EP0477055B1 - Control device for anti surge means of a compressor - Google Patents

Description

The present invention relates to a device for controlling the anti-pumping means of a compressor.

Every compressor has a zone of instability in which it must not operate. This is why the control devices of these compressors include an anti-pumping valve provided with a servomotor, which is connected between the outlet of the compressor and the inlet of the latter.

The servomotor of this anti-pumping valve is controlled from regulation means receiving as input a parameter representative of the compressor flow rate and a setpoint determined from the inlet pressure and the outlet pressure of the latter for injecting a part of the flow at the outlet of the compressor, at the inlet of the latter, in order to maintain this compressor above its point of separation (see EP-A-336,092 and GB-A-2,002,451).

However, the devices known in the prior art have a certain number of drawbacks because the anti-pumping valves have a very long response time and the compressor forays on either side of its nominal operating point are relatively large and can cause it to exceed its point of release and enter instability so that it is then impossible to return it to normal operation without stopping it.

The solutions proposed in the prior art consist in shifting the safety curve of the compressor to move it away from its zone of instability so that incursions on either side of its nominal operating point do not bring about the compressor to cross its hook point.

However, this solution is not very satisfactory insofar as the powers of the compressors tend to increase more and more and / or the response times of these must be the most short possible. Furthermore, these devices are also limited by the stability of the regulation means.

The object of the invention is therefore to solve these problems by proposing a device for controlling anti-pumping means of a compressor which is simple, reliable and which makes it possible to control the operation of the compressor very quickly and safely.

To this end, the subject of the invention is a device for controlling the anti-pumping means of a compressor, comprising an anti-pumping valve provided with a servomotor and connected between the outlet of the compressor and the inlet of the latter. , the servomotor being controlled from regulation means receiving as input a parameter representative of the compressor flow rate and a setpoint determined from the inlet pressure and the outlet pressure thereof, to inject part of the flow rate at the outlet of the compressor, at the inlet of the latter, in order to maintain it above its point of attachment, and an electrovalve for rapid emptying of the actuator of the anti-pumping valve and of the means for controlling the latter and the state of saturation or desaturation of the servomotor, as a function of the value of the difference between said parameter and said setpoint, characterized in that the output of the regulation means is connected to means for selecting a level u low receiving on another input, the output of a generator of ramp increasing in time, to direct towards the servomotor of the anti-pumping valve, the lowest signal.

• la Fig.1 représente un schéma synoptique d'un dispositif de commande de l'état de la technique;
• la Fig.2 représente un schéma synoptique d'un dispositif de commande selon l'invention; et
• la Fig.3 représente un diagramme illustrant le fonctionnement d'un dispositif de commande selon l'invention.

The invention will be better understood with the aid of the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

• Fig.1 shows a block diagram of a state of the art control device;
• Fig.2 shows a block diagram of a control device according to the invention; and
• Fig.3 shows a diagram illustrating the operation of a control device according to the invention.

As can be seen in FIG. 1, a device for controlling the anti-pumping means of a compressor, of the prior art, comprises an anti-pumping valve 1 connected between the output and the input d '' a compressor 2.

In known manner, this anti-pumping valve comprises a servomotor which is controlled from regulation means 3 receiving on an input, a parameter representative of the flow rate of the compressor, this parameter m emanating from measuring means 4 connected for example to the terminals d 'a pressure reducing member 5 of known type, connected to the inlet of the compressor.

K et A étant des constantes déterminées de manière classique en fonction du matériel.These regulation means 3 also receive at the input, a setpoint c determined from the input pressure P1 and the output pressure P2 of the compressor, delivered respectively by sensors 6 and 7 whose inputs are respectively connected to the input and output of the compressor and the outputs of which are connected to a setpoint computer 8 enabling this setpoint c to be determined from the two pressures indicated above and a formula of the type: $${\text{c = K (P}}_{\text{2}}{\text{- AP}}_{\text{1}}\text{)}$$

K and A being constants determined in a conventional manner depending on the material.

The regulation means 3 can be constituted by a PID regulator making it possible, as indicated above, to control the anti-pumping valve and more particularly the servomotor thereof, when the compressor is operating in an area close to its point. dropout.

It will also be noted that means of refrigeration 9 are provided in a manner known per se at the outlet of the compressor.

