WO2019005140A1

WO2019005140A1 - Systems and methods for balancing electrically-islated power sources

Info

Publication number: WO2019005140A1
Application number: PCT/US2017/040454
Authority: WO
Inventors: Zachary T. LOVERING
Original assignee: Airbus Group Hq, Inc.
Priority date: 2017-06-30
Filing date: 2017-06-30
Publication date: 2019-01-03
Also published as: WO2019005140A8

Abstract

An electrical power system (163) for an aircraft (20) can have a plurality of power sources 166 to provide power to the components of the aircraft (20). The voltage levels of the power sources (166) can be balanced while maintaining electrical isolation between the power sources (166). A power system controller (506) can selectively control switches (508) to connect a single power source (166) to an energy storage device (510) to adjust the voltage level of the power source (166) to a desired voltage level by either charging or discharging the power source (166). The power source (166) can charge the energy storage device (510) to lower the voltage level of the power source (166) or the energy storage device (510) can be used to charge the power source (166) to raise the voltage level of the power source (166).

Description

SYSTEMS AND METHODS FOR BALANCING ELECTRICALLY- ISOLATED POWER SOURCES

BACKGROUND

[0001] Electrically-powered aircraft offer various advantages and are becoming increasingly more common as an alternative to other types of aircraft powered by fuel. In this regard, electrically-powered aircraft operate more cleanly and oftentimes have a lower operating expense. In addition, electrically-powered aircraft can operate more quietly making this type of aircraft particularly attractive for use in applications involving flights near urban environments, including self-piloted aircraft designed for personal transport and package delivery.

[0002] The electrical power system of an aircraft can include one or more battery packs that provide electrical power to the systems of the aircraft, such as a propulsion system or a flight control system. Each battery pack can incorporate a plurality of batteries or battery cells to provide a desired voltage (or current) to the other systems of the aircraft.

[0003] In one configuration, the battery packs can be directly connected in parallel to a single electrical bus for carrying power to the systems of the aircraft. The direct connection of the battery packs enables the battery packs to be evenly charged to about the same voltage. Similarly, the direct connection of the battery packs enables the battery packs to be evenly discharged such that they have about the same voltage, relative to each other, during the discharging process. One drawback to directly connecting the battery packs is that a fault in one of the battery packs or the electrical bus connected to the battery packs can result in a failure of the entire power system. As an example, a fault in one battery pack may short connections of the electrical bus so that power cannot be successfully delivered over the electrical bus.

[0004] In another configuration, each of the battery packs can be connected to a separate bus for carrying power to selected systems of the aircraft. The use of separate buses can provide electrical isolation between the battery packs in the event that a fault occurs in one of the battery packs. By isolating the battery packs, the electrical power system can continue to provide power to the other systems of the aircraft not coupled to the failed battery pack. However, the use of separate buses for the battery packs may result in uneven charging and discharging since battery packs from one bus to the next are electrically isolated from each other, and for efficient power usage, it is generally desirable to avoid such uneven charging and discharging. Thus, in designing an electrical power system, trade-offs often exist between safety, performance, and costs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The disclosure can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the disclosure.

[0006] FIG. 1 depicts a perspective view of a self-piloted VTOL aircraft in accordance with some embodiments of the present disclosure.

[0007] FIG. 2 is a block diagram illustrating various components of a VTOL aircraft, such as is depicted by FIG. 1 , in accordance with some embodiments of the present disclosure.

[0008] FIGS. 3 and 4 are block diagrams illustrating motor loads, such as is depicted by FIG. 2, in accordance with some embodiments of the present disclosure.

[0009] FIG. 5 is a block diagram illustrating various components of an electrical power system, such as is depicted by FIG. 2, in accordance with some embodiments of the present disclosure.

[0010] FIG. 6 depicts a flow chart illustrating a method for balancing loads among power sources used by the electrical power system.

