CN113093550A - Method for optimizing open-loop characteristic from coal quantity to main steam pressure of boiler of thermal power generating unit - Google Patents
Method for optimizing open-loop characteristic from coal quantity to main steam pressure of boiler of thermal power generating unit Download PDFInfo
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Abstract
A method for optimizing the open-loop characteristic from the coal quantity of a boiler to the main steam pressure of a thermal power generating unit relates to the technical field of power generation of the thermal power generating unit, in particular to the performance adjustment from the coal quantity of the boiler to the main steam pressure. The invention aims to solve the problems that an open loop link from the coal quantity of a boiler to main steam pressure is not a gradual system and is not beneficial to engineering setting of controller parameters, and an optimal regulation performance cannot be obtained only by using an experimental trial and error method in an AGC (automatic gain control) operation mode of the conventional thermal power generating unit. According to the method for optimizing the open-loop characteristic from the coal quantity of the boiler of the thermal power generating unit to the main steam pressure, the state linear feedback control law is applied to the open-loop system from the coal quantity of the boiler of the thermal power generating unit to the main steam pressure, so that the open-loop system is converted into a gradually stable system, the parameters of a controller can be conveniently adjusted, and the optimal adjusting performance can be obtained.
Description
Technical Field
The invention belongs to the technical field of power generation of thermal power generating units, and particularly relates to performance adjustment from boiler coal quantity to main steam pressure.
Background
The power generation process of the thermal power generating unit is that the boiler burns coal to generate heat to heat water to generate high-temperature and high-pressure steam, so that the steam turbine is pushed to do work, and finally the generator is driven to rotate to generate power. From the perspective of energy conservation, the coal quantity burned by the boiler corresponds to the power generated by the steam turbine one by one, and the power generated by the steam turbine increases as the coal quantity burned by the boiler increases. When the power generation of the steam turbine is constant, the coal quantity burned by the boiler is continuously increased, the redundant energy is converted into the internal energy of the steam, and the steam pressure (main steam pressure) is increased.
With the enlargement of the new energy grid-connected scale, the action of the thermal power generating unit is gradually changed from the previous main power generation force to the current main power adjustment force, and the thermal power generating unit is required to have rapid load change capability. In order to adapt to the quick load change of the thermal power generating unit, the load control of the thermal power generating unit is automatically controlled (namely, an AGC control system of the thermal power generating unit). An AGC (automatic gain control) control system of a thermal power generating unit generally adopts a coordinated control mode mainly comprising a boiler and a steam turbine, namely the steam turbine adjusts the power generation load, and the boiler adjusts the main steam pressure to ensure that the loads of the boiler and the steam turbine are consistent.
When the AGC control system of the thermal power generating unit normally operates, the power generation power of the steam turbine is accurately controlled, the boiler combustion coal quantity corresponds to the power generation power, and the boiler load is ensured to be consistent with the steam turbine load. At the moment, the amount of the coal burned by the boiler is increased, the redundant energy is converted into the internal energy of the steam, the steam pressure (main steam pressure) is continuously increased until the safety value of the main steam pressure is exceeded, and the AGC control system pushes out an automatic state and converts the automatic state into a manual control state. That is, when the AGC control system of the thermal power generating unit normally operates and the main steam pressure is adjusted by the amount of boiler coal, the open loop characteristic from the amount of boiler coal to the main steam pressure (the dynamic response characteristic of the main steam pressure when the amount of boiler coal increases) is an integral link.
At present, in the industrial control process of a thermal power generating unit and the like, the main flow of a control method is PID control, and a small part of the control method adopts predictive control. The PID control engineering setting requires that the open-loop characteristic of the equipment is a gradual stability system, the equipment object of the predictive control is more required to be a gradual stability system, and the open-loop characteristic from the boiler coal quantity to the main steam pressure (the dynamic response characteristic of the main steam pressure when the boiler coal quantity is increased) is an integral link, is not a gradual stability system, is not beneficial to the engineering setting of the controller parameters, only can use an experimental trial and error method, and cannot obtain the optimal regulation performance.
Disclosure of Invention
The invention provides a method for optimizing the open loop characteristic from the coal quantity of a boiler to the main steam pressure of a thermal power generating unit, aiming at solving the problems that the open loop link from the coal quantity of the boiler to the main steam pressure of the existing thermal power generating unit is not a gradual stabilization system, is not beneficial to the engineering setting of the parameters of a controller, can only use an experimental trial and error method and cannot obtain the optimal regulation performance.
An open-loop characteristic optimization method from coal quantity of a boiler of a thermal power generating unit to main steam pressure is characterized in that a state linear feedback control law is applied to an open-loop system from the coal quantity of the boiler of the thermal power generating unit to the main steam pressure, and the open-loop system is converted into a gradual-stable system.
Specifically, the specific method of applying the state linear feedback control law includes:
feeding back the state of the matrix k1 k2]First number k of1Multiplying the steam evaporation flow of the steam pocket at the previous moment to obtain a first feedback value,
feeding back the state of the matrix k1 k2]Second number k of2Multiplying the pressure of the steam drum at the previous moment to obtain a second feedback value,
and subtracting the first feedback value and the second feedback value from the total coal quantity of the boiler to obtain a current input value of the open-loop system, and inputting the current input value into the open-loop system to finish the application of the state linear feedback control law.
