A method for controlling main steam temperature of thermal power unit

Abstract

A method for controlling the main steam temperature of a thermal power unit, belonging to the field of thermal automation control, utilizes an iterative predictive controller to control the primary and secondary desuperheating water regulating valves. The method automatically adjusts the intermediate temperature setpoint based on historical operational data of the thermal power unit's superheating desuperheating water usage and intermediate temperature, maintaining sufficient margin for adjusting the main steam temperature. This method improves the mean main steam temperature, enhances the economic efficiency of the thermal power unit, reduces the amplitude of main steam temperature fluctuation, and reduces the risk of leakage in the final superheater tube wall due to thermal alternating stress. The method provided by the present invention requires fewer adjustment parameters, is highly feasible, and improves control accuracy.

Description

Technical Field

[0001] The present invention relates to the field of automatic control of power systems, and in particular to a method for controlling the main steam temperature of a thermal power unit. Background Art

[0002] The control quality of the steam temperature system of large thermal power units will have a significant impact on the safety and economy of the units. Due to large inertia, large hysteresis and nonlinear problems, the superheated steam temperature system generally suffers from large temperature fluctuations and poor anti-disturbance ability in actual operation.

[0003] Thermal power plants widely use superheated desuperheating water systems to control the main steam temperature. For precise control, these systems are generally divided into two stages, front and back. Currently, most studies on main steam temperature control focus solely on water spray desuperheating. However, during operation, supercritical and ultra-supercritical units may experience inappropriate intermediate temperature, leading to the superheated desuperheating water valve being fully closed or fully open. This results in a lack of a means to quickly adjust the main steam temperature in a short period of time. Overcoming large fluctuations in superheated air temperature and insufficient adjustment margin are urgent issues that need to be addressed. Therefore, this application proposes a method for controlling the main steam temperature using iterative predictive control and real-time verification of the intermediate temperature. Summary of the Invention

[0004] In order to solve the above problems, the present application proposes a main steam temperature control method for a thermal power unit to improve the main steam temperature control accuracy.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention provides a method for controlling the main steam temperature of a thermal power unit, comprising the following steps, characterized in that:

[0007] Step 1: Based on historical operating data, a discrete linearized state space model of the desuperheater valve outlet temperature versus the secondary desuperheater temperature and main steam temperature under different operating conditions is obtained.

[0008] Step 2: Adjust the midpoint temperature setting value according to the main steam temperature control deviation and the superheated desuperheating water flow rate;

[0009] Step 3: Set the iterative predictive controller parameters;

[0010] Step 4: Calculate the valve opening based on the output of the iterative predictive controller in step 3 as the PID setting value of the cooling water flow valve opening.

[0011] As a further improvement of the present invention, the historical data required for the discrete linearized state space model of step 1 include: the superheated and desuperheated water regulating valve outlet temperature on the left and right sides of the first and second stages, the second stage superheated and desuperheated water regulating valve inlet temperature and the main steam temperature.

[0012] As a further improvement of the present invention, the form of the training discrete linearized state space model in step 1 is:

[0013]

[0014] where x=(x1, x2, ..., x n ), u=(u1, u2, ..., u nu ), y=(y1, y2, ..., y ny ) is the n-dimensional state variable, nu-dimensional input variable and ny-dimensional output variable of the superheated desuperheated water system, and is linearized in a small range near the load point Pi, x = x p +Δx,u=u p +Δu,y=y p +Δy,A p 、B p 、C p and D p They are the system matrix, input matrix, output matrix and conversion matrix of the linear model, and they are all Jacobi matrices.

[0015] As a further improvement of the present invention, the intermediate point temperature setting value is adjusted according to the main steam temperature control deviation in step 2 in the form of: where f(e T ) is the main steam temperature deviation e T piecewise function of .

[0016] As a further improvement of the present invention, in step 2, the intermediate point temperature setting value is adjusted according to the superheated desuperheating water flow rate. First, a linear function of the actual power P and the superheated desuperheating water consumption is fitted with reference to the operating data as the reference value D. sp =f(P).

