Steam Pressure Control Method for Combined Cycle Unit under APS Input

Abstract

The present invention discloses a steam pressure control method for a combined cycle unit under APS input, belonging to the technical field of automatic control. The method includes: based on the start-up instruction issued by the combined cycle unit, obtaining the main steam pressure value before the valve of each bypass and the outlet pressure of the high-pressure superheater at start-up; judging whether the outlet pressure of the high-pressure superheater exceeds the set conditions for the input of each bypass control; if so, setting the minimum pressure set value of the corresponding bypass to the function F(x) value of the gas turbine load and the high-pressure cylinder metal temperature; if not, setting the minimum pressure set value of the corresponding bypass to the actual value of the main steam pressure before the valve of this bypass, and linearly increasing with the pipeline pressure; taking the difference between the actual value of the main steam pressure before the valve of each bypass and the minimum voltage set value of this bypass as the input of the corresponding proportional-integral (PI) controller respectively; using the output of the proportional-integral (PI) controller to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic control, and particularly relates to a steam pressure control method for a combined cycle unit under APS input. Background Art

[0002] At present, the main steam system of a gas-steam combined cycle unit Figure 1 As shown, in the main steam system of the combined cycle unit, low-pressure steam, medium-pressure steam, and high-pressure steam all come from the waste heat boiler, and the three-way steam enters the low-pressure cylinder, medium-pressure cylinder, and high-pressure cylinder respectively. However, during the startup process, shutdown process, and abnormal conditions of the combined cycle unit, there are strict requirements for the steam inlet pressures of the high, medium, and low-pressure cylinders, and adjusting the magnitudes of the main steam pressures of each path is achieved by adjusting the opening degrees of the high-pressure bypass valve, medium-pressure bypass valve, and low-pressure bypass valve.

[0003] The existing main steam pressure control system of the combined cycle unit cannot be put into operation throughout the whole process and under all working conditions, and strong manual intervention by the operating personnel is required. That is, during the startup and shutdown processes of the combined cycle unit, the operating personnel need to manually adjust the valve position opening degrees of the bypass valves to control the main steam pressures of each path, which directly reduces the automation level of the combined cycle unit.

[0004] In the related art, the Chinese patent application publication No. CN105781646A discloses a bypass pressure full-automatic control method and system for a gas-steam combined cycle unit. By obtaining the optimal change rate of the main steam pressure and the optimal change rate of the main steam temperature in real time for the control of the minimum valve position, since the optimal change rate of the main steam pressure and the optimal change rate of the main steam temperature are obtained in real time at each stage based on the actual operating conditions, the minimum valve position given value, bypass pressure set value, and the rate of closing the bypass valve automatically determined based on the optimal change rate of the main steam pressure and the optimal change rate of the main steam temperature also change with the change of the working conditions. Furthermore, the bypass pressure full-automatic control system can automatically adjust with the change of the actual working conditions of the gas-steam combined cycle unit; solving the technical problem that the bypass pressure full-automatic control system in the prior art cannot automatically adjust with the change of the actual working conditions of the gas-steam combined cycle unit and has poor adaptability. However, this solution does not specifically give what variable is used to determine the high bypass valve position, but focuses on calculating the optimal change rate of the main steam pressure and the optimal change rate of the main steam temperature in each stage.

[0005] A Chinese invention patent application with the publication number CN113027545A discloses a bypass control method for stabilizing the steam drum level of a gas-steam combined cycle unit. The implementation steps include: the feedback deviation of the high bypass desuperheating control valve PID control adjustment loop is the set value minus the temperature after the high bypass spray valve, and the feedforward quantity of the high bypass desuperheating control valve PID control adjustment loop is the output of the high bypass desuperheating control valve opening function F1(x) corresponding to the opening of the high bypass pressure reducing valve, the high bypass front and rear temperature sensing feedforward quantity A, the high bypass front and rear temperature sensing feedforward quantity B, the high bypass front and rear temperature sensing feedforward quantity C, and the high bypass quick opening preset feedforward quantity D; the feedback deviation of the medium / low bypass desuperheating control valve PID control adjustment loop is the set value minus the temperature after the medium / low bypass spray valve, and the feedforward quantity of the medium / low bypass desuperheating control valve PID control adjustment loop is the output of the medium / low bypass desuperheating control valve opening function corresponding to the opening of the medium / low bypass pressure reducing valve. This method realizes full-automatic control of the bypass throughout the process and stabilizes the steam drum level fluctuation during drastic changes in working conditions. However, the main problem to be solved by the control strategy described in this scheme is to maintain the stability of the steam drum level. Summary of the Invention

[0006] The technical problem to be solved by the present invention is how to achieve full-automatic control of the main steam pressure of a combined cycle unit under all working conditions.

