Patent ID: 12218510

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are 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' 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 disclosure, 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. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

Power generation systems are used to convert energy sources into electrical power. The energy sources may be hydraulic, coal, natural gas, crude oil, nuclear, solar, or wind energy. Gas turbine (also called combustion turbine) power plants run on natural gas or liquid fuels. Gas turbine generators (GTGs) provide operational flexibility. For instance, the gas turbine is a type of internal combustion engine designed to meet increases in power demand quickly.

The main components in the GTG include an upstream rotating compressor(s), a combustor, downstream turbine(s) on the same shaft as the compressor(s), and a generator. Gas turbines are engines used for producing movement to turn electrical generators. The gas turbines are combustion engines that convert natural gas or liquid fuels to rotational mechanical energy, which further drives the generators to produce electrical energy. More specifically, the gas turbines draw in air, compress the intaken air, mix the air with fuel, distribute the air-fuel mixture into a combustor where combustions (triggered by ignitions) of the air-fuel mixture create hot pressurized gases to cause turbine blades to spin. The spinning of the turbine blades drives the generator that is connected (e.g., via a shaft) to the turbine blades to convert rotational energy into electricity.

Industrial facilities, such as factories, electric power plants, offshore oil platform or drilling rigs, may use multiple GTGs operating in a parallel configuration to maintain reliable electrical power supply levels. Systems using multiple GTGs may synchronize the GTGs where the GTGs are operating in parallel. As part of the synchronization, load sharing distributes and shares the load (e.g., proportionally/evenly) throughout the GTGs in the fleet. At least some of the GTGs in the fleet may have independent controllers communicating with a centralized controller (master controller). The master controller may manage the parallel tasks (including the load sharing) for the fleet. When the master controller is offline due to technical/environmental problems (e.g., troubleshooting, maintenance, or extreme weather event), the parallel tasks may be switched to manual operations executed by onsite operator(s) (e.g., using a switchboard configuration) or to a backup centralized controller, if available. However, using manual operations or backup centralized controller may increase the operational complexity that may result in reduced efficiency and/or increased cost.

The subject matter discussed herein relates to a load sharing modules that may be used to maintain stable operations of a group of GTGs in different load sharing scenarios. The reusable and flexible load sharing modules, located in one or more of the GTGs, are configured to select a control mode (such as a droop mode or an isochronous mode) of the respective GTG. The control modes are based on a status and/or other relevant information shared through communications among the GTGs in the group via an interconnection data bus. Therefore, a centralized controller or hierarchical control system for parallel tasks such as load sharing may be omitted and/or operations may continue when communications with the centralized controller fails. Additionally or alternatively, the load set point and other operation preference may be set by a third-party controller.

Turning now to the drawings,FIG.1is a block diagram of an embodiment of a gas turbine system10. As an example, the gas turbine system10may be part of a combined cycle system and/or combined with other gas turbine systems10to power one or more loads12. Specifically, the gas turbine system10is generally configured to drive the load12by combusting a mixture of compressed air and fuel15(e.g., natural gas, light or heavy distillate oil, naphtha, crude oil, residual oil, or syngas). The combustion is performed within a combustor16, which may include one or more combustion chambers. Air14goes into an air intake at the compressor20, is filtered, and is compressed in the compressor20via one or more compression stages.

To begin the combustion process within the combustor16, the air14is injected into the compressor20through a compressed air stream18. The compressed air stream18is mixed with fuel15. Using the mixture of the fuel15and the air14, ignition may occur. The ignition produces hot combustion gases26that power the gas turbine system10. More specifically, the hot combustion gases26flow through a turbine28with one or more compression stages that drives the load12via a shaft30. For example, the combustion gases26may apply motive forces (e.g., via convection, expansion, and the like) to turbine rotor blades within the turbine28to rotate the shaft30. In an example process, the hot combustion gases26may force turbine blades in the turbine28to rotate the shaft30along an axis of the gas turbine system10. As illustrated, the drive shaft30may be connected to various components of the gas turbine system10, including the compressor20or the load12.

