US20140217745A1

US20140217745A1 - Systeme de commande pour regulation multivariable de centrale thermique a flamme

Info

Publication number: US20140217745A1
Application number: US14/122,659
Authority: US
Inventors: Eve Dufosse
Original assignee: Individual
Current assignee: Electricite de France SA
Priority date: 2011-05-26
Filing date: 2012-05-25
Publication date: 2014-08-07
Also published as: EP2715074A1; RU2611113C2; WO2012160206A1; JP6037519B2; EP2715074B1; FR2975797A1; RU2013157365A; FR2975797B1; JP2014522461A; KR20140051179A

Abstract

Control system for multivariable regulation of a fossil fuel power station comprising: —a boiler (103) and auxiliaries assembly (102), with a fuel supply (GC), which is the heat source of a circuit for fluid in steam phase over part of said circuit, said steam supplying —a turbine (114) at a pressure (P) and a temperature (T), which is connected to an alternator producing electrical power (W), the supply of steam being determined by the opening (SR) of regulating valves upstream of said turbine (114), the system comprising: —a loop for regulating the steam pressure (P), —a loop for regulating the electrical power (W), with at least one loop based on a power station internal model command, one considering a pure delay τ in a parameter of the internal model, one variable in each loop acting as a disturbing influence in the other.

Description

GENERAL TECHNICAL FIELD

The invention relates to a control system for fossil fuel power station for generation of electricity from fuel.
The invention relates more precisely to a control device of such a power station for monitoring power and ensuring that some criteria of the state of the superheated steam are respected, as well as a power station comprising such a system, and a control process of a power station by the execution of such a control system.
The invention could apply for example to a coal-fired power station.

PRIOR ART

The control of a fossil fuel power station must take into account several variables of the physical system.
A power station, whereof FIG. 1 presents a schematic illustration, produces electricity from a heat source fed by fuel. The production of heat is governed by the fuel supply GC of the heat source, here a boiler 103. This heat is transmitted to a working fluid circulating in a circuit to have it pass from the liquid state to the gaseous state, such that this working fluid is in steam phase over part of the circuit. Regulating valves whereof the state is defined by their opening SR can regulate the feed of a turbine 114. At its input, the state of the steam is defined by a certain pressure P and a certain temperature T. The steam enables rotation of the turbine 114 which is mechanically connected to an alternator 116, the latter producing electric power W.
The power station illustrated in FIG. 1 will be described in more detail in the description hereinbelow.
The most traditional approach for realiser the commande d′une such a power station consists of using different coordinated monovariable regulators of type PI (integral proportional). A regulator PI is closed-loop regulation which enables regulation of the error between an instruction and measurement of a value. The regulator PI exerts on the error a proportional and integral double action—it multiplies the error by a fixed factor, the gain,—it integrates the error over a certain time span and divides the integrated value by another fixed factor. In this way each variable regulator of the system has an input and an output.
The system in question is of multivariable nature—that is, at least one input exerts an influence on several outputs. Multivariable systems with such monovariable regulators see their stability greatly affected over time. This same multivariable character makes parametering difficult. Also, the performance of thermal power stations varies between high and low load. The regulations must therefore respond to robustness criteria not permitted by monovariable regulators.
It is also possible to utilise multivariable regulators of H∞ type. This method allows designing of optimal commands according to a mathematical standard for linear systems. However, the performance of a fossil fuel power station controlled by such a system is not entirely satisfactory.
Another approach present in the state of the art consists of running a predictive command. Such control requires real-time calculation of the minimum of a quadratic cost function. The necessary capacity of calculation and memory are not often available in existing installations. Also, this approach requires heavy means to be put in place.
An aim of the invention is therefore to propose a power station control system for eliminating these disadvantages.
An aim of the invention is therefore more precisely to propose a power station control system offering regulation for good power dynamics, having interesting characteristics of robustness, stability and rapidity.
Another aim of the invention is that this control system can easily be put in place in existing fossil fuel power stations.

DESCRIPTION OF THE INVENTION

The invention proposes fulfilling these aims.
For this purpose, on propose according to a first aspect a control system for the regulation multivariable d′une fossil fuel power station pour the generation of electricity from fuel comprising:

- an assembly comprising a boiler and its auxiliaires forming the subject matter of a fuel supply to act as heat source in a working fluid circuit such that the latter is in steam phase over part of said circuit,
- a turbine supplied by said steam at steam pressure and temperature, said turbine being mechanically connected to an electrical alternator producing electric power, the steam feed of said turbine being determined by the opening of regulating valves located upstream of said turbine, said system comprising:
  - a loop for regulating steam pressure having
  - a control variable and an instruction,
  - a loop for regulating electric power having
  - a control variable and an instruction,
    and at least one of the regulating loops is based on an internal model command type taking into account a pure delay τ of one of the parameters of the internal model of the power station, and for each of the regulating loops a variable of a loop being taken into account as a disturbing influence in the other loop.

