Electrical power generation system and method for aircraft

A method for generating electrical power comprising operating variable frequency generators using a common prime mover and controlling the variable frequency generators using a mechanical phase difference as follows: wherein MPD is the mechanical phase difference in degrees between rotors between a pair of variable frequency generators, G is a number of variable frequency generators, Φ is a number of electrical phases in a variable frequency generator in the variable frequency generators, and p is a number of pole pairs in the variable frequency generator in the variable frequency generators, wherein the variable frequency generators are controlled such that each variable frequency generator in the variable frequency generators has a selected mechanical phase difference from another variable frequency generator in the variable frequency generators that is an integer multiple of the mechanical phase difference that is less than 360 degrees.

BACKGROUND INFORMATION

The present disclosure relates generally to power generation and, in particular, to a method, apparatus, and system for generating multiphase electrical power. Still more particularly, the present disclosure relates to a method, apparatus, and system generating multiphase power using multiple generators driven by a common prime mover.

Platforms such as aircraft include electrical systems. These electric systems may include, for example, a lighting system, an environmental system, an in-flight entertainment system, a communication system, a navigation computer, and other suitable types of systems. These electrical systems are loads in aircraft that utilize electrical power to operate.

Aircraft systems include components with an ability to generate electrical power. For example, generators are present on commercial aircraft that produce electrical power. These generators are typically driven by sources referred to as prime movers. A prime mover can take the form of an aircraft engine. Further, other types of primers include an auxiliary power unit (APU), a hydraulic motor, a ram air turbine (RAT), a device with a rotating mechanical output or some other suitable type of system that can drive generators.

For example, each aircraft engine can be connected to drive two generators to create electrical power. With two generators per aircraft engine, redundancy is present. The aircraft can operate when one of the two generators does not have a desired level of performance. These generators have outputs connected to an electrical power distribution system. This electrical power distribution system contains one or more buses. The different loads in aircraft are also connected to the buses from which electrical power is distributed for use by the loads.

These generators generate electrical power having three phases. With respect to stability, voltage regulation, efficiency, and reliability, six-phase power is more advantageous than three-phase power. However, regarding six-phase power, additional equipment is often needed. For example, constant frequency generators are used. A challenge is present because the aircraft engine changes speed during different phases and operations of the aircraft. These types of generators employ additional equipment for speed conversion to obtain the constant frequency in view of the changing speeds in the operation of the aircraft engine. This increase in weight in aircraft is undesirable. Further an undesired reduction in power conversion efficiency also can occur.

Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues. For example, it would be desirable to have a method and apparatus that overcome a technical problem with generating electric power with a number of phases while reducing the weight needed to generated higher phase electrical power.

SUMMARY

An embodiment of the present disclosure provides an electrical generator system comprising a plurality of variable frequency generators connected to a common prime mover and a phase controller system configured to control the plurality of variable frequency generators using a mechanical phase difference as follows:

M⁢⁢P⁢⁢D=360G⁢⁢Φ⁢⁢p
wherein MPD is the mechanical phase difference in degrees between rotors between a pair of variable frequency generators, G is a number of variable frequency generators, Φ is a number of electrical phases in a variable frequency generator in the plurality of variable frequency generators, and p is a number of pole pairs in the variable frequency generator in the plurality of variable frequency generators. The phase controller system controls the plurality of variable frequency generators such that each variable frequency generator in the plurality of variable frequency generators has a selected mechanical phase difference from another variable frequency generator in the plurality of variable frequency generators that is an integer multiple of the mechanical phase difference that is less than 360 degrees.

Another embodiment of the present disclosure provides an electrical generator system comprising a plurality of variable frequency generators configured to be connected to a common prime mover and a phase controller system configured to control the plurality of variable frequency generators using a mechanical phase difference as follows:

M⁢⁢P⁢⁢D=360G⁢⁢Φ⁢⁢p
wherein MPD is the mechanical phase difference in degrees between rotors between a pair of variable frequency generators, G is a number of variable frequency generators, Φ is a number of electrical phases in a variable frequency generator in the plurality of variable frequency generators, and p is a number of pole pairs in the variable frequency generator in the plurality of variable frequency generators. The phase controller system controls the plurality of variable frequency generators such that each variable frequency generator in the plurality of variable frequency generators has a selected mechanical phase difference from another variable frequency generator in the plurality of variable frequency generators that is an integer multiple of the mechanical phase difference that is less than 360 degrees.

