Abstract:
A tangible non-transitory computer readable medium may include instructions to analyze a first signal indicative of a speed of a turbine system and transform the first signal into a second signal. The tangible non-transitory computer-readable medium may also include instructions to transmit the second signal to control a speed of the turbine system by actuating a field device. Actuating the field device may include controlling a fluid level in a torque converter mechanically coupled to the turbine system, and the speed may be below a minimum setpoint of the turbine system.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates to turbomachinery systems. Specifically, the embodiments described herein relate to controlling the speed of a turbine in a turbomachinery system. 
         [0002]    In a turbomachinery system, such as a gas turbine system, a starting motor and torque converter may be coupled, for example, in series to the turbine to accelerate the turbine. The starting motor provides an input torque to the torque converter, which converts the input torque to an output torque that is provided to the turbine and causes a turbine shaft to rotate. The torque converter contains guide vanes, with the position of the guide vanes determining the amount of torque that is converted and subsequently the speed of the turbine. A control system in the turbomachinery system may control the starting motor and torque converter to manage the turbine speed according to a desired acceleration profile or steady-state condition. 
         [0003]    In current turbomachinery systems that employ a starting motor and torque converter, once the system has started operation and the torque converter has been filled with fluid, there may be a minimum threshold for the turbine speed. This minimum speed may be defined by the drive line mechanical limitations of the turbine and may be met when the guide vanes of the torque converter are closed to a minimum position (e.g., minimum setpoint). However, there may be situations in which it would be beneficial to reduce the speed of the turbine further below the minimum setpoint. For example, in emergency situations, it may be useful to reduce the turbine speed below the minimum instead of performing a complete shutdown of the turbomachinery system. In another example, reducing the turbine speed below the minimum setpoint may provide an opportunity to gather validation and testing data (e.g. stall validation and compressor mapping) that may be useful to operators and engineers in making informed decisions. Additionally, reducing the turbine speed below the minimum setpoint may extend the operating range of the turbomachinery system such that it can support low to medium loads or be used in off-duty conditions. 
       BRIEF DESCRIPTION 
       [0004]    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. 
         [0005]    In a first embodiment, a system may include a turbine system configured to produce power and a starting motor configured to rotate a first shaft included in the turbine system. The system may also include a torque converter mechanically coupled to the first shaft and mechanically coupled to the turbine system. Finally, the system may include a control system that includes a processor configured to control a speed of the turbine system by controlling a fluid level in the torque converter to arrive at a first turbine system speed below a minimum setpoint. 
         [0006]    In a second embodiment, a system may include a controller that includes a processor configured to receive a first signal indicative of a speed of a turbine system and transform the first signal into a second signal. The processor may also be configured to transmit the second signal to control a desired speed of the turbine system by actuating a field device. Actuating the field device may include controlling a fluid level in a torque converter mechanically coupled to the turbine system to arrive at the desired speed, wherein the desired speed is below a minimum setpoint of the turbine system. 
         [0007]    In a third embodiment, a tangible non-transitory computer readable medium may include instructions to analyze a first signal indicative of a speed of a turbine system and transform the first signal into a second signal. The tangible non-transitory computer-readable medium may also include instructions to transmit the second signal to control a speed of the turbine system by actuating a field device. Actuating the field device may include controlling a fluid level in a torque converter mechanically coupled to the turbine system, and the speed may be below a minimum setpoint of the turbine system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    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: 
           [0009]      FIG. 1  is a block diagram illustrating a turbomachinery system, in accordance with an embodiment of the present approach; 
           [0010]      FIG. 2  is a cross-sectional torque converter included in the turbomachinery system of  FIG. 1 , in accordance with an embodiment of the present approach; 
           [0011]      FIG. 3  is a block diagram illustrating a control system in the turbomachinery system of  FIG. 1 , in accordance with an embodiment of the present approach; 
           [0012]      FIG. 4  is a flowchart depicting a method for reducing the speed of a turbine in the turbomachinery system of  FIG. 1 , in accordance with an embodiment of the present approach; and 
           [0013]      FIG. 5  is a block diagram depicting a particular step in the method of  FIG. 4 , in accordance with an embodiment of the present approach. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    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. 
         [0015]    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. When a set of guide vanes is described as closed, it is intended to mean that the blades of the guide vanes are positioned at a relatively small angle. When a set of guide vanes is described as open, it is intended to mean that the blades of the guide vanes are positioned at a relatively large angle. The phrases “minimum drive line mechanical speed,” “minimum setpoint,” and “minimum speed” may all refer to a minimum speed of a turbine when associated guide vanes are closed. 
