EP1069314A1 - Control of a compressor unit - Google Patents

Abstract

A characteristic parameter for the total volumetric flow to be delivered is determined. Using static functions a first desired value for the inlet valve or guide vanes or compressor speed and a second for the feedback valve are determined. Under normal operating conditions the total volumetric flow is controlled by varying the first value and outside the normal operating range by the second value

Description

Technical field

The invention relates to the field of control engineering. It relates relates to a method and a device for regulating a compressor unit according to the preamble of claims 1 and 7.

State of the art

A turbo compressor is inherently stable in normal operation: due to and outlet pressure and parameters of the compressor Mass flow of a working fluid through the compressor. This Flow, which can be considered as a volume or mass flow, decreases with increasing pressure difference, so that the pressures and the Move flow to an equilibrium state. When sinking Pressure difference becomes a stable work area through a so-called Pumping limit limited: The mass flow decreases with increasing outlet pressure to a certain minimum. After exceeding the surge limit the mass flow flows backwards through the compressor. Thereby the outlet pressure drops until the mass flow flows forward again. This Cycle, called pumping, repeats itself and can mechanically compress the compressor damage or destroy. So it's a job of a compressor controller in addition to a regulation of an outlet pressure or Flow to avoid pumping. This is done, as in the US patent 4,807,150, usually a blow-off or return valve is open, which allows part of the compressed working fluid to escape, respectively feeds the compressor again. Simultaneously with the Valve opening can also vary the speed of the compressor, such as in U.S. Patent 5,306,116. The additional mass flow through the recirculation valve prevents the mass flow through the compressor falls below the surge limit. Usually compressor and recirculation valve regulated by separate control loops.

For safety reasons, the return valve is opened before it is exceeded the surge limit opened. A corresponding safety limit should be possible are far from the surge line. To optimize efficiency However, the security limit is as close as possible to the Pumping limit set. This requires security precautions which add complexity of the control loops increase.

A combination of a compressor with a recirculation valve is as follows Called compressor unit. A compressor unit, which one Gas turbine supplied with gaseous fuel has high demands pressure control are sufficient. For example, in the event of abrupt changes in load the gas turbine and in the event of an associated change an outlet pressure of the compressor of a gas consumption, without a flame from the gas turbine extinguishing and without lines damaged by excessive pressures. In normal operation none Oscillations occur in gas production. Depending on the controller concept Gas turbine, it is also possible for a compressor unit to have a predetermined one Mass flow must deliver. This is opposed to hydraulic systems regulation to a given volume flow of interest.

Axial or radial compressors are used to vary the flow rate equipped with adjustable guide lines. Another way of varying the Flow rate uses a variable speed drive of the compressor. In both cases, the mass flow, with constant entry and exit conditions, from a leading row angle or from one Speed dependent. A corresponding controller for a compressor unit controls at least two manipulated variables, for example a guide row angle and return valve. The existing controller structures are complex, and have decoupled controllers for the two manipulated variables, which is a systematic Controller design mostly impossible. By switching between The dynamics of the controller and different operating states thus the compressor is unmanageable and therefore even more difficult to design and put into operation.

Presentation of the invention

It is therefore an object of the invention, a method and an apparatus to regulate the outlet pressure of a compressor unit, which has a simple structure and a systematic controller design enables.

This object is achieved by a method and a device for regulating the Outlet pressure of a compressor unit with the features of the claims 1 and 7.

In the controller according to the invention for a compressor unit, which is a compressor and has a return valve, a parameter for one delivering total flow is determined, and based on this parameter by means of static functions, a first setpoint for a preliminary series or a Inlet valve or a speed of the compressor and a second setpoint generated for a return valve.

The total flow to be supplied is preferably a mass flow but also be a volume flow.

In a preferred embodiment of the subject matter of the invention Total flow in a normal operating range by varying the first setpoint, and when leaving the normal operating range by varying the second setpoint. Advantageously the total flow rate changes during the transition between these operating areas steadily.

In a further preferred embodiment of the subject matter of the invention are the static functions for determining the first and second Setpoints linear.

Parameters of the static functions are advantageously related to an operating state of the compressor adjusted.

A major advantage of the invention is that the controller dynamics are very simple and that this enables quick regulation. Through the simple controller dynamics also becomes the overall dynamics of the compressor unit no more complicated, and the scheme remains simple to design, commission and maintain.

Further preferred embodiments result from the dependent patent claims forth.

