Patent Description:
Aircraft, such as those utilized by commercial airlines, typically include two or more gas turbine engines mounted in or under the wings of the aircraft. The engines generate thrust, propelling the aircraft forward and allowing operation of the aircraft. A typical engine utilized in this configuration includes a fan forward of a turbine engine core, with the turbine engine core driving the rotation of the fan either via a direct drive system or a geared connection. Some aircraft propulsion systems also include one or more electric motors and/or generators to provide a supplemental power source under certain aircraft operating conditions.

<CIT> discloses a power system for aircraft comprising an energy storage component for supplying an electric motor. The electric motor provides additional power to a spool of the aircraft engine during take-off and climb, and charges the energy storage component during cruise. The energy storage component is a battery or a supercapacitor.

<CIT> discloses a hybrid turbo electric aero-propulsion system control The system comprises an energy storage device, which can be embodied as superconducting energy storage devices, batteries or battery packs, and a hybrid propulsion system optimizer providing optimization of propulsion control, power plant control and energy storage charge/discharge.

<CIT> discloses a power system for an aircraft with dual hybrid energy sources, comprising an ultra-capacitor and a battery.

<CIT> discloses an engine starting system using stored energy. The system comprises an energy storage unit with at least two super-capacitors, and a power source which can comprise one or more batteries.

Disclosed is a power system for an aircraft, where the power system includes an aircraft engine comprising one or more spools, a hybrid energy storage system with at least two energy storage subsystems, each having a different power density and a different energy density. The power system also includes one or more electric motors operably coupled to the hybrid energy storage system and to the aircraft engine. The power system further includes a means for controlling one or more electric power flows between the hybrid energy storage system and the one or more electric motors based on a modeled electric power demand associated with an engine load of one or more spools of the aircraft engine, wherein the modeled electric power demand is determined by a model-based control based on information about current engine loading and an engine load over one or more future time steps from an engine system model.

The power system may include where the means for controlling the one or more electric power flows of the hybrid energy storage system includes a power management controller operable to detect one or more conditions of the at least two energy storage subsystems and configure the one or more electric power flows between the hybrid energy storage system and the one or more electric motors.

The power system may include where the power management controller is operable to configure at least one of the one or more electric power flows from a first energy storage subsystem of the at least two energy storage subsystems to charge a second energy storage subsystem of the at least two energy storage subsystems.

The power system may include where the first energy storage subsystem includes a battery system and the second energy storage subsystem includes a super/ultra-capacitor, and further including a bidirectional converter operably coupled to the super/ultra-capacitor and power conditioning electronics operably coupled to the one or more electric motors.

The power system may include where the power management controller is operable to configure at least one of the one or more electric power flows from the super/ultra-capacitor through the bidirectional converter and the power conditioning electronics to power the one or more electric motors.

The power system may include where the bidirectional converter is operably coupled to the battery system, and the power management controller is operable to configure at least one of the one or more electric power flows from the battery system through the bidirectional converter and the power conditioning electronics to power the one or more electric motors and/or engine subsystem loads.

The power system may include where the power management controller is operable to select between powering the one or more electric motors by the super/ultra-capacitor and/or the battery system based on a power level of the modeled electric power demand and the one or more conditions of the super/ultra-capacitor and the battery system, and further where the power management controller is operable to control the one or more electric motors in a generator mode and charge the super/ultra-capacitor.

The power system may include where the power management controller is operable to select between powering the one or more electric motors by the super/ultra-capacitor and/or the battery system based on an expected duration of the modeled electric power demand and the one or more conditions of the super/ultra-capacitor and the battery system.

The power system may include where the power management controller is operable to predictively switch to source power from the hybrid energy storage system instead of the aircraft engine when the one or more electric motors are being operated.

Also disclosed is a method that includes determining, by a controller, an engine load of one or more spools of an aircraft engine. The controller determines a modeled electric power demand based on the engine load, wherein the modeled electric power demand is determined by a model-based control based on information about current engine loading and an engine load over one or more future time steps from an engine system model. One or more electric power flows of a hybrid energy storage system are configured based on the modeled electric power demand, where the hybrid energy storage system includes at least two energy storage subsystems each having a different power density and a different energy density. One or more electric motors are operably coupled to the hybrid energy storage system and to the aircraft engine.

The method may include detecting one or more conditions of the at least two energy storage subsystems, and configuring the one or more electric power flows between the hybrid energy storage system and the one or more electric motors based on the one or more conditions of the at least two energy storage subsystems.

The method may include configuring at least one of the one or more electric power flows from a first energy storage subsystem of the at least two energy storage subsystems to charge a second energy storage subsystem of the at least two energy storage subsystems.

