Variable vane control system and method

Abstract

A variable vane control system, 100 fig 2, for use with a gas turbine engine, 10 fig 1, including at least one circumferential set of variable vanes 102 including first 104 and second 106 variable van

Description

Field of the disclosure The present disclosure generally relates to a variable vane control system and a method of operating the variable vane control system. Background Variable vane assemblies, including variable inlet guide vanes (IGVs) and variable stator vanes (VSVs), are utilized by gas turbine engines for controlling flow of a fluid, usually air or combustion products, through various compression and expansion stages. Typically, each variable vane of a variable vane assembly is connected at its radially outer end to a lever which, in turn, is pivotally connected to a unison ring extending circumferentially around a casing of the gas turbine engine. The unison ring is mounted on carriers, such that the unison ring is rotatable about its central axis, which usually coincides with a central axis of the gas turbine engine. Rotation of the unison ring is usually achieved by means of a single actuator, or a pair of diametrically oppositely disposed actuators acting on the unison ring. The single actuator or each actuator from the pair of diametrically oppositely disposed actuators exerts a tangential load on the unison ring, thereby causing the unison ring to rotate about its central axis. Rotation of the unison ring actuates each of the levers causing the variable vanes to rotate, in unison, about their respective longitudinal axes. Angular position of the variable vanes may thus be adjusted in order to control flow of the fluid. The variable vanes typically exert a reaction load on the unison ring which may deform the unison ring from its nominal shape causing distortion. This may result in variation in a desired angular position of the variable vanes. Radial stress acting at a given location of the unison ring is dependent on a load being applied on the unison ring via the actuator and a circumferential distance from the actuator. The radial stress is thus greatest at locations furthest away from the region at which the load is applied, which, for a single actuator arrangement, is diametrically opposite to the actuator. The actuator is typically controlled via closed-loop control in order to adjust the angular position of the variable vanes. Current closed-loop control feedback methods utilize a linear variable displacement transformer (LVDT) located within the actuator for controlling the actuator. Although this arrangement provides good closed-loop control of the actuator, mechanical errors downstream of the actuator and the distortion of the unison ring may affect the accuracy to which the angular position of the variable vanes may be adjusted. Thus, additional margins are required to be built into an engine design to accommodate uncertainties in the angular position of the variable vanes, which may affect fuel burn efficiency, engine performance, and may drive early engine overhaul. Summary According to a first aspect, there is provided a variable vane control system for use with a gas turbine engine. The variable vane control system includes at least one circumferential set of variable vanes circumferentially arranged around a central axis. The at least one circumferential set of variable vanes includes a first variable vane and a second variable vane angularly spaced apart from the first variable vane with respect to the central axis. The variable vane control system further includes at least one actuator. The variable vane control system further includes at least one unison ring circumferentially extending 360 degrees about the central axis and operatively coupling the at least one actuator to each variable vane from the at least one circumferential set of variable vanes. Upon actuation by the at least one actuator, the at least one unison ring is rotatable about the central axis to vary an angular position of each variable vane. The variable vane control system further includes a plurality of sensors including a first sensor configured to sense a first angular position of the first variable vane and a second sensor configured to sense a second angular position of the second variable vane. The variable vane control system further includes a controller communicably coupled to the at least one actuator and each of the plurality of sensors. The controller is configured to control the at least one actuator to adjust the angular position of each variable vane based on the first angular position of the first variable vane and the second angular position of the second variable vane. The first sensor is configured to sense the first angular position of the first variable vane and the second sensor is configured to sense the second angular position of the second variable vane. The first variable vane and the second variable vane are angularly spaced apart from each other with respect to the central axis. Thus, the controller may consider the angular position of the variable vanes at more than one location for closed-loop control of the at least one actuator. This may enable measurement of an error existing in the angular position of the variable vanes as a result of a distortion of the at least one unison ring. In some embodiments, the first variable vane may be circumferentially nearest to a region of the at least one unison ring having low distortion and the second variable vane may be circumferentially nearest to a region of the at least one unison ring having high distortion. Thus, the controller may consider variation between the first angular position (at the region of low distortion) of the first variable vane and the second angular position (at the region of high distortion) of the second variable vane for controlling the angular position of each variable vane via the at least one actuator. This variation may be measured in real time by the controller for controlling the angular position of each variable vane, thereby improving a system accuracy. Further, this may remove a significant amount of uncertainty in an ability to control the angular position of each variable vane, thereby improving the specific fuel consumption (SFC) of the gas turbine engine. In some embodiments, the controller is further configured to determine an average angular position as an average of the first angular position and the second angular position. The controller is further configured to control the at least one actuator based on the average angular position. The average angular position may define position feedback that the controller may utilize for controlling the at least one actuator via closed-loop control. In some embodiments, the controller is further configured to determine an error as a difference between a position demand input and the average angular position. The controller is further configured to determine a required actuator position demand based on the error. The controller is further configured to control the at least one actuator based on the required actuator position demand. Thus, the required actuator position demand may be used as the position feedback for controlling the at least one actuator. This may allow the controller to precisely control the angular position of each variable vane, thereby improving the system accuracy. In some embodiments, the at least one unison ring includes a first point and a second point angularly spaced apart from the first point by at least 90 degrees about the central axis. Upon actuation by the at least one actuator, the at least one unison ring has a lowest distortion at the first point and a highest distortion at the second point. Among the at least one circumferential set of variable vanes, the first variable vane is circumferentially nearest to the first point and the second variable vane is circumferentially nearest to the second point. The first sensor may provide the first angular position of the first variable vane that is circumferentially nearest to the first point (with the lowest distortion) and the second sensor may provide the second angular position of the second variable vane that is circumferentially nearest to the second point (with the highest distortion). Thus, the angular position of the variable