EP0684366A1 - Process and system for the control and regulation of the power of a steam power plant - Google Patents

Abstract

The control and regulation system uses a process model (100), for simulating the dynamic response characteristics of the steam power plant and a power regulation (2), with the switching to a new power level effected via signals (B, S) for the fuel feed and the turbine valve setting, so that the regulator is essentially inactive. A pre-regulation is provided by a pre-regulator (101) for fresh steam regulation, supplied with a steam pressure value (Ps) via the process model, ensuring that the pre-regulator also remains essentially inactive.

Description

The invention relates to a method for model-based control and regulation of the output of a steam power plant block according to the preamble of claim 1. The invention also relates to a device for carrying out the method.

Such a method is known from DE 36 32 041 C2. This method, including an addition, which relates to a method for restoring the turbine reserve after correcting a power setpoint change, is also known from DE 41 24 678 C2. The known method is particularly suitable for frequency control by means of a power setpoint change in a steam power plant block, for example due to a drop in network frequency, and in particular in compliance with the requirements for the power dynamics, which are described by the Deutsche Verbundgesellschaft eV, Heidelberg, (DVG) in the publication "Das supply-appropriate behavior of thermal power plants ", DVG, October 1991. The inventive method should also meet the DVG requirements, in particular the defined dynamics in the event of a change in performance.

In the known method, a process model is used which provides signals for a control intervention in the steam generation and turbine inlet valve position, so that only minor deviations from the power regulator need to be corrected. In the event of a predetermined abrupt increase in power, the method ensures a strictly monotonous or at least monotonous transition to the new performance level.

The modification and addition of the method according to DE 36 32 041 C2 described in DE 41 24 678 C2 has the effect that the model-based restoration of the throttling of the turbine inlet valves is also included in the entire control process.

The methods known from the cited documents allow both the operating modes "boiler leads, turbine follows" and "turbine leads, boiler follows".

However, the methods known from the cited publications work only in sliding pressure mode and are therefore not suitable for fixed pressure mode.

There is also a need for a further improvement with regard to the speed and stability of the regulation of heating faults, which occur in particular in lignite-fired boilers due to the nature of the coal.

EP-A2-0100 532 discloses a method for regulating the output of a steam power plant block with a once-through steam generator. The fuel supply to the steam generator is regulated by a power regulator; a parallel control of the fuel supply does not take place. Not even direct or indirect control of the turbine inlet valves.

The process works with a pre-pressure control. The specified pressure setpoint is influenced by a pressure correction signal. The turbine inlet valves are operated in such a way that steam is withdrawn or stored as required. The correction signal is formed using a model-based electrical simulation of the steam generator behavior. The control signal of the power controller is fed to the simulation as an input signal. However, this means that only a low degree of coordination of the pressure setpoint and fuel supply can be achieved. The dynamic behavior of the output controller output signal is not only dependent on the output behavior of the controlled system, but also on the parameters of the output controller.

The electrical simulation of the steam generator used in EP-A2-0100 532 and its use is not to be equated with the process model of the method according to DE 36 32 041 C2 or DE 41 24 678 C2. A control behavior in the sense of the DVG requirements mentioned at the beginning cannot be achieved completely with the method according to EP-A2-0100 532 because a power component to be removed is not explicitly present. There is no clear separation in the recording of the effects of the fuel supply and the turbine control valve position. The output signal of the power regulator used to form the pressure correction signal is in fact influenced by the control deviation "power", and is therefore dependent on the electrical power and thus on the sum of the fuel and valve position-dependent power components, the size of which is not known. Precise targeted control of the pressure setpoint to meet the requirements described at the outset is therefore not possible.

On the basis of the method according to DE 36 32 041 C2, the invention is based on the object of specifying a further development which enables faster regulation of heating faults and also permits a variant for fixed-pressure operation. Compliance with the DVG requirements, including an at least monotonous transition to a new level of performance, should also continue to exist, as should a predominantly controlled intervention in the process. In addition, a facility for carrying out the method is to be specified.

This object is achieved in a method for controlling and regulating the output of a steam power plant block according to the preamble of claim 1 by its characterizing features.

Advantageous refinements and suitable control and regulating devices are specified in further claims.

Advantages of the method according to the invention are, inter alia, that the inclusion of the admission pressure control means that the regulation is very quick and stable, and thus also stable maintenance of the FD pressure, which is subject to the heating faults, and a simulation of the control path behavior that is well adapted to the respective operating mode is practical only controlled transition to a new level of performance is achieved. By switching the power control deviation to the steam pressure setpoint, not only is the error of the process model practically eliminated, but the whole block control is more stable.