DETAILED DESCRIPTION

[0011] The present disclosure generally pertains to systems and methods for balancing power sources that are electrically isolated. In some embodiments, an electrical power system can be used to provide power to motors or other components of an electrically-powered aircraft. The electrical power system can include a plurality of power sources, such as battery packs, that are incorporated into the aircraft. Each power source can provide power to one or more motors or other components of the aircraft and can be electrically isolated from the other power sources of the electrical power system such that a fault or failure associated with one power source does not affect the other power sources. [0012] The electrical power system can have a power system controller that can be used to provide for the substantially even charging and discharging of the power sources of the electrical power system during operation of the aircraft. The power system controller can be used to maintain each of the power sources of the electrical power system at a substantially equal voltage level. If the power system controller determines that a measured voltage for a power source of the electrical power system is above a desired voltage level, the power system controller can arrange for the power source to be discharged and the energy from the power source to be provided to an energy storage device until the voltage level of the power source is decreased to the desired voltage level. In contrast, if the power system controller determines that a measured voltage for a power source of the electrical power system is below the desired voltage level, the power system controller can arrange for the energy storage device (which received energy from the power source above the desired voltage level) to charge (or provide energy to) the power source below the desired voltage level until the voltage level of the power source is increased to the desired voltage level.

[0013] The power system controller can balance the voltages of the power sources, as described above, while maintaining the electrical isolation between the power sources by controlling switches between each power source and the energy storage device. To maintain electrical isolation between the power sources, the power system controller can position each switch into an open state to prevent an electrical connection from occurring between the power sources. If the power system controller determines that a power source is to be charged or discharged, as described above, in order to maintain the desired voltage level, the power system controller can position the switch for the power source into the closed state (while keeping the switches for the other power sources in an open state) so that the transfer of energy between the power source and the energy storage device can occur as needed while maintaining electrical isolation among the power sources. Once the discharging power source has reached the desired voltage level, the power system controller can position the switch for the power source into the open state and position the switch for another power source into the closed state for charging or discharging such other power source. The power system controller can be configured to balance the voltage level of the power sources by transferring energy from some power sources to other power sources via the energy storage device. [0014] FIG. 1 depicts an electrically-powered aircraft 20 in accordance with some embodiments of the present disclosure. The aircraft 20 can be a vertical takeoff and landing (VTOL) aircraft that is autonomous or self-piloted. The aircraft 20 can be capable of flying passengers or cargo to selected destinations under the direction of an electronic controller without the assistance of a human pilot. If desired, the aircraft 20 may be equipped to provide a passenger with flight control so that the passenger may pilot the aircraft at least temporarily rather than rely exclusively on self-piloting by a controller.

[0015] As shown by FIG. 1 , the aircraft 20 has a tandem-wing configuration with a pair of rear wings 25, 26 mounted close to the rear of a fuselage 33 and a pair of forward wings 27, 28 mounted close to the front of the fuselage 33. In some

embodiments, each wing 25-28 has a tilted-wing configuration that enables it to be tilted relative to the fuselage 33. In this regard, the wings 25-28 are rotatably coupled to the fuselage 33 so that they can be dynamically tilted relative to the fuselage 33 to provide vertical takeoff and landing (VTOL) capability and other functions, such as yaw control and improved aerodynamics.

[0016] A plurality of propellers 41 -48 are mounted on the wings 25-28. In some embodiments, two propellers are mounted on each wing 25-28 for a total of eight propellers 41-48, as shown by FIG. 1 , but other numbers of propellers 41-48 are possible in other embodiments.

[0017] The fuselage 33 comprises a frame 52 on which a removable passenger module 55 and the wings 25-28 are mounted. The passenger module 55 has a floor (not shown in FIG. 1) on which at least one seat (not shown in FIG. 1 ) for at least one passenger is mounted. The passenger module 55 also has a transparent canopy through which a passenger may see. The passenger module 55 may be removed from the frame 52 and replaced with a different module (e.g., a cargo module) for changing the utility of the aircraft 20, such as from passenger-carrying to cargo-carrying.

[0018] As shown by FIG. 1 , the wings 25-28 have hinged flight control surfaces

95-98, respectively, for controlling the roll and pitch of the aircraft 20 during forward flight. Additional information regarding the configuration and operation of the aircraft 20 is provided in PCT Application No. PCT/US2017/018182, which is incorporated by reference herein in its entirety, and PCT Application No. PCT/US2017/040413, entitled "Vertical Takeoff and Landing Aircraft with Passive Wing Tilt" and filed on even date herewith, which is incorporated herein by reference. Further, it should be emphasized that the wing configurations described above, including the arrangement of the propellers 41-48 and flight control surfaces 95-98, as well as the size, number, and placement of the wings 25-28, are only examples of the types of wing configurations that can be used to control the aircraft's flight. Various modifications and changes to the wing configurations described above would be apparent to a person of ordinary skill upon reading this disclosure.

