The More Electric Aircraft Why Aerospace Needs Power Electronics Prof Pat Wheeler University of Nottingham, Nottingham, UK Tel. +44 (0) 115 951 5591 Email. Pat.wheeler@Nottingham.ac.uk Tel. +44 (0) 115 951 5591 Email. Pat.wheeler@Nottingham.ac.uk
Introduction l The More Electric Aircraft – a step in the direction a step in the direction of a more energy efficient aircraft
of a more energy efficient aircraft · The More Electric Aircraft concept The More Electric Aircraft concept
· History of more electrical systems in Civil Aircraft History of more electrical systems in Civil Aircraft
· Motivations and systems l Regeneration onto the Aircraft Power System
Regeneration onto the Aircraft Power System ·
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l Power converters and actuation systems
Benefits and issues
Potential solutions
Simulation results The next steps
· The Clean Sky JTI project Power Sources “Conventional” Aircraft Jet Fuel Propulsion Thrust (» 40MW) Gearbox driven generators Electrical 200kW High pressure air “bled” from engine Pneumatic 1.2MW Gearbox driven hydraulic pump Hydraulic 240kW Fuel pumps and oil pumps on engine Mechanical 100kW Total “non­thrust” power thrust” power » 1.7MW
Power Sources “Conventional” Aircraft
“Conventional” Aircraft · Electrical » » » » Avionics Cabin (lights, galley, in­flight entertainment etc) flight entertainment etc) Lights, pumps, fans 115V, 400Hz AC
· Pneumatic » Cabin pressurisation » Air conditioning » Icing protection
· Hydraulic » » » » Flight control surface actuation Landing gear extension/retraction and steering Braking Doors
· Mechanical » Fuel and oil pumps local to engine “More Electric Aircraft” Concept Jet Fuel Rationalisation of power sources and networks Propulsion Thrust (» 40MW)
“Bleedless” engine Engine driven generators Existing electrical loads ELECTRICAL Cabin pressurisation Air conditioning Icing protection Expanded electrical network ELECTRICAL Flight control actuation Landing gear/ Braking Doors ELECTRICAL Fuel pumping Engine Ancillaries New electrical loads Electrical system power » 1MW Electrical system power
“More Electric Aircraft” Some Motivations l Removal of hydraulic system
· reduced system weight
· ease maintenance l “Bleedless” engine
· improved efficiency l Desirable characteristics of electrical systems
Desirable characteristics of electrical systems · controllability » power on demand
· re­configurability » maintain functionality during faults maintain functionality during faults
· advanced diagnostics and prognostics
advanced diagnostics and prognostics » more intelligent maintenance » increased aircraft availability l OVERALL
· Reduced operating costs
· Reduced fuel burn
· Reduced environmental impact More Electric Aircraft l Airbus A380 • 4 x 150kVA Wideband VF on turbofan engines • Flight Control Power – 2 H + 2 E • Actuator Configuration Ø Combination of Hydraulic and Electrical Actuation
Combination of Hydraulic and Electrical Actuation More Electric Aircraft l Vickers VC10 • Electrical System – 4 x 40kVA Generators 4 x 40kVA Generators • Flight Control Power – 2 H + 2 E • Actuator Configuration Ø Combination of Hydraulic and Electrical Actuation • Built 50 Years before the Airbus A380
Built 50 Years before the Airbus A380 More Electric Aircraft l Boeing 787
· 4 x 250kVA Primary Channel Starter Generators » 500kVA per channel • 230VAC VF Primary Power Generation • Electrical Starter/Generators rated at 250/225kVA • Electric ECS, pressurisation and wing anti­Icing Electric ECS, pressurisation and wing anti • Removes need for bleed air from engines
Removes need for bleed air from engines 225kVA 225kVA S/G6 250kVA S/G5 250kVA S/G4 250kVA S/G3 230 VAC 3­Phase VF S/G2 230 VAC 3­Phase VF S/G1 230 VAC 3­Phase VF Electrical Power Distribution System 230 VAC 3­Phase Loads 115 VAC 3­Phase Loads 250kVA 28 VDC Loads More Electric Aircraft l Joint Strike Fighter
· 270V DC Power System
· Electric actuation systems
· 80kW, 2 channel, switched reluctance generator 80kW, 2 channel, switched reluctance generator
· Reduces cost, size and weight of whole aircraft Reduces cost, size and weight of whole aircraft
· Relies on Power Conversion technologies
Relies on Power Conversion technologies » Harsh environment » Efficiency » Reliability More Electric Aircraft A Possible MEA DC Power System Layout A Possible MEA DC Power System Layout
Source: Virginia Polytechnic Typical Power Levels for Electrical Loads Power User Comments Typical Power level 4 x 70kW+ Air Conditioning ECS Flight Controls Primary and secondary 3 kW to 40kW often short duration at high loads about 10kW Wing Ice Protection Landing Gear Thermal mats or similar Retraction, steering and braking Engine starting May be used for additional applications 250kW+ 25kW to 70kW short duration 200kW+ short duration
Fuel pumps AC Power Generation l Mechanical Constant Frequency Gen. [traditional]
Mechanical Constant Frequency Gen. [traditional] Variable speed Engine Shaft Constant Speed Mechanical Drive [Gearbox] Constant Speed Shaft Generator 3­phase 400Hz, 115V
· Mechanical gearbox creates a constant speed shaft from a variable speed input
· Constant speed shaft drives the Generator » Voltage control used for the generator Voltage control used for the generator » 400Hz voltage supply – fixed frequency
fixed frequency · Expensive to purchase and maintain » Single source due to patents Single source due to patents AC Power Generation l Variable Frequency Generation [new aircraft]
Variable Frequency Generation [new aircraft] Variable speed Engine Shaft Generator 3­phase 320Hz to 800Hz 230V or 115V
