SYNCHRONIZING DISTRIBUTED GENERATION SYSTEMS

TECHNICAL FIELD

This disclosure relates to systems and methods for controlling the generation of electric power in an electric power generation and delivery system and, more particularly, to systems and methods for controlling and synchronizing the generation of electric power in an electric power generation and delivery system that includes distributed generation capabilities.

BRIEF DESCRIPTION OF THE DRAWINGS

[0001] Non-limiting and non-exhaustive embodiments of the disclosure are described, including various embodiments of the disclosure, with reference to the figures, in which:

[0002] Figure 1 illustrates a diagram of one embodiment of a system for controlling the generation of electric power in an electric power generation and delivery system that includes distributed electrical generators.

[0003] Figure 2 illustrates a block diagram of an intelligent electronic device for controlling the generation of electric power in an electric power generation and delivery system.

[0004] Figure 3 illustrates a flow diagram of a method for controlling the generation of electric power in an electric power generation and delivery system.

DETAILED DESCRIPTION

[0005] The embodiments of the disclosure will be best understood by reference to the drawings. It will be readily understood that the components of the disclosed embodiments, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the systems and methods of the disclosure is not intended to limit the scope of the disclosure, as claimed, but is merely

representative of possible embodiments of the disclosure. In addition, the steps of a method do not necessarily need to be executed in any specific order, or even sequentially, nor do the steps need be executed only once, unless otherwise specified.

[0006] In some cases, well-known features, structures, or operations are not shown or described in detail. Furthermore, the described features, structures, or operations may be combined in any suitable manner in one or more embodiments. It will also be readily understood that the components of the embodiments, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. For example, throughout this specification, any reference to "one embodiment," "an embodiment," or "the embodiment" means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. Thus, the quoted phrases, or variations thereof, as recited throughout this specification are not necessarily all referring to the same embodiment.

[0007] Several aspects of the embodiments described are illustrated as software modules or components. As used herein, a software module or component may include any type of computer instruction or computer executable code located within a memory device that is operable in conjunction with appropriate hardware to implement the programmed instructions. A software module or component may, for instance, comprise one or more physical or logical blocks of computer instructions, which may be organized as a routine, program, object, component, data structure, etc., that performs one or more tasks or implements particular abstract data types.

[0008] In certain embodiments, a particular software module or component may comprise disparate instructions stored in different locations of a memory device, which together implement the described functionality of the module. Indeed, a module or component may comprise a single instruction or many instructions, and may be distributed over several different code segments, among different programs, and across several memory devices. Some embodiments may be practiced in a distributed computing environment where tasks are performed by a remote processing device linked through a communications network. In a distributed computing environment, software modules or components may be located in local and/or remote memory storage devices. In addition, data being tied or rendered together in a database record may be resident in the same memory device, or across several memory devices, and may be linked together in fields of a record in a database across a network.

[0009] Embodiments may be provided as a computer program product including a non-transitory machine-readable medium having stored thereon instructions that may be used to program a computer or other electronic device to perform processes described herein. The non-transitory machine-readable medium may include, but is not limited to, hard drives, floppy diskettes, optical disks, CD-ROMs, DVD-ROMs, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, solid-state memory devices, or other types of media/machine-readable medium suitable for storing electronic instructions. In some embodiments, the computer or other electronic device may include a processing device such as a microprocessor, microcontroller, logic circuitry, or the like. The processing device may further include one or more special purpose processing devices such as an application specific interface circuit (ASIC), PAL, PLA, PLD, field programmable gate array (FPGA), or any other customizable or

programmable device.

[0010] Electrical power generation and delivery systems are designed to generate, transmit, and distribute electrical energy to loads. Electrical power generation and delivery systems may include equipment, such as electrical generators, electrical motors, power transformers, power transmission and distribution lines, circuit breakers, switches, buses, transmission lines, voltage regulators, capacitor banks, and the like. Such equipment may be monitored, controlled, automated, and/or protected using intelligent electronic devices (lEDs) that receive electric power system information from the equipment, make decisions based on the information, and provide monitoring, control, protection, and/or automation outputs to the equipment.

