Coal-fired power generation unit main steam pressure control method based on rapid AGC

Abstract

The invention relates to a coal-fired power generation unit main steam pressure control method adapting to rapid AGC, and belongs to the technical field of thermal power generation automatic control. The method comprises the following specific steps: judging whether the adjusting direction of a main steam pressure set value P2 is opposite to the change direction of a load instruction in real time, generating a correction signal when lagging occurs, resetting a reference point of a set value generation link, and forcibly enabling the adjusting direction of the reference point to be consistent with the load instruction; according to the main steam pressure deviation and the on-off state of the energy storage battery, a control mode is switched in a self-adaptive mode: when the battery is not put into use and the deviation is large, integral enhancement is triggered to rapidly suppress the deviation; and when the battery is put into use, the inertia time generated by the set value is prolonged, integral reinforcement is stopped, and boiler-side adjustment disturbance is reduced by using the quick power response characteristic of energy storage. According to the method, reverse adjustment in the variable load process is effectively eliminated, and the control quality of the main steam pressure under the rapid AGC working condition and the unit operation stability are improved.

Description

Technical Field

[0001] This invention belongs to the field of automatic control technology for thermal power generation, specifically relating to a method for controlling the main steam pressure of coal-fired power generating units based on fast AGC. Background Technology

[0002] The main steam pressure of a coal-fired power generating unit is a core parameter for measuring the energy balance between the boiler and the turbine, directly affecting the unit's operational safety, economy, and load response performance. The control method for main steam pressure under conventional coordinated control (CCS) is as follows:

[0003] Depending on the operating mode, main steam pressure control is divided into two modes: constant pressure and sliding pressure. In constant pressure mode, the operator sets a fixed main steam pressure setpoint, which is a manual control method. In sliding pressure mode, the main steam pressure changes automatically with the unit load command (or boiler command for units providing heating), generating a static value for the main steam pressure under each load command, called the sliding pressure curve, also known as the main steam pressure target value. To simulate the boiler load combustion and steam system heat exchange process, the sliding pressure curve or constant pressure setpoint is fitted with rate limiting and multi-stage hysteresis loops. The rate limiting and multi-stage hysteresis settings are then fitted according to the actual boiler pressure-starting process to generate the main steam pressure setpoint.

[0004] In the Coordinated Control System (CCS) mode, both boiler commands and turbine commands are in automatic mode. In this mode, the main steam pressure is regulated in a closed loop through the boiler commands. The main steam pressure setpoint and main steam pressure feedback are used to generate the boiler command adjustment amount through closed-loop control. This is combined with the unit load command to generate the boiler master control command. The boiler master control command adjusts the fuel quantity command and the air supply quantity command. Ultra-supercritical units synchronously adjust the feedwater flow command. The feedwater flow of subcritical units is regulated by balancing the steam drum water level without the need for the boiler master control command. Finally, the boiler main steam pressure regulation process is completed.

[0005] To further improve the AGC adjustment rate of the unit, the states of AGC commands are defined as dynamic and steady state. Steady state refers to the command fluctuating within a certain range based on a certain value, while dynamic refers to continuous climbing, descent, or changes in range exceeding the set custom amplitude within a certain period of time.

[0006] With the increase in the proportion of new energy in recent years and the formal implementation of the electricity market, the requirements for the frequency modulation of thermal power units have been raised. The AGC commands for the units are issued more frequently, with a wider command adjustment range and a larger limit range for the amplitude of a single command. The AGC commands change relatively fast while the set value of the main steam pressure lags significantly, resulting in a mismatch between the load command and the adjustment of the main steam pressure. When there are consecutive alternations between increasing and decreasing the load in the load command, there may be adverse situations such as the action directions of the load command and the set value of the main steam pressure being opposite, and a large deviation between the command and the feedback after the alternation of the load change direction. After configuring the energy storage battery system, the AGC adjustment rate of the unit can be significantly improved, enabling the AGC commands to be issued more frequently and the continuous adjustment of the load in a single direction to be larger. Currently, the research and application on the combined control of thermal power and energy storage mainly focus on power control content, and no corresponding adjustment has been made to the control strategy of the boiler main steam pressure on the coal-fired unit side, resulting in poor regulation quality of the main steam pressure on the coal-fired unit side after coupling the energy storage system. Summary of the Invention

[0007] Aiming at the above problems existing in the prior art, the purpose of the present invention is to provide a main steam pressure control method for coal-fired power generation units based on fast AGC.

