professor pat wheeler power electronics, machines...

Power Electronics Research at the University of Nottingham

Professor Pat Wheeler

Email: [email protected]

Power Electronics, Machines and Control (PEMC) Research Group

UNIVERSITY OF NOTTINGHAM, UK

The University of Nottingham



mailto:[email protected]



Technology Development from the More Electric Aircraft

to All Electric Flight

UNIVERSITY OF NOTTINGHAM, UK

mailto:[email protected]

Introduction

• More Electric Aircraft: – why and technology progress– Aircraft electrical equipment, generators and

power Systems

• All Electric Aircraft – Technology requirements, – Progress to date and future prospects

• Electromagnetically assisted aircraft take-off– Technology and benefits

The More Electric Aircraft

What is a More Electric

Aircraft (MEA)?

Why is there so much

interest in MEA?

Why is Power Electronics

important?

Power Sources Conventional Aircraft

Total “non-thrust” power 1.7MW

Jet Fuel

Propulsion

Thrust ( 40MW)

Gearbox driven

hydraulic pump

Electrical

Gearbox driven

generators

Hydraulic

High pressure

air “bled” from

engine

Pneumatic

Fuel pumps

and oil pumps

on engine

Mechanical200kW 1.2MW 240kW 100kW

Figures for a typical civil aircraft

Total Electrical System Power 1MW

Rationalisation of

power sources and

networks

“Bleedless” engine

Expanded electrical network

Engine driven

generators

Existing electrical

loads

New electrical loads

ELECTRICAL

Flight control actuation

Landing gear/ Braking

Doors

ELECTRICAL

Cabin pressurisation

Air conditioning

Icing protection

ELECTRICAL

Fuel pumping

Engine Ancillaries

Jet Fuel

Propulsion

Thrust ( 40MW)

Power Sources More Electric Aircraft

• Removal of hydraulic system– reduced system weight– ease maintenance

• “Bleedless” engine– improved efficiency– simplified design

• Desirable characteristics of electrical systems– controllability

• power on demand – re-configurability

• maintain functionality during faults– advanced diagnostics and prognostics

• more intelligent maintenance• increased aircraft availability

More Electric AircraftMotivations

The “Most” Electric Civil Aircraft Yet

• Boeing 787• Electric environmental control, cabin

pressurisation and wing anti-icing

• Removes need for bleed air from engines

• Still retains a hydraulic system for primary actuation etc

0

200

400

600

800

1000

1200

1400

1600

0 200 400 600 800Ele

ctr

ica

l Syste

m P

ow

er

(kW

)

Aircraft Weight (tons)Conventional aircraft

A380 – slightly

more electric

B787 – much

more electric

20202010200019901980197019601950

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200

300

400

500

600

700

800

900

1000

VC10

B737

Concorde

Caravelle

A320

B747

A330

A340

A350

A380

B787

Power, kW

Year

B777B757

B767

20202010200019901980197019601950

100

200

300

400

500

600

700

800

900

1000

VC10

B737

Concorde

Caravelle

A320

B747

A330

A340

A350

A380

B787

Power, kW

Year

B777B757

B767

AC Power Generation

• Mechanical Constant Frequency Generation

• Variable Speed generator /Constant Frequency Output

• Variable Frequency Output

Variable speed

Engine Shaft

Generator

Constant Speed

Mechanical Drive

[Gearbox]

Constant

Speed Shaft3-phase

400Hz, 115V

Generator

Power Converter

[DC Link or Cyclo-

converter]

3-phase

400Hz, 115V

Variable speed

Engine Shaft

Generator

3-phase

320Hz to 800Hz

230V or 115V

Variable speed

Engine Shaft

Aircraft Actuation Systems

Flight Control Actuation Systems

PITCHElevators

YAWRudder

ROLLAilerons

Roll spoilers

Trailing Edge Flaps

High Lift / drag

Leading Edge Slats

High Lift (High angle of attack)