As previously noted, the drive shaft30may connect the turbine28to the compressor20to form a rotor. The compressor20may include compressor blades coupled to the drive shaft30. Thus, rotation of turbine blades in the turbine28may cause the drive shaft30connecting the turbine28to the compressor20to rotate the compressor blades within the compressor20. This rotation of compressor blades in the compressor20causes the compressor20to compress air14to generate the compressed air stream18. As previously noted, the compressed air stream18is then fed to the combustor16and mixed with other combustion components. The shaft30may drive the compressor20in addition to or in lieu of the load12. As an example, the load12may be a generator of the GTG. Additionally or alternatively, the load12may include a propeller, a transmission, or a drive system, among others.

Once the turbine28extracts work from the hot combustion gases26, a stream of exhaust gas32may be provided to an exhaust section34, where the exhaust gas32may be cooled or further processed. For example, the exhaust section34may include a catalyst section36which includes a carbon monoxide (CO) catalyst, a NOx catalyst, an unburned hydrocarbon catalyst, and/or any similar metal-based catalyst (e.g., platinum-based catalysts). For example, in the illustrated embodiment, the catalyst section36may include a NOx catalyst that is configured to destroy NOx gases within the stream of exhaust gas32or a CO catalyst. The stream of exhaust gas32may then exit the exhaust section34.

As illustrated, gas turbine system10includes a controller38. The controller38may include one or more processors66and memory68, which may be used collectively to support an operating system, software applications and systems, and so forth, useful in implementing the techniques described herein. Particularly, the controller38may include code or instructions stored in a non-transitory machine-readable medium (e.g., memory68) and executed, for example, by the one or more processors66that may be included in the controller38. The processor(s)66may receive parameters of operation from the various components (e.g., via one or more sensors) of the gas turbine system10including a shaft rotation speed, a frequency of electric power generated by the gas turbine system in a generator driven by the shaft30, a voltage of the generated electric power, a demand from one or more load(s)12, or other suitable parameters. In some embodiments, some parameters are measured directly while other parameters are determined indirectly from other measurements. For example, in certain embodiments, the controller38may utilize an algorithmic model or look-up table (e.g., stored in memory) to derive various parameters. The various parameters may include an operating speed of the shaft30or a connected GTG using electrical parameters. The electrical parameters may include a frequency or voltage of the electric power generated by the generator (e.g., the load12). Further, the controller38may monitor operation of various parts of the gas turbine system10. The monitored parameters may be used to control (e.g., adjust) operating parameters of one or more aspects of the gas turbine system10.

As illustrated, the controller38includes a load sharing (LS) module39that may monitor and analyze the shared operational data (such as online/offline status, output power, frequency, or voltage, and the like) from the other online power generation systems (e.g., gas turbine generators) existing on the same power grid as the gas turbine system10. Based on the monitoring and analysis, the load sharing module39may determine a suitable control mode (e.g., droop speed control mode) and/or an appropriate set point (e.g., frequency or voltage) that may contribute to stable operation of the gas turbine system10and/or connected grid(s). The load sharing module39may then cause the controller38to select the determined control mode and/or set point for the gas turbine system10.

The controller38may receive the shared operational data from controllers of other power generation systems within multiple power systems (e.g., a set of gas turbine systems). The load sharing module39may include a physical circuit or may be at least partially embodied using the instructions stored in the memory68and running on the processor66of the controller38.

Load sharing may be defined as a proportional division of the total load (e.g., in kilo-Watt (kW) or kilo-Volt-Ampere-Reactive (KVAR)) between multiple power generation systems on a power grid. Through intercommunications (e.g., via the controllers38) among group(s) of GTGs serving a power grid, coordinated adjustments may be made to distribute and share the load of the power grid proportionally throughout the online GTGs. For example, when the load of the power grid increases, at least some of the online GTGs may increase power output with equal percentage to accept the load change. For example, a group of GTGs may operate in parallel to provide power for an offshore drilling platform. When one of the group of GTGs is offline, the other online GTGs may receive the offline signal through intercommunications, causing the controller(s) to calculate feasible new load distributions among the online GTGs, and increase the power output proportionally if the calculated new load distribution does not exceed a power rating of the online GTGs within the group. Additionally or alternatively, the controller(s) may invoke backup GTG(s) to share the load if the calculated new load distribution exceeds the power rating(s) of one or more online GTGs within the group.