[0008] The present invention provides the following technical solutions: A main steam pressure control method for coal-fired power generation units based on fast AGC, comprising the following steps: S1. By comparing the numerical relationship between the target value P0 of the main steam pressure and the real-time set value P2 and the change direction of P2, determine whether the adjustment of the main steam pressure set value lags behind the change of the load command, and generate a lag correction signal when it is determined to be lagging. S2. When it is determined that there is a lag, reset the calculation reference point of the main steam pressure set value to make its adjustment direction consistent with the change direction of the load command. S3. According to the deviation between the main steam pressure set value and the feedback value and the on-off state of the energy storage battery, switch different pressure control modes.

[0009] Furthermore, the specific process of S1 is as follows: Calculate the change rate R of the main steam pressure set value P2 P2 ; when P0 > P2 and R P2 < 0 or P0 < P2 and R P2 > 0, it is determined that the adjustment of the main steam pressure set value P2 lags, and a pulse signal is generated as the lag correction signal.

[0010] Furthermore, the duration of the pulse signal is 0.5 - 2 s.

[0011] Furthermore, the specific process of S2 is as follows: S2.1. After the main steam pressure setpoint lag pulse signal is issued, the rate limit on P0 is released, so that the value of the main steam pressure setpoint P1 before lag is equal to the current value of P0. S2.2. Pause the delayed calculation of P1 so that the value of P2 tracks the value of P1, thereby unifying the values ​​of P0, P1, and P2. S2.3. After the hysteresis correction signal ends, the normal rate limit and hysteresis calculation of P0 are restored based on a unified value.

[0012] Furthermore, in S2.2, when pausing the lag calculation, the output tracks the input to achieve a smooth switching of P2.

[0013] Furthermore, the specific process of S3 is as follows: S3.1. When the absolute value of the main steam pressure deviation is greater than the first threshold a and lasts for a first duration a1, the first-level deviation signal is triggered; S3.2. When the absolute value of the main steam pressure deviation is greater than the second threshold b and lasts for a second duration b1, the second-level deviation signal is triggered, where b > a; S3.3. Select the corresponding control strategy based on the level of the triggered deviation signal and the activation / deactivation status of the energy storage battery.

[0014] Furthermore, in S3.3, when the energy storage battery is not engaged and the first-level deviation signal is triggered, the integral action of the enhanced controller is strengthened, and the duration T of the strengthened integral action is calculated by the following formula: ; Where Δ is the absolute value of the main steam pressure deviation, and P is... i Main steam pressure rated upper limit, P o σ is the lower limit of the rated main steam pressure, W is the rated power of the unit, and σ is the gain coefficient, which is a constant between 0 and 1.

[0015] Furthermore, in S3.3, when the second-level deviation signal is triggered, the duration of the integral enhancement is extended based on the multiple of the second threshold b and the first threshold a.

[0016] Furthermore, when the energy storage battery is engaged, the following controls are executed: Increase the inertial time constant of the main steam pressure setpoint generation stage, and make the inertial time gain coefficient δ greater than 1; and stop enabling the controller's integral enhancement function.

[0017] Furthermore, the formula for calculating the inertial time gain coefficient δ is as follows: ; in, The load rate setting value for the energy storage battery. The setpoint for the variable load rate of the unit.

[0018] By employing the above-described technology, the beneficial effects of the present invention compared to the prior art are as follows: This invention eliminates the problem of reverse main steam pressure regulation caused by the rapid change of AGC load commands and the slow inertia of the main steam pressure setpoint, ensuring that the adjustment direction of the main steam pressure is always the same as the change direction of the load commands; and can further adjust the generation method of the main steam pressure setpoint and improve the regulation quality of the main steam pressure closed-loop control according to the operation of the energy storage battery. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the main steam pressure setpoint curve after applying the method of the present invention; Figure 2 This is a schematic diagram of the main steam pressure setpoint curve for the conventional method. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0022] Please see Figure 1-2 This invention provides a main steam pressure setpoint control method adapted to rapid AGC. Based on the conventional main steam pressure setpoint control method, it distinguishes the action direction of the main steam pressure setpoint at each calculation node under static target, speed limit, and multi-order inertial lag. When the adjustment direction of the main steam pressure setpoint is opposite to the change direction of the load command, the calculation of the main steam pressure setpoint is reversed to be consistent with the change direction of the load command.

[0023] The main steam pressure setpoint corresponding to the unit load command is defined as the main steam pressure target value P0. After speed limiting, it is called the main steam pressure setpoint before lag P1. The main steam pressure setpoint P2 is obtained through multi-order lag calculation.

