Patent Description:
Aircraft and other vehicles can include electrical power systems that include power sources that provide electric power to power consumers. Conventionally, a centralized approach has been taken to allocate the power output from each power source to meet the power demand of the power consumers. For instance, supervisor controllers have been used to determine the load share that each power source is responsible to output in order to meet the power demand of the power consumers. Such conventional systems may have certain drawbacks.

<CIT> discloses a protection device for an electricity supply circuit for supplying a load with electricity, which immediately disconnects the circuit to protect the electricity supply circuit and the load when an overcurrent flows to the electricity supply circuit.

Reference will now be made in detail to present embodiments of the disclosure, one or more examples of which are illustrated in the accompanying drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the disclosure.

The present disclosure relates to electrical power systems for vehicles, such as aircraft. Such electrical power systems can include power sources that provide electrical power to one or more power consumers. Conventionally, centralized power allocation systems have been implemented to allocate the power output from each power source to meet the power demand of the power consumers. Such conventional power allocation systems typically employ a supervisor controller that determines the load share that each power source is responsible to output in order to meet the power demand. Such conventional centralized systems may have certain drawbacks. For instance, the supervisor controller may act as a single point of failure, robust communication networks are typically needed, and scaling the electrical power system with a greater number of power sources and/or power consumers can be challenging.

Accordingly, in accordance with the inventive aspects of the present disclosure, various embodiments of decentralized electrical power allocation systems are provided. The decentralized electrical power allocation systems provided herein address the drawbacks of conventional centralized power allocation systems and offer collaborative and adaptive control of the power outputs of the power sources to meet a power demand on a power bus applied by the one or more power consumers. Particularly, the power sources are each controlled by their respective power controllers according to an adaptive droop control scheme that leverages an efficiency of the power sources to generate electrical power for a given power output. Each power controller executes adaptive droop control logic in which power feedback associated with a given power source is correlated to a droop function to ultimately determine the power output or load share of the given power source to meet the power demand. The adaptive droop control scheme implemented by the decentralized electrical power system is collaborative in that the droop functions are predefined to optimize the efficiency of the power sources to meet the power demand. The adaptive droop control scheme is adaptive in that the droop functions can be selected from a plurality of droop functions based on, e.g., operating conditions of the vehicle, the health or degradation of components of the electrical power system and/or vehicle generally, etc. In this regard, the droop functions can be selected for correlation purposes based on the unique operating conditions or health status associated with the vehicle or components thereof.

In one example aspect, a decentralized power allocation system for an aircraft is provided. The decentralized power allocation system includes a power bus, such as a direct current power bus (DC power bus) or an alternating current power bus (AC power bus). The decentralized power allocation system also includes one or more electric power consumers electrically coupled with the power bus. Further, the decentralized power allocation system includes at least two power source assemblies, including a first power source assembly and a second power source assembly. The first power source assembly has a fuel cell electrically coupled with the power bus and a first power controller having first power electronics and one or more processors configured to execute adaptive droop control logic so as to cause the first power electronics to control a power output of the fuel cell based at least in part on a first droop function that represents an efficiency of the fuel cell to generate electrical power for a given power output of the fuel cell. The second power source assembly has an electric machine electrically coupled with the power bus. The electric machine is mechanically coupled with a gas turbine engine, such as a turbofan engine. The second power source assembly also includes a second power controller having second power electronics and one or more processors configured to execute adaptive droop control logic so as to cause the second power electronics to control a power output of the electric machine based at least in part on a second droop function that represents an efficiency of the electric machine to generate electrical power for a given power output of the electric machine.

The first droop function and the second droop function are collaboratively defined such that they intersect at a point corresponding to a reference power level and are coordinated so that the power output of the fuel cell is greater than the power output of the electric machine at power levels less than the reference power level and so that the power output of the electric machine is greater than the power output of the fuel cell at power levels greater than the reference power level. Accordingly, when relatively low power is needed, such as during ground idle or taxi operations of an aircraft, the adaptive droop control scheme allows for the fuel cell to handle all or a majority of relatively low power demand on the power bus. This takes advantage of the physics and characteristics of the fuel cell to operate at high efficiency at low power levels whilst also saving fuel and wear on the electric machine and gas turbine engine to which the electric machine is coupled. Moreover, when relatively high power is needed, such as during flight operations of an aircraft, the adaptive droop control scheme allows for the electric machine mechanically coupled with the gas turbine engine to handle a majority of the relatively high power demand on the power bus. This takes advantage of the physics and characteristics of the electric machine to operate at high efficiency at high power levels whilst also using the fuel cell in part to meet the power demand on the power bus.

Referring now to the drawings, wherein identical numerals indicate the same elements throughout the figures, <FIG> provides a schematic top view of an aircraft <NUM> as may incorporate various embodiments of the present disclosure. As shown in <FIG>, the aircraft <NUM> defines a longitudinal direction L and a transverse direction T. The aircraft <NUM> also defines a longitudinal centerline <NUM> that extends therethrough along the longitudinal direction L. The aircraft <NUM> extends between a forward end <NUM> and an aft end <NUM> along the longitudinal direction L.

In addition, the aircraft <NUM> includes a fuselage <NUM> and a pair of wings <NUM>, including a first wing 22A and a second wing 22B. The first wing 22A extends outward from the fuselage <NUM> generally along the transverse direction T, from a port side <NUM> of the fuselage <NUM>. The second wing 22B similarly extends outward from the fuselage <NUM> generally along the transverse direction T from a starboard side <NUM> of the fuselage <NUM>. The aircraft <NUM> further includes a vertical stabilizer <NUM> and a pair of horizontal stabilizers <NUM>. The fuselage <NUM>, wings <NUM>, and stabilizers <NUM>, <NUM> may together be referred to as a body of the aircraft <NUM>.

The aircraft <NUM> of <FIG> also includes a propulsion system. The propulsion system depicted includes a plurality of aircraft engines, at least one of which is mounted to each of the pair of wings 22A, 22B. Specifically, the plurality of aircraft engines includes a first aircraft engine <NUM> mounted to the first wing 22A and a second aircraft engine <NUM> mounted to the second wing 22B. In at least certain embodiments, the aircraft engines <NUM>, <NUM> may be configured as turbofan engines suspended beneath the wings 22A, 22B in an under-wing configuration. Alternatively, in other example embodiments, the aircraft engines <NUM>, <NUM> may be mounted in other locations, such as to the fuselage <NUM> aft of the wings <NUM>. In yet other embodiments, the first and/or second aircraft engines <NUM>, <NUM> may alternatively be configured as turbojet engines, turboshaft engines, turboprop engines, etc. Further, in other embodiments, the aircraft <NUM> can have less or more than two aircraft engines. The aircraft <NUM> can include one or more upper level computing devices <NUM> communicatively coupled with engine controllers of the first and second aircraft engines <NUM>, <NUM> so as to command a thrust output of the first and second aircraft engines <NUM>, <NUM>. The upper level computing devices <NUM> may receive various sensor inputs that may indicate the operating conditions associated with the aircraft <NUM>, such as the flight phase, altitude, attitude, weather conditions, weight of the aircraft <NUM>, etc. The upper level computing devices <NUM> can be communicatively coupled via a communication network with various processing devices onboard the aircraft <NUM>, such as processors associated with power controllers.

As further shown in <FIG>, the aircraft <NUM> includes an electrical power system <NUM>. For this embodiment, the electrical power system <NUM> includes a power bus <NUM> to which a plurality of electric power sources and a plurality of electric power consumers are electrically coupled. Particularly, for the depicted embodiment of <FIG>, the electrical power system <NUM> includes a first electric machine <NUM> mechanically coupled with the first aircraft engine <NUM> (e.g., to a shaft thereof), a second electric machine <NUM> mechanically coupled with the second aircraft engine <NUM> (e.g., to a shaft thereof), and an electric energy storage system <NUM> having one or more batteries, capacitors, etc..

<FIG> provides a schematic, cross-sectional view of the first aircraft engine <NUM> and depicts the first electric machine <NUM> mechanically coupled thereto. As shown in <FIG>, the first aircraft engine <NUM> defines an axial direction A1 (extending parallel to a longitudinal centerline <NUM> provided for reference), a radial direction R1, and a circumferential direction (extending about the axial direction A1; not depicted in <FIG>). The first aircraft engine <NUM> includes a fan section <NUM> and a core turbine engine <NUM> disposed downstream of the fan section <NUM>.

The core turbine engine <NUM> includes an engine cowl <NUM> that defines an annular core inlet <NUM>. The engine cowl <NUM> encases, in a serial flow relationship, a compressor section including a booster or low pressure (LP) compressor <NUM> and a high pressure (HP) compressor <NUM>; a combustion section <NUM>; a turbine section including a high pressure (HP) turbine <NUM> and a low pressure (LP) turbine <NUM>; and a jet exhaust nozzle section <NUM>. The compressor section, combustion section <NUM>, turbine section, and jet exhaust nozzle section <NUM> together define a core air flowpath <NUM> extending from the annular core inlet <NUM> through the LP compressor <NUM>, HP compressor <NUM>, combustion section <NUM>, HP turbine <NUM>, LP turbine <NUM>, and jet exhaust nozzle section <NUM>. A high pressure (HP) shaft <NUM> drivingly connects the HP turbine <NUM> to the HP compressor <NUM>. The HP shaft <NUM> and rotating components of the HP compressor <NUM> and the HP turbine <NUM> that are mechanically coupled with the HP shaft <NUM> collectively form a high pressure spool <NUM>. A low pressure (LP) shaft <NUM> drivingly connects the LP turbine <NUM> to the LP compressor <NUM>. The LP shaft <NUM> and rotating components of the LP compressor <NUM> and the LP turbine <NUM> that are mechanically coupled with the LP shaft <NUM> collectively form a low pressure spool <NUM>.

