REGULATION METHOD AND REGULATION APPARATUS OF A REFRIGERATION PLANT AND RESPECTIVE REFRIGERATION PLANT INCLUDING SUCH APPARATUS

Abstract

Described is a regulation apparatus for a refrigeration plant having defined therein a refrigerant fluid path and a plurality of devices arranged along the refrigerant fluid path. The regulation apparatus includes a first sensor arranged in a first point (P1) and a second sensor arranged in a second point (P3), each along the fluid path of the refrigeration plant, a control unit and an actuation device. The control unit controls a first value measured by the first sensor and obtains a first regulation request deriving from the first measured value as well as a second value measured by the second sensor and derives a second regulation request deriving from the second measured value, compares the first and second regulation requests, and establishes which regulation request is greater. The control unit also commands the actuation device to actuate the most effective regulation request of the refrigeration plant devices.

Claims

1. A regulation apparatus for a refrigeration plant, wherein a refrigerating fluid path is defined in the refrigeration plant and one or more devices are arranged along said refrigerating fluid path, wherein said regulation apparatus includes a first sensor arranged in a first point (P1) along the refrigerating fluid path of the refrigeration plant to detect a first value of a quantity in said first point (P1), a second sensor arranged in a second point (P3) along the fluid path of the refrigeration plant to detect a second value of said quantity in said second point (P3), or a calculation unit to calculate and derive the second value of said quantity in said second point (P3), a control unit, and an actuation device to actuate at least one or more devices of the refrigeration plant, wherein said control unit controls the first value of said quantity measured by said first sensor and obtain a first request for regulation of said one or more devices of the refrigeration giant deriving from said first measured value and wherein said control unit controls the second value measured by said second sensor or calculated by said calculation unit and derive a second request for regulation of said one or more devices of the refrigeration plant deriving from said second value measured or calculated for said second point (P3), comparing the first regulation request with the second regulation request and establishing which regulation request is more effective and/or more suitable for said refrigeration plant between the first regulation request and the second regulation, and wherein said control unit controls the actuation device to actuate the most effective and/or most suitable regulation request for said one or more devices of the refrigeration plant.

2. The regulation apparatus according to claim 1, wherein the most effective and/or most suitable regulation request is the greater regulation request.

3. The regulating apparatus according to claim 1, wherein said regulation request is a calculation having as output a relative percentage (%), and wherein said comparing the first regulation request with the second regulation request is a step of comparing relative percentages (%), a most suitable and/or most effective percentage (%) being then chosen and translated into an regulation command suitable for said actuation device.

4. The regulation apparatus according to claim 1, wherein said at least one or more devices of the refrigeration plant to be controlled is a compressor or a plurality of compressors and the more effective and/or more suitable regulation request is the greater regulation request corresponding to the total capacity of said one compressor or a plurality of compressors in the refrigeration plant.

5. The regulation apparatus according to claim 4, wherein each of the first regulation request (Req_p1) and the second regulation request (Req_p3) is a percentage linked to the maximum total capacity of said compressor or plurality of compressors.

6. The regulation apparatus according to claim 1, wherein said control unit calculates each first regulation request (Req_p1) and second regulation request (Req_p3) by means of a proportional regulation calculated with the following generic formula:
R.sub.eq=Kp*e wherein Kp is a gain constant configured for the said at least one device; and e is a deviation between quantities, g.sub.i-g.sub.set, wherein g.sub.i means a quantity read by the respective sensor at the instant i or calculated for the respective second point, and g.sub.set is the set point or reference quantity in instant i.

7. The regulation apparatus according to claim 1, wherein said control unit calculates each first regulation request (Req_p1) and second regulation request (Req_p3) by means of a proportional and integral regulation, also called P+I regulation, according to the equation $\mathrm{Req}=K_p*\left(e+\frac{1}{T_i}*\int \mathrm{edt}\right)$ where: K.sub.p=gain connected to the differential by the relation: $K_p=\frac{1}{\mathrm{Diff}*2}$ T.sub.i=Integral time [sec] e=deviation (g.sub.i-g.sub.set) and wherein K.sub.p is a gain constant configured for said at least one device; and e is a deviation between quantities, g.sub.i-g.sub.set, wherein g.sub.i means a real or calculated value of said quantity at instant i and g.sub.set is the set point or reference quantity at instant i.

8. The regulation apparatus according to claim 7, wherein the proportional contribution is a central band such that when the quantity g.sub.i corresponds to g.sub.set the regulation request is 50%.

