Abstract:
A system includes a controller configured to control an operational behavior of a turbine system. The controller includes a droop response system configured to detect one or more operational characteristics of the turbine system as an indication of a frequency variation of an electric power system associated with the turbine system. The droop response system is further configured to generate a response to vary an output of the turbine system in response to the indication of the frequency variation. The controller includes a multivariable droop response correction system configured to determine one or more possible errors associated with the one or more operational characteristics of the turbine system, and to generate a plurality of correction factors to apply to the response generated by the droop response system. The plurality of correction factors is configured to correct the response generated by the droop response system.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to industrial control systems, and more specifically, to droop response control industrial control systems for turbines. 
         [0002]    Power generation systems may include certain industrial control systems to provide control and analysis of the turbine and generator systems that may be included in the power generation system. For example, the industrial control systems may include controllers, field devices, and sensors for control and analysis of the turbine and generator systems. The industrial control system may control a droop response, or the percent frequency (or speed) variation required to cause a full (e.g., 100%) power output change of the turbine and generator systems. It may be useful to provide improved methods to control droop in turbine and generator systems. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
         [0004]    In a first embodiment, a system includes a controller configured to control an operational behavior of a turbine system. The controller includes a droop response system configured to detect one or more operational characteristics of the turbine system as an indication of a frequency variation of an electric power system associated with the turbine system. The droop response system is further configured to generate a response to vary an output of the turbine system in response to the indication of the frequency variation. The controller includes a multivariable droop response correction system configured to determine one or more possible errors associated with the one or more operational characteristics of the turbine system, and to generate a plurality of correction factors to apply to the response generated by the droop response system. The plurality of correction factors is configured to correct the response generated by the droop response system. 
         [0005]    In a second embodiment, a method includes receiving a turbine system operating parameter. The turbine system operating parameter includes an indication of a frequency variation of an electric power system associated with the turbine system. The method includes generating a plurality of correction factors to apply to a response generated to vary the output of the turbine system according to the frequency variation. The plurality of correction factors is configured to correct the response generated to vary the output of the turbine system. The method includes varying the output of the turbine system according to the corrected response. 
         [0006]    In a third embodiment, a non-transitory tangible computer-readable medium having computer executable code stored thereon is provided. The code includes instructions to receive a turbine system operating parameter. The turbine system operating parameter includes an indication of a frequency variation of an electric power system associated with the turbine system. The code includes instructions to generate a plurality of correction factors to apply to a response generated to vary the output of the turbine system according to the frequency variation. The plurality of correction factors is configured to correct the response generated to vary the output of the turbine system. The code includes instructions to vary the output of the turbine system according to the corrected response. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0008]      FIG. 1  is a block diagram of an embodiment of a power generation system including a controller, in accordance with present embodiments; 
           [0009]      FIG. 2  is a block diagram of an embodiment of a multivariable droop response correction system included within the controller of  FIG. 1 , in accordance with present embodiments; 
           [0010]      FIG. 3  is a plot diagram illustrating an embodiment of multivariable correction droop response control, in accordance with present embodiments; and 
           [0011]      FIG. 4  is a flow chart of an embodiment of a process suitable for implementing multivariable correction droop response control of the system of  FIG. 1 , in accordance with present embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0013]    When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0014]    Present embodiments relate to systems and methods useful in controlling the droop response, or the percent of regulation of the speed and load reference of, for example, a gas turbine system of a power generation system. As used herein, “droop” may refer to a degree of frequency (e.g., speed) variation that may be necessary to cause a power generating prime mover (e.g., turbines, generators, and so forth) to compensate for a corresponding frequency (e.g., electrical frequency) variation of an electrical power grid that may be coupled to the power generating prime mover. Indeed, because the power output of gas turbine systems may, in response to power grid frequency variation, depend upon the ambient operating conditions (e.g., inlet temperature and pressure, exhaust, and so forth) and the load level of the gas turbine system, certain errors may occur in the droop response control of the gas turbine system. This may result in the gas turbine system and generator failing to comply with certain nationally and/or regionally mandated power generation and transmission quality assurance (QA) standards, codes, and/or requirements governing such systems. Accordingly, a multivariable droop response correction system is provided. 