The invention according to the first aspect is advantageously completed by the following characteristics, taken singly or in any of their technically possible combinations:

- the steam pressure regulating loop comprises a rejection chain of disturbing influence for taking into account a variable of the loop for regulating electric power as a disturbing influence;
- the variable of the loop for regulating electric power taken into account as a disturbing influence in said regulating loop of steam pressure is the opening of regulating valves upstream of the turbine;
- the regulating loop of steam pressure comprises a modelling chain of a transfer function between the fuel supply and the contribution at the steam pressure of the fuel supply, said modelling chain not taking into account the variable of the loop for regulating electric power taken into account in said regulating loop of steam pressure as a disturbing influence;
- the pure delay τ is taken into account in the regulating loop of steam pressure in the modelling chain of the transfer function between the fuel supply and the contribution at the steam pressure of the fuel supply;
- the modelling chain of a transfer function between the fuel supply and the contribution at the steam pressure of the fuel supply is of form G₁(s)·e^−τs, with G₁(s) a stable function of the first order;
- the regulating loop of steam pressure comprises a determination chain of a control variable without disturbing influence for determining a control variable without disturbing influence from a steam pressure instruction.
- the control variable of the regulating loop of steam pressure is the fuel supply achieved by the output of the determination chain of the control variable without disturbing influence from which the output of the rejection chain of disturbing influence is subtracted;
- the system comprises a determination chain of the control variable without disturbing influence, a rejection chain of disturbing influence and a modelling chain of a transfer function between the fuel supply and the contribution at the steam pressure of the fuel supply of form G₁(s)·e^−τs, with G₁(s) a stable function of the first order and in which:
  - the determination chain of the control variable without disturbing influence is constituted by a transfer function inputting a steam pressure instruction, function of type G₁ ⁻¹(s)·F₁(s), with F₁(s) a filter of greater order or equal to the order of G1(s), and
  - the rejection chain of disturbing influence is constituted by a transfer function G₁ ⁻¹(s)·F₂(s), with F₂(s) a filter of greater order or equal to the order of G1(s);
- the steam pressure regulating loop comprises a return loop without delay, for taking into account, in the determination of the fuel supply, the part of said modelling chain of a transfer function between the fuel supply and the contribution at the steam pressure of the fuel supply which is independent of the pure delay τ;
- the variable of the pressure regulating loop taken into account in said loop for regulating electric power as a disturbing influence is the steam pressure;
- the loop for regulating electric power comprises a proportional integral regulator and a rejection chain of disturbing influence and anticipation of follow-up of instruction for taking into account a variable of the regulating loop of steam pressure as a disturbing influence;
- the opening of regulating valves upstream of the turbine is achieved by the output of the integral proportional regulator from which is subtracted the output of the rejection chain of disturbing influence and anticipation of follow-up of instruction of the regulating loop of the electric power;
- parameters of the regulating loop based on an internal model command type are estimated online by an adaptive regulation method, said adaptive regulation inputting variables of the control system.

According to a second aspect, the invention proposes a fossil fuel power station comprising

- an assembly comprising a boiler and its auxiliaires forming the subject matter of a fuel supply for acting as heat source to a working fluid circuit such that the latter is in steam phase over part of said circuit,
- a turbine supplied by said steam at a steam pressure and temperature, said turbine being mechanically connected to an electrical alternator producing electric power, the steam feed of said turbine being determined by the opening of regulating valves located upstream of said turbine,
- a control system according to the first aspect.

According to a third aspect, the invention proposes a control process of a fossil fuel power station according to the second aspect, in which:

- the steam pressure is regulated by a loop for regulating steam pressure, and
- the electric power is regulated by a loop for regulating electric power,
- at least one of the regulating loops being based on an internal model command type taking into account a pure delay τ of one of the parameters of the internal model of the power station, and for each of the regulating loops, a variable of a loop being taken into account as a disturbing influence in the other loop.

PRESENTATION OF FIGURES

Other aspects, aims and advantages of the present invention will emerge from the following detailed description. The invention will also be more clearly understood in reference to this description when considered in conjunction with the attached diagrams, given by way of non-limiting examples and in which:

FIG. 1 is a summarised schema of a fossil fuel power station known to the expert,

FIG. 2 illustrates a diagram for regulation of superheated steam pressure P according to a first embodiment of the system according to the invention,

FIG. 3 illustrates a regulation diagram for superheated steam pressure P according to a second embodiment of the system according to the invention,

FIG. 4 is a diagram for regulation of produced electric power W corresponding to the two embodiments of the system according to the invention,

FIG. 5 is a diagram for adaptive regulation corresponding to the first embodiment of the system according to the invention,

FIGS. 6A and 6B are curves of temporal evolution of several magnitudes in response to an echelon of production of electric power by way of comparison between a control system according to the first embodiment of the invention and a system of H∞ type.