Load sharing may be used by a power grid with multiple power generation systems and various loads to avoid overloading and/or stability problems. As previously noted, for tasks (such as load sharing) within the multiple power systems, the load sharing module39monitors the data from each of the fleet members even without a centralized controller and determines an appropriate way to contribute to a stable operation. In other words, the control mechanism described herein provides a distributed control system. The controller(s) (e.g., the controller38) of two or more individual power generation systems receives an operating status and other relevant information from other power generation systems. The controller(s) of individual power generation system may make adjustment(s) based on the information provided by the other power generation systems. Such control mechanism enables flexible operations of the multiple power systems. For example, operations of one or more power generation systems (e.g., gas turbine system10) may be adjusted to fit particular demands of gas turbines or site operations under normal and/or abnormal conditions, such as adjusting start or shutdown sequences and/or tying breaker operations.

As a reusable and flexible module, the load sharing module39may be pre-installed in the controller38during manufacturing of the gas turbine system10, or may be post-installed in a controller of an existing power generation system (e.g., a backup gas turbine system for the multiple power systems) as a retrofit kit and/or software update. In one or more embodiments, implementation of the load sharing module39may involve no extra instrumentation than the already existing in a power generation system, enabling the any respective controllers38of power generation systems to perform the techniques discussed herein (e.g., with a software update).

The distributed power generation systems may use one of the following modes of operation: stand-alone operation, parallel operation with connection to a utility grid, and island operation. Each operation mode may be associated with specific controls for gas turbines (e.g., gas turbine fuel control) and/or for power generators (e.g., generator excitation control) within the power grid.

With the preceding in mind,FIG.2depicts a power grid system100including a multiple gas turbine generators (GTGs) and respective GTG controllers. Each of the GTGs may operate in a specific mode (stand-alone, parallel or island) depending on power grid configurations, loads, electrical switch (or breaker) states, etc. All three modes of operation are possible due to opening/closing certain electrical switches in the configuration of the power grid system100.

As illustrated, the power grid system100may include a main grid160(e.g., a utility grid), a local grid150, and a power generator grid140. The power generator grid140may include multiple GTGs102,112,122, and132, and respective GTG controllers104,114,124, and134. Any number (e.g., all) of the GTG controller104,114,124, and134may include the load sharing module39as described inFIG.1. The power grid system100may include an interconnection data bus170that is used to handle communications among the GTG controllers104,114,124, and134. Various electrical switches106,116,126,136,152, and162may be used to toggle connections in the power grid system100.

In stand-alone operation, a GTG is not connected with other GTGs and/or the main grid160. For example, as illustrated inFIG.2, when the electrical switches152and106are closed and the switches162,116,142,126, and136are open, the GTG102operates in a stand-alone operation. As an isolated power generation unit, the GTG102supplies power to connected loads on the local grid150.

In one or more embodiments, a GTG working alone may be an emergency GTG when the local grid150loses power from one or more GTGs assigned to the local grid150. For instance, in the example described above, the GTG102may start providing power for the local grid150, which lost power from an assigned group of GTGs (e.g., GTGs122and132). The stand-alone operation may include features such as controlling gas turbine fuel (e.g. the fuel15inFIG.1) supply to raise/lower the output of the GTG102, controlling excitation current to raise/lower the voltage output of the GTG102, and other power management related procedures (e.g., keeping bus frequency and voltage constant for certain control modes), etc. In stand-alone operation, the total loads on the local grid150determines the GTG102output power.

In a parallel operation mode, the GTGs102,112,122, and132operate in parallel to provide power to the main grid160and to the local grid150. In some embodiments, the main grid160may be considered an infinite bus. For example, as illustrated inFIG.2, when all the electrical switches162,152,106,116,142,126, and136are closed, the GTGs102,112,122and132enter into the parallel operation. Running in parallel, the GTGs102,112,122and132supply power to loads on the local grid150and/or the main grid160.

In one or more embodiments, GTGs working in parallel operation may be organized into one or more subgroups of GTGs in a power plant. For instance, in the example described above, the GTGs102and112may form a subgroup A, and the GTGs122and132may form another subgroup B in the power plant. The two subgroups may work together to provide power for the local grid150and the main grid160or work when at least one of the subgroups are offline (e.g., due to maintenance). The parallel operation may include features such as controlling a gas turbine fuel supply to raise/lower active power of the GTGs102,112,122, and132, controlling excitation current to raise/lower the reactive power of the GTGs102,112,122, and132, controlling the difference between total power plant loads and GTG output power, and other power management related procedures (e.g., keeping power constant), etc. In parallel operation, the main grid160determines the operation parameters such as the frequency output, voltage output, and speed.

