EP0757180B1 - Method and device for operating turbomachines with controllers having a high proportional gain - Google Patents

Description

The invention relates to a method and an apparatus for Operating turbomachines to avoid Controller instabilities with high proportional gain of the Regulator with the features of the preamble of claims 1 and 7.

Surge limit regulations are characterized in that they need particularly quickly opening control valves. From the Technical literature is known to achieve a good one Regulator stability same control dynamics with control valves the shortest possible positioning times in the opening direction and Closing direction is required. This means that a Blow-off valve, which, due to the process requirements, must open quickly to achieve good controller stability should also close quickly.

In practice it has been found that there is a certain asymmetry between opening and closing speed is not disturbing. So throttles have always been in the oil circuit hydraulic surge limit controller or relief valves or in the Supply air supply for pneumatic relief valves installed. There the drives of these relief valves are generally designed that a spring opens the relief valves and the closing of the Blow-off valves achieved by oil or air pressure becomes Opening the relief valves Control medium (oil or air) deactivated, for closing however control medium supplied from the supply line. Is now constructively ensured that the free cross sections in the opening direction are very large, however, a throttle point is provided in the closing direction an asymmetrical control behavior is obtained. This control behavior is used to avoid machine hazards with quick-closing blow-off valves avoid. As a rule, the chokes become like this dimensioned that the relief valve in about 20 seconds the fully open to the fully closed position is driven.

The only task of these chokes is with one Intervention by hand in the control loop to avoid that due to incorrect operation the relief valves in 1 - 2 seconds are closed and thus the turbo compressor can get into the unstable area. The blow-off valves on the other hand close in 20 seconds, has the operating personnel even in the event of incorrect operation still enough opportunity, the operating error correct before the relief valve completely closed is.

It is obvious that the throttling points are coming of the control medium must not be arbitrarily small. If the throttling points are too narrow, there is a risk that narrow cross-sections through small dirt particles clog and thus any blow-off valve adjustment is omitted. For this reason, they are practically longer Operating times as 20 seconds for the entire closing process not feasible.

In practice it has been shown that this asymmetry for the Control behavior and controller stability are not inadmissible is harmful.

From DE-A-2 623 899 a surge limit controller is known which has a nonlinear amplifier. This non-linear The amplifier increases the control loop gain when the Blow-off valves by more than 2% by a factor of 5. Since the Pump limit controllers only work optimally if they are in the Normal operation operated with the maximum permissible gain , this gain increase by 5 means that the controller works unstably with this high gain.

Another major improvement to the whole Loop behavior is achieved in that a trackable integral controller is used. This method is described in DE-A-3 809 881. It will always be the exit of the controller with the current position of the relief valve compared.

EP-A-0 336 092 describes a method for protecting a Turbocompressor before pumping by blowing over a Blow-off valve known. The blow-off valve is increased Adjustment speed in the opening direction and at a slower rate Adjustment speed adjusted in the closing direction. Parallel the surge limit control is intervening in an emergency Safety control operated.

EP-A-0 477 055 describes a device or a method to protect a compressor against unstable operation under Use of a surge limit controller and one Pump limit control valve described. The known device assigns an electrovalve to the surge limit control valve Drain the servo motor of the surge limit control valve and one

Ramp generator on in a parallel control loop is arranged. This control device is in Direction of opening of the relief valve no time limit effective, but there is a time limit in the closing direction the closing process of the relief valve provided. The Opening and closing movements are done by the electro valve and made the ramp generator. It does that Solenoid valve the quick opening of the relief valve during the time-limited closings over that in the parallel Control loop arranged ramp generator takes place.

The control difference e used in the control process is defined as the difference between the flow target value W and the Actual flow value X, i. H. e = W - X. A negative sign The control difference e therefore means that the working point the compressor is in the safe working area while a positive sign of the system deviation e means that the Operating point the blow-off line to the left, d. H. towards has exceeded the surge limit. If the exceeds Working point the surge limit, there is a pumping of the Compressor. Make these rule differences inadmissible the controller is switched to follow-up mode and its exit to the current relief valve position switched. This ensures that the manipulated variable of Pump limit controller is not significantly different from the position of the Valve deviates.