· Generator provides variable frequency supply » Voltage control around generator
Voltage control around generator · Direct connection between generator and power bus » Simple and reliable generation
Simple and reliable generation · Nearly all aircraft loads will require power converters for control » Good News for Power Electronics Engineers! Good News for Power Electronics Engineers! Actuation Systems
Actuation Systems Example of an Actuation System · Elimination of hydraulics » Electro­Mechanical Actuator » 30kW matrix converter » integrated with ballscrew housing/heatsink integrated with ballscrew housing/heatsink
· Holistic design of motor/load/power converter » Maximise system efficiency » Minimise system weight
· Advanced thermal management » Copes with intermittent operation Voltage transducers Supply 360Hz to 800Hz Filter LEMs Matrix Converter PM Motor Motor Current 12.5kHz sampling rate 200Hz Bandwidth Supply Voltage LVDT
Resolver Actuator Motor Speed 1.25kHz sampling rate 20Hz bandwidth Control Ram Position 250Hz sampling rate 2Hz bandwidth Ram Position Demand Regeneration: Converters 3­Phase Supply 3­phase supply Energy dissipation in the DC Link 3­Phase Load Traditional Solution:
· DC link chopper and resistor in DC link used to dump regenerative energy
· Lowers system efficiency and increase size and weight of equipment
· Measure DC link voltage and operate chopper when DC link voltage above a set level
· Resistor and associated cooling can double volume and weight of the power converter Bi­ directional switch Load Long Term Solution:
· Allow regeneration onto aircraft power system
· Use a Direct [Matrix] Converter or a controlled rectifier
· Energy returned to supply giving a smaller, lighter power converter
Motor Speed Reversal Phase A current Phase B current Phase C current Motor shaft speed (rpm) q­axis current Torque (Nm)
Motor Speed Reversal REGENERATION Phase A current Phase B current Phase C current Motor shaft speed (rpm) q­axis current Torque (Nm)
Options for Regenerative Energy Management l Regeneration will save considerable weight and volume
Regeneration will save considerable weight and volume ·
l Regenerative energy must be handled correctly to maintain Power Quality Eight methods have been identified for safe electrical regenerative energy management
electrical regenerative energy management ·
Centralised Energy Storage
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Centralised Energy Dissipation
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Local Voltage Control
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Return Energy to Source
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Separate Bus for Regenerative Energy
Separate Bus for Regenerative Energy ·
Local Energy Dissipation
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Local Energy Storage
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Hybrid Structures with Local Dissipation Hybrid Structures with Local Dissipation
Options for Regenerative Energy Management • Local Energy Dissipation – existing solution Local Energy Dissipation Control Recovery Advantages Disadvantages Local to load No Existing solution Size and weight of equipment, sub­ optimum system design Converters Control Bus Generator • • • do not allow regeneration onto the aircraft bus ensure that each item of equipment has ensure that each item of equipment has
energy dissipation if required today’s solution Regenerative Loads Energy Dissipation eg. Resistor with break chopper Options for Regenerative Energy Management • Return Energy to Source Control Recovery Advantages Disadvantages Centralised Yes No large additional hardware Possible change to existing generator control methods Enhanced Control Converters Bus Generator Regenerative Loads • • allow regeneration onto the aircraft bus use the generator as a motor if required • • the regenerative power would be returned to the engine inertia only possible if there is no auxiliary gearbox only possible if there is no auxiliary gearbox
Impact of Regeneration • Modelling study performed in SABER • Sudden change of total actuator power from 40kW motoring to ­55kW regeneration • Simulation for given for a fully preloaded generator Generator Torque reduces • voltages at HVAC Bus 230V and at AC Bus 115V are kept within the envelopes according to MIL are kept within the envelopes according to MIL­ STD­704F MIL_STD­704F envelope for transients
Conclusions • Power Electronics can offer advantages in aerospace applications • System efficiency, • Size and weight • Flexibility • There are challenges for Power Electronics in this There are challenges for Power Electronics in this environment • Losses • Reliability • Integration • Future projects will take these area forward
Future projects will take these area forward Clean Sky JTI l Total project budget – €1.6B
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l l Clean Sky JTI work is split into six “ITDs” Led by 12 companies [Members]
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l l Duration – 7 years Thales, Liebherr, Airbus, Dassualt, Alenia, SAAB, Rolls Royce, Safran, EADS, …. Each ITD then has 5 or 6 other organisations [Associate Members] 25% of funding reserved for Calls for Proposals
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See www.cleansky.eu now for first call and get involved l The University of Nottingham is an Associate member
· Systems for Green Operations ITD
· We are the only University which is an Associate Member in our own right
· Budget of about €10M