In an island operation, a GTG (e.g., GTGs102,112,122, and132) is connected with other GTGs, but the GTG is decoupled from the main grid160. For example, as illustrated inFIG.2, when the electrical switches162and136are open and the other electrical switches152,106,116,142, and126are closed, the GTGs102,112, and122operate in an island operation. Running in parallel, the GTGs102,112, and122supply power to all connected loads on the local grid150.

In one or more embodiments, a group of GTGs working in the island operation may supply power to an isolated system such as a ship, an offshore drilling platform, or an oil production field in a desert. For instance, in the example described above, the GTG102and112may form a set of GTGs in a local power plant on an offshore drilling platform to provide power for the local grid150that may include all electrical devices/machines/equipment on the offshore drilling platform. At least one GTG (e.g., GTG122) may serve as a backup GTG for emergency use only when one or more of the other GTGs (e.g., GTG102and112) is offline). The island operation may include features such as controlling the gas turbine fuel to raise/lower the GTGs active power and bus frequency, controlling the excitation current to raise/lower the GTGs reactive power and bus voltage, and other power management related procedures (e.g., keeping bus frequency and voltage constant while sharing the load proportionally or cost-efficiently among the operating GTGs), etc. In island operation, the total loads on the local grid150may determine the sum of the power to be generated using operating GTGs.

To share information among a group of operating GTGs (either in the parallel operation or in island operation), the interconnection data bus170is used to handle communications among the GTGs102,112,122, and132via GTG controllers104,114,124, and134. The interconnection data bus170may include multiple cables/wires (such as coax signal cables, Ethernet cables, and the like) and/or wireless connections, which carry signals containing information related to load sharing using any suitable communication protocol for communicating between controllers38of the GTGs102,112,122, and132. The load sharing information may include identification information for respective GTG or GTG controller ID, online/offline operating status information of respective GTGs, power output information for the respective GTGs, GTG configuration information (e.g., maximum power output), and the like. The interconnection data bus170serves as a common highway for communications through which the GTGs102,112,122, and132share statuses and relevant information with the others via GTG controllers104,114,124, and134.

The controller38in each of the GTGs102,112,122, and132may use one or more processors66to receive transmitted signals from the interconnection data bus170and store received information in the memory68. The controller38of GTG may use the load sharing module39to monitor and analyze the operational data from the other online GTGs on the same grid and determine a control mode (e.g., droop mode, or isochronous mode) that may contribute to a stable operation of the entire grid. The load sharing module39may then cause the controller38to select the determined control mode for the specific GTG. Furthermore, after the new control mode or new set point is applied to the specific GTG, the controller38may use the load sharing module39to monitor the operational data from the other GTGs to evaluate/verify performance of the group of operating GTGs.

Each operation mode (e.g., stand-alone, parallel or island) of a power generation system on the power grid system100may be associated with specific control mode(s) for a group of GTGs within the power grid100. As described previously, using the stand-alone load sharing module39in a control mechanism enables flexible operations of a group of GTGs. The flexible operations may include droop speed control mode for GTGs, isochronous speed control mode for GTGs, and/or other power control methods to accommodate different island topologies and events transitions, such as GTGs and/or other relevant units coupling to or decoupling from the power grid100). Controlling power and speed for a group of GTGs relies on a coordinated effort based on a power demand on the group of GTGs, a number of GTGs available, parallel or island operation with particular topologies, and/or other relevant information especially during transient conditions and islanding events. Without coordination multiple GTGs operating in parallel may be subjected to unstable operations, for example, over-speed, losing speed reference, erratic power fluctuations, etc. Such unstable operations may cause unexpected power outages and/or lead to possible damage to GTGs or units on the power grid100.

FIG.3is a graph plotting active power202v. frequency204for an isochronous speed control mode that may be used by the multiple GTGs ofFIG.2. For alternating current (AC) generators (including GTGs), the frequency (in Hz) is directly related to the speed (in RPM). As illustrated, in the isochronous speed control mode, a frequency line220of a GTG returns to an original set point line210(e.g., 50 Hz) after a load has been applied or rejected.