[0011] In some embodiments, an IED may include, for example, remote terminal units, differential relays, distance relays, directional relays, feeder relays, overcurrent relays, voltage regulator controls, voltage relays, breaker failure relays, generator relays, motor relays, automation controllers, bay controllers, meters, recloser controls, communication processors, computing platforms, programmable logic controllers (PLCs), programmable automation controllers, input and output modules, governors, exciters, statcom controllers, SVC controllers, OLTC controllers, and the like. Further, in some embodiments, lEDs may be communicatively connected via a network that includes, for example, multiplexers, routers, hubs, gateways, firewalls, and/or switches to facilitate communications on the networks, each of which may also function as an IED. Networking and communication devices may also be integrated into an IED and/or be in communication with an IED. As used herein, an IED may include a single discrete IED or a system of multiple lEDs operating together.

[0012] In certain electrical power generation and delivery systems, generation of electric power may be distributed. For example, in some electric power generation and delivery systems, one or more remotely located (i.e., distributed) electrical generators may generate electric power that is delivered by the system to meet greater system load demands. In certain embodiments, distributed electrical generators may be associated with power sub-grids within a greater grid topology of the electric power delivery system.

[0013] Electrical power generation and delivery system equipment may be monitored and protected from various malfunctions and/or conditions using one or more lEDs. In some circumstances, protecting the system from such malfunctions and/or conditions may require one or more lEDs to isolate a power sub-grid from the greater topology of the electric power delivery system. For example, when the power generation capabilities of an electric power system cannot adequately supply system loads, certain portions of the electric power system may be disconnected and/or isolated from the greater grid topology of the electric power delivery system using one or more lEDs in order to prevent damage to the system and/or its components.

Isolating certain portions of the electric power system may also help to contain various malfunctions and/or conditions within the isolated portions and prevent undesirable service outages {e.g., blackout conditions) affecting a larger portion of the electric power delivery system.

[0014] Conventionally, when portions of an electric power delivery system that include distributed electrical generators are isolated from the greater topology of the electric power deliver system, it may be necessary to shut down the electrical generators due to lack of an ability to adequately control and synchronize the generators. Particularly, if left operating, electrical generation in isolated portions of the electric power system may have a generated voltage phase angle and/or an operating frequency that drifts relative to that of the greater electric power system. Reconnecting the isolated portions of the electric power system after such drift may cause damage to the previously isolated portion and/or the greater system.

[0015] Disclosed herein are systems and methods that allow electrical generators included in an isolated portion of an electric power system to remain operating synchronously with the greater electric power system. By synchronizing the operation of distributed electrical generators of an isolated portion of an electric power system with that of the greater grid, the need to shut down the generators of the isolated portion is reduced. Moreover, synchronizing the operation may allow the isolated portion of the electrical power system to be reconnected to the greater grid without causing damage to the isolated portion and/or the greater grid.

[0016] Figure 1 illustrates a diagram of one embodiment of a system 100 for controlling the generation of electric power in an electric power generation and delivery system that includes distributed electrical generators 102-106 consistent with embodiments disclosed herein. Although illustrated as one-line diagram for purposes of simplicity, the system 100 may also be configured as a three phase power system. Moreover, embodiments disclosed herein may be utilized in any electric power generation and delivery system, and are therefore not limited to the specific system 100 illustrated in Figure 1. For example, systems consistent with embodiments disclosed herein may include any number of distributed electrical generators 102-106, and may be integrated in any suitable configuration. Further, embodiments may be integrated, for example, in industrial plant power generation and delivery systems, deep-water vessel power generation and delivery systems, ship power generation and delivery systems, distributed generation power generation and delivery systems, and utility electric power generation and delivery systems.

[0017] The system 100 may include generation, transmission, distribution, and power consumption equipment. For example, the system 100 may include one or more generators 102-106 that, in some embodiments, may be operated by a utility provider for generation of electrical power for the system 100. In certain embodiments, the generators 102-106 may be associated with one or more sub-grids within a greater topology of an electric power delivery and generation system and be configured to provide power to the sub-grids and/or the greater electrical power delivery system 108. A first generator 102 may be coupled to a first transmission bus 1 10 via a first step up transformer 1 12 that may be configured to step up the voltage provided to the first transmission bus 1 10 from the first generator 102. A second generator 104 may be coupled to a second transmission bus 1 14 via a second step up transformer 1 16 that may be configured to step up the voltage provided to the second transmission bus 1 14 from the second generator 104. A third generator 106 may be coupled to a third transmission bus 1 18 via a third step up transformer 120 that may be configured to step up the voltage provided to the third transmission bus 1 18 from the third generator 106.