As mentioned previously, this structure has a certain number of drawbacks, in particular in terms of the speed of response of the assembly and the stability of the regulation means.

If we now refer to Figure 2, we see that the basic diagram of the control device according to the invention incorporates the same elements as the device of the prior art, namely that this device comprises a valve anti-pumping device 11 connected between the output and the input of a compressor 12. This anti-pumping valve comprises a servomotor controlled from regulating means 13 receiving on an input, a parameter m representative of the flow rate of the compressor and delivered by example by measurement means 14 connected to a pressure-reducing element at the input of the compressor and on another input, a setpoint c delivered by calculation means 15 making it possible to determine this setpoint from the inlet pressure and the compressor outlet pressure, as explained above, to control the anti-pumping valve and inject part of the flow at the outlet of this compressor, at the inlet of the latter in order to maintain it above its hang point. This regulation is conventional and has already been described previously.

According to the invention, a solenoid valve 16 for rapid emptying of the servomotor of the anti-pumping valve 11 is used to improve the speed of response thereof and this solenoid valve for emptying 16 is actuated by control means as a function of the value the difference between the parameter m representing the compressor flow rate and the setpoint c.

These means comprise for example a calculation member 17 receiving on an input, the parameter m at the output of the measurement means 14 and on another input, the setpoint c at the output of the calculation means 15, the output of these calculation means 17 controlling the solenoid valve on opening when the difference between the parameter and the setpoint is greater than a first threshold which will be called DSH hereinafter.

Thus, the opening of this rapid emptying solenoid valve of the booster of the anti-pumping valve makes it possible to accelerate the response of this anti-pumping valve, under the control of the regulating means, when the compressor approaches its point of separation.

In response to this command from the rapid drain solenoid valve of the servomotor, and from the anti-pumping valve, part of the output flow of the compressor is recycled to the inlet thereof, so that the operating point of the compressor moves away very quickly from its point of withdrawal.

The closing of the fast drain solenoid valve of the anti-pumping valve can then be controlled when the difference between the parameter m representative of the compressor flow and the setpoint c, becomes less than this first threshold DSH or a second threshold which will be called DSL thereafter.

To this end, calculation means 18 are connected in parallel to the calculation means 17 and receive on an input, the parameter m and on another input the setpoint c, to determine the difference between these two values, and compare this deviation from the DSL threshold in order to control accordingly, that is to say on closing, the rapid drain solenoid valve 16 of the anti-pumping valve 11.

To improve the operation of the control device, the output of the regulation means 13 can be connected to low level selection means 19 which therefore receive on one input the output of these regulation means 13 and on another input, the output of a ramp generator 20 increasing in time, to direct towards the actuator of the anti-pumping valve, the lowest signal at the output of the regulation means and of the ramp generator.

This ramp improves the gradual return of the assembly in normal operation. The law of growth of this ramp can be linear, logarithmic or any other type.

Of course, this ramp must start at a safety level preventing pumping of the compressor whatever its operating regime and advantageously this ramp starts at a level determined from the position of the anti-pumping valve and more particularly of the check valve. when the drain solenoid valve closes.

To this end, means 21 for copying the position of this anti-pumping valve can be provided. The output of these means 21 is connected to the input of the ramp generator 20 to start the latter at a level corresponding to the position of the valve of the anti-pumping valve when the drain solenoid valve is closed.

Of course, compensation means 22 can also be provided, these compensation means making it possible to add to the output signal means for copying the position of the solenoid valve, a signal for compensating for the error of copying or compensation. faults in the solenoid valve, for example a delay in closing the latter, which may be of the order of 40 ms.

This compensation signal is of course determined according to the characteristics of the anti-pumping valve.

Still with a view to improving the operation of the device, there may also be provided therein means 23 for adding a decreasing ramp in time to the setpoint c, these means being interposed between the means for calculating setpoint 15 and the corresponding input of the regulation means 13. The law of decrease of this ramp can be linear, hyperbolic or of any other type. The duration of the ramp is closely related to that used for the closing ramp since it must be ensured that the overprotection still exists when the closing ramp reaches 100%. The start of this ramp is determined as a function of the control of the drain solenoid valve and more particularly it can be controlled at the opening of this drain solenoid valve.

The operation of such a device is described with reference to FIG. 3 which is a setpoint diagram c / parameter m.