The method can be carried out both with a device that is set up universally for a plurality of selectable operating modes and with a simplified control device that is equipped for a specific operating mode.

• Fig. 1 Gesamtanordnung einer Steuer- und Regeleinrichtung mit einem universellen Prozeßmodell für unterschiedliche Betriebsarten,
• Fig. 2 Blockschema des universellen Prozeßmodells der Anordnung gemäß Fig. 1,
• Fig. 3 Abwandlung der Anordnung gemäß Fig. 1 oder 2 für einen Fall, in dem die Summationsstelle für ein vom Prozeßmodell geliefertes Ventilstellungs-Steuersignal und das Ausgangssignal des Vordruckreglers nicht zur Verfügung steht,
• Fig. 4 vereinfachte Ausführung der Steuer-und Regeleinrichtung für einen Dampfkraftwerksblock mit Vordruckregelung und für Gleitdruckbetrieb,
• Fig. 5 vereinfachte Ausführung der Steuer-und Regeleinrichtung für einen Dampfkraftwerksblock mit Vordruckregelung und für Festdruckbetrieb.

A detailed description of the invention is given below with reference to exemplary embodiments shown in the drawings. Show it:

• 1 overall arrangement of a control and regulating device with a universal process model for different operating modes,
• 2 block diagram of the universal process model of the arrangement according to FIG. 1,
• 3 modification of the arrangement according to FIG. 1 or 2 for a case in which the summation point for a valve position control signal supplied by the process model and the output signal of the admission pressure regulator are not available,
• 4 simplified design of the control and regulating device for a steam power plant block with admission pressure control and for sliding pressure operation,
• Fig. 5 simplified version of the control and regulating device for a steam power plant block with pre-pressure control and for fixed pressure operation.

1 and 2 show a control and regulating device which can be set universally for different operating modes, an overall arrangement being shown in FIG. 1, the process model of which is shown in detail in FIG. 2.

• Ein Brennstoff-Steuersignal B, die Leistungsregelabweichung P_d und ein vorgegebener Leistungs- sollwert P_v. Ausgangssignale sind - abhängig von Betriebsarten-Umschaltern 115 bis 119 - ein Turbineneinlaßventil-Steuersignal S, ein Leistungssollwert P_s, ein Drucksollwertsignal D, ein Dampfdrucksollwert p_s und eine Drucksollwert-Komponente D_s.

A model shown in FIGS. 1 and 2, referred to as a universal process model or universal predictor 100, is supplied as input signals:

• A fuel control signal B, the power control deviation P _d and a predetermined power setpoint P _v . Output signals are - depending on operating mode switches 115 to 119 - a turbine inlet valve control signal S, a power setpoint P _s , a pressure setpoint signal D, a vapor pressure setpoint p _s and a pressure setpoint component D _s .

The overall arrangement also contains further operating mode switches 118 to 120 and 125 to 129, which can be actuated with the aid of an operating mode selector 121. The operating mode selector 121 contains two lines of keys, with each line making a selection by pressing a key.

As stated at the beginning, the invention relates to a further development of the method and the device, which are already known from DE 36 32 041 C2. Device components that have already been described there and are also used again in the device according to the invention are provided with the same reference numerals to facilitate understanding. Signal names have also been adopted.

The fuel control signal B is formed in a function generator 33a, 33b as a function of the required changes in performance and with an adapted override.

The predetermined power P _v supplied as a further input signal to the process model 100 is the output signal of a function generator 19b which ensures an at least monotonous increase in the block power P. The input signal of the function generator 19b is a step amplitude X, which is supplied by a power increase limiter, which takes into account the energy reserve given by throttling.

The process model 100 contains several function formers, namely a function generator 30 with a transfer function between vapor pressure and fuel, a function generator 22 with a transfer function between electrical power and fuel, a function generator 28 with a transfer function between vapor pressure and valve position, a function generator 102 with a transfer function between valve position and steam pressure, a function generator 103 with a transfer function between valve position and electrical power and a function generator 21 with a transfer function between turbine valve position and electrical power as well. Further components of the process model 100 are a P controller 63, addition points 20, 29, 106 to 109, 104 and 114, a selection element 105 and a multiplier 111.

In addition to the above-mentioned components, a power controller 2, a position controller 3, a pressure controller 4 and a pre-pressure controller 101 and addition points 8 to 10, 12, 13, 31, 64, 110, 122 to 124 are arranged outside the process model 100.

The electrical switching of the components and the functioning of the device is determined by the switch positions.