Yet another embodiment of the present disclosure provides a method for generating electrical power comprising operating a plurality of variable frequency generators using a common prime mover and controlling the plurality of variable frequency generators using a mechanical phase difference as follows:

M⁢⁢P⁢⁢D=360G⁢⁢Φ⁢⁢p
wherein MPD is the mechanical phase difference in degrees between rotors between a pair of variable frequency generators, G is a number of variable frequency generators, Φ is a number of electrical phases in a variable frequency generator in the plurality of variable frequency generators, and p is a number of pole pairs in the variable frequency generator in the plurality of variable frequency generators. The plurality of variable frequency generators are controlled such that each variable frequency generator in the plurality of variable frequency generators has a selected mechanical phase difference from another variable frequency generator in the plurality of variable frequency generators that is an integer multiple of the mechanical phase difference that is less than 360 degrees.

DETAILED DESCRIPTION

The illustrative embodiments recognize and take into account one or more different considerations. For example, the illustrative embodiments recognize and take into account that current configurations of generators can place the electrical output of the generators in parallel by relying on synchronizing two or more connected electrical power sources by maintaining the electrical phases in the same electrical phase angle, electrical phase sequence, and electrical frequency. The illustrative embodiments recognize and take into account that the current systems rely on a constant frequency in the operation of the generators. The illustrative embodiments recognize and take into account that speed conversion is utilized to maintain this constant frequency for the generators to take into account the fact that the aircraft engines operate at variable frequencies. These frequencies are for mechanical rotational speeds. The illustrative embodiments recognize and take into account that the use of speed conversion results in losses in efficiency in generating electrical power from a mechanical power source.

Further, the illustrative embodiments recognize that the development of new aircraft generators and engine driven rotating machinery is a multi-year and expensive process. The illustrative embodiments recognize and take in to account that having an ability to connect currently used or installed generators in a parallel configuration is an attractive alternative.

The illustrative embodiments recognize and take into account that current teachings for aerospace power systems are directed to using balanced real and reactive power on generators that have their electrical outputs in parallel. The illustrative embodiments recognize and take into account that, contrary to current teachings, a mismatch or difference in mechanical phases is not necessarily detrimental in generating higher phase electrical power with parallel generators. The illustrative embodiments recognize and take into account that the mismatch or difference in mechanical phases between rotors in generators can be controlled in a manner that provides an increased number of phases when these electrical outputs are placed in parallel. Additionally, this type of control also enables using variable frequency generators to create electrical power. Further, the illustrative embodiments recognize and take into account that through controlling the difference in mechanical phases, reductions in undesired energy oscillations can be achieved in different illustrative examples as described herein.

Thus, the illustrative embodiments provide a method, apparatus, and system for generating electrical power. In one illustrative example, an electrical generator system comprises a plurality of variable frequency generators and a phase controller. The plurality of variable frequency generators is connected to a common prime mover. The phase controller is configured to control the plurality of variable frequency generators using a mechanical phase difference as follows:
MPD=360/GΦp
wherein MPD is the mechanical phase difference in degrees between rotors between a pair of variable frequency generators, G is a number of variable frequency generators, Φ is a number of electrical phases in a variable frequency generator in the plurality of variable frequency generators, and p is a number of pole pairs in the variable frequency generator in the plurality of variable frequency generators.

The controller controls the plurality of variable frequency generators such that each variable frequency generator in the plurality of variable frequency generators has a selected mechanical phase difference from another variable frequency generator in the plurality of variable frequency generators that is an integer multiple of the mechanical phase difference that is less than 360 degrees.

With reference now to the figures and, in particular, with reference toFIG. 1, an illustration of an aircraft is depicted in accordance with an illustrative embodiment. In this illustrative example, aircraft100has wing102and wing104attached to body106. Aircraft100includes engine108attached to wing102and engine109attached to wing104.

Aircraft100is an example of an aircraft in which electrical system120may be implemented in accordance with an illustrative embodiment. As depicted, electrical system120includes variable frequency generator122and variable frequency generator124in engine108. Electrical system120also includes variable frequency generator126and variable frequency generator128in engine109. Variable frequency generator122and variable frequency generator124are driven by engine108. Variable frequency generator126and variable frequency generator128are driven by engine109.

Further, electrical system120includes variable frequency generator130and variable frequency generator132in tail section112. These generators are driven by auxiliary power unit (APU)134in tail section112.

The outputs of these variable frequency generators are connected to bus system136and provide electrical power in electrical system120. Additionally, loads138in electrical system120are connected to bus system136and operate using the electrical power provided through bus system136.

With reference next toFIG. 2, an illustration of a block diagram of a power generation environment is depicted in accordance with an illustrative embodiment. As depicted, power generation environment200includes platform202. In the illustrative example, platform202takes the form of aircraft204. Aircraft100inFIG. 1is an example of one implementation for aircraft204.

As depicted, platform202includes electrical generator system206that is configured to generate electrical power208for use by loads210in platform202. In this illustrative example, electrical generator system206comprises a plurality of variable frequency generators212, phase controller system214, and bus system216.

