A steam turbine main control auxiliary pressure regulating control system and control method under variable load conditions

Abstract

The application discloses a steam turbine main control auxiliary pressure regulating control system and control method under variable load conditions, which comprises a unit load instruction forming loop, a steam turbine main control load set value forming loop and a steam turbine main control instruction forming loop; the steam turbine main control load set value forming loop is composed of a primary frequency modulation load instruction input, a main steam pressure deviation correction loop and a steam turbine load instruction forming loop; the main steam pressure deviation correction loop and the steam turbine main control load set value forming loop together with the primary frequency modulation load instruction constitute a steam turbine main control regulator set value; the steam turbine main control regulator performs PID operation according to the set value and an actual load to obtain a steam turbine main control instruction; and the unit load instruction forming loop independently acts on a boiler side control system. The application improves the unit load change rate and reduces the main parameter fluctuation of the unit under the premise of ensuring the stability of the main steam pressure by means of fuzzy control and predictive control technology, and meets the requirement of the power grid for fast response to the load.

Description

Technical Field

[0001] This invention relates to the field of automatic control technology for thermal power plants, specifically to a main control and auxiliary pressure regulation control system and control method for steam turbines under variable load conditions. Background Technology

[0002] With the continuous growth of installed capacity of new energy sources such as wind power, hydropower, and photovoltaic power, as well as the increasing demand for long-distance power supply outside the region, the peak-shaving pressure on coal-fired power units is constantly increasing. In order to ensure the safe, high-quality, and stable operation of the power system, the State Electricity Regulatory Commission has issued and implemented "two detailed rules," which include strict regulations on the assessment indicators for AGC (Automatic Generation Control).

[0003] To meet the grid load requirements, coal-fired power units employ a coordinated control method based on boiler following in their coordinated control systems. Currently, coal-fired power unit coordinated control systems are designed with boiler load change feedforward loops during load changes. These feedforward signals are applied to fuel commands, feedwater commands, total air volume commands, and desuperheating water control loops to ensure that the boiler heat can meet the turbine's energy demand. The turbine main controller adjusts the unit load to the set value according to the set load change rate. At the same time, the turbine main controller setpoint loop often includes primary frequency regulation load commands and main steam pressure deviation correction values. The existing steam turbine main control system has certain problems: 1. During the load increase process, the main steam pressure is high and rises rapidly. The load is increased at the set rate, and the main steam pressure control relies solely on boiler regulation, resulting in slow recovery. The same applies to the load reduction process. 2. When the main steam pressure deviation is large during load changes, the main steam pressure deviation correction loop can easily cause oscillations in the main steam pressure and large fluctuations in the turbine control valves, leading to instability in parameters such as coal feed, water flow, and total air volume. 3. If the parameters of the main steam pressure deviation pull-back loop are set too high, the unit's load response speed, load response time, and accuracy will not meet the grid requirements. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned problems by providing a main control auxiliary pressure regulation control system and control method for steam turbines under variable load conditions. Through fuzzy control and predictive control technology, while ensuring the stability of the main steam pressure, the system can improve the load change rate of the unit to a certain extent, reduce the fluctuation of the main parameters of the unit, and thus adapt to the requirements of the power grid for rapid load response.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A turbine main control auxiliary pressure regulation control system under variable load conditions includes: an actual load input connected to the input PV of a first PID controller; the input SP of the first PID controller connected to the output of an adder; a primary frequency regulation load command input connected to the first input of the adder; the second input of the adder connected to the output of a first analog switch; a variable load input connected to the switching condition input of the first analog switch; the input Y of the first analog switch connected to the output of an eighth function converter; the output of a second analog switch connected to the input of the eighth function converter, the input N of the first analog switch, and the input Y of the second analog switch; the switching condition input of the second analog switch connected to the primary frequency regulation action input; the input N of the second analog switch connected to the output of a seventh function converter; a main steam pressure deviation input connected to the input of the seventh function converter, the input of the first function converter, the input of a differentiator, and the input of the second function converter; the third input of the adder connected to the output of a first rate limiter; and a target load input signal connected to the first The inputs of the rate limiters are as follows: the positive rate limit input PL of the first rate limiter is connected to the output of the multiplier; the input of the multiplier is connected to the load change rate setting input; the input of the multiplier is connected to the output of the sixth function converter; the input of the sixth function converter is connected to the output of the multiplier; the input of the multiplier is connected to the output of the fourth function converter; the input of the fourth function converter is connected to the output of the differentiator; the input of the multiplier is connected to the output of the second function converter; the negative rate limit input NL of the first rate limiter is connected to the output of the multiplier; the input of the multiplier is connected to the load change rate setting input; the input of the multiplier is connected to the output of the fifth function converter; the input of the fifth function converter is connected to the output of the multiplier; the input of the multiplier is connected to the output of the third function converter; the input of the third function converter is connected to the output of the differentiator; the input of the multiplier is connected to the output of the first function converter; the output of the first PID controller is connected to the input of the first manual control station; the output of the first manual control station is connected to the turbine main control command output to control the turbine regulating valve action.

