Control system and method for an electro-hydraulic servo-actuator, in particular of a turbopropeller engine

Abstract

A control system (50) for an electro-hydraulic servo-actuator (26) envisages: a controller (55), to generate a control current (I.sub.c), designed to control actuation of the electro-hydraulic servo-actuator (26), implementing a position control loop based on a position error (e.sub.p), the position error (e.sub.p) being a difference between a reference position (Pos.sub.ref) and a measured position (Pos.sub.meas) of the electro-hydraulic servo-actuator (26); and a limitation stage (58), coupled to the controller (55) to provide a limitation of the actuator speed of the electro-hydraulic servo-actuator (26); the limitation stage (58) limits a rate of change of a driving current (I.sub.d) to be supplied to the electro-hydraulic servo-actuator (26), in order to limit the actuator speed.

Claims

1. A control system for an electro-hydraulic servo-actuator, comprising: a position sensor, configured to provide a measured position of the electro-hydraulic servo-actuator; a controller configured to generate a control current, designed to control actuation of the electro-hydraulic servo-actuator, implementing a position control loop based on a position error, the position error being a difference between a reference position and a measured position of the electro-hydraulic servo-actuator provided by the position sensor; a limitation stage coupled to the controller and configured to provide a limitation of the actuator speed of the electro-hydraulic servo-actuator, wherein the limitation stage is configured to implement a closed loop control of the actuator speed based on a measured actuator speed and to limit a rate of change of a driving current to provide a rate-limited driving current for controlling the electro-hydraulic servo-actuator in order to limit the actuator speed; and a derivative block coupled to the position sensor to receive the measured position and configured to determine the measured actuator speed as a derivative of the measured position.

2. The control system according to claim 1, wherein the limitation stage comprises: a determination block configured to receive the measured actuator speed and to determine, based on the measured actuator speed, a slew rate limit value for limiting the rate of change of the driving current; and a dynamic rate limiter coupled to the determination block to receive the determined slew rate limit value and configured to limit the slew rate of the driving current based on the slew rate limit value, thus providing the rate-limited driving current for controlling the electro-hydraulic servo-actuator.

3. The control system according to claim 2, wherein the slew rate limit value is designed to determine a maximum ramp slope of a pattern of the driving current versus time.

4. The control system according to claim 2, wherein the determination block is configured to implement a look-up table, providing at an output the slew rate limit value corresponding to an input value of the measured actuator speed.

5. The control system according to claim 4, wherein the look-up table stores matchings between slew rate limit values and measured actuator speeds determined via experimental results.

6. The control system according to claim 4, wherein the slew rate limit values and values of the measured actuator speed are linked by a linear inverse relationship.

7. The control system according to claim 2, wherein the slew rate limit value is proportional to an actuator acceleration value, and the dynamic rate limiter is configured to provide the rate-limited driving current according to the actuator acceleration value.

8. The control system according to claim 2, wherein the determination block is configured to implement a look-up table, providing at an output a slew rate limit value corresponding to the value of a speed difference, between an actuator speed limit and the measured actuator speed.

9. The control system according to claim 1, wherein the driving current is a function of the control current.

10. The control system according to claim 9, further comprising a saturation block interposed between the controller and the electro-hydraulic servo-actuator, configured to receive the control current from the controller, and provide a saturation thereof to maximum and minimum values, in case the control current overcomes the maximum and minimum values, thereby providing the driving current to the limitation stage.

11. A valve arrangement, comprising a first valve and a second valve controlled by a same control fluid; an electro-hydraulic servo-actuator; and a control system to drive the electro-hydraulic servo-actuator designed to control actuation of the first valve in order to limit an actuator speed of the electro-hydraulic servo-actuator, the control system comprising: a position sensor configured to provide a measured position of the electro-hydraulic servo-actuator; a controller configured to generate a control current designed to control actuation of the electro-hydraulic servo-actuator and configured to implement a position control loop based on a position error, the position error being a difference between a reference position and a measured position of the electro-hydraulic servo-actuator provided by the position sensor; a limitation stage coupled to the controller and configured to provide a limitation of the actuator speed of the electro-hydraulic servo-actuator, wherein the limitation stage is configured to implement a closed loop control of the actuator speed based on a measured actuator speed and to limit a rate of change of a driving current to provide a rate-limited driving current for controlling the electro-hydraulic servo-actuator in order to limit the actuator speed; and a derivative block coupled to the position sensor to receive the measured position and configured to determine the measured actuator speed as a derivative of the measured position.