A variable frequency generator in the plurality of variable frequency generators212is a physical device that converts motive power218into electrical power208. In this illustrative example, electrical power208output by the plurality of variable frequency generators212is in the form of an alternating current.

As depicted, common prime mover220provides motive power218to operate electrical generators system206. Common prime mover220is selected from one of an engine, an aircraft engine, an auxiliary power unit, or some other suitable type of device that can generate motive power218to operate the plurality of variable frequency generators212.

In this illustrative example, the plurality of variable frequency generators212is connected to common prime mover220. As depicted, gear system222in phase controller system214mechanically connects the plurality of variable frequency generators212to common prime mover220. Common prime mover220is the common source of motive power218for the plurality of variable frequency generators212. Gear system222is configured such that all of the plurality of variable frequency generators212rotate at the same speed with respect to each other. The plurality of variable frequency generators212, however, can all change the frequency at which they rotate as common prime mover220changes speed.

For example, common prime mover220can be an engine for aircraft204. Common prime mover220can change speed during different phases of operation of aircraft204. This change in speed in the aircraft engine is considered a change in frequency which is propagated to the plurality of variable frequency generators212.

In this illustrative example, phase controller system214is configured to control the plurality of variable frequency generators212using mechanical phase difference224between the different generators in the plurality of variable frequency generators212. As depicted, mechanical phase difference224can be determined as follows:
MPD=360/GΦp

In this equation, MPD is the mechanical phase difference in degrees between rotors between a pair of variable frequency generators, G is a number of variable frequency generators, Φ is a number of electrical phases in a variable frequency generator in the plurality of variable frequency generators, and p is the number of pole pairs in the variable frequency generator in the plurality of variable frequency generators.

Phase controller system214controls the plurality of variable frequency generators212such that each variable frequency generator in the plurality of variable frequency generators212has a selected mechanical phase difference226from another variable frequency generator in the plurality of variable frequency generators212that is integer multiple228of mechanical phase difference224that is less than 360 degrees.

As a result, phase controller system214controls the plurality of variable frequency generators212to operate with reduced undesired energy oscillations. In this example, phase controller system214controls mechanical phase difference224using gear system222.

For example, two variable frequency generators are in plurality of variable frequency generators212and the number of phases is three per variable frequency generator, the number of pole pairs is one, and the mechanical phase difference is 60 degrees, wherein the two variable frequency generators operate in parallel to generate an output voltage having six phases.

In this illustrative example, the electrical outputs of the plurality of variable frequency generators212are connected in parallel to bus system216. This connection is configured to produce electrical power208which is produced with a desired number of electrical phases230to load232in loads210.

The maximum number of system electrical phases available for load232is determined as follows:
MSEP=G*Φ
wherein MSEP is the maximum number of system electrical phases, G is the number of variable frequency generators, and Φ is the number of phases in a variable frequency generator in the plurality of variable frequency generators.

With reference next toFIG. 3, an illustration of a block diagram of a gear system is depicted in accordance with an illustrative embodiment. In the illustrative examples, the same reference numeral may be used in more than one figure. This reuse of a reference numeral in different figures represents the same element in the different figures.

In this illustrative example, gear system222has a number of different types of gears. As depicted, gear system222comprises prime gear300and generator gears302.

Common prime mover220is coupled to prime gear300in gear system222. Common prime mover220may be coupled to prime gear300using a shaft with a spline, which is a gear attached to the shaft. The spline fits within a corresponding spline or some other feature in prime gear300. As a result, prime gear300rotates when the shaft rotates.

As depicted, prime gear300is connected to generator gears302. This connection may be a direct connection between these gears or in direct connection with one or more gears between prime gear300and generator gears302. When common prime mover220rotates prime gear300, prime gear300rotates generator gears302.

Variable frequency generators212are coupled to generator gears302in gear system222. In this illustrative example, variable frequency generators212have rotor shafts304. As depicted, rotor shafts304have features306and are configured to fit within receiving features308in generator gears302.

In this illustrative example, features306and receiving features308are configured such that a feature in features306can fit with rotors310in the plurality of variable frequency generators212being in a particular orientation. The configuration of receiving features308can be selected, designed, or configured such that rotors310in variable frequency generators212are oriented with respect to each other to have selected mechanical phase difference226inFIG. 2as described above.

In this manner, a feature in features306on a rotor shaft of each of the plurality of variable frequency generators212is mechanically connected to a receiving feature in receiving features308in a generator gear in generator gears302in gear system222such that each variable frequency generator in the plurality of variable frequency generators212has a selected mechanical phase difference from another variable frequency generator in the plurality of variable frequency generators212that is an integer multiple of the mechanical phase difference that is less than 360 degrees.

