EP1116885A2 - Method and apparatus to control a turbo compressor to prevent surge - Google Patents

Abstract

The method involves producing a difference signal from a continuously detected compressor operating parameter and a demand value depending on the working point position in a characteristic field and producing a regulator input signal via a delay element to control a valve branching off the compressor outlet. Different delay time constants are used for increasing and decreasing difference signal for slower changes towards the pump limiting line. Independent claims are also included for the following: a device for regulating a turbo compressor to prevent pumping.

Description

The invention relates to a method for regulating a turbo compressor to prevent pumping, of which in the preamble of claim 1 specified type, and a device to carry out the procedure.

Pumps are termed intermittent in compressors or periodic backflow of fluid from the Pressure to suction side. This condition occurs e.g. at too high Final pressure and / or too low throughput. In the map a surge limit line can therefore be defined, which a stable map area from an unstable area separates to the left of the surge line. Operation in an unstable area to the left of the surge line is inadmissible because it is inside serious machine damage occurs in the shortest possible time can. To avoid pumping, i.e. of operation in the unstable area, a surge limit control is used, which controls a valve on the compressor outlet which as a relief valve with the atmosphere or as a blow-off valve is connected to the suction side of the compressor. By opening of the valve is the flow through the compressor far increased that the working point is always within the stable Map area remains. For such a scheme is in the map at a safety distance from the surge line defines a control line (blow-off or blow-off line). When the current working point approaches the control line becomes the blow-off or blow-off valve (in In the following only called relief valve) more or less open.

More specifically, such a scheme works in such a way that the setpoint for the flow control from the compressor pressure or from the pressure ratio between outlet pressure (Final pressure) and inlet pressure, or from one of these Pressure ratio derived size is determined. This The setpoint corresponds to the control line. The measured compressor intake flow is compared with the setpoint, and in the event of a deviation, the relief valve is adjusted. Provided the operating point of the compressor is on the control line is the control difference of the surge limit controller zero and the relief valve remains in its Position. If the working point exceeds the control line in Towards the surge limit, the controller opens the valve further, the working point is to the right of the control line, the controller closes the valve.

The operating point lies in normal operation of the compressor of the compressor clearly to the right of the control line (the design point is typically 20 to 30% right of it) and the relief valve is completely closed. When the operating point is shifted from this operating state out towards the surge line begins conventional controller can only be opened when the actual value falls below the setpoint, i.e. when the operating point exceeded the control line in the direction of the surge limit Has.

A method according to the preamble of claim 1 is known DE-2828124 C2 known. In these known methods the difference signal from setpoint and actual value once without delay and in parallel delayed a subtraction point supplied, from which the input signal for the controller tapped becomes. This has the advantage that the control loop also rapid, transient changes in the working point can handle sufficient security. The effect of Systems is that the setpoint of the controller is an additional one Signal is added, the transient working point shifts a shift in the control line like this causes when the working point approaches the control line the safety distance between surge limit and control line is enlarged and the controller earlier appeals. The control line is shifted almost dynamically and a new "dynamic control line" is effective. This has the consequence that the safety distance between control line and stability limit under transient conditions is significantly larger than under stationary conditions and the compressor clearly in such critical conditions is better protected.

However, the known method has the disadvantage that the safety distance for transient working point shifts, who come in from a steady state In the direction of the surge limit, but that is increased Controller only delayed the changes with that on the delay element set time constant. Full the known method is only effective if the Working point starting from a stationary operating point moves towards the surge limit. The known works against this Procedure in the event of disruption, initially a shift the working point away from the surge line and then again towards the surge line, only unsatisfactory. When moving the working point away from the The surge line is initially transient after the control line left shifted, with a tendency to adjust according to the set Time constant, usually over several Minutes to reset to the stationary value. Only when this condition has subsided can one new steady state can be assumed, and that known methods can show its full effectiveness. To to decay this transient state is the dynamic (this is the effective) control line to the left of the stationary control line. The surge limit control takes effect therefore only with a delay since the operating point is transient cover another path towards the surge line until the controller intervenes.

