PM Generator Characteristics for Oscillatory Engine Based
Portable Power System
A. Zachas, L. Wu, R.G. Harley & J.R. Mayor
Grainger CEME Seminar 5 March 2007
Slide 1 of 26
Sponsored by Powerix Technologies under contract to DARPA DSO
Overview
Introduction Research Objectives Portable Power System Oscillatory Motion Generator Model & Waveform Characteristics Initial Power Estimate Influence of Generator Parameters Experimental Results Conclusion
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Introduction
Need for lightweight portable power system in remote locations
Meso‐scaled internal combustion swing engine (MISCE) developed to operate from several fuel sources
Oscillatory motion as opposed to rotational motion
Characteristics of a surface mount PM generator determined for this motion
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Research Objectives
Understand the oscillatory motion Model oscillatory motion in FEA package Determine characteristic waveforms for oscillatory motion
Evaluate effect of generator parameters on the characteristic waveform
Use waveforms to estimate output power from generator
Experimental validation of simulation results
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Portable Power System
MICSE Power Generation System technology is a synergy of two novel energy conversion devices, micro‐swing engines and swing‐optimized PMAC swing‐generators
Micro Internal Combustion Swing Engine (MICSE) converts high specific energy liquid fuels to oscillatory mechanical power (chemical‐mechanical)
MICSE systems are internal combustion engines with four chambers separated by an oscillating swing arm
Mechanical‐to‐electrical power conversion via a direct‐coupled swing‐optimized permanent magnet AC induction generator
MPG systems are adaptable to a wide range of practical fuels, including butane/propane and JP‐8
MPGs can be based on two‐stroke and four‐stroke MICSE designs and enables application‐specific tailoring of the power system
1 2
34
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Initial Swing-engine Testing In‐chamber static combustion testing
matched earlier calorimeter testing with cold‐start quench losses
MICSE SummaryMTD-1Ex 350W MICSE SystemPower Level (W) 350
Thermal Efficiency 20%
Quenching Loss 20%
Trapping Efficiency 20%
Burned Mass Fraction 80%
Chemical to Mechanical Efficiency 2.2%
Size (LxWxH) 3.3“ x 4“ x 6ʺ
Total mass (with active valve‐train) (g) 1213
Valve‐train power draw (W) 20
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Oscillatory Motion
Harmonic Hz %1 60 89.73 180 7.55 300 1.57 420 0.7
( ) cos(2 )ˆm t ft
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Generator Model
Modeled with 2D finite element package and used a transient solver to apply motion to the rotor
No load back emf and flux linkage determined by the software
A1+A1-
A2-
A2+A3+
A8+
B1+
B8+
B2-B1-
C7-
C8-
C1+C8+
SOUTH
NORTH
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FEM No Load Results
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Initial Power Estimates
Performed FFT analysis on no load back EMF to find dominant harmonics
Estimated winding resistance and winding inductance using machine geometry
Connected no load back EMF as the source to a standard 6‐diode bridge rectifier and a resistive load
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V-
V+
Vb4
Vc4
Va4D1 D5D3
D6D2
Rload
315
Cd
300m
IC = 393
D4
La 0.013581367
Lb 0.013581367
Lc 0.013581367
Vb1
Va3
Vc1 Rc
4.913599306
Ra
4.913599306
Rb
4.913599306
Vb2
Vc2
Vb3
Vc3
C3 5.0955u
R3 1e9
C2 6.1655u
R4 1e9
C1 5.0955u
R5 1e9
Va2 Va5Va1
Vb5
Vc5
Va6 Va7
Vb6 Vb7
Vc6 Vc7
FFT (Ea)FFT (Eb)FFT (Ec)
Initial Power Estimates Maximum current density of
6 x 106A/m2 % of input power used for
additional losses (friction, windage, hysteresis, armature reaction, etc)
Output power of about 417 W
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Case PLoad (W) VLoad ILoad RLoad Pin (W) Papp (W) Iarms Ibrms
Icrms
1 497.7 108.15 4.602 23.5 537.8 632.35 5.06 5.08 4.81
2 489.2 108.35 4.515 24.0 527.2 622.30 4.98 5.00 4.74
3 481.0 108.56 4.431 24.5 518.0 612.45 4.89 4.92 4.67
4 473.1 108.75 4.350 25.0 508.9 602.80 4.81 4.84 4.61
Stray Load 5.18 W
Friction & Windage 5.18 W
Copper 37.00 W
Stator Core
16.25 WArmature Reaction 36.26 W
Loss Breakdown: Case 3 RLoad = 24.5 Ω