vanes at both the first point (i.e., the first angular position) and the second point (i.e., the second angular position) may be used by the controller for controlling the at least one actuator. In some embodiments, the variable vane control system further includes a bridge plate fixedly coupled to the at least one unison ring and including a connecting portion. The variable vane control system further includes a control rod operatively coupling the at least one actuator to the connecting portion of the bridge plate. The connecting portion and the first point of the at least one unison ring are circumferentially aligned with respect to the central axis. The bridge plate may allow the at least one actuator to drive rotation of the at least one unison ring via the connecting portion. In some embodiments, the at least one actuator is a single actuator, such that the first point and the second point are angularly spaced apart by 180 degrees about the central axis. In such cases, the first variable vane and the second variable vane are angularly spaced apart by 180 degrees about the central axis. The single actuator may drive rotation of the at least one unison ring. In some embodiments, the at least one actuator includes a pair of actuators angularly spaced apart by 180 degrees about the central axis, such that the first point and the second point are angularly spaced apart by 90 degrees about the central axis. In such cases, the first variable vane and the second variable vane are angularly spaced apart by 90 degrees about the central axis. The pair of actuators may drive rotation of the at least one unison ring. In some embodiments, each of the plurality of sensors is connected to a corresponding variable vane from the at least one circumferential set of variable vanes, such that the first sensor is connected to the first variable vane and the second sensor is connected to the second variable vane. Thus, the first sensor is directly connected to the first variable vane for sensing the first angular position and the second sensor is directly connected to the second variable vane for sensing the second angular position. In some embodiments, the variable vane control system further includes a set of levers corresponding to the at least one circumferential set of variable vanes. Each lever from the set of levers operatively couples the at least one unison ring to a corresponding variable vane from the at least one circumferential set of variable vanes. The set of levers includes a first lever operatively coupling the first variable vane to the at least one unison ring at the first point and a second lever operatively coupling the second variable vane to the at least one unison ring at the second point. Rotation of the at least one unison ring actuates each lever causing the corresponding variable vane to rotate, in unison, about its longitudinal axis. Thus, the first lever may rotate the first variable vane and the second lever may rotate the second variable vane. In some embodiments, each of the plurality of sensors is connected to a corresponding lever from the set of levers, such that the first sensor is connected to the first lever and the second sensor is connected to the second lever. Thus, the first sensor may sense the first angular position of the first variable vane via the first lever and the second sensor may sense the second angular position of the second variable vane via the second lever. In some embodiments, the at least one circumferential set of variable vanes includes a plurality of circumferential sets of variable vanes axially spaced apart from each other with respect to the central axis. The at least one unison ring includes a plurality of unison rings corresponding to the plurality of circumferential sets of variable vanes. Each unison ring from the plurality of unison rings is operatively coupled to a corresponding circumferential set of variable vanes from the plurality of circumferential sets of variable vanes. Each unison ring is configured to vary the angular position of each variable vane from the corresponding circumferential set of variable vanes. Thus, each unison ring is associated with the corresponding circumferential set of variable vanes for varying the angular position of each variable vane from the corresponding circumferential set of variable vanes. In some embodiments, the variable vane control system further includes a crankshaft operatively coupling the at least one actuator to each unison ring. The crankshaft may allow the at least one actuator to drive rotation of each unison ring. In some embodiments, the first variable vane and the second variable vane are angularly spaced apart from each other by at least 90 degrees about the central axis. Thus, the angular position of the variable vanes at two different locations may be considered by the controller for controlling the at least one actuator. In some embodiments, each variable vane is a variable inlet guide vane or a variable stator vane. Thus, the angular position of each variable inlet guide vane or each variable stator vane may be precisely controlled by the controller. According to a second aspect, there is provided a gas turbine engine including the variable vane control system of the first aspect. According to a second aspect, there is provided a method of operating a variable vane control system having at least one circumferential set of variable vanes circumferentially arranged around a central axis, at least one actuator, and at least one unison ring operatively coupling the at least one actuator to each variable vane from the at least one circumferential set of variable vanes. The method includes controlling, via a controller, the at least one actuator to rotate each variable vane. The method further includes sensing, via a first sensor, a first angular position of a first variable vane from the at least one circumferential set of variable vanes. The method further includes sensing, via a second sensor, a second angular position of a second variable vane from the at least one circumferential set of variable vanes. The second variable vane is angularly spaced apart from the first variable vane with respect to the central axis. The method further includes controlling, via the controller, the at least one actuator to adjust an angular position of each variable vane based on the first angular position of the first variable vane and the second angular position of the second variable vane. In some embodiments, controlling the at least one actuator further includes determining an average angular position as an average of the first angular position and the second angular position. Controlling the at least one actuator further includes controlling the at least one actuator based on the average angular position. In some embodiments, controlling the at least one actuator further includes determining an error as a difference between a position demand input and the average angular position. Controlling the at least one actuator further includes determining a required actuator position demand based on the error. Controlling the at least one actuator further includes controlling the at least one actuator based on the required actuator position demand. In some embodiments, the at least one unison ring includes a first point and a second point angularly spaced apart from the first point by at least 90 degrees about the central axis. Upon actuation by the at least one actuator, the at least one unison ring has a lowest distortion at the first point and a highest distortion at the second point. Among the at least one circumferential set of variable vanes, the first variable vane is circumferentially nearest to the first point and the second variable vane is circumferentially nearest to the second point. In some embodiments, the at least one actuator is a single actuator, such that the first point and the second point are angularly spaced apart by 180 degrees about the central axis. In some embodiments, the at least one actuator includes a pair of actuators angularly spaced apart by 180 degrees about the central axis, such that the first point and the second point are angularly spaced apart by 90 degrees about the central axis. In some embodiments, the first variable vane and the second variable vane are angularly spaced apart from