By actuating the keys a and G of the operating mode selector 121, the switches are brought into the position corresponding to the letter indicated in each case, whereby an operating mode “turbine leads, boiler follows, sliding pressure” is defined. The control and regulating method carried out in this circuit is already known from DE 36 32 041. In this mode of operation, the power controller 2 has a corrective action on the turbine control valves, the positioner 3 has a corrective action on the fuel by means of the pressure controller 4. Due to the pressure setpoint signal D, the pressure regulator 4 is practically inactive during the control process. The circuit arrangement is determined by the switch positions 120 / a, 119 / a, 118 / a, 127 / a, 129 / G and 128 / a.

Pressing the a and F buttons selects an operating mode "turbine leads, boiler follows, fixed pressure" In fixed pressure mode, the pressure regulator 4 receives its setpoint from the addition point 124, the coupling signal D _s formed in the process model 100 causing the pressure regulator 4 to become inactive. The positioner 3 is switched off. The power regulator 2 and the pressure regulator 4 have a corrective action on the fuel.

By pressing the buttons b and G the operating mode "boiler leads, turbine follows, sliding pressure" is defined. In this operating mode, too, the control signals B and S are used for control. The valve control signal S acts on the turbine control valves by means of the setpoint of the positioner 3 (switch 127 / b, 125 / b). The power regulator 2 has a corrective effect on the pressure setpoint (switch positions 120 / b, 119 / b, 126 / b, 129 / G) and the pressure regulator 4 (switch 128 / b) on the fuel via the addition point 8. This mode of operation is known from DE 36 32 041, apart from the control deviation P _{d being} applied to the power controller 2 by means of addition point 121 to the setpoint of the positioner 3. The method variants VG and VF described below are inventive.

By pressing the buttons V and G the operating mode "boiler leads, turbine follows, sliding pressure, pre-pressure control" is selected. The method is described below with reference to FIGS. 4 and 5.

The desired inactivity of the admission pressure regulator 101 during the control by the pressure setpoint p _s supplied by the process model 100 is achieved - in contrast to the arrangement according to FIG. 4 - by the direct control of the turbine valves by means of the valve control signal S and the connection at the addition point 9. Since the pressure setpoint p _{s has} the same time profile as the actual pressure, the control deviation at the addition point 110 is practically zero.

By pressing the keys V and F the operating mode "boiler leads, turbine follows, fixed pressure, pre-pressure control" is selected. Analogous to the aforementioned operating mode VG, the turbine control valves are also controlled directly by the control signal S.

Fig. 3 shows a modification of the arrangement in the event that the realization of the summation point 9 is not possible. The turbine control valves can then only indirectly, i. H. can be controlled by the targeted adjustment of the respective controller 101 or 2. For this purpose, a switch 140 is brought into the position corresponding to the operating mode and the valve control signal S is dynamically deformed by function formers 141 and 142 and additively applied to the respective setpoint via addition points 143 and 144. The dynamic deformation by the function formers 141 and 142 takes place with the inverse transfer function of the respective controller 101 and 2.

5 shows a simplified embodiment of the process model, provided with reference symbol 133F, for a fixed-pressure operation with a pre-pressure control. Deviating from the arrangement according to FIG. 1, a controlled system 1 b is considered here which, in addition to the power plant block 1, comprises the admission pressure regulator 101. The dynamic behavior of the controlled system 1 is simulated by a function generator 131. The operation of the arrangement according to FIG. 5 is described below.

The fuel is controlled by control signal B. Its effect on the increase in output when the primary pressure regulator 101 is switched on is simulated by the function generator 131. At the addition point 20 downstream of the function generator 131, by subtracting the power component P _B supplied by the function generator 131 from the predetermined power P _v, a power part Pp _{s is} formed which can be removed from the boiler by targeted control of the pressure setpoint p _s . The required time course of the pressure setpoint p _s is determined by a function generator 132 as component p _s , _v . This pressure setpoint component p _s , _v is added at the addition point 109 to the fixed pressure setpoint, the nominal pressure setpoint p _s , _N. In the ideal case of the control, ie with exact replication of the controlled system behavior by the signals B and p _s , the power control deviation P _d remains zero. In the event of deviations from this ideal case, the power controller 2 has a corrective action on the fuel mass flow m _B via the addition point 8. To improve the performance dynamics, the control deviation is added to the pressure setpoint via the addition point 108 after amplification by the multiplier 111.

Since in the steady state the output signal of the addition point 108 must be zero, this condition is ensured by a feedback R _{v of} the output signal of the addition point 108 via a multiplier 113 and the addition point 64 to the fuel control signal B.