[0007] The target load input 7 is also connected to the input of the second rate limiter. The positive rate limit input PL and the negative rate limit input NL of the second rate limiter are both connected to the load change rate setting input. The output of the second rate limiter is connected to the unit load command output. This signal constitutes the basic variable load feedforward logic, which is applied to the control of coal feeding, water feeding, air supply, and primary air fan desuperheating water, respectively, to improve the response speed on the boiler side.

[0008] The control method for auxiliary pressure regulation of the main control unit of the steam turbine under variable load conditions includes the following steps:

[0009] Step 1: Calculate the unit load command output based on the target load input 7 and the load change rate setting input, which is used for the variable load feedforward logic design of control loops such as coal feed rate, water feed rate, primary air pressure, total air volume, and desuperheating water.

[0010] Step 2: When the unit changes load, based on the current main steam pressure deviation input and the change in main steam pressure deviation (output of the differentiator), fuzzy control theory is used to correct the unit's load increase rate and load decrease rate.

[0011] When the unit increases load, if the actual value of the main steam pressure is greater than the set value of the main steam pressure or the rate of increase of the actual value of the main steam pressure is greater than the rate of increase of the set value of the main steam pressure, the load increase rate should be appropriately increased. At this time, the actual load change rate of the unit is improved, which is also conducive to the stability of the main parameters of the unit.

[0012] When the unit reduces load, if the actual value of the main steam pressure is less than the set value of the main steam pressure or the rate of increase of the actual value of the main steam pressure is less than the rate of increase of the set value of the main steam pressure, the load reduction rate should be appropriately increased. At this time, the actual load change rate of the unit is improved, which is also conducive to the stability of the main parameters of the unit.

[0013] Step 3: The corrected load command (output of the first rate limiter), the primary frequency regulation load command input, and the main steam pressure deviation correction loop value (output of the analog quantity switch) are combined to form the setpoint of the turbine main control regulator.

[0014] In the main steam pressure deviation correction loop value, when the unit changes load, the parameters are set through the eighth function converter to reduce the main steam pressure deviation correction value during the load change process, which can achieve the purpose of rapid load response and improved load regulation accuracy to a certain extent.

[0015] Step 6: The turbine main control regulator performs PID calculations based on the set value SP (output of the adder) and the actual value PV (unit load input 1), outputs commands to the turbine main control handheld device, and outputs turbine main control commands to the turbine control system to control the turbine regulating valve action.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1) The main control auxiliary pressure regulation control system and control method of the steam turbine under variable load conditions in this invention, based on the study of the load response characteristics of the unit, adopts fuzzy and predictive control technology to adapt the main steam pressure deviation and the change of main steam pressure deviation to the change of unit load output, so as to ensure the stability of main steam pressure during the unit's load change process, reduce the fluctuation of parameters such as coal feed, water flow, primary air pressure, and total air volume, and improve the unit's load response speed.

[0018] 2) During load change, reducing the main steam pressure deviation corrects the load setpoint, thereby reducing the large fluctuations in the turbine control valve caused by changes in main steam pressure. This improves the load regulation accuracy of the unit during load change to a certain extent, reduces turbine control valve operation, and improves the unit's load response speed and reduces load response time.

[0019] 3) Wide range of applications: This control method is applicable to the automatic control logic design of all steam turbine main control systems in power plants. It can quickly reduce the main steam pressure deviation during load change, reduce the fluctuation of the main parameters of the unit during load change, and improve the unit's load response speed and accuracy to a certain extent. Attached Figure Description

[0020] Figure 1 This is the control logic diagram of the present invention.