The invention is based on the object of a method and to improve a device of the known type so that the advantage of increasing the safety distance is always fully usable, regardless of whether the working point is in one before the fault begins stationary operating state or whether previously transient working point shifts have occurred.

The achievement of the object is in claim 1 specified. The other claims relate to others advantageous features of the method according to the invention or the facility for its implementation.

According to the time constant of the delay element designed asymmetrically. With working point shifts the delay element acts in the direction of the surge limit as described in the prior art. With a shift the working point works in the direction away from the boundary line the delay element, however, with a clear smaller time constant. This ensures that the control line for working point shifts away from the Boundary line follows almost instantaneously when shifting in Towards the surge line, however, with the known, clearly slower time constant.

In other words, the known surge limit control according to the invention for turbo compressors with stationary Control line that is at a fixed distance to the right of the surge line is effective around a dynamic control line expanded. This dynamic control line is implemented in such a way that with transient shifts in the compressor operating point the effective position towards the surge limit the control line changed, in such a way that depending on the speed of the approach of the working point the effective control line to the surge limit to the right in the map in the direction of the working point with the consequence that the safety distance between surge limit and control line is enlarged and therefore the Pump limit controller intervenes earlier. With very fast Shifts in the working point in the direction of the surge limit the control line is e.g. by half the distance between the working point and shifted the stationary control line to the right, with slower working point shifts that is Shift of the control line less. Becomes the working point only very slowly, i.e. over e.g. 1 hour towards stationary control line shifted, the dynamic control line is correct almost completely with the stationary control line match.

The control method according to the invention is particularly suitable for those applications in which a controlled variable, in particular the flow signal, by flow eddies at the Measuring point is very noisy. Classic PID controller with differentiating algorithms fail in these applications, because the differential portion on the rate of change the controlled variable reacts. With high-frequency (some Hz) Signal interference with signal swings of a few percent Differentiating control algorithms are not permitted because they Significant signal changes even with stationary machine operation the manipulated variable. You would also at stationary operation in the vicinity of the design point and a complete closing of the valve when stationary Prevent operations to the right of the control line. For reasons of economy, however, the valve is stationary Keep operation completely closed. The invention Process offers clear advantages here as it even with extremely noisy control variable this disadvantage Effect does not show.

Embodiments of the invention are based on the drawing explained in more detail. Fig. 1-7 each show a simplified Scheme of an inventive device for controlling a Turbo compressor to prevent pumping.

1 is in the suction line 1 of a turbo compressor K through sensors 3, 5, the pressure before and after one Throttle orifice (not shown) measured, from which a Transmitter 7 the actual value for the compressor throughput on the suction side V forms. At the compressor outlet includes a sensor 9 with downstream transmitter 11 the actual value of the final pressure P. Both actual values V and P are merged into one Computer 13 entered. The computer 13 has a memory provided, in which the course of a stationary control line (Blow-off line) in which, for example, by P and V shown compressor map, e.g. saved as a polyline is.

wobei

κ =

isentropischer Exponent

R =

Gaskonstante

T₁ =

Temperatur am Kompressoreinlaß

P₁ =

Druck am Kompressoreinlaß

P₂ =

Druck am Kompressorauslaß

The setpoint is preferably calculated on the basis of the enthalpy difference (head) Δh of the compressor according to the formula

in which

κ =

isentropic exponent

R =

Gas constant

T ₁ =

Compressor inlet temperature

P ₁ =

Compressor inlet pressure

P ₂ =

Compressor outlet pressure

The compressor outlet pressure P ₂ can be used to calculate the target value or can itself be the target value if all other parameters are constant.

The computer 13 determines from the actual values of V and P defined position of the working point in the map relative to the control line a setpoint for the throughput V.