[0019] Referring to FIG. 2, the aircraft 20 may operate under the direction and control of an onboard controller 1 10, which may be implemented in hardware or any combination of hardware, software, and firmware. The controller 1 10 may be configured to control the flight path and flight characteristics of the aircraft 20 by controlling at least the propellers 41-48, the wings 25-28, and the flight control surfaces 95-98. In some embodiments, the controller 1 10 includes at least one processor and software executed by the processor in order to implement the control functions described herein for the controller 1 10. Other configurations of the controller 1 10 are possible in other embodiments. Note that it is possible for the control functions to be distributed across multiple processors, such as multiple onboard processors, and for the control functions to be distributed across multiple locations. As an example, some control functions may be performed at one or more remote locations, and control information or instructions may be communicated between such remote locations and the aircraft 20 by the wireless communication interface 142 or otherwise. Additional information regarding the configuration and operation of controller 1 10 is provided in PCT Application No.

PCT/US2017/018182, which is incorporated by reference herein in its entirety.

[0020] The controller 1 10 is coupled to a plurality of motor loads 221 that are associated with one or more of the propellers 41-48, the wings 25-28, and the flight control surfaces 95-98. Each motor load 221 can include at least one motor controller 225 (see FIGS. 3-4) and at least one motor 235 (see FIGS. 3-4) that are used to drive a flight component of the aircraft 20 (e.g., a propeller 41-48, wing 25-28, or flight control surface 95-98). When the controller 1 10 determines to adjust the configuration or operation of a flight component of the aircraft 20 (e.g., adjust the speed of a propeller 41 - 48, adjust the orientation of a wing 25-28, or adjust the angular position of a flight control surface 95-98), the controller 1 10 transmits a control signal that is used by a motor controller 225 to control the corresponding motor 235 associated with the flight component of the aircraft 20. [0021] The aircraft 20 also has an electrical power system 163 for powering various components of the aircraft 20, including the controller 1 10 and the motor loads 221. As shown in FIG. 2, each motor load 221 has a connection, such as may be provided by an electrical bus, to the electrical power system 163 that is separate from the connections for the other motor loads 221. In other words, an electrical bus between a motor load 221 and the electrical power system 163 is electrically isolated from the other electrical buses used to couple the other motor loads 221 to the electrical power system 163.

[0022] In one embodiment, each motor load 221 can include a motor controller

225 and motor 235 for an individual flight component of the aircraft 20, such that the individual flight component of the aircraft 20 has its own electrical connection to the electrical power system 163. In another embodiment, each motor load 221 can include several motor controllers 225 and motors 235 for several flight components of the aircraft 20, such that the group of flight components of the aircraft 20 share an electrical connection to the electrical power system 163. In each of the previously described embodiments for the motor loads 221 , the motor controller(s) 225 of the motor load 221 can be connected to the electrical power system 163 to receive power from the electrical power system 163. The motor controller 225 can then power the corresponding motor 235 connected to the motor controller 225.

[0023] As shown in FIG. 3, the motor controller 225 and motor 235 for the propeller 41 , the motor controller 225 and motor 235 for the flight control surface 98, and the motor controller 225 and motor 235 for the propeller 48 are each identified as a motor load 221 that has a separate electrical connection to the electrical power system 163. In contrast, as shown in FIG. 4, the motor controller 225 and motor 235 for the propeller 41 , the motor controller 225 and motor 235 for the flight control surface 98, and the motor controller 225 and motor 235 for the propeller 48 are collectively identified as a motor load 221 with a single electrical connection to the electrical power system 163. When a motor load 221 includes multiple flight components of the aircraft 20 (with corresponding motors 235 and motor controllers 225), the selection of the flight components of the aircraft 20 associated with the motor load 221 can be based on different factors, such as the proximity of the flight components of the aircraft 20, the functionality of the flight components of the aircraft 20 or safety concerns (e.g., the impact of a failure of the flight components of the aircraft 20 on the operation of the aircraft 20). In still other embodiments, some motor loads 221 may include a single flight component of the aircraft 20 (with corresponding motor 235 and motor controller 225), while other motor loads 221 may include multiple flight components of the aircraft 20 (with corresponding motors 235 and motor controllers 225).

