, or the high-pressure bypass protection fast closing condition is triggered, the RS trigger is reset, that is, the holding solenoid valve loses power, the oil circuit is locked, the control valve maintains the current position, and the current output by the DCS to the proportional valve is 12mA, realizing the dual control strategy of positioning and holding the control valve, and improving the reliability of the control valve positioning and the adjustment accuracy.

[0049] Step 4: Optimize the design of the interlock automatic opening / closing control logic of the high-pressure bypass water spray cooling stop valve; if the instruction of the high-pressure bypass water spray cooling control valve is higher than the set value 61, the pulse action of the pulser 63 is interlocked to automatically open the high-pressure bypass water spray cooling stop valve; if the instruction of the high-pressure bypass water spray cooling control valve is lower than the set value 62, the pulse action of the pulser 64 is interlocked to automatically close the high-pressure bypass water spray cooling stop valve. Using the control valve instruction value instead of quoting the position feedback value can avoid the influence of fluctuations in the position feedback signal and ensure that the stop valve works more reliably.

[0050] Step 5: After DCS configuration, the bypass system is put into actual operation. Combined with the bypass system steam pressure and water spray cooling regulation characteristics, the adjustment parameters are optimized and set online.

[0051] For different working ranges of the control valve, different adjustment parameters need to be set for the electro-hydraulic proportional valve. When the deviation between the control valve instruction and the position feedback is large, an AO output drive current with a large deviation of 12mA needs to be given, that is, the larger the input value of the broken line function operator 35 and the broken line function operator 43, the more the output value deviates from the value 50. When the valve is closed, the deviation between the control valve instruction and the position feedback is in the range of -100% to 0%, the output of the broken line function operator 35 and the broken line function operator 43 is between 100 and 50, and the corresponding output hydraulic proportional valve AO current instruction is 20mA to 12 mA, when the valve is opened, the deviation between the control valve instruction and the position feedback is in the range of 0% to 100%, the output of the broken line function operator 35 and the broken line function operator 43 is between 50 and 0, and the corresponding output hydraulic proportional valve AO current instruction is 12mA to 4mA, ensuring fast and accurate positioning control of the control valve under full stroke working conditions; the pulse action 63 and pulse action 64 of the interlock opening and closing of the water spray cooling stop valve should only be set to 1 to 2 controller operation cycles, that is, about 0.5 seconds. If the pulse time parameter is too large, it will affect the correct opening and closing action timing of the water spray cooling stop valve.

[0052] The following describes the implementation steps and parameter tuning results of a "control method for a hydraulic bypass system based on DCS intelligent positioning" for a supercritical, double-extraction, high-back-pressure generator set at the Huadian Tianjin Nangang Power Plant. This cogeneration unit is equipped with a 350MW supercritical circulating fluidized bed (CFB) once-through furnace manufactured by Dongfang Boiler Co., Ltd., a 170MW supercritical single-shaft, two-cylinder, two-stage, industrial extraction back-pressure steam turbine manufactured by Dongfang Steam Turbine Co., Ltd., a 170MW QF-170-2-15.75 generator manufactured by Dongfang Electric Corporation, and a MAX-DNA DCS system manufactured by Guodian Nanzhong Valmet Controls. The bypass system's DCS controller operation cycle is set to 200ms. The unit provides steam for chemical production at Sinopec, Chengxing Chemical, and Bohai Petrochemical, all within Tianjin's largest planned chemical park. When the unit's turbine trips or the generator is disconnected, the boiler is required to continue to operate and provide two-stage heating steam to the outside through the bypass system and the emergency contact steam supply valve group, so as to achieve effective control of the bypass steam supply without stopping the boiler during shutdown. This requires the turbine bypass system to be able to operate reliably, safely and stably. The high-pressure bypass capacity of the power plant is 100% BMCR and has a fast opening and closing function. The low-pressure bypass capacity meets the unit's cold, warm, hot and extremely hot startup requirements and has a fast opening and closing function. The high and low pressure bypass systems share a set of high-pressure parameter hydraulic oil systems and are equipped with two hydraulic oil pumps, one for use and one for backup. The system is equipped with a total of six hydraulic actuators, of which four hydraulic control valves are equipped with position feedback and electro-hydraulic proportional valve control circuits. The AO drive current command is implemented in the DCS, replacing the servo board hardware positioning function of the traditional hydraulic control valve. Each of the four control valves is equipped with an oil circuit locking solenoid valve. The control strategy of the hydraulic bypass system valve group refers to Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 ,and Figure 6 The control valve positioning system is optimized and configured in the DCS. There is no local positioning device and no expensive servo cards. The specific implementation steps are as follows (taking the high-pressure bypass valve group as an example, the low-pressure bypass valve group has the same principle, refer to steps 2 to 4):

[0053] Step 1: Configure the stop permission conditions of the two mutual backup hydraulic oil pumps. For specific logic, see Figure 2 ;

[0054] Step 2: Configure the PID regulator logic and process value of the high-pressure bypass pressure regulating valve as the main steam pressure. The output command value of the PID regulator is calculated by the difference between the position feedback value of the pressure regulating valve and the hand operator of the human-machine interface, and then the intelligent adjustment and positioning is performed through the variable parameter broken line function. Configure the PID regulator logic and process value of the high-pressure bypass water spray cooling regulating valve as the steam temperature after the water spray cooling regulating valve. The output command value of the PID regulator is calculated by the difference between the position feedback value of the water spray cooling regulating valve and the hand operator of the human-machine interface, and then the intelligent adjustment and positioning is performed through the variable parameter broken line function. For specific logic, see Figure 3 and Figure 4 ;

[0055] Step 3: Configure the energized / de-energized control logic of the holding solenoid valve of the high-pressure bypass pressure regulating valve and the energized / de-energized control logic of the holding solenoid valve of the high-pressure bypass water spray cooling regulating valve. For specific logic, see Figure 5 ;

[0056] Step 4: Configure the interlock automatic opening and interlock automatic closing control logic of the high-pressure bypass water spray desuperheating stop valve. For specific logic, see Figure 6 ;

[0057] Step 5: After DCS configuration, the bypass system is put into actual operation. Combined with the bypass system steam pressure and water spray cooling regulation characteristics, the adjustment parameters are optimized and set online.

