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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!