each other by at least 90 degrees about the central axis. The skilled person will appreciate that except where mutually exclusive, a feature or parameter described in relation to any one of the above aspects may be applied to any other aspect. Furthermore, except where mutually exclusive, any feature or parameter described herein may be applied to any aspect and / or combined with any other feature or parameter described herein. Brief description of the drawings Embodiments will now be described by way of example only, with reference to the Figures, in which: FIG. 1 is a schematic sectional side view of a gas turbine engine, according to an embodiment of the present disclosure; FIG. 2 is a schematic view of a variable vane control system for use with the gas turbine engine, according to an embodiment of the present disclosure; FIG. 3A is a schematic front view of at least one actuator, at least one unison ring, and at least one circumferential set of variable vanes of the variable vane control system, according to an embodiment of the present disclosure; FIG. 3B is a schematic front view of at least one actuator, at least one unison ring, and at least one circumferential set of variable vanes of the variable vane control system, according to another embodiment of the present disclosure; FIG. 4 is a schematic view of the variable vane control system, according to another embodiment of the present disclosure; FIG. 5 is a schematic block diagram of the variable vane control system, according to an embodiment of the present disclosure; FIG. 6 is a schematic block diagram illustrating control logic for controlling an actuator position of the at least one actuator, according to an embodiment of the present disclosure; FIG. 7 is a schematic block diagram of the variable vane control system, according to another embodiment of the present disclosure; and FIG. 8 is a flow chart illustrating a method of operating the variable vane control system, according to an embodiment of the present disclosure. Detailed description Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. FIG. 1 shows a schematic sectional side view of a gas turbine engine 10 having a principal rotational axis X-X’. The gas turbine engine 10 includes, in axial flow series, an air intake 11, a compressive fan 12 (which may also be referred to as a low pressure compressor), an intermediate pressure compressor 13, a high pressure compressor 14, combustion equipment 15, a high pressure turbine 16, an intermediate pressure turbine 17, a low pressure turbine 18, and a core exhaust nozzle 19. A nacelle 21 generally surrounds the gas turbine engine 10 and defines the air intake 11, a bypass duct 22, and a bypass exhaust nozzle 23. The gas turbine engine 10 works in a conventional manner so that the air entering the air intake 11 is accelerated by the compressive fan 12 to produce two air flows: a first air flow A into the intermediate pressure compressor 13, and a second air flow B which passes through the bypass duct 22 to provide a propulsive thrust. The intermediate pressure compressor 13 compresses the first air flow A directed into it before delivering that air to the high pressure compressor 14 where further compression takes place. The compressed air exhausted from the high pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture is combusted. The resulting hot combustion products then expand through, and thereby drive the high, intermediate, and low pressure turbines 16, 17, 18 before being exhausted through the core exhaust nozzle 19 to provide additional propulsive thrust. The high, intermediate, and low pressure turbines 16, 17, 18 respectively drive the high and intermediate pressure compressors 14, 13, and the compressive fan 12 by suitable interconnecting shafts. In some embodiments, the gas turbine engine 10 is used in an aircraft. In some embodiments, the gas turbine engine 10 is an ultra-high bypass ratio engine (UHBPR). In addition, the present invention is equally applicable to other aero gas turbine engines, marine gas turbine engines, and land-based gas turbine engines. FIG. 2 is a schematic view of a variable vane control system 100 for use with the gas turbine engine 10 (shown in FIG. 1). Specifically, FIG. 2 shows a perspective view of a portion of a compressor (e.g., the intermediate pressure compressor 13 or the high pressure compressor 14 shown in FIG. 1) of the gas turbine engine 10. The variable vane control system 100 includes at least one circumferential set of variable vanes 102 (partially visible) circumferentially arranged around a central axis Z-Z’. The term “at least one circumferential set of variable vanes 102” is interchangeably referred to hereinafter as “circumferential set of variable vanes 102”. As shown in FIG. 2, each variable vane 102 from the circumferential set of variable vanes 102 extends at least partially through a casing 108 of the compressor. The at least one circumferential set of variable vanes 102 may form a part of the compressor. However, in alternative embodiments, the circumferential set of variable vanes 102 may be a part of a turbine (e.g., high, intermediate, and low pressure turbines 16, 17, 18 shown in FIG. 1) of the gas turbine engine 10. In some embodiments, the central axis Z-Z’ may coincide with the principal rotational axis X-X’ (shown in FIG. 1). In some embodiments, the circumferential set of variable vanes 102 may be used to control flow of a fluid (e.g., the first air flow A shown in FIG. 1) through various compression stages of the gas turbine engine 10. However, in alternative embodiments, the circumferential set of variable vanes 102 may be used to control combustion products through various expansion stages of the gas turbine engine 10. In some embodiments, each variable vane 102 is a variable inlet guide vane (VIGV) or a variable stator vane (VSV). VIGVs are generally provided within the flow passage upstream of the compression stages. In some embodiments, each variable vane 102 is disposed within a flow passage of the gas turbine engine 10 adjacent to rotor blade assemblies. Each variable vane 102 is rotatably mounted about its longitudinal axis within the flow passage, such that a pitch angle of each variable vane 102 may be adjusted based on operating conditions of the compressor or the turbine. The fluid passing between the circumferential set of variable vanes 102 is directed at an appropriate angle of incidence for the succeeding rotor blade assembly. For example, each compression stage includes an array of rotor blades (not shown) disposed within the flow passage and an array of VSVs disposed adjacent to, and upstream of, the rotor blades. The variable vane control system 100 further includes at least one actuator 110 and at least one unison ring 120 circumferentially extending 360 degrees about the central axis Z-Z’ and operatively coupling the at least one actuator 110 to each variable vane 102 from the at least one circumferential set of variable vanes 102. Specifically, the at least one unison ring 120 circumferentially extends 360 degrees around a circumference of the casing 108. The term “at least one actuator 110” is interchangeably referred to hereinafter as “the actuator 110”. In some embodiments, the at least one actuator 110 includes a single actuator as shown in FIG. 2. However, in some other embodiments, the at least one actuator 110 may include multiple actuators. In some embodiments, the at least one actuator 110 is operatively coupled to the at least one unison ring 120 via a mechanical linkage 130. However, in alternative embodiments, the at least one actuator 110 may be directly coupled to the at least one unison ring 120. The term “at least one unison ring 120” is interchangeably referred to hereinafter as “the unison ring 120”. In some embodiments, the mechanical linkage 130 includes a torque converter 132 which pivots on a shaft 134 extending between supports 136 and 138. In some embodiments, the torque converter 132 includes a crank 133 connected to the at least one actuator 110 via a shaft 135 and to the unison ring 120 via a shaft 137. In alternative embodiments, the torque converter 132 may be any other type of torque converter that functions to increase torque. It should be understood that other suitable arrangements may also be used for operatively coupling