A low-pressure cylinder peak shaving control system under micro-power operation

Abstract

This invention belongs to the field of energy and power engineering control technology, specifically relating to a peak-shaving control system for low-pressure cylinder low-output operation. This system uses a distributed control system as a platform and, without adding new hardware, achieves stable control of a 350 MW supercritical coal-fired unit under 20% rated load and below operating conditions through software logic reconfiguration. It includes: a refined steam flow control module, a low-output safety monitoring and closed-loop regulation module, a seamless operation mode switching control module, and a cold-end system collaborative optimization control module. Through software logic reconfiguration, this invention not only solves the problems of steam flow control instability, safety logic conflicts, and lack of cold-end coordination in 350 MW supercritical coal-fired units under deep peak-shaving conditions at 20% rated load and below, but also achieves high-precision micro-flow regulation, active safety protection, and stable operation under all operating conditions, significantly improving the unit's deep peak-shaving capability and operating economy.

Description

Technical Field

[0001] This invention belongs to the field of energy and power engineering control technology, specifically relating to a peak-shaving control system under low-pressure cylinder low-output operation. Background Technology

[0002] Driven by both the current energy structure transformation and the enhancement of power system flexibility, large coal-fired power generating units have become crucial for ensuring the safe and stable operation of the power grid by undertaking deep peak-shaving tasks. Among them, 350 MW supercritical coal-fired units, with their high thermal efficiency and relatively mature control systems, are widely deployed in load centers in central and eastern my country. These units are typically equipped with distributed control systems (DCS) for centralized monitoring and coordinated control of the boiler, turbine, and auxiliary systems. Under traditional operating conditions, the units mainly operate in pure condensing mode or conventional extraction steam heating mode. Their control logic is optimized around the high-flow steam path near the rated load, especially in the regulation of the low-pressure cylinder inlet steam. A common approach is to apply a single opening command to the regulating valve of the medium- and low-pressure connecting pipe to achieve linear regulation of the low-pressure cylinder's work capacity. This strategy exhibits good response characteristics and control stability in the medium- and high-load range, effectively meeting conventional dispatching requirements.

[0003] However, with the continuous increase in the proportion of new energy installed capacity, the power grid has placed higher demands on the peak-shaving capacity of thermal power units. Some regions have explicitly required 350 MW-class units to have the ability to operate continuously at 20% of rated load or even lower. Against this backdrop, the "micro-output" operation mode—where the low-pressure cylinder maintains only a very small steam flow (typically ranging from 10 t / h to 100 t / h) to provide necessary shaft cooling and exhaust temperature control—has become a key technical path for achieving deep peak shaving. However, existing control systems have not been adapted for this extreme condition and still use traditional control logic. However, traditional control logic still uses a linear regulation model suitable for high-flow-rate conditions. The resolution of its actuators and the sensitivity of its control algorithm decrease significantly in the micro-flow-rate domain, making it difficult for the actual steam intake to accurately track the setpoint, and easily leading to oscillations, hysteresis, or even runaway phenomena. More importantly, there is a fundamental conflict between the existing protection logic of traditional control logic and the goal of low-output operation: on the one hand, to prevent wet steam from eroding the last-stage blades under low load, the original design usually includes rigid protection measures such as "automatic interlocking to close the low-pressure steam inlet valve under low load" or "back pressure abnormality triggering trip"; on the other hand, the low-output mode precisely requires maintaining a small amount of steam flow to the low-pressure cylinder under extremely low load to avoid a sudden rise in exhaust temperature that could cause excessive thermal stress in the equipment. This inherent logical contradiction often forces the unit to shut down due to protection actions when attempting to enter the deep peak-shaving range, or forces operators to manually intervene and temporarily disable critical protection logic, thus introducing significant safety hazards.

[0004] Therefore, the existing control system faces three technical bottlenecks under low-output conditions: First, the control commands lack a layered decoupling mechanism, failing to separate large-scale cutoff from fine-tuning of small flow rates, resulting in amplified nonlinear characteristics of the actuator in the low-opening region; second, the safety monitoring model is still based on steady-state parameter relationships under normal operating conditions, failing to establish a perception and early warning mechanism applicable to special dynamic characteristics such as the evolution of exhaust temperature field and strong nonlinear coupling between inlet pressure and back pressure under extremely low flow rates; third, the operation mode switching process lacks state-driven logic isolation and fault-oriented safety design, causing mutual interference between the old and new control logics under boundary conditions, making it difficult to achieve a smooth transition. Correspondingly, when the unit load drops below 40%, the control system cannot accurately maintain the required small amount of steam intake, lacks the ability to actively suppress the abnormal upward trend of temperature in the last-stage blade region, and cannot coordinately optimize the operating parameters of the cold-end system while ensuring safety. On this basis, if manual experience is relied upon, it will not only be inefficient and slow to respond, but also easily lead to equipment damage or unplanned shutdowns due to judgment errors.

