Bypass control method for stabilizing the steam drum liquid level in medium-pressure steam parallel operation of gas turbine units

Abstract

This invention relates to a bypass control method for stabilizing the steam drum liquid level during intermediate-pressure steam paralleling in a gas turbine unit. The system based on this method includes a high-pressure bypass, an intermediate-pressure bypass, cold reheat steam, a non-return valve, a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, a reheater, and a condenser. High-pressure main steam is converted to cold reheat steam via the high-pressure cylinder or the high-pressure bypass. Intermediate-pressure main steam is connected to the cold reheat steam via an electric valve. The cold reheat steam and intermediate-pressure main steam are connected via a non-return valve to prevent cross-flow. The cold reheat steam is converted to hot reheat main steam via the reheater. The hot reheat main steam is converted to hot reheat main steam via the intermediate-pressure cylinder or discharged to the condenser via the intermediate-pressure bypass. Low-pressure main steam is discharged to the condenser via the low-pressure cylinder. The method includes: 1) high-pressure bypass control; 2) intermediate-pressure linkage equipment control; and 3) intermediate-pressure bypass control. This invention solves the problems of poor drainage of the intermediate-pressure main steam during unit startup and large fluctuations in the intermediate-pressure steam drum liquid level after startup, achieving safe and stable operation of the unit.

Description

Technical Field

[0001] This invention belongs to the field of intelligent control of gas-fired steam combined cycle units, specifically relating to a bypass control method for stabilizing the liquid level in the steam drum during medium-pressure steam connection of a gas turbine unit. Background Technology

[0002] During unit startup, the pressure difference between the intermediate-pressure condensate drain and the reheat condensate drain causes steam resistance, resulting in poor drainage in the intermediate-pressure main steam pipeline. During intermediate-pressure steam connection, the pipeline vibration is easily aggravated by water carried by the steam, which affects the intermediate-pressure steam connection operation of the unit.

[0003] After the unit starts up, the cold reheat steam and the intermediate-pressure main steam are operated in parallel. When the steam pressures of the two are not matched, it is easy to cause difficulties in steam paralleling. Rapid fluctuations in the pressure of the intermediate-pressure main steam will lead to aggravated fluctuations in the liquid level of the intermediate-pressure steam drum.

[0004] If the steam drum liquid level is too high, the internal steam-water separation will deteriorate drastically, potentially leading to saturated steam entering the superheated surfaces, causing increased vibration in the superheated pipes and sudden changes in metal temperature. If the steam drum liquid level is too low, it will disrupt the steam-water circulation, potentially causing the furnace tubes to burst. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a bypass control method for stabilizing the steam drum liquid level in the intermediate-pressure steam circuit of a gas turbine unit. This method solves the problems of poor drainage of the intermediate-pressure main steam during the unit startup process and large fluctuations in the intermediate-pressure steam drum liquid level after startup, thereby achieving safe and stable operation of the unit.

[0006] The present invention is achieved using the following technical solution:

[0007] A bypass control method for stabilizing the steam drum liquid level during intermediate-pressure steam paralleling in a gas turbine unit. The system based on this method includes a high-pressure bypass, an intermediate-pressure bypass, cold reheat steam, a non-return valve, a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, a reheater, and a condenser. High-pressure main steam is converted to cold reheat steam via the high-pressure cylinder or the high-pressure bypass. Intermediate-pressure main steam is connected to the cold reheat steam via an electric valve. Cold reheat steam and intermediate-pressure main steam are connected via a non-return valve to prevent cross-flow issues. Cold reheat steam is converted to hot reheat main steam via the reheater. Hot reheat main steam is converted to hot reheat main steam via the intermediate-pressure cylinder or the intermediate-pressure bypass and discharged to the condenser. Low-pressure main steam is converted to hot reheat main steam via the low-pressure cylinder and discharged to the condenser.

[0008] The method includes: 1) high-voltage bypass control; 2) medium-voltage linkage equipment control; and 3) medium-voltage bypass control.