The method may include where the first energy storage subsystem includes a battery system and the second energy storage subsystem including a super/ultra-capacitor, and the method may include configuring at least one of the one or more electric power flows from the super/ultra-capacitor through a bidirectional converter and power conditioning electronics to power the one or more electric motors.

The method may include configuring at least one of the one or more electric power flows from the battery system through the bidirectional converter and the power conditioning electronics to power the one or more electric motors and/or engine subsystem loads.

The method may include selecting between powering the one or more electric motors by the super/ultra-capacitor and/or the battery system based on a power level of the modeled electric power demand and the one or more conditions of the super/ultra-capacitor and the battery system, and controlling the one or more electric motors in a generator mode to charge the super/ultra-capacitor.

The method may include selecting between powering the one or more electric motors by the super/ultra-capacitor and/or the battery system based on an expected duration of the modeled electric power demand and the one or more conditions of the super/ultra-capacitor and the battery system.

The method may include predictively switching to source power from the hybrid energy storage system instead of the aircraft engine when the one or more electric motors are being operated.

Also disclosed is a system for an aircraft, comprising a power system for an aircraft as described earlier, wherein the aircraft engine is a gas turbine engine comprising at least one shaft, the hybrid energy storage system including a super/ultra-capacitor and a battery system. The system also includes the one or more electric motors operably coupled to the hybrid energy storage system and to the at least one shaft.

The system may include where the means for controlling the one or more electric power flows of the hybrid energy storage system includes a power management controller operable to detect one or more conditions of the super/ultra-capacitor and the battery system and configure the one or more electric power flows from the hybrid energy storage system to the one or more electric motors based on the one or more conditions and the engine load of the at least one shaft.

The system may include where the power management controller is operable to predictively switch to source power from the hybrid energy storage system instead of the gas turbine engine when the one or more electric motors are being operated.

A technical effect of systems and methods is achieved by providing hybrid energy storage system control for an aircraft engine as described herein.

The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans.

"Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R)/(<NUM> °R)]<NUM>,<NUM>.

<FIG> depicts a power system <NUM> of the gas turbine engine <NUM> of <FIG> (also referred to generally as an aircraft engine) according to an embodiment. The power system <NUM> includes a hybrid energy storage system <NUM> with at least two energy storage subsystems <NUM> each having a different power-energy density. In the example of <FIG>, the at least two energy storage subsystems <NUM> include a super/ultra-capacitor <NUM> and a battery system <NUM>. The hybrid energy storage system <NUM> may be sized to store energy to support transient bursts of the gas turbine engine <NUM> for a power assist during a snap acceleration or power shedding during a snap deceleration. Using only the battery system <NUM> for a wide range of acceleration and deceleration conditions may result in oversizing battery capacity with corresponding additional weight carried to meet potential transient demands. The super/ultra-capacitor <NUM> provides a lower storage capacity than the battery system <NUM> but has a higher charge/discharge rate as compared to the battery system <NUM>. The super/ultra-capacitor <NUM> can be comprised of one or more electrochemical double layer capacitors (EDLCs) or electrochemical capacitors that have a high energy density when compared to common capacitors, e.g., several orders of magnitude greater than a high-capacity electrolytic capacitor. The super/ultra-capacitor <NUM> can have higher energy efficiency due to a lower internal resistance than the battery system <NUM>. The super/ultra-capacitor <NUM> can be operatively coupled to the battery system <NUM> through a direct current (DC)-to-DC converter <NUM>. The DC-to-DC converter <NUM> can convert a voltage level of the battery system <NUM> to match a voltage level of the super/ultra-capacitor <NUM> to support charging of the super/ultra-capacitor <NUM> by the battery system <NUM>. In alternate embodiments, the DC-to-DC converter <NUM> can be omitted where regulation between the super/ultra-capacitor <NUM> and the battery system <NUM> is not needed.