The isochronous speed control mode may be used when a GTG is in stand-alone operation, or the GTG is the largest (in power) unit in multiple GTGs (e.g., in the island operation). In the isochronous speed control mode, the energy generated by the prime mover (e.g., the gas turbine28in the gas turbine system10) is regulated tightly in reaction to load changes. For example, an instant load increase (e.g. when a new load is added into an existing power grid) may cause a transient frequency decrease, but because energy is quickly regulated for the prime mover in the isochronous speed control mode, the frequency remains at or quickly returns to a set point. Likewise, an instant load decreases (e.g. when an existing load is removed from an existing power grid) may cause a transient frequency increase, but because the energy is quickly regulated for the prime mover in the isochronous speed control mode, the frequency is maintained at or quickly returned to the set point.

In other words, in the isochronous speed control mode, a GTG maintains a relatively constant speed regardless of the load changes. Certain issue(s) (such as instability) may arise when multiple GTGs in the isochronous speed control mode are operating on the same grid and the load changes frequently. For example, inFIG.2, when the electrical switches162,152,106and116are closed, the GTG102and112provide power in parallel to the main grid160. The main grid160may determine the frequency and voltage of the power generated by the GTG102or112. When the speed set point is slightly lower, the controller38may cause a speed governor of a prime mover (e.g., the gas turbine28) to adjust the gas turbine fuel supply (e.g., fuel15) to lower the speed. Similarly, when the speed set point is slightly higher, the controller38may cause the speed governor of the prime mover to at least partially open the gas turbine fuel supply to raise the speed. Therefore, the power grid may experience relatively small but frequent fluctuations of frequency as the load changes frequently.

When multiple GTGs are operating in parallel, a droop speed control mode may be used to avoid issues such as the fluctuations of frequency as load changes.FIG.4is a graph plotting active power202v. frequency204for a droop speed control mode that may be used by the multiple GTGs ofFIG.2. As illustrated, in the droop speed control mode, the frequency line220of a GTG decreases by a fixed percentage when the GTG is loaded from no-load (0%) to full load (100%). The fixed percentage (e.g., 4%) may be pre-determined based on the power grid configuration and the power rating of a GTG assigned to the power grid. An operator or a power management system may adjust the speed set point depending on operational parameters. The droop speed control mode may provide a stable working point for each load in case of the parallel operation in connection with the main grid160.

The droop speed control mode may be used by AC electrical power generators to reduce a power output of a GTG as the line frequency increases. The droop speed control may be implemented by using the speed governor of a prime mover (e.g., the gas turbine28) driving a synchronous GTG (e.g., the GTG102,112,122, or132) connected to a power grid (e.g., the power grid100). It works by controlling the rate of power produced by the prime mover according to the grid frequency. The droop speed control mode enables synchronous GTGs to run in parallel so that loads may be shared among GTGs with the same or similar droop line(s) or curve(s). Moreover, droop curves used by a group of GTGs on an electrical power grid may be nonlinear or may be different from each other. For example, droop curves may be adjusted by operators in proportion to their power rating. Because the droop speed control mode accommodates changes in frequency, it enables multiple GTGs to work in tandem by dividing loads in proportion to their power. The droop speed control mode may be suitable when employed on power grids with multiple GTGs and/or when dealing with loads with higher degrees of power variance.