[0005] Therefore, how to achieve high-precision flow control, active safety protection, and cross-subsystem collaborative optimization of low-pressure cylinders under low-output conditions through intelligent adjustment strategies involving system-level control logic reconfiguration and multi-parameter coupling without changing the existing hardware architecture has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention provides a peak-shaving control system for low-pressure cylinder low-output operation, aiming to solve the technical problems of unstable steam intake control, conflicting safety protection logic, and lack of cold-end system coordination capabilities caused by the control logic not being adapted to the low-flow operation requirements of existing 350 MW supercritical coal-fired power units under deep peak-shaving conditions.

[0007] To achieve the above-mentioned objectives, this invention is based on a distributed control system. By constructing a refined steam flow control module, a low-output safety monitoring and closed-loop regulation module, a non-disruptive switching control module for operating modes, and a collaborative optimization control module for the cold-end system, a complete system is formed. This effectively ensures that the unit achieves high-precision flow regulation, active safety protection, and stable operation under low-output conditions at 20% rated load and below.

[0008] This invention provides a peak-shaving control system for low-pressure cylinder low-output operation. This system uses a distributed control system as a platform and, without adding new hardware, achieves stable control of a 350 MW supercritical coal-fired unit at 20% rated load or below through software logic reconfiguration. The system includes:

[0009] The steam inlet flow fine control module is used to achieve fine adjustment of the steam inlet flow.

[0010] The low-output safety monitoring and closed-loop regulation module is used to actively suppress abnormal increases in exhaust steam temperature;

[0011] The operation mode seamless switching control module is used to shield the conflict protection logic and ensure smooth mode transition;

[0012] The cold-end system collaborative optimization control module is used to dynamically adjust the condenser back pressure to the economic operating range.

[0013] Preferably, the refined steam flow control module achieves refined adjustment of the steam flow based on a dual-channel command allocation mechanism. This mechanism works as follows: when the distributed control system receives a deep peak-shaving command and the current electrical load command is below a preset threshold, the distributed control system calculates the target steam flow for the low-pressure cylinder and sends this flow to the flow segmentation processing unit. The flow segmentation processing unit then divides the target steam flow into a coarse adjustment range or a fine adjustment range according to a preset flow boundary point. For the coarse adjustment range, a rapid cut-off command is output to the main execution unit, which is a high-flow-capacity regulating valve on the medium-low pressure connecting pipe. For the fine adjustment range, a high-precision adjustment command is generated and dynamically corrected by a proportional-integral-derivative controller before being output to the fine-tuning execution unit. The fine-tuning execution unit is a small-flow-capacity regulating valve independently configured in the bypass of the main execution unit, and its opening degree is linearly related to the flow area.

[0014] Preferably, the flow rate range of the fine-tuning interval is from 10t / h to 100t / h; the input of the proportional-integral-derivative controller is the deviation between the actual steam flow feedback signal and the set value of the fine-tuning interval, and its output directly acts on the opening control loop of the fine-tuning execution unit to achieve stable regulation without oscillation.

[0015] Preferably, the steps of the micro-output safety monitoring and closed-loop regulation module to actively suppress abnormal rises in exhaust steam temperature are as follows:

[0016] The system acquires the low-pressure cylinder inlet steam pressure signal, the last-stage blade region exhaust steam temperature signal, and the condenser vacuum signal in real time. The low-pressure cylinder inlet steam pressure signal is provided by three redundantly arranged pressure transmitters, and its validity is determined by a three-out-of-two voting logic. The last-stage blade region exhaust steam temperature signal is acquired by a multi-point thermocouple array and then filtered and trend analyzed. The condenser vacuum signal is used to participate in the determination of the back pressure safety boundary.

[0017] When the exhaust temperature signal in the last-stage blade region shows a continuous upward trend and approaches the dynamic threshold, the negative feedback regulation loop is activated, outputting a water spray desuperheating control command and simultaneously slightly increasing the opening command of the fine-tuning execution unit. At the same time, a monitoring model for the difference between the low-pressure cylinder inlet pressure and the condenser vacuum is established. When the pressure difference exceeds the safe operating range of this difference monitoring model, the low-output operation mode is forcibly exited and the normal control logic of the main execution unit is restored. The safe operating range of this difference monitoring model is derived from historical data statistics.