Brief description of the drawings

Figur 1

eine schematische Darstellung einer Kompressoreinheit;

Figur 2

ein Kennfeld eines Kompressors;

Figur 3

eines Struktur eines erfindungsgemässen Reglers; und

Figur 4

Zusammenhänge zwischen verschiedenen Grössen des erfindungsgemässen Reglers.

The subject matter of the invention is explained in more detail below on the basis of a preferred exemplary embodiment which is illustrated in the accompanying drawings. Show it:

Figure 1

a schematic representation of a compressor unit;

Figure 2

a map of a compressor;

Figure 3

a structure of a controller according to the invention; and

Figure 4

Relationships between different sizes of the controller according to the invention.

The reference symbols used in the drawings and their meaning are summarized in the list of reference symbols. Basically the same parts are provided with the same reference numerals in the figures.

Ways of Carrying Out the Invention

FIG. 1 shows a compressor unit 10 to which a regulation according to the invention relates. A working fluid, for example air, a gas or a hydraulic oil, reaches a mixer 11 from a generator or a store, in which the working fluid has an inlet pressure p ₁ and an inlet temperature T ₁ . The working fluid passes from the mixer through an inlet 12 into a compressor 13. The compressor 13 has a signal input for a first target value u ₁ . With this setpoint, a map parameter of the compressor 13 is adjusted, for example via a subordinate control loop, for example a leading row angle or a position of an input valve or a speed of the compressor. At an outlet 14 of the compressor 13, a compressor flow w _{C flows} into a branch 15, in which the working fluid has an outlet pressure p ₂ . A total flow w _T flows from the branch 15 to a consumer, and a return flow w _R through a return flow line 16 and a controllable return valve 17 back into the mixer 11. The return valve 17 has a signal input for a second setpoint u ₂ . With this second setpoint, a valve lift of the return valve 17 is adjusted, for example via a subordinate control loop.

In another embodiment of the invention, the working fluid arrives through the return valve 17 not to the compressor inlet but is in blown off the environment. In this case, the return valve 17 is used as a blow-off valve designated. The regulation according to the invention is as follows presented using a feedback valve 17, but is for both types of use of valves applicable.

FIG. 2 schematically shows a typical map of the compressor 13. A pressure ratio p ₂ / p ₁ between the outlet and inlet pressure is plotted along an ordinate. The compressor flow wc is plotted along an abscissa, which is considered to be a mass flow (for example in kg / second) for the following explanations. Wc this compressor flow is usually scaled by the inlet temperature T ₁ and at a given operating condition T _0, p ₀ normalized so that the same graph of the characteristic map for various inlet temperatures T can be used. ₁

In other characteristic diagram representations, along the ordinate, for example, an outlet pressure p ₂ with a constant inlet pressure, or an enthalpy difference of the working fluid between inlet 12 and outlet 14 is plotted. Likewise, a volume flow (for example in m ³ / second) can be plotted along the horizontal axis instead of the mass flow. In such other map representations, the map is only scaled differently without the principle of the regulation explained below changing.

Characteristic curves denoted by u _1.1 to u _{1.3 represent} the behavior of the compressor for different values of the characteristic map parameter determined by u ₁ . For example, for a specific value of u ₁ and for a given pressure ratio p ₂ / p _1, a value of the compressor flow rate w _C is obtained which lies on the line corresponding to u ₁ . It can be seen that with an increase in the pressure ratio p ₂ / p ₁ , for example due to an increase in the outlet pressure p ₂ , the compressor flow wc decreases. If the compressor flow wc falls below the surge limit, that is, the line labeled PG, the pumping described at the beginning occurs. The surge limit PG is determined experimentally, for example during commissioning and / or theoretically. A security limit SG is introduced for security reasons. A regulation should intervene when the compressor flow wc falls below the safety limit SG, so that the pump limit PG is guaranteed never to be fallen below.

FIG. 3 shows a block diagram of a control system according to the invention. This includes the compressor unit 10 already described with its input and output sizes. A value of a measurement of the outlet pressure p _{2 of} the compressor unit 10 leads, with a negative sign, together with an outlet pressure setpoint p _2S to a first summation node 21. A difference or control difference formed in the first summation node 21 leads to a preferably dynamic controller 22 which, for example, is a PI - (Proportional-integral) controller, a PID (proportional-integral-differential) or a non-linear controller. An output of the controller 22 has a value z and leads to the input of a static setpoint generator 23. Two outputs of this static setpoint generator 23, with the values u ₁ and u ₂ , lead to the compressor unit 10. Measured values of the operating conditions of the compressor unit, that is to say inlet pressure p ₁ , inlet temperature T ₁ and outlet pressure p ₂ lead to compressor characteristics 24 and 25. From a first compressor characteristic 24, a first static parameter v leads to a correction unit 26. From a second compressor characteristic 25, a modeled compressor flow wcM leads to a second summation node 27. A measured Compressor flow wcM leads, with a negative sign, to the same second summation node 27, and the difference between these compressor flows leads to correction unit 26. A modified first static parameter v * leads from correction unit 26 to static setpoint generator 23.