The fan section <NUM> may include a fixed or variable pitch fan <NUM> having a plurality of fan blades <NUM> coupled to a disk <NUM> in a spaced apart manner. As depicted, the fan blades <NUM> extend outward from the disk <NUM> generally along the radial direction R1. For the variable pitch fan <NUM> of <FIG>, each fan blade <NUM> is rotatable relative to the disk <NUM> about a pitch axis Px by virtue of the fan blades <NUM> being mechanically coupled to an actuation member <NUM> configured to collectively vary the pitch of the fan blades <NUM> in unison. The fan blades <NUM>, disk <NUM>, and actuation member <NUM> are together rotatable about the longitudinal centerline <NUM> by the LP spool <NUM>. As noted above, in some embodiments, the fan blades <NUM> may be fixed and not rotatable about their respective pitch axes. Further, in other embodiments, the LP spool <NUM> may be mechanically coupled with the fan <NUM> via a gearbox.

Referring still to <FIG>, the disk <NUM> is covered by a spinner or rotatable front hub <NUM> aerodynamically contoured to promote an airflow through the plurality of fan blades <NUM>. Additionally, the fan section <NUM> includes an outer nacelle <NUM> that circumferentially surrounds the fan <NUM> and/or at least a portion of the core turbine engine <NUM>. The nacelle <NUM> is supported relative to the core turbine engine <NUM> by a plurality of circumferentially-spaced outlet guide vanes <NUM>. A downstream section <NUM> of the nacelle <NUM> extends over an outer portion of the core turbine engine <NUM> so as to define a bypass passage <NUM> therebetween.

In addition, for this embodiment, the first electric machine <NUM> is mechanically coupled with the LP spool <NUM>. Particularly, the first electric machine <NUM> is directly mechanically coupled to the LP shaft <NUM>. In other embodiments, the first electric machine <NUM> can be indirectly mechanically coupled to the LP shaft <NUM>, e.g., via a gearbox. In yet other embodiments, the first electric machine <NUM> can be directly or indirectly mechanically coupled to the HP spool <NUM>, such as directly to the HP shaft <NUM> or indirectly with the HP shaft <NUM> by way of a gearbox. In further embodiments, where the first aircraft engine <NUM> has a low pressure spool, an intermediary pressure spool, and a high pressure spool, the first electric machine <NUM> can be directly or indirectly mechanically coupled to the intermediary spool. , such as directly or indirectly to an intermediary shaft of the intermediary spool.

The first electric machine <NUM> includes a rotor 54A and a stator 54B. The rotor 54A is rotatable with the LP shaft <NUM>. The stator 54B includes electric current-carrying elements, such as windings or coils. In this manner, electrical power can be transmitted to or from the electric current-carrying elements, and as will be appreciated, electrical energy can be converted into mechanical energy in a motoring mode or mechanical energy can be converted into electrical energy in a generating mode as the rotor 54A rotates relative to the stator 54B. The rotor 54A has rotor components for creating a rotor magnetic field in order to couple to the stator magnetic field to enable energy conversion. The rotor components of the rotor 54A can be, without limitation, rotor magnets in case of a permanent magnet synchronous machine, a squirrel cage in case of an induction machine, or a field winding in case of a field wound synchronous machine.

It should also be appreciated that the first aircraft engine <NUM> depicted in <FIG> and the first electric machine <NUM> mechanically coupled thereto are provided for example purposes and are not intended to be limiting. In other embodiments, the first aircraft engine <NUM> may have other configurations. For example, in other embodiments, the first aircraft engine <NUM> may be configured as a turboprop engine, a turbojet engine, a differently configured turbofan engine, or an unducted turbofan engine (e.g., without the nacelle <NUM>, but including the stationary outlet guide vanes <NUM>). For example, the gas turbine engine may be a geared gas turbine engine (e.g., having a reduction gearbox between the LP shaft <NUM> and fan <NUM>), may have any other suitable number or configuration of shafts/ spools (e.g., may include an intermediate speed shaft/ turbine/ compressor), etc. Furthermore, it will be appreciated that the second electric machine <NUM> can be configured and mechanically coupled with the second aircraft engine <NUM> (<FIG>) in a same or similar manner as the first electric machine <NUM> is configured and mechanically coupled with the first aircraft engine <NUM>.

Returning now to <FIG>, the first electric machine <NUM>, the second electric machine <NUM>, and the electric energy storage system <NUM> can each act as electric power sources, or in some instances, as electric power consumers. For example, in some instance, the first electric machine <NUM> and/or the second electric machine <NUM> can be electric generators configured to be driven by their respective first and second aircraft engines <NUM>, <NUM> to generate electric power that can be supplied to one or more electric power consumers. In other instances, the first electric machine <NUM> and/or the second electric machine <NUM> can be electric motors configured to drive their respective aircraft engines <NUM>, <NUM>, e.g., in a power assist operation. Accordingly, in such instances, the propulsion system can be a hybrid-electric propulsion system. In some embodiments, the first and/or second electric machines <NUM>, <NUM> can be combination motor/generators controllable in a generator mode or motor mode. The electric energy storage system <NUM> can be controlled to either provide electric power to one or more electric power consumers or draw electric power, e.g., for charging. The electrical power system <NUM> also includes a plurality of electric loads <NUM> that consume but do not produce electric power, such as an aircraft air conditioning system, avionics computing devices, aircraft control systems, cabin lights, etc..

As further depicted in <FIG>, the electrical power system <NUM> also includes a fuel cell assembly <NUM> that is a component of an environmental control system assembly <NUM> (or "ECS assembly <NUM>"). The fuel cell assembly <NUM> can provide electrical power to the plurality of electric loads <NUM> and/or to the first electric machine <NUM>, the second electric machine <NUM>, and/or to the electric energy storage system <NUM> depending on their configurations or mode of operation. The ECS assembly <NUM> is located generally at a juncture between the first wing 22A and the fuselage <NUM>. However, in other exemplary embodiments, the ECS assembly <NUM> may additionally or alternatively be located at other locations within the aircraft <NUM>, such as at a juncture between the second wing 22B and the fuselage <NUM>, at the aft end <NUM> of the aircraft <NUM>, etc. In some embodiments, the ECS assembly <NUM> can include more than one fuel cell assembly, such as two fuel cell assemblies.

<FIG> provides a schematic perspective view of the fuel cell assembly <NUM> of <FIG>. The fuel cell assembly <NUM> includes a fuel cell stack <NUM>. The fuel cell stack <NUM> includes a housing <NUM> having an outlet side <NUM> and a side that is opposite to the outlet side <NUM>, a fuel and air inlet side <NUM> and a side that is opposite to the fuel and air inlet side <NUM>. The fuel cell stack <NUM> can include a plurality of fuel cells <NUM> that are "stacked," e.g., side-by-side from one end of the fuel cell stack <NUM> (e.g., fuel and air inlet side <NUM>) to another end of the fuel cell stack <NUM> (e.g., side <NUM>). As such, the outlet side <NUM> includes a plurality of outlets <NUM>, each from a respective fuel cell <NUM> of the fuel cell stack <NUM>. During operation, output products <NUM> are directed from the outlets <NUM> out of the housing <NUM>. In some embodiments, the outlets <NUM> can include separate fuel outlets (which may be in fluid communication with, e.g., a fuel exhaust line) and air outlets (which may be in fluid communication with e.g., a fuel cell outlet line of a cabin exhaust delivery system). The fuel and air inlet side <NUM> includes one or more fuel inlets <NUM> and one or more air inlets <NUM>. Optionally, one or more of the inlets <NUM>, <NUM> can be on another side of the housing <NUM>. Each of the one or more fuel inlets <NUM> can be fluidly coupled with, e.g., a fuel delivery line of a fuel delivery system. Each of the one or more air inlets <NUM> can be fluidly coupled with, e.g., a fuel cell inlet line of an air delivery system.

<FIG> provides a close-up, schematic view of one fuel cell <NUM> of the fuel cell stack <NUM> of <FIG>. The fuel cells <NUM> of the fuel cell assembly <NUM> are electro-chemical devices that may convert chemical energy from a fuel into electrical energy through an electro-chemical reaction of the fuel, such as hydrogen, with an oxidizer, such as oxygen contained in the atmospheric air. Accordingly, the fuel cell assembly <NUM> can advantageously be utilized as a power source. The example fuel cell <NUM> depicted in <FIG>, and each of the fuel cells <NUM> of the fuel cell stack <NUM> of <FIG>, are configured as proton exchange membrane fuel cells ("PEM fuel cells"), also known as a polymer electrolyte membrane fuel cell. PEM fuel cells have an operating temperature range and operating temperature pressure determined to work well with the conditions associated with aircraft and other vehicles.

As depicted schematically in <FIG>, the fuel cell <NUM> includes a cathode side <NUM>, an anode side <NUM>, and an electrolyte layer <NUM> positioned between the cathode side <NUM> and the anode side <NUM>. The cathode side <NUM> can include a cathode <NUM> and the anode side <NUM> can include an anode <NUM>. Further, the cathode side <NUM> includes a cathode inlet <NUM> and a cathode outlet <NUM> and the anode side <NUM> includes an anode inlet <NUM> and an anode outlet <NUM>. The cathode side <NUM> of the fuel cell <NUM>, and more specifically, the cathode inlet <NUM> of the cathode side <NUM>, can be in fluid communication with, e.g., a cabin exhaust delivery system, and more specifically, a fuel cell inlet line of the cabin exhaust delivery system. The cathode outlet <NUM> is in fluid communication with a fuel cell outlet line of the cabin exhaust delivery system. Similarly, the anode side <NUM> of the fuel cell <NUM>, and more specifically, the anode inlet <NUM> of the anode side <NUM>, is in fluid communication with, e.g., a fuel delivery line of a fuel delivery system. The anode outlet <NUM> is in fluid communication with e.g., a fuel exhaust line of the fuel delivery system. Accordingly, air may pass through the cathode side <NUM> and fuel may pass through the anode side <NUM>.

