Low-load water supply three-impulse control method for heat supply unit

Abstract

The invention discloses a low-load water supply three-impulse control method for a heat supply unit, which comprises the following steps of: taking a steam drum water level as a controlled variable, introducing a steam flow fitting value and water supply flow as auxiliary regulating variables, and realizing dynamic control through a PID (Proportion Integration Differentiation) regulating formula, the steam flow fitting value is calculated through a formula with a dynamic correction coefficient based on the main steam heat supply flow, the regulating stage pressure, the high bypass opening degree and the hot reheat supply flow, the problem that steam flow measurement is not accurate under the low load is solved, meanwhile, a parameter self-adaption strategy is designed according to the working conditions such as starting and stopping, and the measurement accuracy is improved. According to the method, the fluctuation amplitude of the steam drum water level under the low load can be reduced to + / -30 mm, the adjusting time is shortened to be within 30 seconds, and the stability and safety of low-load operation of a heat supply unit are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of thermal power generation and heating control technology, specifically relating to a three-impulse control method for steam drum feedwater of a heating unit under low load conditions, applicable to extraction condensing or back pressure heating units with high-pressure bypass, low-pressure bypass and heat reheating systems. Background Technology

[0002] When heating units operate at low loads, traditional three-impulse control often encounters the following problems due to large fluctuations in steam flow and strong coupling between heating and power generation loads: Inaccurate steam flow measurement: Under low loads, the signal-to-noise ratio of main steam flow and reheat steam flow signals is low, and a single measurement value is insufficient to reflect the actual steam volume; Significant regulation lag: When switching between main steam and reheat steam for heating, sudden changes in steam flow lead to feedwater regulation lag, causing significant fluctuations in the steam drum water level; Poor parameter adaptability: Fixed PID parameters cannot adapt to the nonlinear changes in fuel, pressure, and flow under low loads, easily resulting in overshoot or oscillation. Existing technologies have addressed this by adding filtering stages to smooth the steam flow signal, but this ignores the dynamic characteristics during heating switching; others use variable parameter PID, but without combining multi-parameter fitting with steam flow feedforward, resulting in insufficient control accuracy under low loads. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of low accuracy and weak anti-interference ability of feedwater three-impulse control under low load conditions of heating units. By constructing a multi-parameter fitting steam flow calculation model and optimizing the dynamic adaptation logic of adjustment parameters, stable control of steam drum water level can be achieved, thereby improving the safety and economy of unit operation under low load.

[0004] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0005] This invention discloses a three-impulse control method for feedwater in a heating unit under low load. The method is characterized by using the steam drum water level H as the controlled variable, and introducing the steam flow rate fitting value D and feedwater flow rate W as auxiliary adjustment variables. The adjustment is achieved through the following control logic:

[0006]

[0007] Wherein, ΔW is the feedwater flow rate adjustment increment, Kp is the proportional coefficient, Ki is the integral coefficient, Kd is the differential coefficient, Kf is the feedforward coefficient, and ΔH is the steam drum water level deviation; the steam flow rate fitting value D is based on the main steam heating flow rate D. 主供 Regulating stage pressure P 调 High lateral opening u 高旁 and heat reheat flow rate D 热再供 The calculation yielded the result.

[0008] Preferably, the formula for calculating the steam flow rate fitting value D is:

[0009] D = D 主供 ×α+P 调 ×β+μ 高旁 ×γ+D 热再供 ×δ;

[0010] Among them, α, β, γ, and δ are dynamic correction coefficients, and α+β+γ+δ=1. Each coefficient is dynamically calibrated according to the unit load range; less than 30% of the rated load.

[0011] Preferably, when the unit load is less than 15% of the rated load, the value of α is 0.4-0.6, the value of β is 0.2-0.3, the value of Y is 0.1-0.2, and the value of δ is 0.05-0.15.

[0012] Preferably, the low load setting of the heating unit is set to the unit's electrical load ≤ 30% of the rated load, and the ratio of heating flow to electrical load ≥ 1.2.

[0013] Preferably, when the reheater temperature T occurs... 再热 >540℃ or desuperheating water regulating valve opening (μ) 减温 When the increase is greater than 80%, the feedforward coefficient K is automatically reduced. f To 60%-80% of the original value.