[0018] A first set of one or more loads 122 may be coupled to the first transmission bus 1 10 and receive electrical power generated by the first generator 102. Similarly, a second set of one or more loads 124 may be coupled to the third transmission bus 1 18 and receive electrical power generated by the third generator 106. In some

embodiments, the electric power delivered to the loads 122, 124 may be further stepped down from distribution levels to load levels via step down transformers included in the system (not shown). In certain embodiments, the loads 122, 124 may be associated with a distribution site {e.g., a refinery, smelter, paper production mill, or the like), which may include a distributed generator (not shown) configured to provide power to the distribution site produced by, for example, a turbine configured to produce electric power from the burning of waste, the use of waste heat, or the like. Further, while the system 100 illustrated in Figure 1 does not include, for example, loads coupled to the second transmission bus 1 14, embodiments disclosed herein may be incorporated in a system that includes any suitable configuration of loads, electrical generators, busses, feeders, transformers, transmissions lines, lEDs, breakers, and the like.

[0019] The first transmission bus 1 10 and third transmission bus 1 18 may be coupled to a main first transmission bus 126 via a first breaker 128 and a third breaker 132, respectively. The second transmission bus 1 14 may be coupled to a second main transmission bus 150 via a second breaker 130. The first main transmission bus 126 may be coupled to the second main transmission bus via breaker 146. The first main transmission bus 126 may be coupled to the greater electric power delivery system 108 via a first transmission line 148 and a breaker 154. The second main transmission bus 150 may be coupled to the greater electric power delivery system 108 via a second transmission line 134 and a breaker 152. The greater electric power delivery system 108 may include any suitable configuration of distributed generators, loads,

transmission components, and the like.

[0020] As discussed above, lEDs may be configured to control, monitor, protect, and/or automate the system 100 and/or its components. As used herein, an IED may refer to any microprocessor-based device that monitors, controls, automates, and/or protects monitored equipment within an electric power system. In some embodiments, lEDs may gather status information from one or more pieces of monitored equipment. Further, lEDs may receive information concerning monitored equipment using sensors, transducers, actuators, and the like.

[0021] In some embodiments, lEDs may be configured to monitor and communicate information, such as voltages, currents, equipment status, temperature, power system frequency, pressure, density, infrared absorption, radio-frequency information, partial pressures, velocity, speed, rotational velocity, mass, switch status, valve status, circuit breaker status, tap status, meter readings, and the like. Further, lEDs may be configured to communicate calculations, such as phasors (which may or may not be synchronized as synchrophasors), events, fault distances, differentials, impedances, reactances, frequency, and the like. lEDs may also communicate settings information, IED identification information, communications information, status information, alarm information, and the like. Information of the types listed above, or more generally, information about the status of monitored equipment, may be generally referred to herein as monitored system data and/or information.

[0022] In certain embodiments, lEDs may issue control instructions to the monitored equipment in order to control various aspects relating to the monitored equipment. For example, one or more lEDs may be in communication with a circuit breaker {e.g., breakers 128-132), and may be capable of sending an instruction to open and/or close the circuit breaker, thus disconnecting (i.e., isolating) or connecting a portion of a power system. In another example, an IED may be in communication with a recloser and capable of controlling reclosing operations of the recloser. In another example, an IED may be in communication with a voltage regulator and capable of instructing the voltage regulator to tap up and/or down. Information of the types listed above, or more generally, information or instructions directing an IED or other device to perform a certain action, may be generally referred to as control instructions.

[0023] The operation of generators 102-106 may be controlled by lEDs 136-140 through control instructions issued by the lEDs 136-140. In certain embodiments, the lEDs 136-140 may operate as speed controllers for the generators 102-106. For example, IED 136 may control the speed {e.g., the rotational speed) and operation of generator 102, thereby controlling the generation of electricity by generator 102. In conventional lEDs operating as speed controllers, the IED may receive both an indication of a reference speed {e.g., from a preset signal or the like) and status information providing an indication of the actual speed of the generator. Through a feedback system, the conventional IED operating as a speed controller may control the generator to adjust its actual speed to match that of the indicated reference speed.

