Abstract:
A system includes a controller including a processor configured to execute a program stored in a memory of the controller to generate and transmit a first output comprising a total flow demand value to a plurality of valves communicatively coupled to the controller. Each of the plurality of valves is configured to receive a respective portion of the total flow demand value. The processor is configured to receive an input indicative of a decoupling of a first valve of the plurality of valves and to generate a second output based at least in part on the first output and a first operational characteristic of the first valve. The second output is configured to vary a second operational characteristic of a second valve of the plurality of valves to maintain the total flow demand value.

Description:
BACKGROUND 
     The subject matter disclosed herein relates to steam turbine systems and, more specifically, to valve test compensation for the steam turbine systems. 
     Certain steam turbine systems and associated components may periodically be subject to or undergo certain testing. For example, operational testing may be serially performed on inlet flow control valves used in steam turbine systems. However, operational parameters, such as the pressure of the steam turbine, may be increased when online valve testing is performed due to frequent closing, opening, and/or reopening of the turbine valves under test. Furthermore, certain control schemes for the control valves may be hindered based on the configuration of the valve and turbine arrangement. It is desirable to provide methods to improve online valve testing in steam turbine systems. 
     BRIEF DESCRIPTION 
     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. 
     In accordance with a first embodiment, a system includes a controller including a processor configured to execute a program stored in a memory of the controller to generate and transmit a first output including a total flow demand value to a plurality of valves communicatively coupled to the controller. Each of the plurality of valves is configured to receive a respective portion of the total flow demand value. The processor is configured to receive an input indicative of a decoupling of a first valve of the plurality of valves, and to generate a second output based at least in part on the first output and a first operational characteristic of the first valve. The second output is configured to vary a second operational characteristic of a second valve of the plurality of valves to maintain the total flow demand value. 
     In accordance with a second embodiment, a non-transitory computer-readable medium having code stored thereon, the code includes instructions to generate and transmit a first output including a total flow demand value to a plurality of valves. Each of the plurality of valves is configured to receive a respective portion of the total flow demand value. The code includes instructions to receive an input indicative of a decoupling of a first valve of the plurality of valves, and to generate a second output based at least in part on the first output and a first operational characteristic of the first valve. The second output is configured to vary a second operational characteristic of a second valve of the plurality of valves to maintain the total flow demand value. 
     In accordance with a third embodiment, a system includes a controller configured to control one or more operational parameters of a turbine system, and configured to generate and transmit a first output including a total flow demand value to a plurality of valves communicatively coupled to the controller. Each of the plurality of valves is configured to receive a respective portion of the total flow demand value to regulate a flow of fluid to the turbine system including the plurality of valves. The controller is configured to receive an input indicative of a decoupling of a first valve of the plurality of valves, and to generate a second output based at least in part on the first output and a first operational characteristic of the first valve. The second output is configured to vary a second operational characteristic of a second valve of the plurality of valves to maintain the total flow demand value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a block diagram of an embodiment of a turbine-generator system including a number of valves, in accordance with present embodiments; 
         FIG. 2  is a block diagram of an embodiment of a controller to control the valves included within the system of  FIG. 1 , in accordance with present embodiments; 
         FIG. 3  is a block diagram of one embodiment of a feed-forward valve flow compensation controller as the controller of  FIG. 2 , in accordance with present embodiments; 
         FIG. 4  is a block diagram of another embodiment of the feed-forward valve flow compensation controller as the controller of  FIG. 2 , in accordance with present embodiments; 
         FIG. 5  is a flow chart of an embodiment of a process suitable for implementing feed-forward valve flow compensation control of the valves of  FIG. 1 , in accordance with present embodiments; and 
         FIG. 6  is a flow chart of an alternative process suitable for implementing feed-forward valve flow compensation control of the valves of  FIG. 1 , in accordance with present embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     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. 
