Control Technology Needs for Electrified Aircraft Propulsion Systems

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National Aeronautics and Space Administration

Control Technology Needs for

Electrified Aircraft Propulsion Systems

Paper GT2019 - 91413 Donald L. Simon Joseph W. Connolly Dennis E. Culley NASA Glenn Research Center NASA Glenn Research Center NASA Glenn Research Center 21000 Brookpark Road 21000 Brookpark Road 21000 Brookpark Road Cleveland, OH, 44135 Cleveland, OH, 44135 Cleveland, OH, 44135 ASME Turbo Expo 2019 June 17 - 21, 2019 Phoenix, AZ www.nasa.gov

Outline

• Electrified Aircraft Propulsion (EAP) Background

• Comparison of Conventional versus EAP Control Architectures

• EAP Control Technology Needs

 Modeling Tools to Support Control Design

 Control Strategies

 Test Facilities

 Certification Considerations

• Summary

National Aeronautics and Space Administration Control Technology Needs for Electrified Aircraft Propulsion Systems 2

Electrified Aircraft Propulsion (EAP) Background

• EAP relies on the generation, storage, and transmission of electrical power for aircraft propulsion • Enables aircraft designs that apply advanced propulsion concepts such as distributed electric propulsion and boundary layer ingestion fans • Benefits include a potential reduction in emissions, fuel burn, noise, and cost N3 - X X - 57 Maxwell STARC - ABL Distributed Turboelectric All Electric Partial Turboelectric Quadrotor Side - by - Side Helicopter Tiltwing All Electric Hybrid Electric Turboelectric NASA Aeronautics Strategic Implementation Plan Example NASA EAP Concept Vehicles National Aeronautics and Space Administration Control Technology Needs for Electrified Aircraft Propulsion Systems 3

Electrified Aircraft Propulsion (EAP) Background

EAP Architecture Options

(the focus of this presentation is on architectures that contain gas turbine engine technology)

• EAP presents multiple technology challenges

 Increased battery specific energy  Flight quality electric machines with high efficiency and specific power  Power electronics and power distribution technology to enable high voltage operation at altitude  Turbomachinery advances to enable high levels of power extraction

• The focus of this presentation is on EAP controls technology challenges

National Aeronautics and Space Administration Control Technology Needs for Electrified Aircraft Propulsion Systems 4

Comparison of Conventional and EAP Control Architectures

Electrified Aircraft Propulsion Conventional Aircraft Propulsion Control Architecture (notional) Control Architecture • EAP control architectures are more distributed, more complex, and more coupled • This presents both control design challenges and control design opportunities!

National Aeronautics and Space Administration Control Technology Needs for Electrified Aircraft Propulsion Systems 5

Modeling Tools to Support Electrified Aircraft Propulsion

(EAP) Control Design

• Dynamic propulsion models used Turbomachinery

Turbomachinery for control design must capture: Electrical Engine Engine ‒ Relevant system dynamics Components Control ‒ Performance/efficiency variations To Engine Var. Freq.

due to changes in operating point Bus Gen.

Induction Generator PLA ‒ Operational limits ‒ System degradation and faults Induction Torque Motor Tailfan To Motor Inverter Motor Control Control

• EAP control design will require

Turbo - Induction Motor machinery

integrated dynamic models

consisting of turbomachinery, Example control architecture for a turboelectric propulsion system

electrical components, and thermal

management systems

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EAP Optimal Energy Management

• Optimal energy management is relevant for hybrid designs that include energy storage devices • Commonly applied in Hybrid EAP Power Schedule (Feasible Operating Modes): automotive industry for control of hybrid cars Mode Engine Battery • Allows engine to operate ① Off Discharging closer to its point of optimal ② On Charging efficiency over a greater ③ On Static portion of the flight ④ On Discharging • Seeks to minimize fuel burn and emissions while adhering to operating constraints such Hybrid EAP Power Schedule as operability, structural, and thermal constraints National Aeronautics and Space Administration Control Technology Needs for Electrified Aircraft Propulsion Systems 7

EAP Transient Control Schedules and Limit Logic

• Transient control design accounts for approximately 75% of the control law design and development effort for conventional aircraft gas turbine engines • EAP transient control design challenges: ‒ P resents new design constraints and pinch points to coordinate transient response of integrated components Compressor map indicating engine steady - state ‒ In addition to gas turbine control limits, operation, transient operation, and operating limits additional limits are required on speed and torque levels of electric machines, battery charge/discharge rates, electric load rate of change, power levels, etc.

• EAP transient control design opportunities: ‒ Hybrid designs with the capability to either extract or supply engine shaft power enables supplemental control of the engine Turbine Electrified Energy Management (TEEM) in addition to fuel flow technology applies electric machines to either supply or extract power to gas turbine engine shafts National Aeronautics and Space Administration Control Technology Needs for Electrified Aircraft Propulsion Systems 8

Novel Cycle Engines and More Electric Engines

• Novel Cycle Engines: • High percentage of power extraction requires novel gas turbine engine cycle designs • This introduces the need for control strategies to schedule operation of the engine and its variable geometry in coordination with the power extraction demands placed on the engine • More Electric Engine (MEE) Designs • MEE replaces conventional mechanical and pneumatic driven accessories with electrical - mechanical actuators.

NASA hFan (Parallel Hybrid Electric Turbofan) • Readily available source of electricity is expected with Variable Area Fan Nozzle (VAFN) to accelerate transition to More Electric Engine (MEE) controls and accessories National Aeronautics and Space Administration Control Technology Needs for Electrified Aircraft Propulsion Systems 9

Facilities for Testing and Maturation of EAP Systems

• Test facilities are required to develop and mature a variety of EAP technologies, including controls o Facilities required for subsystem - level as well as system - level testing o Reconfigurable, with capability to test a variety of EAP design architectures and power levels o Altitude test capability to evaluate EAP control designs at representative operating conditions NASA Electric Aircraft o Flight test vehicles to enable flight Hybrid - Electric Integrated Testbed (NEAT) Systems Testbed (HEIST) testing of EAP concepts, including controls National Aeronautics and Space Administration Control Technology Needs for Electrified Aircraft Propulsion Systems 10

EAP Control Design Considerations to Address

Certification Requirements

• Established aerospace practices define guidelines for the development of civil aircraft and systems, and for conducting safety assessments on these systems ‒ System development and safety assessment processes occur concurrently in an integrated/coordinated fashion ‒ All functional failures/hazards must be identified and appropriately mitigated Aerospace Recommended Practices, Regulatory Agency Compliance Guidelines • Control design will play a significant role in assuring that EAP systems comply with the airworthiness standards set forth by regulatory agencies. This includes: ‒ Control fault detection and mitigation logic for compliance with development assurance level (DAL) allocations ‒ Reversionary control modes and activation logic ‒ Coordination of supervisory and subsystem level controllers in the presence of system faults • The inherent coupling in EAP designs may necessitate certification of the EAP system as a whole Aircraft Engine Controls Development Process National Aeronautics and Space Administration Control Technology Needs for Electrified Aircraft Propulsion Systems 11

Summary

• Electrified Aircraft Propulsion offers a paradigm shift towards the design and control of aircraft propulsion systems • EAP systems are expected to be more complex and require coordinated operation between turbomachinery and electrical components • Dynamic coupling between EAP turbomachinery and electrical components offers several control design challenges and opportunities

Including control considerations early in the EAP design process can

improve overall efficiency and performance!

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