[0024] As discussed above, when an electrical generator becomes isolated from the greater topology of an electric power delivery system, even when the generator is speed controlled by an IED according to a reference speed indication, the voltage phase angle and/or frequency of the generated electric power may drift relative to that of the greater electric power system. A resulting angle difference may cause damage to the isolated portion and/or the greater electric power system if the isolation portion is recoupled to the system. Consistent with embodiments disclosed herein, lEDs 136-140 may be configured to synchronize the speed of the generators 102-106 based, at least in part, on monitored system data 144 received from the greater electrical power delivery system 108, information received from other lEDs 136-140, a reference speed indication, and/or a common time signal 142. By synchronizing the speed of the generators 102-106 based on operating conditions of the greater electrical power delivery system 108 as indicated by monitored system data 144, information received from other lEDs 136-140, a reference speed or phase indication, and/or a common time signal 142 rather than a fixed reference speed or phase, the generators 102-106 may remain synchronized with the greater electrical power delivery system 108 regardless of whether they are coupled to or isolated {e.g., by opening breakers 128-132) from the greater electrical power delivery system 108.

[0025] In certain embodiments, monitored system data 144 relating to the electrical power delivery system 108 may be generated by other lEDs included in the electrical power delivery system 108 designed to monitor, control, and/or protect equipment included in the electrical power delivery system 108. In certain embodiments, the monitored system data 144 may include current signals obtained, for example, from a current transformer (CT), voltage signals obtained, for example, from a potential transformer (PT), and/or time-synchronized phasors (i.e., synchrophasors) of monitored currents and/or voltages obtained from one or more locations in the electrical power delivery system 108. In certain embodiments, synchrophasor data may be calculated by lEDs included in the electrical power delivery system 108 and/or lEDs 136-140 using a variety of methods including, for example, the methods described in U.S. Patent No. 6,662,124, U.S. Patent No. 6,845,333, and U.S. Patent No. 7,480,580, which are herein incorporated by reference in their entireties. In some embodiments, synchrophasor measurements and communications may comply with the IEC C37.1 18 protocol.

[0026] Based in part on the received monitored system data 144, the lEDs 136-140 may, autonomously or collectively, control the operation of generators 102-106 such that the output of the generators 102-106 (e.g., speed, phase angle, and/or frequency) is synchronized with the greater electric power delivery system 108. In this manner, the generators 102-106 may remain synchronized with the greater electrical power delivery system 108 regardless of whether they are coupled to or isolated from the greater electrical power delivery system 108.

[0027] In certain embodiments, lEDs 136-140 may receive a common time signal 142 that is used in synchronizing the generators 102-106 (e.g., by applying time stamps or the like). lEDs and equipment included in the greater electrical power delivery system 108 may also utilize the common time signal 142 to manage, control, and synchronize their operations. In some embodiments, the common time signal 142 may be provided using a GPS satellite {e.g., IRIG), a common radio signal such as WWV or WWVB, a network time signal such as IEEE 1588, or the like. As the common time signal 142 may be shared between the lEDs 136-140 configured to control generators 102-106 as well as lEDs and equipment included in the greater electrical power delivery system 108, the common time signal 142 may be utilized as a common reference for coordinating and synchronizing the operation of the entire system 100.

[0028] As illustrated in Figure 1 , lEDs 136-140 may be communicatively coupled with each other, allowing some lEDs 136-140 to operate autonomously (i.e.,

individually) and/or as a group. In certain embodiments, an IED of the lEDs 136-140 may be able to determine their relative position and/or relative interconnectivity with respect to other lEDs 136-140 in the system 100 they are connected with (i.e., the lEDs 136-140 may be "system aware"). Further, in some embodiments, lEDs 136-140 may be able to determine if they are isolated (i.e., islanded) from the greater electrical power delivery system 108 on a specific sub-grid. For example, if breaker 128 and breaker 132 are opened (e.g., in response to control instructions issued by one or more lEDs), IED 136 and IED 140 may determine that they are communicatively coupled with each other and that they or the equipment they are associated with has become isolated (i.e., islanded) from the greater electrical power delivery system 108 on a particular sub-grid.