the at least one actuator 110 to the at least one unison ring 120 based on application requirements. In some embodiments, the variable vane control system 100 further includes a set of levers 140 corresponding to the at least one circumferential set of variable vanes 102. Each lever 140 from the set of levers 140 operatively couples the unison ring 120 to a corresponding variable vane 102 from the at least one circumferential set of variable vanes 102. Upon actuation by the at least one actuator 110, the unison ring 120 is rotatable about the central axis Z-Z’ to vary an angular position (or the pitch angle) of each variable vane 102. Specifically, the at least one actuator 110 may actuate the torque converter 132 (or the crank 133) via the shaft 135, thereby rotating the torque converter 132 about the shaft 134. The torque converter 132 may in turn rotate the unison ring 120 about the central axis Z-Z’ via the shaft 137, thereby rotating each lever 140. Upon rotation of each lever 140, the corresponding variable vane 102 rotates about its longitudinal axis, thereby varying the angular position of the corresponding variable vane 102. The variable vane control system 100 further includes a plurality of sensors 150. In the illustrated embodiment, each of the plurality of sensors 150 is connected to a corresponding variable vane 102 from the at least one circumferential set of variable vanes 102. For example, each of the plurality of sensors 150 is fixedly attached to the corresponding variable vane 102. Each sensor 150 may sense the angular position of the corresponding variable vane 102. Alternatively, or in addition, each of the plurality of sensors 150 is connected to a corresponding lever 140 from the set of levers 140. In a further alternative embodiment, one or more sensors 150 may be connected to the mechanical linkage 130 between the unison ring 120 and the circumferential set of variable vanes 102. In a further alternative embodiment, the plurality of sensors 150 may include multiple sensors 150 distributed at various locations around the unison ring 120. In some embodiments, each sensor 150 may be a contact-type position sensor for determining the angular position of the corresponding variable vane 102 as the variable vane 102 rotates. In some embodiments, each sensor 150 may be a magnetic sensor, such as a Hall effect sensor, a giant magnetoresistance (GMR) sensor, a colossal magnetoresistance (CMR) sensor, or an anisotropic magnetoresistance (AMR) sensor. It should be understood that other suitable type of sensors may also be used based on application requirements. FIG. 3A is a schematic front view of the at least one actuator 110, the at least one unison ring 120, and the circumferential set of variable vanes 102, according to an embodiment of the present disclosure. In the illustrated embodiment, the at least one actuator 110 is directly coupled to the unison ring 120, i.e., without the mechanical linkage 130 (shown in FIG. 2). However, in some other cases, the at least one actuator 110 may be coupled to the unison ring 120 via the mechanical linkage 130 (shown in FIG. 2). Further, the at least one actuator 110 includes a single actuator. The circumferential set of variable vanes 102 are shown partially in FIG. 3A for the purpose of illustration. In some embodiments, the at least one unison ring 120 includes a first point 122 and a second point 124 angularly spaced apart from the first point 122 by at least 90 degrees about the central axis Z-Z’. Upon actuation by the at least one actuator 110, the at least one unison ring 120 has a lowest distortion at the first point 122 and a highest distortion at the second point 124. This is caused in particular due to occurrence of tangential forces acting on the unison ring 120 through the set of levers 140 when the at least one actuator 110 is operated. The lowest distortion occurs at a point of actuation of the unison ring 120 (i.e., the first point 122) where the actuator 110 is coupled to the unison ring 120. The distortion increases when moving circumferentially away from the point of actuation with respect to the central axis Z-Z’ due to cumulative effect of the tangential forces acting through the set of levers 140 when moving circumferentially away from the point of actuation. Therefore, the highest distortion of the unison ring 120 occurs farthest from the point of actuation of the unison ring 120, i.e., the second point 124. This means that the unison ring 120 is not evenly loaded around the central axis Z-Z’. As a result, the circumferential set of variable vanes 102 may have varying angular positions around the circumference of the unison ring 120. In the illustrated embodiment, the at least one actuator 110 is the single actuator, such that the first point 122 and the second point 124 are angularly spaced apart by 180 degrees about the central axis Z-Z’. The at least one circumferential set of variable vanes 102 includes a first variable vane 104 and a second variable vane 106 angularly spaced apart from the first variable vane 104 with respect to the central axis Z-Z’. Specifically, among the at least one circumferential set of variable vanes 102, the first variable vane 104 is circumferentially nearest to the first point 122 and the second variable vane 106 is circumferentially nearest to the second point 124. In some embodiments, the first variable vane 104 and the second variable vane 106 are angularly spaced apart from each other by at least 90 degrees about the central axis Z-Z’. In the illustrated embodiment of FIG. 3A, the first variable vane 104 and the second variable vane 106 are angularly spaced apart from each other by 180 degrees about the central axis Z-Z’. In some embodiments, the set of levers 140 includes a first lever 142 operatively coupling the first variable vane 104 to the at least one unison ring 120 at the first point 122 and a second lever 144 operatively coupling the second variable vane 106 to the at least one unison ring 120 at the second point 124. The plurality of sensors 150 includes a first sensor 152 configured to sense a first angular position P1 of the first variable vane 104 and a second sensor 154 configured to sense a second angular position P2 of the second variable vane 106. In some embodiments, the first sensor 152 is connected to the first variable vane 104 and the second sensor 154 is connected to the second variable vane 106. In alternative embodiments, the first sensor 152 is connected to the first lever 142 and the second sensor 154 is connected to the second lever 144. Due to the distortion, the first angular position P1 of the first variable vane 104 is different from the second angular position P2 of the second variable vane 106. Since the first variable vane 104 is circumferentially nearest to the first point 122 having the lowest distortion and the second variable vane 106 is circumferentially nearest to the second point 124 having the highest distortion, a difference between a value of the first angular position P1 and the second angular position P2 may be highest. Thus, when the actuator 110 may be controlled to adjust the angular position of each variable vane 102, the first angular position P1 of the first variable vane 104 may be closest to the desired angular position while the second angular position P2 may be different from the desired angular position. The angular position of the variable vanes 102 circumferentially nearest to regions of the unison ring 120 having the lowest distortion (i.e., the first variable vane 104) and the highest distortion (i.e., the second variable vane 106) may be considered for controlling the at least one actuator 110. FIG. 3B is a schematic front view of the at least one actuator 110, the at least one unison ring 120, and the circumferential set of variable vanes 102, according to another embodiment of the present disclosure. In the illustrated embodiment, the at least one actuator 110 is directly coupled to the unison ring 120. The circumferential set of variable vanes 102 are shown partially in FIG. 3B for the purpose of illustration. In the illustrated embodiment, the at least one actuator 110 includes a pair of actuators 110-1, 110-2 angularly spaced apart by 180 degrees about the central axis Z-Z’, such that the first point 122 and the second point 124 are