[0009] A further improvement of the present invention is that: 1) high-speed bypass control includes: a first constant module connected to the "N" terminal of the first switching module, a second constant module connected to the "Y" terminal of the first switching module, a switch input terminal of the turbine start-up signal connected to the input terminal of the first switching module, where the output is the value of the "Y" terminal when it is "1" and the output is the value of the "N" terminal when it is "0"; the output terminal of the first switching module connected to the "N" terminal of the second switching module, a third constant module connected to the "Y" terminal of the second switching module, and a switch input signal of the minimum valve position signal connected to the input terminal of the second switching module, where the output is the value of the "Y" terminal when it is "1" and the output is the value of the "N" terminal when it is "0".

[0010] The analog input signal of the differential pressure between the cold reheat steam pressure and the medium-pressure main steam pressure is connected to the function module. The output of the function module is connected to the "N" terminal of the fourth switching module. The fifth constant module is connected to the "Y" terminal of the fourth switching module. The digital input signal for the start of medium-pressure steam connection is connected to the input of the fourth switching module. When it is "1", the output is the value of the "Y" terminal; when it is "0", the output is the value of the "N" terminal. The fifth constant module is connected to the "N" terminal of the fourth switching module. The output of the fourth switching module is connected to the "Y" terminal of the third switching module. The digital input signals for the incomplete cold reheat pipeline warm-up and the incomplete medium-pressure steam connection are connected to the first OR module. The output of the first OR module is connected to the third switching module. When it is "1", the output is the value of the "Y" terminal; when it is "0", the output is the value of the "N" terminal.

[0011] The outputs of the second switching module and the third switching module are both connected to the first limiting module, and the output of the first limiting module is connected to the upper limit of the high bypass valve position.

[0012] A further improvement of this invention lies in the following specific control method:

[0013] After the cold re-drainage is completed, the high-pressure bypass valve is ready to be opened quickly; however, since the medium-pressure main steam drainage work is not yet completed, the opening of the high-pressure bypass valve must be limited while reducing the pressure difference between the cold re-drainage and the medium-pressure main steam.

[0014] A further improvement of the present invention is that 2) medium-pressure linkage equipment control includes: a switch input signal when the gas turbine is ignited and the medium-pressure steam drum pressure is greater than a certain pressure, a switch input signal when the medium-pressure main steam electric valve is in the closed position, and a switch input signal when the medium-pressure main steam outlet drain pipe wall temperature is greater than a certain temperature are all connected to the first AND module, and the output end of the first AND module is connected to the medium-pressure main steam bypass electric valve.

[0015] The following conditions are all connected to the second module: the difference between the cold repressure and the medium-pressure main steam pressure is less than a certain differential pressure; the medium-pressure main steam bypass electric valve has been open for a certain period of time; and the temperature of the medium-pressure main steam outlet drain pipe wall is greater than a certain temperature. The output of the second module is connected to the medium-pressure main steam electric valve.

[0016] A further improvement of this invention lies in the following specific control method:

[0017] When the gas turbine is ignited and the intermediate pressure steam drum pressure is greater than a certain value, and the intermediate pressure main steam electric valve is in the closed position and the intermediate pressure main steam outlet drain pipe wall temperature is greater than a certain temperature, the intermediate pressure main steam bypass electric valve is opened; the intermediate pressure main steam bypass electric valve opens, reducing the reheat pressure and the intermediate pressure main steam differential pressure.

[0018] A further improvement of the present invention is that the specific control method further includes: the temperature of the drain pipe wall of the medium-pressure main steam outlet is greater than a certain temperature, and the difference between the cold repressure and the medium-pressure main steam pressure is less than a certain differential pressure, and the medium-pressure main steam bypass electric valve has been opened for a certain period of time, and the medium-pressure main steam electric valve is opened in conjunction.

[0019] A further improvement of the present invention is that, 3) intermediate bypass control includes: the switch input signal for unit startup and the switch input signal for intermediate bypass actual value less than the set value are connected to the third AND module; the switch input signal for intermediate pressure start-up and the switch input signal for intermediate bypass actual value greater than the set value are connected to the fourth AND module; the output terminals of the third AND module and the fourth AND module are both connected to the second OR module; the analog input signal for intermediate bypass actual value is connected to the "Y" terminal of the fifth switching module; the first constant module is connected to the "N" terminal of the fifth switching module; the output terminal of the second OR module is connected to the fifth switching module; when it is "1", the output is the value of the "Y" terminal; when it is "0", the output is the value of the "N" terminal; the output terminal of the fifth switching module is connected to the intermediate bypass setting.