[0024] The specific steps of the method of the present invention are as follows: S1. Differentiate the main steam pressure setpoint P2 and determine the rate R of the main steam pressure setpoint P2. P2 : ; If the rate is positive, it is defined as the main steam pressure setpoint increasing; if the rate is negative, it is defined as the main steam pressure setpoint decreasing. Compare the main steam pressure target value P0 with the main steam pressure setpoint P2. If P0 > P2 and the main steam pressure setpoint decreases, or if P0 < P2 and the main steam pressure setpoint increases, it is considered that the main steam pressure setpoint adjustment is lagging, and a 1s pulse is sent.

[0025] S2. The main steam pressure setpoint lag pulse signal is issued, the main steam pressure target value P0 is released from the rate limit, and the lag-before main steam pressure setpoint P1 is generated. The lag-before main steam pressure setpoint P1 directly switches to the value of the main steam pressure target value P0 at the time the lag pulse signal is issued. The lag pulse signal delays for one scan cycle before switching the lag-before main steam pressure setpoint P1 to the current output value, stopping the lag circuit calculation. The lag circuit output tracks the input, which is the lag-before main steam pressure setpoint P1 maintaining its current value. The main steam pressure setpoint P2 is kept at its current value to prevent interference caused by control signal jumps and achieve a smooth switching. After the 1-second pulse ends, the calculation direction of the main steam pressure setpoint is set. At this time, the main steam pressure target value P0, the main steam pressure setpoint before lag P1, and the main steam pressure setpoint P2 are the same value. Based on this, the main steam pressure target value P0 is recalculated for speed limit and lag, generating the main steam pressure setpoint before lag P1 and the main steam pressure setpoint P2. The reference point is reset again when the main steam pressure setpoint adjustment lag signal appears again.

[0026] S3. Determine the deviation between the main steam pressure setpoint and the feedback value: If the absolute value of the deviation is greater than a MPa, trigger the first deviation signal for main steam pressure stabilization after a delay of a1 time; if the absolute value of the deviation is greater than b MPa, trigger the second deviation signal for main steam pressure stabilization after a delay of b1 time, and b > a. Under the steady-state condition of the AGC command, the control modes are divided into the following three modes according to the operation of the energy storage battery: S3.1. If the energy storage battery is not engaged, a large deviation signal in the main steam pressure stability is triggered, and integral reinforcement is performed. If the first deviation signal is triggered, the integral time is set to τ seconds (or the integral coefficient n=60 / τ), and the action time T is: ; Δ: Absolute value of main steam pressure deviation; P i Main steam pressure rated upper limit; P o Main steam pressure lower limit; W: Rated power of the unit; σ: Gain coefficient, a constant between 0 and 1.

[0027] The second deviation signal trigger extends the action time according to the b / a ratio. During the integral enhancement process, the main steam pressure deviation decreases to within the value of a. When the large deviation signal disappears, the integral enhancement action is immediately stopped and the boiler command integral parameters are restored to their original values.

[0028] S3.2. Energy storage battery activation: Since energy storage can quickly replenish part of the active power difference, the operation of the energy storage battery reduces the consumption of the main steam pressure regulation margin and slows down the adjustment of the main steam pressure setpoint. Therefore, the inertia time of the main steam pressure setpoint is extended, and an inertia time gain coefficient δ is set, δ>1, to reduce the deviation between the main steam pressure setpoint and the feedback value. Furthermore, no integral enhancement is performed when the energy storage battery is activated, reducing the overshoot generated when the AGC load command changes direction. ; Where Rsoc: Energy storage battery load rate setting value; R: Unit variable load rate setting value.

[0029] Example: This example provides a main steam pressure setpoint control method adapted to rapid AGC, applicable to all coal-fired power generating units. This method was applied to a 1000MW ultra-supercritical unit. Based on conventional main steam pressure setpoint control methods, the action direction of the main steam pressure setpoint at each calculation node is distinguished under static target, speed limit, and multi-order inertial lag conditions. The sliding pressure curve of this unit is shown in the table below: Table 1 Static target values ​​for main steam pressure setting Unit load command Main steam pressure setpoint 0 8.67 300 8.67 400 11.31 500 13.97 600 16.79 750 21.18 1000 28.00

[0030] The main steam pressure setpoint corresponding to the unit load command is defined as the main steam pressure target value P0. After speed limiting, it is called the main steam pressure setpoint before lag P1. The main steam pressure setpoint P2 is obtained through third-order lag calculation. When the adjustment direction of the main steam pressure setpoint is opposite to the change direction of the load command, the calculation of the main steam pressure setpoint is reversed to be consistent with the change direction of the load command.