9. The regulation apparatus according to claim 1, wherein said control unit calculates each first regulation request (Req_p1) and second regulation request (Req_p3) with the following formula: $\mathrm{Req}=\mathrm{Prop}+\mathrm{Integr}=\left[0.5+\left(\frac{1}{\mathrm{Diff}*2}*e\right)\right]+\frac{1}{\mathrm{Diff}*2}*\left(\frac{1}{T_i}*\int \mathrm{edt}\right)$ where K.sub.p(P1) is the constant of proportionality for the first sensor; T.sub.i(P1)=at the integral time for the first point, Setpoint (P1) is the reference or setpoint pressure value for the first point; K.sub.p(P3) is the constant of proportionality for the second sensor or second point; T.sub.i (P3)=at the integral time for the second point, Setpoint (P3)=at the reference or setpoint pressure value for the second point, and wherein the deviations are thereby calculated e1=(p.sub.iP1−p.sub.setp1) e2=(p.sub.iP3−p.sub.setp3) and wherein said control unit compares the two requests Req_p1 and Req_p3 at every instant i and choose the greater of the two as the total request with which to actuate said at least one or more devices.

10. A refrigeration plant including, or in combination with, a regulation apparatus according to claim 7.

11. A refrigeration plant according to claim 10, including a compression device, a heat exchanger, an ejector a receiver, an expander and an evaporator, wherein said refrigeration plant is configured so that a fluid leaving the compression device enters the heat exchanger and, leaving the heat exchanger, is introduced into a first inlet in the ejector, and wherein an outlet of the ejector is connected to the receiver, and wherein said receiver is connected to the evaporator to supply a liquid part of the fluid and is connected to the compression device to supply a gaseous part of the fluid, and wherein a further connection is provided between the evaporator and a second inlet of the ejector, and wherein a check valve is provided on a connecting section between the evaporator and the compression device, and wherein said first sensor is placed at the exit of the evaporator and positioned upstream of the check valve and said second point (P) is upstream of the compression device, downstream of said check valve, and wherein said first sensor identifies a pressure at the exit of the evaporator, before the check valve and wherein said regulation apparatus identifies in said second point (P3) a pressure entering the compression device, and wherein the first regulation request is a regulation request calculated downstream of the evaporator while the second regulation request is a regulation request calculated upstream of the compression device, and wherein the control unit checks which request is greater and consequently act on the capacity of the compression device.

12. The refrigeration plant according to claim 11, wherein a second sensor is arranged in said second point (P3).

13. A method for regulation of a refrigeration plant comprising at least one or more devices, wherein a path of refrigerant fluid is defined in the refrigeration plant and a plurality of devices are arranged along said path of refrigerant fluid, wherein the method provides for detecting a quantity (g.sub.i1) by means of a first sensor arranged at a first point (P1) along the refrigerant fluid path of the refrigeration plant, detecting or calculating a quantity (g.sub.i3) at a second point (P3) along the fluid path of the refrigeration plant, checking a first value of said quantity (g.sub.i1) measured by said first sensor and obtaining a first regulation request (Req_p1) of said at least one or more devices of the refrigeration plant deriving from said first measured value, checking a second value of said quantity (g.sub.i3) in said second point (P3) and deriving a second regulation request (Req_p3) of said at least one or more devices of the refrigeration plant deriving from said second value, comparing the first regulation request (Req_p1) with the second regulation request (Req_p3), and establishing which regulation request is more effective and/or more suitable between the first regulation request (Req_p1) and the second regulation (Req_p3), actuating the most effective and/or most suitable regulation request for said at least one or more devices of the refrigeration plant.

14. The regulation method according to claim 13, wherein said at least one or more devices of the refrigeration plant to be controlled is a compressor or a plurality of compressors, and the more effective and/or more suitable regulation request is the greater regulation request corresponding to the total capacity of said one compressor or a plurality of compressors in the refrigeration plant.

