High-Specific-Power Electric Machines for Electrified

Transportation Applications –Technology OptionsXiaolong Zhang

Aug 29, 2016

Outline

Background

High-Specific-Power (HSP) Machine Survey

HSP Machine Topologies

HSP Outer-Rotor PMSM Architecture

Background – Aircraft Electrified Propulsion

Two configurations for electrified propulsion: hybrid electric & turbo electric.

Benefits: reduce noise, emission and energy consumption.

Technology

Benefits

Technology Generations (Technology

Readiness Level = 4-6)

N+1 (2015) N+2 (2020) N+3 (2025)

Noise -32 dB -42 dB -71 dB

LTO NOx

Emissions-60% -75% -80%

Cruise NOx

Emissions-55% -70% -80%

Fuel/Energy

Consumption-33% -50% -60%

NASA Subsonic Transport System Level Metrics1

Note: Projected benefits vary by vehicle size and mission. N+1 and N+3 values

are referenced to a 737-800 with CFM56-7B engines, N+2 values are

referenced to a 777-200 with GE90 engines.

N3-X Hybrid Wing Body (HWB) Aircraft Concept

with Distributed Turboelectric Propulsion System2

[1] Sarlioglu, Bulent, and Casey T. Morris. "More electric aircraft: Review, challenges, and opportunities for commercial transport aircraft." Transportation Electrification,

IEEE Transactions on 1.1 (2015): 54-64.

[2] Brown, Gerald V. "Efficient Flight-Weight Electric Systems." (2012).

HSP Machine Survey

Fifty-five HSP machines with specific power > 1kW/kg.

Mechanical speed: a few thousand r/min to 200 thousand r/min

Rated power: a few kilo-Watts to the Mega-Watt level

Applications: military and civil aircraft, small unmanned electric aircraft,

electrical and hybrid-electrical vehicles, spindle drives, and centrifugal

compressors.

HSP Machine Survey

Machine Types:

Permanent-magnet synchronous machines (PMSM)

– Radial Flux PM (RFPM)

– Axial Flux PM (AFPM)

Induction machines (IM)

Switched reluctance machines (SRM)

Wound-field synchronous machines (WFSM)

HSP Machine Survey

Specific Power versus Rated Power (kW Rating range) Specific Power versus Rated Power (MW Rating range)

The specific power tends to reduce as power rating increases.

HSP Machine Survey

Specific Power versus Rotational Speed Specific Power versus Rotational Speed (only PMSM)

The specific power tends to increase as the maximum machine speed

increases.

HSP Machine Survey

Specific Power versus Rotor Tip Speed Specific Power versus Electrical Frequency

HSP machines have a relatively high tip speed (>50m/s), compared to

general-purpose motors that have lower specific power.

The electrical frequency of HSP machines ranges from hundreds of Hertz to a

few kilo-Hertz, significantly higher than the traditional 50/60 Hz motors.

HSP Machine Survey

Specific Power versus Shear StressSpecific Power versus Shear Stress times

Electrical Frequency

High-specific-torque machines tend to have high shear stress.

The product of shear stress and electrical frequency is a good indicator on how

much iron material is used.

HSP Machine Design Considerations

Magnetic loading Bg1

– Steel flux saturation

– Iron losses

Electric loading Ks, Current

density J

– Copper DC and AC losses

– Cooling capability

Rotor tip speed v

– Centrifugal stresses

– Friction and windage losses

– Rotor dynamics stability

Electrical frequency f

– Power electronics drive limits

– Iron losses, Copper AC losses

High SpeedAggressive

CoolingAdvanced EM &

Structural Material

HSP Machine Cooling Techniques

An increase of Bg1, Ks, J, v, or f, all lead to higher loss density in some

corresponding machine parts. This necessitates aggressive cooling

techniques to dissipate the heat.

Active Cooling Techniques Used in HSP Machines

Cooling Type Description

Forced Air forced air through radial/axial ducts

Indirect Water water cooling on stator frame/yoke

Indirect Oil oil cooling on stator frame/yoke

Liquid Bathed whole machine bathed in refrigerant/oil

Direct Liquid direct water/oil cooling on conductors

Oil Spray oil spray for cooling rotor/stator end

Hollow Shaft cooling oil flowing through hollow shaft

HSP Machine Topologies

Permanent Magnet Synchronous Machines (PMSM)

High airgap flux density, high power factor, and low copper loss

High-pole-count, short-pole-pitch designs

Airgap winding for reducing iron losses

Halbach array for increasing magnetic loading

HSP Machine Topologies

Commercial HSP PMSM Products

TG7140 by ThinGap

• Electric airplane

• 3.85 kW

• 8,100 r/min

• 3.3 kW/kg

JM1 by Joby Motors

• Electric Airplane

• 20.1 kW

• 9,000 r/min

• 3.8 kW/kg

HVH410 by REMY Motors

• EV

• 250 kW

• 6,000 r/min

• 2.0 kW/kg

Siemens PSM

• EV

• 141 kW

• 10,000 r/min

• 1.2 kW/kg

http://www.thingap.com/standard-products/

http://www.jobymotors.com/public/views/pages/products.php

http://www.remyinc.com/docs/hybrid/REM-12_HVH410_DataSht.pdf

http://www.siemens.com/press/pool/de/events/2013/industry/2013-03-hannovermesse-pk/expert-talk-inside-e-car-e.pdf

HSP Machine Topologies

HSP PMSM Topologies – Airgap Winding

(a) stator with conventional teethed iron core (b) stator with airgap winding and no teeth

HSP Machine Topologies

HSP PMSM Topologies – Airgap Winding

HSP PMSM for aerospace

(University of Central Florida):

• Airgap winding

• Litz wire

• Oval-shape magnet

• Water-cooled

• 8 kW/kg

Zheng, Liping, Thomas X. Wu, Dipjyoti Acharya, Kalpathy B. Sundaram, Jay Vaidya, Limei Zhao, Lei Zhou et al. "Design of a superhigh-speed cryogenic permanent

magnet synchronous motor." Magnetics, IEEE Transactions on 41, no. 10 (2005): 3823-3825.