Returning to <FIG>, the electrical power system <NUM> includes a plurality of power controllers. Each power controller can include one or more processors and one or more non-transitory memory devices, e.g., embodied in a controller, and power electronics to convert electrical power, e.g., from alternating current (AC) to direct current (DC) or vice versa, or to condition the electrical power to a desired voltage, current, or both. As depicted in <FIG>, the first electric machine <NUM> has an associated power controller <NUM> that controls the electric power between the first electric machine <NUM> and the power bus <NUM>. Likewise, the second electric machine <NUM> has an associated power controller <NUM> that controls the electric power between the second electric machine <NUM> and the power bus <NUM>. The electric energy storage system <NUM> also has an associated power controller <NUM> that controls the electric power between the electric energy storage system <NUM> and the power bus <NUM>. In addition, the fuel cell assembly <NUM> has an associated power controller <NUM> that controls the electric power between the fuel cell assembly <NUM> and the power bus <NUM>. Similarly, power controllers <NUM> can be arranged to control the electric power provided from the power bus <NUM> to the power consuming one or more electric loads <NUM>.

For this embodiment, the electrical power system <NUM> is configured as a decentralized power allocation system. That is, the architecture of the electrical power system <NUM> enables the power controllers to control the electrical power outputs of their respective power sources to meet the power demands of the power consumers collaboratively, adaptively, and without active supervision, e.g., from a supervisor controller. Decentralized control of electric power transmission from power sources to one or more power consumers can provide certain advantages, benefits, and technical effects. For instance, the decentralized electrical power allocation systems provided herein may address the drawbacks of conventional centralized power allocation systems and offer collaborative and adaptive control of the power outputs of the power sources to meet a power demand on a power bus applied by the one or more power consumers. In this regard, less computing resources and communication networks may be needed (which has the added benefit of reducing the weight of a vehicle), and localized control can be achieved whilst still being collaborative with other power sources and adaptive to meet to the power demand on the power bus. The inventive aspects of a decentralized power allocation system, which may be incorporated into the electrical power system <NUM> of the aircraft <NUM> of <FIG> as well as other vehicles, will be provided below in detail.

<FIG> provides a system diagram of an electrical power system <NUM> according to an example embodiment of the present disclosure. The electrical power system <NUM> is configured as a decentralized power allocation system in <FIG>. The electrical power system <NUM> can be implemented in a vehicle, such as the aircraft <NUM> of <FIG>, ships, trains, unmanned aerial vehicles, automobiles, etc..

As depicted in <FIG>, the electrical power system <NUM> includes a direct current power bus (or DC power bus <NUM>), a plurality of power source assemblies <NUM> electrically coupled with the DC power bus <NUM>, and one or more electric power consumers <NUM> electrically coupled with the DC power bus <NUM>. The electrical power system <NUM> further includes a communication bus <NUM> (shown in dashed lines in <FIG>), which may include one or more wired or wireless communication links. The communication bus <NUM> enables communication between various components of the electrical power system <NUM>.

For this embodiment, the plurality of power source assemblies <NUM> include a first power source assembly <NUM> and a second power source assembly <NUM>. Each power source assembly includes an electric power source and a power controller. For instance, the first power source assembly <NUM> has a first power source <NUM> and a first power controller <NUM>. The second power source assembly <NUM> has a second power source <NUM> and a second power controller <NUM>. For this example embodiment, the first power source <NUM> is a fuel cell and the second power source <NUM> is an electric machine configured as an electric generator or operable in a generator mode. As represented in <FIG>, the plurality of power source assemblies <NUM> can include more than two (<NUM>) power source assemblies in other example embodiments, or N-S number of power source assemblies, wherein N-S is an integer equal to or greater than two (<NUM>).

The first power source <NUM> and the second power source <NUM> are electrically coupled with the DC power bus <NUM>. The first power controller <NUM> controls electric power provided from the first power source <NUM> to the DC power bus <NUM>. Similarly, the second power controller <NUM> controls electric power provided from the second power source <NUM> to the DC power bus <NUM>. The first power controller <NUM> and the second power controller <NUM> each include one or more processors and one or more non-transitory memory devices embodied in a first controller <NUM> and a second controller <NUM>, respectively. The first power controller <NUM> includes first power electronics <NUM> to convert or condition electrical power provided from the first power source <NUM> to the DC power bus <NUM>. The first power electronics <NUM> can include a plurality of switches controllable in a switching scheme, for example. Similarly, the second power controller <NUM> includes second power electronics <NUM> to convert or condition electrical power provided from the second power source <NUM> to the DC power bus <NUM>. The second power electronics <NUM> can include a plurality of switches controllable in a switching scheme, for example. The first controller <NUM> and the second controller <NUM> are communicatively coupled with one another (and to other components) via the communication bus <NUM>.

The one or more electric power consumers <NUM> include a first power consumer <NUM> and a second power consumer <NUM> in this example embodiment. In some embodiments, the first power consumer <NUM> can represent one or more mission critical or essential loads and the second power consumer <NUM> can represent one or more non-essential loads. The one or more electric power consumers <NUM>, or sensors or communication interfaces thereof, can be communicatively coupled with the first controller <NUM> and the second controller <NUM> of the first and second power source assemblies <NUM>, <NUM> via the communication bus <NUM>. As represented in <FIG>, the one or more electric power consumers <NUM> can include one or more power consumers, or N-C number of power consumer assemblies, wherein N-C is an integer equal to or greater than one (<NUM>).

In addition, for the depicted embodiment of <FIG>, the first power consumer <NUM> and the second power consumer <NUM> are both directly electrically coupled with the DC power bus <NUM>. However, in other embodiments, the first power consumer <NUM> and/or the second power consumer <NUM> can be indirectly electrically coupled with the DC power bus <NUM>. For example, an intermediate power bus and/or other power electronics can be positioned electrically between the DC power bus <NUM> and the first power consumer <NUM> and/or the second power consumer <NUM>.

The decentralized power allocation control aspects will now be provided with reference to <FIG>, <FIG> provides a logic flow diagram for allocating power to be output by the first power source <NUM> to meet the power demand on the DC power bus <NUM>. <FIG> provides a logic flow diagram for allocating power to be output by the second power source <NUM> to meet the power demand on the DC power bus <NUM>.

As shown particularly in <FIG> and with general reference to <FIG>, the first controller <NUM> includes adaptive droop control logic <NUM> in accordance with an adaptive droop control scheme. In executing the adaptive droop control logic <NUM>, the one or more processors of the first controller <NUM> can regulate the power output of the first power source <NUM>, which as noted above, is a fuel cell in this example embodiment (hence the "FC" designations in <FIG>).

A power feedback Pfbk-FC is input into a droop control block <NUM>. The power feedback Pfbk-FC can be a measured, calculated, or predicted value indicating the power output of the first power source <NUM>. For instance, one or more sensors can sense the voltage, frequency, and/or the electric current proximate the first power source <NUM> to measure, calculate, or predict the power output of the first power source <NUM>. At the droop control block <NUM>, the power feedback Pfbk-FC is used for correlation purposes. Particularly, the power feedback Pfbk-FC can be correlated with a first droop function fdrp-FC associated with the first power source <NUM> to determine a voltage setpoint vREF-FC. The voltage setpoint vREF-FC can be determined as the y-component of the point along the first droop function fdrp-FC that corresponds with the power feedback Pfbk-FC. The first droop function fdrp-FC or curve represents an efficiency of the first power source <NUM> to generate electrical power for a given power output of the first power source <NUM>.

The first droop function fdrp-FC used for the correlation can be selected from a plurality of first droop functions associated with the first power source <NUM> as represented in <FIG>. The first droop function fdrp-FC used for correlation purposes can be selected based at least in part on one or more operating conditions <NUM> (<FIG>) associated with the vehicle in which the electrical power system <NUM> is implemented. For instance, for an aircraft, the first droop function fdrp-FC can be selected based on a phase of flight, an altitude of the aircraft, a number of passengers onboard the aircraft, weather conditions, a combination of the foregoing, etc. These noted operating conditions may each affect the power demand on the DC power bus <NUM>.

As one example, the plurality of first droop functions can include a first droop function for each phase of flight, such as one for takeoff, one for climb, one for cruise, one for descent, and one for approach and landing. As another example, the plurality of first droop functions can include a first droop function for different altitude ranges, such as one for zero (<NUM>) to ten thousand (<NUM>,<NUM>) feet, one for ten thousand one (<NUM>,<NUM>) to twenty thousand (<NUM>,<NUM>) feet, and one for twenty thousand one (<NUM>,<NUM>) feet and above. The altitude ranges can be defined with respect to feet above sea level or above ground level. As yet another example, the plurality of first droop functions can include a first droop function for different ranges of passengers onboard, such as one first droop function for a first range of passengers (e.g., <NUM> to <NUM> passengers), one for a second range of passengers (e.g., <NUM> to <NUM> passengers), and one for a third range of passengers (e.g., <NUM> passengers and up). The plurality of first droop functions selectable for correlation purposes can each have different slopes and/or different y-intercepts. The first droop functions or curves each represent an efficiency of the first power source <NUM> to generate electrical power for a given power output of the first power source <NUM> at a given set of operating conditions.