[0018] Preferably, the low-output safety monitoring and closed-loop regulation module has a built-in dynamic temperature threshold curve, which is updated in real time according to the ambient temperature, circulating water inlet temperature and unit load rate; the exhaust temperature signal of the last stage blade area is analyzed by a trend analysis algorithm module, which uses the sliding window least squares method to fit the slope of temperature change, and when the slope is greater than the preset threshold, it is determined to be a continuous upward trend.

[0019] Preferably, the operation mode seamless switching control module includes five discrete states: normal heating mode, preparing to enter low-output mode, low-output operation mode, preparing to exit low-output mode, and emergency reset mode, wherein:

[0020] When preparing to enter the low-output mode, the original protection logic of "automatic interlocking to close the low-pressure steam inlet valve under low load" and "tripping triggered by abnormal back pressure" is temporarily disabled by setting the internal software flag, and the dedicated control logic for low output is loaded.

[0021] In emergency reset mode, all software control outputs are forcibly cleared and a full-open command is sent to the main execution unit and the fine-tuning execution unit.

[0022] Preferably, the conditions for switching from the conventional heating mode to the low-output mode include: the electrical load command is below 40% of the rated load for three consecutive control cycles, the furnace pressure fluctuation is less than ±200Pa, the main steam temperature deviation is less than ±5℃, the main steam pressure is 16.7±0.3MPa, and the main steam temperature is 571±5℃. Before switching to the low-output operation mode, it is also necessary to confirm that the valve position feedback is normal, the temperature field is stable, and the pressure difference is within the safe range.

[0023] Preferably, in the low-output operation mode, the cold-end system collaborative optimization control module architecture calculates the optimal back pressure target value based on the current exhaust steam heat load, ambient temperature, and circulating water system operating parameters using a built-in back pressure optimization algorithm. This target value is limited to between 1.5 kPa and 2.0 kPa. The optimal back pressure target value is then input as a setpoint to the condenser pressure control loop.

[0024] The condenser pressure control loop consists of an outer loop and an inner loop forming a cascade structure. The outer loop is a back pressure setpoint tracking loop, and its outer loop controller receives the deviation between the actual back pressure feedback signal and the optimal back pressure target value, and outputs the setpoint of the inner loop. The inner loop is a circulating water flow and vacuum capacity adjustment loop, and its actuators include the cooling tower fan frequency converter and the baffle electric actuator.

[0025] Preferably, when the ambient temperature is below the antifreeze threshold, the cold end system collaborative optimization control module maintains the minimum circulating water volume to prevent the cold end from freezing, and adjusts the vacuum system to make the actual back pressure approach the optimal back pressure target value; when the ambient temperature is above the antifreeze threshold, the cold end system collaborative optimization control module optimizes the cooling tower fan speed and the baffle opening with minimizing the plant power consumption as the optimization goal.

[0026] Preferably, each functional module is deployed in the distributed control system as an independent functional block group. The target steam inlet flow rate, exhaust steam temperature trend slope, differential pressure safety status flag, current operating mode code and optimal back pressure target value are exchanged through a shared memory area. All logical operations are completed within the cycle scan time of the distributed control system. A self-diagnostic unit is configured to monitor the effectiveness of the execution unit feedback, the saturation state of the control loop output and abnormal state transition conditions. In case of a fault, a degraded operation strategy or a safe shutdown procedure is triggered.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention achieves high-precision flow control, active safety protection, disturbance-free mode switching, and cold-end system collaborative optimization for low-pressure cylinders under low-output conditions by systematically reconstructing the internal logic of a distributed control system without altering the existing hardware architecture. This system completely resolves the technical bottlenecks caused by amplified nonlinear characteristics, conflicting protection logic, and isolated subsystem operation under extremely low loads in traditional control logic. It significantly improves the operational safety, stability, and economy of 350 MW-class supercritical coal-fired power units under deep peak-shaving conditions, providing reliable technical support for new power systems that adapt to high-proportion renewable energy integration in thermal power units. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the overall structure of a peak-shaving control system under low-pressure cylinder low-output operation in this invention;

[0031] Figure 2 This is a logic block diagram of the refined steam flow control module in this invention;

[0032] Figure 3 This is a schematic diagram of the signal processing and control flow of the micro-output safety monitoring and closed-loop regulation module in this invention;