In embodiments, one or more electric motors <NUM> are operably coupled to the hybrid energy storage system <NUM> and to at least one shaft <NUM> of an aircraft engine, such as the inner shaft <NUM> of low speed spool <NUM> or the outer shaft <NUM> of high speed spool <NUM> of the gas turbine engine <NUM> of <FIG>. In the example of <FIG>, the hybrid energy storage system <NUM> is operably coupled to a bidirectional DC-to-DC converter <NUM> which is operably coupled to power conditioning electronics <NUM> that interface with the one or more electric motors <NUM>. The bidirectional DC-to-DC converter <NUM> can perform any voltage conversions needed between the hybrid energy storage system <NUM> and the power conditioning electronics <NUM> depending on whether the one or more electric motors <NUM> are operating in a motor mode or a generator mode. The power conditioning electronics <NUM> can include inverter/motor drive circuitry that applies known motor control techniques to control the speed and/or torque produced by the one or more electric motors <NUM>. For example, during a snap acceleration, electric power from the hybrid energy storage system <NUM> is provided through the bidirectional DC-to-DC converter <NUM> and the power conditioning electronics <NUM> to drive the one or more electric motors <NUM> in a motor mode to supplement rotation of the engine shaft <NUM> as opposed by an engine load. The engine load on the engine shaft <NUM> can vary depending upon a flight regime and accessory loading from generators, environmental control systems, engine bleeds, and other known loading factors. During a snap deceleration, the one or more electric motors <NUM> can operate in a generator mode to increase the engine load on the engine shaft <NUM>, with resulting current passed through the bidirectional DC-to-DC converter <NUM> for storage in the hybrid energy storage system <NUM>. The bidirectional DC-to-DC converter <NUM> can be operably coupled to the super/ultra-capacitor <NUM> and/or the battery system <NUM>. In some embodiments, the bidirectional DC-to-DC converter <NUM> is electrically coupled to the DC-to-DC converter <NUM>.

In embodiments, the power system <NUM> also includes a means for controlling one or more electric power flows of the hybrid energy storage system <NUM> to/from the one or more electric motors <NUM> based on a modeled electric power demand of an engine load of the aircraft engine that is a current time step and predicted at one or more future time steps. The means for controlling the one or more electric power flows of the hybrid energy storage system <NUM> can be a power management controller <NUM> (also referred to as controller <NUM>) operable to detect one or more conditions of the super/ultra-capacitor <NUM> and the battery system <NUM> and configure the one or more electric power flows between the hybrid energy storage system <NUM> and the one or more electric motors <NUM>. Detectable conditions can include a current charge level, a remaining storage capacity, health/fault status, and other such information. Further, the conditions may be derived based on environmental factors or aging effects. For example, if a temperature of the battery system <NUM> impacts the storage capacity and/or charge/discharge rate, then such information can be determined in assessing the condition of the battery system <NUM>.

The power management controller <NUM> can interface with and control multiple elements of the power system <NUM> and the gas turbine engine <NUM>, such as switches, current sensors, voltage sensors, temperature sensors, communication buses, and the like. In an embodiment, the controller <NUM> includes a memory system <NUM> to store instructions that are executed by a processing system <NUM> of the controller <NUM>. The executable instructions may be stored or organized in any manner and at any level of abstraction, such as in connection with a controlling and/or monitoring operation of the power system <NUM> and/or the gas turbine engine <NUM>. The processing system <NUM> can include one or more processors that can be any type of central processing unit (CPU), including a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. Also, in embodiments, the memory system <NUM> may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and control algorithms in a non-transitory form.

An example of electric power flows of the hybrid energy storage system <NUM> can include a first electric power flow <NUM> from the battery system <NUM> through the DC-to-DC converter <NUM> to charge the super/ultra-capacitor <NUM>. Another example of electric power flows of the hybrid energy storage system <NUM> can include a second electric power flow <NUM> from the super/ultra-capacitor <NUM> through the bidirectional DC-to-DC converter <NUM> and the power conditioning electronics <NUM> to power the one or more electric motors <NUM>. A further example of electric power flows of the hybrid energy storage system <NUM> can include a third electric power flow <NUM> from the battery system <NUM> through the bidirectional DC-to-DC converter <NUM> and the power conditioning electronics <NUM> to power the one or more electric motors <NUM>. Other electric power flow variations are contemplated, such as reverse flows of the electric power flows <NUM>, <NUM> during generator mode of the one or more electric motors <NUM>. Selection and timing for engaging the various electric power flows <NUM>-<NUM> can be controlled by the power management controller <NUM>. As one example, the power management controller <NUM> may be implemented as a predictive controller or other model-based control as further described in reference to <FIG>.