     Present embodiments relate to utilizing feed-forward valve flow compensation techniques to control fluid flow to a turbine configured according to one or more of a full arc admission (e.g., in which valve actuation may be concurrent and/or synchronized to allow equal flow of fluid through each of the individual valves to the turbine) or a partial arc admission (e.g., in which valve actuation may be substantially independent and/or unsynchronized to independently regulate the flow of fluid through each of the individual valves to the turbine). In certain embodiments, a controller may use valve stroke and/or valve stem position information as feedback into a flow compensation control loop to maintain a total flow demand (e.g., the total amount of fluid movement and/or flow required by the turbine to perform one or more various operations) of the turbine during operational testing (e.g., testing by opening, closing, and/or reopening of a valve) of at least one valve of a number of valves coupled to the turbine. 
     Specifically, an operator, for example, may select a valve to undergo operational testing. Once selected, the controller may determine to remove the valve undergoing testing from closed-loop control and/or automatic control, and place the valve undergoing testing under open-loop and/or manual control. The remaining valves may then be re-calibrated to control the remainder of the total flow demand due to the loss of flow demand contribution of the valve undergoing testing, so as to minimize flow disturbance to the turbine that may be due to the closing, opening, and/or reopening of the valve undergoing testing. In one embodiment, a difference between the pre-testing flow demand contribution of the valve undergoing testing may be added to the total flow demand. In another embodiment, the flow demand contribution of the valve undergoing testing may be directly subtracted from the total flow demand. In either case, the controller may determine a new valve stroke and/or valve stem position for each of the remaining valves under closed-loop control (e.g., valves not currently undergoing testing) to maintain the total flow demand of the turbine. Indeed, the present embodiments may allow for feed-forward flow compensation for valve and turbine partial arc admission configurations, as well as full arc admission configurations. 
     With the foregoing in mind, it may be useful to describe a turbine-generator system, such as an example turbine-generator system  10  illustrated in  FIG. 1 . As depicted, the system  10  may include a steam turbine  12  (or gas turbine  12 ), a generator  14  coupled to a load  16 , and a controller  18 . The steam turbine  12  may be further coupled to one or more valves  20 , which may control the steam intake  22  to the steam turbine  12 . The steam turbine  12  may use the steam intake  22  to deliver an output (e.g., mechanical power output) via a shaft  23  to the generator  14 . 
     In certain embodiments, the valves  20  may include a number of parallel valves (e.g., 2, 3, 4, or more valves), and may regulate the steam intake  22  of the steam turbine  12  according to a full arc admission, partial arc admission, or other similar fluid admission technique. For example, using full arc admission, the one or more valves  20  may be actuated and/or positioned (e.g., controlled by the controller  18 ) concurrently, allowing equal steam intake  22  to the steam turbine  12 . In a similar example, using partial arc admission, the valves  20  may regulate the steam intake  22  of the steam turbine  12  by, for example, a subset (e.g., 3 out of 4 valves, or other similar arrangement) of the valves  20  being actuated and/or positioned (e.g., controlled by the controller  18 ) concurrently, while the remaining valve(s)  20  of the set may be actuated and/or positioned after a period of time. Thus, using partial arc admission, the steam intake  22  to the steam turbine  12  may be regulated separately and/or independently with respect to the different valves  20 . 
     As previously noted, the system  10  may also include the controller  18 . The controller  18  may be suitable for generating and implementing various control algorithms and techniques to control the valves  20 , and by extension the steam intake  22  to the steam turbine  12 . The controller  18  may also provide an operator interface through which an engineer or technician may monitor the components of the turbine-generator system  10  such as, components (e.g., sensors) of the steam turbine system  12  and the generator  14 . Accordingly, the controller  18  may include a processor  24  that may be used in processing readable and executable computer instructions, and a memory  25  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  25  and/or other storage of the controller  18 . Furthermore, the processor  24  and the memory  25  may allow the controller  18  to be programmably retrofitted with the instructions to carry out the presently disclosed techniques without the need to include, for example, additional hardware components. 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. For example, the controller  18  may support GE ControlST™ available from General Electric Co., of Schenectady, N.Y. 