[0024] Referring to FIG. 5, the electrical power system 163 has distributed power sources 166 that are mounted on the frame 52 of the aircraft 20 at various locations. In one embodiment, each power source 166 can include one or more batteries or battery cells arranged into one or more battery packs. In an embodiment, the power sources 166 for powering various components of aircraft 20 may be stored in one or more compartments (not shown) within the frame 52 beneath the fuselage 33 or at other locations as may be desired. The power sources 166 may be loaded into the

compartments and coupled to an electrical interface (not depicted) of the electrical power system 163 such that the electrical power system 163 can provide electrical power from the power sources 166 to the various components and systems of the aircraft 20 as described above. In one embodiment, the frame 52 may have a corresponding port for each compartment through which a power source 166 may be loaded into the compartment. In some embodiments, rails, guides, tracks or other components may be coupled to the frame 52 within each compartment for securing power sources 166 and aiding in the loading and removal of the power sources 166. In another embodiment, the power sources 166 may be "hot-swappable" in that the power sources 166 are capable of being removed and replaced without powering down the aircraft 20.

[0025] In one embodiment, each of the power sources 166 can incorporate power conditioning circuitry (not shown) that conditions the electrical power from the batteries or battery cells of the power source 166 for distribution to the electrical components of the aircraft 20. The power conditioning circuitry can combine electrical power from the batteries or battery cells of the power source 166 to provide a direct current (DC) power signal for the electrical components of the aircraft 20. In another embodiment, the power conditioning circuitry may be external to the power source 166 and used to condition the electrical power from the power source 166.

[0026] Each of the power sources 166 can be connected to a corresponding electrical bus 502 of the electrical power system 163. The electrical buses 502 can have conductive connections for carrying power to various components of the aircraft 20 (e.g., the controller 1 10 and the motor loads 221). As shown in FIG. 5, each of the

connections between an electrical bus 502 and a corresponding power source 166 is electrically isolated from the other electrical buses 502 and their corresponding power sources 166. The output voltage (e.g. , a DC voltage) provided by each of the power sources 166 to its corresponding bus 502 can be measured by a corresponding sensor 504. A power system controller 506 can be coupled to sensors 504 to receive voltage or current measurements regarding the power sources 166 from the sensors 504. In other embodiments, the sensors 504 can measure other parameters of the power sources 166 that are indicative of the amount of energy in the power sources 166.

[0027] The power system controller 506 may be implemented in hardware, software, or any combination thereof. In some embodiments, the power system controller 506 includes at least one processor and software executable by the processor in order to implement the control functions described herein for the power system controller 506. Other configurations of the power system controller 506 are possible in other embodiments. Note that it is possible for the control functions to be distributed across multiple processors, such as multiple onboard processors.

[0028] The power system controller 506 can be connected to a plurality of switches 508 and provide control signals to the switches to control the opening and closing of the switches 508 (i.e. , positioning the switches 508 in an open state or a closed state). In one embodiment, each switch 508 may incorporate one or more transistors such as field effect transistors (FETs) to provide the switching functionality. However, in other embodiments, the switches 508 may incorporate other electrical components to perform the switching function. The switches 508 can be used to selectively connect the power sources 166 to an energy storage device 510. In one embodiment, the energy storage device 510 is a capacitive element that may include one or more capacitors for storing charge. However, in other embodiments, other energy storing devices can be used for the energy storage device 510. The energy storage device 510 can be used to receive and store energy from a power source 166 or provide energy to a power source 166 depending on a parameter (e.g. , voltage) indicative of the amount of energy or charge in the power source 166 when the corresponding switch 508 for the power source 166 is closed by the power system controller 506 thereby connecting the power source 166 and the energy storage device 510.

[0029] Any suitable technique for transferring energy between the energy storage 510 and the connected power source 166 can be used, including techniques that may require inputs from the power system controller 506. For example, additional circuit elements (not shown in FIG. 5), such as diodes, transistors, capacitors, resistors, switches, etc. , may be incorporated in the connection path between the energy storage device 510 and the connected power source 166 to facilitate the transfer of energy between the energy storage device 510 and the connected power source 166. In addition, the additional circuit elements may be arranged such that there is a "charge path" used for charging the power source 166 and a "discharge path" used for discharging the power source 166, which discharge path may include some, all or none of the additional circuit elements of the charge path. Depending on the configuration of the additional circuit elements, the power system controller 506 may provide

corresponding control signals (e.g., signals to control a switch) to facilitate the corresponding transfer operation between the energy storage device 510 and the connected power source 166.