[0007] The present invention solves the above technical problems through the following technical means:

[0008] The present invention proposes a steam pressure control method for a combined cycle unit under APS input. The method includes:

[0009] Based on the start-up instruction issued by the combined cycle unit, obtain the valve front main steam pressure value and the high-pressure superheater outlet pressure of each bypass during start-up;

[0010] Judge whether the high-pressure superheater outlet pressure exceeds the set conditions for the input of each bypass control;

[0011] If so, set the minimum pressure set value of the corresponding bypass to the value of the function F(x) of the gas turbine load and the high-pressure cylinder metal temperature;

[0012] If not, set the minimum pressure set value of the corresponding bypass to the actual value of the valve front main steam pressure of the bypass, and linearly increase with the pipeline pressure;

[0013] Respectively use the difference between the actual value of the valve front main steam pressure of each bypass and the minimum voltage set value of the bypass as the input of the corresponding proportional-integral PI controller;

[0014] Use the output of the proportional-integral PI controller to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve.

[0015] During the process of the invention cooperating with the waste heat boiler to increase the temperature and pressure, the opening of the bypass regulating valve is restricted and controlled according to the allowable pressure increase rate of the high-pressure steam drum of the waste heat boiler to obtain appropriate temperature and pressure increase rates. And according to the output power of the gas turbine or the output steam flow of the waste heat boiler, the minimum bypass pressure set value is obtained through the operation of the function generator, and different pressure set values are taken in different operation stages. The difference between the actual value and the set value of the main steam pressure before the bypass is used as the input of the corresponding proportional-integral (PI) controller, and the output of the controller drives the bypass valve actuator to adjust the opening of the bypass valve.

[0016] Further, the main steam pressure values before the valves of each bypass include the high-pressure steam pressure value of the high-pressure bypass, the steam pressure value of the medium-pressure bypass, and the steam pressure value of the low-pressure bypass.

[0017] The bypass valves include a high-pressure bypass valve, a medium-pressure bypass valve, and a low-pressure bypass valve.

[0018] Further, the set conditions include a first set value, a second set value, and a third set value respectively used for comparing with the high-pressure steam pressure value, the medium-pressure steam pressure value, and the low-pressure steam pressure value.

[0019] Further, the driving of the bypass valve actuator by the output of the proportional-integral (PI) controller to adjust the opening of the corresponding bypass valve includes:

[0020] When the input of the proportional-integral (PI) controller is greater than zero, the proportional-integral (PI) controller outputs a control instruction to drive the bypass valve actuator to increase the opening of the corresponding bypass valve;

[0021] When the input of the proportional-integral (PI) controller is equal to zero, the proportional-integral (PI) controller outputs a control instruction to drive the bypass valve actuator to keep the opening of the corresponding bypass valve unchanged;

[0022] When the input of the proportional-integral (PI) controller is less than zero, the proportional-integral (PI) controller outputs a control instruction to drive the bypass valve actuator to decrease the opening of the corresponding bypass valve.

[0023] Further, the method further includes:

[0024] When the main steam pressure parameters of each bypass meet the steam admission conditions of the steam turbine, the high-pressure main steam regulating valve, the medium-pressure main steam regulating valve, and the low-pressure main steam regulating valve are opened;

[0025] Control the minimum pressure set value of each bypass to be higher than the actual value of the main steam pressure before the valve of each bypass, so that the opening of each bypass valve becomes smaller until it is in a closed state.

[0026] Further, the opening condition of the high-pressure main steam control valve is that all high-pressure bypass valves are closed and the steam turbine meets the corresponding steam inlet conditions under cold, warm, and hot states, or the gas turbine load > 50%;

[0027] The opening condition of the intermediate-pressure main steam control valve is that all intermediate-pressure bypass valves are closed and the steam turbine meets the corresponding steam inlet conditions under cold, warm, and hot states, or the gas turbine load > 50%;

[0028] The opening condition of the low-pressure main steam control valve is that all low-pressure bypass valves are closed and the steam turbine meets the corresponding steam inlet conditions under cold, warm, and hot states, or the gas turbine load > 50%.

[0029] Further, the output of the proportional-integral (PI) controller is within the (H, L) interval, where H is the high limit and L is the low limit;

[0030] During normal operation, the upper and lower limits of the output of the proportional-integral (PI) controller corresponding to the high-pressure bypass valve and the intermediate-pressure bypass valve are (102, -2), and the upper and lower limits of the output of the proportional-integral (PI) controller corresponding to the low-pressure bypass valve are (102, -5).

[0031] Further, the method further includes:

[0032] When the unit is shut down normally or emergently, control the low-pressure main steam control valve to close sequentially from the current opening;

[0033] After logically determining that the low-pressure main steam control valve is at 30% opening, close the high-pressure main steam control valve and the intermediate-pressure main steam control valve in logical sequence;

[0034] During the closing process of each control valve, as the pressure of the main steam pipeline increases, control each bypass valve to open first and then close.

[0035] Further, the method further includes:

[0036] Under abnormal conditions, use the low limit of the output of the proportional-integral (PI) controller as the low valve position forced value and delay for 5 s.

[0037] Further, when the abnormal condition is load rejection, the method further includes:

[0038] Control the low valve position forced value of each bypass valve at the moment of load rejection to be a function of the main steam flow rate at the same moment.

[0039] Further, the method further includes:

[0040] When the condenser protection condition is established, forcefully close the intermediate-pressure bypass valve and the low-pressure bypass valve.