         [0015]    The multivariable droop response correction system may enable the droop response of the gas turbine system to be invariant and repeatable. Although, the presently disclosed embodiments may be discussed primarily with respect to a gas turbine system, it should be appreciated that the presently disclosed embodiments may apply to any power generating system including steam turbine systems, wind turbine systems, hydroelectric power generating systems, geothermal power generating systems, and the like. 
         [0016]    With the foregoing in mind, it may be useful to describe an embodiment of a power generation system incorporating techniques disclosed herein, such as an industrial power generation system  10  illustrated in  FIG. 1 . As depicted, the system  10  may include a gas turbine system  12 , a generator  14 , a power grid  16 , and a controller  18 . The gas turbine system  12  may further include a combustor  20 , a turbine  22 , a compressor  26 , and an intake  28 . The combustor  20  may receive fuel that may be mixed with air, for example, to create combustion in a chamber within the combustor  20 . The combustor  20  may create hot pressurized exhaust gases. The combustor  20  may then direct the exhaust gases through the turbine  22  toward one or more exhaust outlets. Thus, the turbine  22  may be part of a rotor. As the exhaust gases pass through the turbine  22 , the gases may force turbine blades to rotate a drive shaft  24  along an axis of the gas turbine system  12 . As will be discussed in further detail, the drive shaft  24  may be coupled to various components of the system  10 , including not only components of the gas turbine system  12 , but also the generator  14 . In certain embodiments, operational parameters (e.g., pressure, temperature, speed, torque, and so forth) may be sensed or estimated from one or more of the gas turbine system  12 , the generator  14 , and the drive shaft  24  to control droop of the gas turbine system  12 , as will be discussed in more detail with respect to  FIG. 2  below. 
         [0017]    The drive shaft  24  may include one or more shafts that may be, for example, concentrically aligned. The drive shaft  24  may include a shaft connecting the turbine  22  to the compressor  26  to form a rotor. Similarly, the compressor  26  may include blades coupled to the drive shaft  24 . Thus, rotation of turbine blades in the turbine  22  causes the shaft connecting the turbine  22  to the compressor  26  to rotate blades within the compressor  20 . Such a mechanism may compress air in the compressor  20 . The rotation of blades in the compressor  26  may compress air that may be received via the air intake  28 . The compressed air may be fed to the combustor  20  and mixed with fuel, for example, to allow for higher efficiency combustion. In certain embodiments, the gas turbine system  12  may also generate mechanical power to drive the generator  14  to produce electrical power for the power grid  16 . 
         [0018]    The gas turbine system  12  may further include a number of sensors and field devices configured to monitor various physical and operational parameters related to the operation and performance of the power generation system  10 . The sensors and field devices may include, for example, inlet sensors and field devices  30  and outlet sensors and field devices  32  (e.g., pressure transmitters, temperature transmitters, flow transmitters, fuel sensors, clearance sensors, and the like). Although not illustrated, it should also be appreciated that the generator  14  may also include a number of sensors and field devices  30  and  32 . The inlet sensors and field devices  30  and outlet sensors and field devices  32  may also measure environmental (e.g., ambient) conditions of the gas turbine system  12  and the generator  14 . 
         [0019]    For example, the inlet sensors and field devices  30  and outlet sensors and field devices  32  may measure the ambient temperature, ambient pressure, humidity, and air quality (e.g., particulate in air). The inlet sensors and field devices  30  and outlet sensors and field devices  32  may also measure engine parameters related to the operation and performance of the gas turbine system  12 , such as, exhaust gas temperature, rotor speed, engine temperature, engine pressure, fuel temperature, engine fuel flow, exhaust flow, vibration, clearance between rotating and stationary components, compressor discharge pressure, pollution (e.g., nitrogen oxides, sulfur oxides, carbon oxides and/or particulate count), and turbine  22  exhaust pressure. Further, the sensors and field devices  30  and  32  may also measure actuator information such as valve position, switch position, throttle position, and a geometry position of variable geometry components (e.g., air inlet). As will be discussed in greater detail, the controller  18  may use the measurements to derive and generate multivariable correction factors of the sensed ambient condition parameters to actively control one or more of the gas turbine system  12  (e.g., turbine  22 , compressor  26 , intake  28 ) and the generator  14 , and by extension, the electrical power output to the power grid  16 . 