angularly spaced apart by 90 degrees about the central axis Z-Z'. Thus, the first variable vane 104 and the second variable vane 106 are angularly spaced apart from each other by 90 degrees about the central axis Z-Z’. The first sensor 152 is configured to sense the first angular position P1 of the first variable vane 104 and the second sensor 154 is configured to sense the second angular position P2 of the second variable vane 106. In some other cases, at least one of the pair of actuators 110-1, 110-2 may be coupled to the unison ring 120 via the mechanical linkage 130 (shown in FIG. 2). FIG. 4 is a schematic view of the variable vane control system 100, according to another embodiment of the present disclosure. Some components of the variable vane control system 100, e.g., the circumferential set of variable vanes 102, the plurality of sensors 150, the set of levers 140, etc., are not shown for the purpose of illustration. Specifically, FIG. 4 shows a schematic partial front view of the at least one unison ring 120. In some embodiments, the variable vane control system 100 further includes a bridge plate 160 fixedly coupled to the at least one unison ring 120 and including a connecting portion 162. The bridge plate 160 circumferentially extends at least partially around a circumference of the unison ring 120. A central portion of the bridge plate 160 extends radially outwardly from the unison ring 120 with respect to the central axis Z-Z’ to define the connecting portion 162. In some embodiments, the bridge plate 160 is fixedly coupled to the unison ring 120 via bolts 166. However, the bridge plate 160 may be fixedly coupled to the unison ring 120 via any other suitable attachment mechanism, e.g., welding, adhesive, etc., or may be integral with the unison ring 120. In some embodiments, the variable vane control system 100 further includes a control rod 164 operatively coupling the at least one actuator 110 to the connecting portion 162 of the bridge plate 160. In some embodiments, the bridge plate 160 may allow the at least one actuator 110 to drive rotation of the at least one unison ring 120 via the connecting portion 162. In some embodiments, the connecting portion 162 and the first point 122 of the at least one unison ring 120 are circumferentially aligned with respect to the central axis Z-Z’. Specifically, the connecting portion 162 and the first point 122 are located at a same circumferential position but are radially spaced apart from each other with respect to the central axis Z-Z'. FIG. 5 is a schematic block diagram of the variable vane control system 100, according to an embodiment of the present disclosure. The variable vane control system 100 includes the actuator 110, the control rod 164, the bridge plate 160, the unison ring 120, the circumferential set of variable vanes 102, and the set of levers 140. The variable vane control system 100 further includes a controller 170 communicably coupled to the at least one actuator 110 and each of the plurality of sensors 150. In some embodiments, the controller 170 may be embodied in a number of different ways. For example, the controller 170 may be embodied as various processing means, such as one or more of a microprocessor or other processing elements, a coprocessor, or various other computing or processing devices including integrated circuits, such as, e.g., an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), or the like. As such, whether configured by hardware or by a combination of hardware and software, the controller 170 may represent an entity (e.g., physically embodied in circuitry - in the form of processing circuitry) capable of performing operations according to some embodiments while configured accordingly. Thus, for example, when the controller 170 is embodied as an executor of software instructions, the instructions may specifically configure the controller 170 to perform the operations described herein. Alternatively, as another example, when the controller 170 is embodied as an ASIC, FPGA, or the like, the controller 170 may have specifically configured hardware for conducting the operations described herein. In some embodiments, the variable vane control system 100 further includes an actuator sensor 112 (e.g., a linear variable displacement transformer or LVDT) connected to the actuator 110 for sensing a position of the actuator 110. In some embodiments, the controller 170 is configured to control the position of the actuator 110 based on feedback from the actuator sensor 112. The controller 170 is further configured to control the at least one actuator 110 to adjust the angular position of each variable vane 102 based on the first angular position P1 of the first variable vane 104 and the second angular position P2 of the second variable vane 106. In operation, the controller 170 provides signals to the actuator 110 to adjust the angular position of each variable vane 102. The actuator 110 responds by actuating the control rod 164, which moves the unison ring 120 via the bridge plate 160. Consequently, the unison ring 120 rotates each variable vane 102 via the corresponding lever 140. The first sensor 152 and the second sensor 154 send signals to the controller 170 representing the first angular position P1 and the second angular position P2 of the first variable vane 104 and the second variable vane 106, respectively. The actuator sensor 112 also sends a signal to the controller representing the actuator position of the actuator 110. In an alternative embodiment, the controller 170 may determine the angular position of the variable vane 102 circumferentially nearest to the point of actuation, i.e., the first angular position P1 of the first variable vane 104, via the actuator position received from the actuator sensor 112. The controller 170 may consider the angular position of the variable vanes 102 at more than one location for closed-loop control of the at least one actuator 110. This may enable measurement of an error existing in the angular position of the variable vanes 102 as a result of the distortion in the at least one unison ring 120. In some embodiments, the controller 170 may consider variation between the first angular position P1 of the first variable vane 104 and the second angular position P2 of the second variable vane 106 for controlling the angular position of each variable vane 102 via the at least one actuator 110. This variation can be measured in real time by the controller 170 for controlling the angular position of each variable vane 102, thereby improving an accuracy of the variable vane control system 100. Further, this may remove a significant amount of uncertainty in an ability to control the angular position of each variable vane 102, thereby improving the specific fuel consumption (SFC) of the gas turbine engine 10 (shown in FIG. 1). In some embodiments, the controller 170 is further configured to determine an average angular position P3 as an average of the first angular position P1 and the second angular position P2, i.e., P3 = (P1 + P2) / 2. In some embodiments, the controller 170 is further configured to control the at least one actuator 110 based on the average angular position P3. The average angular position P3 may be used as position feedback for closed-loop control of the actuator 110 whereby the controller 170 may be able to adjust the angular position of each variable vane 102 so as to compensate for the distortion in the unison ring 120. FIG. 6 is a schematic block diagram 180 illustrating control logic for controlling an actuator position of the actuator 110 (shown in FIGS. 2-6). The control logic may be implemented through a software running in one or a plurality of processors associated with the controller 170. Referring to FIGS. 5 and 6, a signal S1 represents the first angular portion P1 determined by the first sensor 152. A signal S2 represents the second angular portion P2 determined by the second sensor 154. At block 182, the controller 170 is further configured to determine the average angular position P3 as the average of the first angular position P1 and the second angular position P2. A signal S3 represents the average angular position P3. A signal S4 represents a position demand input P4 desired for each variable vane 102. At subtractor 184, the controller 170 is further