Applications are known in which the position of the Valve is not measured or within the scheme is not available. To even in these cases "Divergence" of controller output and limited Preventing manipulated variable can instead of feedback the current valve position also the limited manipulated variable be reported back to the controller. This ultimately leads to the same results as one Feedback of the valve position.

The behavior of the Pump limit controller essentially through its proportional gain certainly. The higher the proportional gain is selected, the greater the change the controller output signal and thus the position of the Relief valves. Another blow-off valve is rather able to use a compressor before pumps protect as a little opening.

However, the proportional gain cannot be arbitrary be chosen large, as this leads to instabilities of the Control loop leads. Cause of these instabilities are inevitable delays in the controlled system.

It is therefore the task of a process of Generic type in such a way to the Control behavior of a turbo compressor improve that the proportional gain significantly can be raised without making the control loop unstable becomes or vibrations of the control element (Relief valve) tends.

The task is solved in the manner in which The main claim is specified, the sub-claims 2 - 6 represent advantageous process steps, the claims 7-11 characterize the features according to the invention the device for performing the method.

Due to an asymmetry for the control behavior of the Blow-off valve will close and slow The blow-off valve opened quickly.

The stability behavior of the surge limit control loops according to the invention have a positive influence in that an electronic limitation of the closing speed of the relief valve is made. Consequently can have surge limiters with significantly higher Proportional gain can be operated stably. For this purpose, one enters the output of the surge limit controller electronic gradient limiter inserted. This Gradient limiter is asymmetrical, i. H. there is none in the opening direction of the relief valve time limit is effective, in the closing direction however, a freely parameterizable time limit the closing process of the relief valve provided or programmed. Have the best practical results with opening times of 1 second and closing times of more than 5 minutes. With this realization closing times of 10 minutes or set more.

A surge limit control with such a gradient limitation is largely independent from very high controller gains. A very high one selected controller gain inevitably leads to the fact that the controller circuit becomes unstable. Without this limitation would the controller output and thus the valve position swing. With this limitation in the controller output would however, this vibration affects the first half wave restrict, d. that is, the gain would be too high the relief valve further than an optimally set one Open the controller, the subsequent quick closing process would go away, however, and the valve would only with the set gradient, d. H. slowly, conclude.

In practice, the time that is required to the relief valve to the desired target position drive, are sufficient to the process disturbance, which the Regulator deflection has caused it to subside. If this is not the case, it can become one the controller engages again in the direction of the valve opening come. This then leads to the valve another violent opening movement and itself the process described above is repeated again. In most cases, the disorder is after some Regulator swings subsided. It stands as a degree of freedom here the freely adjustable gradient in the closing direction of the valve available, which are chosen in this way can ensure that this requirement is met.

If the proportional gain and incorrectly chosen gradient can lead to the fact that a comparison is omitted and the described The process is repeated periodically. Without the invention Such a process leads to enlargement too much violent continuous vibrations of z. B. 1 - 3 sec. Period duration and large amplitude. Will with the inventive method z. B. a closing time of 10 min. Selected, and the relief valve leads during of the unstable process by a stroke of 10%, then this means that the period lasts for 1 min. is enlarged. Such instability, moreover is still sawtooth-shaped, is process engineering much more acceptable than a 1-3 second vibration with significantly larger valve deflections.

The main advantage of the invention is that significantly larger proportional gains can be selected are. As a result, the surge limit controller intervenes at one Process disruption significantly more powerful and protects the Compressor much better before pumps.

The manipulated variable limiter is a function block imagine its output in the stationary Operating case is always the same as its entrance. this applies also for dynamic processes in the direction of valve opening. Control commands in the closing direction are also unaffected switched through from input to output, as long as the gradient for the manipulated variable change is less than the set limit. He follows this change of input with a steeper Gradient, the output size changes with the as Gradients set until the Gradient of the input is smaller than the set one Border.