[0033] Figure 4 This is the state transition diagram of the operation mode seamless switching control module in this invention;

[0034] Figure 5 This is a schematic diagram of the cascade control structure of the cold-end system collaborative optimization control module in this invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] like Figure 1-5As shown, this invention provides a peak-shaving control system for low-pressure cylinder low-output operation. Its core lies in achieving stable, safe, and efficient operation of a 350 MW supercritical coal-fired unit under deep peak-shaving conditions at or below 20% rated load, without adding new hardware, through software logic reconfiguration and system-level integration. The system uses a Distributed Control System (DCS) as its platform, dividing the control logic into four functional modules: a refined steam flow control module, a low-output safety monitoring and closed-loop regulation module, a seamless switching control module for operating modes, and a collaborative optimization control module for the cold-end system. Each module is deployed as an independent functional block within the DCS, exchanging key variables through a shared memory area and completing all logical operations within the DCS's periodic scan time, ensuring the real-time performance and determinism of control commands.

[0038] like Figure 2 As shown, the implementation of the refined steam inlet flow control module is as follows: When the distributed control system receives a deep peak-shaving command from the dispatching side, and the current electrical load command remains below a preset threshold, the distributed control system calculates the target steam inlet flow required by the low-pressure cylinder based on the boiler main control output signal and the built-in turbine thermodynamic model. This target steam inlet flow signal is sent to the flow segmentation processing unit, which divides the total flow demand into a coarse adjustment range and a fine adjustment range according to a preset flow boundary point. Here, the preset flow boundary point is set to 100 t / h, the coarse adjustment range is set to a range greater than 100 t / h, and the fine adjustment range is set to a range from 10 t / h to 100 t / h.

[0039] In this embodiment of the application, the preset threshold is 40% of the rated load.

[0040] For flow requirements within the coarse adjustment range, the logic unit generates a rapid cut-off command, which is transmitted to the main execution unit via a digital data acquisition card. The main execution unit is a large-flow-capacity regulating valve originally configured on the medium- and low-pressure connecting pipe, and its structural design is suitable for large-flow regulation within the conventional load range. For flow requirements within the fine adjustment range, the logic unit generates a high-precision adjustment command, which is sent to a proportional-integral-derivative (PID) controller for real-time dynamic correction. The input of the PID controller is the deviation between the actual inlet steam flow feedback signal and the fine adjustment range setpoint. Its output directly acts on the opening control loop of the fine adjustment execution unit, thereby ensuring linear, controllable, and oscillation-free stable regulation within a small flow range of 0 t / h to 100 t / h. The fine adjustment execution unit is a small-flow-capacity regulating valve independently configured in the bypass of the main execution unit. Its valve core adopts a linear characteristic design, and the flow area and opening degree have a strictly linear relationship, ensuring oscillation-free, high-response stable regulation within a small flow range. This dual-channel structure effectively avoids the control instability problem caused by the nonlinear characteristics of a single regulating valve in the low opening region, and achieves seamless connection from normal load to low output conditions.

[0041] like Figure 3 As shown, the implementation method of the micro-output safety monitoring and closed-loop regulation module is as follows: the analog input module in the distributed control system is used to collect three types of key signals in real time: the low-pressure cylinder inlet pressure signal, the exhaust temperature signal of the last stage blade area, and the condenser vacuum signal.

[0042] The low-pressure cylinder inlet steam pressure signal is provided by three redundantly arranged pressure transmitters. The validity of the signal is determined by a three-out-of-two voting logic. The pressure signal is considered valid and used for subsequent logic judgment only when the deviation between any two channel values ​​is less than the preset tolerance.

[0043] In this embodiment of the application, the preset tolerance is ±0.5kPa.

[0044] The exhaust temperature signal in the last-stage blade region originates from a multi-point thermocouple array arranged behind the last-stage moving blade of the low-pressure cylinder. This multi-point thermocouple array contains no fewer than six measuring points, which are evenly distributed along the circumference. The collected raw temperature data is first subjected to noise suppression through a first-order inertial filter, and then input to the trend analysis algorithm module. This trend analysis algorithm module uses the sliding window least squares method to fit the slope of the temperature change in order to characterize the evolution of the temperature field.

[0045] The condenser vacuum signal is provided by a high-precision absolute pressure transmitter, which has a measurement range of 0-10 kPa and an accuracy class of no less than 0.1, and is simultaneously used to determine the back pressure safety boundary.