On this diagram, curve 1 represents the actual pumping line of the compressor and we see on the right of this curve, a curve 2 of DSH action corresponding to the first threshold mentioned above.

Curve 3 represents the setpoint protection line that the calculation means 17 calculate the difference between the operating point of the compressor and this protection line c in the direction of the action line DSH to trigger the opening of the anti-pumping valve when this DSH action line is reached or exceeded.

The line referenced by 4 represents the temporary overprotection line which relates to the addition of the generator ramp 23 to the setpoint and allows the device to be brought back much more flexibly to normal operation.

Finally, the line referenced by 5 is a desaturation line corresponding to the DSL threshold allowing the device to close the solenoid valve for rapid emptying of the actuator of the anti-pumping valve when this threshold is reached or exceeded and also to ensure the desaturation of this anti-pumping valve when the operating point of the compressor passes to the left of this curve to improve the speed of response of the assembly as will be explained in more detail below.

In normal operation, the device according to the invention adjusts the opening of the anti-pumping valve in order to ensure the compressor a minimum flow rate to prevent it from reaching its unstable operating zone.

The solenoid valve for rapid emptying of the servomotor of this anti-pumping valve is closed and the output of the ramp generator 20 connected to the output of the regulation means 13 is saturated, so that the output of the regulation means 13 is found again. exit from these selection means.

The PID actions of the regulation means are optimized to obtain a response speed as large as possible, compatible with the stability of the regulation loop and of the other regulations of the assembly connected to the output of the compressor.

In the event of disturbance of this assembly such that the regulation means fail to avoid a parameter-setpoint deviation lower than the first determined threshold DSH, in the direction of pumping, this threshold DSH is reached and the device then takes control in safety of the anti-pumping valve, firstly by forcing this anti-pumping valve to open by action in particular on the rapid drain solenoid valve and secondly by incrementing the setpoint, ie by triggering the ramp generator 23 connected to the setpoint input of the regulating means 13.

These safety actions are maintained as many scan cycles of the regulator as necessary to arrive at the DSL threshold corresponding to a parameter-setpoint deviation towards the large flow rates of the compressor. The device then closes the drain solenoid valve and takes into account the actual opening of the anti-pumping valve by the copying means 21 to initialize the ramp generator 20.

Consequently, the anti-pumping valve closes according to the setting of this ramp at the outlet of the generator 20 and when approaching the provisional overprotection curve, gives back control to the normal regulation means.

The temporary overprotection is thus gradually canceled along this ramp at the outlet of the generator 20.

It will also be noted that the servomotors of the anti-pumping valves generally operate with a driving pressure greater than what is strictly necessary in order to obtain an optimal level of tightness. This saturation pressure is used to place the valve of the solenoid valve very firmly on its seat in order to avoid any leaks.

To improve the speed of response of the device, it is possible to use the second DSL threshold to desaturate the actuator of the anti-pumping valve when this threshold is reached, i.e. when the difference between the parameter and the setpoint is lower than said second DSL level. To do this, two different pressure sources are used either via a solenoid valve depending on the DSL threshold.

In fact, under these conditions, the compressor arrives in an operating zone close to the zone in which it is necessary to control the anti-pumping valve and by desaturating beforehand the servomotor of this valve, the response speed is improved by this and therefore of the whole.

It will also be noted that means for counting for a determined time the number of times that said parameter-setpoint deviation becomes greater than said first level DSH, can be used to trigger an alarm when this number is greater than a determined value.

Indeed, when this number is greater than this value, it can be considered that the device is not operational and that for example the anti-pumping valve has a fault and that it is necessary to warn the users of this fault. , before any deterioration of the whole.

It is also possible to anticipate disturbances, by action on the compressor inlet regulating valve referenced by 24 in FIG. 2.

In fact, to compensate for the residual dead time of the anti-pumping valve, when the calculation means 17 are called, it is possible to send a brief additional opening pulse on the control of the inlet valve 24 of the compressor which is still in regulation.

Thus, the compressor immediately receives an additional flow even before the anti-pumping valve can act.

The flow through the inlet valve is a function of its upstream pressure, its downstream pressure and its opening.

The inlet pressure of a compressor operating in the vicinity of its protection and connected to a discharge network varies very little as a function of the recycled flow rate, which means that oscillations of the anti-pumping valve cannot destabilize the regulation. compressor inlet pressure.