         [0020]    In certain embodiments, the generator  14  may include one or more rotors (not illustrated), of which may rotate at a fixed and/or variable speed with respect to the operating frequency (e.g., approximately 50 Hz for most countries of Europe and Asia and approximately 60 Hz for countries of North America) of the power grid  16 . In certain embodiments, variations in operating frequency of the power grid  16  may indicate that the power generation supply to the power grid  16  is inadequate to meet the load demand on the power grid  16 , or otherwise that the power generation supply to the power grid  16  is more than the load demand on the power grid  16 . In such cases, it may be useful to provide a control mechanism to vary the power output (e.g., fuel flow) of the gas turbine system  12 , and by extension the speed of the generator  14 , to compensate for the frequency variations on the power grid  16 . Such a control mechanism may generally be referred to as the “droop response” of the gas turbine system  12 . Specifically, the droop response of the gas turbine system  12 , and by extension the generator  14 , may be determined in terms of the percent frequency variation relating to a 100% change in gas turbine system  12  power output. For example, in one embodiment, the gas turbine system  12  and the generator  14  may be controlled to operate with a 4% droop response. That is, the power output of the gas turbine system  12  gas turbine load output may experience a 100% change for a 4% variation in frequency of the power grid  16 . Thus, a 4% droop variation may correspond to a change gas turbine system  12  output of 25% per each 1% power grid  16  frequency change (e.g., per each 1% turbine shaft  24  speed change since the power grid  16  frequency and turbine  22  speed may be proportional with respect to each other). As will be further appreciated, the droop response of the gas turbine system  12  may be controlled to compensate for variations in frequency and/or load of the power grid  16 . Further, the droop of the gas turbine system  12  may be controlled irrespective of the ambient conditions (e.g., temperature, pressure, and so forth) and load level of the gas turbine system  12 . 
         [0021]    As previously noted, the system  10  may also include the controller  18 . The controller  18  may suitable for generating and implementing various control algorithms and techniques to control droop response of the gas turbine system  12 . The controller  18  may also provide an operator interface through which an engineer or technician may monitor the components of the power generation system  10  such as, components of the gas turbine system  12  and the generator  14 . Accordingly, the controller  18  may include a processor that may be used in processing readable and executable computer instructions, and a memory that may be used to store the readable and executable computer instructions and other data. These instructions may be encoded in programs stored in tangible non-transitory computer-readable medium such as the memory and/or other storage of the controller  18 . In certain embodiments, the controller  18  may also host various industrial control software, such as a human-machine interface (HMI) software, a manufacturing execution system (MES), a distributed control system (DCS), and/or a supervisor control and data acquisition (SCADA) system. The controller  18  may further support one or more industrial communications (e.g., wired or wireless) protocols such as, Hart and/or Wireless Hart. For example, the controller  18  may support GE Energy GE ControlST, which may assign and distribute configuration tools and similar control data to various field equipment and devices. 
         [0022]    As such, the controller  18  may be communicatively coupled to the inlet and outlet sensors and field devices  30  and  32 , gas turbine system  12 , and the generator  14 . The controller  18  may support one or more operating systems capable of running and supporting various software applications and systems, as well as managing the various hardware (e.g., processors, storages, gateways, programmable logic controllers [PLCs], and so forth) that may be included as part of the controller  18 . Indeed, in certain embodiments, the controller  18  may support one or more droop response control systems and/or algorithms, such as a droop response control system  34 . 