12. A turbopropeller engine for an aircraft, comprising: a propeller assembly; and a gas turbine coupled to the propeller assembly, the gas turbine having a valve arrangement and a compressor coupled to an air intake, the valve arrangement comprising: a first valve and a second valve controlled by a same control fluid; an electro-hydraulic servo-actuator; and a control system to drive the electro-hydraulic servo-actuator designed to control actuation of the first valve in order to limit an actuator speed of the electro-hydraulic servo-actuator, the control system comprising: a position sensor configured to provide a measured position of the electro-hydraulic servo-actuator; a controller configured to generate a control current designed to control actuation of the electro-hydraulic servo-actuator and configured to implement a position control loop based on a position error, the position error being a difference between a reference position and a measured position of the electro-hydraulic servo-actuator provided by the position sensor; a limitation stage coupled to the controller and configured to provide a limitation of the actuator speed of the electro-hydraulic servo-actuator, wherein the limitation stage is configured to implement a closed loop control of the actuator speed based on a measured actuator speed and to limit a rate of change of a driving current to provide a rate-limited driving current for controlling the electro-hydraulic servo-actuator in order to limit the actuator speed; and a derivative block coupled to the position sensor to receive the measured position and configured to determine the measured actuator speed as a derivative of the measured position, and wherein the first valve is coupled to the compressor to partialize air flow to the compressor, and the second valve is a fuel metering valve configured to control fuel supply to the turbopropeller engine, the control fluid being fuel coming from a fuel tank and provided by a fuel pump.

13. A control method for an electro-hydraulic servo-actuator, comprising: providing, by a position sensor, a measured position of the electro-hydraulic servo-actuator; generating a control current to control actuation of the electro-hydraulic servo-actuator; implementing a position control loop based on a position error, the position error being a difference between a reference position and the measured position of the electro-hydraulic servo-actuator provided by the position sensor; and providing a limitation of an actuator speed of the electro-hydraulic servo-actuator, wherein providing the limitation comprises implementing a closed loop control of the actuator speed based on a measured actuator speed and limiting a rate of change of a driving current to provide a rate-limited driving current for controlling the electro-hydraulic servo-actuator in order to limit the actuator speed, and wherein the measured actuator speed is determined as a derivative of the measured position by a derivative block coupled to the position sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the present invention, preferred embodiments thereof are now described, purely as non-limiting examples, with reference to the attached drawings, wherein:

(2) FIG. 1 is a perspective view of an aircraft provided with a turbopropeller engine;

(3) FIG. 2 is a schematic block diagram of the turbopropeller engine of the aircraft;

(4) FIG. 3 is a schematic diagram of a Variable Stator Vane (VSV) device of the turbopropeller engine;

(5) FIG. 4 is a schematic block diagram relating to fuel supply in the turbopropeller engine;

(6) FIG. 5 is a schematic block diagram of a known control system of an electro-hydraulic servo-actuator;

(7) FIG. 6 shows plots of characteristic curves of the electro-hydraulic servo-actuator;

(8) FIG. 7 is a schematic block diagram of a control system of an electro-hydraulic servo-actuator, according to an embodiment of the present solution;

(9) FIG. 8 is a schematic block diagram of a rate-limitation stage in the control system of FIG. 7;

(10) FIGS. 9A-9B shows plots of electrical quantities relating to performance of the control system of FIG. 7, compared to a known control system; and

(11) FIG. 10 is a schematic block diagram of a rate-limitation stage in the control system of FIG. 7, according to a different embodiment of the present solution.

BEST MODE FOR CARRYING OUT THE INVENTION

(12) As will be discussed in the following, an aspect of the present control solution envisages a closed loop control of the actuator slew rate (maximum operating speed), independently of the speed vs current characteristic curve; in particular, this closed loop control for the actuator speed envisages use of the actual actuator speed (evaluated as the derivative of a measured actuator position) in order to limit the rate of change of the actuator driving current, and therefore limit the maximum actuator speed.

(13) FIG. 7 shows a control system, denoted with 50, according to a first embodiment of the present solution, exploiting the above discussed control solution, in order to provide a driving current to an electro-hydraulic servo-actuator, for example to the electro-hydraulic servo-actuator 26 of the VSV device 25 in the turbopropeller engine 2 (see also the above discussion).