As noted above, the selected first droop function fdrp-FC can be used to schedule or determine the voltage setpoint vREF-FC associated with the first power source <NUM>. More specifically, the voltage setpoint vREF-FC can be determined as the y-component of the point along the first droop function fdrp-FC that corresponds with the power feedback Pfbk-FC. In this regard, the voltage setpoint vREF-FC is set as a function of the power feedback Pfbk-FC. The y-intercept of the first droop function fdrp-FC selected for correlation purposes in <FIG> is denoted as vSET-FC.

As further shown in <FIG>, the determined voltage setpoint vREF-FC is output from the droop control block <NUM> and forwarded to a voltage loop of the adaptive droop control logic <NUM>. Particularly, the voltage setpoint vREF-FC is input into a first summation block <NUM> and compared to a voltage feedback vfbk-FC. The voltage feedback vfbk-FC can be a measured, calculated, or predicted value indicating the voltage at the first power source <NUM>, e.g., at output terminals thereof. A voltage difference vΔ-FC is determined at the first summation block <NUM>, e.g., by subtracting the voltage setpoint vREF-FC from the voltage feedback vfbk-FC or vice versa. The voltage difference vΔ-FC is then input into a proportional-integral control <NUM>, which generates one or more outputs that can be input into a switching logic control <NUM> that controls modulation of switching devices of the first power electronics <NUM>, e.g., in a Pulse Width Modulated (PWM) switching scheme. Accordingly, a power output <NUM> of the first power source <NUM> is achieved. The power output <NUM> is affected by a disturbance, which is a power demand <NUM> on the DC power bus <NUM>, as represented at a second summation block <NUM>.

As shown particularly in <FIG> and with general reference to <FIG>, the second controller <NUM> includes adaptive droop control logic <NUM> in accordance with the adaptive droop control scheme. In executing the adaptive droop control logic <NUM>, the one or more processors of the second controller <NUM> can regulate the power output of the second power source <NUM>, which as noted above, is an electric generator or electric machine operable in a generator mode in this example embodiment (hence the GEN" designations in <FIG>).

A power feedback Pfbk-GEN is input into a droop control block <NUM>. The power feedback Pfbk-GEN can be a measured, calculated, or predicted value indicating the power output of the second power source <NUM>. For instance, one or more sensors can sense the voltage, frequency, and/or the electric current proximate the second power source <NUM> to measure, calculate, or predict the power output of the second power source <NUM>. At the droop control block <NUM>, the power feedback Pfbk-GEN is used for correlation purposes. Particularly, the power feedback Pfbk-GEN can be correlated with a second droop function fdrp-GEN associated with the second power source <NUM> to determine a voltage setpoint vREF-GEN. The voltage setpoint vREF-GEN can be determined as the y-component of the point along the second droop function fdrp-GEN that corresponds with the power feedback Pfbk-GEN. The second droop function fdrp-GEN or curve represents an efficiency of the second power source <NUM> to generate electrical power for a given power output of the second power source <NUM>.

The second droop function fdrp-GEN used for the correlation can be selected from a plurality of second droop functions associated with the second power source <NUM> as represented in <FIG>. The second droop function fdrp-GEN used for correlation purposes can be selected based at least in part on one or more operating conditions <NUM> (<FIG>) associated with the vehicle in which the electrical power system <NUM> is implemented. For instance, for an aircraft, the second droop function fdrp-GEN can be selected based on a phase of flight, an altitude of the aircraft, a number of passengers onboard the aircraft, weather conditions, a combination of the foregoing, etc. These noted operating conditions may each affect the power demand on the DC power bus <NUM>. The one or more operating conditions <NUM> received by the second controller <NUM> of <FIG> can be the same as the one or more operating conditions <NUM> received by the first controller <NUM> of <FIG>. The plurality of second droop functions selectable for correlation purposes can each have different slopes and/or different y-intercepts. The second droop functions or curves each represent an efficiency of the second power source <NUM> to generate electrical power for a given power output of the second power source <NUM> at a given set of operating conditions.

As noted previously, the selected first droop function fdrp-GEN can be used to schedule or determine the voltage setpoint vREF-GEN associated with the second power source <NUM>. More particularly, the voltage setpoint vREF-GEN can be determined as the y-component of the point along the second droop function fdrp-GEN that corresponds with the power feedback Pfbk-GEN. In this regard, the voltage setpoint vREF-GEN is set as a function of the power feedback Pfbk-GEN. The y-intercept of the second droop function fdrp-GEN selected for correlation purposes in <FIG> is denoted as vSET-GEN.

The voltage setpoint vREF-GEN is output from the droop control block <NUM> and forwarded to a voltage loop of the adaptive droop control logic <NUM>. Particularly, the voltage setpoint vREF-GEN is input into a first summation block <NUM> and compared to a voltage feedback vfbk-GEN. The voltage feedback Vfbk-GEN can be a measured, calculated, or predicted value indicating the voltage at the second power source <NUM>, e.g., at output terminals thereof. A voltage difference vΔ-GEN is determined at the first summation block <NUM>, e.g., by subtracting the voltage setpoint vREF-GEN from the voltage feedback vfbk-GEN or vice versa. The voltage difference vΔ-GEN is then input into a proportional-integral control <NUM>, which generates one or more outputs that can be input into a switching logic control <NUM> that controls modulation of switching devices of the second power electronics <NUM>, e.g., in a PWM switching scheme. Accordingly, a power output <NUM> of the second power source <NUM> is achieved. The power output <NUM> is affected by a disturbance, which is the power demand <NUM> on the DC power bus <NUM>, as represented at a second summation block <NUM>.

Accordingly, each power controller of the power source assemblies <NUM> includes executable adaptive droop control logic, e.g., similar to the adaptive droop control logic <NUM>, <NUM> depicted in <FIG>. When a given power controller executes its adaptive droop control logic, the one or more processors of the given power controller cause its associated power electronics to control the power output of its associated power source. This adaptive droop control scheme executed by each power controller of the power source assemblies <NUM> enables intelligent decentralized power allocation for meeting power demands on the DC power bus <NUM> applied by the electric power consumers <NUM>. Specifically, implementation of the adaptive droop control scheme enables decentralized DC bus regulation according to the efficiencies of the power sources at given power outputs.

For instance, with reference to <FIG> and <FIG> provides a graph representing the first droop function fdrp-FC associated with the first power source <NUM> overlaid with the second droop function fdrp-GEN associated with the second power source <NUM> on a DC bus voltage versus power output graph. As noted above, the first droop function fdrp-FC represents an efficiency of the first power source <NUM> to generate electrical power for a given power output of the first power source <NUM> and the second droop function fdrp-GEN represents an efficiency of the second power source <NUM> to generate electrical power for a given power output of the second power source <NUM>. According, the droop functions are also functions of power output efficiency η.

As shown in <FIG>, the droop functions have different slopes and different y-intercepts, with the first droop function fdrp-FC having a steeper slope than the second droop function fdrp-GEN and the first droop function fdrp-FC having a greater y-intercept than the second droop function fdrp-GEN. Also, the droop functions intersect at a point PInt corresponding to a reference power level PRF. Accordingly, the first power source <NUM>, or fuel cell for this example, is more efficient at outputting electric power at lower power levels than the second power source <NUM>, or electric machine in this example. In contrast, at higher power levels, the second power source <NUM> is more efficient at outputting electric power than the first power source <NUM>. In this regard, the droop functions are coordinated so that the power output of the first power source <NUM>, or fuel cell, is greater than the power output of the second power source <NUM>, or electric machine, at power levels less than the reference power level PRF and so that the power output of the second power source <NUM>, or electric machine, is greater than the power output of the first power source <NUM>, or fuel cell, at power levels greater than the reference power level PRF.

Particularly, as shown in <FIG>, for a given DC bus voltage, the working point of both the first power source <NUM> and the second power source <NUM> will both be on the same horizontal line as the first and second power sources <NUM>, <NUM> are electrically coupled to a common power bus, or DC power bus <NUM> in this example. For instance, for a first DC bus voltage vDC BUS <NUM>, the working point of the first power source <NUM>, or fuel cell, and the working point of the second power source <NUM>, or electric machine, are on the same horizontal line. The working point of the first power source <NUM> is denoted as PT1-FC and the working point of the second power source <NUM> is denoted as PT1-GEN. For the first DC bus voltage vDC BUS <NUM>, the first power source <NUM>, or fuel cell, has a power output of P1 while the second power source <NUM>, or electric machine, has a power output of P0.

Accordingly, the first power source <NUM> has a greater load share or power output at the first DC bus voltage vDC BUS <NUM> than does the second power source <NUM>. The power output of P0 is equal to zero (<NUM>) in this instance, as the y-intercept of the second droop function fdrp-GEN is less than the first DC bus voltage vDC BUS <NUM>. Accordingly, to meet the first DC bus voltage vDC BUS <NUM>, only the first power source <NUM>, or fuel cell, outputs electric power. Thus, the load share split is <NUM>%/<NUM>%, with the first power source <NUM> being at <NUM>% and the second power source <NUM> at <NUM>%. Advantageously, when relatively low power is needed, such as during ground idle or taxi operations of an aircraft, the adaptive droop control scheme allows for the first power source <NUM>, or fuel cell, to handle all or most of the relatively low power demand on the DC power bus <NUM>. This takes advantage of the physics and characteristics of the fuel cell to operate at high efficiency at low power levels whilst also saving fuel and wear on the electric machine and gas turbine engine to which the electric machine is coupled.