FIG.5is a flow chart depicting a load sharing process for the power grid system100ofFIG.2when a GTG in the power grid system100is brought online or offline. For example, inFIG.2, when the electrical switches162and136are open, and the electrical switches152,106,116,142, and126are closed, the GTG102, GTG112and GTG122are in parallel serving the local grid150. The local grid150has a total load (e.g., 600 kW), the GTG102, GTG112and GTG122may have power ratings (e.g., 400 kW, 200 kW, and 200 kW respectively). The total load of the local grid150is a percentage (e.g., 75%) of the total power ratings combined from GTG102, GTG112, and GTG122(e.g., 400+200+200=800 kW). As described previously, to achieve a load balancing operation, the power outputs of the GTG102, GTG112and GTG122may be set to respective outputs (e.g., 300 kW, 150 kW, and 150 kW). In other words, the GTG102, GTG112and GTG122may be driven to the same percentage (75%) load to reach load balancing. The GTG controller104(with the load sharing module39) may determine power generated (block402) on GTG102(300 kW). The GTG controller104may publish power generated to other GTG controllers (block404) such as GTG controller114and GTG controller124. The publication is made through the interconnection data bus170. The GTG controller114and GTG controller124may determine the power generated on GTG112and GTG122respectively (e.g., 150 kW and 150 kW) and publish the power generated via the interconnection data bus170. The GTG controller104may retrieve the power generated by other GTGs (block406) such as the GTG112and GTG122. The GTG controller104determines whether an indication of an online/offline GTG has been received (block408) is received. For instance, the indication may be a signal from another controller indicating that a GTG corresponding to the other controller is going or has gone offline. Additionally or alternatively, the indication may include receiving no communications from the other controller for a period longer than a threshold duration, and/or lower power generated by an amount indicating that a GTG has gone offline. In the event that no indication is received, the GTG controller104restarts the load sharing process at block402.

If at a particular moment, a GTG (e.g., GTG122) is brought offline by opening a respective electrical switch (e.g., electrical switch126), the GTG controller104and/or the GTG controller114receives the indication of an offline GTG. If the remaining GTGs (e.g., GTGs102and112) are able to meet power demand of the local grid150that has a total load (e.g., 600 kW), the GTG controller104and the GTG controller114may determine new power level to be generated (block410). For example, the GTG controller104and the GTG controller114may determine the power generated on GTG102and GTG112respectively (e.g., 400 kW and 200 kW). The GTG102and GTG112may receive instructions from the GTG controller104and the GTG controller114respectively to increase the power output to compensate the power supply loss due to the offline GTG122. The instructions may cause the GTG102and GTG112to output new power levels (block412). For example, the GTG102and GTG112may operate at new power levels (e.g., 400 kW and 200 kW) to meet power demand of the local grid150. If the remaining GTGs (e.g., GTGs102and112) are unable to meet power demand of the local grid150that has a total load (e.g., 700 kW), the GTG controller104and the GTG controller114may instruct the GTG102and GTG112to go offline because the total load on the local grid150is exceeding a total capacity of remaining GTGs.

FIG.6is a flow chart depicting a load sharing process for the power grid system100ofFIG.2when an electrical switch changes state. For example, an event of the state changing (from OFF to ON state, or vice versa) may occur when a GTG is brought online or offline from operation by an operator via a switchboard, or when the electrical switch is tripped due to excessive electricity flowing through the electrical switch. The electrical switch state changing event may be reported to a power management system in the power grid system100where the electrical switch is installed. The power management system may publish the electrical switch state changing event to relevant power units (e.g., GTGs102,112,122, and132ofFIG.2), which are equipped with communication devices (e.g., the GTG controller104,114,124, and134) to receive the published event from the power management system directly, or receive shared information related to the published event from the other power units via intercommunication (e.g., using the interconnection data bus170).

The first three blocks402,404, and406ofFIG.6are the same asFIG.5. Using the example described previously, when the electrical switches162and136inFIG.2are open, and the electrical switches152,106,116,142, and126are closed, the GTG102, GTG112and GTG122are in parallel serving the local grid150. The GTG102may determine power generated (block402), publish power generated to other GTG controller(s) (block404), and retrieve power generated by other GTG(s) (block406). If an electrical switch (e.g., electrical switch162) is closed, a mode of operation may change. The GTG controller104may determine whether a state changing event has occurred (block508). The GTG controller104may determine whether the state change corresponds to a change of mode at operation to make a change (block510). For example, change of power grid configuration may correspond to change between modes (e.g., isochronous mode v. droop mode). For example, before the switch162is closed, the GTG102was connected to the local grid150with the other GTGs such as GTG112and GTG122, forming an isolated system. As discussed previously, in the isolated system, the GTG102, GTG112, and GTG122work in the island operation to supply power to all connected loads on the local grid150. Accordingly, the GTG102may be selected to operate in isochronous speed control mode to maintain a constant speed (frequency) regardless of the load changes on the local grid150(e.g., an oil field isolated from the nearby utility grid).