     Turning now to  FIG. 2 , a block diagram of an embodiment of the controller  18  is illustrated. As depicted, the controller  18  may be useful in controlling one or more valves  20 , or a series of four valves  26  (e.g., Valve 1),  27  (e.g., Valve 2),  28  (e.g., Valve 3), and  29  (e.g., Valve 4). Indeed, the controller  18  may utilize feed-forward control to control valve position as feedback to reduce flow disturbance caused by the operation (e.g., closing, opening, and/or reopening) of the valves  26 ,  27 ,  28 , and  29  during periodic operational testing. For example, as illustrated in  FIG. 2 , a total flow demand input  30  for all of the valves  26 ,  27 ,  28 , and  29  may be generated as a function of control valve position (e.g., position or stroke of the stem of the valves  26 ,  27 ,  28 , and  29 ). Specifically, the total flow demand input  30  may represent the mass flow being demanded (e.g., the amount of steam intake  22  that may be required by the steam turbine  12  to perform more efficiently) as a percentage value. The total flow demand input  30  may be divided (e.g., equally divided and/or unequally divided) via flow dividers  32 ,  34 ,  36 , and  38 , and input into respective valve flow-stroke converters  40 ,  42 ,  44 , and  46  for each of the respective valves  26 ,  27 ,  28 , and  29 . 
     In certain embodiments, the valve flow-stroke converters  40 ,  42 ,  44 , and  46 , as illustrated by respective flow-stroke curves, may represent the different flow characteristics between the valves  26 ,  27 ,  28 , and  29 . For example, the horizontal axis of the flow-stroke curves of the flow-stroke converters  40 ,  42 ,  44 , and  46  may represent valve stroke (e.g., valve stem positioning) in inches. Similarly, the vertical axis may represent flow in pounds mass per hour (lbm/hr). Indeed, the flow-stroke converters  40 ,  42 ,  44 , and  46  may each include one or more data arrays (e.g., two-dimensional look up table) that may map, for example, an individual flow demand value (e.g., percentage or portion of the total flow demand input  30 ) to corresponding stroke or valve stem position for each of the individual valves  26 ,  27 ,  28 , and  29  (e.g., as illustrated by the respective flow-stroke curves of the flow-stroke converters  40 ,  42 ,  44 , and  46 ). As previously noted, in certain embodiments, the controller  18  may generate a signal to actuate one or more of the valves the valves  26 ,  27 ,  28 , and  29  such that the steam intake  22 , for example, is admitted to the steam turbine  12  according to partial arc admission. For example, as further illustrated in  FIG. 2 , the stroke (e.g., as shown via the flow-stroke converters  40 ,  42 , and  44 ,) of the valves  26 ,  27 , and  28  may be generated substantially at the same time, while the stroke (e.g., as shown via the flow-stroke converter  46 ) of the valve  29  may be changed at a point time afterwards. As will be further appreciated, because of the partial arc admission configuration, the controller  18  may be hindered in dividing the total flow demand input  30  evenly amongst the valves  26 ,  27 ,  28 , and  29 . 
       FIG. 3  is a block diagram illustrating an embodiment of the controller  18 , in which the mass flow through each of the valves  26 ,  27 ,  28 , and  29  in a partial arc configuration is controlled during an operational testing of at least one of the valves  26 ,  27 ,  28 , and  29 . As depicted, during a valve operational test of valve  28 , for example, the valve  28  may be removed from control loop  31  (e.g., closed-loop control), and placed under open-loop and/or manual control via test control input  45 . As noted above with respect to  FIG. 2 , the total flow demand input  30  (e.g. 70, 80, 90% of the maximum flow rating of the steam turbine  12 ) may be shared (e.g., an approximate percentage of the total flow demand) across the valves  26 ,  27 ,  28 , and  29 . However, when one of the valves  26 ,  27 ,  28 , and  29  (e.g., valve  28 ) is selected (e.g., by an operator) to undergo operational testing, the input flow demand based on the total flow demand input  30  may be readjusted to compensate for the loss of flow due to the testing of the valve  28 . Specifically, in one embodiment, a change in the flow of the tested valve (e.g., valve  28 ) during testing may be calculated and added to the total flow demand input  30 . In another embodiment, the flow of the tested valve (e.g., valve  28 ) may be subtracted from the total flow demand input  30 . In either embodiment, a new stroke command may be generated for each of the valves (e.g., valves  26 ,  27 , and  29 ) not undergoing operational testing to maintain, for example, the initial total flow demand of the steam turbine  12 . 