The present invention is described in detail hereinbelow within the particular, though non-limiting, scope of a control system of a coal-fired power station.

DETAILED DESCRIPTION

FIG. 1 is a summarised and simplified diagram of a fossil fuel power station 100. The solid arrows 107 represent circulation of the working fluid both in liquid and gaseous phase. This working fluid is a heat-transfer fluid which is most often water. So, in the interests of simplification, the working fluid is water in the present description. The simplified operating principle is the following.
The fuel supply GC causes the fuel to be directed to the assembly 102 comprising the boiler 103 and its auxiliaires. The fuel undergoes treatment, then combustion per se. Combustion of the fuel releases heat, represented by the white arrows 105, which is especially transferred to water which circulates in the tubes of an exchanger 104. This water passes into the steam state. The balloon 106 separates liquid water from steam, the latter partant in an assembly of superheaters 108. The superheaters 108 can be subject to additional injections of water via the water injection system 110, whereof one of the actuators allows the control of injection of overheating desuperheating water Q_DSHT.
In the superheaters of the assembly 108, the temperature and the pressure of water increase sharply. Water passes to the superheated steam state. This steam is conveyed to the turbine 114, passing through regulating valves 112 located upstream of the first body of the turbine and whereof the opening is defined by the parameter SR. Between the regulating valves 112 and the turbine 114, the superheated steam has a temperature T and pressure P.
Once in the high-pressure body HP of the turbine, the steam undergoes relaxation which allows rotation of the turbine wheels. The water then rfeturns to the system 108, via a resuperheater, before rejoining the body of average pressure MP, then the low-pressure body BP of the turbine. In the body MP and BP a similar relaxation phenomenon also enables rotation of the turbine wheels 114. Such rotation drives the electrical alternator 116, producing electric power W. Once the relaxed steam has passed through the turbine it is admitted to the condenser 118, where it is cooled. It then goes into the liquid state and could begin a new cycle.
The applicant has noticed that fossil fuel power stations are governed by non-linear equations whereof control systems of the prior art make a linear approximation which is unsatisfactory. This non-linearity results especially from the pure delay affecting the effect of the fuel supply GC on the magnitudes to be controlled.
Also the fuel supply GC has oscillations during strong power demands, which causes major stress on the boiler 103 and depollution elements present at the evacuation level of the boiler 103.
The applicant has noted that the invention produces a fuel supply which causes no excessive stress on the boiler and the depollution elements, extending their service life. Also, the invention circumvents problems inherent in the presence of a delay resulting from the conveying, processing and possible heating of the fuel.
A first embodiment of the invention in the event of a control system of a coal-fired power station is illustrated by FIGS. 2 and 4.
According to this embodiment, the control system relates to a coal-fired power station whereof the operation corresponds to FIG. 1 described hereinabove. The system to be controlled is of multivariable type.
The inputs of this system are:

- the opening of regulating valves upstream of the turbine SR(t),
- the coal feed GC(t),
- the injection of overheating desuperheating water Q_DSHT(t).
- The outputs of this system are:
- the electric power produced W(t),
- the superheated steam pressure P(t),
- the temperature of superheated steam T(t).

Identification of the dynamic performance of the system derives from linearised equations based on physical laws:

- For the electric power W:

W(t)=a·SR(t)+b·P(t)
W therefore depends linearly on the opening of regulating valves SR and the steam pressure P, superheated steam pressure in this embodiment. The coefficients a and b are coefficients defined according to considerations experimental the characteristics of the power station and according to considerations of security, efficacy and service life of installations. For example, a and b can respectively have as possible values 0.77 and 3.4.

- For the superheated steam pressure P,

T ₁ ·{dot over (P)} ₁(t)+P ₁(t)=K ₁ ·GC(t−τ)
T ₂ ·{dot over (P)} ₂(t)+P ₂(t)=K ₂ ·SR(t)
P(t)=P ₁(t)+P ₂(t)
T₁, K₁, T₂and K₂and the pure delay τ are constants. They are defined according to experimental considerations, the characteristics of the power station and according to considerations of security, efficacy and service life of installations. For example possible, values of these constants are respectively T₁=190; K₁=1.8; T₂=193; K₂=−0.326 and τ=100. P1(t) and P2(t) represent respectively the contribution of the fuel supply GC and of the opening of regulating valves SR at steam pressure P.