The setpoint and actual value are fed to a subtracting point 17, which forms a difference signal x _d (control deviation). The difference signal x _d is supplied to another subtraction point 19 once without delay via a signal path 21 and once with a delay via a delay element 23. The difference between the undelayed and the delayed signal formed at the subtracting point 19 is fed as an input signal to a controller R, which generates a control signal for controlling a blow-off valve or blow-by valve 27 provided on the output line of the compressor K in order to control the surge limit control in accordance with a control algorithm implemented therein to carry out in a manner known per se. In this respect, the arrangement described corresponds to the method known from DE-2828124 C2.

According to the invention, the delay element 23 is a first-order delay element which is asymmetrical in terms of its time constant. When the operating point shifts to the left in the direction of the surge limit line G, ie when the time change of the difference signal x _d formed at the subtracting point 17 has a positive slope, the delay element 23 operates with a normal delay. If, on the other hand, the operating point shifts to the right, ie away from the surge line G, and thus the change in time of the difference signal x _d formed at the subtraction point 17 has a negative sign, the delay element 23 operates with a significantly smaller time constant, typically approx. 1 sec. This ensures that the controller R can also follow rapid changes in the working point, which are directed away from the surge line G and are therefore “harmless”, almost without delay.

In the method according to the invention, no differentiation is made Controller used. In particular, that in controller R implemented control algorithm not differentiating. How already mentioned, a differentiating controller can only then be used when the input signals are largely free of signal noise. Without a differentiating controller then working method according to the invention can be used when the input signals are strong Have signal noise, e.g. through vortex formation in the area of the flow sensors 35 is caused.

In a more general view, that between the summers 17 and 19 lying, the asymmetrical delay element 23 containing circuit branch as "gradient sensor" be considered with the direction and speed from working point shifts to the surge limit or from your way will be captured. The mode of action can then be like are described as follows: The memory 13 is the stationary one Control line entered as a polyline. In the summer 17 the difference from the stationary control line (setpoint for the Surge limit control) and the current flow of the compressor educated. This (current) control difference is the Controller R switched on, its output according to the implemented Control algorithm changes. Furthermore, the current control difference by means of the gradient sensor 23 and the summer 19 a virtual control difference as Sum of the difference between the stationary control line and the current one Flow and the output signal of the gradient Sensor 23 formed. This virtual control difference will the controller R as an additional input variable. This results in a virtual control line one transient working point shift with a set one Time constant (typically 20 to 60 seconds) follows. After this time constant has been removed, the virtual control line is correct with the stationary control line.

For the gradient sensor, which in FIG. 1 is represented by the link 23 different configurations are possible, which are explained below.

2 contains the dashed frame as a gradient sensor effective circuit part 40 an integrator 32, whose output signal is fed back to the input and by means of a summing element 30 the input signal of the integrator 32 is added with a negative sign. The time constant of the integrator 32 changes depending on the dependency from the movement of the working point.

Fig. 3 shows an embodiment in which an additional Function generator 41 (e.g. polygon generator) one additional dynamic control line is specified, in addition to that specified by the function generator or computer 13 stationary control line. The dynamic control line 41 is formed from the same input variables as that stationary control line 13, however a "gradient sensor" shifts 40 with downstream summer 19 the dynamic Control line by a portion by which the difference from stationary control line and current compressor flow, formed in summer 17, changes dynamically. The Gradient sensor remembers the stationary distance between stationary control line and current compressor intake flow and add this size of the dynamic control line 41 on. In the summer 18, the difference becomes more dynamic Control line and current intake flow formed and applied as a control difference to controller R, which in turn, the blow-off / blow-off valve adjusted accordingly. The gradient sensor is designed such that the dynamic control line only in the direction of the larger one Flow shifts, that means to the safe side for the compressor.

According to the invention, a transient shift follows the working point away from the surge limit of the gradient sensor the new distance between the working point and the control line without delay. To follow towards the control line the output of the gradient sensor is delayed, the means slow, and thereby causes a continuous Settling into steady state.