Specifically, the method for obtaining the state feedback matrix includes:
the method comprises the following steps: linearizing a mathematical model of an open loop system from the coal quantity of a boiler of a thermal power generating unit to main steam pressure, converting the obtained linearized model into a state space model,
step two: adding a state feedback controller in the state space model to obtain a closed-loop system space state model,
step three: and adjusting a feedback coefficient in the state feedback controller by using the linear quadratic regulator until the pole of the closed-loop control system reaches a preset expected value, wherein the feedback coefficient at the moment is a state feedback matrix.
Specifically, in the first step, the expression of the state space model is as follows:
wherein x (t) is the deviation of the state at time t, Δ μB(t) open-loop system input μ at time tBDeviation amount of (t), Δ PT(t) is the open-loop system output quantity P at the time tT(t), A is a state matrix, B is an input matrix, C is an output matrix, and D is a feedforward matrix.
Specifically, the expression of the state feedback controller in the second step is as follows:
u(t)＝-Kx(t)
wherein u (t) is the output quantity of the state feedback controller, and K is the state feedback matrix.
Specifically, the closed-loop system spatial state model expression in the second step is as follows:
the invention adopts an LQR (linear response) positive-fixed-state linear feedback control law to convert the open-loop characteristic of the boiler coal quantity instruction-main steam pressure from an unstable system (an integral link) into a gradually stable system, so that the parameters of the controller can be conveniently set, and the optimal regulation performance can be obtained.
Drawings
FIG. 1 is a schematic diagram showing the influence of a boiler coal amount command on main steam pressure in a normal operation state of an AGC control system of a thermal power generating unit, wherein muBTau is the pure delay time of the combustion channel, T, for the total coal quantityFIs the inertia time constant of the combustion channel, SDIs the steam evaporation flow of the steam drum, SFMain steam flow, CBIs the heat storage time constant, P, of the steam drumdIs drum pressure, PTMain steam pressure, KshIs the resistance coefficient of the superheater tubes;
FIG. 2 is a schematic diagram showing the influence of a boiler coal amount command on main steam pressure after a state linear feedback control law is added when an AGC control system of a thermal power generating unit operates normally;
FIG. 3 is an open-loop characteristic curve diagram of a boiler coal amount command-main steam pressure when an AGC control system of a thermal power generating unit is in normal operation;
fig. 4 is an open-loop characteristic curve diagram of a boiler coal quantity instruction-main steam pressure when the AGC control system of the thermal power generating unit is in normal operation and after a state linear feedback control law is added.
Detailed Description
The first embodiment is as follows: referring to fig. 1 to 4, the present embodiment is described in detail, where the LQR (linear quadratic regulator) theory is a state space design method that is the earliest and most mature in modern control theory, and can simply define a state linear feedback control law to set an unstable system, thereby obtaining a gradually stable system. In the method for optimizing the open-loop characteristic from the coal quantity of the boiler of the thermal power generating unit to the main steam pressure according to the embodiment, a state linear feedback control law is applied to an open-loop system from the coal quantity of the boiler of the thermal power generating unit to the main steam pressure, and a state feedback matrix is set based on the LQR theory, so that the open-loop system is converted into a gradually stable system.
The specific process is as follows:
linearizing the linear mathematical model of the open-loop system from the boiler coal amount to the main steam pressure of the thermal power generating unit in fig. 1 by taking the boiler coal amount instruction as an input amount and the main steam pressure as an output amount, and converting the obtained linear model into a state space model
The state space model expression is as follows:
wherein x (t) is the deviation of the state at time t, Δ μB(t) open-loop system input μ at time tBDeviation amount of (t), Δ PT(t) is the open-loop system output quantity P at the time tT(t), A is a state matrix,
B is an input matrix,
C is an output matrix,
D is feedforward matrix, D ═ 0]。
Step two: adding a state feedback controller in the state space model to obtain a closed-loop system space state model,
the state feedback controller expression is as follows:
u(t)＝-Kx(t)
where u (t) is the output of the state feedback controller, K is the state feedback matrix, and K ═ K1 k2]，K＝[1.60 1.77]。
The closed-loop system space state model expression is as follows:
step three: using linear quadraticThe type regulator adjusts a feedback coefficient in the state feedback controller until a pole of the closed-loop control system reaches a preset expected value, and the feedback coefficient at the moment is a state feedback matrix. The linear quadratic regulator adjusts the state feedback matrix by varying the state change weight Q and the control input change weight R, where R is 0.39,
the specific method for applying the state linear feedback control law comprises the following steps:
feeding back the state of the matrix k1 k2]First number k of1Multiplying the steam evaporation flow of the steam pocket at the previous moment to obtain a first feedback value,
feeding back the state of the matrix k1 k2]Second number k of2Multiplying the pressure of the steam drum at the previous moment to obtain a second feedback value,
and subtracting the first feedback value and the second feedback value from the total coal quantity of the boiler to obtain a current input value of the open-loop system, and inputting the current input value into the open-loop system to finish the application of the state linear feedback control law.