[0046] The low-output safety monitoring and closed-loop control module has a built-in dynamic temperature threshold curve. This curve uses ambient temperature, circulating water inlet temperature, and unit load rate as independent variables and is updated in real time through table lookup interpolation or polynomial fitting. When the exhaust temperature monitoring value in the last-stage blade region shows a continuous upward trend and approaches the dynamic threshold, the temperature field monitoring algorithm does not trigger the trip protection but instead prioritizes activating the negative feedback control loop. Here, the continuous upward trend refers to an exhaust temperature change slope greater than the preset threshold of 0.5℃ / min.

[0047] The negative feedback regulation loop outputs a water spray de-cooling control command to the low-pressure cylinder water spray device, and simultaneously adds a 2% micro-increment to the opening command of the fine-tuning execution unit to increase the micro-steam flux, thereby suppressing the abnormal rise in exhaust steam temperature by increasing convective heat transfer.

[0048] Furthermore, the micro-output safety monitoring and closed-loop regulation module of this invention also includes a monitoring model for the difference between the low-pressure cylinder inlet steam pressure and the condenser vacuum. This difference monitoring model sets a safe operating range, which is derived from historical operating data. Its upper and lower limits correspond to the maximum allowable pressure difference under different load rates. Once the real-time calculated pressure difference exceeds this range, the logic judgment unit immediately generates a forced exit command for the micro-output mode. This forced exit command will cut off the control output of the fine-tuning execution unit and restore the normal control logic of the main execution unit, ensuring that the coal-fired unit system returns to a safe operating state.

[0049] like Figure 4As shown, the seamless switching control module for operating modes employs a multi-state automatic switching approach to construct its control logic framework. This framework defines five discrete states: normal heating mode, preparing to enter low-output mode, low-output operation mode, preparing to exit low-output mode, and emergency reset mode. Initially, the seamless switching control module is in normal heating mode. In this state, the existing low-load interlock protection logic is activated, including "automatic interlocking to close the low-pressure steam inlet valve under low load" and "back pressure abnormality triggering trip." When the seamless switching control module determines that the electrical load command is below 40% of the rated load for three consecutive control cycles, and the boiler combustion is stable and the main steam parameters meet the switching conditions, the state transition condition is met, and the seamless switching control module automatically switches to preparing to enter low-output mode. Stable boiler combustion is characterized by furnace pressure fluctuations of less than ±200 Pa and main steam temperature deviations of less than ±5℃. Meeting the switching conditions for main steam parameters is characterized by main steam pressure at 16.7 ± 0.3 MPa and main steam temperature at 571 ± 5℃. In this transitional state, the logic shielding module is triggered. This module temporarily shields the original protection logic by setting an internal software flag. The shielding operation only affects the internal logic judgment of the distributed control system and does not affect the physical connection of the hard-wired protection circuit. Simultaneously, the dedicated low-output control logic is loaded and initialized, including the pre-configuration of dual-channel flow control parameters, safety monitoring thresholds, and cold-end collaborative setpoints. Once all preconditions are met, the system enters the low-output operation mode. At this time, the refined steam flow control module and the low-output operating condition safety monitoring and closed-loop regulation module are fully effective. Preconditions include valve position feedback confirmation, temperature field stability, and differential pressure within the safe range.

[0050] When the system is in low-output operation mode, if the operation mode seamless switching control module determines that the electrical load command is higher than 40% of the rated load for three consecutive control cycles, or receives a manual exit command from the operator, and the unit's main steam parameters, boiler combustion status, and key monitoring parameters of the low-pressure cylinder all return to the stable range, then the state transition condition is met, and the operation mode seamless switching control module automatically switches to prepare to exit the low-output mode. In this transitional state, the dedicated low-output control logic gradually exits output, the logic shielding module gradually resets the software flags, the original low-load interlock protection logic is gradually restored and activated according to the time sequence, and simultaneously, the dual-channel flow control smoothly switches back to the main execution unit control, ensuring a smooth and impact-free exit process. After all switching processes are completed and the unit's operating status is completely stable, the operation mode seamless switching control module automatically returns to the normal heating mode.

[0051] If a control power loss signal or turbine trip signal is detected in any operating state, the system immediately enters emergency reset mode via a hard-wired input to the DI input module of the distributed control system. In this mode, all software control outputs are forcibly cleared to zero, and a full-open command is sent to the main execution unit and the fine-tuning execution unit (outputting a high-level signal through the DO output module) to ensure that the medium and low pressure connecting pipes restore maximum flow capacity and prevent overpressure in the exhaust system due to valve malfunction. The entire mode switching process is recorded by a status register, including the status code, switching timestamp, and trigger conditions. This information is uploaded to the human-machine interface via the OPC protocol to display the current status and switching reason in real time, ensuring operational transparency and traceability for real-time monitoring and post-event traceability by operators.