[0020] The analog input signal of the actual value of the intermediate adjustment is connected to the "Y" terminal of the sixth switching module, the second constant module is connected to the "N" terminal of the sixth switching module, the output terminal of the fourth AND module is connected to the sixth switching module. When it is "1", the output is the value of the "Y" terminal, and when it is "0", the output is the value of the "N" terminal. The output terminal of the sixth switching module is connected to the intermediate adjustment pressure setting.

[0021] A further improvement of this invention lies in the following specific control method:

[0022] The control functions include adding a medium-pressure bypass coordination side pressure tracking circuit and a bypass local pressure tracking circuit; and adding the rate switching logic within the DEH during the steam paralleling process.

[0023] The present invention has at least the following beneficial technical effects:

[0024] The bypass control method for stabilizing the steam drum liquid level during intermediate-pressure steam connection of a gas turbine unit, as described in this invention, solves the problems of poor drainage of the intermediate-pressure main steam during the unit startup process and large fluctuations in the steam drum liquid level during intermediate-pressure steam connection, thus achieving safe and stable operation of the unit. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the high-speed bypass control.

[0026] Figure 2 This is a schematic diagram of the control of medium-voltage linkage equipment.

[0027] Figure 3 This is a schematic diagram of the center-side control.

[0028] Figure 4 This is a schematic diagram of the system structure. Detailed Implementation

[0029] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] The bypass control method for stabilizing the steam drum liquid level in intermediate-pressure steam paralleling of a gas turbine unit, provided by the present invention, includes:

[0031] 1) The above Figure 1 This is a schematic diagram of the high-pressure bypass control, which specifically includes: turbine start-up signal 001, minimum valve position signal 002, cold reheat pipe warm-up not completed 003, intermediate pressure steam connection not completed 004, differential pressure value between cold reheat steam pressure and intermediate pressure main steam pressure 005, intermediate pressure steam connection started 006, first constant module 007, second constant module 008, third constant module 009, fourth constant module 010, fifth constant module 011, first switching module 012, second switching module 013, third switching module 014, fourth switching module 015, first OR module 016, first limiting module 017, function module 018, high-pressure bypass valve position upper limit 019.

[0032] Figure 1The control strategy logic diagram includes: the first constant module 007 is connected to the "N" terminal of the first switching module 012; the second constant module 008 is connected to the "Y" terminal of the first switching module 012; the switch input terminal of the turbine start-up signal 001 is connected to the input terminal of the first switching module 032. When it is "1", the output is the value of the "Y" terminal; when it is "0", the output is the value of the "N" terminal. The output terminal of the first switching module 012 is connected to the "N" terminal of the second switching module 033; the third constant module 029 is connected to the "Y" terminal of the second switching module 013; the switch input signal of the minimum valve position signal 002 is connected to the input terminal of the second switching module 013. When it is "1", the output is the value of the "Y" terminal; when it is "0", the output is the value of the "N" terminal.

[0033] The analog input signal of the differential pressure value 005 between the cold reheat steam pressure and the medium-pressure main steam pressure is connected to the function module 018. The output of the function module 018 is connected to the "N" terminal of the fourth switching module 015. The fifth constant module 011 is connected to the "Y" terminal of the fourth switching module 015. The digital input of the medium-pressure steam connection start 006 is connected to the input of the fourth switching module 015. When it is "1", the output is the value of the "Y" terminal. When it is "0", the output is the value of the "N" terminal. The fifth constant module 031 is connected to the "N" terminal of the fourth switching module 035. The output of the fourth switching module 015 is connected to the "Y" terminal of the third switching module 014. The digital input signals of the cold reheat pipeline warm-up incomplete 003 and the medium-pressure steam connection incomplete 004 are connected to the first OR module 016. The output of the first OR module 016 is connected to the third switching module 014. When it is "1", the output is the value of the "Y" terminal. When it is "0", the output is the value of the "N" terminal.

[0034] The output terminals of the second switching module 013 and the third switching module 014 are both connected to the first limiting module 017, and the output terminal of the first limiting module 017 is connected to the upper limit of the high bypass valve position 019.