In one illustrative example, features306on rotor shafts304may take the form of male splines with receiving features308in generator gears302taking the form of female splines configured to receive the male splines with desired orientations of rotors310to obtain selected mechanical phase difference226inFIG. 2. For example, a spline in the female splines may have a different shape or length such that only corresponding spline in the male splines can fit within the female splines with the desired orientation of the rotor shaft. Thus, the orientation of rotors310in the plurality of variable frequency generators212can be set in a desired orientation when features306are engaged with receiving features308.

In one illustrative example, one or more technical solutions are present that overcome a technical problem with generating electrical power with a desired level of efficiency. As a result, one or more technical solutions in the illustrative examples can provide a technical effect of enabling connecting the electrical output of variable frequency generators in a manner that reduces undesired energy oscillations.

Also, one or more of the technical solutions can reduce undesired energy oscillations that include, for example, real and reactive instantaneous power oscillations and unwanted exchanges between generators, gears in gear systems, prime movers, and loads or other components connected to an electrical bus. Further, one or more of the technical solutions enable using variable frequency generators having a lower number of phases that can be combined in parallel to provide a higher number of phases for use by loads.

Further, one or more technical solutions in the illustrative examples enable utilization of smaller generators to provide a desired number of phases in electrical power for loads that is not possible with currently available configurations of generators driven by aircraft engines or other common prime movers in an aircraft.

For example, although the depicted example shows platform202in the form of aircraft204, electrical power208can be generated for loads210located in other types of platforms. For example, the platform can be selected from one of a mobile platform, a stationary platform, a land-based structure, an aquatic-based structure, a space-based structure, a commercial aircraft, a rotorcraft, a surface ship, a tank, a personnel carrier, a train, a spacecraft, a space station, a satellite, a submarine, an automobile, a power plant, a wind turbine, a geothermal, hydroelectric or tidal electrical power generation system, a bridge, a dam, a house, a manufacturing facility, and a building.

As another example, one or more prime movers in addition to common prime mover220can be present in electrical generator system206. These additional common prime movers can be used to provide the power for different groupings of variable frequency generators212. As yet another example, gear system222may be located in one or more housings not shown in the depicted illustrations.

In yet another illustrative example, the control of mechanical phase difference224between variable frequency generators212by phase controller system214can be performed using a hydraulic system in addition to or in place of gear system222.

When using a hydraulic system to mechanically drive a plurality of generators, the hydraulic motor outputs can produce the mechanical phase difference through mechanical phase control interface between the motor rotor and generator rotor or have each respective hydraulic motor swashplate adjusted and the plurality of hydraulic motors installed so that mechanical phase difference is maintained.

In still another illustrative example, an alternating current to direct current components can be employed to generate direct current electrical power from the alternating current electrical power output as electrical power208from variable frequency generators212. The alternating current to director current component may be implemented in a number of different ways. For example, this component can be implemented using rectification unit. The rectifier unit can be used with or without a transformer. Further, the rectifier can also be implemented to change the voltage of electrical power208.

With reference now toFIG. 4, an illustration of an electrical generator system is depicted in accordance with an illustrative embodiment. In this illustrative example, electrical generator system400is an example of one implementation for electrical generator system206inFIG. 2.

As depicted, electrical generator system400is powered by engine402, which can be an aircraft engine. For example, variable frequency generator (G1)404and variable frequency generator (G2)406in electrical generator system400are powered by engine402. Engine402is a common prime mover for variable frequency generator (G1)404and variable frequency generator (G2)406. In this depicted example, variable frequency generator (G1)402and variable frequency generator (G2)404have a mechanical phase difference of 180 degrees or plus or minus 60 degrees. The output of these variable frequency generators is electrical power in the form of an alternating current.

The output of variable frequency generator (G1)402is connected to bus408by switch410. The output of variable frequency generator (G2)404is connected to bus412by switch414. Bus408and bus412form bus system413, which is an example of an implementation of bus system216inFIG. 2.

In this example, these variable frequency generators are connected in parallel. The electrical power output by each of these variable frequency generators has three phases.

As depicted, load416is connected to bus408by switch418and to bus412by switch420. This connection to bus406and bus408provides an alternating current with six-phase power to load416. Load416can be, for example, a line replaceable unit (LRU) in an aircraft such as a flight entertainment system, an environmental system, a navigation system, an engine indicating and crew alerting system (EICAS), or some other suitable system.

In this example, the size and weight of variable frequency generator (G1)404and variable frequency generator (G2)406can be less as compared to using generators that are designed to provide six-phase power. Further, the ability to provide six-phase power provides a reduction in the equipment for magnetics and transformers to provide phase power to load416.