configured to determine an error 190 as a difference between the position demand input P4 and the average angular position P3. At block 186, the controller 170 is further configured to determine a required actuator position demand P5 based on the error 190. The controller 170 is further configured to control the at least one actuator 110 based on the required actuator position demand P5. A signal S5 represents the required actuator position demand P5 to be sent to the actuator 110. FIG. 7 is a schematic block diagram of the variable vane control system 100, according to another embodiment of the present disclosure. In the illustrated embodiment, the at least one circumferential set of variable vanes 102 includes a plurality of circumferential sets of variable vanes 102-1, 102-2, ..., 102-M (collectively, circumferential sets of variable vanes 102) axially spaced apart from each other with respect to the central axis Z-Z’ (shown in FIGS. 2-4), wherein M is a positive integer corresponding to a total number of the circumferential sets of variable vanes 102. The plurality of circumferential sets of variable vanes 102 may form a part of a ganged variable stator vane (VSV) system. Further, the at least one unison ring 120 includes a plurality of unison rings 120-1. 120-2..... 120-N (collectively, unison rings 120) corresponding to the plurality of circumferential sets of variable vanes 102, where N is a positive integer corresponding to a total number of the unison rings 120. Each unison ring 120 from the plurality of unison rings 120 is operatively coupled to a corresponding circumferential set of variable vanes 102 from the plurality of circumferential sets of variable vanes 102. For example, the unison ring 120-1 is operatively coupled to the circumferential set of variable vanes 102-1, the unison ring 120-2 is operatively coupled to the circumferential set of variable vanes 102-2, and so on. Each unison ring 120 is configured to vary the angular position of each variable vane 102 from the corresponding circumferential set of variable vanes 102. The variable vane control system 100 further includes a crankshaft 192 operatively coupling the at least one actuator 110 to each unison ring 120. The crankshaft 192 may transmit actuating motion from the actuator 110 to each unison ring 120, thereby effectuating change in angular positions of each variable vane 102 from the corresponding circumferential set of variable vanes 102. In operation, the controller 170 provides signals to the actuator 110 to adjust the angular position of each variable vane 102 of the corresponding circumferential set of variable vanes 102. The actuator 110 responds by actuating the control rod 164, which moves each unison ring 120 via the crankshaft 192. Consequently, each unison ring 120 rotates each variable vane 102 of the corresponding circumferential set of variable vanes 102 via the corresponding lever 140. In the illustrated embodiment, the first sensor 152 and the second sensor 154 from the plurality of sensors 150 are mounted on a first stage of the ganged VSV system, i.e., the circumferential set of variable vanes 102-1. Additionally, or alternatively, the plurality of sensors 150 may also be mounted on other stages of the ganged VSV system. The first sensor 152 and the second sensor 154 send signals to the controller 170 representing the first angular position P1 and the second angular position P2 of the first variable vane 104 and the second variable vane 106, respectively, in the circumferential set of variable vanes 102-1. FIG. 8 is a flow chart illustrating a method 200 of operating the variable vane control system 100 (shown in FIGS. 2, 4-5 and 7) having the at least one circumferential set of variable vanes 102 circumferentially arranged around the central axis Z-Z’, the at least one actuator 110, and the at least one unison ring 120 operatively coupling the at least one actuator 110 to each variable vane 102 from the at least one circumferential set of variable vanes 102. The method 200 may be implemented using the variable vane control system 100 of FIGS. 2, 4-5 and 7. Referring to FIGS. 2-8, at step 202, the method 200 includes controlling, via the controller 170, the at least one actuator 110 to rotate each variable vane 102. At step 204, the method 200 further includes sensing, via the first sensor 152, the first angular position P1 of the first variable vane 104 from the at least one circumferential set of variable vanes 102. At step 206, the method 200 further includes sensing, via the second sensor 154, the second angular position P2 of the second variable vane 106 from the at least one circumferential set of variable vanes 102. The first variable vane 104 and the second variable vane 106 are angularly spaced apart from each other with respect to the central axis Z-Z’. In some embodiments, the first variable vane 104 and the second variable vane 106 are angularly spaced apart from each other by at least 90 degrees about the central axis Z-Z’. In some embodiments, the at least one unison ring 120 includes the first point 122 and the second point 124 angularly spaced apart from the first point 122 by at least 90 degrees about the central axis Z-Z’. In some embodiments, the at least one actuator 110 is the single actuator, such that the first point 122 and the second point 124 are angularly spaced apart by 180 degrees about the central axis Z-Z’. In some embodiments, the at least one actuator 110 includes the pair of actuators 110-1, 110-2 angularly spaced apart by 180 degrees about the central axis Z-Z’, such that the first point 122 and the second point 124 are angularly spaced apart by 90 degrees about the central axis Z-Z’. Upon actuation by the at least one actuator 110, the at least one unison ring 120 has the lowest distortion at the first point 122 and the highest distortion at the second point 124. Among the at least one circumferential set of variable vanes 102, the first variable vane 104 is circumferentially nearest to the first point 122 and the second variable vane 106 is circumferentially nearest to the second point 124. At step 208, the method 200 further includes controlling, via the controller 170, the at least one actuator 110 to adjust an angular position of each variable vane 102 based on the first angular position P1 of the first variable vane 104 and the second angular position P2 of the second variable vane 106. In some embodiments, controlling the at least one actuator 110 further includes determining the average angular position P3 as the average of the first angular position P1 and the second angular position P2. In some embodiments, controlling the at least one actuator 110 further includes controlling the at least one actuator 110 based on the average angular position P3. In some embodiments, controlling the at least one actuator 110 further includes determining the error 190 as the difference between the position demand input P4 and the average angular position P3. In some embodiments, controlling the at least one actuator 110 further includes determining the required actuator position demand P5 based on the error 190. In some embodiments, controlling the at least one actuator 110 further includes controlling the at least one actuator 110 based on the required actuator position demand P5. Referring to FIGS. 2-8, the variable vane control system 100 and the method 200 may consider variation between the first angular position P1 (at the first point 122) of the first variable vane 104 and the second angular position P2 (at the second point 124) of the second variable vane 106 for controlling the angular position of each variable vane 102 via the at least one actuator 110. This may enable measurement of an error existing in the angular position of the variable vanes 102 as a result of the distortion in the at least one unison ring 120. The variation may be measured in real time by the controller 170 for controlling the angular position of each variable vane 102, thereby improving an accuracy of the variable vane control system 100. Further, this may remove a significant amount of uncertainty in an ability to control the angular position of each variable vane 102, thereby improving the specific fuel consumption (SFC) of the gas turbine engine 10. It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

