CN105387449A - Method for controlling steam temperature of boiler through second-order differential - Google Patents

Abstract

The invention discloses a method for controlling steam temperature of a boiler through the second-order differential and belongs to the technical field of boiler automatic control. The method comprises the following steps that 1, a high-order inertia transfer function model of a boiler steam temperature process inert segment is obtained through a steam temperature system feature test; 2, the high-order inertia transfer function model in the step 1 is converted into a state space model; 3, based on the state space model in the step 2, a state observer of a state variable is designed; 4, a second-order differential signal of an outlet steam temperature signal is structured according to the state observer in the step 3; 5, the control gain Kd2 of the second-order differential signal is set; 6, the control gain Kd2 in the step 5 is multiplied by the second-order differential signal in the step 4 and added to an output function u0(t) of a proportional plus integral plus derivative controller, and an adjusted controller output function is obtained. The method has the beneficial effect that the control performance quality of a big-delay and great-inertia steam temperature object is improved.

Description

A kind of control method using second-order differential in boiler steam temperature controls

Technical field

The invention belongs to Automatic Control of Boiler technical field, relate to the control method of boiler steam temperature, especially relate to a kind of control method using second-order differential in boiler steam temperature controls.

Background technology

The control of station boiler vapor (steam) temperature is one of basic control system of large-scale power station unit automation operation.But due to the particularity of thermal power generation production process and the complexity of jet chimney structure, more difficult to the control of vapor (steam) temperature object.Wherein because the randomness of unit load fluctuates, cause disturbance frequent and disturbance quantity is comparatively large, especially for the disturbance of unit load or equivalently steam flow, cause steam temperature often to fluctuate.Regulatory PID control scheme is difficult to obtain satisfied control effects.Because regulatory PID control has obvious limitation for the Great inertia system that vapor (steam) temperature process is such: lack the foresight to to-be development trend.Although its differential action describes the development trend of signal, the effect of first differential is still not enough for Great inertia system, is equivalent to us and just knows the speed that signal is current.If introduce second derivative action, be equivalent to the acceleration being aware of signal, this has no report in utility boiler control field, one of reason is that second-order differential is very responsive for the measurements interference of signal, because the polytropy of the complexity of environment, fuel source etc. factor makes measurements interference be seen everywhere in the measuring system of station boiler parameter, therefore the antinoise of second-order differential is calculated and just become the key of dealing with problems.

As seen from the above analysis, existing boiler steam temperature PID control method has some limitations or defect.

Summary of the invention

Technical problem to be solved by this invention is: provide a kind of control method increasing second-order differential in the main PID controller of station boiler vapor (steam) temperature external loop, and the building method to the insensitive second-order differential signal of measurement noises, the control performance quality of the vapor (steam) temperature object of raising large delay, Great inertia.

The technical scheme that technical solution problem of the present invention adopts comprises the steps:

Step 1. is tested by vapor (steam) temperature system performance, obtains the Higher-order inertia link transfer function model in boiler steam temperature process inertia district;

In described step 1, the form of the Higher-order inertia link transfer function model in inertia district is as shown in the formula shown in (1):

$\frac{y\left(s\right)}{z\left(s\right)}=\frac{K}{{(Ts+1)}^n}---\left(1\right)$

Wherein, s represents Laplace operator;

Y (s) represents the Laplace transform of outlet steam temperature signal y;

Z (s) represents the Laplace transform of steam temperature signal z after direct-contact desuperheater;

K represents the steady-state gain of steam temperature object inertia section model;

T represents the time constant of steam temperature object inertia section model;

N represents the order of steam temperature object inertia section model, span 3 ~ 6.

Higher-order inertia link transfer function model in step 1 is converted to state-space model by step 2.;

In described step 2, the form of the state-space model that Higher-order inertia link transfer function model is converted to is as shown in the formula shown in (2):

$\left\{\begin{array}{c}{\stackrel{\·}{x}}_1=-\frac{1}{T}{x}_1+\frac{1}{T}{x}_2\\ {\stackrel{\·}{x}}_2=-\frac{1}{T}{x}_2+\frac{1}{T}{x}_3\\ .\\ .\\ .\\ {\stackrel{\·}{x}}_n=-\frac{1}{T}{x}_n+\frac{K}{T}z\end{array}\right.---\left(2\right)$

Wherein, y=x ₁, y represents outlet steam temperature signal;

X ₁, x ₂..., x _nrepresent n state of vapor (steam) temperature process inertia zone state spatial model respectively;

represent the first differential of n state of vapor (steam) temperature process inertia zone state spatial model respectively.