[0041] In addition, the present invention also provides a steam pressure control system for a combined cycle unit under APS input, and the system includes:

[0042] An acquisition module, configured to acquire the valve front main steam pressure value and the high-pressure superheater outlet pressure of each bypass during startup based on a startup instruction sent by the combined cycle unit;

[0043] A judgment module, configured to judge whether the high-pressure superheater outlet pressure exceeds the set conditions for the input of each bypass control;

[0044] A first setting module, configured to, when the judgment result of the judgment module is yes, set the minimum pressure setting value of the corresponding bypass to the value of the function F(x) of the gas turbine load and the high-pressure cylinder metal temperature;

[0045] A second setting module, configured to, when the judgment result of the judgment module is no, set the minimum pressure setting value of the corresponding bypass to the actual value of the valve front main steam pressure of the bypass, and linearly increase with the pipeline pressure;

[0046] A control module, configured to use the difference between the actual value of the valve front main steam pressure of each bypass and the minimum voltage setting value of the bypass as the input of the corresponding proportional-integral (PI) controller respectively, and drive the bypass valve actuator by using the output of the proportional-integral (PI) controller to adjust the opening of the corresponding bypass valve.

[0047] The advantages of the present invention are as follows:

[0048] (1) During the process of coordinating the heating-up and pressure-rising of the waste heat boiler, the present invention restricts and controls the opening of the bypass regulating valve according to the allowable pressure-rising rate of the high-pressure steam drum of the waste heat boiler to obtain a suitable heating-up and pressure-rising rate, and obtains the minimum pressure setting value of the bypass through the operation of the function generator according to the output power of the gas turbine or the output steam flow of the waste heat boiler. Different minimum pressure setting values are taken in different operation stages, and the difference between the actual value of the main steam pressure before the bypass and the setting value is used as the input of the corresponding proportional-integral (PI) controller. The output of the controller drives the bypass valve actuator to adjust the opening of the bypass valve. The setting value of each main steam pressure can be accurately calculated according to the main equipment parameters of the combined cycle unit (such as the gas turbine load, the output steam flow of the waste heat boiler) and the whole-process operation conditions, without manual intervention.

[0049] (2) The switching of steam pressure control is realized. For the switching of steam pressure from bypass control to turbine control, a bypass sequential closing function is designed.

[0050] (3) When the unit sheds load, the bypass valve is quickly opened to a certain opening (and maintained for a certain time), and the opening size is a function of the current steam flow, so as to stabilize the system pressure, taking into account how to control the main steam pressure under abnormal conditions during the operation of the combined cycle unit.

[0051] (4) The output of the proportional-integral (PI) controller is limited high and low to achieve the corresponding coordination of the bypass opening under various operating conditions.

[0052] (5) The subsystem of the APS control system involved in the framework of the one-key start-stop of APS in the present invention is seamlessly connected to the APS control system, thereby realizing the main steam pressure control without manual intervention, and can be applied not only to the split-shaft combined cycle unit, but also to the single-shaft combined cycle unit.

[0053] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. Description of the Drawings

[0054] Figure 1 is the structural diagram of the main steam system of the gas-steam combined cycle unit mentioned in the background art part of the present invention;

[0055] Figure 2 is the schematic flow chart of the steam pressure control method of the combined cycle unit under the input of APS proposed in an embodiment of the present invention;

[0056] Figure 3 is the schematic diagram of the main steam pressure control principle of the gas-steam combined cycle unit proposed in an embodiment of the present invention;

[0057] Figure 4 is the control principle diagram of the APS control system in an embodiment of the present invention;

[0058] Figure 5 is the schematic diagram of the condition judgment for the input of the bypass control in an embodiment of the present invention;

[0059] Figure 6 is the schematic diagram of the normal operation process of the combined cycle unit in an embodiment of the present invention;

[0060] Figure 7 is the schematic diagram of the condition judgment for the input of the pressure control of the high-pressure and medium-pressure main steam regulating valves in an embodiment of the present invention;

[0061] Figure 8 is the schematic diagram of the condition judgment for the input of the pressure control of the low-pressure main steam regulating valve in an embodiment of the present invention;

[0062] Figure 9 is the schematic diagram of the control under abnormal conditions in an embodiment of the present invention;

[0063] Figure 10 is the structural diagram of the steam pressure control system of the combined cycle unit under the input of APS proposed in another embodiment of the present invention;

[0064] Figure 11 It is a schematic diagram of the overall structure of the steam pressure control system of a combined cycle unit under APS input proposed in another embodiment of the present invention. Specific embodiments

[0065] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0066] As Figure 2 , Figure 3 and Figure 4 shown, a steam pressure control method for a combined cycle unit under APS input is proposed in the first embodiment of the present invention. The method includes the following steps:

[0067] S10. Based on the start-up instruction issued by the combined cycle unit, obtain the valve front main steam pressure value and the high-pressure superheater outlet pressure at start-up for each bypass;

[0068] S20. Determine whether the high-pressure superheater outlet pressure exceeds the set conditions for the input of each bypass control. If so, execute step S30; if not, execute step S40;

[0069] S30. Set the minimum pressure set value of the corresponding bypass to the function F(x) value of the gas turbine load and the high-pressure cylinder metal temperature;

[0070] S40. Set the minimum pressure set value of the corresponding bypass to the actual value of the valve front main steam pressure of the bypass, and linearly increase with the pipeline pressure;

[0071] S50. Take the difference between the actual value of the valve front main steam pressure of each bypass and the minimum voltage set value of the bypass as the input of the corresponding proportional-integral (PI) controller respectively, and use the output of the proportional-integral (PI) controller to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve.