         [0016]    Present embodiments relate to systems and methods for controlling turbine speed in turbomachinery systems. Specifically, the embodiments described herein relate to reducing turbine speed below a minimum setpoint determined by the drive line mechanical limitations of the turbine. The techniques described herein relate to a full or partial drain of fluid from a torque converter within the turbomachinery system that, in conjunction with a starting motor, accelerate the turbine. The techniques may include automatically draining and/or refilling of the fluid in the torque converter once the desired speed is reached. By providing systems and methods to reduce turbine speed below the associated minimum setpoint, the present embodiments may provide an alternative to a complete shutdown of the turbomachinery system, for example, in emergency situations, add opportunities to capture validation and testing data at low speeds, and extend the operating speed range of the turbomachinery system to include off-duty situations and low to medium loads, among other things. 
         [0017]    With the foregoing in mind,  FIG. 1  illustrates a turbomachinery system  10  that may be used to provide power to a load, such as an electric generator, a mechanical load, and so on. The turbomachinery system may include a starting motor  12 , a torque converter  14 , a turbine  16 , a control system  18 , and a fluid supply  20 . The starting motor  12  may be an electric, pneumatic, or hydraulic motor or any other suitable device for rotating a shaft. The torque converter  14  may include guide vanes  22  that may be used to directly and/or indirectly control certain aspects of the turbomachinery system  10 , such as the amount of torque provided by the torque converter  14  and the speed of the turbine  16 . The turbine  16  may be a gas turbine system, steam turbine system, hydro turbine system, wind turbine system, turbo expander system, or centrifugal pump system. For example,  FIG. 1  depicts a gas turbine  16  configured to generate power and/or electricity from the combustion of combustible materials (e.g., carbonaceous fuel). 
         [0018]    As shown in  FIG. 1 , the starting motor  12  may be coupled to the torque converter  14  via a torque converter (TC) input shaft  24 , and the torque converter  14  may be coupled to the turbine  16  via a TC output shaft  26 . The starting motor  12  may transmit an input torque to the torque converter  14  via the input shaft  24 . In the depicted embodiment, with the torque converter  14  filled with fluid, an angle (e.g., pitch) of the guide vanes  22  of the torque converter  14  may determine an amount of power the torque converter  14  draws from the starting motor  12 . Specifically, the starting motor  12  may not be able to transmit a relatively large input torque to the torque converter  14  if the guide vanes  22  are mostly closed but may be able to transmit the relatively large input torque to the torque converter  14  if the guide vanes  22  are substantially open or fully open. The control system  18  may control the angle of the guide vanes  22  such that the torque converter  14  does not draw too much power that may lead to undesired effects to the turbomachinery system  10 . 
         [0019]    The torque converter  14  may receive the input torque from the starting motor  12  and convert it to an output torque that is transmitted to the turbine  16 . The torque converter  14  may include an impeller  28 , a turbine  30 , and a stator  32  contained within a housing  34 . The torque converter may also contain fluid (e.g., oil) whose flow allows the torque converter  14  to operate. As such, the torque converter  14  may be coupled via a conduit  36  to the fluid supply  20 , and a fluid supply valve  54  may be used to control the amount and/or rate of fluid flow from the fluid supply  20  to the torque converter  14 . Further, as described below, the torque converter  14  may also be coupled to a fluid drain  38 , and a fluid drain valve  56  may be used to control the amount and/or rate of fluid flow from the torque converter  14  to the fluid drain  38 . 
         [0020]    It may be beneficial to describe further operations of the torque converter  14 . Accordingly, turning now to  FIG. 2 , the figure shows further details of an embodiment of the torque converter  14  shown in  FIG. 1 . In the depicted embodiment, the impeller  28  may be coupled to the TC input shaft  24  while the turbine  30  may be coupled to the TC output shaft  26 , as shown in the cross-sectional view of  FIG. 2 . The stator  32  may be disposed between the impeller  32  and the turbine  30 , but may not be directly coupled to either of the elements. During operation of the torque converter  14 , the impeller  28  may spin and “push” or bias the fluid against the turbine  30 , causing the turbine  30  and the TC output shaft  26  to spin. The stator  32 , which includes its own set of guide vanes  22 , may control the amount of fluid that the impeller  28  biases against the turbine  30 ; the movement of the stator  32  may determine how much of the fluid the guide vanes  22  redirects back to the impeller  28 . Once the fluid has been “pushed” against the turbine  30 , the stator  32  may move to allow the fluid to flow back to the impeller  28 . 
         [0021]    The control system  18  (shown in  FIG. 1 ) may control the angle of the guide vanes  22  to set the amount of torque converted by the torque converter  14  by directing fluid flow within the torque converter  14 . For example, when the angle of the guide vanes  22  is broad, fluid flow may be permitted such that a relatively substantial fraction of the fluid flows from the impeller  28  to the turbine  30  such that a substantial fraction of the input torque is converted to output torque. However, when the angle of the guide vanes  22  is shallow, the fluid flow may be restricted such that only a relatively small fraction of the fluid flows from the impeller  28  to the turbine  30  such that only a relatively small fraction of the input torque is converted to output torque. The output torque may be controlled by the control system  18  to control the speed of the TC output shaft  26 . 