[0014] Preferably, in shutdown mode, when the original high bypass angle u 高旁 When the steam flow rate is >40%, the formula for calculating the fitted value D is corrected as follows:

[0015] D = D 主供 ×α+P 调 ×β+μ 高旁 ×γ×1.2+D 热再供 ×δ.

[0016] Preferably, in start-up mode, as the unit load increases from 0 to 15% of the rated load, the proportional coefficient Kp increases linearly with the load, with an initial value of 0.3 and a final value of 0.6.

[0017] Preferably, the water supply flow rate W is calculated using a weighted average of the dual-channel measurement values, and the formula is as follows:

[0018] W = W1 × 0.7 + W2 × 0.3; where W1 is the measured value of the electromagnetic flowmeter and W2 is the measured value of the differential pressure flowmeter.

[0019] Preferably, the dead zone of the steam drum water level deviation ΔH is set to ±3mm. When |ΔH|≤3mm, the integral term K i The accumulation of ∫(ΔH)dt is paused.

[0020] The present invention provides a control system for implementing a three-impulse control method for low-load feedwater of a heating unit, comprising a parameter acquisition module, a flow fitting module, a PID control module, and an actuator, wherein the flow fitting module incorporates the steam flow fitting algorithm described above.

[0021] Beneficial effects: Improved steam flow measurement accuracy: By fitting multiple parameters such as main steam heating flow and regulating stage pressure, the deviation between the fitted steam flow value and the actual value is ≤5%, solving the problem of inaccurate measurement of a single signal under low load; Enhanced anti-interference capability: During heating switching, the fluctuation range of the steam drum water level is reduced from ±100mm to ±30mm, and the adjustment time is shortened to less than 30 seconds; Adaptable to wide load fluctuations: Through dynamic correction coefficients and variable parameter PID, it can stably cover the 10%-30% rated load range, meeting the unit's deep peak shaving and heating needs; Improved system reliability: The introduction of parameter adaptive strategy under no-increase / no-decrease conditions avoids regulation failure caused by reheater overheating or valve jamming. Attached Figure Description

[0022] Figure 1 This is a block diagram illustrating the principle of the present invention. Detailed Implementation

[0023] 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.

[0024] like Figure 1 The specific embodiment shown focuses on the water supply control problem of heating units under low load conditions, and provides a complete three-impulse control scheme for low load water supply. The details are as follows:

[0025] I. The core control logic uses the drum water level as the core controlled variable, constructing a three-impulse regulation system of "drum water level - steam flow fitted value - feedwater flow". Dynamic control is achieved through the following PID regulation formula:

[0026]

[0027] Where △W is the incremental adjustment of water supply flow, and K p K is the proportionality coefficient. i K is the integral coefficient. d K is the differential coefficient. f ΔH is the feedforward coefficient, ΔH is the steam drum water level deviation, D is the fitted value of steam flow rate, and W is the feedwater flow rate.

[0028] II. Innovative Design for Steam Flow Fitting To address the challenge of steam flow measurement under low load conditions, a multi-parameter coupled fitting model is proposed, with the following formula:

[0029] D = D 主供 ×α+P 调 ×β+μ 高旁 ×γ+D 热再供 ×δ;

[0030] In the formula, D_main_supply is the main steam heating flow rate, P_adjustment is the regulating stage pressure, u_high_side is the high_side opening degree, and D_heat_resupply is the heat_resupply flow rate; α, β, Y, and δ are dynamic correction coefficients (summing up to 1), which are dynamically calibrated according to the load range (<30% of rated load). For example, when the load is <15% of rated load, α is taken as 0.4-0.6, β is taken as 0.2-0.3, etc., to ensure the fitting accuracy under different heating distribution ratios.

[0031] III. Operating Condition Adaptation Strategy

[0032] Low load definition: Low load is defined as the unit's electrical load ≤ 30% of the rated load, and the ratio of heat flow to electrical load ≥ 1.2, with targeted adjustment parameters designed accordingly.

