Electrified Aircraft Propulsion Systems: Potential Failure ...

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Electrified Aircraft Propulsion Systems: Potential Failure Modes and Failure

Mitigation Strategies

Donald L. Simon & Joseph W. Connolly

NASA Glenn Research Center

EnergyTech 2019

Cleveland, OH

October 21-25, 2019

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Outline

• Electrified Aircraft Propulsion (EAP) Background

• Overview of EAP Fault Management Process

• EAP System Failure Modes and Effects• Subsystem failure modes and effects

• Coupled subsystem failure modes and effects

• Example of Potential Failure Modes and Failure Mitigation Strategies for a NASA EAP Concept Aircraft

• Summary

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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

Example NASA EAP Concept Vehicles

N3-X

Distributed TurboelectricX-57 Maxwell

All Electric

Quadrotor

All Electric

Side-by-Side Helicopter

Hybrid Electric

Tiltwing

Turboelectric

STARC-ABL

Partial Turboelectric

NASA Aeronautics Strategic Implementation Plan

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Electrified Aircraft Propulsion (EAP) System Fault Management

• Fault Management capabilities are necessary to enable certification of aircraft systemso Any potential failure modes and

hazards must be identified and properly mitigated

• Electrified Aircraft Propulsion (EAP) systems are complex and tightly coupled, requiring integrated control and fault management functionalityo Presents new design challenges that

must be addressed

NASA Single-aisle Turboelectric AiRCraft with Aft Boundary Layer propulsor (STARC-ABL) Concept Aircraft

STARC-ABL Architecture

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Overview of EAP System Components

Generic EAP System Architecture

EAP System Components• Supervisory Control: Interface between vehicle and

propulsion system.

• Gas Turbine Engines: Turbomachinery that converts fuel into mechanical power.

• Gearboxes and Mechanical Drives: Used for transferring mechanical power throughout EAP system.

• Electric Machines: Generators and motors. Used for converting mechanical power into electricity or vice versa.

• Power Electronics and Power Distribution Systems: Handles switching, power conversion, and transmission of electrical power throughout system.

• Energy Storage Systems: Systems for the storage of electrical energy such as batteries and supercapacitors.

• Propulsors: Motor driven propellers or fans used to generate thrust.

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EAP Subsystem Failure Modes and Effects

Gas Turbine Engine Failure Modes and Effects

Failure Modes Failure Effects

Bearing spalling, failure

Gear/Gearbox misalignment, failure

Offtake/drive shaft failure

Loss of drive/gearbox oil pump

Loss of drive/gearbox oil cooler

Complete or partial loss of engine mechanical power offtake and ability to drive electric generators

Complete or partial loss of ability to drive electric motor driven propulsors

Gearbox, Transmission, Mechanical Drive Failure Modes and Effects

Failure Modes Failure Effects

Shaft failure

Bearing failure

Stator winding failure (short circuit, open circuit)

Insulation failure

Rotor mass unbalance

Broken rotor bar

Air gap eccentricity

Loss of cooling

Overheating/fire

Power supply-related electrical fault (voltage or current levels, phasing)

Phase loss

Partial power loss

Complete loss of power

Electric Machine Failure Modes and Effects

Failure Modes Failure Effects

Fuel exhausted

Engine Fire

Uncontained failure

Rotor seizure

Engine separation

Engine shutdown (various causes)

Partial power loss (various causes)

Loss of speed control

Complete loss of engine power

Partial loss of engine power

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EAP Subsystem Failure Modes and Effects (cont.)

Failure Modes Failure Effects

Potential Power Electronics Failures o AC supply-line failure (open-

circuit, short-circuit, phase-to-phase short, etc.)

o Diode failure o Link capacitor failure o Transformer failure o DC supply voltage failure o Transistor failure o Motor terminal supply line failure o Loss of cooling o Controller failures o Loss of motor speed control

Potential Electric Bus Failure Modes o Short circuit o Open circuit o Corona discharge o Arcing

Voltage sag, high current levels

Degraded power quality (voltage ripple, power instabilities)

Low power

Complete loss of power

Power Electronics and Power Distribution Systems Failure Modes and Effects

Failure Modes Failure Effects

Internal shorts

Thermal runaway / fire

Aging and internal mechanical stress (anode, cathode, separator), energy density degradation

Depleted state of charge (various faults)

Battery management system faults

External short/open circuit

Reduction in energy storage capacity

Reduction in discharge/charge rate

Complete loss of functionality

Energy Storage (Battery) Failure Modes and Effects

Failure Modes Failure Effects

Seizure

Shaft failure

Bearing failure

Blade damage/failure

Foreign object damage (FOD)

Environmental particulates (icing, volcanic ash)

Loss of control functionality (VAFN, pitch, speed, etc.)