15. The regulation method according to claim 14, wherein each step of deriving the first regulation request (Req_p1) and second regulation request (Req_p3) is a proportional regulation
R.sub.eqK.sub.p*e or a request for proportional and integral regulation, also called P+I regulation, according to the equation $\mathrm{Req}=K_p*\left(e+\frac{1}{T_i}*\int \mathrm{edt}\right)$ where: K.sub.p=gain linked to the differential by the relation: $K_p=\frac{1}{\mathrm{Diff}*2}$ configured for said at least one device; and e=deviation (g.sub.i-g.sub.set) that means a deviation between quantities, g.sub.ig.sub.set, wherein g.sub.i means the quantity read by the respective sensor or calculated for the respective point at instant i and g.sub.set is the set point or reference quantity at instant i and T.sub.i=Integral time [sec]

16. The regulation method according to claim 15, wherein the proportional contribution is a central band such that when the quantity gi corresponds to g.sub.et each first regulation request (Req_p1) and second regulation request (Req_p3) is 50%.

17. The regulation method according to claim 14, wherein each first regulation request (Req_p1) and second regulation request (Req_p3) are derived with the following formula: $\mathrm{Req}=\mathrm{Prop}+\mathrm{Integr}=\left[0.5+\left(\frac{1}{\mathrm{Diff}*2}*e\right)\right]+\frac{1}{\mathrm{Diff}*2}*\left(\frac{1}{T_i}*\int \mathrm{edt}\right)$ where K.sub.p(P1) is the constant of proportionality for the first sensor; T.sub.i(P1)=at the integral time for the first sensor, Setpoint (P1) is the reference or setpoint pressure value for the first sensor; K.sub.p(P3) is the constant of proportionality for the second sensor or for the second point; T.sub.i(P3)=at the integral time for the second point, Setpoint (P3)=at the reference or setpoint pressure value for the second point, and wherein the deviations are thereby calculated
e1=(p.sub.iP1−p.sub.setp1)
e2=(p.sub.iP3−p.sub.setp3) and wherein each first regulation request (Req_p1) and second regulation request (Req_p3) is compared at each instant (i) and the greater of the first regulation request (Req_p1) and second regulation request (Req_p3) chosen as total request with which to actuate said at least one or more devices.

18. The regulation method according to claim 17, wherein the plant includes a compression device, a heat exchanger, an ejector a receiver, an expander and an evaporator, wherein said plant is configured so that a fluid leaving the compression device enters the heat exchanger and, leaving the heat exchanger, is fed into a first input in the ejector, and in which an output of the ejector is connected to the receiver, and wherein said receiver is connected to the evaporator to supply a liquid part of the fluid and is connected to the compression device to supply a gaseous part of the fluid, and wherein a further connection is provided between the evaporator and a second inlet of the ejector, and wherein a check valve is provided on a connecting section between the evaporator and the compression device, and wherein said first sensor is placed at the exit of the evaporator positioned upstream of the check valve and said second point is upstream of the compression device, downstream of said check valve, and wherein sad first sensor is suitable to identify a pressure at the exit of the evaporator, before the check valve and wherein a pressure entering the compression device is identified, and wherein the first regulation request is a regulation request calculated downstream of the evaporator while the second regulation request is a regulation request calculated upstream of the compressor, and wherein it is verified which request is greater and consequently the capacity of the compression device is acted upon.

19. The regulation method according to claim 18, wherein each first regulation request (Req_p1) and second regulation request (Req_p3) are derived and compared continuously over time, so as to regulate the operation of said one or more devices based on the value of the greater request.

20. The regulation method according to claim 18, wherein the refrigeration plant includes a flash gas valve for the interception of gas coming from the receiver towards the compression device, and wherein a third probe or third sensor is provided, capable of measuring a pressure (P2) at the receiver, and wherein a pressure difference is measured between the pressure at the third probe with respect to the first probe, or with respect to a reference pressure value at the first probe, and the method provides for calculating a regulation request on the flash gas valve and acting on the flash valve gas to maintain said pressure difference within a predefined range and wherein in said second point (P3) a second probe or second sensor is provided for measuring the quantity in said second point (P3).

21. The regulation method according to claim 13, wherein said regulation request is a calculation having as output a relative percentage (%), and wherein comparing the first regulation request with the second regulation request is a step of comparing relative percentages (%), the most suitable and/or most effective percentage (%) being then chosen and translated into a regulation command.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Reference will be made to the accompanying drawings, wherein:

[0061] FIG. 1 shows a view of a diagram representing a refrigeration plant according to an embodiment of the invention;

[0062] FIG. 2 shows a view of a block diagram representing a method for control regulation of a refrigeration plant according to an embodiment of the invention,

[0063] FIG. 3 shows a view of a graph relative to the regulation requests according to the proportional only mode;

[0064] FIG. 4 shows a view of a diagram representing a refrigeration plant according to an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0065] With reference to the accompanying drawings, the numeral 10 denotes a refrigeration plant. The refrigeration plant 10 comprises, connected in fluid communication in a circuit, a compression device 12 or compressor, a heat exchanger 15, an ejector 16, a receiver 17, an expansion valve 18 and an evaporator 19. The compression plant 10 preferably includes in the embodiment shown at least a second expander 20 and a second evaporator 21 and a further compression device 22 to serve users at a low temperature with respect to the first above-mentioned components. Further expanders, evaporators and compression devices may be provided without departing from the scope of the invention.