[0030] The power system controller 506 can cyclically select each power source

166 of the electrically power system 163 and determine whether the selected power source 166 is operating at a target voltage level determined for the power sources 166. If the voltage level of the selected power source 166 is below the target voltage level, the power system controller 506 can arrange for the selected power source 166 to be charged by the energy storage device 510 until the voltage level of the selected power source 166 is raised to the target voltage level. In contrast, if the voltage level of the selected power source 166 is above the target voltage level, the power system controller 506 can arrange for the selected power source 166 to discharge energy to the energy storage device 510 until the voltage level of the selected power source 166 is lowered to the target voltage level. The power system controller 506 can control switches 508 connected to the energy storage device 510 to individually connect the selected power source 166 to the energy storage device 510 for charging or discharging operations while still maintaining the electrical isolation between the power sources 166 and their corresponding buses 502. By maintaining all of the power sources 166 at the target voltage level (via the charging and discharging operations), the power system controller 506 is able to balance the voltage levels of the power sources 166 so that the power sources 166 equally share in the electrical load for the aircraft 20.

[0031] In one embodiment, the power system controller 506 can initially charge the energy storage device 510 by first selecting some or all of the power sources 166 that are above the target voltage level to provide energy to the energy storage device 510. For such power sources 166, the controller 506 may step through the power sources 166 one-by-one successively connecting each power source 166 to the energy storage device 510 for discharging energy from such power source 166 while the energy storage device 510 is electrically isolated from the other power sources 166. Thus, the power sources 166 remain electrically isolated from each other during this charging of the energy storage device 510.

[0032] Once the energy storage device 510 has received energy from some or all of the power sources 166 above the target voltage level, the power system controller 506 can then select some or all of the power sources 166 below the target voltage level to receive energy from the energy storage device 510. For such power sources 166, the controller 506 may step through the power sources 166 one-by-one successively connecting each power source 166 to the energy storage device 510 for supplying energy to such power source 166 while the energy storage device 510 is electrically isolated from the other power sources 166. Thus, the power sources 166 remain electrically isolated from each other during this discharging of the energy storage device 510. Depending on the storage capacity of the energy storage device 510 or the differentials between the voltage levels of the power sources 166 and the target voltage level, the power system controller 506 may repeat the charging/discharging cycle for the energy storage device 510 as described above in order to keep the voltage levels of the power sources 166 balanced.

[0033] An exemplary use and operation of the power system controller 506 in order to balance the voltages of the power sources 166 of the aircraft 20 will be described in more detail below with reference to FIG. 6.

[0034] The flow chart of FIG. 6 begins with the power system controller 506 selecting a power source 166 at step 601. The power system controller 506 can then sense the voltage of the selected power source 166 with the corresponding sensor 504 for the selected power source 166 at step 602. A determination is then made as to whether the voltage of the selected power source 166 is above a target voltage level at step 604. The target voltage level can correspond to a desired operating voltage for each of the power sources 166. In other words, each of the power sources 166 is intended to operate at the target voltage level during normal operation. In one embodiment, the target voltage level can be predefined for the power sources 166 based on the expected operation of the aircraft 20. In another embodiment, the target voltage level can be determined by the system controller 506 based on the measured voltages for each of the power sources 166. For example, the target voltage level can correspond to a mean of the measured voltages from each of the power sources 166 or an average of the measured voltages from each of the power sources 166.