[0033] Special operating condition handling: Conditions where increases are prohibited (reheater temperature > 540℃ or desuperheating water regulating valve opening > 80%): Automatically adjust the feedforward coefficient K. f Reduce the value to 60%-80% of the original value to avoid over-adjustment.

[0034] Shutdown mode: When the original high bypass degree is >40%, the steam flow fitting formula is modified by multiplying the γ coefficient by 1.2 to enhance the feedforward response.

[0035] Start-up mode: When the load increases from 0 to 15% of the rated load, the proportional coefficient Kp increases linearly from 0.3 to 0.6 to adapt to the dynamic characteristics of the load increase process.

[0036] IV. Assisted Optimization Design for Water Supply Flow Measurement: A dual-channel weighted average (70% electromagnetic flowmeter + 30% differential pressure flowmeter) is adopted to improve measurement reliability. Water Level Deviation Dead Zone: A ±3mm dead zone is set; the integral term accumulation is paused within the dead zone to reduce adjustment oscillations.

[0037] V. The supporting system consists of a parameter acquisition module (acquiring various flow, pressure, and opening signals), a flow fitting module (executing a steam flow fitting algorithm), a PID control module (implementing three-impulse control logic), and an actuator, forming a closed-loop control system. This invention solves the problems of inaccurate steam flow measurement and lag in regulation under low load by fitting steam flow with multiple parameters and dynamically adapting adjustment parameters, significantly improving the stability of the steam drum water level during low-load operation of the heating unit.

[0038] VI. Description of each module of the control system

[0039] 6.1 Parameter Acquisition Module: The parameter acquisition module is responsible for acquiring key parameters of the unit during low-load operation in real time, providing raw data for subsequent calculations and adjustments. Its core functions include:

[0040] Signal acquisition range: Covering the main steam heating flow rate (D) 主供 ), regulating stage pressure (P) 调 High lateral opening (μ) 高旁 ), heat reheat flow rate (D) 热再供 Key parameters such as steam drum water level (H) and dual-channel feedwater flow rate (electromagnetic flowmeter W1 and differential pressure flowmeter W2) are sampled at a frequency of 10Hz to ensure real-time data accuracy.

[0041] Signal preprocessing: The acquired pressure and flow signals are subjected to second-order low-pass filtering (cutoff frequency 1Hz) to eliminate high-frequency noise such as pipeline vibration and electromagnetic interference; the steam drum water level signal is subjected to temperature compensation to correct the measurement deviation caused by changes in steam drum pressure.

[0042] Compensation formula: H 修正 =H 实测 +0.02×(P 实测 -P 额定 ).

[0043] Fault diagnosis: When a parameter signal exceeds the normal range (such as main steam heating flow rate > 200t / h) or remains unchanged for 3 consecutive seconds, the redundancy switching is automatically triggered. For example, the feedwater flow rate is preferentially used by W1. When W1 fails, it seamlessly switches to W2 and issues an alarm signal.

[0044] 6.2 Flow Fitting Module: The flow fitting module is the core calculation unit of the system. It incorporates the steam flow fitting algorithm described above and is responsible for converting multiple parameters into accurate steam flow fitting values ​​(D). The specific working logic is as follows: Algorithm execution flow: Receive the D output from the parameter acquisition module. 主供 P 调 μ 高旁 D 热再供 The real-time value; based on the current unit load (calculated from the regulating stage pressure), a dynamic correction coefficient (α, β, γ, δ) is matched, for example, at 10% rated load, α = 0.6, β = 0.2, γ = 0.1, δ = 0.1; according to the formula D = D 主供 ×α+P 调 ×β+μ 高旁 ×γ+D 热再供 ×δ; Calculate the fitted value, where P adjustment needs to be performed first using the pressure-flow conversion formula ( K (where K is the unit characteristic coefficient) is converted into the corresponding steam flow rate; the calculation result is then subjected to a limiting process (the upper limit is 30% of the rated steam flow rate) and output to the PID control module.

[0045] Adaptive correction under operating conditions: When the original high bypass angle is detected to be greater than 40% in shutdown mode, the correction formula is automatically activated:

[0046] D = D 主供 ×α+P 调 ×β+μ 高旁 ×γ×1.2+D 热再供 ×δ, by amplifying the weights of high lateral opening, improves the fitting accuracy.