In the example of <FIG> with continued reference to <FIG> and <FIG>, the power management controller <NUM> includes a model-based control <NUM>, such as a model predictive control, operable to output one or more electric power flow control signals <NUM> based on a super/ultra-capacitor model <NUM>, a battery system model <NUM>, and an engine system model <NUM>. The models <NUM>, <NUM>, <NUM> can comprise maps, equations, and the like that relate voltage, current, electrical power, and state-of-charge, for example. The system-level control algorithm integrates the models associated with each subsystem and includes their respective constraints. The electric motor(s) can be modeled as Tmotor = Fmotor(Iphase, V, Nshaft) where the function can be an equation, a look-up table, a map that relates the currents in all the motor phases, the voltage, and the shaft rotational speed to generated motor torque. Several constraints are defined and included in the overall control problem definition. These are related to motor torque, Tmotor, min ≤Tmotor≤Tmotor, max, shaft angular speed, Nshaft, min ≤Nshaft≤Nshall, max. Similarly, a model Fgenerator(Iphase, V, Nshaft) and constraints Tgenerator, min ≤Tgenerator≤Tgenerator, max are defined for the generator(s). The phase currents that control the motor torque can be generated by a motor drive/inverter and related to the direct current through another set of equations, Iphase = Finv(V, IDC, Nshaft), where Finv could be a set of equations, maps or look-up tables. The direct current, IDC, depends upon to the current provided by the ultra-capacitor or supercapacitor IDC, UC and/or the current supplied by the batteries, IDC, Bat, and needs to be bounded IDC, min ≤IDC≤IDC, max (with the positive upper bound active during discharging, and the negative, lower bound active during charging). Each of the current depends on the state-of-charge and state-of-health of the ultra-capacitor and battery system, IDC,UC=FI,UC(SOCUC, V, mode) and IDC,Bat=FI,Bat(SOCBat, V, mode). The state-of-charge and state-of-health are dynamical states that are interrelated and depend on the current supplied by each storage subsystem. Because they have different dynamics depending on whether they are charging or discharging the functions that relate current, SOC, SOH are specific to each mode of operation. In order to ensure that the batteries continue to operate correctly for many charging-discharging cycles, the two key parameters are bounded: SOCBat,min≤SOCBat≤SOCBat,max and SOHBat,min≤SOHBat. All the models mentioned above and their associated constraints are lumped into an integrated, dynamical system-level model dXSys = Fsys(XSys, mode) and constraints XSys, min≤XSys<XSys,max. The objective in controlling the hybrid energy storage system is to meet the requested shaft torque; a cost function that penalizes the errors between the motor torque TMotor and the requested shaft torque TShaft,Req can be used ∫[TMotor(t)- TShaft,Req(t)]dt, where the integral is calculated at each time step over a receding horizon [<NUM>, Dt], assuming that the requested motor torque is known over this time interval. The motor torque request can be set based on various external conditions such as: shaft speed and acceleration; overall system operating condition. The optimization problem including the defined cost function, system dynamics and constraints has as control inputs the current supplied by the battery system and modes of operation (charging, discharging) for each subsystem, and it is therefore a mixed-integer programming problem which can be solved numerically by using customized solvers.

The super/ultra-capacitor model <NUM> can model performance of the super/ultra-capacitor <NUM> of <FIG> using observed conditions and a physics-based model that incorporates sizing parameters, for example, to determine predicted charge time, discharge time, capacity, available charge, and other such information. Similarly, the battery system model <NUM> can model performance of the battery system <NUM> of <FIG> using observed conditions and a physics-based model that incorporates sizing parameters, for example, to determine predicted charge time, discharge time, capacity, available charge, and other such information. The engine system model <NUM> may model an engine load on the engine shaft <NUM> presently and at one or more future time steps. The engine system model <NUM> may receive engine parameters from an engine control or flight computer system (not depicted) that assist with load predictions. The load predictions can include flight regime (e.g., idle, takeoff, climb, cruise, decent, thrust reverse, etc.) along with demands due to known loads and operating status of other propulsion system elements (e.g., operational status of other engines on the aircraft). The power flow control signals <NUM> can control switching states and times of elements within the DC-to-DC converter <NUM>, the bidirectional DC-to-DC converter <NUM>, the power conditioning electronics <NUM>, and/or other circuitry (not depicted).

As one example, at each computational time step, the model-based control <NUM> receives information about current engine loading and an engine load over one or more future time steps from the engine system model <NUM>. The model-based control <NUM> can access the super/ultra-capacitor model <NUM> and the battery system model <NUM> with corresponding power constraints to determine power profiles for the super/ultra-capacitor <NUM> and the battery system <NUM> such that a power demand is met. Constraints can include healthy values, rates, and/or ranges for associated parameters. For instance, if a power demand exceeds the modeled capability of the battery system <NUM>, then electric power can be provided by the super/ultra-capacitor <NUM> via the second electric power flow <NUM>. After the super/ultra-capacitor <NUM> is discharged, the power management controller <NUM> can perform recharging from the battery system <NUM> using the first electric power flow <NUM>. As another example, the power demand can be initially met by the battery system <NUM> via the third electric power flow <NUM>, but upon exceeding the power demand provided by battery system <NUM>, additional power can be provided by the super/ultra-capacitor <NUM> via the second electric power flow <NUM>. In some embodiments, time-based analysis selects either or both of the super/ultra-capacitor <NUM> and the battery system <NUM>, for instance, by determining current demand and charge/discharge rates and capacity.