(14) The control system 50 includes, in a manner similar to what discussed before with reference to FIG. 5:

(15) a first adder block, here denoted with 54, receiving at a first (positive, or summation) input the reference position Pos.sub.ref and at a second (negative, or subtraction) input the measured position Pos.sub.meas, as a feedback, measured by a position sensor, here denoted with 52, e.g. an inductive position sensor, such as a LVDT transducer, and providing at the output a position error e.sub.p, as a function of the subtraction between the reference position Pos.sub.ref and the measured position Pos.sub.meas;

(16) a controller, here denoted with 55, e.g. of the PID (Proportional Integral Derivative) type, receiving at its input the position error e.sub.p and generating at its output, based on a regulation scheme, a control quantity I.sub.c, for example an electrical current, designed to control actuation of the electro-hydraulic servo-actuator 26; and

(17) a saturation block, here denoted with 56, interposed between the controller 55 and the electro-hydraulic servo-actuator 26, configured to receive the control quantity I.sub.c and provide a saturation thereof to maximum and minimum values Max, Min, in case the same control quantity I.sub.c overcomes the same maximum and minimum values Max, Min, thereby providing a driving quantity I.sub.d, in particular a driving current, for the electro-hydraulic servo-actuator 26.

(18) In the present solution, the maximum and minimum values Max, Min coincide with the limit values defined by the nominal characteristic curve of the electro-hydraulic servo-actuator 26, set by the manufacturer (see again FIG. 6 and the associated discussion), and are not set to lower values for safety reasons, as in known control solutions.

(19) Operation of the saturation block 56 is such as to limit the maximum (absolute) value of the actuator speed, by limiting the maximum (absolute) value for the driving quantity I.sub.d. As discussed above, however, this limitation may not be sufficient during transients, when, due to inertia effects, the instantaneous actuator speed may overcome the set maximum limits, notwithstanding the imposed driving current limitations.

(20) According to an aspect of the present solution, the control system 50 therefore further comprises:

(21) a derivative block 57, coupled to the position sensor 52, to receive the measured position Pos.sub.meas, and configured to determine a measured actuator speed Speed.sub.meas, as the derivative of the measured position Pos.sub.meas; and

(22) a limitation stage 58, coupled to the derivative block 57 to receive the measured actuator speed Speed.sub.meas and to the output of the saturation block 56 to receive the driving current I.sub.d, and configured to limit the rate of change of the driving current I.sub.d based on the measured actuator speed Speed.sub.meas, thereby providing a rate-limited driving current I.sub.d′ for controlling the electro-hydraulic servo-actuator 26.

(23) In more detail, and as shown in FIG. 8, the limitation stage 58 comprises a determination block 59 implementing a look-up table 59a, to determine a maximum rate of change of the actuator current according to the actual actuator speed.

(24) In particular, the look-up table 59a provides at the output a slew rate limit value dI.sub.d/dt for limiting the rate of change of the driving current I.sub.d, corresponding to the value of the measured actuator speed Speed.sub.meas received at the input; the values stored in the look-up table 59a (in particular, the matching between the values of the slew rate limit value dI.sub.d/dt and the measured actuator speed Speed.sub.meas are determined via experimental results, aimed at determining the slew rate limit values dI.sub.d/dt that allow not to overcome the desired actuator speed limits, Speed.sub.Max, Speed.sub.Min.

(25) In the embodiment shown in FIG. 8, the slew rate limit values dI.sub.d/dt and the values of the measured actuator speed Speed.sub.meas are linked by a linear inverse relationship, namely when the measured actuator speed Speed.sub.meas increases, the slew rate limit value dI.sub.d/dt decreases, and vice versa.

(26) The limitation stage 58 further comprises a dynamic rate limiter 60, coupled to the determination block 59 to receive the determined slew rate limit value dI.sub.d/dt, and to the output of the saturation block 56 to receive the driving current I.sub.d.

(27) The dynamic rate limiter 60 is configured to limit the slew rate of the input signal (i.e. the driving current I.sub.d) based on the slew rate limit value dI.sub.d/dt, thus providing the rate-limited driving current I.sub.d′ for controlling the electro-hydraulic servo-actuator 26. The dynamic rate limiter 60 may be implemented in any known manner, here not discussed in detail, as will be clear for a skilled person.

(28) In particular, as shown in the same FIG. 8, the slew rate limit value dI.sub.d/dt determines the maximum ramp slope of the pattern of the driving current I.sub.d vs time; in other words, the rate of change of the driving current I.sub.d is not allowed to exceed the slew rate limit value dI.sub.d/dt.