[0052] like Figure 5 As shown, the implementation of the cold-end system collaborative optimization control module is as follows: In the low-output operation mode, the cold-end system collaborative optimization control module calculates the optimal back pressure target value under the current operating conditions based on the current exhaust steam heat load, ambient temperature, and circulating water system operating parameters using a built-in back pressure optimization algorithm. This back pressure optimization algorithm uses minimizing the plant power consumption rate as the objective function, with constraints including the condenser heat transfer end difference, circulating water pump power characteristics, and cooling tower fan efficiency curves. After iterative solution, it outputs the optimal back pressure target value, limited to a range of 1.5 kPa to 2.0 kPa. This optimal back pressure target value is used as the setpoint and input to the condenser pressure control loop. The condenser pressure control loop consists of an outer loop and an inner loop forming a cascade structure. The outer loop is the back pressure setpoint tracking loop, whose controller receives the deviation between the actual back pressure feedback signal and the optimal back pressure target value, and outputs the setpoint of the inner loop. The inner loop is the circulating water flow and vacuum capacity adjustment loop, whose actuators include the cooling tower fan frequency converter and the baffle electric actuator. When the ambient temperature is below the preset antifreeze threshold, the cold-end system collaborative optimization control module prioritizes maintaining the minimum circulating water volume to prevent cold-end icing. Simultaneously, it adjusts the number of operating vacuum system units or the frequency of the water jet pumps to bring the actual back pressure close to the optimal target value. When the ambient temperature is above the antifreeze threshold, the cold-end system collaborative optimization control module optimizes by minimizing plant power consumption, dynamically adjusting the cooling tower fan speed and baffle opening to ensure stable condenser back pressure within the economic range. The cooling tower fan frequency converter receives a 4-20mA analog signal from the inner loop controller to adjust the fan speed; the baffle electric actuator receives a pulse width modulation (PWM) signal to control the baffle opening. Both interact in real-time with the cold-end system collaborative optimization control module via a data bus, ensuring that the cold-end system response is synchronized with the turbine control. This collaborative optimization control effectively avoids the back pressure deviation from the economic range caused by independent operation of the cold-end system in traditional control systems, significantly improving thermal economy under low-output conditions.

[0053] In this embodiment, the preset antifreeze threshold is 5°C, and the minimum circulating water volume is 30% of the design flow rate.

[0054] In a preferred embodiment of the present invention, the peak-shaving control system is deployed as independent functional blocks within the distributed control system. Each functional block is written in Structured Text or Function Block Diagram language conforming to the IEC 61131-3 standard. Key variables, including target inlet steam flow, exhaust steam temperature change slope, differential pressure safety range, current operating mode status, and optimal back pressure target value, are exchanged between modules via a shared memory area. The shared memory area employs a double-buffering mechanism to ensure data read / write consistency. All logical operations are completed within the periodic scan time of the distributed control system, with a typical scan cycle of 100ms, ensuring the real-time performance and determinism of control commands. The peak-shaving control system is also equipped with a self-diagnostic unit, which periodically performs the following checks: the validity of feedback signals from each execution unit, whether the control loop output is saturated, and whether the state transition conditions are abnormal. Upon detecting a fault, the self-diagnostic unit immediately triggers a degraded operation strategy or a safe shutdown procedure, and records the fault code and timestamp to the historical database.

[0055] In this embodiment, the validity of the feedback signal of each execution unit refers to whether the signal passes the signal range verification and rate of change limit; whether the control loop output is saturated refers to whether the output value reaches the upper or lower limit; and the abnormal state transition condition is that the condition is not met for a long time or is frequently switched.

[0056] In this embodiment, the downgraded operation strategy is to switch to single-channel control, and the safe shutdown procedure is to issue an alarm and start the emergency reset mode.

[0057] To verify the effectiveness of the technical solution of this invention, comparative experiments were conducted using the following embodiments and comparative examples. The experimental subject was a 350 MW supercritical coal-fired unit in a power plant. Before the modification, it used traditional control logic; after the modification, the peak-shaving control system of this invention was applied. The experimental conditions were set as follows: the unit operated stably at 20% of its rated load for 4 hours.