Ailerons

Elevators

Rudder

Trimming Tailplane

pitch attitude influence stabilizer

RH & LH Synchronisation

Airbrakes

lift dump + drag

Thrust Reversers

supplement to wheel brakes

Roll Spoilers

supplement ailerons

Electronic

Controllers

Flight Control

• Primary Actuation– Roll - Ailerons on trailing edges of wings

– Pitch - Elevators on trailing edge of tail-plane

– Yaw - Rudder

– Flight critical

• Secondary Actuation– Flaps - Trailing edge of wing

• Used for take off and landing – increase lift at low speed

– Slats - Leading edge of wing, used for same reason as Flaps

– Airbrakes - Spoilers and lift dumpers on wings to increase drag

– Not actually required for flight, but very useful!

Electrically Driven Actuators

• Electro Mechanical Actuator – EMA

• Actuator is moved as motor spins

– Each turn of the motor moves the actuator a fixed amount

– Direct connection between motor and actuator arm

• EMA issues

– Direct drive solution

– Any potential jamming failure modes must be addressed

– Potentially the most compact solution

Power Converter

Electric Motor

BallScrew

3-phase supply

Reduction gearbox

• Electro Hydrostatic Actuator – EHA

• Actuator is moved as motor spins using local Hydraulic system

– Each turn of the motor moves the actuator a fixed amount

– No direct connection between motor and actuator arm

• EHA Issues

– Benign failure modes

– Based on a familiar technology for aircraft component manufactures

– Hydraulic fluid may leak

Power Converter

Electric Motor

3-phase supply

Hydraulic Ram

Fixed Displacement

pump


PEMC Research GroupPEMC Research GroupPEMC Research Group


• EMA– Direct drive solution– Any potential jamming failure modes

must be addressed– Potentially the most compact solution

• EHA– Benign failure modes– Based on a familiar technology for aircraft

component manufactures– Hydraulic fluid may leak

All Electric Aircraft

• Airbus Electric 2-seater

• flies for just 20 minutes

• Solar Impulse

• PV powered Aircraft

• Flew ½ way around the world in 30 days!

All Electric Aircraft

Hybrid and All Electric Propulsion

Series Hybrid

Propulsion

Parallel Hybrid

Propulsion

All Electric

Propulsion

Targets for Aircraft Propulsion

Electrical Machines• Short term (5-10 years) 7-10 kW/kg • Mid Term (10 to 15 years) 10-20 kW/kg • Long Term ( >>15 years) 20 -50 kW/kg

• Longer term goals may have to be achieved through superconducting or newtechnologies.

• Short-Medium term goals likely to be achieved using “more conventional” machines with a strong level of innovation.

Power distribution network cables• Short term (5-10 years) 1 kg/km/A• Mid Term (10 to 15 years) 0,5 kg/km/A• Long Term ( >>15 years) 0,1 kg/km/A

State of the Art Enabling Technologies

• Drivetrain Integration– Mechanical– Power Electronics

• Materials (Devices, Magnetic, Electric, Thermal, Structural)– Exciting improvement using nano

materials

• Machine-drive topologies working at high frequency – High poles/high speed

• Manufacturing – automation, additive– New structures

• Advanced thermal management

Electrical and mechanical integration

High frequency

machines

20kW/L,

SiC converter

Thermal material

integration

Performance Limits

Hybrid Propulsion Systems

Modern Trends in Aircraft Electric Power Systems and in Onboard Electric Power Generation

Engine Propulsion

Fuel Energy Storage

EMEMEMEM EMEM EMEMEMEM EMEMEMEM

TurbineTurbine

Electric Propulsion Electric Propulsion

Electric Starter/Generators

Power Electronic Converters

Battery Electrical Energy Storage

Fuel Cell Electrical Energy Storage

Fast-Responce Electrical Energy

Storage (SuperCap)

Electric Loads (WIPS, EPS, EMA, etc)

EPS control and energy

management

TurbineTurbine

“Single-bus” approach is employed!