[0035] Figure 1 The specific control functions are as follows:

[0036] After the cold re-drainage is completed, the high-pressure bypass valve is ready to open quickly. However, because the medium-pressure main steam drainage is not yet complete, the opening of the high-pressure bypass valve must be limited while simultaneously reducing the pressure difference between the cold re-drainage and the medium-pressure main steam.

[0037] 2) The above Figure 2This is a schematic diagram of the control of the medium-pressure linkage equipment, which specifically includes: gas turbine ignition and medium-pressure steam drum pressure greater than a certain pressure 020, medium-pressure main steam electric valve in the closed position 021, medium-pressure main steam outlet drain pipe wall temperature greater than a certain temperature 022, cold reheat pressure and medium-pressure main steam pressure deviation less than a certain differential pressure 023, medium-pressure main steam bypass electric valve has been open for a certain period of time 024, medium-pressure main steam outlet drain pipe wall temperature greater than a certain temperature 025, first and second modules 026, second and third modules 027, joint opening of medium-pressure main steam bypass electric valve 028, joint opening of medium-pressure main steam electric valve 029.

[0038] Figure 2 The control strategy logic diagram includes: the switch input signal 020 when the gas turbine is ignited and the pressure of the intermediate steam drum is greater than a certain pressure, the switch input signal 021 when the electric valve of the intermediate steam is in the closed position, and the switch input signal 022 when the wall temperature of the drain pipe of the intermediate steam outlet is greater than a certain temperature are all connected to the first AND module 026. The output terminal of the first AND module 026 is connected to the electric valve 028 for opening the intermediate steam bypass.

[0039] The following conditions are connected to the second AND module 027: the cold repressure and the medium-pressure main steam pressure deviation is less than a certain differential pressure (023); the medium-pressure main steam bypass electric valve has been open for a certain period of time (024); and the medium-pressure main steam outlet drain pipe wall temperature is greater than a certain temperature (025). The output terminal of the second AND module 027 is connected to the medium-pressure main steam electric valve (029).

[0040] Figure 2 The specific control functions are as follows:

[0041] When the gas turbine is ignited and the intermediate pressure steam drum pressure is greater than a certain value, and the intermediate pressure main steam electric valve is in the closed position and the intermediate pressure main steam outlet drain pipe wall temperature is greater than a certain temperature, the intermediate pressure main steam bypass electric valve is opened; the intermediate pressure main steam bypass electric valve opens, reducing the reheat pressure and the intermediate pressure main steam differential pressure.

[0042] The temperature of the drain pipe wall at the outlet of the medium-pressure main steam is greater than a certain temperature, and the difference between the cold reheat pressure and the medium-pressure main steam pressure is less than a certain differential pressure. The electric bypass valve of the medium-pressure main steam has been open for a certain period of time. The electric bypass valve of the medium-pressure main steam is then opened.

[0043] 3) The above Figure 3 This is a schematic diagram of the intermediate bypass control, which specifically includes: intermediate bypass actual value 030, unit start 031, intermediate bypass actual value less than set value 032, intermediate pressure start steam connection 033, intermediate bypass actual value greater than set value 034, intermediate regulation actual value 035, third AND module 036, fourth AND module 037, second OR module 038, fifth switching module 039, sixth switching module 040, first constant module 041, second constant module 042, intermediate bypass setting 043, intermediate regulation pressure setting 044.

[0044] Figure 3The control strategy logic diagram includes: the switch input signal of unit start 031 and the switch input signal of intermediate bypass actual value less than set value 032 are connected to the third AND module 036; the switch input signal of intermediate pressure start and steam connection 033 and the switch input signal of intermediate bypass actual value greater than set value 034 are connected to the fourth AND module 037; the output terminals of the third AND module 036 and the fourth AND module 037 are both connected to the second OR module 038; the analog input signal of intermediate bypass actual value 030 is connected to the "Y" terminal of the fifth switching module 039; the first constant module 041 is connected to the "N" terminal of the fifth switching module 039; the output terminal of the second OR module 038 is connected to the fifth switching module 039. When it is "1", the output is the value of the "Y" terminal; when it is "0", the output is the value of the "N" terminal; the output terminal of the fifth switching module 039 is connected to the intermediate bypass setting 043.