[0029] In certain embodiments, lEDs 136-140 may determine whether they or the equipment they are associated with has become isolated from the greater electrical power delivery system 108 and/or determine whether they reside on a particular sub- grid (i.e., island) based on monitored system data including, for example, system operating frequencies, operating phases, and/or synchrophasor measurements provided by one or more lEDs monitoring the system 100. In certain embodiments, this determination may be performed using a variety of methods including, for example, the methods described in U.S. Patent No. 7,930,1 17, which is herein incorporated by reference in its entirety.

[0030] Upon determining that a group of lEDs 136-140 are associated with a particular sub-grid (i.e., island), the lEDs 136-140 may determine whether they should control their respective generators 102-106 autonomously (i.e., individually) or collectively (i.e., as a group). In certain embodiments, the determination of whether lEDs 136-140 should control their respective generators 102-106 autonomously or collectively may be based on an optimization process that utilizes monitored system data received by the lEDs 136-140.

[0031] If the lEDs 136-140 determine they should control their respective generators 102-106 autonomously, the lEDs 136-140 may independently control their respective generators 102-106 irrespective of the behavior of the other IEDS 136-140. An IED 136-140 controlling its generator 102-106 autonomously may generate a reference phasor signal based on a common time signal 142. The reference phasor signal may be used as a phase input signal to a controller included in the IED 136-140. In certain embodiments, the controller may operate drive an error between the phase input signal and a measured output phase signal to zero.

[0032] If any of the combination of lEDs 136-140 determines that they should collectively control their respective generators 102-106, a combination of lEDs 136-140 may operate as a group. Under such circumstances, the group of lEDs 136-140 may collectively share their operating characteristics {e.g., phase or speed reference signals) and operate accordingly and/or operate according to user-defined operating parameters. In certain embodiments, speed and/or phase angle control of the group of lEDs 136-140 may be accomplished using a reference phasor signal generated based on the common time signal 142 and/or monitored system data 144 received from the greater electrical power delivery system 108. For example, if breaker 128, breaker 146, and breaker 132 are opened, IED 136 and IED 140 may determined that they are electrically decoupled from the greater electrical power delivery system 108 and/or each other. IED 136 and IED 140 may then control their respective generators 102, 106 using a common reference time signal 142, information from other lEDs 136-140, and/or monitored system data 144. Once synchronized, a sub-grid including

generators 102 and 106 may be established by closing breaker 128 and 132, and lEDs 136 and 132 may collectively control their respective generators using a common reference time signal 142, information from other lEDs 136-140, and/or monitored system data 144. Further, by synchronizing the operation of generator 102 and generator 106 with the greater electrical power delivery system 108, generator 102 and 106 may be reconnected to the greater electrical power delivery system by closing breaker 146.

[0033] In certain embodiments, lEDs 136-140 may also be communicatively coupled to a central IED (not shown) that may be configured to provide control and monitoring of the lEDs 136-140 and/or the system 100 as a whole. For example, in certain embodiments, a central lED coupled to lEDs 136-140 may be used in determining whether lEDs 136-140 have become isolated on a particular sub-grid, whether lEDs 136-140 should control their respective generators 102-106 autonomously or collectively, and/or which of lEDs 136-140 should function as a primary lED and/or follower lEDs. In some embodiments, the central lED may be a central controller, synchrophasor vector processor, automation controller, programmable logic controller (PLC), real-time automation controller, Supervisory Control and Data Acquisition (SCADA) system, or the like. For example, in some embodiments, the central lED may be a synchrophasor vector processor, as described in U.S. Patent Application

Publication No. 2009/0088990, which is incorporated herein by reference in its entirety. In other embodiments, the central lED may be a real-time automation controller, such as is described in U.S. Patent Application Publication No. 2009/0254655, which is incorporated herein by reference in its entirety. The central lED may also be a PLC or any similar device capable of receiving communications from other lEDs {e.g., IEDS 136-140) and processing the communications therefrom. In certain embodiments, other lEDs {e.g., IEDS 136-140) may communicate with the central lED directly or via a communications network.

[0034] Figure 2 illustrates a block diagram of an lED 200 for controlling the generation of electric power in an electric power generation and delivery system. As illustrated, lED 200 may include a processor 202, a random access memory (RAM) 204, a communications interface 206, a user interface 208, and a computer-readable storage medium 210. The processor 202, RAM 204, communications interface 206, user interface 208, and computer-readable storage medium 210 may be

communicatively coupled to each other via a common data bus 212. In some embodiments, the various components of lED 200 may be implemented using hardware, software, firmware, and/or any combination thereof.