[0031] The specific steps of the method in this embodiment are as follows: S1. Differentiate the main steam pressure setpoint P2 and determine the rate R of the main steam pressure setpoint P2. P2 : ; If the rate is positive, it is defined as the main steam pressure setpoint increasing; if the rate is negative, it is defined as the main steam pressure setpoint decreasing. Compare the main steam pressure target value P0 with the main steam pressure setpoint P2. If P0 > P2 and the main steam pressure setpoint decreases, or if P0 < P2 and the main steam pressure setpoint increases, it is considered that the main steam pressure setpoint adjustment is lagging, and a 1s pulse is sent.

[0032] S2. The main steam pressure setpoint lag pulse signal is issued, the main steam pressure target value P0 is released from the rate limit, and the lag-before main steam pressure setpoint P1 is generated. The lag-before main steam pressure setpoint P1 directly switches to the value of the main steam pressure target value P0 at the time the lag pulse signal is issued. The lag pulse signal delays for one scan cycle before switching the lag-before main steam pressure setpoint P1 to the current output value, stopping the lag circuit calculation. The lag circuit output tracks the input, which is the lag-before main steam pressure setpoint P1 maintaining its current value. The main steam pressure setpoint P2 is kept at its current value to prevent interference caused by control signal jumps and achieve a smooth switching. After the 1-second pulse ends, the calculation direction of the main steam pressure setpoint is set. At this time, the main steam pressure target value P0, the main steam pressure setpoint before lag P1, and the main steam pressure setpoint P2 are the same value. Based on this, the main steam pressure target value P0 is recalculated for speed limit and lag, generating the main steam pressure setpoint before lag P1 and the main steam pressure setpoint P2. The reference point is reset again when the main steam pressure setpoint adjustment lag signal appears again.

[0033] Configure this method in the DCS software system and perform simulation; the curves are shown in the attached figure. Figure 1 As shown, the unit load command continuously increased from 600MW to 800MW. After speed limiting, the load command approached 800MW and then decreased to 700MW. Due to a lag in the main steam pressure setpoint calculation, the load continued to rise during load reduction. This indicates a lag in the main steam pressure setpoint adjustment, and the lag calculation is immediately terminated. (See attached diagram). Figure 1 , 2 As shown, the main steam pressure setpoint without lag detection and switching reached a maximum of 22.544 MPa. After adopting this method, the main steam pressure setpoint reached a maximum of 22.305 MPa, after which it was determined that the main steam pressure regulation lag had occurred, and it began to decrease following the unit load command.

[0034] S3. Determine the deviation between the main steam pressure setpoint and the feedback value: If the absolute value of the deviation is greater than a MPa, a is set to 0.5 MPa, and the first deviation signal for stabilizing the main steam pressure is triggered after a 120s delay; if the absolute value of the deviation is greater than b MPa, b is set to 1 MPa, and the second deviation signal for stabilizing the main steam pressure is triggered after a 120s delay. Under the steady-state condition of the AGC command, the control modes are divided into the following two modes according to the operation of the energy storage battery:

[0035] S3.1. If the energy storage battery is not engaged, a large deviation signal in the main steam pressure stability is triggered, and integral reinforcement is performed. If the first deviation signal is triggered, the integral time is set to τ seconds (or the integral coefficient n=60 / τ), and the action time T is: ; Δ: Absolute value of main steam pressure deviation; Pi Main steam pressure rated upper limit; P o Main steam pressure lower limit; W: Rated power of the unit; σ: Gain coefficient, a constant between 0 and 1.

[0036] Assuming τ is set to 30s, If set to 1, the duration of action is T = 207 × Δ.

[0037] The second deviation signal trigger extends the action time according to the b / a ratio. During the integral enhancement process, the main steam pressure deviation decreases to within the value of a. When the large deviation signal disappears, the integral enhancement action is immediately stopped and the boiler command integral parameters are restored to their original values.