As shown in fig. 1, the linear mathematical model is a model reflecting the influence of the boiler coal amount command on the main steam pressure when the boiler coal amount command adjusts the main steam pressure when the AGC control system of the thermal power unit normally operates. The open loop characteristic (step response) of the boiler coal amount command-main steam pressure is shown in fig. 3, and is an integral link.
As shown in fig. 2, the mathematical model is a mathematical model reflecting the influence of a boiler coal amount command on the main steam pressure after a state linear feedback control law is added when the AGC control system of the thermal power generating unit operates normally. The open-loop characteristic of the boiler coal quantity instruction-main steam pressure is converted into a gradual-stabilization system from an integral link through a state linear feedback control law. The open loop characteristic (step response) of the boiler coal amount command-main steam pressure is shown in fig. 4, and is a gradual system.
In fig. 1 and 2, s is the complex frequency of the laplace transform, e-τsRepresenting a pure delay element with a delay time of tau,
representing an inertia time constant of TFThe first-order inertia element of (1),
representing the integration element.
Claims (10)
1. A method for optimizing the open-loop characteristic from the coal quantity of a boiler of a thermal power generating unit to main steam pressure is characterized in that a state linear feedback control law is applied to an open-loop system from the coal quantity of the boiler of the thermal power generating unit to the main steam pressure, and the open-loop system is converted into a gradual-stable system.
2. The method for optimizing the open-loop characteristic from the coal quantity to the main steam pressure of the thermal power generating unit boiler according to claim 1, wherein the specific method for applying the state linear feedback control law comprises the following steps:
feeding back the state of the matrix k1 k2]First number k of1Multiplying the steam evaporation flow of the steam pocket at the previous moment to obtain a first feedback value,
feeding back the state of the matrix k1 k2]Second number k of2Multiplying the pressure of the steam drum at the previous moment to obtain a second feedback value,
and subtracting the first feedback value and the second feedback value from the total coal quantity of the boiler to obtain a current input value of the open-loop system, and inputting the current input value into the open-loop system to finish the application of the state linear feedback control law.
3. The method for optimizing the open-loop characteristic from the coal quantity to the main steam pressure of the thermal power generating unit boiler according to claim 2, wherein the state feedback matrix is obtained by a method comprising the following steps:
the method comprises the following steps: linearizing a mathematical model of an open loop system from the coal quantity of a boiler of a thermal power generating unit to main steam pressure, converting the obtained linearized model into a state space model,
step two: adding a state feedback controller in the state space model to obtain a closed-loop system space state model,
step three: and adjusting a feedback coefficient in the state feedback controller by using the linear quadratic regulator until the pole of the closed-loop control system reaches a preset expected value, wherein the feedback coefficient at the moment is a state feedback matrix.
4. The method for optimizing the open-loop characteristic from the coal quantity to the main steam pressure of the thermal power generating unit boiler according to claim 3, wherein in the first step, the expression of the state space model is as follows:
wherein x (t) is the deviation of the state at time t, Δ μB(t) open-loop system input μ at time tBDeviation amount of (t), Δ PT(t) is the open-loop system output quantity P at the time tT(t), A is a state matrix, B is an input matrix, C is an output matrix, and D is a feedforward matrix.
5. The method for optimizing the open-loop characteristic from the coal quantity to the main steam pressure of the thermal power generating unit boiler according to claim 3, wherein in the second step, the expression of the state feedback controller is as follows:
u(t)＝-Kx(t)
wherein u (t) is an output quantity of the state feedback controller, K is a state feedback matrix, and x (t) is a deviation quantity of a state at the time t.
6. The method for optimizing the open-loop characteristic from the coal quantity to the main steam pressure of the thermal power generating unit boiler according to claim 3, wherein the expression of the closed-loop system space state model in the second step is as follows:
wherein x (t) is the deviation of the state at time t, K is the state feedback matrix, and Δ μB(t) is at time tInput quantity mu of ring systemBDeviation amount of (t), Δ PT(t) is the open-loop system output quantity P at the time tT(t), A is a state matrix, B is an input matrix, C is an output matrix, and D is a feedforward matrix.
7. The method for optimizing the open loop characteristic from the coal quantity of the thermal power unit boiler to the main steam pressure according to claim 4, 5 or 6,
D＝[0]。
8. the method for optimizing the open-loop characteristic from the coal quantity to the main steam pressure of the thermal power generating unit boiler according to claim 7, wherein the linear quadratic regulator adjusts the state feedback matrix by changing the state change weight Q and the control input change weight R.
9. The method for optimizing the open-loop characteristic from the coal quantity to the main steam pressure of the thermal power generating unit boiler according to claim 8, wherein R is 0.39,
10. the method for optimizing the open-loop characteristic of the coal quantity to the main steam pressure of the thermal power unit boiler according to claim 9, wherein K is [ 1.601.77 ].
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