Loss of propulsor thrust

Reduction in propulsor thrust

Loss of propulsor pitch control

Propulsor Failure Modes and Effects

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EAP Coupled Subsystem Failure EffectsMatrix listing of EAP subsystem failures and their coupled effects on other subsystems• EAP system designs are

highly integrated and coupled

• The failure of one subsystem can negatively impact the operation of other subsystems

• Any hazards posed by coupled failure effects must be properly identified and mitigated

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Example Failure Modes, Effects, and Mitigation Strategies for a NASA EAP Concept Aircraft

NASA Single-aisle Turboelectric AiRCraft with Aft Boundary Layer propulsor (STARC-ABL)

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STARC-ABL Overview

NASA Single-aisle Turboelectric AiRCraft with Aft Boundary Layer propulsor (STARC-ABL)

• Two wing-mounted geared turbofan engines produce thrust and supply mechanical offtake power to generate electricity

• Generators and rectifiers convert mechanical power into electricity

• Electricity transferred over two parallel direct current power buses

• Invertors and motors convert electricity into mechanical power supplied to tailfan propulsor

• Tailfan propulsor applies boundary layer ingestion for increased propulsive efficiency

GTF 1

GTF 2

Tailfan

Pwr Sys 1

Pwr Sys 2

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STARC-ABL Subsystem Failure Modes and Coupled Effects

GTF 1 GTF 2

Tailfan

Pwr Sys 1 Pwr Sys 2

STARC-ABL Architecture STARC-ABL Failure Modes and Effects Matrix(Off-diagonal “X’s” denote coupled failure effects)

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STARC-ABL (Notional) Design Considerations for Failure Mitigation

Freewheeling clutches allow tailfan propulsorto continue to operate in the event of a failure in one string

• Parallel turbofan and power strings for added redundancy

• System sized to provide 50% max thrust in the event of any single point failure

• Break away spline coupling for catastrophic failures

• Actuated disconnects to allow generators to be decoupled from engine if failure detected

• Control limit logic for over-speed protection and operability

• Reversionary control modes in the presence of failures

Circuit breakers to guard against over-current conditions

Supervisory control• Communicates with

vehicle• Receives health and

status information from propulsion subsystems

• Issues reconfiguration commands to subsystems in the event of a failure

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STARC-ABL Geared Turbofan (GTF)Reversionary Control Modes for Failure Mitigation

Turbomachinery Coupled Failure Effects:1) Geared Turbofan (GTF): No power extraction2) Geared Turbofan (GTF): Increased power extraction3) Tailfan: Reduction in available power

GTF 1 GTF 2

Tailfan

PwrSys 1

PwrSys 2

STARC-ABL Architecture

Geared Turbofan (GTF)

Power extracted from low pressure shaft for electrical power generation

Variable Bleed Valve (VBV) maintains low pressure

compressor (LPC) operability

Fuel controller ensures safe, reliable engine transient

operation

EM

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Power Extraction Fault Mitigation (Revised Variable Bleed Valve (VBV) Control Schedule)

VBV opens at low rotor speeds to ensure Low Pressure Compressor (LPC) operability(results shown at Alt = 25k feet, MN = 0.6 operating condition)

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Power Extraction Fault Mitigation (Revised Fuel Flow Control Gains)

Fuel controller ensures safe, reliable engine transient operation(results shown at Alt = 25k feet, MN = 0.6, PLA = 61 operating condition)

PI Control Gains (Nominal):Kp = 7.50 10-3

Ki = 8.63 10-3

PI Control Gains (No Power Extraction):Kp = 6.31 10-3

Ki = 4.96 10-3

PI Control Gains (Increased Power Extraction):Kp = 8.50 10-3

Ki = 12.16 10-3

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Summary

• Electrified Aircraft Propulsion (EAP) systems are novel, tightly integrated designso Many candidate EAP architectures exist, each presenting

unique failure modeso Any potential hazards associated with failures must be

identified and properly mitigated to enable certification

• Research and development is necessary to ensure appropriate fault management strategies for EAPo Fault management needed at both at the subsystem and

system levelo Expected to require multi-disciplinary, system-level design

approaches

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• This work was conducted under the NASA Advanced Air Vehicles Program, Advanced Air Transport Technology Project

Acknowledgments