     For example, the controller  18  may also include a flow compensation control loop  33  to control valve stroke and/or valve stem positions by adjusting the flow through the parallel control valves  26 ,  27 , and  29 , and thus minimize flow disturbance of the steam turbine  12  that may be caused by the closing, opening, and/or reopening of the valve  28  during operational testing. The controller  18  may receive stroke and/or valve stem position data of the valves  26 ,  27 ,  28 , and  29  via one or more sensors  56 . In certain embodiments, the sensors  56  may include, for example, a linear variable differential transformer (LVDT), a linear variable differential reactor (LVDR), or any device useful in measuring linear position and/or displacement of the stem of the valves  26 ,  27 ,  28 , and  29 . The controller  18  may use the valve stroke and/or valve stem position data collected via the sensors  56  to generate a corresponding flow value via stroke-flow converters  58 ,  60 ,  62 , and  64  based on the stroke of the valves  26 ,  27 ,  28 , and  29 . 
     In certain embodiments, the stroke-flow converters  58 ,  60 ,  62 , and  64  may include inversions of the curves and/or data arrays of the corresponding flow-stroke converters  40 ,  42 ,  44 , and  46 . For example, should the valves  26  and  27  each be controlled and/or clamped to a certain percentage (e.g., 20-25%) of the total flow demand input  30  by way of one or more latches  66  and the valve  29  be controlled and/or clamped to a certain lesser percentage (e.g., 10-15%) via the latches  66 , a change in flow may be calculated for each of the valves  26 ,  27 , and  29 , as well as the valve  28  undergoing testing. Specifically, a difference between the pre-testing flow contribution (e.g., pre-test percentage of the total flow demand input  30 ) for each of the valves  26 ,  27 ,  28 , and  29  pre-testing of the valve  28  and the flow during operational testing derived based on the stroke data received via the sensors  56  may be calculated. In certain embodiments, the difference between the valves  26 ,  27 , and  29  not undergoing testing may be substantially zero, while the difference between the flow contribution for the valve  28  undergoing operational testing and the flow derived based on the stroke data may vary throughout the testing of the valve  28 . 
     The respective difference outputs may be input to a selector  68 , which may produce a signal output  69  to add to the pre-testing total flow demand input  30  to control the flow through the valves  26 ,  27 , and  29  (e.g., valves under closed-loop control and/or automatic control during testing of valve  28 ), and by extension, the mass flow steam intake  22  into the turbine  12 . Particularly, the signal output  69  may include the difference between the pre-testing flow demand contribution of the valve  28  (e.g., valve undergoing testing) and the flow demand contribution of the valve  28  during testing, as the flow demand contribution of the valve  28  may vary, for example, between 1%, 5%, 10%, 15%, 20%, or more as the testing of the valve  28  progresses. Accordingly, the signal output  69  may be the flow compensation (e.g., a percentage value) of the valve undergoing testing (e.g., valve  28 ) that may be added to the total flow demand input  30 , such that flow demand contribution of each of the valves  26 ,  27 , and  29  (e.g., valves under closed-loop control and/or automatic control during testing of valve  28 ) may be adjusted by deriving a new stroke command for each of the valves  26 ,  27 , and  29  based on the sum of the signal output  69  of the selector  68  and the total flow demand input  30 . Thus, the controller  18  may compensate for loss of flow contribution by generating a signal to adjust the flow through the valves  26 ,  27 , and  29  not undergoing testing to maintain the total flow demand (e.g., total flow demand input  30 ) and compensate for any reduced flow capacity of the valve  28  during operational testing. Thus, the potential of a flow disturbance to the steam turbine  12  due to the testing (e.g., closing, opening, and/or reopening) of the valve  28  may be minimized. 
