Systems and methods of droop response control of turbines

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.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to industrial control systems, and more specifically, to droop response control industrial control systems for turbines.

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

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.

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.

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.

DETAILED DESCRIPTION OF THE INVENTION

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.

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.

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 system10illustrated inFIG. 1. As depicted, the system10may include a gas turbine system12, a generator14, a power grid16, and a controller18. The gas turbine system12may further include a combustor20, a turbine22, a compressor26, and an intake28. The combustor20may receive fuel that may be mixed with air, for example, to create combustion in a chamber within the combustor20. The combustor20may create hot pressurized exhaust gases. The combustor20may then direct the exhaust gases through the turbine22toward one or more exhaust outlets. Thus, the turbine22may be part of a rotor. As the exhaust gases pass through the turbine22, the gases may force turbine blades to rotate a drive shaft24along an axis of the gas turbine system12. As will be discussed in further detail, the drive shaft24may be coupled to various components of the system10, including not only components of the gas turbine system12, but also the generator14. 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 system12, the generator14, and the drive shaft24to control droop of the gas turbine system12, as will be discussed in more detail with respect toFIG. 2below.

The drive shaft24may include one or more shafts that may be, for example, concentrically aligned. The drive shaft24may include a shaft connecting the turbine22to the compressor26to form a rotor. Similarly, the compressor26may include blades coupled to the drive shaft24. Thus, rotation of turbine blades in the turbine22causes the shaft connecting the turbine22to the compressor26to rotate blades within the compressor20. Such a mechanism may compress air in the compressor20. The rotation of blades in the compressor26may compress air that may be received via the air intake28. The compressed air may be fed to the combustor20and mixed with fuel, for example, to allow for higher efficiency combustion. In certain embodiments, the gas turbine system12may also generate mechanical power to drive the generator14to produce electrical power for the power grid16.

The gas turbine system12may 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 system10. The sensors and field devices may include, for example, inlet sensors and field devices30and outlet sensors and field devices32(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 generator14may also include a number of sensors and field devices30and32. The inlet sensors and field devices30and outlet sensors and field devices32may also measure environmental (e.g., ambient) conditions of the gas turbine system12and the generator14.

For example, the inlet sensors and field devices30and outlet sensors and field devices32may measure the ambient temperature, ambient pressure, humidity, and air quality (e.g., particulate in air). The inlet sensors and field devices30and outlet sensors and field devices32may also measure engine parameters related to the operation and performance of the gas turbine system12, 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 turbine22exhaust pressure. Further, the sensors and field devices30and32may 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 controller18may 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 system12(e.g., turbine22, compressor26, intake28) and the generator14, and by extension, the electrical power output to the power grid16.

In certain embodiments, the generator14may 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 grid16. In certain embodiments, variations in operating frequency of the power grid16may indicate that the power generation supply to the power grid16is inadequate to meet the load demand on the power grid16, or otherwise that the power generation supply to the power grid16is more than the load demand on the power grid16. 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 system12, and by extension the speed of the generator14, to compensate for the frequency variations on the power grid16. Such a control mechanism may generally be referred to as the “droop response” of the gas turbine system12. Specifically, the droop response of the gas turbine system12, and by extension the generator14, may be determined in terms of the percent frequency variation relating to a 100% change in gas turbine system12power output. For example, in one embodiment, the gas turbine system12and the generator14may be controlled to operate with a 4% droop response. That is, the power output of the gas turbine system12gas turbine load output may experience a 100% change for a 4% variation in frequency of the power grid16. Thus, a 4% droop variation may correspond to a change gas turbine system12output of 25% per each 1% power grid16frequency change (e.g., per each 1% turbine shaft24speed change since the power grid16frequency and turbine22speed may be proportional with respect to each other). As will be further appreciated, the droop response of the gas turbine system12may be controlled to compensate for variations in frequency and/or load of the power grid16. Further, the droop of the gas turbine system12may be controlled irrespective of the ambient conditions (e.g., temperature, pressure, and so forth) and load level of the gas turbine system12.