[0038] S3.2. Energy storage battery activation: Since energy storage can quickly replenish part of the active power difference, the operation of the energy storage battery reduces the consumption of the main steam pressure regulation margin and slows down the adjustment of the main steam pressure setpoint. Therefore, the inertia time of the main steam pressure setpoint is extended, and an inertia time gain coefficient δ is set, δ>1, to reduce the deviation between the main steam pressure setpoint and the feedback value. Furthermore, no integral enhancement is performed when the energy storage battery is activated, reducing the overshoot generated when the AGC load command changes direction. ; Rsoc: Energy storage battery load rate setting value; R: Unit load change rate setpoint; The maximum power regulation rate of the unit equipped with the energy storage battery is 36MW / min, and the setpoint of the coal-fired power unit is 15MW / min, so δ=1.55.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the main steam pressure of a coal-fired power generating unit based on fast AGC, characterized in that, Includes the following steps: S1. By comparing the numerical relationship between the main steam pressure target value P0 and the real-time set value P2 and the direction of change of P2, it is determined whether the adjustment of the main steam pressure set value lags behind the load command change, and a lag correction signal is generated when lag is determined. S2. When a lag is detected, reset the calculation reference point of the main steam pressure setpoint to make its adjustment direction consistent with the direction of load command change; S3. Based on the deviation between the main steam pressure setpoint and the feedback value, as well as the activation / deactivation status of the energy storage battery, switch between different pressure control modes.

2. The main steam pressure control method for coal-fired power generating units based on fast AGC according to claim 1, characterized in that, The specific process of S1 is as follows: Calculate the change rate R of the main steam pressure set value P2 P2 ; When P0 > P2 and R P2 < 0 or P0 < P2 and R P2 > 0, it is determined that the adjustment of the main steam pressure set value P2 lags, and a pulse signal is generated as the lag correction signal.

3. The main steam pressure control method for coal-fired power generating units based on rapid AGC according to claim 2, characterized in that, The duration of the pulse signal is 0.5-2 seconds.

4. The main steam pressure control method for coal-fired power generating units based on fast AGC according to claim 1, characterized in that, The specific process of S2 is as follows: S2.

1. After the main steam pressure setpoint lag pulse signal is issued, the rate limit on P0 is released, so that the value of the main steam pressure setpoint P1 before lag is equal to the current value of P0. S2.

2. Pause the delayed calculation of P1 so that the value of P2 tracks the value of P1, thereby unifying the values ​​of P0, P1, and P2. S2.

3. After the hysteresis correction signal ends, the normal rate limit and hysteresis calculation of P0 are restored based on a unified value.

5. The main steam pressure control method for coal-fired power generating units based on rapid AGC according to claim 4, characterized in that, In S2.2, when pausing the lag calculation, the output tracks the input to achieve a smooth switching of P2.

6. The main steam pressure control method for coal-fired power generating units based on fast AGC according to claim 1, characterized in that, The specific process of S3 is as follows: S3.

1. When the absolute value of the main steam pressure deviation is greater than the first threshold a and lasts for a first duration a1, the first-level deviation signal is triggered; S3.

2. When the absolute value of the main steam pressure deviation is greater than the second threshold b and lasts for a second duration b1, the second-level deviation signal is triggered, where b > a; S3.

3. Select the corresponding control strategy based on the level of the triggered deviation signal and the activation / deactivation status of the energy storage battery.

7. The main steam pressure control method for coal-fired power generating units based on rapid AGC according to claim 6, characterized in that, In S3.3, when the energy storage battery is not engaged and the first-level deviation signal is triggered, the integral action of the enhanced controller is activated. The duration T of the enhanced integral action is calculated by the following formula: ； Where Δ is the absolute value of the main steam pressure deviation, and P is... i Main steam pressure rated upper limit, P o σ is the lower limit of the rated main steam pressure, W is the rated power of the unit, and σ is the gain coefficient, which is a constant between 0 and 1.

8. The main steam pressure control method for coal-fired power generating units based on rapid AGC according to claim 7, characterized in that, In S3.3, when the second-level deviation signal is triggered, the duration of the integral enhancement is extended based on the ratio of the second threshold b to the first threshold a.

9. The main steam pressure control method for coal-fired power generating units based on fast AGC according to claim 8, characterized in that, When the energy storage battery is engaged, the following controls are executed: Increase the inertial time constant of the main steam pressure setpoint generation stage, and make the inertial time gain coefficient δ greater than 1; and stop enabling the controller's integral enhancement function.

10. The main steam pressure control method for coal-fired power generating units based on rapid AGC according to claim 9, characterized in that, The formula for calculating the inertial time gain coefficient δ is as follows: ； in, The load rate setting value for the energy storage battery. The setpoint for the variable load rate of the unit.

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