       FIG. 4  illustrates another embodiment of the controller  18 , in which the mass flow through each of the valves  26 ,  27 ,  28 , and  29  in a partial arc configuration is controlled during an operational testing of at least one of the valves  26 ,  27 ,  28 , and  29 . In the illustrated embodiment, the valve  27  may be selected to undergo testing. However, it should be appreciated that one, two, or more of the valves  26 ,  27 ,  28 , and  29  may be selected to undergo valve testing in series or in parallel. Similar to that noted above with respect to  FIG. 3 , the valve (e.g., valve  27 ) undergoing testing may be removed from closed-loop control, and placed under open-loop and/or manual control via test control input  45 . Further, as previously noted, the total flow demand input  30  (e.g. 70, 80, 90%) may be shared (e.g., distributed) across the respective valves  26 ,  27 ,  28 , and  29 . However, in the present embodiment, once the valve  27  is removed from the closed-loop control for operational testing, under test control  45 , the controller  18  may use the valve stroke data collected via the sensor  56  to generate a flow command via the stroke-flow converter  60  based on the stroke of the valve  27  (e.g., the valve undergoing operational testing). Specifically, the flow demand contribution (e.g., shared percentage of the total flow demand input  30 ) of the valve  27  may be subtracted from the total flow demand input  30 . Based on this calculated difference, a new stroke command may be generated via the respective flow-stroke converters  40 ,  44 , and  46  for each of the valves  26 ,  28 , and  29  to compensate for the loss flow demand contribution of the valve  27 . That is, the flow through parallel valves  26 ,  28 , and  29  may be adjusted to maintain the total flow demand (e.g., total flow demand input  30 ), for example, and thus minimize flow disturbance of the steam turbine  12 . 
     Turning now to  FIG. 5 , a flow diagram is presented, illustrating an embodiment of a process  70  useful in controlling the mass flow through each of a number of valves in a partial arc configuration during operational testing, by using, for example, the controller  18  included in the system  10  depicted in  FIG. 1 . The process  70  may include code or instructions stored in a non-transitory machine-readable medium (e.g., the memory  25 ) and executed, for example, by one or more processors (e.g., processor  24 ) included in the controller  18 . The process  70  may begin with the controller  18  receiving (block  72 ) an indication corresponding to a selection of a valve to undergo operational testing. For example, one or more of the valves  26 ,  27 ,  28 , and  29  may be selected to undergo operational testing while in operation and coupled to the turbine  12 . The process  70  may continue with the controller  18  determining to remove (block  74 ) the selected valve from closed-loop control (e.g., automatic control) to undergo operational (e.g., closing, opening, and/or reopening) testing. Specifically, the valve undergoing testing may be placed under manual and/or open-loop control. 
     The process  70  may then continue with the controller  18  calculating (block  76 ) the change in flow (e.g., a change in the flow contribution of the valve undergoing testing) while the valve (e.g. valve  28  as illustrated in  FIG. 3 ) undergoing testing changes stroke and/or valve stem position. Specifically, a difference between the pre-testing flow contribution for each of the valves  26 ,  27 ,  28 , and  29  and the flow derived based on the stroke data received via the sensors  56  may be calculated. The process  70  may then continue with the controller  18  adding (block  78 ) the change in flow (e.g., percentage value) to the total flow demand (e.g., percentage value of the flow demand for all of the valves  26 ,  27 ,  28 , and  29  to collectively deliver to the steam turbine  12 ). The process  70  may then conclude with the controller  18  generating a control signal to adjust (block  79 ) the flow demand contribution of each of the valves  26 ,  27 , and  29  not undergoing testing by deriving a new stroke command for each of the valves  26 ,  27 , and  29  based on the sum of the change in individual flow demand contribution and the total flow demand. 