[0045] The analog input signal of the actual value 035 of the intermediate adjustment is connected to the "Y" terminal of the sixth switching module 040. The second constant module 042 is connected to the "N" terminal of the sixth switching module 040. The output terminal of the fourth AND module 037 is connected to the sixth switching module 040. When it is "1", the output is the value of the "Y" terminal. When it is "0", the output is the value of the "N" terminal. The output terminal of the sixth switching module 040 is connected to the intermediate adjustment pressure setting 044.

[0046] Figure 3 The specific control functions are as follows:

[0047] The control functions include adding a pressure tracking loop on the intermediate-pressure bypass coordination side and a local pressure tracking loop on the bypass; it also adds rate switching logic within the DEH during the steam coupling process. These three combinations ensure stable water levels in the intermediate-pressure steam drum.

[0048] 4) System Diagram

[0049] The Figure 4 The system structure diagram includes: high-pressure main steam 045, medium-pressure main steam 046, low-pressure main steam 047, high-pressure bypass 048, medium-pressure bypass 049, cold reheat steam 050, non-return valve 051, medium-pressure main steam electric valve 052, medium-pressure main steam bypass electric valve 053, high-pressure cylinder 054, medium-pressure cylinder 055, low-pressure cylinder 056, reheater 057, and condenser 058.

[0050] The specific process flow of the present invention is as follows: high-pressure main steam is converted into cold reheat steam by performing work in the high-pressure cylinder or by passing through the high-pressure bypass; medium-pressure main steam is connected to cold reheat steam by passing through the medium-pressure main steam electric valve; cold reheat steam and medium-pressure main steam are connected and reversed by passing through the non-return valve; cold reheat steam is converted into hot reheat main steam by passing through the reheater; hot reheat main steam is converted into hot reheat main steam by performing work in the medium-pressure cylinder or by passing through the medium-pressure bypass to the condenser; low-pressure main steam is converted into hot reheat main steam by performing work in the low-pressure cylinder to the condenser.

[0051] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A bypass control method for pressure and steam in a steam drum in a gas turbine unit, characterized by, The system based on the method comprises a high bypass (048), a middle bypass (049), a cold re-steam (050), a check valve (051), a high pressure cylinder (054), a middle pressure cylinder (055), a low pressure cylinder (056), a reheater (057), and a condenser (058); high pressure main steam is converted into cold re-steam through the high pressure cylinder or the high bypass; the middle pressure main steam is combined with the cold re-steam through a middle pressure main steam electric gate; the cold re-steam and the middle pressure main steam are combined in reverse through the check valve; the cold re-steam is converted into hot re-steam through the reheater; The hot re-steam is converted into work through the middle pressure cylinder or discharged to the condenser through the middle bypass; the low pressure main steam is converted into work through the low pressure cylinder and discharged to the condenser; The method comprises: 1) high bypass control, and the specific control method is as follows: After the cold re-steam is completed, the high bypass valve has a condition of being capable of being quickly opened; because the middle pressure main steam drainage work is not completed, the opening of the high bypass valve must be limited and the pressure difference between the cold re-steam and the middle pressure main steam must be reduced; 2) middle pressure linkage device control, comprising: a switch input signal of a fuel engine ignition and a middle pressure steam drum pressure greater than a certain pressure (020), a switch input signal of a middle pressure main steam electric gate in a closed position (021), and a middle pressure main steam outlet drainage pipe wall temperature greater than a certain temperature are all connected to a first and module (026), an output end of the first and module (026) is connected to a linkage opening middle pressure main steam bypass electric gate (028); a cold re-steam pressure and a middle pressure main steam pressure deviation less than a certain pressure difference (023), the middle pressure main steam bypass electric gate having been opened for a certain time (024), and the middle pressure main steam outlet drainage pipe wall temperature greater than a certain temperature are all connected to a second and module (027), an output end of the second and module (027) is connected to a linkage opening middle pressure main steam electric gate (029); and 3) middle bypass control, and the specific control method is as follows: A control function increases a middle pressure bypass coordinated side pressure tracking loop, increases a bypass local pressure tracking loop, and increases a DEH inherent rate switching logic in a combined process.