[0072] It should be noted that after the unit issues a start command, with the end of the gas turbine purging process, the gas turbine ignites. When the gas turbine ignites successfully, since the main steam pressure parameters of each bypass are different during start-up, if the main steam pressure is relatively high at this time and meets the set conditions for bypass input control, the minimum voltage setpoint is directly set to the gas turbine load function value. SP is the function value F(x) of the current gas turbine load and the high-pressure cylinder metal temperature, which is used as the minimum pressure setpoint of the bypass. F(x) can be represented by a piecewise function; otherwise, wait for the natural pressure rise of the pipeline, and the setpoint increases as the pipeline pressure rises. The pressure setpoint of the bypass valve has a gradual change characteristic. If the setpoint directly takes the main steam pressure value before the bypass, that is, SP = PV, the input error of the bypass valve at this stage is 0, and the bypass valve will not open. The controller setpoint increases as the pressure in the pipeline (i.e., the initial pressure) gradually rises.

[0073] In this embodiment, during the process of coordinating the heating and pressure rise of the waste heat boiler, the opening of the bypass regulating valve is restricted and controlled according to the allowable pressure rise rate of the high-pressure steam drum of the waste heat boiler to obtain appropriate heating and pressure rise rates. At the same time, according to the output power of the gas turbine or the output steam flow of the waste heat boiler, and based on the metal temperature of the high-pressure cylinder of the steam turbine, the minimum bypass pressure setpoint is obtained through the operation of the function generator. Different minimum pressure setpoints are taken at different operating stages. The difference between the actual value and the set value of the main steam pressure before the bypass is used as the input of the corresponding proportional-integral PI controller, and the output of the controller drives the bypass valve actuator to adjust the opening of the bypass valve, so as to achieve precise and stable control of the main steam pressure of the combined cycle unit throughout the entire operating condition and process.

[0074] Furthermore, in this embodiment, based on the metal temperature of the high-pressure cylinder measured by the APS control system and corrected by the main steam temperature parameter, the appropriate impulse pressure before the steam inlet valve of the steam turbine is obtained, without rigidly distinguishing between cold, warm, and hot operating conditions, realizing automatic pressure setting under all operating conditions. The bypass pressure setpoint is quickly calculated based on the impulse pressure, enabling the high-pressure bypass control to be put into operation at the beginning of the unit start-up and completing the full-automatic control of the entire bypass system. At the same time, this method can also utilize the temperature margin of the steam turbine, increasing the impulse pressure and accelerating the start-up speed.

[0075] This embodiment focuses on obtaining the set value of the main steam pressure through relevant reference variables, better realizing the temperature and pressure matching with the steam turbine. The acquisition of relevant reference variables is obtained through the APS system, and the entire control method adopts a more scientific and effective calculation method, accelerating the unit start-up speed.

[0076] In one embodiment, the main steam pressure values before the valves of each bypass include the high-pressure steam pressure value of the high-pressure bypass, the steam pressure value of the intermediate-pressure bypass, and the steam pressure value of the low-pressure bypass;

[0077] The bypass valves include a high-pressure bypass valve, an intermediate-pressure bypass valve, and a low-pressure bypass valve.

[0078] The object of the control method proposed in this embodiment is the high bypass valve, the intermediate bypass valve, and the low bypass valve. By controlling the opening degrees of the three bypass valves, the high-pressure steam pressure, the intermediate-pressure steam pressure, and the low-pressure steam pressure are controlled.

[0079] In one embodiment, the set conditions include a first set value, a second set value, and a third set value respectively used for comparison with the high-pressure steam pressure value, the intermediate-pressure steam pressure value, and the low-pressure steam pressure value.

[0080] Specifically, as Figure 5 shown, the judgment conditions for the high-pressure bypass control to be put into operation: after ignition is successful, the pressure at the outlet of the high-pressure superheater is greater than the first set value, and the first set value is taken as 4.8 MPa. The judgment conditions for the intermediate-pressure bypass control to be put into operation: after ignition is successful, the pressure at the outlet of the high-pressure superheater is greater than the second set value, and the second set value is taken as 1.25 MPa. The judgment conditions for the low-pressure bypass control to be put into operation: after ignition is successful, the pressure at the outlet of the high-pressure superheater is greater than the third set value, and the third set value is taken as 1.25 MPa.

[0081] In one embodiment, step S50 includes the following steps:

[0082] When the input of the proportional-integral PI controller is greater than zero, the proportional-integral PI controller outputs a control instruction to drive the bypass valve actuator to increase the opening degree of the corresponding bypass valve;

[0083] When the input of the proportional-integral PI controller is equal to zero, the proportional-integral PI controller outputs a control instruction to drive the bypass valve actuator to keep the opening degree of the corresponding bypass valve unchanged;

[0084] When the input of the proportional-integral PI controller is less than zero, the proportional-integral PI controller outputs a control instruction to drive the bypass valve actuator to decrease the opening degree of the corresponding bypass valve.