Conversely, any oscillation of the position of the inlet valve is perceived as a variation in the measurement of the differential pressure Δ h, that is to say of the parameter m, which requires anti-pumping regulation. try to compensate for variations that originate from the compressor inlet pressure regulation.

To avoid this conflict, the opening of the inlet valve is connected to the opening of the anti-pumping valve, so that the inlet flow of the compressor is as constant as possible in the event of oscillation of the position. of the inlet valve. The different control means used for this purpose are referenced by 25 in Fig. 2.

Consequently, a measurement-setpoint deviation from process regulation, deviation calculated in module 26 and whose amplitude is modified in gain module 27 which follows, and producing for example an opening of the inlet valve, directly leads to by subtraction at 28 at the outlet of the regulator 13, a corresponding closure of the anti-pumping valve without the regulator 13 having to intervene.

In the example described, the illustration is made from a suction pressure regulation acting on a compressor inlet valve, but the same principle is applicable regardless of the parameter to be set (suction pressure , discharge, flow ...), and whatever the means used ( inlet, discharge, speed ...) to adjust the process without conflict with anti-pumping.

Claims (13)

1. Control device for anti-pumping means of a compressor, comprising an anti-pumping valve (11) fitted with a servomotor and connected between the outlet of the compressor (12) and the inlet thereof, said servomotor being controlled by controlling means (13) receiving as input a parameter (m) representing the flow rate of the compressor and a reference variable (c) determined from the input pressure (P1) and the output pressure (P2) thereof to inject part of the outflow rate of the compressor into it in order to maintain it above its cut-out point, and a rapid-emptying electrovalve (16) of the servomotor of the anti-pumping valve and operating means (17, 18) for said anti-pumping valve and for the saturation or desaturation state of the servomotor in relation to the value of the difference between said parameter and said reference variable, characterised in that the output of the controlling means (13) is connected to means (19) for selecting a low level to receive at another input the output of a means (20) for generating a ramp ascending over time in order to direct the lowest signal to the servomotor of the anti-pumping valve.
2. Device according to Claim 1, characterised in that it comprises operating means (17) to open said electrovalve when said difference is greater than a first threshold (DSH).
3. Device according to Claim 2, characterised in that it comprises operating means (17) to close said electrovalve when said difference is less than said first threshold (DSH).
4. Device according to Claim 2, characterised in that it comprises operating means (18) to close said electrovalve when said difference is greater than a second threshold (DSL).
5. Device according to any of the preceding claims, characterised in that the means (20) for generating said ramp are disengaged at a safety level to prevent pumping of the compressor whatever its operating conditions.
6. Device according to any of the preceding claims, characterised in that said ramp generator means is connected to means (21) for duplicating the position of the anti-pumping valve to disengage said ramp at a given level in accordance with the position of the anti-pumping valve at the time of closure of the rapid-emptying electrovalve.
7. Device according to any one of the preceding claims, characterised in that it comprises means (23) for adding a ramp descending over the time of the reference variable (c), the disengagement of which is determined in accordance with the operation of the rapid-emptying electrovalve.
8. Device according to Claim 7, characterised in that the addition means (23) are disengaged to open the emptying electrovalve.
9. Device according to any one of the preceding claims, characterised in that it comprises desaturation means (18) for the servomotor of the anti-pumping valve when said difference is lower than said second level (DSL).
10. Device according to any one of the preceding claims, characterised in that it comprises means for counting the number of times said difference between the reference variable and the measurement is greater than said first level (DSH) over a given time in order to actuate an alarm when this number is higher than a given value.
11. Device according to any one of the preceding claims, characterised in that it comprises means (25) for acting on a member (24) for controlling the process to anticipate the corrective action required at the anti-pumping valve when a fault causes a difference between the parameter and the reference variable which is greater than the first threshold (DSH).
12. Device according to Claim 11, characterised in that said control member is an inlet valve (24) of the compressor.
13. Device according to any one of the preceding claims, characterised in that it comprises means (26, 27, 28) for restricting the conflict between the process and the anti-pumping control on the basis of the difference between the parameter and the reference variable, acting on the output of the controlling means (13) so that they do not compensate for faults originating from control of the process.

Images