2. The bypass control method for stabilizing the level of liquid in the drum in a gas turbine unit according to claim 1, characterized in that, 1) high bypass control, comprising: a first constant module (007) connected to an "N" end of a first switching module (012), a second constant module (008) connected to a "Y" end of the first switching module (012), a switch input end of a steam turbine start-up signal (001) connected to an input end of the first switching module (012), when being "1", outputting a value of the "Y" end, when being "0", outputting a value of the "N" end; an output end of the first switching module (012) connected to an "N" end of a second switching module (013), a third constant module (019) connected to a "Y" end of the second switching module (013), and a switch input signal of a minimum valve position signal (002) connected to an input end of the second switching module (013), when being "1", outputting a value of the "Y" end, when being "0", outputting a value of the "N" end; The analog input signal of the cold re-steam pressure and the pressure difference value (005) of the medium-pressure main steam pressure is connected to the function module (018), the output end of the function module (018) is connected to the "N" end of the fourth switch module (015), the fifth constant module (011) is connected to the "Y" end of the fourth switch module (015), the on-off input end of the medium-pressure and-steam starting (006) is connected to the input end of the fourth switch module (015), when being "1", the output is the value of the "Y" end, when being "0", the output is the value of the "N" end; the fifth constant module (011) is connected to the "N" end of the fourth switch module (015), the output end of the fourth switch module (015) is connected to the "Y" end of the third switch module (014), the on-off input signals of the cold re-pipe warming pipe unfinished (003) and the medium-pressure and-steam unfinished (004) are connected to the first OR module (016), the output end of the first OR module (016) is connected to the third switch module (014), when being "1", the output is the value of the "Y" end, when being "0", the output is the value of the "N" end; The output ends of the second switch module (013) and the third switch module (014) are both connected to the first limiting module (017), the output end of the first limiting module (017) is connected to the upper limit of the high bypass valve position (019).

3. The bypass control method for stabilizing the level of liquid in the drum in a gas turbine unit according to claim 1, characterized in that, The specific control method of the medium-pressure linkage device control is as follows: When the gas turbine is ignited, the medium-pressure steam drum pressure is greater than a certain value, the medium-pressure main steam electric door is in the closed position, and the medium-pressure main steam outlet drain pipe wall temperature is greater than a certain temperature, the medium-pressure main steam bypass electric door is opened. The opening of the medium-pressure main steam bypass electric door reduces the cold re-pressure and the medium-pressure main steam pressure difference.

4. The bypass control method for stabilizing the level of liquid in the drum in a gas turbine unit according to claim 3, characterized in that, The specific control method further comprises: when the medium-pressure main steam outlet drain pipe wall temperature is greater than a certain temperature, the cold re-pressure and the medium-pressure main steam pressure difference is less than a certain pressure difference, and the medium-pressure main steam bypass electric door has been opened for a certain time, the medium-pressure main steam electric door is opened.

5. The bypass control method for stabilizing the level of liquid in the drum in a gas turbine unit according to claim 1, characterized in that, 3) The medium-pressure bypass control comprises: the on-off input signal of the unit starting (031) and the on-off input signal of the medium-pressure bypass actual value being less than a set value are connected to the third AND module (036), the on-off input signal of the medium-pressure and-steam starting (033) and the on-off input signal of the medium-pressure bypass actual value being greater than a set value are connected to the fourth AND module (037), the output end of the third AND module (036) and the output end of the fourth AND module (037) are both connected to the second OR module (038), the analog input signal of the medium-pressure bypass actual value (030) is connected to the "Y" end of the fifth switch module (039), the first constant module (041) is connected to the "N" end of the fifth switch module (039), the output end of the second OR module (038) is connected to the fifth switch module (039), when being "1", the output is the value of the "Y" end, when being "0", the output is the value of the "N" end, the output end of the fifth switch module (039) is connected to the medium-pressure bypass setting (043). The analog input signal of the middle regulating actual value (035) is connected to the "Y" end of the sixth switch module (040), the second constant module (042) is connected to the "N" end of the sixth switch module (040), the output end of the fourth and module (037) is connected to the sixth switch module (040), when being "1", the output is the value of the "Y" end, when being "0", the output is the value of the "N" end, the output end of the sixth switch module (040) is connected to the middle regulating pressure setting (044).

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