[0085] It should be noted that when transitioning from the actual pressure mode to the minimum pressure mode, the setpoint changes stepwise from the pressure value before the bypass at the moment when the high-pressure regulating valve closes during the shutdown process to the actual value of the pressure before the bypass after ignition. As the unit warms up, raises pressure, and increases load, the setpoint shows a slow upward change trend. When the actual value PV (i.e., the actual pressure before the bypass) is greater than the setpoint, the input of the controller ΔP = PV - setpoint > 0, and the bypass valve opens wider; when the actual value PV is less than the setpoint, the input of the controller ΔP = PV - setpoint < 0, and the bypass valve closes smaller.

[0086] In this embodiment, as the unit load varies, the setpoint is corrected by a corresponding function, so that the main steam pressure PV before the bypass valve changes with the change of the setpoint.

[0087] Furthermore, when the combined cycle unit transitions from the startup state to the normal operation state, the method further includes:

[0088] When the main steam pressure parameters of each bypass meet the steam admission conditions of the steam turbine, open the high-pressure main steam regulating valve, the intermediate-pressure main steam regulating valve, and the low-pressure main steam regulating valve;

[0089] Control the minimum pressure setpoint of each bypass to be higher than the actual value of the main steam pressure before the valve of each bypass, so that the opening degree of each bypass valve becomes smaller until it is in the closed state.

[0090] It should be noted that as Figure 6 shown, when the main steam pressure of each path meets the steam admission conditions of the steam turbine, the high-pressure and intermediate-pressure main steam regulating valves open. At this time, the bypass valve gradually closes as the regulating valve opens wider until it is fully closed. When the bypass valve is fully closed and the gas turbine load is greater than a certain value, set the pressure setpoint of the bypass valve slightly higher than the actual pressure. The input of the PI controller error = PV - setpoint < 0 is always negative to ensure that the bypass valve is in the closed state, and the unit enters the stage of controlling the pressure by the main steam regulating valve.

[0091] After the main steam valve of the steam turbine opens, as the steam turbine rotates impulsively and is synchronized to carry load, during this stage, the high-pressure main steam pressure is controlled by the steam turbine, and the task of the high-pressure bypass is to limit the upper limit of the high-pressure main steam pressure. At this time, immediately raise the pressure setpoint of the bypass to the pressure setpoint for load control (determined by the APS control system) plus about 0.5 MPa, gradually close the high-pressure bypass valve, and ensure that the high-pressure bypass valve remains fully closed during the normal operation stage of the unit.

[0092] Furthermore, to prevent overpressure, if the steam pressure rises to the setpoint of the backup pressure, the bypass control valve will open to release the pressure easily.

[0093] In one embodiment, as Figures 7 to 8 shown, the opening condition of the high-pressure main steam regulating valve is that all high-pressure bypass valves are closed and the steam turbine meets the corresponding steam inlet conditions under cold, warm, and hot states, or the gas turbine load > 50%;

[0094] The opening condition of the intermediate-pressure main steam regulating valve is that all intermediate-pressure bypass valves are closed and the steam turbine meets the corresponding steam inlet conditions under cold, warm, and hot states, or the gas turbine load > 50%;

[0095] The opening condition of the low-pressure main steam regulating valve is that all low-pressure bypass valves are closed and the steam turbine meets the corresponding steam inlet conditions under cold, warm, and hot states, or the gas turbine load > 50%.

[0096] In one embodiment, when the circulating unit shuts down due to normal or emergency situations, the method further includes:

[0097] When the unit shuts down normally or emergently, control the low-pressure main steam regulating valve to close sequentially starting from the current opening;

[0098] After logically judging that the low-pressure main steam regulating valve is at 30% opening, close the high-pressure main steam regulating valve and the intermediate-pressure main steam regulating valve in logical sequence;

[0099] During the closing process of each regulating valve, as the pressure of the main steam pipeline increases, control each bypass valve to open first and then close.

[0100] It should be noted that during the normal or emergency shutdown process of the unit, the low-pressure main steam regulating valve will be programmed to close starting from the current opening. When the low-pressure main steam regulating valve starts to close sequentially, the low-pressure bypass starts to act logically. When it is logically judged that the low-pressure regulating valve reaches 30% opening, the high-pressure main steam regulating valve is closed in logical sequence, and the high- and intermediate-pressure bypasses start to act logically.

[0101] During the closing process of each main steam regulating valve, the pressure of the main steam pipeline increases, the bypass valves gradually open to release the pressure. As the load decreases, the flue gas heat entering the waste heat boiler gradually decreases, and the bypass valves start to close slowly to maintain the main steam pressure before the bypass.

[0102] In particular, after shutdown, for the steam drum in the heat preservation and pressure maintenance state, its pressure basically remains unchanged, slightly higher than the bypass setpoint.