1. A variable vane control system (100) for use with a gas turbine engine (10), the variable vane control system (100) comprising:at least one circumferential set of variable vanes (102) circumferentially arranged around a central axis (Z-Z’), the at least one circumferential set of variable vanes (102) comprising a first variable vane (104) and a second variable vane (106) angularly spaced apart from the first variable vane (104) with respect to the central axis (Z-Z’);at least one actuator (110);at least one unison ring (120) circumferentially extending 360 degrees about the central axis (Z-Z’) and operatively coupling the at least one actuator (110) to each variable vane (102) from the at least one circumferential set of variable vanes (102), wherein, upon actuation by the at least one actuator (110), the at least one unison ring (120) is rotatable about the central axis (Z-Z’) to vary an angular position of each variable vane (102);a plurality of sensors (150) comprising a first sensor (152) configured to sense a first angular position (P1) of the first variable vane (104) and a second sensor (154) configured to sense a second angular position (P2) of the second variable vane (106); anda controller (170) communicably coupled to the at least one actuator (110) and each of the plurality of sensors (150), wherein the controller (170) is configured to control the at least one actuator (110) to adjust the angular position of each variable vane (102) based on the first angular position (P1) of the first variable vane (104) and the second angular position (P2) of the second variable vane (106).

2. The variable vane control system (100) of claim 1, wherein the controller (170) is further configured to:determine an average angular position (P3) as an average of the first angular position (P1) and the second angular position (P2); andcontrol the at least one actuator (110) based on the average angular position (P3).