- For the temperature of superheated steam (T):

a ₂ ˜{umlaut over (T)}(t)+a ₁ ·{dot over (T)}(t)+T(t)=K ₃ ·Q _DSHT(t)+K ₄ GC(t−τ)+K ₅ ·SR(t)+K ₆ ·P(t)
According to this embodiment of the invention, the aim is to adapt the internal model control method to the power station, which is defined in that the control system of the power station must comprise a representation of the physical process to be controlled.
The present embodiment of the invention comprises:

- a regulating loop 200 of superheated steam pressure P, shown in FIG. 2,
- a regulating loop 400 of electric power W, shown in FIG. 4.

For each of the regulating loops 200, 400, a variable of a loop is taken into account as a disturbing influence in the other loop. Also, each of said loops comprises a control variable the actioning of which regulates performance of the power station.
FIG. 2 shows a regulating loop 200 of superheated steam pressure P corresponding to the first embodiment of the invention described. The regulating loop 200 comprises a rejection chain of disturbing influence 202, a determination chain of the control variable without disturbing influence 204 and a modelling chain 206 of a transfer function H_GC-P1between the fuel supply GC and the contribution P1 at the steam pressure P of the fuel supply GC.
Rejection chain of disturbing influence in the present description means a regulating loop element taking into account by its input a variable considered as a disturbing influence in said regulating loop with the aim of rejecting it, that is, exempting it from its effect, by its being taken into account upstream of the determination of the control variable of said regulating loop.
The input of the regulating loop 200 is the reference pressure P_REFas an instruction pressure whereof the value is especially fixed according to the characteristics of the power station and according to considerations of security, efficacy and service life of installations. The output of the regulating loop 200 is the superheated steam pressure P and takes into account as a disturbing influence to be rejected the opening of the regulating valves SR upstream of the turbine 114.
The functional diagram of FIG. 2 shows a real chain 208 whereof the transfer functions H_GC-P1and H_SR-P2represent the real operation of installations of the power station 100 such as described in FIG. 1. This representation of the real chain 208 decomposes the superheated steam pressure P into two components P1 and P2. The first component of the pressure P1 is the component dependent on the coal feed GC which does not consider the opening of regulating valves SR. P1 therefore represents the contribution of the fuel supply GC at the steam pressure P. The second component of the pressure P2 is the component dependent on the opening of regulating valves SR. P2 therefore represents the contribution of the opening of regulating valves SR at the steam pressure P.
The real chain 208 here comprises two transfer functions. The transfer function H_GC-P1is the function linking the fuel supply GC to the contribution P1 of the latter at the steam pressure P. The transfer function H_SR-P2is the function linking the opening of regulating valves SR to the contribution P2 of the latter at the steam pressure P.
The modelling chain 206 models the transfer function H_GC-P1between the coal feed GC and the contribution P1 at the steam pressure P of the coal feed GC. This modelling chain 206 does not consider the opening of regulating valves SR which comes from the regulating loop 400 of power W.
The regulating loop 200 of steam pressure P takes into account a pure delay τ. The pure delay τ between the coal feed GC and the pressure P is taken into account in the modelling chain 206 of the transfer function H_GC-P1between the coal feed GC and the contribution P1 at the steam pressure P of the fuel supply GC. The modelling of the transfer function H_GC-P1is of form G₁(s)·e^−τs, with G₁(s) a stable function of the first order, reversible. At present, for the expert and for the present description those functions having s for variable are Laplace transforms.
The output magnitude of the modelling chain 206 is subtracted at the steam pressure P to obtain the input of the rejection chain of disturbing influence 202.
The determination chain of the control variable without disturbing influence 204 is constituted by a transfer function inputting an instruction of steam reference pressure P_REF, function of type G₁ ⁻¹(s)·F₁(s), with F₁(s) a filter of type
$\frac{1}{{(1 + λ_{1} \cdot s)}^{n}},$
with λ₁>0 and n greater than the order of G₁ ⁻¹(s).
The rejection chain of disturbing influence 202 is constituted by a transfer function G₁ ⁻¹(s)·F₂(s), with F₂(s) a filter of type
$\frac{1}{{(1 + λ_{2} \cdot s)}^{m}},$
with λ₂>0 and m greater than the order of G₁ ⁻¹(s). Its result is subtracted from that of the determination chain of the control variable without disturbing influence 204 to obtain the coal feed GC.