As previously noted, the system10may also include the controller18. The controller18may suitable for generating and implementing various control algorithms and techniques to control droop response of the gas turbine system12. The controller18may also provide an operator interface through which an engineer or technician may monitor the components of the power generation system10such as, components of the gas turbine system12and the generator14. Accordingly, the controller18may 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 controller18. In certain embodiments, the controller18may 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 controller18may further support one or more industrial communications (e.g., wired or wireless) protocols such as, Hart and/or Wireless Hart. For example, the controller18may support GE Energy GE ControlST, which may assign and distribute configuration tools and similar control data to various field equipment and devices.

As such, the controller18may be communicatively coupled to the inlet and outlet sensors and field devices30and32, gas turbine system12, and the generator14. The controller18may 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 controller18. Indeed, in certain embodiments, the controller18may support one or more droop response control systems and/or algorithms, such as a droop response control system34.

Accordingly,FIG. 2is a schematic diagram of an embodiment of a droop response control system34. The droop response control system34may be included as part of the controller18, and may further include a droop response system36and a multivariable droop response correction system38. Particularly, the droop response control system34may be a software system, a hardware system, or a combination thereof. The droop response control34may be used to control droop response, such that the gas turbine system12power output, and by extension the power output of the generator14, is adjusted according to variations in electrical frequency of the power grid16. Specifically, the droop response control system34may monitor the frequency (e.g., received by the controller18) of the power grid16or the speed of the generator14, and adjust the fuel flow to the gas turbine system12and the output of the generator14according to the degree of frequency variation from the nominal frequency (e.g., 60 Hz) of the power grid16. For example, for a 0.1 Hz frequency increase (e.g., 60.1 Hz indicating that the power generation supply to the power grid16is more than the load demand on the power grid16), the fuel flow and/or intake28of the gas turbine system12may be decreased to a reduced power output to maintain balance between the gas turbine system12, the generator14, and the power grid16of the system10. 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 grid16is less than the load demand on the power grid16), the fuel flow and/or intake28of the gas turbine system12may be increased to a greater power output to maintain balance between the gas turbine system12, the generator14, and the power grid16of the system10.

As depicted, the droop response system36may include a turbine speed/load reference input40and operating frequency input42. As previously noted with respect toFIG. 1, the inputs40and42may be received by the controller18via, for example, the inlet sensors and field devices30and outlet sensors and field devices32or other devices. As it may be worth noting, the frequency input42may be an electrical frequency measured directly from the power grid16, or derived based on the speed of the shaft24coupled to the gas turbine system12and the generator14. Specifically, the turbine speed/load reference input40may be the turbine26speed 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 input42may be represented as percentage value, in which each 1% variation in power grid16frequency may correspond to a 25% change in power output (MW) of the gas turbine system12. Thus, as illustrated, a difference of the inputs40and42may be computed to calculate a speed/load error percentage, which may be multiplied by a fuel command constant gain46. The fuel command constant gain46may 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 gain46may be then combined with the fuel command constant48(e.g., the fuel command at full-speed of the generator14) to derive a nominal fuel flow command, which may be then passed to a clamp50. 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 system12to adjust the fuel flow to the gas turbine systems12, and by extension, control the droop response of the gas turbine system12.

However, because the power output of the gas turbine system12may depend upon the ambient operating conditions (e.g., compressor26inlet temperature and pressure, turbine22temperature) and the load level of the gas turbine system12, certain errors may occur in the droop response control of the gas turbine system12. For example, as a 1% power grid16frequency variation may necessitate a 10 MW adjustment in gas turbine system12power 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 grid16frequency 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 system12and generator14failing 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, it may be useful to provide a multivariable droop response correction system38. Indeed, the multivariable droop response correction system38may adjust the normal fuel flow command, such that for a given variation in frequency of the power grid16, the droop power response may be irrespective of the ambient operating conditions (e.g., compressor26inlet temperature and pressure, turbine22temperature) and the load level of the gas turbine system12. Thus, the multivariable droop response correction system38may enable the frequency droop response of the gas turbine system12to be consistent and repeatable throughout, for example, periods of quality assurance (QA) testing, safety integrity level (SIL) testing, operation, and the like.