         [0023]    Accordingly,  FIG. 2  is a schematic diagram of an embodiment of a droop response control system  34 . The droop response control system  34  may be included as part of the controller  18 , and may further include a droop response system  36  and a multivariable droop response correction system  38 . Particularly, the droop response control system  34  may be a software system, a hardware system, or a combination thereof. The droop response control  34  may be used to control droop response, such that the gas turbine system  12  power output, and by extension the power output of the generator  14 , is adjusted according to variations in electrical frequency of the power grid  16 . Specifically, the droop response control system  34  may monitor the frequency (e.g., received by the controller  18 ) of the power grid  16  or the speed of the generator  14 , and adjust the fuel flow to the gas turbine system  12  and the output of the generator  14  according to the degree of frequency variation from the nominal frequency (e.g., 60 Hz) of the power grid  16 . For example, for a 0.1 Hz frequency increase (e.g., 60.1 Hz indicating that the power generation supply to the power grid  16  is more than the load demand on the power grid  16 ), the fuel flow and/or intake  28  of the gas turbine system  12  may be decreased to a reduced power output to maintain balance between the gas turbine system  12 , the generator  14 , and the power grid  16  of the system  10 . In a similar example, for a 0.1 Hz frequency decrease (e.g., 59.9 Hz indicating that the power generation supply to the power grid  16  is less than the load demand on the power grid  16 ), the fuel flow and/or intake  28  of the gas turbine system  12  may be increased to a greater power output to maintain balance between the gas turbine system  12 , the generator  14 , and the power grid  16  of the system  10 . 
         [0024]    As depicted, the droop response system  36  may include a turbine speed/load reference input  40  and operating frequency input  42 . As previously noted with respect to  FIG. 1 , the inputs  40  and  42  may be received by the controller  18  via, for example, the inlet sensors and field devices  30  and outlet sensors and field devices  32  or other devices. As it may be worth noting, the frequency input  42  may be an electrical frequency measured directly from the power grid  16 , or derived based on the speed of the shaft  24  coupled to the gas turbine system  12  and the generator  14 . Specifically, the turbine speed/load reference input  40  may be the turbine  26  speed reference represented as a percentage value, in which a 100% value represents a zero power output (MW) and a 104% value represents full-power output (MW). Similarly, the operating frequency input  42  may be represented as percentage value, in which each 1% variation in power grid  16  frequency may correspond to a 25% change in power output (MW) of the gas turbine system  12 . Thus, as illustrated, a difference of the inputs  40  and  42  may be computed to calculate a speed/load error percentage, which may be multiplied by a fuel command constant gain 46. The fuel command constant gain 46 may represent the fuel command change per each percentage of the speed/load error. The result of the product of the speed/load error percentage and the fuel command constant gain 46 may be then combined with the fuel command constant  48  (e.g., the fuel command at full-speed of the generator  14 ) to derive a nominal fuel flow command, which may be then passed to a clamp  50 . The nominal fuel flow command may be then output to one or more effectors (e.g., actuators, valves, and the like) of the gas turbine system  12  to adjust the fuel flow to the gas turbine systems  12 , and by extension, control the droop response of the gas turbine system  12 . 
         [0025]    However, because the power output of the gas turbine system  12  may depend upon the ambient operating conditions (e.g., compressor  26  inlet temperature and pressure, turbine  22  temperature) and the load level of the gas turbine system  12 , certain errors may occur in the droop response control of the gas turbine system  12 . For example, as a 1% power grid  16  frequency variation may necessitate a 10 MW adjustment in gas turbine system  12  power output, depending on the ambient conditions (e.g., on a cold or hot day as compared to a day of normal temperature, and/or cooler or warmer periods of a single day), the 1% power grid  16  frequency variation may, for example, result in a droop response change of 11-12 MW on a cold (e.g., 50-70 degrees) day or a change of 8-9 MW on a hot (e.g., 80-100 degrees) day. This may result in the gas turbine system  12  and generator  14  failing to comply with certain nationally and/or regionally mandated power generation and transmission quality assurance (QA) standards, codes and/or requirements governing such systems. 