[0047] 6.3 PID Control Module: This is the system's decision control unit, which dynamically adjusts the water supply flow rate based on three-impulse signals. Its core functions include:

[0048] Control logic implementation: Receive the setpoint (H0) and measured value (H) of the steam drum water level, and calculate the water level deviation ΔH = H0 - H;

[0049] Introducing the output D from the flow fitting module and the output W (W = W1 × 0.7 + W2 × 0.3) from the parameter acquisition module, according to the formula:

[0050]

[0051] Calculate the feedwater regulation increment; when |ΔH| ≤ 3mm, pause the accumulation of the integral term to reduce oscillation; when the increment restriction condition is triggered (reheater temperature > 540℃), reduce Kf from 0.8 to 0.64.

[0052] Dynamic parameter adaptation: During startup, the PID parameters are automatically adjusted according to load changes. For example, when the load increases from 0 to 15% of the rated load, Kp increases linearly from 0.3 to 0.6 to ensure that the regulation performance matches the operating conditions.

[0053] 6.4 Implementing agency

[0054] The actuator is the system's action unit, responsible for translating the PID control module's instructions into actual operations, including: Feedwater regulating valve: Employing an intelligent electric actuator, it receives the ΔW signal and proportionally adjusts the valve opening (adjustment range 0-100%), with a response time ≤5 seconds; Interlocking protection device: When the steam drum water level exceeds ±100mm (dangerous value), it forcibly opens the feedwater bypass valve and simultaneously cuts off the main regulating valve control to prevent water level runaway; Feedback verification: Real-time acquisition of the actual valve opening signal, comparison with the command value, and automatic correction when the deviation >5% to ensure adjustment accuracy.

[0055] The various modules in the system interact via industrial Ethernet to form a closed-loop control: the parameter acquisition module synchronously sends the preprocessed signal to the flow fitting module and the PID control module; the D calculated by the flow fitting module is used as a feedforward signal input to the PID control module; the ΔW output by the PID control module drives the actuator, and the actual adjustment effect of the actuator (reflected by changes in water level and flow rate) is captured in real time by the parameter acquisition module, completing the entire control cycle. This collaborative mechanism ensures the speed and stability of water supply regulation under low-load conditions.

[0056] Example 1:

[0057] The following example, using a 300MW extraction condensing heating unit, details the implementation process of this invention:

[0058] 1. Parameter Acquisition and Preprocessing

[0059] Acquisition signal: Main steam heating flow rate D 主供 (Measuring range 0-200t / h), regulating stage pressure P 调 (Measuring range 0-10MPa), high lateral opening u 高旁 (0-100%), Heat Resupply Flow Rate D 热再供 (Measuring range 0-150t / h), steam drum water level H (measuring range -300-+300mm), feed water flow rate W1 (electromagnetic flow meter), W2 (differential pressure flow meter).

[0060] Signal filtering: Second-order low-pass filtering is used for pressure and flow signals with a cutoff frequency of 1Hz to eliminate high-frequency noise.

[0061] 2. Calculation of steam flow rate fitting value

[0062] When the unit load is 20% of the rated load (60MW) and the heating flow rate is 80t / h:

[0063] The dynamic correction coefficients are set as follows: α = 0.5, β = 0.25, γ = 0.15, δ = 0.1.

[0064] Measured parameters: D main supply = 50t / h, P regulation = 3MPa (corresponding to steam volume 20t / h), u high bypass = 20% (corresponding to steam volume 10t / h), D heat resupply = 15t / h;

[0065] Fitting calculation:

[0066] D=50×0.5+20×0.25+10×0.15+15×0.1=25+5+1.5+1.5=33t / h.

[0067] 3. Three-impulse adjustment execution

[0068] The water level setpoint H0 = 0 mm, the current water level H = -20 mm, then ΔH = 20 mm;

[0069] PID parameters:

[0070] K p =0.5, K i =0.05, K d =0.1, K f =0.8;

[0071] Water supply flow rate:

[0072] W=W1×0.7+W2×0.3=30×0.7+28×0.3=21+8.4=29.4t / h

[0073] Adjust the increment:

[0074] ΔW=0.5×20+0.02×∫20dt+0.1×(d(20) / dt)+0.8×(33-29.4)=10+0+0+2.88=12.88t / h

[0075] That is, the water supply flow rate increased from 29.4 t / h to 42.28 t / h.