In summary, in the system shown in FIG. 2, a reference pressure instruction P_REFpasses via a transfer function of type G₁ ⁻¹(s)·F₁(s), then the output of the rejection chain of disturbing influence 202 is subtracted from the output of this transfer function.
The resulting fuel supply GC is then taken as input of a transfer function H_GC-P1whereof the output is added to the output of a transfer function H_SR-P2inputting the opening of regulating valves SR.
The addition of these outputs, which represent the respective contributions P₁and P₂of the fuel supply GC and the opening of regulating valves SR at pressure P, is therefore this same pressure P, since P=P₁+P₂. The output of a transfer function of modelling 206 of type G₁(s)·e^−τ·staking the fuel supply GC as input is subtracted at the pressure P.
The result of this subtraction is an input for the rejection transfer function of disturbing influence 202 of type G₁ ⁻¹(s)·F₂(s), whereof the output is subtracted from the output of the transfer function 204 of type G₁ ⁻¹(s)·F₁(s) inputting the reference pressure instruction P_REF, as shown earlier.
FIG. 4 shows a regulating loop 400 of electric power W corresponding to the embodiment described. The regulating loop 400 of electric power comprises an integral proportional regulator 402 and a rejection chain of disturbing influence and anticipation of follow-up of instruction 404.
The regulating loop 400 inputs the instruction of electric power W_REF, whereof the value is fixed especially as a function of the power station load and of the demand for electricity, and also as a function of the physical characteristics of the power station.
The output of the regulating loop 400 is the electric power W and takes into account as a disturbing influence the superheated steam pressure P, which is a variable of the regulating loop 200 of steam pressure P. The functional diagram of FIG. 4 shows a real chain 406 whereof the functions represent the real operation of installations of the power station 100 such as described in FIG. 1 in the form of a transfer function H_SR-Wbetween the opening of regulating valves SR and the electric power W.
The integral proportional regulator 402 inputs the difference ε between the instruction of electric power W_REFand the electric power W produced by the power station.
A rejection chain of disturbing influence and anticipation of follow-up of instruction 404 inputs the reference instruction of electric power W_REFand the steam pressure P, the latter variable being taken into account as a disturbing influence to be rejected. The steam pressure P is multiplied by the coefficient b of the internal model of the power station which connects the steam pressure P to the electric power W in the equation W(t)=a·SR(t)+b·P(t). The result is subtracted from the reference instruction of electric power W_REF.
The result of this subtraction is then divided by the coefficient a of the internal model of the power station which connects the opening of regulating valves SR to the electric power W in the equation W(t)=a·SR(t)+b·P(t).
The opening of regulating valves SR upstream of the turbine 114 is achieved by the output of the integral proportional regulator 402 from which is subtracted the output of the rejection chain of disturbing influence and anticipation of follow-up of instruction 404 of the regulating loop 400 of the electric power W.
Regulating of electric power W shown by the regulating loop 400 is therefore done by anticipations on the power instruction W_REFand the superheated steam pressure P. In fact, the equation governing the performance of electric power shows that there is no dynamic effect.
In summary, in the system illustrated by FIG. 4, a regulator PI inputs reference a instruction of electric power W_REFfrom which is subtracted the electric power W; this regulator rejects the modelling errors of the electric power W.
The reference instruction of electric power W_REF, from which is subtracted the steam pressure P multiplied by b, is also divided by the coefficient a in a rejection chain of disturbing influence and anticipation of follow-up of instruction 404.
The result of this rejection chain of disturbing influence and anticipation of follow-up of instruction 404 is subtracted from the output of the regulator PI to give the opening of regulating valves SR.
The opening of regulating valves SR is an input for a transfer function H_SR-Wof the system to be controlled and which outputs the electric power W.
As described above, the control system described by the invention is based on models of the process used in a fossil fuel power station. The different parameters of these models can derive from onsite measurements. To identify the transfer functions H_GC-P1and H_SR-P1of the regulating loop 200 of the steam pressure P, the Strejc method could for example be applied. For the transfer function H_SR-Wof the produced electric power W, it is possible to use the method of least squares.