         [0022]    Referring back to the turbomachinery system of  FIG. 1 , an additional starting motor and torque converter may be coupled in series to the starting motor  12  in some embodiments. The additional starting motor may have a substantially lower rating than the original starting motor  12 . As a result, the additional starting motor and torque converter may be used primarily for low to medium loads (e.g. starting the turbomachinery system  10 .) 
         [0023]    Turning now to  FIG. 3 , the control system  18  may generally manage various facets of the turbomachinery system  10 , such as controlling the angle of the guide vanes  22 . Accordingly, the control system  18  may include a processor  40 , memory  42 , display  44 , a user input device  46 , and a hardware interface  48  used by the processor  40  to communicate with sensors  50  and actuators  52 , as shown in the embodiment of  FIG. 3 . As depicted, the processor  40  and/or other data processing circuitry may be operably coupled to memory  42  to retrieve and execute instructions for managing the turbomachinery system  10 . For example, these instructions may be encoded in programs that are stored in memory  42 , which may be an example of a tangible, non-transitory computer-readable medium, and may be accessed and executed by the processor  40  to allow for the presently disclosed techniques to be performed. The memory  42  may be a mass storage device, a FLASH memory device, removable memory, or any other non-transitory computer-readable medium. Additionally and/or alternatively, the instructions may be stored in an additional suitable article of manufacture that includes at least one tangible, non-transitory computer-readable medium that at least collectively stores these instructions or routines in a manner similar to the memory  42  as described above. The control system  18  may also include the display  44  for a user to view various data regarding the turbomachinery system  10  and a user input device  46  (e.g., a keyboard, mouse, touchscreen, gesture input device, etc.) to allow the user to interact with the control system  18 . 
         [0024]    The control system  18  may also communicate with sensors  50  and actuators  52  via the hardware interface  48 . The control system  18  may monitor the current state of the turbomachinery system  10  using various sensors  50  such rotational speed sensors on the starting motor  12 , the input shaft  24 , the torque converter  14 , the output shaft  26 , and the turbine  16 ; fluid-level sensors in the torque converter  14 , the fluid supply  20 , and the fluid drain  38 ; and position sensors on the guide vanes  22 . Other sensors  50  may include pressure sensors, temperature sensors, clearance sensors (e.g., distance between stationary and rotary components), fluid flow sensors, and the like. The control system  18  may alter the state of the components of the turbomachinery system  10  by using actuators  52 ; these may include valves, pumps, positioners, inlet guide vanes, switches, and so on, useful in performing control actions. For example, referring back to  FIG. 1 , the control system  18  may control the fluid flow into and out of the torque converter  14  via a fluid supply valve  54  and a fluid drain valve  56  coupled to the fluid supply  20  and the fluid drain  38  respectively. The fluid supply valve  54  and the fluid drain valve  56  may be a solenoid or modulating valve. Alternately or additionally, the control system  18  may use actuators  52  to control the acceleration and deceleration rate of the fluid flow from the fluid supply  20  or to the fluid drain  38 . Further, the control system  18  may also use position sensors  50  on the fluid supply  46  and the fluid drain valve  56  to monitor the current position of the valves. 
         [0025]    In some embodiments, the control system  18  (excluding the sensors  50  and actuators  52 ) may be a single device, such as a bang/bang controller (e.g., hysteresis controller switching between two states), a proportional integral derivative (PID) controller, a model based controller (MBC), and/or a setpoint controller. For those embodiments, the control system  18  may be an autonomous controller within a larger distributed control system for the turbomachinery system  10 . In other embodiments, the control system  18  (including the sensors  50  and actuators  52 ) may be directed as part of a larger distributed control system for the turbomachinery system  10 . 
         [0026]    As mentioned above, among other things, the control system  18  may control the amount of power the torque converter  14  draws from the starting motor  12 , the amount of torque converted by the torque converter  14 , and the speed of the turbine  16 . To do so, the control system  18  may be configured to receive current condition data of the turbomachinery system  10 , determine a current input power supplied by the staring motor  12 , and determine a current output power supplied by the torque converter  14 . Specifically, the control system  18  may be configured to receive a control signal representative of the input torque and compare it to rating data of the starting motor  12 . The rating data of the starting motor  12  may be stored on the memory  42 . Based on the comparison, the control system  18  may adjust the angle of the guide vanes  22  to prevent the torque converter  14  from drawing undesired power from the staring motor  12  while still adhering as much as possible to a desired acceleration profile for the turbine  16 . In some embodiments, the control system  18  may also receive a control signal represent of the output torque and a control signal representative of turbine speed to use in determining the adjustment to the angle of the guide vanes  22 . 