Step 3. based on the state-space model in step 2, the state observer of design point variable;

In described step 3, the formula (3) of the state observer of design point variable is as follows:

$\left\{\begin{array}{c}{\stackrel{\·}{\hat{x}}}_1=-\frac{1}{T}{\hat{x}}_1+\frac{1}{T}{\hat{x}}_2+L_{1}e\\ {\stackrel{\·}{\hat{x}}}_2=-\frac{1}{T}{\hat{x}}_2+\frac{1}{T}{\hat{x}}_3+L_{2}e\\ .\\ .\\ .\\ {\stackrel{\·}{\hat{x}}}_n=-\frac{1}{T}{\hat{x}}_n+\frac{K}{T}z+L_{n}e\end{array}\right.---\left(3\right)$

Wherein, represent that the observer of outlet steam temperature signal exports;

represent the observation of n state of vapor (steam) temperature process inertia zone state spatial model respectively;

represent the first differential of the observation of n state of vapor (steam) temperature process inertia zone state spatial model respectively;

E represents measured value y and its observation of outlet steam temperature signal between deviation, namely

L ₁, L ₂..., L _nrepresent the gain of state observer respectively, design according to modern control theory.

Step 4. is based on the second-order differential signal of the state observer structure outlet steam temperature signal in step 3

The second-order differential signal of the outlet steam temperature signal of structure in described step 4 formula (4) as follows:

$\stackrel{\·\·}{y}\≈\stackrel{\·\·}{\hat{y}}=\frac{1}{T}\×({\hat{x}}_1-2{\hat{x}}_2+{\hat{x}}_3)---\left(4\right)$

Wherein, represent the second-order differential of vapor (steam) temperature and observation thereof respectively.

Step 5. is adjusted second-order differential signal ride gain K _d2;

Second-order differential signal in described step 5 ride gain K _d2=K _p× T _d2, T _d2=N × n × T × T _d1;

Wherein, N is coefficient, span 0.03 ~ 0.1;

K _pit is the proportional gain of PID controller;

T _d1and T _d2first differential time and second-order differential time respectively.

Step 6. is by the ride gain K in step 5 _d2be multiplied by the second-order differential signal in described step 4 and with the output function u of PID (PID) controller ₀t () is added, controller output function u (t) after being adjusted, namely $u\left(t\right)=u_0\left(t\right)+K_{d2}\stackrel{\·\·}{y}.$

Beneficial effect of the present invention: to the vapor (steam) temperature object of large delay, Great inertia, by the introducing of second-order differential regulating action, only need by carrying out simple configuration realization in widely used scattered control system, vapor (steam) temperature adjusting function more better than conventional cas PID control can be obtained, the stability of enhancing system and robustness, improve economy and the security of unit operation.

Accompanying drawing explanation

Fig. 1 is conventional vapor (steam) temperature cas PID control systematic schematic diagram.

Fig. 2 is the cascade control system schematic diagram using second-order differential during vapor (steam) temperature provided by the invention controls.

Wherein symbol description: y _rfor vapor (steam) temperature setting value; Y is vapor (steam) temperature measured value; z _rfor the output of external loop PID controller, be then the output of the PID controller with second-order differential for the present invention, be also leading steam temperature setting value simultaneously; Z is leading steam temperature measured value; U is the output of inner looping PI controller, as the control signal driving desuperheating water valve; K _d2for the ride gain of external loop second-order differential signal of the present invention; " ∫ " represents integral sign; E is the error between vapor (steam) temperature measured value and observer observation.

Detailed description of the invention

Below in conjunction with specific embodiments and the drawings, 1 ~ 2 couple of the present invention is described in more detail.

As shown in Fig. 1 ~ 2, the concrete steps of embodiment are as follows:

Step 1.n gets 4, is tested by vapor (steam) temperature system performance, and the Higher-order inertia link transfer function model obtaining boiler steam temperature process inertia district obtains

Wherein, s represents Laplace operator;

Y (s) represents the Laplace transform of outlet steam temperature signal y;

Z (s) represents the Laplace transform of steam temperature signal z after direct-contact desuperheater.