[0103] This embodiment realizes the switching of steam pressure control, from bypass control to steam turbine control for steam pressure, and is designed with a bypass sequential closing function.

[0104] In one embodiment, the output of the proportional-integral PI controller is within the (H, L) interval, where H is the high limit and L is the low limit;

[0105] During normal operation, the upper and lower limits of the output of the proportional-integral (PI) controllers corresponding to the high-pressure bypass valve and the intermediate-pressure bypass valve are (102, -2), and the upper and lower limits of the output of the PI controller corresponding to the low-pressure bypass valve are (102, -5).

[0106] It should be noted that in this embodiment, by setting the upper and lower limits of the PI controller output, the opening of the bypass valve acts between fully open and fully closed, realizing the corresponding coordination of the bypass opening under various working conditions.

[0107] In one embodiment, the method further includes:

[0108] Under abnormal working conditions, the lower limit of the output of the proportional-integral (PI) controller is used as the low valve position forced value and delayed for 5 s.

[0109] Specifically, the abnormal working conditions in this embodiment include but are not limited to TRIP, load rejection, and OPC action, etc. When an abnormal working condition occurs, the control logic forces the lower limit to be the low valve position forced value and delays for 5 s.

[0110] Since the output of the PI controller is controlled by the upper and lower limit functions, the output can only be greater than or equal to the current logic forced value. Therefore, the bypass valve is quickly forced to open at the specified opening according to the logic within 5 s after the generator grid-connected switch is disconnected. After 5 s, the lower limit returns to the original value and the output of the PI controller is normal. By controlling the opening of the bypass valve through proportional-integral control, the main steam pressure PV before the bypass is maintained at the actual value at the moment when the high-pressure bypass regulating valve opens.

[0111] In one embodiment, as Figure 9 shown, when the abnormal working condition is load rejection, the method further includes:

[0112] Controlling the low valve position forced values of each bypass valve at the moment of load rejection as a function of the main steam flow rate at the same moment.

[0113] In one embodiment, the method further includes:

[0114] When the condenser protection condition is established, the intermediate-pressure bypass valve and the low-pressure bypass valve are forced to close.

[0115] It should be noted that through the intermediate- and low-pressure bypass control with the condenser protection logic, when the condenser protection condition is established, the intermediate- and low-pressure bypass valves are forced to close to prevent the condenser from being damaged under abnormal working conditions.

[0116] In addition, as Figures 10 to 11 shown, the second embodiment of the present invention also proposes a steam pressure control system for a combined cycle unit under APS input, and the system includes:

[0117] An acquisition module 10, configured to acquire the main steam pressure value before the valve of each bypass and the outlet pressure of the high-pressure superheater at startup based on a startup instruction issued by a combined cycle unit;

[0118] A judgment module 20, configured to judge whether the outlet pressure of the high-pressure superheater exceeds the set condition for the input of each bypass control;

[0119] A first setting module 30, configured to, when the judgment result of the judgment module is yes, set the minimum pressure set value of the corresponding bypass to the value of the function F(x) of the gas turbine load and the high-pressure cylinder metal temperature;

[0120] A second setting module 40, configured to, when the judgment result of the judgment module is no, set the minimum pressure set value of the corresponding bypass to the actual value of the main steam pressure before the valve of this bypass, and increase linearly with the pipeline pressure;

[0121] A control module 50, configured to use the difference between the actual value of the main steam pressure before the valve of each bypass and the minimum voltage set value of this bypass as the input of the corresponding proportional-integral (PI) controller respectively, and use the output of the proportional-integral (PI) controller to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve.

[0122] It can be understood that in this embodiment, by setting a minimum pressure control module, the minimum pressure control module includes the above-mentioned acquisition module, judgment module, first setting module, second setting module and control module, and is used to control the startup process of the APS system. After the unit issues a startup instruction, as the gas turbine purging process ends, the gas turbine ignites.

[0123] Before ignition, this control system still stays in the actual pressure tracking module stage. After ignition, this control system enters the minimum pressure control module.

[0124] Since the main steam pressure parameters are different at startup, if the main steam pressure is high at this time and meets the conditions of the aforementioned stage two, the setpoint is directly set to the value of the gas turbine load function; if the pressure is low and does not meet the conditions of stage two, then wait for the pipeline to naturally boost pressure, and the setpoint increases as the pipeline pressure rises.

[0125] When transitioning from the actual pressure mode to the minimum pressure mode, the setpoint changes stepwise from the pressure value before the bypass at the moment when the high-pressure regulating valve closes during the shutdown process to the actual value of the pressure before the bypass after ignition. As the unit warms up, increases in pressure, and increases in load, the setpoint shows a slow upward trend. When the actual value PV (i.e., the actual pressure before the bypass) is greater than the setpoint, the input of the controller ΔP = PV - setpoint > 0, and the bypass valve opens wider; when the actual value PV is less than the setpoint, the input of the controller ΔP = PV - setpoint < 0, and the bypass valve closes smaller.

[0126] As the load of the unit varies, the setpoint makes corresponding function corrections, causing the main steam pressure PV before the bypass valve to change with the change of the setpoint.