For a second DC bus voltage vDC BUS <NUM>, which corresponds to a lower voltage level than the first DC bus voltage vDC BUS <NUM>, the working point of the first power source <NUM>, or fuel cell, and the working point of the second power source <NUM>, or electric machine, are on the same horizontal line. The working point of the first power source <NUM> is denoted as PT2-FC and the working point of the second power source <NUM> is denoted as PT2-GEN. For the second DC bus voltage vDC BUS <NUM>, the first power source <NUM>, or fuel cell, and the second power source <NUM>, or electric machine, both have the same power output, which corresponds to the reference power level PRF. Accordingly, the first power source <NUM> and the second power source <NUM> have a same load share or power output at the second DC bus voltage vDC BUS <NUM>. Thus, the load share split is <NUM>%/<NUM>%, with the first power source <NUM> being at <NUM>% and the second power source <NUM> being at <NUM>% to meet the power demand on the DC power bus <NUM>.

Further, for a third DC bus voltage vDC BUS <NUM>, which corresponds to a lower voltage level than the second DC bus voltage vDC BUS <NUM>, the working point of the first power source <NUM>, or fuel cell, and the working point of the second power source <NUM>, or electric machine, are on the same horizontal line. The working point of the first power source <NUM> is denoted as PT3-FC and the working point of the second power source <NUM> is denoted as PT3-GEN. For the third DC bus voltage vDC BUS <NUM>, the first power source <NUM>, or fuel cell, has a power output of P2 while the second power source <NUM>, or electric machine, has a power output of P3, which is greater than the power output of P2.

Accordingly, the second power source <NUM> has a greater load share or power output at the third DC bus voltage vDC BUS <NUM> than does the first power source <NUM>. The load share split can be <NUM>%/<NUM>%, with the first power source <NUM> being at <NUM>% and the second power source <NUM> at <NUM>%, for example. Advantageously, when relatively high power is needed, such as during flight operations of an aircraft, the adaptive droop control scheme allows for the second power source <NUM>, or electric machine mechanically coupled with a gas turbine engine, to handle most of the relatively high power demand on the DC power bus <NUM>. This takes advantage of the physics and characteristics of the electric machine to operate at high efficiency at high power levels whilst also using the fuel cell in part to meet the power demand on the DC power bus <NUM>.

Accordingly, the power allocation for the power sources is set according to the characteristics of the droop functions, such as their slopes, y-intercepts, and overall shapes. For the depicted embodiment of <FIG>, as the droop functions converge toward one another, the load share between the first power source <NUM> and the second power source <NUM> becomes more balanced, as represented at the second DC bus voltage vDC BUS <NUM>. Conversely, as the droop functions diverge away from one another, the load share between the first power source <NUM> and the second power source <NUM> becomes less balanced, as represented at the first DC bus voltage vDC BUS <NUM> and the third DC bus voltage vDC BUS <NUM>.

The droop functions depicted in <FIG>, and <FIG>, are linear functions. However, one or more of the droop functions can be non-linear functions in other example embodiments. For instance, <FIG> provides a graph representing a non-linear first droop function fdrp-FC associated with the first power source <NUM> overlaid with the second droop function fdrp-GEN associated with the second power source <NUM> on a DC bus voltage versus power output graph. The non-linear first droop function fdrp-FC may better represent the efficiency of the first power source <NUM>, or fuel cell, to output electric power at a given power output. Further, the second droop function fdrp-GEN may be linear, but may be a piecewise linear function. For this example embodiment, the piecewise linear second droop function fdrp-GEN includes a first segment having a first slope and a second segment having a second slope that is different than the first slope. For this example, the first segment is steeper than the second segment of the second droop function fdrp-GEN. Such a piecewise linear second droop function fdrp-GEN having various slopes may better represent the efficiency of the second power source <NUM>, or electric machine, to output electric power at a given power output. The droop functions can have other curves or shapes as well, such as polynomial shapes.

<FIG> provides a system diagram of an electrical power system <NUM> according to another example embodiment of the present disclosure. The electrical power system <NUM> is configured as a decentralized power allocation system in <FIG>. The electrical power system <NUM> of <FIG> can be implemented in a vehicle, such as the aircraft <NUM> of <FIG>, ships, trains, unmanned aerial vehicles, automobiles, etc. The electrical power system <NUM> of <FIG> is configured in a similar manner as the electrical power system <NUM> of <FIG>, and therefore, like parts will be identified with like numerals with it being understood that the description of the like parts of the electrical power system <NUM> applies to the electrical power system <NUM> unless otherwise noted. Notably, the electrical power system <NUM> of <FIG> includes an alternating current power bus (or AC power bus <NUM>) to which the plurality of power source assemblies <NUM> and the one or more electric power consumers <NUM> are electrically coupled. Single or multiphase power can be transmitted along the AC power bus <NUM>.

In addition, for the depicted embodiment of <FIG>, the first power consumer <NUM> and the second power consumer <NUM> are both directly electrically coupled with the AC power bus <NUM>. However, in other embodiments, the first power consumer <NUM> and/or the second power consumer <NUM> can be indirectly electrically coupled with the AC power bus <NUM>. For example, an intermediate power bus and/or other power electronics can be positioned electrically between the AC power bus <NUM> and the first power consumer <NUM> and/or the second power consumer <NUM>.

For the electrical power system <NUM> of <FIG> having the AC power bus <NUM>, the adaptive droop control scheme is implemented in a similar manner as described above with reference to the DC power bus <NUM> of <FIG>, except as provided below. As will be appreciated, a sinusoidal voltage waveform on an AC power bus has both a frequency and an amplitude. The frequency of a voltage waveform is highly coupled with active power, or power that is utilized and consumed for useful work in electrical systems. The amplitude of a voltage waveform is highly coupled with reactive power, or power that "bounces" back and forth between the power source(s) and power consumer(s) in electrical systems. Accordingly, active power is more sensitive to changes in frequency on the AC power bus <NUM> while reactive power is more sensitive to changes in amplitude.

With these considerations in mind, the decentralized power allocation control aspects will now be provided with reference to <FIG>, <FIG>, and <FIG>. <FIG> provides a logic flow diagram for allocating power to be output by the first power source <NUM>, or fuel cell, to meet the power demand on the AC power bus <NUM>. <FIG> provides a logic flow diagram for allocating power to be output by the second power source <NUM>, or electric machine, to meet the power demand on the AC power bus <NUM>.

As shown particularly in <FIG> and with general reference to <FIG>, the first controller <NUM> includes adaptive droop control logic <NUM> in accordance with an adaptive droop control scheme for AC power bus systems. In executing the adaptive droop control logic <NUM>, the one or more processors of the first controller <NUM> can regulate the power output of the first power source <NUM>, which as noted above, is a fuel cell in this example embodiment (hence the "FC" designations in <FIG>).

The adaptive droop control logic <NUM> includes active power droop control. As depicted, a power feedback Pfbk-FC, which relates to active power, is input into an active power droop control block <NUM>. The power feedback Pfbk-FC can be a measured, calculated, or predicted value indicating the active power output of the first power source <NUM>. For instance, one or more sensors can sense the voltage, frequency, and/or the electric current proximate the first power source <NUM> to measure, calculate, or predict the active power output of the first power source <NUM>. At the active power droop control block <NUM>, the power feedback Pfbk-FC is used for correlation purposes. Particularly, the power feedback Pfbk-FC can be correlated with a first active droop function fdrp-FC-A associated with the first power source <NUM> to determine a frequency setpoint fREF-FC.

The first active droop function fdrp-FC-A used for the correlation can be selected from a plurality of first active droop functions associated with the first power source <NUM>. The first active droop function fdrp-FC-A can be selected based at least in part on one or more operating conditions <NUM> (<FIG>) associated with the vehicle in which the electrical power system <NUM> is implemented. For instance, for an aircraft, the first active droop function fdrp-FC-A can be selected based on a phase of flight, altitude of the aircraft, number of passengers onboard the aircraft, weather conditions, a combination of the foregoing, etc. The first droop functions or curves represent an efficiency of the first power source <NUM> to generate electrical power for a given power output of the first power source <NUM> at a given set of operating conditions.

The selected first active droop function fdrp-FC-A can be used to schedule or determine the frequency setpoint fREF-FC associated with the first power source <NUM>. More particularly, the frequency setpoint fREF-FC can be determined as the y-component of the point along the first active droop function fdrp-FC-A that corresponds with the power feedback Pfbk-FC. In this regard, the frequency setpoint fREF-FC is set as a function of the power feedback Pfbk-FC. The y-intercept of the first active droop function fdrp-FC-A selected for correlation purposes in <FIG> is denoted as FSET-FC.

The frequency setpoint fREF-FC is output from the droop control block <NUM> and input into a first summation block <NUM> and compared to a frequency feedback ffbk-FC. The frequency feedback ffbk-FC can be a measured, calculated, or predicted value indicating the frequency at the first power source <NUM>, e.g., at output terminals thereof. A frequency difference fΔ-FC is determined at the first summation block <NUM>, e.g., by subtracting the frequency setpoint fREF-FC from the frequency feedback ffbk-FC or vice versa.

As further shown in <FIG>, for AC power bus systems, the adaptive droop control logic <NUM> includes reactive power droop control in addition to the active power droop control disclosed above. As illustrated, a power feedback Qfbk-FC, which relates to reactive power, is input into a reactive power droop control block <NUM>. The power feedback Qfbk-FC can be a measured, calculated, or predicted value indicating the reactive power at the first power source <NUM>, or rather the power that moves back and forth between the first power source <NUM> and the one or more electric power consumers <NUM>. For instance, a varmeter can be used to measure, calculate, or predict the reactive power at the first power source <NUM>. At the reactive power droop control block <NUM>, the power feedback Qfbk-FC is used for correlation purposes. Specifically, the power feedback Qfbk-FC can be correlated with a first reactive droop function fdrp-FC-R associated with the first power source <NUM> to determine a voltage amplitude setpoint vREF_AC-FC.