The method according to the invention functions as follows: The first summation node 21 forms a control deviation p _2S -p ₂ . The dynamic controller 22 calculates the parameter z. If the dynamic controller 22 is a PI controller, z is calculated according to x 1 = p 2 S - p 2 x 2 = x 1 e.g. = ax 1 + bx 2 where a and b are parameters of the PI controller. On the basis of the value of z, the static setpoint generator 23 determines a first setpoint ui and a second setpoint u ₂ according to e.g. > 0 ⇒ u 1 = e.g. + v * u 2 = 0 e.g. = 0 ⇒ u 1 = v * u 2 = 0 e.g. <0 ⇒ u 1 = v * u 2 = - concentration camp

Here v * is a modified first static parameter and k is a second static parameter. The value of v * is selected as a function of the measured values p1, T1, p2 of the compressor unit 10 such that the operating state of the compressor for u1 = v * and u ₂ = 0 is on the safety limit SG. A value of z = 0 corresponds to this operating state, as can be seen from the above equations for u ₁ and u ₂ . Any other value of z could also be assigned to this operating state, but this would only complicate the equations without changing their functionality. FIG. 4 shows, by way of example, the relationships described above between the characteristic variable z, the target values u ₁ and u ₂ and the total flow w _T.

The setpoints u ₁ and u ₂ formed in the static setpoint generator 23 are transmitted to the compressor unit 10. With the first setpoint u ₁ , a map parameter of the compressor 13 is adjusted in the compressor unit 10, for example via a subordinate control loop, in particular a leading row angle or a position of an input valve or a speed of the compressor. A characteristic curve of the compressor 13 in FIG. 2 shifts for increasing values of u ₁ from that with u _1.1 to that with u _1.2 to the characteristic marked with u _1.3 . This increase in u1 corresponds to an opening of the feed line or an opening of the inlet valve or an increase in the speed of the compressor 13. For the sake of simplicity, only the regulation with adjustable feed lines is described below. However, the considerations and the control are also readily applicable to an adjustable input valve or a variable-speed compressor 13.

With the second setpoint u ₂ , the valve stroke of the recirculation valve 17 is adjusted in the compressor unit 10, for example via a subordinate control loop. An increase in u ₂ corresponds to an opening of the return valve 17 and an increase in the return flow W _R. The return valve 17 is closed for u ₂ = 0.

In accordance with the values of u ₁ and u ₂ and a characteristic of the consumer, a total flow w _T and an outlet pressure p _{2 are established} . If this outlet pressure p _{2 is,} for example, higher than the outlet pressure setpoint p _2S , the control difference becomes negative and the dynamic controller 22 leads to a decrease in the parameter z. The resulting change in the setpoints u ₁ and u ₂ is explained with reference to FIG. 2: The compressor is in a state labeled S1 in a normal operating range of the compressor, that is to say the compressor flow rate wc is greater than at a point on the safety limit SG with the same pressure ratio. Thus u ₂ = 0 and the recirculation valve 17 are closed, the total flow w _T is equal to the compressor flow w _c and is regulated by the first setpoint u ₁ and adjustment of the preliminary line. The decrease in z leads via u ₁ to a closure of the pilot line and to a reduction in the total flow w _T. For small changes, the pressure conditions are considered constant, so that the state of the compressor 13 shifts along a line L in the direction of the safety limit SG and the total flow w _T decreases. If the state reaches a point designated S2 on the safety limit SG, this corresponds to a value of z = 0 because of the choice of v * described above and because u ₁ = z + v *. If z is reduced further, u ₁ = v * and thus the state of the compressor at point S2 remains at the safety limit. The return valve 17, on the other hand, is opened according to u ₂ = -kz, so that the total flow w _T now decreases further according to the difference between the compressor flow wc and the return flow w _R. The value of k is chosen such that a gradient of the total flow w _T as a function of z remains at least approximately constant at the transition to the opening of the return valve 17, that is to say it is

In Figure 4, the dashed lines indicate the course of the total flow w _T if k is not selected as described above. In a further variant of the invention, k is adapted to the operating state of the compressor by means of a compressor characteristic.