An added advantage of the present invention is to allow application of the adaptive regulation, as illustrated by FIG. 5 described hereinbelow, to the regulating loop 200 of steam pressure P. The online estimation of parameters can be done for example by the ARX method (from the English Auto Regressive model with eXternal inputs for auto-regressive model with external inputs).
The temperature control of the superheated steam T is done by a regulator of type H∞, as the dynamic modelling of the temperature is not reliable. The intrinsic robustness of the regulator H∞ is therefore interesting in this very case.
The different regulation laws are then associated to produce coordinated multivariable control of the magnitudes to be controlled.
A second embodiment of the present invention corresponds to a system equivalent to that described in the first embodiment, by substituting the regulating loop 300 of steam pressure P shown in FIG. 3 for the regulating loop 200 of steam pressure P shown in FIG. 2.
FIG. 3 shows a regulating loop 300 of superheated steam pressure P corresponding to a second embodiment of the invention described hereinbelow. The regulating loop 300 comprises a rejection chain of disturbing influence 302, a determination chain of the control variable 304, a modelling chain 306 of a transfer function H_GC-P1between the fuel supply GC and the contribution P1 at the steam pressure P of the fuel supply GC and a return loop without delay 316.
The regulating loop 300 inputs the reference pressure P_REFas a pressure instruction whereof the value is fixed especially according to the characteristics of the power station and according to considerations of security, efficacy and service life of installations.
The regulating loop 300 outputs the superheated steam pressure P and considers as disturbing influence to be rejected the opening of regulating valves SR upstream of the turbine 114. The functional diagram of FIG. 3 shows a real chain 308 whereof the functions H_GC-P1and H_SR-P2represent the real operation of installations of the power station 100 such as described in FIG. 1. This representation of the real chain 308 decomposes the superheated steam pressure P into two components P1 and P2. The first component of the pressure P1 is the component dependent on the coal feed GC which does not consider the opening of regulating valves SR. The second component of the pressure P2 is the component dependent on the opening of regulating valves SR which does not consider the coal feed GC.
The real chain 308 is here composed of two transfer functions. The transfer function H_GC-P1is the function linking the fuel supply GC to the contribution P1 of the latter at the steam pressure P. The transfer function H_SR-P2is the function linking the opening of regulating valves SR to the contribution P2 of the latter at the steam pressure P.
The modelling chain 306 models a transfer function H_GC-P1between the coal feed GC and the contribution P1 at the steam pressure P of the coal feed GC. This modelling chain 306 does not consider the variable SR which comes from the regulating loop 400 of power W.
The regulating loop 300 of steam pressure P takes into account a pure delay τ. The pure delay τ is taken into account in the modelling chain 306, modelling chain of a transfer function H_GC-P1between the fuel supply GC and the contribution P1 at the steam pressure P of the fuel supply GC.
The modelling of the transfer function H_GC-P1between GC and P1 is of form G₁(s)·e^−τs, with G₁(s) a stable function of the first order, reversible. It is however decomposed into two transfer functions G₁(s) and e^−τs, G₁(s) located upstream of e^−τson the modelling chain 306, G₁(s) being the component independent of the pure delay τ and e^−τsthe component corresponding to the pure delay. The output magnitude of the modelling chain 306 is subtracted at the steam pressure P to produce the input of the rejection chain of disturbing influence 302.
The regulating loop 300 of pressure P comprises a return loop without delay 316 inputting the magnitude at output of the transfer function G₁(s) of the modelling chain 306 corresponding to the component of the modelling independent of the pure delay τ. This magnitude at output therefore has value G₁(s)·GC(s). The latter value is subtracted by the return loop without delay 316 from the instruction of superheated steam pressure P_REFat the level of the determination chain 304 of the control variable. The rejection chain of disturbing influence 302 models a transfer function R₂(s) applied at the steam pressure P. The transfer function R₂(s) defines the response to disturbing influences. R₂(s) is of form 1−M(s)·e^−L·s.
It verifies the following conditions:

- the zeros of the function 1−M(s)·e^—Lsmust compensate the slowest poles of G₁(s),
- M(0)=1,
- The poles of M(s) are placed to produce the preferred dynamic.

Its result is subtracted from the instruction of superheated steam pressure P_REF.
The determination chain of the control variable 304 inputs the instruction of superheated steam pressure P_REF. The result of the rejection chain of disturbing influence 302 and the result of the return loop without delay 316 are subtracted from the instruction of superheated steam pressure P_REF. The fuel supply GC is achieved from the application of a transfer function R₁(s) to the magnitude resulting from these comparisons. This transfer function R₁(s) of the determination chain of the control variable 306 defines the dynamic of the instruction follow-up and can be for example a regulator of type PID (proportional integral derivative).
In summary, in the system shown in FIG. 3, is subtracted the output of a rejection chain of disturbing influence 302, then the output of a loop without delay 316 is subtracted from a reference pressure instruction P_REF. The result on completion of these two subtractions passes via a transfer function R₁(s) to give the fuel supply GC.
This fuel supply GC passes via a transfer function H_GC-P1of the system to be controlled to give the contribution P₁of the fuel supply GC at the steam pressure P.
The opening of regulating valves SR passes via a transfer function H_SR-P2of the system to be controlled to give the contribution P₂of the opening of regulating valves SR at the steam pressure P.
The sum of respective contributions P₁and P₂of the fuel supply GC and the opening of regulating valves SR gives the steam pressure P.
The fuel supply GC passes via a transfer function G₁(s), whereof the output is both returned by the loop without delay 316 as mentioned above, and also is an input for a transfer function e^−τ·swhereof the output is subtracted from the superheated steam pressure P. The result of this subtraction passes via a transfer function R₂(s) of the rejection chain of disturbing influence 302 whereof the output is subtracted from the reference pressure instruction P_REF, as mentioned above aut.
FIG. 5 illustrates the possibility of executing adaptive regulation known to the expert within the scope of the first embodiment. It presents non-limiting a possible application of adaptive regulation to the regulating loop 200 of steam pressure P.
FIG. 5 shows adaptive regulation inputting variables of the system, possibly present in the regulating loop 200 of steam pressure P, such as fuel supply GC, opening of regulating valves SR, and steam pressure P.
From the measurement of these variables, adaptive regulation can conduct online estimation of parameters of the regulating loop 200 of steam pressure P, for example those present in the transfer functions of the rejection chain of disturbing influence 202, the determination chain of the control variable without disturbing influence 204, and the modelling chain 206 of a transfer function H_GC-P1between the fuel supply GC and the contribution P1 at the steam pressure P of the fuel supply GC. The measurement of input variables, undertaken regularly, updates the values taken by the parameters estimated online by adaptive regulation.
Online estimation of parameters can be done for example by the ARX method (from the English Auto Regressive model with eXternal inputs for auto-regressive model with external inputs). Equivalent adaptive regulation is possible for the second embodiment of the invention whereof the particular features are shown in FIG. 3.
FIGS. 6A and 6B show a comparison between the responses from a coal-fired power station controlled by means of the control system according to the first embodiment of the invention and a control system as per regulators of type H∞.
FIG. 6A presents the comparison of regulations according to the invention in solid lines and with the regulations of type H∞ in dashes in terms of produced electric power W and of steam pressure P, in response to echelons of instruction of electric power W. The system according to the invention allows better follow-up of power W, especially faster, and limits oscillations. The steam pressure P is better regulated to the extent where it oscillates less relative to an instruction of 155 bar.
FIG. 6B shows the comparison of regulations according to the invention en trait continu and with the regulations of type H∞ in dashes in terms of fuel supply GC and opening of the regulating valves SR in response to the same echelons of electric power as in FIG. 6A.
The system according to the invention allows notable reduction of oscillations in the fuel supply GC. This control quality reduces stresses on the assembly 102 comprising the boiler 103 and its auxiliaires and permits optimal exploitation of depollution elements. Regulation of the power station 100 by the system according to the invention is more dynamic and ensures lower stress on the boiler 103.
According to a second aspect, the invention proposes a fossil fuel power station comprising

- an assembly 102 comprising a boiler 103 and its auxiliaires forming the subject matter of a fuel supply GC for acting as heat source to a working fluid circuit such that the latter is in steam phase over part of said circuit,
- a turbine 114 supplied by said steam at steam pressure P and temperature T, said turbine 114 being mechanically connected to an electrical alternator 116 producing electric power W, the steam feed of said turbine 114 being determined by the opening SR of regulating valves located upstream of said turbine 114,
- a control system according to the first aspect.
  According to a third aspect, the invention proposes a control process of a fossil fuel power station according to the second aspect, in which
- the steam pressure P is regulated by a loop for regulating steam pressure P, and
- the electric power is regulated by a loop for regulating electric power W,
  the regulating loops being based on an internal model control of the power station, one of the regulating loops taking into account a pure delay τ of one of the parameters of the internal model of the power station, and for each of the regulating loops a variable of a loop being taken into account as a disturbing influence in the other loop.

More generally, the third aspect of the invention relates to any execution of a control system according to the first aspect in a fossil fuel power station, and any control process of a fossil fuel power station executed by the control process according to the first aspect.

Claims

1. A control system for multivariable regulation of a fossil fuel power station for the generation of electricity from fuel, said power station comprising:

an assembly (102) comprising a boiler (103) and its auxiliaires forming the subject matter of a fuel supply (GC) for acting as heat source to a working fluid circuit such that the latter is in steam phase over part of said circuit,

a turbine (114) supplied by said steam at a steam pressure (P) and temperature (T), said turbine (114) being mechanically connected to an electrical alternator (116) producing electric power (W), the steam feed of said turbine (114) being determined by the opening (SR) of regulating valves located upstream of said turbine (114), said control system comprising:

a regulating loop (200, 300) of steam pressure (P) having a control variable and an instruction (P_REF),

a regulating loop (400) of electric power (W) having a control variable and an instruction (W_REF),

characterised in that at least one of the regulating loops (200, 300, 400) is based on an internal model command type, defined in that it comprises a representation of a physical process to be controlled, taking into account a pure delay τ of one of the parameters of the internal model of the power station, and

for each of the regulating loops (200, 300, 400) a variable of a loop is taken into account as a disturbing influence in the other loop.

2. The control system according to claim 1, in which the regulating loop (200, 300) of steam pressure (P) comprises a rejection chain of disturbing influence (202, 302) for taking into account a variable of the loop for regulating electric power (W) as a disturbing influence.

3. The control system according to any one of the preceding claims, in which the variable of the regulating loop (400) of electric power (W) taken into account as a disturbing influence in said regulating loop of steam pressure (P) is the opening of regulating valves (SR) upstream of the turbine (114).