3. The variable vane control system (100) of claim 2, wherein the controller (170) is further configured to:determine an error (190) as a difference between a position demand input (P4) and the average angular position (P3);determine a required actuator position demand (P5) based on the error (190); andcontrol the at least one actuator (110) based on the required actuator position demand (P5).

4. The variable vane control system (100) of any preceding claim, wherein the at least one unison ring (120) comprises a first point (122) and a second point (124) angularly spaced apart from the first point (122) by at least 90 degrees about the central axis (Z-Z’), wherein, upon actuation by the at least one actuator (110), the at least one unison ring (120) has a lowest distortion at the first point (122) and a highest distortion at the second point (124), and wherein, among the at least one circumferential set of variable vanes (102), the first variable vane (104) is circumferentially nearest to the first point (122) and the second variable vane (106) is circumferentially nearest to the second point (124).

5. The variable vane control system (100) of claim 4, further comprising:a bridge plate (160) fixedly coupled to the at least one unison ring (120) and comprising a connecting portion (162); anda control rod (164) operatively coupling the at least one actuator (110) to the connecting portion (162) of the bridge plate (160);wherein the connecting portion (162) and the first point (122) of the at least one unison ring (120) are circumferentially aligned with respect to the central axis (Z-Z’).

6. The variable vane control system (100) of claim 4 or 5, wherein the at least one actuator (110) is a single actuator, such that the first point (122) and the second point (124) are angularly spaced apart by 180 degrees about the central axis (Z-Z’).

7. The variable vane control system (100) of claim 4 or 5, wherein the at least one actuator (110) comprises a pair of actuators (110-1, 110-2) angularly spaced apart by 180 degrees about the central axis (Z-Z’), such that the first point (122) and the second point (124) are angularly spaced apart by 90 degrees about the central axis (Z-Z’).

8. The variable vane control system (100) of any preceding claim, wherein each of the plurality of sensors (150) is connected to a corresponding variable vane (102) from the at least one circumferential set of variable vanes (102), such that the first sensor(152) is connected to the first variable vane (104) and the second sensor (154) is connected to the second variable vane (106).

9. The variable vane control system (100) of any preceding claim, further comprising a set of levers (140) corresponding to the at least one circumferential set of variable vanes (102), wherein each lever (140) from the set of levers (140) operatively couples the at least one unison ring (120) to a corresponding variable vane (102) from the at least one circumferential set of variable vanes (102), and wherein the set of levers (140) comprises a first lever (142) operatively coupling the first variable vane (104) to the at least one unison ring (120) at the first point (122) and a second lever (144) operatively coupling the second variable vane (106) to the at least one unison ring (120) at the second point (124).

10. The variable vane control system (100) of claim 9, wherein each of the plurality of sensors (150) is connected to a corresponding lever (140) from the set of levers (140), such that the first sensor (152) is connected to the first lever (142) and the second sensor (154) is connected to the second lever (144).

11. The variable vane control system (100) of any preceding claim, wherein the at least one circumferential set of variable vanes (102) comprises a plurality of circumferential sets of variable vanes (102) axially spaced apart from each other with respect to the central axis (Z-Z’), wherein the at least one unison ring (120) comprises a plurality of unison rings (120) corresponding to the plurality of circumferential sets of variable vanes (102), wherein each unison ring (120) from the plurality of unison rings (120 is operatively coupled to a corresponding circumferential set of variable vanes (102) from the plurality of circumferential sets of variable vanes (102), and wherein each unison ring (120) is configured to vary the angular position of each variable vane (102) from the corresponding circumferential set of variable vanes (102).

12. The variable vane control system (100) of claim 11, further comprising a crankshaft (192) operatively coupling the at least one actuator (110) to each unison ring (120).

13. The variable vane control system (100) of any preceding claim, wherein the first variable vane (104) and the second variable vane (106) are angularly spaced apart from each other by at least 90 degrees about the central axis (Z-Z’).

14. The variable vane control system (100) of any preceding claim, wherein each variable vane (102) is a variable inlet guide vane or a variable stator vane.

15. A gas turbine engine (10) including the variable vane control system (100) of any preceding claim 1 to 14.

16. A method (200) of operating a variable vane control system (100) having at least one circumferential set of variable vanes (102) circumferentially arranged around a central axis (Z-Z’), at least one actuator (110), and at least one unison ring (120) operatively coupling the at least one actuator (110) to each variable vane (102) from the at least one circumferential set of variable vanes (102), the method (200) comprising:controlling, via a controller (170), the at least one actuator (110) to rotate each variable vane (102);sensing, via a first sensor (152), a first angular position (P1) of a first variable vane (104) from the at least one circumferential set of variable vanes (102);sensing, via a second sensor (154), a second angular position (P2) of a second variable vane (106) from the at least one circumferential set of variable vanes (102), wherein the second variable vane (106) is angularly spaced apart from the first variable vane (104) with respect to the central axis (Z-Z’); andcontrolling, via the controller (170), the at least one actuator (110) to adjust an angular position of each variable vane (102) based on the first angular position (P1) of the first variable vane (104) and the second angular position (P2) of the second variable vane (106).

17. The method (200) of claim 16, wherein controlling the at least one actuator (110) further comprises:determining an average angular position (P3) as an average of the first angular position (P1) and the second angular position (P2); andcontrolling the at least one actuator (110) based on the average angular position (P3).

18. The method (200) of claim 17, wherein controlling the at least one actuator (110) further comprises:determining an error (190) as a difference between a position demand input (P4) and the average angular position (P3);determining a required actuator position demand (P5) based on the error (190); andcontrolling the at least one actuator (110) based on the required actuator position demand (P5).

19. The method (200) of any one of claims 16 to 18, wherein the at least one unison ring (120) comprises a first point (122) and a second point (124) angularly spaced apart from the first point (122) by at least 90 degrees about the central axis (Z-Z’), wherein, upon actuation by the at least one actuator (110), the at least one unison ring (120) has a lowest distortion at the first point (122) and a highest distortion at the second point (124), and wherein, among the at least one circumferential set of variable vanes (102), the first variable vane (104) is circumferentially nearest to the first point (122) and the second variable vane (106) is circumferentially nearest to the second point (124).

20. The method (200) of claim 19, wherein the at least one actuator (110) is a single actuator, such that the first point (122) and the second point (124) are angularly spaced apart by 180 degrees about the central axis (Z-Z’).

21. The method (200) of claim 19, wherein the at least one actuator (110) comprises a pair of actuators (110-1, 110-2) angularly spaced apart by 180 degrees about the central axis (Z-Z’), such that the first point (122) and the second point (124) are angularly spaced apart by 90 degrees about the central axis (Z-Z’).

22. The method (200) of any one of claims 16 to 21, wherein the first variable vane (104) and the second variable vane (106) are angularly spaced apart from each other by at least 90 degrees about the central axis (Z-Z’).

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