[0035] Referring to step 604, if the sensed voltage for the selected power source

166 is not above the target voltage in step 604, the power system controller 506 can proceed to step 608 to determine whether the sensed voltage of the selected power source 166 is below the target voltage level. However, if the sensed (or measured) voltage for the selected power source 166 is above the target voltage, the selected power source 166 can transfer energy to the energy storage device 510 at step 606. In one embodiment, the power system controller 506 can determine the capacity of the energy storage device 510 prior to transferring energy to the energy storage device 510. The power system controller 506 can determine the capacity of the energy storage device 510 to receive additional energy based on a measurement from a sensor (not shown) or based on one or more calculations using information from prior charging or discharging operations. If the energy storage device 510 does not have enough capacity (i.e., has too much charge or voltage) to receive and store energy from the selected power source 166, no energy transfer occurs at step 606 and the power system controller 506 proceeds to select a new power source at step 601 (via step 612). In such case, since the energy storage device 510 has a high charge or voltage level, the power system controller 506 may attempt to select a power source 166 at step 601 that may require charging by the energy storage device 510 to lower the charge or voltage level of the energy storage device 510.

[0036] Note that in other embodiments, the controller 506 may first select the power sources 166 to be discharged and process these power sources 166 for discharging to the energy storage device 510. Thereafter, the controller 506 may select the power sources 166 be charged and process these power sources 166 for charging from the energy storage device 510. Yet other algorithms are possible in other embodiments.

[0037] For the embodiment depicted by FIG. 6, if the energy storage device 510 has sufficient capacity to receive energy, the selected power source 166 transfers energy to the energy storage device 510 until the voltage level of the selected power source 166 is lowered to the target voltage level as measured by sensor 504. To transfer energy from the selected power source 166 to the energy storage device 510, the power system controller 506 can close the corresponding switch 508 (i.e., position the switch 508 in a closed state) coupled to the selected power source 166 to complete a circuit between the energy storage device 510 and the selected power source 166. Alternatively, the power system controller 506 may close the switch 508 corresponding to the selected power source 166 prior to making the determination in step 604. For example, the power system controller 506 may close the corresponding switch 508 upon the selection of the power source 166 or in conjunction with the sensing of the voltage for the selected power source 166. The power system controller 506 can maintain or position the remaining switches 508 coupled to the other power sources 166 in an open state to provide open circuits between the energy storage device 510 and the remaining power sources 166, and thereby maintain the electrical isolation between the power sources 166, as well as electrical isolation between the buses 502. Upon the closing of the switch 508 and/or other triggering event, such as a control signal from the power source controller 506, the power source 166 can be discharged and the energy transferred to the energy storage device 510. After completing the transfer of energy to the storage device 510 (i.e., the voltage level of the selected power source 166 is substantially equal to the target voltage level), the process can proceed to step 612.

[0038] Referring to step 608, if the sensed voltage is not below the target voltage in step 608, the selected power source 166 is operating at the target voltage level and the process proceeds to step 612. However, if the sensed (or measured) voltage for the selected power source 166 is below the target voltage, the energy storage device 510 can transfer energy to the selected power source 166 at step 610. In one embodiment, the power system controller 506 can determine the capacity of the energy storage device 510 to supply energy prior to transferring energy from the energy storage device 510. If the energy storage device 510 does not have enough capacity (i.e., not enough charge or voltage) to provide energy to the selected power source 166, no energy transfer occurs at step 610 and the power system controller 506 proceeds to select a new power source at step 601 (via step 612). In such case, since the energy storage device 510 has a low charge or voltage level, the power system controller 506 may attempt to select a power source 166 at step 601 that may require discharging to the energy storage device 510 to raise the charge or voltage level of the energy storage device 510.

[0039] If the energy storage device 510 has sufficient capacity to provide energy, the energy storage device 510 transfers energy to the selected power source 166 until the voltage of the selected power source 166 is raised to the target voltage level as measured by sensor 504. To transfer energy from the energy storage device 510 to the selected power source 166, the power system controller 506 can close the corresponding switch 508 (i.e. , position the switch 508 in a closed state) coupled to the selected power source 166 to complete a circuit between the energy storage device 510 and the selected power source 166. Alternatively, as described above, the power system controller 506 may close the switch 508 corresponding to the selected power source 166 prior to making the determination in step 608. The power system controller 506 can maintain or position the remaining switches 508 coupled to the other power sources 166 in an open state to provide open circuits between the energy storage device 510 and the remaining power sources 166, and thereby maintain the electrical isolation between the power sources 166, as well as between the electrical buses 502 connected to them. Upon the closing of the switch 508 and/or other triggering event, the energy storage device 510 can be discharged and the energy transferred to the selected power source 166. After completing the transfer of energy from the storage device 510 (i.e., the voltage level of the selected power source 166 is substantially equal to the target voltage level), the process can proceed to step 612. In step 612, a determination is made as to whether further monitoring of the power sources 166 is desired. If no further monitoring is required in step 612, the process can end. If additional monitoring is desired in step 612, the process returns to step 601 for the selection of a new power source 166.