[0017] As a further improvement of the present invention, in step 2, the intermediate point temperature setting value is adjusted according to the superheating and cooling water flow rate, and the actual superheating and cooling water consumption D is different from the superheating and cooling water consumption D. sp The deviation is used as the input of the pure integrator, and the output of the integrator is the correction value of the mid-point temperature setting.

[0018] As a further improvement of the present invention, in step 2, the intermediate point temperature setting value is adjusted according to the superheated desuperheating water flow rate, and the integration time of the pure integrator is 30000s.

[0019] As a further improvement of the present invention, the step 3 sets the sampling time of the iterative predictive controller parameters

[0020] T s=2s, control time domain m=5, error weighting coefficient matrix Q=0.0001I, control increment weighting coefficient matrix R=I,

[0021] The prediction time domain p=100.

[0022] As a further improvement of the present invention, the iterative predictive controller in step 4 is a main controller, and the sub-controller is a PI controller.

[0023] As a further improvement of the present invention, the parameter range of the PI controller of the auxiliary controller in the step is: the first-stage superheated desuperheating water regulating valve K1 = 0.5-1.5, T i1 =60-150, secondary superheating and desuperheating water regulating valve K2=1.0-2.5, T i2 =100-180.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The method described in this invention utilizes an iterative predictive control approach to overcome the numerous disturbances and significant nonlinearity inherent in superheated desuperheated water systems. Furthermore, a real-time correction strategy for intermediate temperature is incorporated to enhance the flexibility of desuperheated water regulation. The control algorithm is simple and readily applicable in engineering practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a control diagram of the superheated desuperheating water system of a thermal power unit. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0028] Figure 1 This is a control diagram of the superheated desuperheating water system of a thermal power unit, which mainly includes the following steps:

[0029] A method for controlling the main steam temperature of a thermal power unit comprises the following steps:

[0030] The present invention provides a main steam temperature control method for a thermal power unit, comprising the following steps, characterized in that:

[0031] Step 1: Based on historical operating data, a discrete linearized state-space model is obtained for the relationship between the desuperheating water valve outlet temperature and the secondary desuperheater temperature and the main steam temperature under different operating conditions. The discrete linearized state-space model is established using the superheating desuperheating water valve outlet temperature on the left and right sides of the primary and secondary systems, the secondary superheating desuperheating water valve inlet temperature, and the main steam temperature. The discrete linearized state-space model is in the form of:

[0032]

[0033] where x=(x1, x2, ..., x n ), u=(u1, u2, .., u nu ), y=(y1, y2, ..., y ny ) is the n-dimensional state variable, nu-dimensional input variable, and ny-dimensional output variable of the superheated and desuperheated water system. Linearization is performed in a small range near the load point Pi, x = x p +Δx,u=u p +Δu,y=y p +Δy,A p 、B p 、C p and D p They are the system matrix, input matrix, output matrix and conversion matrix of the linear model, and they are all Jacobi matrices.

[0034] Step 2: Adjust the midpoint temperature setting value according to the main steam temperature control deviation and the superheated desuperheating water flow rate. The form of adjusting the midpoint temperature setting value according to the main steam temperature control deviation is: where f(e T ) is the main steam temperature deviation e T Piecewise function of . Generally refer to:

[0035] <![CDATA[Main steam temperature deviation e T / ℃]]> Midpoint temperature correction / ℃ -100 -5 -10 -5 -4 -1 4 1 10 5 100 5

[0036] Adjust the midpoint temperature setting value according to the superheated desuperheating water flow rate, and refer to the operating data to fit the linear function of the actual power P and the superheated desuperheating water consumption as the benchmark value D sp =f(P). Actual superheating and desuperheating water consumption D and superheating and desuperheating water consumption D sp The deviation is used as the input of the pure integrator, and the output of the integrator is the correction value of the midpoint temperature setting. The integration time of the pure integrator is 30000s.

[0037] Step 3: Set the iterative predictive controller parameters, such as Figure 1 As shown, the iterative predictive controller is the main controller and the sub-controller is the PI controller. Set the iterative predictive controller parameter sampling time T s = 2s, control time domain m = 5, error weighting coefficient matrix Q = 0.0001I, control increment weighting coefficient matrix R = I,

[0038] The prediction time domain p=100.