In a further embodiment of the invention, the Gradient switchable. this will required if at a greater distance from the Working point from the surge limit a faster Closing speed is allowed and close the surge limit to a slower speed is switched. This happens when the Working point, for example, more than 20% away from the blow-off line, then the valve can be used a positioning time of z. B. 20 seconds or even Close for 1 second for the entire stroke; approaches however, the working point is closer to the blow-off line and falls below the 20% limit, then for example to a positioning time of 5 minutes for the entire Hub switched.

According to the invention, several switching stages are also possible or it can also be a continuously variable limit be chosen for the gradient that is a function of the control difference, the distance between the working point and blow-off line, is.

The invention is based on schematic Exemplary embodiments explained in more detail.

Fig. 1

ein Schaltschema zur Vermeidung von Reglerinstabilitäten,

Fig. 2

ein Schaltbild des elektronischen Gradientenbegrenzers.

Show it:

Fig. 1

a circuit diagram to avoid controller instabilities,

Fig. 2

a circuit diagram of the electronic gradient limiter.

1, the turbocompressor (1) is on the intake side connected to an intake pipe (10). Delivery side is the turbo compressor (1) with an exhaust pipe (11) connected via a check valve (12) the medium compressed by the turbocompressor (1) leads to a downstream process. In front of the check valve (12) branches from the discharge line (11) a blow-off line (20) into which a blow-off valve (2) with silencer (3) with a pneumatic or hydraulic actuator (21) is turned on with a control line (22) is connected.

The intake side is connected to the intake line (10) connected flow meter (31) to the Compressor (1) flowing flow of the to be compressed Medium recorded. By means of one with the discharge line (11) connected pressure meter (32) is the compressor end pressure detectable. The pressure gauge (32) is a function generator (33) downstream, based on saved Data associated with a particular print, just permissible minimum flow value outputs for the compressor (1). The one from the flow meter (31) Actually measured actual flow value and that of Function transmitter (32) output flow setpoint are fed to a subtractor (34), in which the difference from this by subtracting the actual value is formed from the setpoint.

The control parameter generated in the subtractor (34) is given to a surge limit controller (41), the Subtractor (34) is connected downstream.

The surge limit controller (41) ensures a continuous Regulation, d. H. an exact adjustment of the Blow-off valve (2) depending on the position of the Working point in the map. The output works for this the surge limit controller (41) over a gradient limiter (50) and via a control line (22) to the Actuating device (21) of the relief valve (2).

From the actuator (21) with a Positioner supplies pressure media (23) to a piston-cylinder unit, not shown specifically or membrane unit for generating the Force for the adjustment movement of the relief valve (2) in the closing and opening direction. The power for Adjustment movement of the relief valve (2) in the opening direction is generally used for security reasons an energy storage element, e.g. B. a tense Spring generated to in the event of failure of the scheme automatic opening of the relief valve (2) ensure.

The output of the control line (22) acts on a pneumatic one or hydraulic actuating device (21). As a result, the relief valve (2) in the event of a process failure by lowering the control signal in the opening direction adjusted until the compressor operating point in the safe map area is reset with only the constructive design of valve (2) and actuator (21) dependent actuating speed.

If the surge limit controller (41) is too violent react and the relief valve (2) opened too far have, the output signal of the surge limit controller increases (41) again. The gradient limiter (50) limits the rise of the control signal (22) on the set limit and thus causes a time delay Closure of the relief valve (2) from the last position reached.

To prevent the output signal of the surge limit controller (41) when the gradient limiter intervenes (50) the position of the valve (2) is not permitted leads the position of the valve (2) over the Return line (60) to the surge limit controller (41) returned. The surge limit controller (41) limits now internally adjust its output size by tracking the valve position. If position measurement is missing on Valve (2) can also control signal (22) on the Pump limit controller (41) are returned.