4. The control system according to any one of the preceding claims, in which the regulating loop (200, 300) of steam pressure (P) comprises a modelling chain (206, 306) of a transfer function (H_GC-P1) between the fuel supply (GC) and the contribution (P1) at the steam pressure (P) of the fuel supply (GC), said modelling chain (206, 306) not taking into account the variable of the regulating loop (400) of electric power (W) taken into account in said regulating loop (200, 300) of steam pressure (P) as a disturbing influence.

5. The control system according to claim 4, in which the pure delay τ is taken into account in the regulating loop (200, 300) of steam pressure (P) in the modelling chain (206, 306) of the transfer function (H_GC-P1) between the fuel supply (GC) and the contribution (P1) at the steam pressure (P) of the fuel supply (GC).

6. The control system according to any one of claims 4 or 5, in which the modelling chain (206) of a transfer function (H_GC-P1) between the fuel supply (GC) and the contribution (P1) at the steam pressure (P) of the fuel supply (GC) is of form G₁(s)·e^−τs, with G₁(s) a stable function of the first order.

7. The control system according to any one of the preceding claims, in which the regulating loop (200) of steam pressure (P) comprises ane determination chain (204) of a control variable without disturbing influence for determining a control variable without disturbing influence from a steam pressure (P_REF) instruction.

8. The control system according to claims 2 and 7 in combination, in which the control variable of the regulating loop (200) of steam pressure (P) is the fuel supply (GC) achieved by the output of the determination chain (204) of the control variable without disturbing influence from which is subtracted the output of the rejection chain of disturbing influence (202).

9. The control system according to any one of the preceding claims, in which the system comprises a determination chain (204) of the control variable without disturbing influence, a rejection chain of disturbing influence (202) and a modelling chain (206) of a transfer function (H_GC-P1) between the fuel supply (GC) and contribution (P1) at the steam pressure (P) of the fuel supply (GC) of the form G₁(s)·e^−τs, with G₁(s) a stable function of the first order and in which:

the determination chain (204) of the control variable without disturbing influence is constituted by a transfer function inputting a steam pressure instruction (P_REF), function of type G₁ ⁻¹(s)·F₁(s), with F₁(s) a filter of greater order or equal to the order of G1(s), and

the rejection chain of disturbing influence (202) is constituted by a transfer function G₁ ⁻¹(s)·F2(s), with F₂(s) a filter of greater order or equal to the order of G1(s).

10. The control system according to claim 5, in which the regulating loop (300) of steam pressure (P) comprises a return loop without delay (316) for taking into account, in the determination of the fuel supply (GC), the part of said modelling chain (306) of a transfer function between the fuel supply (GC) and contribution (P1) at the steam pressure (P) of the fuel supply (GC) which is independent of the pure delay τ.

11. The control system according to any one of the preceding claims, in which the variable of the regulating loop (200, 300) of pressure (P) taken into account in said regulating loop (400) of electric power (W) as a disturbing influence is the steam pressure (P).

12. The control system according to any one of the preceding claims, in which the regulating loop (400) of electric power (W) comprises an integral proportional regulator (402) and a rejection chain of disturbing influence and anticipation of follow-up of instruction (404) for taking into account a variable of the regulating loop (200) of steam pressure (P) as a disturbing influence.

13. The control system according to claim 12, in which the opening of regulating valves (SR) upstream of the turbine (114) is achieved by the output of the integral proportional regulator (402) from which is subtracted the output of the rejection chain of disturbing influence and anticipation of follow-up of instruction (404) of the regulating loop (400) of the electric power (W).

14. The control system according to any one of the preceding claims, in which parameters of the regulating loop (200, 300) based on an internal model command type are estimated online by an adaptive regulation method, said adaptive regulation inputting variables (GC, SR, P) of the control system.

15. A fossil fuel power station comprising:

an assembly (102) comprising a boiler (103) and its auxiliaires forming the subject matter of a fuel supply (GC) to serve as heat source to a working fluid circuit such that the latter is in steam phase over part of said circuit,

a turbine (114) supplied by said steam at a steam pressure (P) and temperature (T), said turbine (114) being mechanically connected to an electrical alternator (116) producing electric power (W), the steam feed of said turbine (114) being determined by the opening (SR) of regulating valves located upstream of said turbine (114),

characterised in that it comprises a control system according to any one of the preceding claims.

16. A control process of a fossil fuel power station according to claim 15, characterised in that:

the steam pressure (P) is regulated by a regulating loop (200, 300) of steam pressure (P), and

the electric power is regulated by a regulating loop (400) of electric power (W),

at least one of the regulating loops (200, 300, 400) being based on an internal model command type taking into account a pure delay τ of one of the parameters of the internal model of the power station, and for each of the regulating loops (200, 300, 400) a variable of a loop being taken into account as a disturbing influence in the other loop.