The first reactive droop function fdrp-FC-R used for the correlation can be selected from a plurality of first reactive droop functions associated with the first power source <NUM>. The first reactive droop function fdrp-FC-R can be selected based at least in part on one or more operating conditions <NUM> (<FIG>) associated with the vehicle in which the electrical power system <NUM> is implemented. For instance, for an aircraft, the first reactive droop function fdrp-FC-R can be selected based on a phase of flight, altitude of the aircraft, number of passengers onboard the aircraft, weather conditions, a combination of the foregoing, etc..

The selected first reactive droop function fdrp-FC-R can be used to schedule or determine the voltage amplitude setpoint vREF_AC-FC associated with the first power source <NUM>. More particularly, the voltage amplitude setpoint vREF_AC-FC can be determined as the y-component of the point along the first reactive droop function fdrp-FC-R that corresponds with the power feedback Qfbk-FC. In this regard, the voltage amplitude setpoint vREF_AC-FC is set as a function of the power feedback Qfbk-FC, which corresponds to reactive power feedback. The y-intercept of the first reactive droop function fdrp-FC-R selected for correlation purposes in <FIG> is denoted as vSET-FC. The power feedback Qfbk-FC is bound by an inductive limit -QMax and a capacitive limit QMax.

The voltage amplitude setpoint vREF_AC-FC is output from the reactive power droop control block <NUM> and input into a second summation block <NUM>. The voltage amplitude setpoint vREF_AC-FC is compared to a voltage amplitude feedback ffbk_AC-FC at the second summation block <NUM>. The voltage amplitude feedback ffbk_AC-FC can be a measured, calculated, or predicted value indicating the voltage amplitude at the first power source <NUM>, e.g., at output terminals thereof. A voltage amplitude difference vΔ-FC is determined at the second summation block <NUM>, e.g., by subtracting the voltage amplitude setpoint vREF_AC-FC from the voltage amplitude feedback ffbk_AC-FC or vice versa.

The frequency difference fΔ-FC and the voltage amplitude difference vΔ-FC are input into a voltage synthesizer <NUM>, which generates one or more outputs (e.g., a modulation index) that can be input into a switching logic control <NUM> that controls modulation of switching devices of the first power electronics <NUM>, e.g., in a PWM switching scheme. Accordingly, a power output <NUM> of the first power source <NUM> is achieved. The power output <NUM> has an active power component and a reactive power component. The power output <NUM> is affected by a disturbance, which is a power demand <NUM> on the AC power bus <NUM>, as represented at a third summation block <NUM>.

Like the adaptive droop control logic <NUM> (<FIG>) associated with the first power source assembly <NUM>, the adaptive droop control logic <NUM> associated with the second power source assembly <NUM> includes both active power droop control and reactive droop control. For the active droop control aspect of the adaptive droop control logic <NUM>, a power feedback Pfbk-GEN, which relates to active power, is input into an active power droop control block <NUM>. The power feedback Pfbk-GEN can be a measured, calculated, or predicted value indicating the active power output of the second power source <NUM>. For instance, one or more sensors can sense the voltage, frequency, and/or the electric current proximate the second power source <NUM> to measure, calculate, or predict the active power output of the second power source <NUM>. At the active power droop control block <NUM>, the power feedback Pfbk-GEN is used for correlation purposes. Specifically, the power feedback Pfbk-GEN can be correlated with a second active droop function fdrp-GEN-A associated with the second power source <NUM> to determine a frequency setpoint fREF-GEN.

The second active droop function fdrp-GEN-A used for the correlation can be selected from a plurality of second active droop functions associated with the second power source <NUM>. The second active droop function fdrp-GEN-A can be selected based at least in part on one or more operating conditions <NUM> (<FIG>) associated with the vehicle in which the electrical power system <NUM> is implemented. For instance, for an aircraft, the second active droop function fdrp-GEN-A can be selected based on a phase of flight, altitude of the aircraft, number of passengers onboard the aircraft, weather conditions, a combination of the foregoing, etc. The second droop functions or curves represent an efficiency of the second power source <NUM> to generate electrical power for a given power output of the second power source <NUM>. The one or more operating conditions <NUM> received by the second controller <NUM> of <FIG> can be the same as the one or more operating conditions <NUM> received by the first controller <NUM> of <FIG>.

As noted above, the selected second active droop function fdrp-GEN-A can be used to schedule or determine the frequency setpoint fREF-GEN associated with the second power source <NUM>. More particularly, the frequency setpoint fREF-GEN can be determined as the y-component of the point along the second active droop function fdrp-GEN-A that corresponds with the power feedback Pfbk-GEN. In this regard, the frequency setpoint fREF-GEN is set as a function of the power feedback Pfbk-GEN. The y-intercept of the second active droop function fdrp-GEN-A selected for correlation purposes in <FIG> is denoted as fSET-GEN.

The frequency setpoint fREF-GEN is output from the droop control block <NUM> and input into a first summation block <NUM> and compared to a frequency feedback ffbk-GEN. The frequency feedback ffbk-GEN can be a measured, calculated, or predicted value indicating the frequency at the second power source <NUM>, e.g., at output terminals thereof. A frequency difference fΔ-GEN is determined at the first summation block <NUM>, e.g., by subtracting the frequency setpoint fREF-GEN from the frequency feedback ffbk-GEN or vice versa.

As noted above, the adaptive droop control logic <NUM> includes reactive power droop control in addition to the active power droop control disclosed above. As illustrated, a power feedback Qfbk-GEN, which relates to reactive power, is input into a reactive power droop control block <NUM>. The power feedback Qfbk-GEN can be a measured, calculated, or predicted value indicating the reactive power at the second power source <NUM>, or rather the power that moves back and forth between the second power source <NUM> and the one or more electric power consumers <NUM>. A varmeter can be used to measure, calculate, or predict the reactive power at the second power source <NUM>. At the reactive power droop control block <NUM>, the power feedback Qfbk-GEN is used for correlation purposes. Particularly, the power feedback Qfbk-GEN can be correlated with a second reactive droop function fdrp-GEN-R associated with the second power source <NUM> to determine a voltage amplitude setpoint VREF_AC-GEN.

The second reactive droop function fdrp-GEN-R used for the correlation can be selected from a plurality of second reactive droop functions associated with the second power source <NUM>. The second reactive droop function fdrp-GEN-R can be selected based at least in part on one or more operating conditions <NUM> (<FIG>) associated with the vehicle in which the electrical power system <NUM> is implemented. For instance, for an aircraft, the second reactive droop function fdrp-GEN-R can be selected based on a phase of flight, altitude of the aircraft, number of passengers onboard the aircraft, weather conditions, a combination of the foregoing, etc..

The selected second reactive droop function fdrp-GEN-R can be used to schedule or determine the voltage amplitude setpoint vREF_AC-GEN associated with the second power source <NUM>. More specifically, the voltage amplitude setpoint vREF_AC-GEN can be determined as the y-component of the point along the second reactive droop function fdrp-GEN-R that corresponds with the power feedback Qfbk-GEN. In this regard, the voltage amplitude setpoint vREF_AC-GEN is set as a function of the power feedback Qfbk-GEN, which corresponds to reactive power feedback. The y-intercept of the second reactive droop function fdrp-GEN-R selected for correlation purposes in <FIG> is denoted as vSET-GEN. The power feedback Qfbk-GEN is bound by an inductive limit -QMax and a capacitive limit QMax.

The voltage amplitude setpoint vREF_AC-GEN is output from the reactive droop control block <NUM> and input into a second summation block <NUM>. The voltage amplitude setpoint vREF_AC-GEN is compared to a voltage amplitude feedback ffbk_AC-GEN at the second summation block <NUM>. The voltage amplitude feedback ffbk_AC-GEN can be a measured, calculated, or predicted value indicating the voltage amplitude at the second power source <NUM>, e.g., at output terminals thereof. A voltage amplitude difference vΔ-GEN is determined at the second summation block <NUM>, e.g., by subtracting the voltage amplitude setpoint vREF_AC-GEN from the voltage amplitude feedback ffbk_AC-GEN or vice versa.

The frequency difference fΔ-GEN and the voltage amplitude difference vΔ-GEN are input into a voltage synthesizer <NUM>, which generates one or more outputs (e.g., a modulation index) that can be input into a switching logic control <NUM> that controls modulation of switching devices of the second power electronics <NUM>, e.g., in a PWM switching scheme. Accordingly, a power output <NUM> of the second power source <NUM> is achieved. The power output <NUM> has an active power component and a reactive power component. The power output <NUM> is affected by a disturbance, which is the power demand <NUM> on the AC power bus <NUM>, as represented at a third summation block <NUM>. In alternative embodiments, the frequency difference fΔ-GEN and the voltage amplitude difference vΔ-GEN are each input into respective proportional-integral controls and then fed into the switching logic control <NUM>.

Accordingly, each power controller of the power source assemblies <NUM> includes executable adaptive droop control logic, e.g., similar to the adaptive droop control logic <NUM>, <NUM> depicted in <FIG> and <FIG>. When a given power controller executes its adaptive droop control logic, the one or more processors of the given power controller cause its associated power electronics to control the power output of its associated power source. This adaptive droop control scheme executed by each power controller of the power source assemblies <NUM> enables intelligent decentralized power allocation for meeting power demands on the AC power bus <NUM> applied by the electric power consumers <NUM>. Specifically, implementation of the adaptive droop control scheme enables decentralized AC bus regulation according to the efficiencies of the power sources at given power outputs.