         [0027]    For a turbomachinery system  10  that includes a starting motor  12  and torque converter  14 , there may be a minimum setpoint for the speed of the turbine  16 . Once the turbine  16  is turned on, the speed may not be lower than that setpoint without completely shutting down the turbine  16 . This minimum setpoint may be defined by the drive line mechanical limitations of the turbine  16  and may be met when the guide vanes  22  are closed. 
         [0028]    However, there may be several types of situations in which it may be useful to reduce the speed of the turbine  16  below the minimum setpoint. For example, it may be preferred to reduce the turbine speed below the minimum setpoint rather than completely shut down the turbomachinery system  10 . Reducing the speed of the turbine  16  may below the minimum setpoint may also provide an opportunity to capture validation and testing data (e.g. stall validation and compressor mapping) which may be provided to operators and engineers for more informed decision-making. Additionally, being able to reduce the turbine speed below the minimum setpoint may allow operators to extend the operating range of the turbomachinery system  10  to include off-duty situations and low to medium loads. 
         [0029]    To reduce the speed of the turbine  16  below the minimum setpoint, the control system  18  may drain fluid from the torque converter  14  via the fluid drain  38  to reduce the output torque. This may be a partial or complete drain. In one embodiment, the draining may occur only when the guide vanes  22  are closed. Depending on the type of fluid used, the fluid drained from the torque converter  14  may be “recycled,” that is, sent back to the fluid supply  20 . 
         [0030]      FIG. 4  illustrates an embodiment of a process  60  that the control system  18  may use to reduce the turbine speed below the minimum setpoint. The process  60  may be implemented as executable computer code stored in the memory  42  and executed by the processor  40 . At block  62 , the process  60  may have completely closed the guide vanes  22  such that the turbine  16  is at the minimum speed. Then, at decision  64 , the process  60  may determine whether the turbine speed should be reduced below the minimum setpoint. If the turbine speed should not be reduced below the minimum setpoint, then the process  60  may proceed back to block  62 . If the turbine speed should be reduced below the minimum setpoint, then the process  60  may proceed to block  66 , in which it drains some or all of the fluid from the torque converter  14  to achieve the desired speed. 
         [0031]    Referring now to  FIG. 5 , the process  60  may determine the amount of fluid to drain from the torque converter  14  based on a variety of inputs  74 , as shown in the figure. The inputs  74  may include, among other things, the properties of the fluid in the torque converter  14  (e.g. viscosity, density, etc.), the current fluid level of the torque converter  14 , the fill rate of the fluid, the drain rate of the fluid, the properties of the guide vanes  22  (e.g. the number and/or size of the blades), the speed of the turbine  16 , and the speed of the starting motor  12 . These values may be stored in memory  42  or may be determined using data from sensors  50 . For example, the properties of various types of fluids in the torque converter  14  may be stored in memory. In another example, the current fluid level of the torque converter  14  may be determined by monitoring the power of the turbine  16  (i.e., when the power is near 0 MW the torque converter  14  is fully drained) or by using a fluid level sensor or flow meter. The inputs  74  may additionally or alternatively include current positions of the fluid supply valve  54  and the fluid drain valve  56 . The control system  18  may process the inputs  74  to determine a new fluid supply valve position  76  and a new fluid drain valve position  78 , and may then move the fluid supply valve  54  and the fluid drain valve  56  to their new positions. 
         [0032]    Referring back to  FIG. 4 , once the process  60  has drained fluid from the torque converter  14  in block  66  and the turbine  16  has decelerated in block  68 , the process  60  may determine whether the turbine  16  has reached the desired speed in decision  70 . If the speed of the turbine  16  needs to be decreased further, the process  60  may proceed back to block  66  to drain more fluid from the torque converter  14 . If the desired speed of the turbine  16  has been reached, the process  60  may proceed to block  72 , at which it automatically fills the torque converter  14  to return the turbine  16  to the minimum setpoint speed before proceeding to block  62 . In some embodiments, the process  60  may automatically fill the torque converter  14  such that it returns to a nominal speed setpoint other than the minimum setpoint. In yet other embodiments, the process  60  may not refill the torque converter  14  until it determines that the speed of the turbine  16  should be increased. By filling and draining the torque converter  14  alternative to or in addition to controlling the guide vanes  26 , the techniques described herein may expand operations below a minimum drive line mechanical speed. 
         [0033]    Technical effects of the invention include systems and methods to reduce the speed of a turbine in a turbomachinery system below the minimum setpoint defined by the drive line mechanical limitations of the turbine. The present embodiments may provide an alternative to a complete shutdown of the turbomachinery system in certain situations, an opportunity to capture validation and testing data, and a way to extend the operating range of the turbomachinery system to include off-duty situations and low to medium loads, among other things. The technical effects and technical problems in the specification are exemplary and not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems. 
         [0034]    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.