[0066] In such a refrigeration plant 10, a fluid leaving the compression device 12 enters the heat exchanger 15 where it is cooled. The fluid leaving the heat exchanger 15 is introduced into a first inlet 16a in the ejector 16. An output of the ejector is normally connected to the receiver 17, where a liquid part of the fluid is separated from the gaseous part. The liquid part of the fluid is supplied to the evaporator 19, passing through the expander 18. The gaseous part of the refrigerant can be supplied to the compression device 12, as will described in more below. A further connection is provided between the evaporator 19 and a second inlet 16b of the ejector 16.

[0067] A first check valve 24 is preferably provided interposed between the evaporator 19 and the compression device 12, and a second check valve 25 is interposed between the evaporator 19 and the second inlet 16b of the ejector 16.

[0068] It will be noted that a fluid path is identified in the above-mentioned circuit which runs from the compression device 12 towards the receiver 17 passing through the heat exchanger 15 and the ejector 16, and which continues from the receiver 17 towards the compression device 12 passing through the expander 18 and the evaporator 19. A further fluid path is provided between the evaporator 19 and the ejector 16 passing through a respective check valve 25. With respect to said fluid paths, a downstream position and an upstream position for each component of the plant are identified in the circuit and in the plant. In other words, for each device of the refrigeration plant, a position upstream and downstream with respect to the path of the fluid in the region of the device is identified (and must be understood).

[0069] Therefore, for example, the ejector 16 is in a downstream position with respect to the heat exchanger 15 and the ejector 16 can be considered in a position upstream of the evaporator for the liquid part of the fluid, but downstream of the evaporator for a gaseous part that arrives from the evaporator passing through the check valve.

[0070] As is known, an ejector uses the Venturi effect to increase the pressure of the gaseous part at the second inlet by means of the fluid arriving at the first inlet.

[0071] Furthermore, the plant 10 includes a first probe 31 at the outlet from the evaporator 19, for example positioned upstream of the first check valve 24, and a second probe 33 positioned upstream of the compression device 12. In practice, the check valve 24 separates the outlet from the evaporator 19, for example a so-called medium temperature evaporator, from the inlet of the compression device 12. It will be noted that the first probe 31 is able to identify a pressure p1 which is the pressure at the outlet of the medium temperature evaporators, upstream of the first check valve 24. The second probe 33 is able to identify a pressure p3, that is to say the suction pressure at the compression device 12.

[0072] The first probe 31 and the second probe 33 are also part of a regulation apparatus 50, including a control unit 51 (or processing unit) operatively connected to the first probe 31 and to the second probe 33. The regulation apparatus 50 further includes an actuation device 52 operatively connected to the processing unit 51 and to the compression device 12 or compressor 12 to actuate the compressor on the basis of inputs received from the control unit 51. It should be noted that the second probe 33 may be absent or not used to measure the pressure. In this case, a pressure can be derived in the area of the second probe 33 (corresponding to a so-called second point) by deriving a calculated value, for example but not exclusively from the value of the pressure measured by the first probe 31, or from other characteristics of the plant, such as plant actuators. Where the second probe 33 is described, it must be understood implicitly that this probe could be absent and the relative pressure value is derived or calculated without direct measurement.

[0073] According to an aspect of the invention, in order to optimize an operation of the plant 10, a calculation is made of a request for regulation of the compression device 12 both on the basis of a pressure value measured by the first probe 31 and on the basis of a pressure value measured by the second probe 33, or derivative.

[0074] A system is therefore provided for calculating a first regulation request on the basis of the pressure value measured at the point of the first probe 31 and for calculating a second regulation request on the basis of the measured pressure vainer or, as mentioned, derived in the point of the second probe 33. The two regulation requests are compared and the greater regulation request is chosen as the total regulation request of the compression device 12.