The electronic gradient limiter according to the invention (50) is shown in detail in Fig. 2. It exists from the signal input block, a control factor or Gain (51), a limiter (52) and an integrator (53). From the control line (22) branches to the Integrator (53) from a feedback line (54), which are directly connected to the control factor or gain (51) is. The limits for the gradients are called Upper and lower limit of the limiter (52) set.

For the gradient limiter (50) and the surge limit controller (41) can advantageously be known components be used so that the implementation of the Process and the production of a suitable Device comparatively simple and inexpensive are.

List of reference numbers:

1

Turbocompressor

2nd

Blow-off valve

3rd

Silencer

10th

Suction pipe

11

Output line

12th

Check valve

20th

Blow-off line

21

pneumatic / hydraulic actuation device

22

Control line

23

Media line

31

Flow meter

32

Pressure gauge

33

Function transmitter (flow setpoint)

34

Subtractor

41

Pump limit controller

50

Gradient delimiter

51

Adjustment factor / gain

52

Delimiter

53

Integrator

54

Feedback

60

Feedback of the valve position

Claims (11)

1. Method of operating a turbo-compressor for the avoidance of regulator instabilities of surge limiting regulations with high proportional amplification of the regulator by means of blowing-off by way of a relief valve, wherein in the method a regulating parameter is determined from measurement values at least for the compressor throughflow and compressor final pressure as well as from predetermined or predeterminable target values and on the basis of this parameter an immediate opening of the relief valve is carried out by a surge limiting regulator by means of a pneumatic or hydraulic actuating device via a pressure medium, wherein no time limitation is effective in the opening direction of the relief valve (2), but a freely parameterisable time limitation of the closing process of the relief valve (2) is provided or programmed-in in the closing direction, characterised in that not only the limitation of the closing speed of the relief valve (2) is electronically (50) undertaken, but also the opening of the relief valve (2) is caused by an asymmetrically formed gradient limiter.
2. Method according to claim 1, characterised in that a faster closing speed of the relief valve (2) is allowed for a greater spacing of the working point from the surge limit, and a slower closing speed of the relief valve (2) is achieved in the proximity of the surge limit, by a gradient limiter (50) which can be switched over.
3. Method according to claim 1 and 2, characterised in that the closing speed on approach of the working point to the blow-off line is reduced in steps by a gradient limiter (50) with several switching stages.
4. Method according to claim 1 and 2, characterised in that on approach of the working point to the blow-off line the closing speed of the relief valve (2) is constantly reduced by a constantly variable limit value of the gradient.
5. Method according to claim 1, characterised in that the setting of the relief valve (2) is fed back to the surge limiting regulator (41).
6. Method according to claim 1, characterised in that the signal of the control line (22) is fed back to the surge limiting regulator (41).
7. Device for operating turbo-compressors for the avoidance of regulator instabilities of surge limiting regulations with high proportional amplification of the regulator, consisting of a surge limiting regulator (41) for adjustment of a relief valve (2) via a pressure medium by means of a pneumatic or hydraulic actuating device (21) with a setting regulator with a piston-cylinder unit or a diaphragm-cylinder unit and further consisting of a control line (22) for an actuation, in case of need, of the relief valve (2) in opening direction without time limitation and in closing direction with a freely parameterisable time limitation of the closing process, characterised in that an electronic, asymmetrically formed gradient limiter (50) is connected between the surge limiting regulator (41) and the control line (22).
8. Device according to claim 7, characterised in that the gradient limiter (50) consists of a setting factor (51), limiter (52) and integrator (53).
9. Device according to claim 7, characterised in that a feedback (54) to the setting factor (51) is branched off after the integrator (53).
10. Device according to claim 7, characterised in that a feedback line (60) for indication of the valve position is arranged between the surge limiting regulator (41) and the pneumatic/hydraulic actuating device (21) of the relief valve (2).
11. Device according to claim 7, characterised in that the control line (22) is coupled with the feedback line (60) by way of the pneumatic/hydraulic actuating device (21).

Images