[0127] In one embodiment, the control system further includes a preliminary pressure control module for implementing the following steps:

[0128] When the main steam pressure parameters of each bypass meet the steam admission conditions of the steam turbine, open the high-pressure main steam regulating valve, the intermediate-pressure main steam regulating valve, and the low-pressure main steam regulating valve;

[0129] Control the minimum pressure setpoint of each bypass to be higher than the actual value of the main steam pressure before the valve of each bypass, so that the opening degree of each bypass valve becomes smaller until it is in a closed state.

[0130] It should be noted that during the normal operation of the unit, when the main steam pressure of each path meets the steam admission conditions of the steam turbine, the high- and intermediate-pressure main steam regulating valves open. At this time, under the action of this control system, the bypass valve gradually closes as the regulating valve opens wider until it is fully closed. When the bypass valve is fully closed and the load of the gas turbine is greater than a certain value, this control system switches to the preliminary pressure control module.

[0131] After enabling the preliminary pressure control module, the pressure setpoint of the bypass valve is slightly higher than the actual pressure, and the input of the PI controller error = PV - setpoint < 0 is always negative. At this time, the bypass valve always remains fully closed, and the unit enters the stage of controlling the pressure by the main steam regulating valve.

[0132] To prevent overpressure, if the steam pressure rises to the setpoint of the backup pressure, the bypass control valve will open to release the pressure easily.

[0133] In one embodiment, the control system further includes an actual pressure tracking module for implementing the following steps:

[0134] During normal shutdown or emergency shutdown of the unit, control the low-pressure main steam regulating valve to close sequentially starting from the current opening degree;

[0135] After the logic determines that the low-pressure main steam regulating valve is at 30% opening, the high-pressure main steam regulating valve and the intermediate-pressure main steam regulating valve are closed in logical sequence;

[0136] During the closing process of each regulating valve, as the pressure in the main steam pipeline increases, control each bypass valve to open first and then close.

[0137] It should be noted that this pressure tracking module is used during the normal or emergency shutdown of the unit. The low-pressure main steam regulating valve will be programmed to close starting from the current opening. When the low-pressure main steam regulating valve starts to close sequentially, this control system controls the low-pressure bypass to enter the actual pressure tracking mode from the standby pressure mode, and the low-pressure bypass starts to act logically. When the logic determines that the low-pressure regulating valve reaches 30% opening, the high-pressure main steam regulating valve is closed in logical sequence. At this time, the high- and intermediate-pressure bypass systems also enter the actual pressure tracking mode from the standby pressure mode, and the high- and intermediate-pressure bypasses start to act logically. The increase in the pressure of the main steam pipeline caused by the closing of each main steam regulating valve causes the bypass valve to gradually open to release the pressure.

[0138] As the load decreases, the heat of the flue gas entering the waste heat boiler gradually decreases, and the bypass valve starts to close slowly again to maintain the main steam pressure before the bypass. After shutdown, for the steam drum in the heat preservation and pressure maintenance state, its pressure basically remains unchanged, slightly higher than the bypass setpoint.

[0139] It should be noted that for other embodiments or implementation methods of the steam pressure control system of the combined cycle unit under the APS input of the present invention, reference can be made to the above method embodiments, and details are not repeated here.

[0140] It should be noted that the logic and / or steps represented in the flowchart or described otherwise herein, for example, can be considered as a definite sequence list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch instructions from the instruction execution system, apparatus, or device and execute the instructions), or in combination with these instruction execution systems, apparatuses, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by or in combination with an instruction execution system, apparatus, or device. More specific examples (non-exhaustive list) of the computer-readable medium include the following: an electrical connection part (electronic device) having one or more wirings, a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or, if necessary, other suitable processing, and then stored in a computer memory.

[0141] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

[0142] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0143] Furthermore, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0144] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A steam pressure control method for a combined cycle unit under APS input, characterized in that The method includes: Based on the startup instruction issued by the combined cycle unit, obtaining the main steam pressure value before the valve of each bypass and the outlet pressure of the high-pressure superheater during startup; Judging whether the outlet pressure of the high-pressure superheater exceeds the set conditions for the input of each bypass control; If so, setting the minimum pressure set value of the corresponding bypass as the value of the function F(x) of the gas turbine load and the high-pressure cylinder metal temperature; If not, setting the minimum pressure set value of the corresponding bypass as the actual value of the main steam pressure before the valve of this bypass, and linearly increasing with the pipeline pressure; Taking the difference between the actual value of the main steam pressure before the valve of each bypass and the minimum voltage set value of this bypass as the input of the corresponding proportional-integral (PI) controller respectively, and using the output of the proportional-integral (PI) controller to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve, including: when the input of the proportional-integral (PI) controller is greater than zero, the proportional-integral (PI) controller outputs a control instruction to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve to increase; when the input of the proportional-integral (PI) controller is equal to zero, the proportional-integral (PI) controller outputs a control instruction to drive the bypass valve actuator to keep the opening of the corresponding bypass valve unchanged; when the input of the proportional-integral (PI) controller is less than zero, the proportional-integral (PI) controller outputs a control instruction to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve to decrease.