In this example, a first variable frequency generator, variable frequency generator (G1)402, in the two variable frequency generators has an output with three phases connected to a first bus, bus408. A second variable frequency generator, variable frequency generator (G2)404, in the two variable frequency generators has a second output with three phases connected to a second bus, bus412. The first bus and the second bus provide a six-phase output to a load, such as load416, that uses six phases.

With reference next toFIG. 5, an illustration of a phasor diagram showing a relationship between phases in an operation of two variable frequency three electrical phase generators is depicted in accordance with an illustrative embodiment. In this illustrative example, phasor diagram500illustrates phases that may occur during operation of variable frequency generator (G1)404and variable frequency generator (G2)406inFIG. 4.

Phasor diagram500depicts the relative arrangement for three phases from generator (G1)404as A1, B1 and C1 in 120 electrical degrees of displacement, and three phases from generator (G2)406as A2, B2 and C2 with 120 electrical degrees of displacement. Relative to generator (G1)404and generator (G2)406, the rotation of 180 electrical degrees, as illustrated, between phases A1 and A2, B1 and B2, and C1 and C2 produces a six-phase input to load416. Two advantages of this six-phase input are (1) elimination of an internal load416transformer to convert three phases to six phases, and (2) higher electrical efficiency and if a rectifier is used, 230 volts line to line root-mean-square instead of 200 volts line to line root-mean-square result in up to a 15 percentage reduction in feeder currents for the same load electrical power consumption. Reduction of current to load416results in reduced electrical wire weight. Additionally, a balanced average current on each wire to load416results in a six-phase configuration, results in lower neutral currents with lower weight for aircraft, or other vehicle or structure, installations.

For load416with six phase, phasor diagram500depicts the adjacent phase terminal connections that enable a reduced line to line, or phase to phase, voltage difference. In an input termination to load416, an A1, C2, B1, A2, C1 and B2 terminal arrangement would have 115 volts root mean square difference between adjacent terminal connections. In a three-phase arrangement, the A1, B1, C1 and A2, B2, C2 terminal arrangement would have 200 Volt root mean square voltage differences. This can allow closure connections or offer greater reliability for existing spacing. Scaling this arrangement to higher voltage systems, the load connection spacing to load416can be greatly reduced from if an only three-phase arrangement are used.

With reference now toFIG. 6, an illustration of an electrical generator system is depicted in accordance with an illustrative embodiment. In this illustrative example, electrical generator system600is an example of another implementation for electrical generator system206inFIG. 2.

As depicted, electrical generator system600is powered by engine602, engine604, and auxiliary power unit (APU)606. These components are common prime movers and can be located in a platform such as aircraft100inFIG. 1or aircraft204inFIG. 2. For example, engine602can be an example of engine108inFIG. 1and engine604can be an example of engine109inFIG. 1. Auxiliary power unit (APU)606can be an example of auxiliary power unit (APU)134inFIG. 1.

Engine602is a common prime mover for variable frequency generator (L1)608and variable frequency generator (L2)610, and engine604is a common prime mover for variable frequency generator (R1)612and variable frequency generator (R2)614. Auxiliary power unit (APU)606is a common prime mover for generator (A)616.

In this example, bus system618includes bus620, bus622, bus624, and bus626. Bus system618is an example of an implementation for bus system216inFIG. 2.

Variable frequency generator (L1)608is connected to bus620by switch628, and variable frequency generator (L2)610is connected to bus622by switch630. As depicted, variable frequency generator (R1)612is connected to bus624by switch632, and variable frequency generator (R2)614is connected to bus626by switch634.

Variable frequency generator (A)616is connected to switch336, which in turn is connected to switch638and switch640. This grouping of switches provides an ability to connect variable frequency generator (A)616to other buses in bus system618such that variable speed frequency generator (A)616can act as a backup for or failover in case one of the other variable frequency generators does not operate with a desired level of performance.

As depicted, bus620is connected to switch642, bus622is connected to switch644, bus624is connected to switch646, and bus626is connected to switch648. These switches also provide an ability for the variable frequency generators to be connected to other buses and act as backups or failover in case one or more variable frequency generators do not have a desired level of performance.

In this illustrative example, bus620is connected to auto transformer rectifier unit650by switch652. Bus622is connected to auto transformer rectifier unit650by switch654. This provides a parallel configuration of variable frequency generator (L1)608and variable frequency generator (L2)610with respect to auto transformer rectifier unit650. Auto transformer rectifier unit650can change the voltage of the electrical power and convert alternating current power into a direct current power. Auto transformer rectifier unit650is connected to bus656, which may in turn be connected to load658which uses direct current power in this illustrative example.

As depicted, bus624is connected to auto transformer rectifier unit660by switch662. Bus626is connected to auto transformer rectifier unit660by switch664. These switches provide a parallel connection of variable frequency generator (R1)612and variable frequency generator (R2)614. Auto transformer rectifier unit660is connected to bus666. Load668connected to bus666can use direct current power in this example.