     Similarly,  FIG. 6  depicts a flow diagram, illustrating embodiment of a process  80  useful in controlling the mass flow through each of a number of valves in a partial arc configuration during operational testing, by using, for example, the controller  18  included in the system  10  depicted in  FIG. 1 . In certain embodiments, the process  80  may be implemented as an alternative to the process  70 . Similar to the process  70 , the process  80  may include code or instructions stored in a non-transitory machine-readable medium (e.g., the memory  25 ) and executed, for example, by one or more processors (e.g., processor  24 ) included in the controller  18 . The process  80  may begin with the controller  18  receiving (block  82 ) an indication corresponding to a selection of a valve to undergo operational testing. As noted above, one or more of the valves  26 ,  27 ,  28 , and  29  may be selected to undergo operational testing while in operation and while coupled to the turbine  12 . 
     The process  80  may continue with the controller  18  determining to remove (block  84 ) the selected valve from closed-loop control (e.g., automatic control) to undergo operational (e.g., closing, opening, and/or reopening) testing. The process  80  may continue with the controller  18  adjusting (block  85 ) the scaling of flow data (e.g., via the flow-stroke converters  40 ,  44 , and  46  as illustrated in  FIG. 4 ) of the valves (e.g. valves  26 ,  28 , and  29 ) not undergoing testing to compensate for the loss of flow of the valve undergoing testing (e.g. valve  27  as illustrated in  FIG. 4 ). Specifically, to compensate for the loss of flow of the valve (e.g. valve  27 ) undergoing testing, the flow data may be scaled via the flow-stroke converters  40 ,  44 , and  46  such that the reduced flow value may yield the same stroke positions as before for the valves (e.g. valves  26 ,  28 , and  29 ) not undergoing testing. 
     The process  80  may then continue with the controller  18  subtracting (block  86 ) the flow demand contribution of the valve (e.g. valve  27  as illustrated in  FIG. 4 ) undergoing testing from the total flow demand (e.g., percentage value of the flow demand for all of the valves  26 ,  27 ,  28 , and  29 ). Indeed, as the valve (e.g., valve  27 ) undergoing testing is closed (e.g., as part of the testing), the subtracted flow demand contribution of the valve undergoing testing may decrease while the total flow demand increases. Similarly, as the valve (e.g., valve  27 ) undergoing testing is opened (e.g., as part of the testing), the subtracted flow demand contribution of the valve undergoing testing may increase while the total flow demand decreases. Thus, the process  80  may conclude with the controller  18  generating a control signal to adjust (block  88 ) the flow demand contribution of each of the valves  26 ,  27 , and  29  not undergoing testing by deriving new stroke commands to transmit to each of the respective valves  26 ,  27 , and  29  based on the difference between the flow demand contribution of the valve (e.g., valve  27 ) undergoing testing and the total flow demand for each of the valves  26 ,  27 ,  28 , and  29  to collectively deliver to the turbine  12 . 
     Technical effects of the present embodiments include utilizing feed-forward valve flow compensation techniques to control fluid flow to a turbine configured according to one or more of a partial arc admission or a full arc admission. In certain embodiments, a controller may use control valve stroke and/or valve stem position information as feedback into a flow compensation control loop to maintain a total flow demand of the turbine during an operational testing (e.g., testing by opening, closing, and/or reopening of a valve) of at least one valve of a number of valves coupled to the turbine. Specifically, an operator, for example, may select a valve to undergo operational testing. Once selected, the controller may determine to remove the valve undergoing testing from closed-loop control and/or automatic control, and place the valve under open-loop and/or manual control. The remaining valves may then be re-calibrated to control the remainder of the total flow demand due to the loss of flow demand contribution of the valve undergoing testing. In one embodiment, a difference between the pre-testing flow demand contribution of the valve undergoing testing may be added to the total flow demand. In another embodiment, flow demand contribution of the valve undergoing testing may be directly subtracted from the total flow demand. In either case, the controller may determine a new valve stroke and/or valve stem position for each of the remaining valves under closed-loop control (e.g., valves not currently undergoing testing) to maintain the total flow demand of the turbine. Indeed, the present embodiments may allow for feed-forward flow compensation for valve and turbine partial arc admission configurations, as well as full arc admission configurations. 
     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 languages of the claims.