After connecting to the main grid160, the GTG controller104may monitor and analyze relevant information whether to switch the speed control mode of the GTG102. The relevant information may include the frequency and voltage of the main grid160, the load changing in the main grid160and/or the local grid150, the power generated by other online GTGs including GTG112and GTG122, and the like. As mentioned previously, when the GTGs are in parallel operation with the main grid160, and the load changes frequently, continuing working in the isochronous speed control mode may lead to instability issues as the GTGs in isochronous speed control mode will tend to maintain a constant speed regardless of the load changes. Based on the monitoring and analysis, the load sharing module39may determine a new suitable control mode that will contribute to a stable operation of the main grid160. The load sharing module39may cause the GTG controller104to switch mode for the GTG102(block512). For instance, the control mode of the GTG102may be switched from previous isochronous speed control mode to droop speed control mode so that the speed will decrease by a fixed percentage as previously discussed.

If the load sharing module39determines no change is to be made (block510), the load sharing module39may determine a new power level (block514) based on the load (on the main grid160and/or the local grid150) and power output from the other GTGs (e.g., GTGs112and122). The load sharing module39may cause the GTG controller104to change the set point of the GTG102to output at new power level to accommodate load changes in the power grid and/or power output changes for the GTGs (block515).

FIG.7is a flow chart depicting a load sharing process for the power grid system100ofFIG.2when a potential shut down situation may occur. As previously discussed, the GTG102and GTG112may form a subgroup A and the GTG122and GTG132may form a subgroup B in the power grid system100ofFIG.2. Each of the subgroups, and/or the power grid system100may perform coordinated operations. The GTGs102,112,122and132may provide power to meet a demand of the local grid150, and/or the main grid160.

If at a particular moment, an electrical switch (e.g., electrical switch126) is tripped so that a GTG goes offline. Remaining GTG(s) in the subgroup or in the power grid system100may receive an instruction to increase the power output to compensate the power supply loss due to the offline GTG. The instruction may cause the remaining GTG(s) be left to meet a demand over their power ratings (e.g., 200 kW) but within the limit of maximum power (e.g., 220 kW). However, the remaining GTG(s) may not be recommended to operate within a threshold of maximum power (e.g., 95% of maximum power) for certain amount of time. A respective GTG controller (e.g., GTG controller104) may receive an indication that another GTG (e.g., GTG132) is within an impermissible/undesirable threshold of maximum power (block602). The indication may also indicate that the other GTG will go offline after certain amount of time. Furthermore, the GTG controller may receive a command that a yet another GTG (GTG102) is to be shut down (block604) because the total load (e.g., 630 kW) on the local grid150is exceeding the total capacity of remaining GTGs (e.g., GTGs102and112). By using the load sharing module39to analyze the indication that the other GTG is within a threshold of maximum power and other relevant information, the GTG controller104may determine to increase the power output of online GTG(s) other than the other GTG (GTG132) (e.g., from 70% to 78.75% of the power rating(s)). Accordingly, the other GTG controller (GTG controller134) may determine to decrease the power output (e.g., from 105% to 78.75% of the power rating) so that the projected offline situation will not occur. Furthermore, the GTG controller104may prevent shutdown of the GTG102based on at least in part on the changes (block606). For example, maintenance may be delayed and/or shutdown conditions may change due to power production adjustment over the interconnection data bus170. The GTG controller104may generate a waring and send the warning to an operator to indicate that the shutdown of the GTG102may be prevented.

The technologies described in present disclosure may be applicable to a variety of power generation systems (gas turbine generators, steam turbine generators, hydroelectric turbine generators, and the like). The load sharing module provides solutions for different load sharing scenarios, such as load sharing in isochronous mode, load sharing on islands that may include separable islands, load sharing in parallel mode when frequent load changes occurred, etc. Independent operation may be achieved as no master controller (centralized controller) is implemented and the GTG controllers (equipped with the load sharing module) may determine an appropriate way (e.g., a speed control mode) to contribute to stable operation based on the information provided by the others generators. The load sharing module enables flexible operation for a set of generators, which may be adjusted to fit particular needs of site operations in normal or abnormal conditions. For instance, when a GTG controller loses communication from other GTG controller(s), the GTG controller may instruct a corresponding GTG to maintain a mode in which the corresponding GTG is currently operating. Additionally or alternatively, the load set point and other operation preference (e.g., operation mode) may be set by customers via suitable device(s) such as a third-party controller.

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.