In this particular example, switch670and switch672connect to switch638and switch640, respectively. This connection allows for electrical power from variable frequency generator (A)616to be input into auto transformer rectifier unit674, which is connected to bus680. Load682connected to bus680obtains direct current electrical power from variable frequency generator (A)616.

In this particular example, auto transformer rectifier unit650, auto transformer rectifier unit674and auto transformer rectifier unit660are identical units to reduce different part designs in electrical generator system600. For example, these auto transformer rectifier unit may be six-phase rectifiers selected to reduce the need of an auto transformer section for weight and cost considerations.

In another example, these auto transformer rectifier units may be multi-phase rectifiers above six phases for improved direct current power quality, such as twelve phases with twenty-four rectification diodes. These auto transformer rectifier units may have design features that takes advantage of a six-phase input or to mitigate non-normal conditions where only the phases from a single generator or non-synchronized combinations of three-phase electrical power if different prime move generators are mixed in their input to a common six-phase load.

In this illustrative example, since the auto transformer rectifier units, or rectifier units, can accommodate a three-phase input at reduced electrical power loading, a half power limit, the center direct current bus, bus680, may be powered solely by the auxiliary power unit generator, variable frequency generator (A)616, by closing switch636, switch638and switch670and/or switch636, switch640and switch672. Relative to the direct current buses, bus656, bus680, and bus666, electrical generator system600becomes a “split” three channel system. A single loss of an engine or auxiliary power unit, or a fault on an alternating current bus such as bus620, bus622, bus624or bus626, or a direct current bus such as bus656, bus680or bus666, will still offer instantaneously two redundant electrical power direct current buses such as bus656and bus680; bus680and bus666; or bus656and bus666for flight critical loads or loads affecting flight characteristics of the aircraft100as a whole.

In this depicted example, variable frequency generator (A)616is an auxiliary power unit (APU) driven single three-phase generator that has a speed control unit. The speed control unit can adjust the shaft speed of the auxiliary power unit (APU)606so that variable frequency generator (A)616will match a disconnected main engine driven generator.

Being an independent engine, not related to the speed of the aircraft as in the main engines, engine602and engine604, the speed control unit can control the mechanical phase through fuel control and electrical phase sensing with signals from the respective electrical generator system controls or generator control units for at least one of for variable frequency generator (L1)608and variable frequency generator (L2)610, and engine604is a common prime mover for variable frequency generator (R1)612or variable frequency generator (R2)614.

If variable frequency generator (L1)608is not available, the relative rotor angle for generator (A)616can be adjusted and maintained in the desired mechanical phase relative to variable frequency generator (L2)610, and connected to bus620through closing switches, such as switch636, switch638, and switch642. If variable frequency generator (L2)610is not available, the relative rotor angle for generator (A)616can be adjusted and maintained in the desired mechanical phase relative to variable frequency generator (L1)610and connected to bus622through closing switches such as switch636, switch640, and switch644.

If variable frequency generator (R1)612is not available, the relative rotor angle for generator (A)616can be adjusted and maintained in the desired mechanical phase relative to variable frequency generator (R2)614, and connected to bus624through closing switches, such as switch636, switch638, and switch646. If variable frequency generator (R2)614is not available, the relative rotor angle for generator (A)616can be adjusted and maintained in the desired mechanical phase relative to variable frequency generator (R1)612and connected to bus626through closing switches such as switch636, switch640, and switch664.

In this particular example, the electrical architecture in electrical generator system600offers the ability of an aircraft operator, or other vehicle with such a system, to operate in the event of a non-operational electrical generator. For twin propulsion engine aircraft, this enables “dispatch” (flight operations) with sufficient redundancy with a single generator out enabling greater aircraft, or vehicle, availability for use over single generator per propulsion engine architectures.

With reference now toFIG. 7, an illustration of a gear system connected to a pair of variable frequency generator rotors is depicted in accordance with an illustrative embodiment. A single prime mover rotates prime gear701, which in turn rotates generator gear702and generator gear703to mechanically rotate variable frequency generator704and variable frequency generator705. These two variable frequency generators are two-pole generators in the depicted example.

In this illustrative example, variable frequency generator704and variable frequency generator705are examples of variable frequency generators212inFIG. 2. As depicted, prime gear701is an example of prime gear300shown in block form in gear system222inFIG. 3. Generator gear702and generator gear703are examples of generator gears302in gear system222shown in block form inFIG. 3.

Generator gear702is installed within gearbox706, such that the receiving feature707in generator gear702is aligned180mechanical degrees from receiving feature708for generator gear703. In this illustrative example, receiving feature707and receiving feature708are examples of receiving features308shown in block form inFIG. 3.