[0075] In other words, a so-called comparison of regulation requests is performed on the basis of the pressure value measured upstream of the first check valve 24 and of the pressure value measured downstream of the first check valve 24 and therefore upstream of the compression device 12. In other words, a pressure reading p1, p3 is taken (or the latter calculated/derived) and, for each respective position in the circuit, a regulation request value is calculated, that is, a calculation of a regulation request to operate the plant in conditions of optimization for the position of the first probe 31 and of the second probe 33.

[0076] It follows that for each sensor or probe 31, 33, a regulation request occurs, that is, how much, for example, in percentage terms, a plant needs to be regulated to reach a reference value, in the area of the first probe, and in the area of the second probe respectively. The greater request is chosen as the total request with which to actuate the compression device.

[0077] The regulation apparatus 50 is therefore provided including the control unit 51 where a reference value or set point is stored for the quantity measured by the first sensor 31, and a reference value or set point for the quantity measured by the second. sensor 33, or, as mentioned, the derived quantity. The calculation of the regulation request is also processed in the control unit 51.

[0078] More specifically, the control unit 51 is configured to compare the first regulation request on the first sensor with the regulation request on said second sensor 33, establishing which regulation request is greater between the first regulation request and the second regulation request. The control unit is configured to command the actuation device 52 to actuate the greater regulation request on the compressor 12.

[0079] More particularly with reference to FIG. 3, the regulation can be carried out based on a proportional regulation only.

[0080] The formula is therefore

R.sub.eq=Prop=e*K.sub.p

[0081] It will be noted that, as shown in FIG. 3, the proportional contribution is central band, so when the pressure value corresponds to the setpoint value the request (proportional part only) is not 0 but 50%.

[0082] The calculation of the regulation request can be carried out with the proportional+integral mode, the so-called P+I mode.

[0083] The P+I regulation is calculated with the following formula

[00006]$\mathrm{Req}=\mathrm{Prop}+\mathrm{Integr}=\left[0.5+\left(\frac{1}{\mathrm{Diff}*2}*e\right)\right]+\frac{1}{\mathrm{Diff}*2}*\left(\frac{1}{T_i}*\int \mathrm{edt}\right)$ [0084] T.sub.i=Integral time [sec] [0085] e=deviation [barg] [0086] e=(p.sub.i−p.sub.set)

[0087] And in addition, Diff is linked to the gain according to the following formula

[00007]$K_p=\frac{1}{\mathrm{Diff}*2}$ [0088] T.sub.iIntegral time [sec] [0089] e=deviation [barg] [0090] e=(p.sub.i−p.sub.set)

[0091] With p.sub.i pressure read at instant i and p.sub.set setpoint pressure at instant i (it could be a constant value or variable in the case, for example, of a floating setpoint enabled). It is therefore possible to set a Diff (p1) for the first probe 31 and a differential Diff (p3) for the second probe 33.

[0092] In addition, the errors are calculated

e1=(p.sub.iP1−p.sub.setp1)

e2=(p.sub.iP3−p.sub.setp3)

[0093] In the case of P+I regulation, the integral action is added to the effect of the proportional action described above, which makes it possible to obtain a regulation deviation at zero speed. The integral action is linked to the time and the distance from the setpoint. It allows the request to be modified if the regulation value remains distant from the setpoint over time.

[0094] The value of the integral time set represents the speed of actuation of the integral control: [0095] Low values result in quick and energetic regulations [0096] High values result in slower and more stable regulations.

[0097] The two requests Req_p1 and Req_p3 are compared and the greater of the two is chosen as the total request with which to actuate the compression device 12.

[0098] It is to be understood that other calculation techniques can be envisaged starting from the concepts-principles described here.

[0099] It should also be noted that request calculation techniques according to the proportional or proportional+integral mode described here can also be applied to a single probe. For example, the calculation techniques can be applied in more standard refrigeration cycles, for example without an ejector, where it is necessary to calculate the feedback request on a quantity to be controlled, such as, for example, but not exclusively, the pressure control for the management of compressors in a simple refrigeration cycle. In any case, as mentioned, what is relevant for the invention concerns a comparison between requests and a comparison between the regulation requests and the selection of a maximum regulation request or a most suitable regulation request for said refrigeration plant.

[0100] FIG. 4 illustrates a further refrigeration plant 10 with regulation apparatus according to an alternative embodiment of the invention. For this alternative embodiment, components having an identical function retain the same reference numerals.