[0021] In the picture:

[0022] F(x) – Function converter; DIFF – Differentiator; MUL – Multiplier;

[0023] ADD – Adder; T – Analog Switcher; RATE – Rate Limiter;

[0024] PID – PID controller; M / A – handheld controller; Detailed Implementation

[0025] A turbine main control auxiliary pressure regulation control system under variable load conditions includes: actual load input 1, primary frequency regulation load command input 2, variable load input 3, primary frequency regulation action input 4, main steam pressure deviation input 5, load change rate setting input 6, target load input 7, first function converter 8, differentiator 9, second function converter 10, third function converter 11, fourth function converter 12, multiplier 13, multiplier 14, fifth function converter 15, sixth function converter 16, multiplier 17, multiplier 18, first rate limiter 19, adder 20, first analog quantity switcher 21, eighth function converter 22, second analog quantity switcher 23, seventh function converter 24, first PID controller 25, first manual control station 26, second rate limiter 28, turbine main control command output 27, and unit load command output 29.

[0026] The actual load input 1 is connected to the input PV of the first PID controller 25. The input SP of the first PID controller 25 is connected to the output of the adder 20. The primary frequency regulation load command input 2 is connected to the first input of the adder 20. The second input of the adder 20 is connected to the output of the first analog switch 21. The variable load input 3 is connected to the switching condition input of the first analog switch 21. The input Y of the first analog switch 21 is connected to the output of the eighth function converter 22. The output of the second analog switch 23 is connected to the input of the eighth function converter 22 and the first analog switch 23, respectively. The input N of the first analog converter 1 and the input Y of the second analog converter 23 are connected. The switching condition input of the second analog converter 23 is connected to the primary frequency modulation action input 4. The input N of the second analog converter 23 is connected to the output of the seventh function converter 24. The main steam pressure deviation input 5 is connected to the input of the seventh function converter 24, the input of the first function converter 8, the input of the differentiator 9, and the input of the second function converter 10. The third input of the adder 20 is connected to the output of the first rate limiter 19. The target load input signal 7 is connected to the input of the first rate limiter 19. The first rate limiter 19... The positive rate limit input PL is connected to the output of multiplier 18; input 1 of multiplier 18 is connected to the load change rate setting input 6; input 2 of multiplier 18 is connected to the output of the sixth function converter 16; the input of the sixth function converter 16 is connected to the output of multiplier 14; input 1 of multiplier 14 is connected to the output of the fourth function converter 12; the input of the fourth function converter 12 is connected to the output of differentiator 9; input 2 of multiplier 14 is connected to the output of the second function converter 10; the negative rate limit input NL of the first rate limiter 19 is connected to the output of multiplier 17; multiplication... Input 1 of multiplier 17 is connected to load change rate setting input 6. Input 2 of multiplier 17 is connected to the output of the fifth function converter 15. The input of the fifth function converter 15 is connected to the output of multiplier 13. Input 1 of multiplier 13 is connected to the output of the third function converter 11. The input of the third function converter 11 is connected to the output of differentiator 9. Input 2 of multiplier 13 is connected to the output of the first function converter 8. The output of the first PID controller 25 is connected to the input of the first manual station 26. The output of the first manual station 26 is connected to the turbine main control command output 27 to control the turbine regulating valve action.The target load input 7 is also connected to the input of the second rate limiter 28. The positive rate limit input PL and the negative rate limit input NL of the second rate limiter 28 are both connected to the load change rate setting input 6. The output of the second rate limiter 25 is connected to the unit load command output 29. This signal constitutes the basic variable load feedforward logic, which is applied to the control of coal feeding, water feeding, air supply, and primary air fan desuperheating water, respectively, to improve the response speed on the boiler side.

[0027] Based on the above-mentioned control method for auxiliary pressure regulation of the main control unit of the steam turbine under variable load conditions, the method includes reducing the main steam pressure deviation and correcting the load command loop under variable load conditions, which reduces the load response time and improves the load response speed and accuracy to a certain extent; using the main steam pressure deviation and its change, and through fuzzy control theory, the load change rate setting of the variable load process is corrected, thereby reducing the main steam pressure deviation during the variable load process, which is conducive to the stability of coal feed, water flow, and total air volume commands during the variable load process, while improving the unit load change rate.

[0028] The specific control method for auxiliary pressure regulation of the main control unit of the steam turbine under variable load conditions includes the following steps:

[0029] Step 1: Calculate the unit load command output 29 based on the target load input 7 and the load change rate setting input 6, which is used for the boiler side load change feedforward logic design;

[0030] Step 2: When the unit changes load, based on the current main steam pressure deviation input 5 and the change in main steam pressure deviation (output of differentiator 9), the load increase rate and load decrease rate of the unit are corrected using fuzzy control theory.