The controller according to the invention has the advantage that the essential controller dynamics can be determined by the dynamic controller 22 and that this controller acts on only one parameter z. This eliminates the problems of coordinating dynamic processes during design and operation with dynamic multivariable controllers. This is made possible by the inventive consideration and regulation of the compressor unit as a whole and by the static determination of the setpoints u ₁ and u ₂ from the individual parameter z.

The following describes how the state-dependent first static parameter v and the modified first static parameter v * are determined: The first compressor characteristic 24 determines the first static parameter v from the measured values of the compressor unit 10, i.e. from the inlet pressure p ₁ , inlet temperature T ₁ and outlet pressure p ₂ , and from the known value of the first setpoint u ₁ . This is done, for example, by describing the compressor characteristics using an equation of the form w CM = f ( u 1 , p 1 , p 2 , T 1 ) went out. This determines a modeled compressor flow rate w _CM as a function of u ₁ and the measured values of the compressor unit 10. Also given as an element of the compressor characteristic 24 is an equation which calculates a so-called pump error S _E , that is to say a distance between a compressor state and the safety limit SG

The value of u ₁ , for which this expression becomes zero, is equal to the value sought for the first static parameter v.

The above equations for describing the compressor characteristics and the pump error are implicit in the compressor characteristics 24, 25 and correspond to a static model of the compressor behavior. The equations are determined by measurements and / or theoretical analyzes. They are advantageously scaled, standardized and stored in tabular form. U ₁ and v are determined, for example, by numerically solving the equation for the pump error s _E , or by calculating and tabulating solutions of the equation in advance.

A real compressor 13 will behave differently from the modeled, expected compressor characteristics. In order to compensate for this deviation of the compressor characteristics 24, 25 from a real compressor behavior, the first static parameter v is corrected on the basis of a measurement, so that the transition between the regulation by the preliminary series and the regulation by the return valve 17 remains at the safety limit SG, and in particular not shifted towards the surge limit. For example, the compressor flow w _{C is} selected as the measurement. In a second compressor characteristic 25, the modeled compressor flow w _{CM is determined} according to the equation already shown above. The measured compressor flow w _{C is} subtracted from this modeled compressor flow w _CM in summation block 21. On the basis of the difference w _CM -w _C , the modified first static parameter v * is, for example, as in the correction unit 26 v * = v + K ( w CM - w C. ) determined, where K is a constant. Instead of this linear correction, a non-linear and / or a dynamic dependence of v * on the difference w _CM -w _{C is also} used, for example.

If the measurement of the compressor flow wc fails, a warning signal is advantageously output and the control is continued with a last measured value of w _C. Since a relevant deviation of the real from the modeled compressor behavior develops over the course of days to weeks, this is not critical.

In a further variant of the regulator according to the invention, the total flow w _{T is} specified instead of the outlet pressure p ₂ . In this case, the same structure as in FIG. 3 is used, but with different coefficients of the dynamic controller 22. The regulated total flow W _T is either a mass flow or a volume flow. In a further variant of the controller according to the invention, the dynamic controller 22 is a combined feedforward / feedback controller with p _2S and w _TS as inputs, or a controller cascade for p ₂ and w _T. Other controller variants are also possible, all of which are based on the idea of a common parameter for a map parameter and the feedback valve 17.

The regulation according to the invention becomes a regulation in a preferred variant of a radially acting gas compressor for supplying fuel to a Gas turbine used. The first setpoint ui gives values for one adjustable front row. This regulation of a gas compressor was in Simulations tested, the gas requirement of the gas turbine within 4 seconds decreased from 100% to 10%. The regulation behaves at least just as good as conventional, much more complicated control structures.

In further preferred variants of the control according to the invention, it is used to control axial compressors, turbochargers, or to control the speed of variable-speed compressors via the first setpoint u ₁ .

Reference list

10th

Compressor unit

11

mixer

12th

inlet

13

compressor

14

exit

15

Junction

16

Return line

17th

Valve, return valve

21

first summation node

22

Dynamic controller

23

Static setpoint generator

24th

first compressor characteristic

25th

second compressor characteristic

26

Correction unit

27

second summation node

k

second static parameter

p ₁

Entry pressure

P ₂

Outlet pressure

P _2S

Outlet pressure setpoint

PG

Surge limit

S _E

Pump failure

SG

Security limit

T ₁

Inlet temperature

u ₁

first setpoint

u ₂

second setpoint

v

first static parameter

v *

modified first static parameter

W _C

Compressor flow

W _CM

modeled compressor flow

w _R

Reflux

w _T

Total flow

W _TS

Total flow set point

e.g.