Potential TeDP EPS architecture:- gas turbines drive generators, and optionally may act as direct propulsion devices- distributed electrical machines drive propulsion devices- energy storage devices can be used to buffer energy- overall EPS control/energy management

Modern Trends in Aircraft Electric Power Systems and in Onboard Electric Power Generation

High-power machine design for hybrid platforms

- MW-class equipment

- Efficiency/losses become a critical design factor

- High speed gen-sets- Close Integration with GT- Very high power density requirement- Thermally/Mechanically challenged

- Low-speed propulsion motors- Very high torque density- Electromagnetically/Thermally

challenged

Generator

Gas Turbine

Propulsors

EM

EM

Converter

Case 1: Starter/Generator System

Aircraft Starter/Generator

Overall drive system – machine choice

Selected Solution• Slot-Pole Combination – 36-6

• 6 pole to limit switching

frequency loses

• distributed winding

• low rotor losses

• Solid rotor with a CF sleeve retention

• Stiff rotor

• Quasi Hallbach array

• Large airgap = low rotor loses & adoption

of a stator sleeve

8k rpm

19k rpm

32k rpm

motoring

generating

Aircraft Starter/Generator

Power Converter Selection

• Up to 1.6kHz electrical frequency at maximum speed

• Maximum current: 260Arms peak, 270V DC

• Low harmonic content to minimize rotor losses

• Air cooled – significant impact on heat sink weight

2 Level , fs = 20kHz 3 Level , fs= 16kHz Same output

current THD

High Power Density Starter Generator

3-Level NPC drive

Rotor assembly and Low loss laminations

Lightweight Housing Components

E-machine

Helicopter Swash Plate Actuation

Design ConceptSwashplate attachment and EMA arrangement

Jam-tolerant design required due to the jamming risk in ball screw

Redundant EMAs

Requirement to replicate hydraulic system space envelope

Arrangement of 2 EMAs side by side

Hydraulic swashplate actuator arrangement 6 EMAs, each pair

connected to output rods

• Models needed for all the parts of the system

– Reliability– Functional– scalable

Optimisation System Optimisation - models and tools

Parameter Lower Boundary Upper Boundary Unit

Airgap Diameter d 24 35 mm

Split Ratio SR = d/D 0.4 0.6 -

Tooth-width factor 0.5 0.7 -

Fin extension 1 8 mm

Fin thickness 1 3 mm

Fin pitch/thickness 2 8 -

Optimisation with Particle Swarm Optimisation algorithm:

• Simulates behaviour of bird flocks to find optimum of non-linear

functions

• Number of particles with random initial position and velocity

• At each iteration step velocity is

updated with attraction to personal

best particle position

• Efficient optimisation method for

electromechanical problems

• Optimisation with 6 parameters

applied for this design:

dD

L

Particle Projection Evolution of Drive Weight

Optimisation Detailed Design Optimisation

Hardware ConstructionActuator, Motor and Power Converter

Stator

Phase A1

Phase C1

Phase B1

Phase B2

Phase C2

Phase A2

Rotor

Completed Motor

PowerConverter

Short Circuit Motor Current and Drag Torque

Actuatorwith two motors, each motor has two independent stators

Electromagnetic Aircraft Launch Systems for Civil Aircraft

• Electromagnetic Launch (EML) system used

to replace steam catapults on the deck of

aircraft carrier.

• Steam catapult have a number of disadvantages

• Operate without feedback control

• Bulky and heavy

• Highly maintained

• Inefficient (4-6%)

• Adoption of EML in military application was slow

• Recently technical advances have been good for the technology:

• Pulsed power

• Power conditioning

• Energy storage

devices

• Advanced

controls

Electromagnetic Launch Systems

Requirements Data

Aircraft mass 73500 kg

Take-off speed 85.73 m/s

Acceleration 0.60 g

Peak Thrust 502.9 kN

Runway length 624 m

Take-off time 14.57 s

Minimum cycle time 90 s

Electromagnetic Launch Benefits 1

1) Runway length reduction

An acceleration of 0.6G was chosen - compliance with the maximum axial acceleration that a human body can comfortably withstand.