[0058] In one specific embodiment, the peak-shaving control system of the present invention is applied to the coal-fired unit. During low-output operation, the steam flow rate of the low-pressure cylinder is stably controlled at 85 tons / hour, with a fluctuation range of ±2 tons / hour; the exhaust steam temperature is maintained at 78°C without a continuous upward trend; the condenser back pressure is stable at 1.75 kPa; no protection actions are triggered, and the mode switching process is smooth and undisturbed.

[0059] In a comparative example, the coal-fired unit used the traditional control logic before the modification. Under the same load conditions, due to the nonlinear characteristics of the single regulating valve in the low opening range, the steam flow fluctuated drastically, ranging from ±15 tons / hour; the exhaust temperature began to rise continuously after 2 hours of operation, reaching 92°C after 3 hours, triggering the trip protection and causing an unplanned shutdown; the condenser back pressure fluctuated between 1.2 and 2.3 kPa, and the plant power consumption was 12% higher than that of the example.

[0060] The table below summarizes the key performance indicators of the embodiments and comparative examples:

[0061]

[0062] Experimental data show that the peak-shaving control system described in this invention significantly improves flow control accuracy, temperature field stability, and overall system safety under low-pressure cylinder low-output operating conditions, effectively avoiding unplanned shutdowns caused by mismatched control logic, while also optimizing the economic efficiency of cold-end operation.

[0063] In summary, this invention forms a complete and engineerable system by constructing a refined steam flow control module, a low-output safety monitoring and closed-loop regulation module, a seamless operation mode switching control module, and a cold-end system collaborative optimization control module within a distributed control system. This system is entirely based on software logic, requiring no additional hardware. By simply reconstructing and integrating existing control logic, it enables 350 MW supercritical coal-fired power units to achieve high-precision flow regulation, active safety protection, and full-condition operational stability under deep peak-shaving conditions at 20% rated load and below. This provides reliable technical support for new power systems where thermal power units adapt to a high proportion of renewable energy integration.

[0064] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A peak-shaving control system for low-pressure cylinder low-output operation, characterized in that, This system uses a distributed control system as its platform and achieves stable control of a 350 MW supercritical coal-fired power unit at 20% rated load or below through software logic reconfiguration without adding new hardware. The system includes: The steam inlet flow fine control module is used to achieve fine adjustment of the steam inlet flow. The low-output safety monitoring and closed-loop regulation module is used to actively suppress abnormal increases in exhaust steam temperature; The operation mode seamless switching control module is used to shield the conflict protection logic and ensure smooth mode transition; The cold-end system collaborative optimization control module is used to dynamically adjust the condenser back pressure to the economic operating range.

2. The peak-shaving control system under low-pressure cylinder micro-output operation according to claim 1, characterized in that, The steam inlet flow fine control module realizes fine adjustment of steam inlet flow based on the dual-channel command allocation mechanism. The dual-channel command allocation mechanism is as follows: when the distributed control system receives a deep peak shaving command and the current electrical load command is lower than the preset threshold, the distributed control system calculates the target steam inlet flow of the low-pressure cylinder and sends the flow to the flow segmentation processing unit. The flow segmentation processing unit divides the target steam inlet flow into the coarse adjustment range or the fine adjustment range according to the preset flow boundary point. For the coarse adjustment range, a fast cut-off command is output to the main execution unit, which is a large flow capacity regulating valve on the medium and low pressure connecting pipe; for the fine adjustment range, a high-precision adjustment command is generated and dynamically corrected by a proportional-integral-derivative controller before being output to the fine adjustment execution unit, which is a small flow capacity regulating valve independently configured in the bypass of the main execution unit, and its opening degree is linearly related to the flow area.

3. The peak-shaving control system under low-pressure cylinder micro-output operation according to claim 2, characterized in that, The flow rate range of the fine-tuning interval is from 10t / h to 100t / h; the input of the proportional-integral-derivative controller is the deviation between the actual steam flow feedback signal and the set value of the fine-tuning interval, and its output directly acts on the opening control loop of the fine-tuning execution unit to achieve stable regulation without oscillation.