Higher-order inertia link transfer function model in step 1 is converted to state-space model by step 2.:

$\left\{\begin{array}{c}{\stackrel{\·}{x}}_1=-\frac{1}{49}{x}_1+\frac{1}{49}{x}_2\\ {\stackrel{\·}{x}}_2=-\frac{1}{49}{x}_2+\frac{1}{49}{x}_3\\ {\stackrel{\·}{x}}_3=-\frac{1}{49}{x}_3+\frac{1}{49}{x}_4\\ {\stackrel{\·}{x}}_4=-\frac{1}{49}{x}_4+\frac{1.6}{49}z\end{array}\right.$

y＝x ₁

Wherein, x ₁, x ₂, x ₃, x ₄represent 4 states of vapor (steam) temperature process inertia zone state spatial model;

represent the first differential of 4 states of vapor (steam) temperature process inertia zone state spatial model.

Step 3. based on the state-space model in step 2, the state observer of design point variable:

$\left\{\begin{array}{c}{\stackrel{\·}{\hat{x}}}_1=-\frac{1}{49}{\hat{x}}_1+\frac{1}{49}{\hat{x}}_2+L_{1}e\\ {\stackrel{\·}{\hat{x}}}_2=-\frac{1}{49}{\hat{x}}_2+\frac{1}{49}{\hat{x}}_3+L_{2}e\\ {\stackrel{\·}{\hat{x}}}_3=-\frac{1}{49}{\hat{x}}_3+\frac{1}{49}{\hat{x}}_4+L_{3}e\\ {\stackrel{\·}{\hat{x}}}_4=-\frac{1}{49}{\hat{x}}_4+\frac{1.6}{49}z+L_{4}e\end{array}\right.$

$\hat{y}={\hat{x}}_1$

Wherein, represent the observation of 4 states of vapor (steam) temperature process inertia zone state spatial model;

represent the first differential of the observation of 4 states of vapor (steam) temperature process inertia zone state spatial model;

E represents measured value y and its observation of outlet steam temperature signal between deviation, namely

According to modern control theory, the gain of design point observer is respectively L ₁=0.1633, L ₂=0.4898, L ₃=0.6531, L ₄=0.3265.

Step 4. is based on the second-order differential signal of the state observer structure outlet steam temperature signal in step 3

$\stackrel{\·\·}{y}\≈\stackrel{\·\·}{\hat{y}}=\frac{1}{T}\×({\hat{x}}_1-2{\hat{x}}_2+{\hat{x}}_3)$

Wherein, represent the second-order differential of vapor (steam) temperature and observation thereof respectively.

Step 5. is adjusted second-order differential signal ride gain K _d2=K _pt _d2;

Further, the ride gain K of second-order differential signal in described step 5 _d2=K _p× T _d2, T _d2=(0.03 ~ 0.1) × 4 × T × T _d1, wherein K _pthe proportional gain of PID controller, T _d1and T _d2first differential time and second-order differential time respectively.

Step 6. is by the ride gain K in step 5 _d2act on the second-order differential signal in step 4 and the output function u of conventional PID (PID) controller that is added to ₀(t), thus form new controller output u (t), namely obtain $u\left(t\right)=u_0\left(t\right)+K_{d2}\stackrel{\·\·}{y}=u_0\left(t\right)+K_{d2}\stackrel{\·\·}{y}.$

Bottom in Fig. 2 is that observer realizes, and symbol is wherein shown in the related content in description.

Above-mentioned detailed description is illustrating for possible embodiments of the present invention, and this embodiment is also not used to limit the scope of the claims of the present invention, all do not depart from of the present invention equivalence implement or change, all should be contained in the scope of patent protection of this case.