Fig. 4 shows a very similar arrangement as Fig. 5, but for a sliding pressure operation with upstream pressure control. P the pressure setpoint _s is switched in this case, instead of the nominal pressure value p _{s, N} at the summation point 109, a control signal D _B. The control signal D _B is formed in a function generator 136; its course over time corresponds to the change in live steam pressure in response to the fuel mass flow m _B changed by the control (B). The power component P _B is formed in a function generator 134 adapted to the sliding pressure operation.

While the process models 133G, 133F shown in FIGS. 4 and 5 are each set up for a specific operating mode, all of the operating modes described above can be operated with the universal process model 100 according to FIG. 3. The simulation of the power component P _B for sliding pressure and fixed pressure takes place differently, depending on the position of the switch 115.

As long as you are in the power control range with sliding FD pressure, the signals from the function formers 102 and 103 are zero when the switch 115 is in the G position. If the FD pressure simulated by the function generator 30 after an increase in output by the fuel control signal B exceeds the nominal pressure setpoint p _s , _N , the difference present is detected by means of the selection element 105 and the addition point 106. The function generator 102, 103 and the addition point 104 firstly activate the simulation of the power component P _B for the fixed pressure and secondly the turbine control valves are opened further by the signal Sp. After the thermal energy has been stored in the boiler, only the signal Sy at the output of the function generator 20 becomes zero, specifically because of the effect of the feedback R,, ₂ (or RV if the switch 117 is in the appropriate position). When operating with the back pressure regulator, switch 116 is in the G position; in the power control range, in which the output signal of the addition point 106 is not zero, the signal D _B originally supplied by the function generator 30 is set by the signal from 106 in 107 for the fixed pressure, ie the signal D _B corresponds to the nominal pressure setpoint p _s , _N .

For the operation with fixed pressure in the entire capacity control range of the power plant block, the switch 115 is to be brought into the F position and the output signals of the function formers 102 and 103 are changed in terms of output.

The signal Sy stores the power from the boiler and the signal Sy in turn is brought to zero by the effect of the respective feedback mentioned above.

Reference list

• 1 power plant block
• 2 power controllers
• 3 positioners
• 4 pressure regulators
• 8 fuel value addition point
• 9 first manipulated variable addition point
• 10 second manipulated variable addition point
• 11 valve position setpoint adjuster
• 12 pressure value addition point
• 13 Performance value addition point
• 19b function generator (non-linear element of the first order whose time constant T depends on the jump amplitude X)
• 20 addition point (formation of the missing power section Pp _s )
• 21 function generator (transfer function between turbine valve position and electrical power)
• 22 function generator (transfer function between electrical power and fuel)
• 28 function generator (transfer function between steam pressure and valve position)
• 29 addition point
• 30 function generator (transfer function between vapor pressure and fuel)
• 31 addition point
• 33a, b function generator (overloading of the signal P _f2 , different for sudden or ramp-shaped change in power)
• 63 P controller
• 64 addition point
• 100 universal predictor
• 101 pre-pressure regulator
• 102 function generator (transfer function between valve position and steam pressure)
• 103 function generator (transfer function between valve position and electrical power)
• 104 addition point
• 105 selector
• 106 addition point
• 107 addition point
• 108 addition point
• 109 addition point
• 110 addition point
• 111 multiplier
• 112 multiplier
• 113 multiplier
• 114 addition point
• 115 switches
• 116 switches
• 117 switches
• 118 switches
• 119 switches
• 120 switches
• 121 mode selector (two parameters must be set)
• 122 addition points
• 123 addition points
• 124 addition points
• 125 switches
• 126 switches
• 127 switches
• 128 switches
• 129 switches
• 131 function generator (simulates the effect of the fuel supply on the increase in performance)
• 132 function generator (replication of the time course of the pressure setpoint)
• 133F predictor for fixed pressure operation
• 133G predictor for sliding pressure operation
• 134 function generator (transfer function between electrical power and fuel)
• 135 converter (transfer function between pressure setpoint and electrical power)
• 140 switches
• 141 function generator (inverse transfer function of the upstream pressure regulator)
• 142 function generator (inverse transfer function of the power controller)
• 143 addition point
• 144 addition point

Signal names

• B fuel control signal
• D pressure setpoint signal
• D _B Pressure setpoint component
• D _s pressure setpoint component (decoupling signal for pressure regulator)
• K correction factor
• m _B fuel mass flow
• m _B Fuel mass flow change
• p Actual steam pressure value
• p _s Vapor pressure setpoint
• p _s , _N steam pressure setpoint at nominal output (max. steam pressure)
• P _s , v steam pressure setpoint component
• P Block power electrical
• P _f2 power _{setpoint component} (depending on grid frequency deviation)
• P _d power control deviation
• Pp _s
• P _s power setpoint
• (P _B ) _F , _G simulated fuel-dependent power component in F or G operation
• P _v specified power setpoint
• R ₁ , ₂ return
• R _v feedback
• S valve control signal
• Sy output signal of the function generator 20
• Sp output signal of the function generator 102
• T time constant
• X jump amplitude
• Y turbine valve position