2. The steam pressure control method for a combined cycle unit under APS input according to claim 1, characterized in that, The main steam pressure values before the valves of each bypass include the high-pressure steam pressure value of the high-pressure bypass, the steam pressure value of the medium-pressure bypass, and the steam pressure value of the low-pressure bypass; The bypass valves include high-pressure bypass valves, medium-pressure bypass valves, and low-pressure bypass valves.

3. The steam pressure control method for a combined cycle unit under APS input according to claim 2, wherein, The set conditions include a first set value, a second set value, and a third set value respectively used for comparison with the high-pressure steam pressure value, the medium-pressure steam pressure value, and the low-pressure steam pressure value.

4. The steam pressure control method of the combined cycle unit under APS input according to claim 2, characterized in that, The method further includes: When the main steam pressure parameters of each bypass meet the steam admission conditions of the steam turbine, opening the high-pressure main steam regulating valve, the medium-pressure main steam regulating valve, and the low-pressure main steam regulating valve; Controlling the minimum pressure set value of each bypass to be higher than the actual value of the main steam pressure before the valve of each bypass, so that the opening of each bypass valve becomes smaller until it is in the closed state.

5. The steam pressure control method of a combined cycle unit under APS input according to claim 4, characterized in that, The opening condition of the high-pressure main steam regulating valve is: all high-pressure bypass valves are closed and the steam turbine meets the corresponding steam admission conditions in cold, warm, and hot states or the gas turbine load > 50%; The opening condition of the medium-pressure main steam regulating valve is: all medium-pressure bypass valves are closed and the steam turbine meets the corresponding steam admission conditions in cold, warm, and hot states or the gas turbine load > 50%; The opening condition of the low-pressure main steam regulating valve is: all low-pressure bypass valves are closed and the steam turbine meets the corresponding steam admission conditions in cold, warm, and hot states, or the gas turbine load > 50%.

6. The steam pressure control method for a combined cycle unit under APS input according to claim 2, characterized in that, The output of the proportional-integral (PI) controller is within the interval (H, L), where H is the high limit and L is the low limit; During normal operation, the high and low limits of the output of the proportional-integral (PI) controller corresponding to the high-pressure bypass valve and the medium-pressure bypass valve are (102, -2), and the high and low limits of the output of the proportional-integral (PI) controller corresponding to the low-pressure bypass valve are (102, -5).

7. The steam pressure control method for a combined cycle unit under APS input according to claim 4, characterized in that The method further includes: When the unit is shut down normally or emergently, control the low-pressure main steam regulating valve to close sequentially starting from the current opening; After the logic determines that the low-pressure main steam regulating valve is at an opening of 30%, close the high-pressure main steam regulating valve and the intermediate-pressure main steam regulating valve in logical sequence; During the closing process of each regulating valve, as the pressure in the main steam pipeline rises, control each bypass valve to open first and then close.

8. The steam pressure control method of the combined cycle unit under APS input according to claim 6, characterized in that, The method further includes: Under abnormal conditions, use the output lower limit of the proportional-integral (PI) controller as the low valve position forced value and delay for 5 s.

9. The steam pressure control method for a combined cycle unit under APS input according to claim 8, characterized in that, When the abnormal condition is load rejection, the method further includes: Control the low valve position forced value of each bypass valve at the moment of load rejection to be a function of the main steam flow rate at the same moment.

10. The steam pressure control method for a combined cycle unit under APS input according to claim 2, characterized in that, The method further includes: When the condenser protection condition is established, forcibly close the intermediate-pressure bypass valve and the low-pressure bypass valve.

11. A steam pressure control system for a combined cycle unit under APS input, characterized in that, The system includes: An acquisition module, configured to acquire the main steam pressure value in front of the valve of each bypass and the outlet pressure of the high-pressure superheater during unit startup based on the startup instruction issued by the combined cycle unit; A judgment module, configured to judge whether the outlet pressure of the high-pressure superheater exceeds the set condition for the input of each bypass control; A first setting module, configured to, when the judgment result of the judgment module is yes, set the minimum pressure set value of the corresponding bypass to the value of the function F(x) of the gas turbine load and the high-pressure cylinder metal temperature; A second setting module, configured to, when the judgment result of the judgment module is no, set the minimum pressure set value of the corresponding bypass to the actual value of the main steam pressure in front of the valve of this bypass and increase linearly with the pipeline pressure; A control module, configured to use the difference between the actual value of the main steam pressure in front of the valve of each bypass and the minimum voltage set value of this bypass as the input of the corresponding proportional-integral (PI) controller respectively, and use the output of the proportional-integral (PI) controller to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve, including: when the input of the proportional-integral (PI) controller is greater than zero, the proportional-integral (PI) controller outputs a control instruction to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve to increase; when the input of the proportional-integral (PI) controller is equal to zero, the proportional-integral (PI) controller outputs a control instruction to drive the bypass valve actuator to keep the opening of the corresponding bypass valve unchanged; when the input of the proportional-integral (PI) controller is less than zero, the proportional-integral (PI) controller outputs a control instruction to drive the bypass valve actuator to adjust the opening of the corresponding bypass valve to decrease.

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