[0031] a) When the unit increases its load, if the actual value of the main steam pressure is greater than the set value of the main steam pressure, the output of the second function converter 10 will be greater than 1.

[0032] The parameter settings for the second function converter are shown in the table below:

[0033]

[0034] b) When the unit increases load, if the actual value of the main steam pressure rises faster than the set value of the main steam pressure rises faster, the output of the fourth function converter 12 will be a value greater than 1.

[0035] The parameter settings for the fourth function converter are shown in the table below:

[0036]

[0037] c) When the load increases, the output of the second function converter 10 is multiplied by the output of the fourth function converter 12 and then used to correct the load increase rate.

[0038] To ensure that the actual load change rate of the unit is not lower than the load change rate set value, the output of the sixth function converter 16 is not less than 1;

[0039] The parameter settings for the sixth function converter are shown in the table below:

[0040] enter 0.7 1 1.2 1.5 Output 1 1 1.2 1.4

[0041] d) When the unit reduces load, if the actual value of the main steam pressure is less than the set value of the main steam pressure, the output of the first function converter 8 will be greater than 1.

[0042] The parameter settings for the first function converter are shown in the table below:

[0043]

[0044] e) When the unit reduces load, if the actual value of the main steam pressure decreases at a rate greater than the rate of decrease of the set value of the main steam pressure, the output of the third function converter 11 will be a value greater than 1.

[0045] The parameter settings for the third function converter are shown in the table below:

[0046]

[0047] f) During load reduction, the output of the first function converter 8 and the output of the third function converter 11 are multiplied together to correct the load reduction rate;

[0048] To ensure that the actual load change rate of the unit is not lower than the load change rate set value, the output of the fifth function converter 15 is not less than 1;

[0049] The parameter settings for the fifth function converter are shown in the table below:

[0050] enter 0.7 1 1.2 1.5 Output 1 1 1.2 1.4

[0051] Step 3: The turbine-side unit load command (output of the first rate limiter 18), the primary frequency regulation load command input 2, and the main steam pressure deviation correction loop value (output of the analog quantity switcher 21) are superimposed to form the set value of the turbine main control PID regulator 25.

[0052] In the main steam pressure deviation correction loop value (seventh function converter 24), when the unit changes load, the parameters are corrected by the eighth function converter 22 to reduce the main steam pressure deviation correction value during the load change process, so as to achieve the purpose of rapid load response and improved load regulation accuracy.

[0053] The parameter settings for the seventh function converter are shown in the table below:

[0054] Main steam pressure deviation (MPa) -1 -0.5 -0.2 0 0.2 0.5 1 Load correction (%) -2 -1 0 0 0 1 2

[0055] The parameter settings for the eighth function converter are shown in the table below:

[0056] enter -2 0 2 Output 1 0 1

[0057] Step 4: The turbine main control regulator 25 performs calculations based on the set value SP (output of adder 20) and the actual value PV (unit load input 1), outputs commands to the turbine main control handheld device 26, and outputs turbine main control commands 27 to the turbine control system to control the turbine regulating valve action.