         [0026]    Accordingly, it may be useful to provide a multivariable droop response correction system  38 . Indeed, the multivariable droop response correction system  38  may adjust the normal fuel flow command, such that for a given variation in frequency of the power grid  16 , the droop power response may be irrespective of the ambient operating conditions (e.g., compressor  26  inlet temperature and pressure, turbine  22  temperature) and the load level of the gas turbine system  12 . Thus, the multivariable droop response correction system  38  may enable the frequency droop response of the gas turbine system  12  to be consistent and repeatable throughout, for example, periods of quality assurance (QA) testing, safety integrity level (SIL) testing, operation, and the like. 
         [0027]    As illustrated, similar to the nominal droop response control system  36 , the multivariable droop response correction system  38  may include a fuel flow control loop, which may include the turbine speed/load reference input  40  and operating frequency input  42 . The inputs  40  and  42  may be summed (e.g., subtracted) and divided by a droop constant  52  (e.g., value 4 to normalize to a 4% droop configuration) calculate a turbine load level in per unit (e.g., p.u.) via a load estimator  54 . An output of the load estimator  54  may be multiplied by a constant value (e.g., 100%) to convert load level from per unit (p.u.) to percentage (%). The turbine load level may be then outputted to a droop response correction factor generator  58 . Also inputted to the droop response correction factor generator  58  may be a compressor  26  inlet temperature (or ambient temperature) input  60  via a lag filter  62  (e.g. first-order). The lag filter  62  may be included to filter undesirable signal distortions that may be present in the compressor  26  inlet temperature input  60 . It should be appreciated that any errors relating to the input  60  may be determined by the droop response correction factor generator  58 , or may, for example, be compared to a reference value during the period the input  60  is passed through the lag filter  62 . 
         [0028]    In certain embodiments, the droop response correction factor generator  58  may be a two-dimensional (2-D) (or larger dimensional) interpolation table, which may use one or more variable interpolation techniques (e.g., linear interpolation, bilinear interpolation, cubic interpolation, bicubic interpolation, trilinear interpolation, spline interpolation, proximal interpolation, and or any multivariate interpolation technique) to interpolate (e.g., estimate the value of a function that lies between possibly known values) multivariable functions such as the ambient operating conditions (e.g., compressor  26  inlet temperature and pressure, turbine  22  temperature) and the load level and/or power output (MW) of the gas turbine system  12 . Specifically, the droop response correction factor generator  58  may be loaded with a series of off-line calculated correction factors corresponding to the gas turbine system  12  calculated load level and the compressor  26  inlet temperature input  60 . Thus, the droop response correction factor generator  58  may output correction factors for the fuel flow command based on the ambient operating conditions and the load level of the gas turbine system  12 . An initial correction factors output may be passed to a clamp  63  to adjust the correction factors between predetermined upper limit  64  and lower limit  66 . 
         [0029]    In certain embodiments, the correction factors output may then be passed to a selector  68 , which may be used to alternatively (e.g., user-configurably) select between enabling the multivariable droop response correction system  38  via an enable input  70 . Enabled, the multivariable droop response correction system  38  may output a final correction factors output that may be multiplied by the nominal fuel flow command of the droop response system  36  to produce a droop response fuel flow command such that the droop power response of the gas turbine system  12  is invariant with respect to the ambient operating conditions and the load level of the gas turbine system  12 . In other words, for any variation in power grid  16  frequency, the droop response of the gas turbine system  12  may be substantially commensurate with the frequency variation. As such, a 1% power grid  16  frequency variation, for example, may warrant a substantially 10 MW adjustment in gas turbine system  12  power output, as opposed to a higher (e.g., 11-12 MW) or lower (e.g., 8-9 MW) power output response that may result due to ambient conditions (e.g., on a cold or hot day as compared to a day of normal temperature, and/or cooler or warmer periods of a single day) and load level of the gas turbine system  12 . On the other hand, if the enable input  70  is not enabled, a correction factor unity constant input  72  (e.g., value 1) may be passed to the selector  68 , in which case the fuel flow command output will be substantially equal to the nominal fuel flow command output of the nominal droop response control system  36 . 