[0035] The user interface 208 may be used by a user to enter user defined settings such as, for example, indications of reference speeds, parameters utilized in

determining whether a group of lEDs should operate autonomously or collectively, and the like. The user interface 208 may be integrated in the lED 200 or, alternatively, may be a user interface for a laptop or other similar device communicatively coupled with the lED 200. Communications interface 206 may be any interface capable of

communicating with lEDs and/or other electric power system equipment {e.g., a generator) communicatively coupled to lED 200. For example, communications interface 206 may be a network interface capable of receiving communications from other lEDs over a protocol such as the IEC 61850 or the like. In some embodiments, communications interface 206 may include a fiber-optic or electrical communications interface for communicating with other lEDs.

[0036] The processor 202 may include one or more general purpose processors, application specific processors, microcontrollers, digital signal processors, FPGAs, or any other customizable or programmable processing device. The processor 202 may be configured to execute computer-readable instructions stored on the computer- readable storage medium 210. In some embodiments, the computer-readable instructions may be computer executable functional modules. For example, the computer-readable instructions may include an islanding determination module 214 configured to cause the processor to perform the islanding (i.e., isolated sub-grid) determination operations, as described above in reference to Figure 1. The computer- readable instructions may further include an autonomous/collective operation module 216 configured to perform the operations related to the above-described determination of whether the lED 200 should operate autonomously or collectively with other lEDs after a determination that the lED 200 is operating on an isolated sub-grid. The computer-readable instructions may also include a primary/follower determination module 218 configured to perform the determinations described above regarding whether a collectively operating lED should operate as a primary lED or a follower lED. In addition, the computer-readable instructions may also include a control instruction generation module 220 configured to generate an appropriate control instruction to control a generator coupled to the lED 200 based on the above-described

determinations. The computer-readable instructions may also include any other functional modules configured to implement the functionality of lEDs 102-106 described above in reference to Figure 1.

[0037] Figure 3 illustrates a flow diagram of a method 300 for controlling the generation of electric power in an electric power generation and delivery system. At 302, an lED may determine that the lED and/or a generator the lED is configured to monitor and control has become isolated from the greater electric power delivery system. In certain embodiments, this determination may be made using monitored system data received from other lEDs including, for example, synchrophasor measurements. If the lED determines that the lED has become isolated from the greater system, the lED may determine whether other lEDs configured to monitor and control distributed generators have also become isolated from the greater system on the same sub-grid at 304.

[0038] If the lED determines that no other lEDs controlling distributed generators are operating on the same isolated sub-grid, at 306 the lED may independently control and synchronize the operation of the generator the lED is configured to control with that of the greater system. In certain embodiments, this synchronization operation may be based on monitored system data {e.g., synchrophasor information), a common time signal {e.g., a GPS timing signal), information received from other lEDs, and/or an indication of a reference speed. If, however, the lED determines other lEDs controlling distributed generators are operating on same isolated sub-grid, at 308 the lED may then determine whether it should operate autonomously or collectively with the other isolated lEDs on the same sub-grid.

[0039] When the lED determines that it should operate autonomously, the method may proceed to 306 and the lED may control and synchronize the operation of its associated generator with that of the greater system independent of other lEDs. When the lED determines, however, that it should operate collectively with other lEDs operating on the same isolated sub-grid, the method may proceed to 310. At 310, the lED may determine, individually or collectively with other lEDs, whether the lED should operate as a primary lED or whether it should "follow" another lED operating as a primary lED on the same isolated sub-grid in controlling its associated generator.

[0040] If the lED determines that it should operate as a primary lED, at 312, the lED may control and synchronize the operation of its associated generator with that of the greater system and provide a reference to other lEDs on the same isolated sub-grid configured to "follow" the primary lED for use in synchronizing their associated generators. If, however, the lED determines that it should "follow" another primary lED, at 314, the lED may control and synchronize the operation of its associated generator based on a reference received from a primary lED.

[0041] While specific embodiments and applications of the disclosure have been illustrated and described, it is to be understood that the disclosure is not limited to the precise configurations and components disclosed herein. Accordingly, many changes may be made to the details of the above-described embodiments without departing from the underlying principles of this disclosure. The scope of the present invention should, therefore, be determined only by the following claims.