Claims

1. A method for main control and auxiliary pressure regulation control of a steam turbine under variable load conditions, characterized in that, The system includes a unit load command formation loop, a turbine main control load setpoint formation loop, and a turbine main control command formation loop. The turbine main control load setpoint formation loop consists of a primary frequency regulation load command input, a main steam pressure deviation correction loop, and a turbine load command formation loop. The main steam pressure deviation correction loop, the turbine main control load setpoint formation loop, and the primary frequency regulation load command together constitute the turbine main control regulator setpoint. The turbine main control regulator performs PID calculations based on the setpoint and the actual load to obtain the turbine main control command. The unit load command formation loop acts independently on the boiler-side control system for controlling total air volume, feedwater flow rate, coal feed rate, and desuperheating water. The method includes the following steps: Step 1: Calculate the unit load command output based on the target load input and load change rate setting input, which is used for the variable load feedforward logic design of the coal feed rate, water feed rate, primary air pressure, total air volume, and desuperheating water control loop; Step 2: When the unit changes load, based on the current main steam pressure deviation input and the output of the main steam pressure deviation change differentiator, fuzzy control theory is used to correct the unit's load increase rate and load decrease rate. When the unit increases load, if the actual value of the main steam pressure is greater than the set value of the main steam pressure or the rate of increase of the actual value of the main steam pressure is greater than the rate of increase of the set value of the main steam pressure, the load increase rate should be appropriately increased. At this time, the actual load change rate of the unit is improved, which is also conducive to the stability of the main parameters of the unit. When the unit reduces load, if the actual value of the main steam pressure is less than the set value of the main steam pressure or the rate of increase of the actual value of the main steam pressure is less than the rate of increase of the set value of the main steam pressure, the load reduction rate should be appropriately increased. At this time, the actual load change rate of the unit is improved, which is also conducive to the stability of the main parameters of the unit. Step 3: The output of the first rate limiter of the corrected load command, the input of the primary frequency regulation load command, and the output of the analog quantity switcher of the main steam pressure deviation correction loop value are superimposed to form the set value of the turbine main control regulator. In the main steam pressure deviation correction loop value, when the unit changes load, the parameters are set through the eighth function converter to reduce the main steam pressure deviation correction value during the load change process, so as to achieve the purpose of rapid load response and improving load regulation accuracy. Step 4: The turbine main control regulator performs PID calculations based on the output of the setpoint SP adder and the actual value PV unit load input, and sends the output command to the turbine main control handheld device. It also outputs the turbine main control command to the turbine control system to control the turbine regulating valve action.

2. The turbine main control auxiliary pressure regulation control method under variable load conditions according to claim 1, characterized in that, The unit load command generation loop includes a target load input, which is connected to the input of the second rate limiter. The positive rate limit input PL and the negative rate limit input NL of the second rate limiter are both connected to the load change rate setting input. The output of the second rate limiter is connected to the unit load command output. The boiler-side load change feedforward logic is generated through the unit load command output signal, which acts on the coal feeding control, water feeding control, air supply control, primary air pressure control and desuperheating water control loops respectively, thereby improving the response speed on the boiler side.

3. The turbine main control auxiliary pressure regulation control method under variable load conditions according to claim 1, characterized in that, The main steam pressure deviation correction loop includes a main steam pressure deviation input. The main steam pressure deviation input signal is connected to the input of the seventh function converter. The output of the seventh analog switch is connected to the input N of the second analog switch. The switching condition input of the second analog switch is connected to the primary frequency regulation action input. The output of the second analog switch is connected to the input Y of the second analog switch, the input N of the first analog switch, and the input of the eighth function converter. The input Y of the first analog switch is connected to the output of the eighth function converter. The switching condition of the first analog switch is connected to the variable load input. The output of the first analog switch is the main steam pressure deviation correction value.

4. The turbine main control and auxiliary pressure regulation control method under variable load conditions according to claim 1, characterized in that, The turbine load command formation loop includes a target load input signal, which is connected to the input of the first rate limiter. The positive rate limit input (PL) of the first rate limiter is connected to the output of the multiplier. The input of the multiplier is connected to the load change rate setting input. The input of the multiplier is connected to the output of the sixth function converter. The input of the sixth function converter is connected to the output of the multiplier. The input of the multiplier is connected to the output of the fourth function converter. The input of the fourth function converter is connected to the output of the differentiator. The main steam pressure deviation input is connected to the input of the first function converter and the input of the differentiator, respectively. The input of the second function converter is connected to the output of the multiplier. The negative rate limit input NL of the first rate limiter is connected to the output of the multiplier. The input of the multiplier is connected to the load change rate setting input. The input of the multiplier is connected to the output of the fifth function converter. The input of the fifth function converter is connected to the output of the multiplier. The input of the multiplier is connected to the output of the third function converter. The input of the third function converter is connected to the output of the differentiator. The input of the multiplier is connected to the output of the first function converter. The output of the first rate limiter is the turbine load command.

5. The turbine main control auxiliary pressure regulation control method under variable load conditions according to claim 1, characterized in that, The turbine main control load setpoint, i.e. the output of the adder, is formed by superimposing the primary frequency regulation load command input, the output of the first analog quantity switcher of the main steam pressure deviation correction value, and the output of the first rate limiter of the turbine load command.

6. The turbine main control auxiliary pressure regulation control method under variable load conditions according to claim 1, characterized in that, The turbine main control command generation loop includes the actual load input, the actual load input signal is connected to the input PV of the first PID controller, the input SP of the first PID controller is connected to the output of the adder, the output of the first PID controller is connected to the input of the first manual station, and the output of the first manual station is connected to the turbine main control command output to control the turbine regulating valve action.

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