4. The peak-shaving control system under low-pressure cylinder micro-output operation according to claim 1, characterized in that, The specific steps of the low-output safety monitoring and closed-loop regulation module to actively suppress abnormal rises in exhaust steam temperature are as follows: The system acquires the low-pressure cylinder inlet steam pressure signal, the last-stage blade region exhaust steam temperature signal, and the condenser vacuum signal in real time. The low-pressure cylinder inlet steam pressure signal is provided by three redundantly arranged pressure transmitters, and its validity is determined by a three-out-of-two voting logic. The last-stage blade region exhaust steam temperature signal is acquired by a multi-point thermocouple array and then filtered and trend analyzed. The condenser vacuum signal is used to participate in the determination of the back pressure safety boundary. When the exhaust temperature signal in the last-stage blade region shows a continuous upward trend and approaches the dynamic threshold, the negative feedback regulation loop is activated, outputting a water spray desuperheating control command and simultaneously slightly increasing the opening command of the fine-tuning execution unit. At the same time, a monitoring model for the difference between the low-pressure cylinder inlet pressure and the condenser vacuum is established. When the pressure difference exceeds the safe operating range of this difference monitoring model, the low-output operation mode is forcibly exited and the normal control logic of the main execution unit is restored. The safe operating range of this difference monitoring model is derived from historical data statistics.

5. A peak-shaving control system for low-pressure cylinder micro-output operation according to claim 4, characterized in that, The low-output safety monitoring and closed-loop regulation module has a built-in dynamic temperature threshold curve, which is updated in real time according to the ambient temperature, circulating water inlet temperature and unit load rate. The exhaust temperature signal in the last stage blade area is analyzed by a trend analysis algorithm module. This trend analysis algorithm module uses the sliding window least squares method to fit the slope of temperature change. When the slope is greater than the preset threshold, it is determined to be a continuous upward trend.

6. The peak-shaving control system under low-pressure cylinder micro-output operation according to claim 1, characterized in that, The seamless switching control module for operating modes includes five discrete states: normal heating mode, preparing to enter low-output mode, low-output operation mode, preparing to exit low-output mode, and emergency reset mode. When preparing to enter the low-output mode, the original protection logic of "automatic interlocking to close the low-pressure steam inlet valve under low load" and "tripping triggered by abnormal back pressure" is temporarily disabled by setting the internal software flag, and the dedicated control logic for low output is loaded. In emergency reset mode, all software control outputs are forcibly cleared and a full-open command is sent to the main execution unit and the fine-tuning execution unit.

7. A peak-shaving control system for low-pressure cylinder micro-output operation according to claim 6, characterized in that, The conditions for switching from the conventional heating mode to the low-output mode include: the electrical load command is below 40% of the rated load for three consecutive control cycles, the furnace pressure fluctuation is less than ±200Pa, the main steam temperature deviation is less than ±5℃, the main steam pressure is 16.7±0.3MPa, and the main steam temperature is 571±5℃. Before switching to the low-output operation mode, it is also necessary to confirm that the valve position feedback is normal, the temperature field is stable, and the pressure difference is within the safe range.

8. The peak-shaving control system under low-pressure cylinder micro-output operation according to claim 1, characterized in that, In the low-output operation mode, the cold-end system collaborative optimization control module architecture uses a distributed control system to calculate the optimal back pressure target value based on the current exhaust steam heat load, ambient temperature, and circulating water system operating parameters. This target value is limited to between 1.5 kPa and 2.0 kPa. The optimal back pressure target value is then input as the setpoint to the condenser pressure control loop. The condenser pressure control loop consists of an outer loop and an inner loop forming a cascade structure. The outer loop is a back pressure setpoint tracking loop, and its outer loop controller receives the deviation between the actual back pressure feedback signal and the optimal back pressure target value, and outputs the setpoint of the inner loop. The inner loop is a circulating water flow and vacuum capacity adjustment loop, and its actuators include the cooling tower fan frequency converter and the baffle electric actuator.

9. A peak-shaving control system for low-pressure cylinder micro-output operation according to claim 8, characterized in that, When the ambient temperature is below the antifreeze threshold, the cold end system collaborative optimization control module maintains the minimum circulating water volume to prevent the cold end from freezing, and adjusts the vacuum system to make the actual back pressure approach the optimal back pressure target value; when the ambient temperature is above the antifreeze threshold, the cold end system collaborative optimization control module optimizes the cooling tower fan speed and the baffle opening with minimizing the plant power consumption as the optimization goal.

10. A peak-shaving control system for low-pressure cylinder micro-output operation according to claim 1, characterized in that, Each functional module is deployed in the distributed control system as an independent functional block group. They exchange target steam inlet flow rate, exhaust steam temperature trend slope, differential pressure safety status flag, current operating mode code, and optimal back pressure target value through a shared memory area. All logical operations are completed within the cycle scan time of the distributed control system. A self-diagnostic unit is configured to monitor the effectiveness of the execution unit feedback, the saturation state of the control loop output, and abnormal state transition conditions. In case of a fault, a degraded operation strategy or a safe shutdown procedure is triggered.

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