In this illustrative example, variable frequency generator704and variable frequency generator705are installed via mechanical systems, such as a bolt pattern with bolts. As a result, the stators in variable frequency generator704and variable frequency generator705have the same orientation. These features are used for mechanical phase alignment.

As variable frequency generator704is mechanically inserted into position on gearbox706, rotor709with feature710is placed into generator gear702with receiving feature707. Similarly, when variable frequency generator705is installed onto gearbox706, rotor711with feature712is aligned with receiving feature708in generator gear703.

The result of this alignment of variable frequency generator704and variable frequency generator705is a 180 electrical degree orientation difference between rotor main field713and rotor main field714. A rotor main field is the section of the variable frequency generator that generates a magnetic field to produce the main power of the variable frequency generator in its stator. The rotor main field produces a magnetic field that rotates from the spinning rotor.

Turning next toFIG. 8, an illustration of a flowchart of a process for generating electrical power is depicted in accordance with an illustrative embodiment. The process illustrated inFIG. 8can be implemented in electrical generator system206to generate electrical power208loads210inFIG. 2.

The process begins by operating a plurality of variable frequency generators using a common prime mover (operation800). The process controls the plurality of variable frequency generators using a mechanical phase difference (operation802). The process terminates thereafter. In operation802, the mechanical phase difference is as follows:
MPD=360/GΦp+cf
wherein MPD is the mechanical phase difference in degrees between rotors between a pair of variable frequency generators, G is a number of variable frequency generators, Φ is a number of electrical phases in a variable frequency generator in the plurality of variable frequency generators, p is a number of pole pairs in the variable frequency generator in the plurality of variable frequency generators, and cf is a correction factor based on an alignment of stators in the variable frequency generators.

Further in operation802, the plurality of variable frequency generators is controlled such that each variable frequency generator in the plurality of variable frequency generators has a selected mechanical phase difference from another variable frequency generator in the plurality of variable frequency generators that is an integer multiple of the mechanical phase difference that less than 360 degrees.

With reference toFIG. 9, an illustration of a flowchart of a process for determining a correction factor for a mechanical phase difference is depicted in accordance with an illustrative embodiment. In this flowchart, operations are shown to determine a correction factor when the stators in the variable frequency generators are not identically positioned.

The change in positioning could occur due to environmental factors. These environmental factors may include, for example, the presence of installation volume limits, electrical wiring limitations for bending, proximity to hot sections of the engine installation, accessibility to generator oil servicing, accessibility for oil level inspection, or other objects that may cause a slight rotation or change in the orientation of the housing containing the stators.

The process begins by identifying a difference in the positioning of stators in a variable frequency generator with respect to other stators and other variable frequency generators (operation900). The process identifies a correction factor for the mechanical phase difference (operation902). If all of the stators in all of the variable frequency generators have the same orientation, the correction factor (cf) is zero. The process adjusts the mechanical phase difference taking into account the correction factor (operation904). The mechanical phase difference with the adjustments forms the mechanical phase difference. The process terminates thereafter.

When implemented in hardware, the hardware may, for example, take the form of integrated circuits that are manufactured or configured to perform one or more operations in the flowcharts or block diagrams. When implemented as a combination of program code and hardware, the implementation may take the form of firmware. Each block in the flowcharts or the block diagrams may be implemented using special purpose hardware systems that perform the different operations or combinations of special purpose hardware and program code run by the special purpose hardware.

Illustrative embodiments of the disclosure may be described in the context of aircraft manufacturing and service method1000as shown inFIG. 10and aircraft1100as shown inFIG. 11. Turning first toFIG. 10, an illustration of a block diagram of an aircraft manufacturing and service method is depicted in accordance with an illustrative embodiment. During pre-production, aircraft manufacturing and service method1000may include specification and design1002of aircraft1100inFIG. 11and material procurement1004.

During production, component and subassembly manufacturing1006and system integration1008of aircraft1100inFIG. 11takes place. Thereafter, aircraft1100inFIG. 11may go through certification and delivery1010in order to be placed in service1012. While in service1012by a customer, aircraft1100inFIG. 11is scheduled for routine maintenance and service1014, which may include modification, reconfiguration, refurbishment, and other maintenance or service.

With reference now toFIG. 11, an illustration of a block diagram of an aircraft is depicted in which an illustrative embodiment may be implemented. In this example, aircraft1100is produced by aircraft manufacturing and service method1000inFIG. 10and may include airframe1102with plurality of systems1104and interior1106. Examples of systems1104include one or more of propulsion system1108, electrical system1110, hydraulic system1112, and environmental system1114. In the illustrative example, electrical system1110can be implemented by electrical system120inFIG. 1. One or more components in electrical generators system206can be implemented in electrical system1110.