[0040] In one embodiment, the determinations of steps 604 and 608 can be based on thresholds slightly above or below the target voltage so as to avoid discharging or charging a power source when its voltage is close to the target voltage. For example, the condition in step 604 can be satisfied if the measured voltage for the power source 166 is greater than an upper threshold slightly higher than the target voltage and the condition in step 608 can be satisfied if the measured voltage for the power source 166 is less than a lower threshold slightly lower than the target voltage.

[0041] The foregoing is merely illustrative of the principles of this disclosure and various modifications may be made by those skilled in the art without departing from the scope of this disclosure. The above described embodiments are presented for purposes of illustration and not of limitation. The present disclosure also can take many forms other than those explicitly described herein. Accordingly, it is emphasized that this disclosure is not limited to the explicitly disclosed methods, systems, and apparatuses, but is intended to include variations to and modifications thereof, which are within the spirit of the following claims. As an example, electrical power systems have been described herein for use within aircraft, but such electrical power systems may be used with other types of devices or systems as may be desired.

[0042] As a further example, variations of apparatus or process parameters

(e.g., dimensions, configurations, components, process step order, etc.) may be made to further optimize the provided structures, devices and methods, as shown and described herein. In any event, the structures and devices, as well as the associated methods, described herein have many applications. Therefore, the disclosed subject matter should not be limited to any single embodiment described herein, but rather should be construed in breadth and scope in accordance with the appended claims.

Claims

CLAIMS What is claimed is:

1. An electrical power system, comprising:

a plurality of power sources that are electrically isolated from each other;

a plurality of sensors, each sensor of the sensors configured to measure a parameter indicative of an amount of energy in a corresponding one of the power sources;

a plurality of switches coupled to the power sources;

an energy storage device coupled to the switches; and

a controller configured to control the switches for selectively coupling the energy storage device to each of the power sources, wherein the controller is further configured to control the energy storage device and the switches, based on the parameters measured by the sensors, such that energy is drawn from at least one of the power sources to the energy storage device and energy is supplied by the energy storage device to at least one of the power sources to balance voltages of the power sources while electrical isolation between the power sources is maintained.

2. The system of claim 1 , wherein the controller is configured to select one of the power sources for charging or discharging based on the parameters measured by the sensors and to transition one of the switches coupled to the selected power source to a closed state while each of the switches coupled to the other power sources is in an open state.

3. The system of claim 1 , wherein the power sources include a first power source and a second power source, wherein the first power source is electrically coupled to a first motor for driving a first propeller of an aircraft, and wherein the second power source is electrically coupled to a second motor for driving a second propeller of the aircraft.

4. The system of claim 1 , wherein the parameter measured by at least one of the sensors is a voltage level of the corresponding one of the power sources.

5. The system of claim 1 , wherein the parameter measured by at least one of the sensors is a current level of the corresponding one of the power sources.

6. A method for use in an electrical power system, comprising:

providing electrical power from a plurality of power sources to a plurality of loads across a plurality of electrical buses, each power source coupled to a respective one of the loads by a respective one of the electrical buses, wherein the power sources are electrically isolated from each other;

for each of the power sources, sensing with at least one sensor a parameter indicative of an amount of energy in the respective power source;

balancing voltages of the power sources based on the sensing, wherein the balancing comprises drawing energy from at least one of the power sources to the energy storage device and supplying energy from the energy storage device to at least one of the power sources; and

controlling a plurality of switches coupled between the power sources and the energy storage device such that the power sources remain electrically isolated from each other during the balancing.

7. The method of claim 6, further comprising selecting one of the power sources for charging or discharging based on the sensing, wherein the controlling comprises transitioning one of the switches coupled to the selected power source to a closed state while each of the switches coupled to the other power sources is in an open state.

8. The method of claim 6, wherein the power sources include a first power source and a second power source, and wherein the method further comprises:

providing electrical power from the first power source to a first motor;

driving a first propeller of an aircraft with the first motor;

providing electrical power from the second power source to a second motor; and

driving a second propeller of the aircraft with the second motor.