[0076] 4. Special working condition handling

[0077] In shutdown mode, when the original high bypass angle increases to 45%, the correction formula is triggered:

[0078] D=50×0.5+20×0.25+10×0.15×1.2+15×0.1=25+5+1.8+1.5=33.3t / h

[0079] The feedforward signal is enhanced to prevent sudden drops in water level. When the reheater temperature reaches 550℃ (a condition where incrementing is prohibited), Kf automatically decreases to 0.64, and the adjustment increment is slowed down to prevent overshoot.

[0080] Finally, it should be noted that the present invention is not limited to the above embodiments, and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for three-injection control of feed water at low load of a heat supply unit, characterized by, Taking the drum water level H as the controlled variable, introducing the steam flow fitting value D and the feed water flow W as auxiliary adjusting variables, the following control logic is used to realize the adjustment: Wherein, △W is the feed water flow adjustment increment, Kp is the proportional coefficient, Ki is the integral coefficient, Kd is the differential coefficient, Kf is the feed forward coefficient, △H is the drum water level deviation; the steam flow fitting value D is based on the main steam heating flow D 主供 , the adjusted stage pressure P 调 , the high bypass ratio u 高旁 , and the heat reheat flow D 热再供 .

2. The method according to claim 1, wherein, The calculation formula of the steam flow fitting value D is: D = D 主供 x a + P 调 x β + μ 高旁 x γ + D 热再供 x δ; Wherein, α, β, γ, δ are dynamic correction coefficients, and α+β+γ+δ=1, each coefficient is dynamically calibrated according to the unit load interval; less than 30% rated load.

3. The method according to claim 2, wherein, When the unit load is less than 15% rated load, the value range of α is 0.4-0.6, the value range of β is 0.2-0.3, the value range of Y is 0.1-0.2, and the value range of δ is 0.05-0.

15.

4. The method according to claim 1, wherein, The low load of the heating unit is set as the unit electric load ≤30% rated load, and the ratio of the heating flow to the electric load ≥1.

2.

5. The method of claim 1, wherein the three-injection control method is applied to a heating unit. When the reheater temperature T 再热 > 540℃ or the temperature reducing water regulating valve opening μ 减温 > 80% of the forbidden increase condition, automatically reduce the feedforward coefficient K f to 60%-80% of the original value.

6. The method according to any one of claims 1 to 3, wherein the three-injection control method is applied to a heating unit at a low load. In the shutdown mode, when the original high bypass ratio u 高旁 When the high bypass ratio u is greater than 40%, the calculation formula of the steam flow fitting value D is modified as follows: D = D 主供 x a + P 调 x β + μ 高旁 x γ x 1.2 + D 热再供 x δ.

7. The method according to claim 1, wherein, In the start-up mode, when the unit load increases from 0 to 15% rated load, the proportional coefficient Kp increases linearly with the load, the initial value is 0.3, and the final value is 0.

6.

8. The method of claim 1, wherein, The feed water flow W adopts the weighted average of the double-channel measurement value, and the calculation formula is: W=W1*0.7+W2*0.3; wherein, W1 is the measurement value of the electromagnetic flowmeter, and W2 is the measurement value of the differential pressure flowmeter.

9. The method according to claim 1 or 8, wherein, The dead zone of the drum water level deviation AH is set to ±3mm, when |AH|≤3mm, the integral term K i ∫(AH)dt is suspended accumulation.

10. A control system implementing the method of any one of claims 1-9, characterized by It comprises a parameter acquisition module, a flow fitting module, a PID adjusting module and an actuator, and the flow fitting module is built-in with the steam flow fitting algorithm of claim 2. It comprises a parameter acquisition module, a flow fitting module, a PID adjusting module and an actuator, and the flow fitting module is built-in with the steam flow fitting algorithm of claim 2.

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