For instance, with reference to <FIG> and <FIG> provides a graph representing the first droop function fdrp-FC-A associated with the first power source <NUM> overlaid with the second droop function fdrp-GEN-A associated with the second power source <NUM> on an AC bus frequency versus power output graph. The first droop function fdrp-FC-A represents an efficiency of the first power source <NUM> to generate active electrical power for a given power output of the first power source <NUM> and the second droop function fdrp-GEN-A represents an efficiency of the second power source <NUM> to generate active electrical power for a given power output of the second power source <NUM>. According, the droop functions are also functions of power output efficiency η.

As shown in <FIG>, the active power droop functions have different slopes, with the first droop function fdrp-FC-A having a steeper slope than the second droop function fdrp-GEN-A. Also, the droop functions intersect at a point PInt corresponding to a reference power level PRF. The first power source <NUM>, or fuel cell for this example, is more efficient at outputting electric power at lower power levels than the second power source <NUM>, or electric machine in this example. In contrast, at higher power levels, the second power source <NUM> is more efficient at outputting electric power than the first power source <NUM>. In this regard, the droop functions are coordinated so that the power output of the first power source <NUM>, or fuel cell, is greater than the power output of the second power source <NUM>, or electric machine, at power levels less than the reference power level PRF and so that the power output of the second power source <NUM>, or electric machine, is greater than the power output of the first power source <NUM>, or fuel cell, at power levels greater than the reference power level PRF.

Particularly, as shown in <FIG>, for a given AC bus frequency, the working point of both the first power source <NUM> and the second power source <NUM> will both be on the same horizontal line as the first and second power sources <NUM>, <NUM> are electrically coupled to a common power bus, or AC power bus <NUM> in this example. For instance, for a first AC bus frequency fAC BUS <NUM>, the working point of the first power source <NUM>, or fuel cell, and the working point of the second power source <NUM>, or electric machine, are on the same horizontal line. The working point of the first power source <NUM> is denoted as PT1-FC-A and the working point of the second power source <NUM> is denoted as PT1-GEN-A. For the first AC bus frequency fAC BUS <NUM>, the first power source <NUM>, or fuel cell, has a power output of P1 while the second power source <NUM>, or electric machine, has a power output of P0.

Accordingly, the first power source <NUM> has a greater load share or power output at the first AC bus frequency fAC BUS <NUM> than does the second power source <NUM>. The power output of P0 is equal to zero (<NUM>) in this instance, as the y-intercept of the second droop function fdrp-GEN-A is less than the first AC bus frequency fAC BUS <NUM>. Accordingly, to meet the first AC bus frequency fAC BUS <NUM>, only the first power source <NUM>, or fuel cell, outputs electric power. Thus, the load share split is <NUM>%/<NUM>%, with the first power source <NUM> being at <NUM>% and the second power source <NUM> at <NUM>%. Advantageously, when relatively low power is needed, such as during ground idle or taxi operations of an aircraft, the adaptive droop control scheme allows for the first power source <NUM>, or fuel cell, to handle all or most of the relatively low power demand on the AC power bus <NUM>. This takes advantage of the physics and characteristics of the fuel cell to operate at high efficiency at low power levels whilst also saving fuel and wear on the electric machine and gas turbine engine to which the electric machine is coupled.

For a second AC bus frequency fAC BUS <NUM>, which corresponds to a lower frequency level than the first AC bus frequency fAC BUS <NUM>, the working point of the first power source <NUM>, or fuel cell, and the working point of the second power source <NUM>, or electric machine, are on the same horizontal line. The working point of the first power source <NUM> is denoted as PT2-FC-A and the working point of the second power source <NUM> is denoted as PT2-GEN-A. For the second AC bus frequency fAC BUS <NUM>, the first power source <NUM>, or fuel cell, and the second power source <NUM>, or electric machine, both have the same power output, which corresponds to the reference power level PRF. Accordingly, the first power source <NUM> and the second power source <NUM> have a same load share or power output at the second AC bus frequency fAC BUS <NUM>. Thus, the load share split is <NUM>%/<NUM>%, with the first power source <NUM> being at <NUM>% and the second power source <NUM> being at <NUM>% to meet the power demand on the AC power bus <NUM>.

Further, for a third AC bus frequency fAC BUS <NUM>, which corresponds to a lower frequency level than the second AC bus frequency fAC BUS <NUM>, the working point of the first power source <NUM>, or fuel cell, and the working point of the second power source <NUM>, or electric machine, are on the same horizontal line. The working point of the first power source <NUM> is denoted as PT3-FC-A and the working point of the second power source <NUM> is denoted as PT3-GEN-A. For the third AC bus frequency fAC BUS <NUM>, the first power source <NUM>, or fuel cell, has a power output of P2 while the second power source <NUM>, or electric machine, has a power output of P3, which is greater than the power output of P2.

Accordingly, the second power source <NUM> has a greater load share or power output at the third AC bus frequency fAC BUS <NUM> than does the first power source <NUM>. The load share split can be <NUM>%/<NUM>%, with the first power source <NUM> being at <NUM>% and the second power source <NUM> at <NUM>%, for example. Advantageously, when relatively high power is needed, such as during flight operations of an aircraft, the adaptive droop control scheme allows for the second power source <NUM>, or electric machine mechanically coupled with a gas turbine engine, to handle most of the relatively high power demand on the AC power bus <NUM>. This takes advantage of the physics and characteristics of the electric machine to operate at high efficiency at high power levels whilst also using the fuel cell in part to meet the power demand on the AC power bus <NUM>.

Accordingly, the power allocation for the power sources is set according to the characteristics of the droop functions, such as their slopes, y-intercepts, and overall shapes. For the depicted embodiment of <FIG>, as the droop functions converge toward one another, the load share between the first power source <NUM> and the second power source <NUM> becomes more balanced, as represented at the second AC bus frequency fAC BUS <NUM>. Conversely, as the droop functions diverge away from one another, the load share between the first power source <NUM> and the second power source <NUM> becomes less balanced, as represented at the first AC bus frequency fAC BUS <NUM> and the third AC bus frequency fAC BUS <NUM>.

It will be appreciated that, like the active power allocation scheme disclosed above and represented in <FIG>, reactive power allocation for the power sources can be set according to the coordination and characteristics of the reactive droop functions, such as their slopes, y-intercepts, and overall shapes.

Moreover, in some embodiments, the reactive power control aspects of the adaptive droop control logic <NUM>, <NUM> are optionally not implemented or not a part of the adaptive droop control logic <NUM>, <NUM>. In such embodiments, a voltage regulating device can be employed to regulate the voltage on the AC power bus <NUM>.

Further, the droop functions depicted in <FIG>, <FIG>, and <FIG>, are linear functions. However, one or more of the droop functions can be non-linear functions in other example embodiments. In other embodiments, one or more of the droop functions may be piecewise linear functions, polynomial functions, etc..

In accordance with the adaptive droop control schemes disclosed herein, such control schemes can also be deemed "adaptive" in that droop functions selected for correlation purposes can be selected or otherwise adjusted based on a health status of one or more of the power sources or components associated therewith, such as their respective power controllers, and particularly, their respective power electronics.

By way of example and with reference to <FIG>, for a given power demand and operating conditions of the vehicle in with the electrical power system <NUM> is implemented, the one or more processors of the first controller <NUM> can receive a health status <NUM> associated with the first power source <NUM> and/or the first power controller <NUM>, wherein the health status <NUM> indicates a degree of degradation from a baseline health status, such as a new condition first power source and/or new condition first power electronics. Likewise, for a given power demand and operating conditions of the vehicle in which the electrical power system <NUM> is implemented, the one or more processors of the second controller <NUM> can receive a health status <NUM> associated with the second power source <NUM> and/or the second power controller <NUM>, wherein the health status <NUM> indicates a degree of degradation from a baseline health status, such as a new condition second power source and/or new condition second power electronics.

With reference now to <FIG> in addition to <FIG>, <FIG> provides a graph depicting a first droop function fdrp-FC-<NUM> associated with the first power source <NUM> overlaid with a second droop function fdrp-GEN-<NUM> associated with the second power source <NUM> of the electrical power system <NUM> of <FIG>, the first droop function fdrp-FC-<NUM> and the second droop function fdrp-GEN-<NUM> being selected based on a first set of operating conditions and at a first time t1 at which the first power source <NUM> has a first health status indicating a first level of health and the second power source <NUM> has a first health status indicating a first level of health. <FIG> provides a graph depicting a first droop function fdrp-FC-<NUM> associated with the first power source <NUM> overlaid with a second droop function fdrp-GEN-<NUM> associated with the second power source <NUM> of the electrical power system <NUM> of <FIG>, the first droop function fdlp-FC-<NUM> and the second droop function fdrp-GEN-<NUM> being selected based on the first set of operating conditions (the same operating conditions as in <FIG>) and at a second time t2 that is later in time than time t1 of <FIG>. At time t2, the first power source <NUM> has a second health status indicating a second level of health and the second power source <NUM> has a second health status indicating a second level of health. The second health status of the first and second power sources <NUM>, <NUM> indicates greater deterioration from a baseline health status compared to the first health status of the first and second power sources <NUM>, <NUM>.