[0058] After various working condition adjustment tests, the best adjustment parameters were obtained. The parameter values ​​are shown in the following table:

[0059] Table 1 Constants

[0060]

[0061] Table 2 Constants

[0062]

[0063] Table 3 Parameter values ​​of the broken line function operator 35

[0064]

[0065] Table 4 Parameter values ​​of the broken line function operator 43

[0066]

[0067] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0068] Although the present invention has been disclosed above with reference to the embodiments, it is not intended to limit the scope of protection of the present invention. Any changes and modifications made by any technician familiar with the technology without departing from the concept and scope of the present invention should fall within the scope of protection of the present invention.

Claims

1. A control method for a hydraulic bypass system based on DCS intelligent positioning, characterized by: The steps include: Step 1: Optimize the design of the stop permission conditions of the two backup hydraulic oil pumps to prevent misoperation and ensure the reliable operation of the hydraulic system; Step 2: Configure the PID regulator logic of the high-pressure bypass pressure regulating valve, compare the difference between the output command value of the PID regulator and the position feedback value of the pressure regulating valve, and then perform intelligent adjustment and positioning through the variable parameter broken line function F1(X). Configure the PID regulator logic of the high-pressure bypass water spray cooling regulating valve, compare the difference between the output command value of the PID regulator and the position feedback value of the water spray cooling regulating valve, and then perform intelligent adjustment and positioning through the variable parameter broken line function F2(X); Step 3: Optimize the design of the energized / de-energized control logic for the holding solenoid valve of the high-pressure bypass pressure regulating valve and the holding solenoid valve of the high-pressure bypass water spray cooling regulating valve. In the third step, the electro-hydraulic proportional valve and the holding solenoid valve cooperate to perform analog control of the regulating valve: when the holding solenoid valve is energized, the hydraulically controlled one-way valve opens, and hydraulic oil enters the regulating valve cylinder through the proportional valve. When the regulating valve reaches the required command position, the holding solenoid valve loses power, locking the oil circuit and maintaining the current position of the regulating valve. The DCS outputs a current of 12mA to the proportional valve, achieving dual positioning and holding of the regulating valve, improving the reliability and regulation accuracy of the regulating valve positioning. Step 4: Optimize the design of the interlock automatic opening / closing control logic of the high-pressure bypass water spray cooling stop valve. In the fourth step, a pulse action interlock is used to automatically open the high-pressure bypass water spray cooling stop valve when the command of the high-pressure bypass water spray cooling control valve is higher than the set value. When the command of the high-pressure bypass water spray cooling control valve is lower than the set value, the pulse action interlock is used to automatically close the high-pressure bypass water spray cooling stop valve. Using the control valve command value instead of the position feedback value can avoid the influence of fluctuations in the position feedback signal and ensure more reliable operation of the stop valve. Step 5: After DCS configuration, the bypass system is put into actual operation. Combined with the bypass system steam pressure and water spray cooling regulation characteristics, the adjustment parameters are optimized and set online.

2. The control method of the hydraulic bypass system based on DCS intelligent positioning according to claim 1 is characterized in that: In the first step, when the boiler stops operating MFT or BT and the main steam pressure is lower than the set value, or the other hydraulic oil pump is running and the oil pressure is normal, the standby hydraulic oil pump is allowed to stop to prevent misoperation and ensure the reliable operation of the hydraulic system. The bypass system can be put into operation normally during the unit startup phase or shutdown without stopping the boiler.

3. The control method of the hydraulic bypass system based on DCS intelligent positioning according to claim 1 is characterized in that: In the second step, the difference between the output command value of the PID regulator of the control valve and the position feedback value of the control valve is calculated and then intelligently adjusted and positioned through the variable parameter broken line function F(X). The greater the deviation between the command and feedback, the more the output AO command deviates from 12mA, and the smaller the deviation between the command and feedback, the closer the output AO command is to 12mA, ensuring better adjustment response rate and positioning accuracy of the control valve.

4. The control method of the hydraulic bypass system based on DCS intelligent positioning according to claim 1 is characterized in that: In the fifth step, different adjustment parameters are set for the electro-hydraulic proportional valve for different working ranges of the control valve. When the deviation between the control valve command and the position feedback is large, an AO output drive current with a large deviation from 12mA is given. That is, the larger the input values ​​of F1(X) and F2(X), the more the output value deviates from the value of 50, ensuring fast and accurate positioning control of the control valve under full stroke conditions; the pulse time for the interlock opening and closing of the water spray cooling stop valve is set to only 1 to 2 controller operation cycles, that is, 0.5 seconds. If the pulse time parameter is too large, it will affect the correct opening and closing action timing of the water spray cooling stop valve.

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