(29) It is to be noted that the slew rate limit value dI.sub.d/dt is proportional to the actuator acceleration (since the driving current I.sub.d is proportional to the actuator speed); accordingly, the dynamic rate limiter 60 operates according to the actuator acceleration providing the rate-limited driving current I.sub.d′ so that the actuator speed limits (Speed.sub.Max, Speed.sub.min) are not overcome. In case the actuator speed increases, the acceleration command (i.e. the slew rate limit value dI.sub.d/dt) decreases; this implements a preview control action that anticipates the speed reduction. The look-up table 59a is properly tuned to set the maximum rate of change of the actuator speed.

(30) FIGS. 9A-9B show simulation results relating to the performance of the discussed control action compared to known control solutions.

(31) In particular, FIG. 9A shows the plot of the driving current I.sub.d versus time, in the control system 50 according to the present solution (shown in continuous line) and in a known control system (shown in dashed line), where the above discussed control solution is not implemented (e.g. the control system 40 of FIG. 5); FIG. 9A clearly shows the rate-limitation of the driving current I.sub.d envisaged by the present control solution.

(32) FIG. 9B shows the plot of the actuator speed versus time, again showing with a continuous line the plot according to the present control solution and with a dashed line the plot according to the known control solution. FIG. 9B also shows the actuator speed limits, Speed.sub.max, Speed.sub.min. FIG. 9B clearly shows that the present control solution allows to avoid the actuator speed to overcome the actuator speed limits, Speed.sub.Max, Speed.sub.min, contrary to the known control solution.

(33) The advantages of the present solution are clear from the previous discussion.

(34) In any case, it is again underlined that the present solution provides an effective system to control operation of an electro-hydraulic servo-actuator 26, properly limiting the maximum speed of the same actuator, i.e. the actuator slew rate. Advantageously, the actuator speed is limited dynamically and independently of the nominal characteristic curve (speed vs driving current) of the electro-hydraulic servo-actuator.

(35) In particular, contrary to known electronic control solutions, the present control system 50 allows to fully exploit the capability of the electro-hydraulic servo-actuator 26; contrary to known mechanical control solutions, the present control system 50 does not require complex and expensive control mechanisms.

(36) Finally, it is clear that modifications and variations can be made to what is described and illustrated herein, without thereby departing from the scope of the present invention as defined in the appended claims.

(37) In particular, as shown in FIG. 10, in a different embodiment of the limitation stage 58 of the control system 50, the same limitation stage 58 may comprise a second adder block, here denoted with 64, receiving at a first (positive, or summation) input the actuator speed limit Speed.sub.Max (the absolute value thereof), and at a second (negative, or subtraction) input the measured actuator speed Speed.sub.meas, and providing at the output a speed difference e.sub.speed, as a function of the subtraction between the actuator speed limit Speed.sub.Max and the measured actuator speed Speed.sub.meas.

(38) The look-up table 59a in this case receives at the input the above speed difference e.sub.speed, and provides the slew rate limit value dI.sub.d/dt based on the same speed difference e.sub.speed.

(39) In this case, the slew rate limit values dI.sub.d/dt and the values of the speed difference e.sub.speed are linked by a linear direct relationship, at least up to a given value of the same speed difference e.sub.speed, namely when the speed difference e.sub.speed increases/decreases, the slew rate limit value dI.sub.d/dt correspondingly increases/decreases.

(40) In other words, when the measured actuator speed Speed.sub.meas is far from the actuator speed limit Speed.sub.Max, the slew rate limit values dI.sub.d/dt are higher; as the measured actuator speed Speed.sub.meas approaches the actuator speed limit Speed.sub.Max, the slew rate limit values dI.sub.d/dt is decreased, so as to limit the actuator acceleration.

(41) In particular, also in this embodiment, the slew rate limit value dI.sub.d/dt is supplied to the dynamic rate limiter 60, which also in this case is configured to limit the slew rate of the driving current I.sub.d based on the slew rate limit value dI.sub.d/dt, to provide the rate-limited driving current I.sub.d′ for controlling the electro-hydraulic servo-actuator 26.

(42) Moreover, it is underlined that, although the present disclosure has made explicit reference to control of the electro-hydraulic servo-actuator 26 of the VSV device 25 in the turbopropeller engine 2 of the aircraft 1, it is clear that the control system 50 may advantageously be employed for controlling any electro-hydraulic servo-actuator.

(43) In particular, use of the control system 50 is advantageous every time a first valve, e.g. a variable geometry (VG) valve, and a second, different, valve are to be controlled using a same control fluid, to limit the actuator speed of the first valve in order to avoid steering too much control fluid towards the same first valve and away from the second valve.