Input Power 518 W
Total Losses 100 W
Average Power 418 W
Efficiency 81%
Generator Parameters
Magnet pitch to coil pitch• full pitch to maximize induced back EMF
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Generator Parameters
Tooth and stator thickness and material• maximize material utilization through FEA studies• minimize core loss effects due to increased oscillation frequency• carried out extensive material study• considering fabrication & availability, fine non‐oriented
electrical steel (Si Fe) was selected
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Material Saturation Flux DensityCore Loss at 400Hz (@ 1T)
M19 – 26 Gauge (0.47 mm) 1.7 T (17 kG) 24.48 W/kg
Cogent NO 005 (0.12 mm) 1.8 T (18 kG) 11.8 W/kg
Metglas™ 2605C0 (0.023 mm) 1.8 T (14 kG) 6.0 W/kg
Hiperco® 50 2.2 T (22 kG) 17.64 W/kg
Generator Parameters
Number of magnet poles• more poles produce “conventional shape at peak speed
60 slot 20 pole rotational
60 slot 20 pole oscillation
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Generator Parameters
Number of magnet poles• more poles produce “conventional shape at peak speed
18 slot 6 pole oscillation
30 slot 10 pole oscillation
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Generator Parameters
Magnet thickness• large compared to airgap, yet try not waste material
1mm magnet thickness
2mm magnet thickness
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Generator Parameters
Magnet thickness• large compared to airgap, yet try not waste material
3mm magnet thickness
3.5mm magnet thickness
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Generator Parameters
Cogging torque• reduce by skewing of the magnets• Stagger magnets to create skew• 3 steps of 4o to give 12o skew
Rotor Starting position• found to have little or no effect if the number of poles and swing angle were large
Rotor Speed• increased through use of a 1:4 gearbox by maintaining the same swing frequency but covering a larger swing angle
Swing-optimized PMAC Prototype
MTD-1G1 MTD-1G2Stator outer diameter (mm) 62Rotor outer diameter (mm) 32.5Axial length (mm) 40Rotor Inertia (kg.m2) 2.615 x 10‐5Air Gap (mm) 0.25Number of stator slots 30Number of poles 10Winding AWG 22 bifilarNo. turns per phase 130,130,130 140,130,140Phase Resistance at 100oC (Ω) 0.681 0.61,0.58Max RMS current (A) 5
Thermo‐mechanical design optimization studies resulted in integrated cooling fins and to allow >6A/m2 current densities
Stator windings were potted with thermally conductive epoxy improve winding thermal management
Two 450W PMAC swing‐optimized generators were fabricated with different winding configurations for maximum copper fill factor
Stator ring and spider laminates
Experimental Validation 1 Four‐bar linkage built to
simulate MICSE motion –converts rotational motion to oscillatory motion
Gearing provides 4x increase in speed and amplitude compared to direct drive
A
BC
Front
Rotation
Oscillation
Experimental Results 1
MTD 1G2: Maxwell 2D Back EMF vs Time
-30
-20
-10
0
10
20
30
0 0.02 0.04 0.06 0.08 0.1 0.12
Time (sec)
Volta
ge (V
)
Phase A Maxwell Phase B MaxwellPhase C Maxwell
MTD-1G1 No-load 8.4Hz
-30
-20
-10
0
10
20
30
0.000 0.020 0.040 0.060 0.080 0.100 0.120
Time (s)
Volta
ge (V
)
Phase APhase BPhase C
MTD-1Gx Model Validation
Simulated Back EMF at 8.4Hz
Measured Back EMF at 8.4Hz (MTD-1G1)
Slight differences in model & prototype
Mismatch between simulation & test frequencies
Approximate velocity profile 2D FEA model without skew Mechanical slip and
vibration present in four‐bar linkage
Load Oscillatory Performance
Test Freq. Vrms Power
1 2.15 2.5 3.8
2 4 5.0 15.1
3 8.66 10.3 63.2
4 16 18.9 213.5
55 ~700
Oscillatory Power Testing
Actual power measured at frequencies up to 16Hz Estimated power at 55Hz is >700W based on FEA
simulation
Experimental Results 2
MTD-1Gx Model Validation
Simulated Back EMF at 16Hz
Measured Back EMF at 16Hz (MTD-1G1)
No load back EMF Generator coupled directly
to MICSE and operating at approximately 16Hz oscillation frequency
Conclusion
Ultra portable power delivery system has been introduced
Approximate velocity profile for oscillatory motion for use in FEA has been determined
Influence of generator parameters has been evaluated
Characteristic no load waveforms presented Simulations have been validated with experimental and test data
Questions