As illustrated, similar to the nominal droop response control system36, the multivariable droop response correction system38may include a fuel flow control loop, which may include the turbine speed/load reference input40and operating frequency input42. The inputs40and42may be summed (e.g., subtracted) and divided by a droop constant52(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 estimator54. An output of the load estimator54may 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 generator58. Also inputted to the droop response correction factor generator58may be a compressor26inlet temperature (or ambient temperature) input60via a lag filter62(e.g. first-order). The lag filter62may be included to filter undesirable signal distortions that may be present in the compressor26inlet temperature input60. It should be appreciated that any errors relating to the input60may be determined by the droop response correction factor generator58, or may, for example, be compared to a reference value during the period the input60is passed through the lag filter62.

In certain embodiments, the droop response correction factor generator58may 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., compressor26inlet temperature and pressure, turbine22temperature) and the load level and/or power output (MW) of the gas turbine system12. Specifically, the droop response correction factor generator58may be loaded with a series of off-line calculated correction factors corresponding to the gas turbine system12calculated load level and the compressor26inlet temperature input60. Thus, the droop response correction factor generator58may output correction factors for the fuel flow command based on the ambient operating conditions and the load level of the gas turbine system12. An initial correction factors output may be passed to a clamp63to adjust the correction factors between predetermined upper limit64and lower limit66.

In certain embodiments, the correction factors output may then be passed to a selector68, which may be used to alternatively (e.g., user-configurably) select between enabling the multivariable droop response correction system38via an enable input70. Enabled, the multivariable droop response correction system38may output a final correction factors output that may be multiplied by the nominal fuel flow command of the droop response system36to produce a droop response fuel flow command such that the droop power response of the gas turbine system12is invariant with respect to the ambient operating conditions and the load level of the gas turbine system12. In other words, for any variation in power grid16frequency, the droop response of the gas turbine system12may be substantially commensurate with the frequency variation. As such, a 1% power grid16frequency variation, for example, may warrant a substantially 10 MW adjustment in gas turbine system12power 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 system12. On the other hand, if the enable input70is not enabled, a correction factor unity constant input72(e.g., value 1) may be passed to the selector68, 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 system36.

As a further illustration of the presently disclosed techniques,FIG. 3displays a plot diagram80illustrating an embodiment of multivariable correction droop response control, as discussed above with respect toFIG. 2. The plot diagram80may include droop response plots82and84depicting the droop response of the gas turbine system12. The droop response plot82represents a droop response dependent upon gas turbine system12ambient conditions. As illustrated by response plot82, the power output (MW) of the gas turbine system12may vary inversely with the ambient temperature of the gas turbine system12. 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 system12may decrease during that time period. As previously noted, this may result in the gas turbine system12and generator14failing 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 plot84as illustrated may be invariant with respect to ambient conditions. Indeed, the response plot84may 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 plot82.

Turning now toFIG. 4, a flow diagram is presented, illustrating an embodiment of a process90useful in generating multivariable correction factors for droop response control, by using, for example, the controller18included in the power generation system10depicted inFIG. 1. The process90may 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 controller18. The process90may begin with the controller18receiving (block92) the gas turbine system12operating parameters. As previously discussed, the multivariable droop response correction system38of controller18may receive operating parameters (e.g., turbine22and compressor26inlet temperature and pressure) of the gas turbine system12based 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 shaft24coupled to the gas turbine system12and the generator14, or the electrical frequency of the power grid16. The process90may then continue with the multivariable droop response correction system38of the controller18generating (block98) droop response correction factors of the calculated load level and the compressor26inlet temperature (or ambient temperature), or various other operating parameters of the gas turbine system12. For example, as previously noted, the multivariable droop response correction system38of the controller18may 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 system38of the controller18may then output (block100) a fuel flow command based on the generated droop response correction factors. The fuel flow command may be used by the controller18to adjust (block102) one or more control effectors (e.g., actuators, valves, and the like) coupled to the gas turbine system12. For example, one or more actuator control signals may be generated by the controller18to control, for example, the fuel flow to the gas turbine system12.

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.