4 shows a possible embodiment of the "gradient sensor", as inserted into block 40 of FIG. 3 is. A feedback integrator 32 is an asymmetrical one Limiter 31 connected upstream. The output signal of the Integrator 32 is on the adder 30 at the input with a negative Sign switched on. The asymmetrical limiter 31 is set to input signals that by moving the compressor operating point in the direction Pumping limit are generated to very small values, e.g. 0.02, limited. Input signals that shift the Correspond to the compressor operating point away from the surge limit, are hardly limited, e.g. by a limit of 1.

The effect will be explained using an example. Accepted be a shift in the compressor operating point towards the surge line, e.g. such that the working point almost jump from a working point at a distance of 20% from the control line to a point at a distance of 10% jumps off the control line. Due to the agreement "control difference xd = setpoint minus actual value "this means a Change in the control difference xd from -0.2 to -0.1. The The output of the integrator 32 is before the start of the fault -0.2, the input of summer 30 jumps from -0.2 to - 0.1. The output of summer 30 is +0.1. Since the Limiter 31 positive values limited to a maximum of 0.02 the integrator has an input signal of 0.02 and integrated thereby with a time constant of 50 seconds. The output is only correct after this settling time has subsided of the integrator 32 matches its input. in the Summer 19 becomes the difference from the input of the summer 30 and output of the integrator formed and the dynamic Control line activated. Is in steady state the output of the summer 19 zero, with transient shifts of the working point in the direction of the surge limit the output of the summer 19 transiently a positive Value whose amplitude is proportional to the size of the working point shift as well as proportional to the speed is the working point shift.

If the working point moves away from the control line, grasps the lower limit of the limiter 31 and the integrators follows with a small time constant, e.g. 1 second. The gradient sensor is thus almost in this direction ineffective. However, this has the advantage of being the integrator takes on the new stationary value very quickly. If the operating point changes transiently, e.g. first from -0.2 to -0.3, then to go to -0.1, follows according to the invention the output of the integrator very quickly on - 0.3. The full dynamic of the system is available. In a prior art method the integrator of the change from -0.2 to -0.3 with the follow the same time constants as in the other direction. With a short succession of both faults, the movement would almost ignored away from the control line.

5 shows a further embodiment of the gradient sensor 40. Instead of the limiter 32, two amplifiers 33 and 34, the outputs of which are used via a changeover switch 35 are connected to the integrator 31. The amplifiers are set to different gain factors, the Amplifier 33 e.g. to 0.02 and amplifier 34 to 1. The switch 35 is by a differentiator or Sign generator 36 controls and switches, depending on the sign of the input to one or the other amplifier around. This ensures that in the event of an operating point shift a small gain towards the surge limit and therefore a large time constant is effective and with a shift in the direction away from the surge limit a large gain, that is, a small target constant.

A further embodiment is shown in FIG. 6. Here, instead of the limiter 31 is an integrator 32 with parameter adaptable Time constant used. Depending on the direction of change of the input signal becomes the time constant of the integrator via the adaptation block 37 between a large and a small value switched.

Fig. 7 shows a further embodiment, the gradient sensor 40 a special structure-switchable integrator NFI 32 used. Via a control input that is connected to the output of the differentiator 36, the integrator switches between the two operating modes Integrate and track around. The working point shifts of the compressor towards the surge limit, the Differentiator DIF 36 integrator 32 in the mode Integrate. The integrator follows with his set Time constants (typically e.g. 50 seconds) of the change of the input signal to summer 30. Shifts the operating point, on the other hand, switches away from the surge limit the differentiator 36 the integrator 32 in the mode Tracking. The integrator's output follows without any Time delay the second input, that is, the output of the totalizer 17. As soon as the operating point again moves towards the surge limit, the differentiator switches 36 the integrator 32 again in the integrating mode. The output of the integrator follows from this state with its set time constant the new value.