Operating mode designations

• a turbine leads
• b boiler leads
• F fixed pressure
• G sliding pressure
• V Form pressure control

Claims (7)

1. A method for controlling and regulating the power of a steam power plant block with the aid of a control and regulating device, which contains a process model that simulates the dynamic behavior of the power plant process and a power controller a) a given energy reserve by throttling the turbine inlet valves and used with a power component that ensures an increase in power with a strictly monotonic or monotonic transition to a higher power level, and b) a transition to a new performance level takes place with the aid of signals (B, S) for a controlled intervention in the fuel supply and the turbine valve position, so that the control device remains largely inactive,
characterized in that with the aid of a pre-pressure regulator (101) a live steam pre-pressure control is included, whereby c) the process model (100, 133) forms a vapor pressure setpoint (p _s ) for the upstream pressure regulator (101), and this causes the upstream pressure regulator (101) to remain largely inactive, d) the vapor pressure setpoint (p _s ) for sliding or fixed pressure operation is formed in different ways, e) the vapor pressure setpoint (p _s ) additively (108) the control deviation (P _d ) of the power regulator (2), which acts directly and correctively on the fuel supply, and f) the output signal of the admission pressure regulator (101) is added (9) to the control signal (S) to form the control signal (Y) for the turbine inlet valves. 2. The method according to claim 1, characterized in that the vapor pressure setpoint (p _s ) is formed in fixed pressure operation on the basis of a replica of the expected vapor pressure change (F _B p) _{G in} response to a changed fuel supply. 3. The method according to claim 1, characterized in that the vapor pressure setpoint (p _s ) is formed in sliding pressure operation on the basis of a replica of the expected change in performance (F _BP ) _{G in} response to a changed fuel supply. 4. The method according to any one of the preceding claims, characterized in that the output signal of the admission pressure regulator (101) is not added to the control signal (S) to form the control signal (Y) for the turbine inlet valves, but the control signal (S) with the respective one Inverse transfer function (1 / F _R ) of the power or the pre-pressure regulator dynamically deformed, the respective setpoint (P _s , p _s ) is added (143, 144). 5. The method according to any one of claims 1 to 3, modified in that the output signal of the admission pressure regulator (101) is not added to the control signal (S) to form the control signal (Y) for the turbine inlet valves, but the output signal of the admission pressure regulator (101 ) is used directly as a manipulated variable (Y) for the turbine inlet valve position. 6. Device for controlling and regulating the power (P) of a steam power plant block (1), which contains the following components: a) a process model (100) which forms control signals (B, S) for a control of the fuel supply (m _B ) and the turbine inlet valve position (on the basis of a power setpoint specification (P _v ) which brings about an increase in power with a strictly monotonic or at least monotonic course) Y), b) a power controller (2), c) a turbine inlet valve positioner (3), and d) a steam pressure regulator (4),
characterized in that e) a live steam admission pressure regulator (101) is also arranged, f) the process model (100) is designed as a universal model with setting options for each of the operating modes (F, G, V, a, b) mentioned in features g) and h), g) means (115, 116, 121, 129) are available for optionally switching to one of the operating modes sliding pressure (G) or fixed pressure (F), and h) Means (117 to 121, 125 to 128) are available to selectively switch to one of the operating modes "FD admission pressure control" (V) or "turbine leads, boiler follows" (a) or "boiler leads, turbine follows" (b ). 7. Device for controlling and regulating the power (P) of a steam power plant block (1 d) which contains the following components: a) a process model (133F, 133G), which forms a control signal (B) for controlling the fuel supply (M _B ) on the basis of a power setpoint specification (P _v ) which brings about an increase in power with a strictly monotonous or at least monotonous curve, and b) a power controller (2)
characterized in that c) an FD admission pressure regulator (101) is arranged in the steam power plant block (1 d), which delivers a manipulated variable (Y) for setting the turbine inlet valves, and d) the process model (133F, 133G) has means (131, 20, 132, 108, 109) for fixed pressure operation or (134 to 135, 20, 108, 109, 111) for sliding pressure operation) to form a heat / Power or fuel-dependent FD pressure setpoint (p _s ), which is supplied to the admission pressure controller (101) as a setpoint.

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