HSP Machine Topologies

HSP PMSM Topologies – Halbach Array

Halbach Magnet Array Structure for Flux Strengthening

Fault-tolerant HSP PMSM for aerospace

(University of Newcastle):

• Halbach array magnet

• Litz wire

• Immersed in cooling fuel

• 5 kW/kg

Mecrow, Barrie C., Alan G. Jack, David J. Atkinson, Simon R. Green, Glynn J. Atkinson, Andrew King, and Brian Green. "Design and testing of a four-phase fault-tolerant

permanent-magnet machine for an engine fuel pump." Energy conversion, ieee transactions on 19, no. 4 (2004): 671-678.

HSP Machine Topologies

High Speed HSP PMSM Topologies

A High Speed PMSM for spindle applications:

(Darmstadt University of Technology):

• 40 kW, 40,000 r/min

• Magnetic bearings for rotor suspension

• Carbon fiber ring for magnet retaining

• 3.3 kW/kg

A High Speed IPM Machine for air blower

(Samsung Electronics):

• 8 kW, 40,000 r/min

• Litz wire

• Optimized rotor shape

• 3.2 kW/kg

HSP Machine Topologies

HSP Axial Flux PMSM

Dual-rotor single-stator AFPM for aircraft by

Launchpoint:

• 5.2 kW, 8,400 r/min, 95% efficiency

• Halbach array, high magnetic field (>1T)

• Composite stator/rotor ( No iron )

• Forced air cooling

• 7 kW/kg

HSP Machine Topologies

Induction Machines (IM)

Robust rotor structure for high speed: cage rotor or solid rotor

Higher rotor losses than PMSM

15,000 r/min, 8 MW Cage IM for flywheel, 2 kW/kg

Solid Rotor IM for Centrifugal Compressor (J. F. Gieras et. al.)

• 60,000 r/min, 300 kW

• Forced air and water circulation

• Rotor tip speed 400 m/s

• 3.8 kW/kg

HSP Machine Topologies

HSP Switched Reluctance Machines for Aerospace Applications

Switched Reluctance Machines (SRM)

Robust rotor for high speed application

Good fault tolerance

Poor power factor

Machine

TypeApplications

Speed,

kr/min

Power,

kWCooling

SP,

kW/kg

6/4 SRM Starter/generator 48 32 direct and indirect oil ~3

SRM Fuel pump 25 90 oil 9.0

8/6 SRM Fuel/lube pump 12.5 3.675 6.4 liters per minute, oil 2.2

6/4 SRM Starter/generator 47 30 11.7 L/min oil 3.9

12/8 SRM Starter/generator 22 250oil, direct conductor

cooling, back iron,

hollow shaft4.5

18/12 SRM Starter/generator 18 250 - ~3.3

8/6 SRM Starter/generator 28 25 spray oil ~1.1

HSP Machine Topologies

Wound-Field Synchronous Machines (WFSM)

Capable of high power, high electromagnetic loading

Need accessory parts such as brushes and slip rings, exciter machines, etc.

An oil-cooled WFSM for airborne weapon

by Electrodynamics Associates, Inc. :

• 15,000 r/min, 2.5 MW

• 1,500 Hz

• Oil spray for rotor windings, 30 A/mm2

• Duty cycle: 6 min on and 12 min off

• Peak specific power: 14 kW/kg

HSP Outer-Rotor PMSM Architecture

High Speed, High Frequency, Air-cooled, Outer-Rotor PMSM

High pole count for yoke reduction

Airgap winding and Halbach array to reduce iron usage

High strength, lightweight carbon fiber ring to retain NdFeB magnets

Litz wire to reduce high frequency AC losses

Parameter Dimensions

Rated Power 1 MW

Rotational Speed 14,000 r/min

Outer Diameter 337.2 mm

Active Length 223.5 mm

Poles Count 20

Frequency 2,500 Hz

Airgap Surface Velocity 217 m/s

Current Density 8 A/mm2

Airgap Flux Density 0.6 T

Total Weight 71 kg

Specific Power 14 kW/kg

Summary

Survey results of actual HSP machines are reported, including those with

multiple machine topologies and for various application areas.

The range and distribution of key physical parameters in these machines

together with proposed design considerations for specific power improvement

are discussed.

Technology options such as different machine topologies, winding structures,

magnet placement and cooling schemes are discussed.

An HSP permanent magnet synchronous machine architecture is proposed.

Acknowledgment

This research is supported by the Grainger Center for Electric Machinery and Electromechanics

and NASA “High Speed, High Frequency Air-core Machine and Drive” project (Grant Number

NNX14AL79A).

Thank you!