[0039] Step 4: Calculate the valve opening according to the output of the iterative predictive controller in step 3 as the PID setting value of the desuperheating water flow valve opening. The parameter range of the PI controller of the auxiliary controller is: the first stage superheating desuperheating water regulating valve

[0040] K1=0.5-1.5,Ti1 =60-150, secondary superheating and desuperheating water regulating valve K2=1.0-2.5, T i2 =100-180.

[0041] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent variation based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A method for controlling main steam temperature of thermal power unit , comprising the following steps, characterized in that: Step 1: Based on historical operating data, a discrete linearized state space model of the desuperheater valve outlet temperature versus the secondary desuperheater temperature and main steam temperature under different operating conditions is obtained. Step 2: Adjust the midpoint temperature setting value according to the main steam temperature control deviation and the superheated desuperheating water flow rate; In step 2, the intermediate point temperature setting value is adjusted according to the main steam temperature control deviation in the form of: , where f(e T ) is the main steam temperature deviation e T Piecewise function of ; Step 3: Set the iterative predictive controller parameters; Step 4: Calculate the valve opening based on the output of the iterative predictive controller in step 3 as the PID setting value of the cooling water flow valve opening.

2. according to claim 1 A method for controlling main steam temperature of thermal power unit , characterized in that: The historical data required for the discrete linearized state space model of step 1 include: the superheated and desuperheated water regulating valve outlet temperature on the left and right sides of the first and second stages, the second stage superheated and desuperheated water regulating valve inlet temperature and the main steam temperature.

3. according to claim 1 A method for controlling main steam temperature of thermal power unit , characterized in that: The form of the training discrete linearized state space model in step 1 is: ； where x=(x1, x2, ..., x n ), u=(u1, u2, ..., u nu ), y=(y1, y2, ..., y ny ) is the n-dimensional state variable, nu-dimensional input variable and ny-dimensional output variable of the superheated desuperheated water system, and is linearized in a small range near the load point Pi, x = x p +Δx,u=u p +Δu,y=y p +Δy,A p 、B p 、C p and D p are the system matrix, input matrix, output matrix and transfer matrix of the linearized state space model, and are all Jacobi matrices.

4. according to claim 1 A method for controlling main steam temperature of thermal power unit , characterized in that: In step 2, the midpoint temperature setting value is adjusted according to the superheated desuperheating water flow rate. First, the linear function of the actual power P and the superheated desuperheating water consumption is fitted with reference to the operating data as the reference value D. sp =f(P).

5. according to claim 4 A method for controlling main steam temperature of thermal power unit , characterized in that: In step 2, the midpoint temperature setting value is adjusted according to the superheating and cooling water flow rate, and the actual superheating and cooling water consumption D is different from the superheating and cooling water consumption D sp The deviation is used as the input of the pure integrator, and the output of the integrator is the correction value of the mid-point temperature setting.

6. according to claim 5 A method for controlling main steam temperature of thermal power unit , characterized in that: In step 2, the midpoint temperature setting value is adjusted according to the superheated desuperheating water flow rate, and the integration time of the pure integrator is 30,000 seconds.

7. according to claim 1 A method for controlling main steam temperature of thermal power unit , characterized in that: Step 3 sets the sampling time T of the iterative predictive controller parameters s =2s, control time domain m=5, error weighting coefficient matrix Q=0.0001I, control increment weighting coefficient matrix R=I, prediction time domain p=100.

8. according to claim 1 A method for controlling main steam temperature of thermal power unit , characterized in that: In step 4, the iterative predictive controller is the main controller and the secondary controller is the PI controller.

9. according to claim 1 A method for controlling main steam temperature of thermal power unit , characterized in that: The parameter range of the PI controller of the auxiliary controller in the step is: the first-stage superheated desuperheating water regulating valve K1 = 0.5-1.5, T i1 =60-150, secondary superheating and desuperheating water regulating valve K2 = 1.0-2.5, T i2 =100-180.

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