This effect is also explained in the example below. If the operating point changes transiently, e.g. first from -0.2 to -0.3 to then go to -0.1 follows according to the invention the output of the integrator very quickly to -0.3. Because the differentiator 36 the shift away from the surge limit, i.e. change in the control difference xd from -0.2 to -0.3, the integrator will during this process in tracking mode always the same Accept value like the control difference, i.e. the output signal of the totalizer 17. The output of the totalizer 19 is always zero and thus the gradient sensor at one Work shift away from the surge line has no effect.

If, on the other hand, the operating point moves towards the surge limit, that is, the control difference xd changes from -0.3 to -0.1, the differentiator 36 detects the change in direction and switches the integrator into the integrating mode. The output of the integrator 32 follows the input variable with the set time constant (e.g. 50 seconds). This makes the adder 18 transient positive Add up size that has the same effect as that described dynamic control line.

The full dynamics of the system are available because the gradient sensor already at the beginning of the working point shift is effective from the xd = -0.3 position. In a prior art system, the gradient sensor in quick successive processes the control line in only at a control difference of -0.2 Shift direction away from the surge line. In short Sequence of both disturbances would make the movement go away almost ignored by the control line.

The embodiment variants of the Gradient sensor 40 can also be used in the embodiment 2 are used. It only needs in the 2 of the integrator 32 and totalizer 30 existing gradient sensor 40 by one of the Gradient sensors 40 according to Fig. 4-7 to be replaced. Of a separate graphic representation and description no such arrangements are given here. The advantage 2 compared to that of FIGS. 3 and their variants according to Fig. 4-7 is that only one Function generator 13 (polygon generator) for mapping the stationary control line is required while a function generator 41 omitted for the dynamic control line and the dynamic control line only exists virtually, since they are each the distance between the stationary Control line and the current working point is calculated.

Claims (5)

Method for regulating a turbo compressor to prevent pumping,
wherein a difference signal (x _d) is produced from a continuously detected actual value of an operating variable of the compressor (K) and a dependent of the position of the working point in the characteristic field target value and from the difference signal (x _d) using a delay element, an input signal for a controller (R) is obtained which controls a valve (24) branching from the compressor outlet,
characterized in that the difference signal (x _d ) is delayed depending on its direction of change (increase or decrease) with different time constants such that the controller (R) reacts more slowly to working point shifts towards the surge line and faster to working point shifts in the opposite direction. A method according to claim 1, characterized in that the difference signal is fed once via the delay element and once without delay to a subtraction point (19) from which the input signal for the controller (R) is taken. Method according to claim 1 or 2, characterized in that the delay of the delay element is substantially or almost zero when the working point shifts are directed away from the surge line. Device for regulating a turbocompressor to prevent pumping, with measuring sensors (3, 5) for recording the actual value of one or more operating variables characteristic of the operating point of the compressor (K), a set point sensor (13) with a predefined profile and a control line (A) in Compressor map, a differential element (17) for generating a differential signal (x _d ) from the setpoint and actual value, a controller (R) which generates a control signal for a valve (27) at the compressor outlet, and one with the differential signal (x _d ), a circuit containing a delay element (23) for generating the input signal for the controller (R),
characterized in that the delay element (23) is an asymmetrical delay element, the delay of which is greater when the difference signal (x _d ) changes, which corresponds to a shift in the operating point in the direction of the surge line (G), than when the difference signal (x _d ) in the opposite direction. Device for regulating a turbocompressor to prevent pumping, with measuring sensors (3, 5) for recording the actual value of one or more operating variables characteristic of the operating point of the compressor (K), a set point sensor (13) with a predefined profile and a control line (A) in Compressor map, a differential element (17) for generating a differential signal (x _d ) from the setpoint and actual value, a controller (R) which generates a control signal for a valve (27) at the compressor outlet,
characterized in that it contains a gradient sensor (40) which detects the magnitude and direction of the change in the difference signal (x _d ), and in that the output signal of the gradient sensor (40) controls a function generator (41) in which a dynamic control line is stored , the sum of the output signal of the function generator (41) and the actual value of the compressor throughput (V) being fed to the controller (R) as an input signal.

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