         [0030]    As a further illustration of the presently disclosed techniques,  FIG. 3  displays a plot diagram  80  illustrating an embodiment of multivariable correction droop response control, as discussed above with respect to  FIG. 2 . The plot diagram  80  may include droop response plots  82  and  84  depicting the droop response of the gas turbine system  12 . The droop response plot  82  represents a droop response dependent upon gas turbine system  12  ambient conditions. As illustrated by response plot  82 , the power output (MW) of the gas turbine system  12  may vary inversely with the ambient temperature of the gas turbine system  12 . Specifically, the power output (MW) may decrease as the ambient temperature increases. Thus, as the ambient temperature may change over a period of a day (e.g., from 70 deg. in the morning to 80 deg. in the afternoon), the power output (MW) of the gas turbine system  12  may decrease during that time period. As previously noted, this may result in the gas turbine system  12  and generator  14  failing to comply with certain nationally and/or regionally mandated power generation and transmission quality assurance (QA) standards and/or requirements. On the other hand, the response plot  84  as illustrated may be invariant with respect to ambient conditions. Indeed, the response plot  84  may be the result of implementing the presently disclosed multivariable correction droop response control techniques. Accordingly, as shown, the power output (MW) may be substantially the same MW value for ambient temperatures of 0 deg. through 100 deg, and thus may be repeatable and predictable, as opposed to a power output (MW) dependent upon ambient conditions as illustrated by response plot  82 . 
         [0031]    Turning now to  FIG. 4 , a flow diagram is presented, illustrating an embodiment of a process  90  useful in generating multivariable correction factors for droop response control, by using, for example, the controller  18  included in the power generation system  10  depicted in  FIG. 1 . The process  90  may include code or instructions stored in a non-transitory computer-readable medium (e.g., a memory) and executed, for example, by one or more processors included in the controller  18 . The process  90  may begin with the controller  18  receiving (block  92 ) the gas turbine system  12  operating parameters. As previously discussed, the multivariable droop response correction system  38  of controller  18  may receive operating parameters (e.g., turbine  22  and compressor  26  inlet temperature and pressure) of the gas turbine system  12  based on data received via one or more sensors. The operating parameters may also include power grid frequency parameters (e.g., speed, torque, frequency, and so forth) based, for example, on the speed of the shaft  24  coupled to the gas turbine system  12  and the generator  14 , or the electrical frequency of the power grid  16 . The process  90  may then continue with the multivariable droop response correction system  38  of the controller  18  generating (block  98 ) droop response correction factors of the calculated load level and the compressor  26  inlet temperature (or ambient temperature), or various other operating parameters of the gas turbine system  12 . For example, as previously noted, the multivariable droop response correction system  38  of the controller  18  may generate the multivariable correction factors by using one or more interpolation techniques such as, for example, linear interpolation, bilinear interpolation, cubic interpolation, bicubic interpolation, trilinear interpolation, spline interpolation, proximal interpolation, and so forth. The multivariable droop response correction system  38  of the controller  18  may then output (block  100 ) a fuel flow command based on the generated droop response correction factors. The fuel flow command may be used by the controller  18  to adjust (block  102 ) one or more control effectors (e.g., actuators, valves, and the like) coupled to the gas turbine system  12 . For example, one or more actuator control signals may be generated by the controller  18  to control, for example, the fuel flow to the gas turbine system  12 . 
         [0032]    Technical effects of the present embodiments may include systems and methods useful in controlling the droop response of gas turbine systems of power generation systems. Specifically, a multivariable droop response correction system may adjust the normal fuel flow command, such that for a given variation in frequency of the electrical power grid coupled to the gas turbine system, the droop power response may be irrespective of the ambient operating conditions and the load level of the gas turbine system. Thus, the multivariable droop response correction system may enable the droop response of the gas turbine system to be invariant and repeatable. 
         [0033]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.