In comparing the first droop function of <FIG> with the first droop function of <FIG>, the first droop function of <FIG>, which represents the efficiency of the first power source at time t1 and for the first set of operating conditions, is steeper than the first droop function of <FIG>, which represents the efficiency of the first power source at time t2 and for the first set of operating conditions. In this regard, the first droop function selected for correlation purposes is adapted or intelligently selected as the first power source deteriorates over time. Likewise, in comparing the second droop function of <FIG> with the second droop function of <FIG>, the second droop function of <FIG>, which represents the efficiency of the second power source at time t1 and for the first set of operating conditions, is steeper than the second droop function of <FIG>, which represents the efficiency of the second power source at time t2 and for the first set of operating conditions. Accordingly, the second droop function selected for correlation purposes is adapted or intelligently selected as the second power source deteriorates over time.

As will further be appreciated by comparing <FIG>, the first and second droop functions of <FIG> diverge more significantly as they move away from the reference power level PRF than do the first and second droop functions of <FIG>. Moreover, the reference power level PRF has shifted to the right in <FIG> along the X-axis from its position in <FIG>. These differences indicate the adaptive power allocation of the power sources over time made possible by the adaptive droop control scheme when accounting for the health status of the power sources. It will be appreciated that the teachings relating to accounting for health status in selecting a droop function for correlation purposes applies equally to AC power bus systems, such as the electrical power system <NUM> of <FIG>.

<FIG> provides a flow diagram of a method <NUM> of operating a decentralized power allocation system for an aircraft. For instance, the method <NUM> can be utilized to operate the electrical power systems <NUM>, <NUM> of <FIG> or <FIG>.

At <NUM>, the method <NUM> includes controlling a first power output of a first power source to meet a power demand on a power bus applied by one or more power consumers, the first power output being controlled based at least in part on a correlation of a power feedback of the first power source and a first droop function that represents an efficiency of the first power source to generate electrical power for a given power output of the first power source. For instance, a first power controller associated with the first power source can control the first power output of the first power source. One or more processors of the first power controller can receive the power feedback of the first power source and can correlate the power feedback to the first droop function. As one example, the power feedback can be compared to a power setpoint to determine a power difference. The power difference can be used to adjust, if necessary, the power feedback from a previous timestep of the one or more processors. The adjusted power feedback is then correlated with the first droop function.

In implementations where the power bus is a direct current power bus, a voltage setpoint is determined based on the correlation between the adjusted power feedback and the first droop function. First power electronics of the first power controller (e.g., switches thereof) can be controlled based on the voltage setpoint to output the first power output. In implementations where the power bus is an alternating current power bus, a frequency setpoint is determined based on the correlation between the adjusted power feedback and the first droop function. The first power electronics of the first power controller (e.g., switches thereof) can be controlled based on the frequency setpoint to output the first power output. In some instances, the first power output is not equal to zero (<NUM>). In such instances, the first power source has a load share in meeting the power demand on the power bus. In other instances, the first power output can be equal to zero. In this regard, in some instances, the load share of the first power source in meeting the power demand on the power bus is zero (<NUM>).

At <NUM>, the method <NUM> includes controlling a second power output of a second power source to meet the power demand on the power bus, the second power output being controlled based at least in part on a correlation of a power feedback of the second power source and a second droop function that represents an efficiency of the second power source to generate electrical power for a given power output of the second power source, and wherein the first droop function and the second droop function are coordinated so that the first power output of the first power source is greater than the second power output of the second power source at power levels less than a reference power level and so that the second power output of the second power source is greater than the first power output of the first power source at power levels greater than the reference power level.

For instance, a second power controller associated with the second power source can control the second power output of the second power source. One or more processors of the second power controller can receive the power feedback of the second power source and can correlate the power feedback to the second droop function. As one example, the power feedback can be compared to a power setpoint to determine a power difference. The power difference can be used to adjust, if necessary, the power feedback from a previous timestep of the one or more processors of the second power controller. The adjusted power feedback is then correlated with the second droop function.

In implementations where the power bus is a direct current power bus, a voltage setpoint is determined based on the correlation between the adjusted power feedback and the second droop function. Second power electronics of the second power controller (e.g., switches thereof) can be controlled based on the voltage setpoint to output the second power output. In implementations where the power bus is an alternating current power bus, a frequency setpoint is determined based on the correlation between the adjusted power feedback and the second droop function. The second power electronics of the second power controller (e.g., switches thereof) can be controlled based on the frequency setpoint to output the second power output. In some instances, the second power output is not equal to zero (<NUM>). In such instances, the second power source has a load share in meeting the power demand on the power bus. In other instances, the second power output can be equal to zero. In this regard, in some instances, the load share of the second power source in meeting the power demand on the power bus is zero (<NUM>).

In some implementations, the power bus is an alternating current power bus, and wherein the reference power level corresponds to a point at which the first droop function and the second droop function intersect, wherein the first and second droop functions are represented as functions of a frequency of the alternating current power bus versus power output of the first and second power sources. In other implementations, the power bus is a direct current power bus, and wherein the reference power level corresponds to a point at which the first droop function and the second droop function intersect, wherein the first and second droop functions are represented as functions of a voltage of the direct current power bus versus power output of the first and second power sources.

In some implementations, the first power source is a fuel cell assembly and the second power source is an electric machine mechanically coupled with a gas turbine engine. In other implementations, the first power source is a first fuel cell assembly and the second power source is a second fuel assembly. In some further implementations, the first power source is a first electric machine mechanically coupled with a first gas turbine engine and the second power source is a second electric machine mechanically coupled with a second gas turbine engine.

<FIG> provides a computing system <NUM> according to example embodiments of the present disclosure. The computing devices or elements described herein, such as the controllers <NUM>, <NUM> (<FIG> and <FIG>), may include various components and perform various functions of the computing system <NUM> provided below.

The computing system <NUM> can include one or more computing device(s) <NUM>. The computing device(s) <NUM> can include one or more processor(s) 1110A and one or more memory device(s) 1110B. The one or more processor(s) 1110A can include any suitable processing device, such as a microprocessor, microcontroller, integrated circuit, logic device, and/or other suitable processing device. The one or more memory device(s) 1110B can include one or more computer-executable or computer-readable media, including, but not limited to, non-transitory computer-readable medium, RAM, ROM, hard drives, flash drives, and/or other memory devices.

The one or more memory device(s) 1110B can store information accessible by the one or more processor(s) 1110A, including computer-readable instructions 1110C that can be executed by the one or more processor(s) 1110A. The instructions 1110C can be any set of instructions that, when executed by the one or more processor(s) 1110A, cause the one or more processor(s) 1110A to perform operations, such executing adaptive droop control schemes. The instructions 1110C can be software written in any suitable programming language or can be implemented in hardware. Additionally, and/or alternatively, the instructions 1110C can be executed in logically and/or virtually separate threads on processor(s) 1110A. The memory device(s) 1110B can further store data 1110D that can be accessed by the processor(s) 1110A. For example, the data 1110D can include models, lookup tables, databases, etc., and particularly, sets of droop control functions.

The computing device(s) <NUM> can also include a network interface 1110E used to communicate, for example, with the other components of the computing system <NUM> (e.g., via a communication network). The network interface 1110E can include any suitable components for interfacing with one or more network(s), including for example, transmitters, receivers, ports, controllers, antennas, and/or other suitable components.

Claim 1:
A decentralized power allocation system (<NUM>, <NUM>) for an aircraft (<NUM>), comprising:
a power bus (<NUM>, <NUM>);
one or more electric power consumers (<NUM>) electrically coupled with the power bus (<NUM>, <NUM>); and
a plurality of power source assemblies (<NUM>), each one of the plurality of power source assemblies (<NUM>) comprising:
a power source (<NUM>, <NUM>) electrically coupled with the power bus (<NUM>, <NUM>); and
a power controller (<NUM>, <NUM>) for controlling electrical power provided from the power source (<NUM>, <NUM>) to the power bus (<NUM>, <NUM>), the power controller (<NUM>, <NUM>) having power electronics (<NUM>, <NUM>) and one or more processors configured to:
cause the power electronics (<NUM>, <NUM>) to control a power output (<NUM>, <NUM>, <NUM>, <NUM>) of the power source (<NUM>, <NUM>) to meet a power demand (<NUM>, <NUM>) on the power bus (<NUM>, <NUM>) applied by the one or more electric power consumers (<NUM>) in accordance with an adaptive droop control scheme in which the power output (<NUM>, <NUM>, <NUM>, <NUM>) of the power source (<NUM>, <NUM>) is controlled based at least in part on a correlation of a power feedback (Pfbk-FC, Pfbk-GEN. Qfbk-FC, Qfbk-GEN) of the power source (<NUM>, <NUM>) and a droop function (fdrp-FC, fdrp-GEN, fdrp-FC-A, fdrp-FC-R, fdrp-GEN-A, fdrp-GEN-R) that represents an efficiency of the power source (<NUM>, <NUM>) to generate electrical power for a given power output (<NUM>, <NUM>, <NUM>, <NUM>) of the power source.
characterised in that the power sources comprises at least a fuel cell (<NUM>) and an electric generator (<NUM>) wherein the droop functions (fdrp-FC, fdrp-GEN, fdrp-FC-A, fdrp-FC-R, fdrp-GEN-A, fdrp-GEN-R) associated with the power sources (<NUM>, <NUM>) are coordinated with one another so that the power output (<NUM>, <NUM>) of a first power source (<NUM>) of the power sources (<NUM>, <NUM>) is greater than the power output (<NUM>, <NUM>) of a second power source (<NUM>) of the power sources (<NUM>, <NUM>) at power levels less than a reference power level (PRF) and so that the power output (<NUM>, <NUM>) of the second power source (<NUM>) is greater than the power output (<NUM>, <NUM>) of the first power source (<NUM>) at power levels greater than the reference power level (PRF).