<FIG> is a flow chart illustrating a method <NUM> of controlling a hybrid energy storage system <NUM> of a gas turbine engine <NUM> in accordance with an embodiment. The method <NUM> of <FIG> is described in reference to <FIG> and may be performed with an alternate order and include additional steps. The method <NUM> can be performed, for example, by the power system <NUM> of <FIG> or an alternate configuration.

At block <NUM>, controller <NUM> can determine an engine load of one or more spools of an aircraft engine, such as loads on the engine shaft <NUM> operably coupled to the one or more electric motors <NUM>. At block <NUM>, controller <NUM> can determine a modeled electric power demand based on the engine load. Modeled values can be determined using the model-based control <NUM> of <FIG>. At block <NUM>, the controller <NUM> can configure one or more electric power flows <NUM>-<NUM> of the hybrid energy storage system <NUM> based on the modeled electric power demand.

In embodiments, the controller <NUM> can detect one or more conditions of the at least two energy storage subsystems <NUM>, such as the super/ultra-capacitor <NUM> and the battery system <NUM> and configure the one or more electric power flows <NUM>-<NUM> between the hybrid energy storage system <NUM> and the one or more electric motors <NUM> based on the one or more conditions of the super/ultra-capacitor <NUM> and the battery system <NUM>. For example, the controller <NUM> can configure at least one of the one or more electric power flows <NUM>-<NUM> from a first energy storage subsystem of the at least two energy storage subsystems <NUM> to charge a second energy storage subsystem of the at least two energy storage subsystem <NUM>, such as from the battery system <NUM> through a DC-to-DC converter <NUM> to charge the super/ultra-capacitor <NUM>. The controller <NUM> can configure at least one of the one or more electric power flows <NUM>-<NUM> from the super/ultra-capacitor <NUM> through a bidirectional DC-to-DC converter <NUM> and power conditioning electronics <NUM> to power the one or more electric motors <NUM>. Alternatively, the controller <NUM> can configure at least one of the one or more electric power flows <NUM>-<NUM> from the battery system <NUM> through the bidirectional DC-to-DC converter <NUM> and the power conditioning electronics <NUM> to power the one or more electric motors <NUM> and/or engine subsystem loads. The controller <NUM> may select between powering the one or more electric motors <NUM> by the super/ultra-capacitor <NUM> and/or the battery system <NUM> based on a power level of the modeled electric power demand and the one or more conditions of the super/ultra-capacitor <NUM> and the battery system <NUM>. Further, the controller <NUM> may select between powering the one or more electric motors <NUM> by the super/ultra-capacitor <NUM> and/or the battery system <NUM> based on an expected duration of the modeled electric power demand and the one or more conditions of the super/ultra-capacitor <NUM> and the battery system <NUM>. Further, the controller <NUM> can control the one or more electric motors <NUM> in a generator mode to charge the super/ultra-capacitor <NUM>.

In some embodiments, the power management controller <NUM> is operable to predictively switch horsepower extractions from the gas turbine engine <NUM> to source power from the hybrid energy storage system <NUM> instead of the gas turbine engine <NUM> when the one or more electric motors <NUM> are being operated. Power transfers may be achieved by one or more automatic bus transfers (ABT). Further, if additional bus power is needed, an uninterruptable power supply (UPS) may be used to enhance electric bus stiffness.

Claim 1:
A power system (<NUM>) for an aircraft, the power system comprising:
an aircraft engine (<NUM>) comprising one or more spools (<NUM>, <NUM>);
a hybrid energy storage system (<NUM>) comprising at least two energy storage subsystems (<NUM>) each having a different power density and a different energy density;
one or more electric motors (<NUM>) operably coupled to the hybrid energy storage system and to the aircraft engine (<NUM>) ; and
a means for controlling (<NUM>) one or more electric power flows (<NUM>, <NUM>, <NUM>) between the hybrid energy storage system and the one or more electric motors (<NUM>) based on a modeled electric power demand associated with an engine load of the one or more spools (<NUM>, <NUM>) of the aircraft engine, wherein the modeled electric power demand is determined by a model-based control (<NUM>) based on information about current engine loading and an engine load over one or more future time steps from an engine system model (<NUM>).