Claims (6)

1. in boiler steam temperature controls, use a control method for second-order differential, it is characterized in that step is as follows: step 1. is tested by vapor (steam) temperature system performance, obtain the Higher-order inertia link transfer function model in boiler steam temperature process inertia district;

Higher-order inertia link transfer function model in step 1 is converted to state-space model by step 2.;

Step 3. based on the state-space model in step 2, the state observer of design point variable;

Step 4. is based on the second-order differential signal of the state observer structure outlet steam temperature signal in step 3

Step 5. is adjusted second-order differential signal ride gain K _d2;

Step 6. is by the ride gain K in step 5 _d2be multiplied by the second-order differential signal in described step 4 and with the output function u of PID (PID) controller ₀t () is added, controller output function u (t) after being adjusted, namely $u\left(t\right)=u_0\left(t\right)+K_{d2}\stackrel{\·\·}{y}.$

2. a kind of control method using second-order differential in boiler steam temperature controls according to claim 1, is characterized in that: in described step 1, the form of the Higher-order inertia link transfer function model in inertia district is as shown in the formula shown in (1):

$\frac{y\left(s\right)}{z\left(s\right)}=\frac{K}{{(Ts+1)}^n}---\left(1\right)$

Wherein, s represents Laplace operator;

Y (s) represents the Laplace transform of outlet steam temperature signal y;

Z (s) represents the Laplace transform of steam temperature signal z after direct-contact desuperheater;

K represents the steady-state gain of steam temperature object inertia section model;

T represents the time constant of steam temperature object inertia section model;

N represents the order of steam temperature object inertia section model, span 3 ~ 6.

3. a kind of control method using second-order differential in boiler steam temperature controls according to claim 2, is characterized in that: in described step 2, the form of the state-space model that Higher-order inertia link transfer function model is converted to is as shown in the formula shown in (2):

$\left\{\begin{array}{c}{\stackrel{\·}{x}}_1=-\frac{1}{T}{x}_1+\frac{1}{T}{x}_2\\ {\stackrel{\·}{x}}_2=-\frac{1}{T}{x}_2+\frac{1}{T}{x}_3\\ \·\\ \·\\ \·\\ {\stackrel{\·}{x}}_n=-\frac{1}{T}{x}_n+\frac{K}{T}z\end{array}\right.---\left(2\right)$

Wherein, y=x ₁, y represents outlet steam temperature signal;

X ₁, x ₂..., x _nrepresent n state of vapor (steam) temperature process inertia zone state spatial model respectively;

represent the first differential of n state of vapor (steam) temperature process inertia zone state spatial model respectively.

4. a kind of control method using second-order differential in boiler steam temperature controls according to claim 3, is characterized in that: in described step 3, the formula (3) of the state observer of design point variable is as follows:

$\left\{\begin{array}{c}{\stackrel{\·}{\hat{x}}}_1=-\frac{1}{T}{\hat{x}}_1+\frac{1}{T}{\hat{x}}_2+L_{1}e\\ {\stackrel{\·}{\hat{x}}}_2=-\frac{1}{T}{\hat{x}}_2+\frac{1}{T}{\hat{x}}_3+L_{2}e\\ \·\\ \·\\ \·\\ {\stackrel{\·}{\hat{x}}}_n=-\frac{1}{T}{\hat{x}}_n+\frac{K}{T}z+L_{n}e\end{array}\right.---\left(3\right)$

Wherein, represent that the observer of outlet steam temperature signal exports;

represent the observation of n state of vapor (steam) temperature process inertia zone state spatial model respectively;

represent the first differential of the observation of n state of vapor (steam) temperature process inertia zone state spatial model respectively;

E represents measured value y and its observation of outlet steam temperature signal between deviation, namely

L ₁, L ₂..., L _nrepresent the gain of state observer respectively, design according to modern control theory.

5. a kind of control method using second-order differential in boiler steam temperature controls according to claim 4, is characterized in that: the second-order differential signal of the outlet steam temperature signal of structure in described step 4 formula (4) as follows:

$\stackrel{\·\·}{y}\≈\stackrel{\·\·}{\hat{y}}=\frac{1}{T}\×({\hat{x}}_1-2{\hat{x}}_2+{\hat{x}}_3)---\left(4\right)$

Wherein, represent the second-order differential of vapor (steam) temperature and observation thereof respectively.

6. a kind of control method using second-order differential in boiler steam temperature controls according to claim 5, is characterized in that: second-order differential signal in described step 5 ride gain K _d2=K _p× T _d2, T _d2=N × n × T × T _d1;

Wherein, N is coefficient, span 0.03 ~ 0.1;

K _pit is the proportional gain of PID controller;

T _d1and T _d2first differential time and second-order differential time respectively.