The runway length computed assuming a uniformly accelerated motion to the rotation speed VR plus a safety distance equal to the 25% of the acceleration path.

𝑽𝑹 = Τ𝟏. 𝟎𝟓 𝑽𝟐 𝟏. 𝟏𝟏


2) Fuel consumption and exhaust emission reduction

Assume all the energy required to accelerate the aircraft can be saved.

Consider a CFM56-5B4 on the Airbus A320-200, the total fuel burnt during take-off can be computed as

𝐹𝑢𝑒𝑙 𝑏𝑢𝑟𝑛𝑡 = 2 𝑒𝑛𝑔𝑖𝑛𝑒𝑠 ∙ 1.166𝑘𝑔

𝑠∙ 42 𝑠 = 𝟗𝟕. 𝟗𝟒 𝑘𝑔

Considering an airport like Heathrow with 650 flights per day yields

𝐹𝑢𝑒𝑙 𝐵𝑢𝑟𝑛𝑡 𝐷𝑎𝑖𝑙𝑦 = 97.94𝑘𝑔

𝑡𝑎𝑘𝑒 𝑜𝑓𝑓∙ 650

𝑡𝑎𝑘𝑒 𝑜𝑓𝑓

𝑑𝑎𝑦= 𝟔𝟑𝟔𝟔𝟏

𝑘𝑔

𝑑𝑎𝑦

The NOx emission is equivalent of that of 80180 diesel car son daily base

HC CO NOx

Emission indices (g/kg) 0.1 0.5 28.7

Daily emission reduction (kg) 6.37 31.83 1827.07


3) Noise Emission reduction

Aircraft engines usually take 4-5 seconds to accelerate from idle to maximum powercondition. The overall noise emission reduction at ground level is expected to be

𝑁𝑜𝑖𝑠𝑒 𝑟𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 =42 − 5 𝑠

42 𝑠∙ 100 = 𝟖𝟖. 𝟏 %

4) Engine size reduction

In the hypothesis of an EML system installation on a large number of airports, the enginerated thrust could be updated to that required during climbing or during emergencyprocedure (approximately 85% of the thrust required at take-off).

This would lead to reduced aircraft drag and weight

EML System Requirements

Requirements F-35C A320-200 Comments

Take-off speed [m/s] 78 70Data taken from references

Aircraft mass [kg] 37000 73500

Acceleration [G] 3.3 0.6F-35C launcher length is set by the dimensions of the aircraft

carrier and the launch acceleration is function of it. The

launcher acceleration for civil application is a requirement and

its length is later determined.Runway length [m] 94 535

Peak thrust [MN] 1.198 0.548 (0.455)Peak Thrust and Launch Energy of military launcher are

calculated considering only aircraft inertia, while those for the

civil application consider the contributions of aerodynamic

drag and ground friction. Inertia contribution is reported

between brackets.Launch energy [MJ] 113 210 (182)

Comparison of launcher requirements for F-35C and for an A320-200 .

Motor Technologies

Superconducting Permanent Magnet Induction

Complex design, costly and significant additional equipment

Linear Permanent Magnet has higher efficiency and

simpler and cheaper. The mover is more robust and lighter.

Expensive, efficiency savingsnot significant in this application

Lacks robustness, may incur magnets demagnetization

Lower efficiency, but this is a system with a low duty cycle

Superconducting linear motor

design

Permanent magnet linear motor performance

Permanent magnet and

induction motors

IntroductionEML?

• Electric Ground Aircraft Launch Systems

• Reduce engine requirements

• Extend maximum flight distances

• Save aviation fuel

• Increase payload

• A different way of thinking…

Landing

• More Electric Aircraft: – Still challenges to address– Flying aircraft a good way to test technology

• All Electric Aircraft – Technology requirements are demanding and

not possible today– Hybrid will be followed by true electric if we can

address all issues

• Electromagnetically assisted aircraft take-off– An out-of-the-box approach– Advantages are many– Infrastructure requirements are daunting!

Thank you!

professor pat wheeler power electronics, machines...

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