Parameter

Claims (12)

Control method for a compressor unit (10) which has a compressor (13) and a valve (17), the valve (17) being a recirculation valve or a relief valve, the compressor (13) having a compressor flow rate w _C , the valve (17 ) has a backflow w _R , and a total flow w _{T is} equal to a difference w _C -w _R , characterized in that
that from a single parameter z for a total flow w _T to be delivered, a first setpoint u ₁ for controlling a preliminary line or an inlet valve or a speed of the compressor (13) by means of a first static function and a second setpoint u ₂ for using a second static function Control of the valve (17) is calculated. Control method according to claim 1, characterized in that the total flow rate w _{T is} regulated in a normal operating range by means of the first setpoint u ₁ , the valve (17) remaining closed, and for values of the total flow rate w _T which are used for a on the compressor (13 ) prevailing pressure ratio are smaller than in the normal operating range, is regulated by means of the second setpoint u ₂ and the valve (17), the first setpoint u _{1 being} left constant. Control method according to claim 1, characterized in that the static functions can be selected linearly piece by piece. Control method according to claim 1, characterized in that the calculation of the target values
for z> 0 according to u ₁ = z + v * and u ₂ = 0,
for z = 0 according to u ₁ = v * and u ₂ = 0, and
for z <0 according to u ₁ = v * and u ₂ = -k · z, where the value of v * is a value of the first setpoint at which the compressor (13) is at a safety limit (SG) a surge limit (PG), and the value of k is determined in such a way that a gradient of the total flow w _T as a function of the characteristic variable z remains at least approximately constant when passing over a point z = 0. Control method according to claim 4, characterized in that the Value of v * based on a first compressor characteristic (24) and based on of measured values of operating conditions of the compressor unit is calculated, and thereby adapted to the state of the compressor (13) becomes. Control method according to claim 5, characterized in that the Value of v * based on a second compressor characteristic (25) and based on is corrected by measured values of the compressor flow wc, and thereby deviations in the compressor characteristics (24, 25) from a real compressor behavior can be compensated. Device for controlling a compressor unit (10), the compressor unit having a compressor (13) and a valve (17), the valve (17) being a recirculation valve or a blow-off valve, the compressor (13) having a compressor flow rate wc, the valve ( 17) has a reflux w _R , and a total flow w _{T is} equal to a difference w _C -w _R , characterized in that
that the device has a static setpoint generator (22) with a first static function for calculating a first setpoint ui for controlling an advance line or an inlet valve or a speed of the compressor and with a second static function for calculating a second setpoint u ₂ for controlling the valve ( 17), the static functions being dependent on a common parameter z for a total flow w _T to be supplied. Apparatus according to claim 7, characterized in that the total flow w _T in a normal operating range is dependent on the first setpoint u ₁ , the valve (17) being closed, and for values of the total flow w _T which are for a on the compressor (13) prevailing pressure ratio is smaller than in the normal operating range, is dependent on the second setpoint u ₂ and the position of the valve (17), the first setpoint u _{1 being} constant. Device according to claim 7, characterized in that the static Functions are piecewise linear. Apparatus according to claim 7, characterized in that the calculation of the target values u ₁ and u ₂
for z> 0 equal to u ₁ = z + v * and u ₂ = 0,
for z = 0 equal to u ₁ = v * and u ₂ = 0, and
for z <0 are u ₁ = v * and u ₂ = -kz,
wherein the value of v * is a value of the first setpoint at which a state of the compressor (13) is at a safety limit (SG) before a surge limit (PG), and the value of k is such that a gradient of the total flow w _T remains at least approximately constant as a function of the parameter z when passing over a point z = 0. Device according to claim 10, characterized in that it has a first compressor characteristic (24) for determining the value of v * and for adapting the value of v * to the state of the compressor (13) on the basis of measured values of operating conditions (p ₁ , T ₁ , p ₂ ) of the compressor unit. Device according to claim 11, characterized in that it has a second compressor characteristic (25) for generating a modeled compressor flow w _CM , and in that it has a correction unit (26) for correcting the value of v * and for compensating for deviations in the compressor characteristics (24, 25) of a real compressor behavior based on a difference in the modeled compressor flow w _CM from measured values of the compressor flow w _C.

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