Any number of other systems may be included. Although an aerospace example is shown, different illustrative embodiments may be applied to other industries. For example, other industries include the automotive industry, shipbuilding industry, manufacturing and production facilities, test facilities, or other suitable industries.

Apparatuses and methods embodied herein may be employed during at least one of the stages of aircraft manufacturing and service method1000inFIG. 10. As used herein, the phrase “at least one of,” when used with a list of items, means different combinations of one or more of the listed items may be used, and only one of each item in the list may be needed. In other words, “at least one of” means any combination of items and number of items may be used from the list, but not all of the items in the list are required. The item may be a particular object, a thing, or a category.

As depicted, components for electrical generator system206inFIG. 2may be designed during specification and design1002. The different components can be manufactured during component and subassembly manufacturing1006and assembled during system integration1008. Further, electrical generator system206can be implemented or changes to mechanical phase difference as can be made while aircraft1100is in maintenance and service1014for different operations such as modification, reconfiguration, refurbishment, and other maintenance or service.

In one illustrative example, components or subassemblies produced in component and subassembly manufacturing1006inFIG. 10may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft1100is in service1012inFIG. 10. As yet another example, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during production stages, such as component and subassembly manufacturing1006and system integration1008inFIG. 10. One or more apparatus embodiments, method embodiments, or a combination thereof may be utilized while aircraft1100is in service1012, during maintenance and service1014inFIG. 10, or both. The use of a number of the different illustrative embodiments may substantially expedite the assembly of aircraft1100, reduce the cost of aircraft1100, or both expedite the assembly of aircraft1100and reduce the cost of aircraft1100.

Thus, the illustrative examples provide a method, apparatus, and system for generating electrical power. In one illustrative example, a method for generating electrical power includes operating variable frequency generators using a common prime mover. The mechanical phase difference between the variable frequency generators are controlled in a manner that reduces undesired energy oscillations. A mechanical phase difference is identified as follows:
MPD=360/GΦp
wherein MPD is the mechanical phase difference in degrees between the rotors between a pair of variable frequency generators, G is a number of variable frequency generators, Φ is a number of electrical phases in a variable frequency generator in the plurality of variable frequency generators, and p is the number of pole pairs in the variable frequency generator in the plurality of variable frequency generators. The variable frequency generators are controlled such that each variable frequency generator in the plurality of variable frequency generators has a selected mechanical phase difference from another variable frequency generator in the plurality of variable frequency generators that is an integer multiple of the mechanical phase difference that less than 360 degrees.

Thus, one or more illustrative examples provide an ability to align phases of different variable frequency generators with mechanical phase offsets in a manner that generates a different number of phases in the overall system of variable frequency generators. In the illustrative examples, the phase alignment of the variable frequency generators using a phase controller in the form of a gear system. This gear system can be a gearbox assembly that is connected to the common prime mover and the plurality of variable frequency generators.

One or more technical solutions are present in the illustrative example that overcome a technical problem with generating electrical power. As a result, one or more technical solutions in the illustrative examples can provide a technical effect of enabling connecting the electrical output of variable frequency generators in a manner that reduces undesired energy oscillations.

Also, one or more of the technical solutions can reduce undesired energy oscillations that include, for example, real and reactive instantaneous power oscillations and unwanted exchanges between generators, gears in gear systems, prime movers, and loads or other components connected to an electrical bus. Further, one or more of the technical solutions enable using variable frequency generators having a lower number of phases that can be combined in parallel to provide a higher number of phases for use by loads.

In the depicted example of the electrical architecture inFIG. 6, the speed control unit in auxiliary power unit (APU)606controls the speed of the auxiliary power unit (APU). This speed control unit can include the sense, communication and control logic, and features to enable generator (A)616to be controlled to replace any one of engine602or engine604driving generator (L1)608, generator (L2)610, generator (R1)612, or generator (R2)614.

Further, one or more technical solutions in the illustrative examples enable utilization of smaller generators to provide a desired number of phases in electrical power for loads that are not possible with currently available configurations of generators driven by aircraft engines or other common prime movers in an aircraft. Additionally, with the ability to operate smaller generators that output electrical power with phases equal to those by larger generators, a reduction weight and complexity can be achieved using one or more of the illustrative examples. Smaller generator diameters may enable smaller diameter engine installation designs, reducing overall engine nacelle drag and optimizing other performance measures.

The description of the different illustrative embodiments has been presented for purposes of illustration and description and is not intended to be exhaustive or limited to the embodiments in the form disclosed. The different illustrative examples describe components that perform actions or operations. In an illustrative embodiment, a component may be configured to perform the action or operation described. For example, the component may have a configuration or design for a structure that provides the component an ability to perform the action or operation that is described in the illustrative examples as being performed by the component.