[0101] In particular, with reference to FIG. 4, a refrigeration plant 10 includes a flash gas valve 40 for the interception of gas coming from the receiver 17. At the flash gas valve 40, which is also called a modulating valve, a third probe or third sensor is provided, denoted with reference numeral 42, which is capable of measuring a pressure P2 at the receiver 17.

[0102] In particular, when the ejector 16 is able to suck gas from the evaporator and therefore the first check valve 24 between the second sensor 33 and the first sensor 31 is closed (it does not allow the flow from the point of the second sensor 33 towards the point of the first sensor 31), in this case, except for the pressure drops, the pressure at the third probe 42 can be approximately equal to the pressure of the second sensor 33, that is to say, P2 is approximately equal to P3. Preferably, there is additionally an on-off (open/closed) type flash gas solenoid valve 45 installed in parallel with the fresh gas valve 40 and with the same function, but to increase the passage area and reduce head losses due to the flash gas valve 40.

[0103] The flash gas valve 40 is managed with a conventional regulation called PID (Proportional+Integral+Derivative), calculated on a reference Delta called Delta_set, which can be set, compared with the Delta difference evaluated at each program run.

[0104] The Delta can be defined (as a user choice setting) as: [0105] Delta=p2−p1 (with p1 value evaluated/measured at each program run) Or [0106] Delta=p2−p1_set (that is, comparing p2 not with the actual value of p1 but with the setpoint set for p1).

[0107] The aim is to keep Delta preferably within values that balance the optimal operation of the ejector between its capacity to create a pressure increase (lift defined as p2−p1) and the flow rate drawn by the evaporator 19.

[0108] Example Delta_set=3 bar (value that can be set by a user), at each program run the Delta difference is evaluated and consequently the PID regulation request of the flash gas valve 40 is calculated to reach the set Delta_set; if Delta>delta_set the valve opens, if Delta<Delta_set the valve closes.

[0109] The pressure p1 is typically measured by a transducer. The pressure p2 of the receiver can be measured by means of a transducer or derived from other known quantities as mentioned above in general for the measurement of a pressure in the refrigeration plant; for example if in the summer operation the ejector is able to suck the flow rate from the evaporator (from p1) generating an increase in pressure between p1 and p2 such as to close the check valve 24 which separates p1 from p3. In this case p2 is approximately equal to p3 less the pressure drops, so in this operation it is possible to deduce p2 from p3 with any offset.

[0110] In another sense, one of the characteristics of the ejector is the lift defined as the pressure difference p2−p1 which it is able to generate. Knowing the performance characteristic curve of the ejector 16, p2 could be obtained by adding to p1 the lift generated by the ejector itself, knowing its operating conditions at the instant evaluated, for example.

[0111] In practice, in addition to a comparison between the regulation requests for the first sensor and for the second sensor, there is also a specific management of the flash gas valve 40, which connects the receiver 17 with the suction of the compression device 12. This management is based on the pressures p1 and p2, where p2 is the pressure of the receiver 17.

[0112] In use, the gas, which is discharged from the receiver 17 towards the suction of the compression device 12 through this flash gas valve 40, can itself influence the trend of the pressure p3. Furthermore, this adjustment of the flash gas valve 42 has the aim of optimizing the delta pressure between p2 and p1 to make the ejector 16 work at its best, and therefore influencing the ejector will also indirectly influence p1 and p3 as trends in the machine.

[0113] As mentioned above, a flash gas solenoid valve 45 (FGSL) can be installed in parallel to the flash gas valve 42, therefore with non-modulating operation but completely open or closed.

[0114] In this case, a logic such as the following can be actuated:

[0115] If the opening of FGV >x% (where x% is a parameter which can be set, for example 90%) then after a certain delay time t in which FGV opening remains >x%, the opening of the FGSL valve is commanded. This valve can manage more flow with less pressure drops thus ensuring a rapid decrease of the Delta p2-p1 and at the same time leaving the FGV valve in parallel to regulate more finely.

[0116] If, on the other hand, the opening of the FGV valve falls below a threshold y% (where y% can be set and y%<x%, for example 70%) then, after a certain settable delay time t2, the FGSL valve is closed and only the FGV valve is regulated.

[0117] The invention, described according to preferred embodiments, allows the set aims and objectives to be achieved for overcoming the limits of the prior art.

[0118] The invention has thus far been described with reference to its embodiments. It is to be understood that there may be other embodiments pertaining to the same inventive core, all falling within the scope of protection of the claims set forth below.