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Perry Tsao, Matt Senesky, Seth SandersUniversity of California, Berkeley Perry’s thesis defense presented www-power.eecs.berkeley.edu May 15, 2003
A Homopolar Inductor Motor/Generator andA Homopolar Inductor Motor/Generator and Six-step Drive Flywheel Energy Storage Six-step Drive Flywheel Energy Storage
System System
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Flywheel Energy Storage SystemFlywheel Energy Storage System
Prototype design goals– 30 kW (40 hp)– 15 s discharge– 500 kJ (140 W-hr)– 1 kW/kg (30 kg, 66 lbs.)
Integrated
Flywheel
Flywheel Rotor
Motor StatorBearings
Containment
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FlywheelsFlywheels
Integrated flywheel– Single-piece solid steel rotor– Combines energy storage and
electromagnetic rotor– Motor housing provides
Vacuum containment Burst containment
Integrated
Flywheel
Flywheel Rotor
Motor StatorBearings
Containment
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Homopolar Inductor Motors (HIM)Homopolar Inductor Motors (HIM)
S id e v iew
To p v iew
B o tto m v iew
C ro ss-sec tio n s
Rotor for HIM
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Armature Winding ConstructionArmature Winding Construction
Bladder
FR4
Arm. Windings FR4
Stator Inner Bore
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Six-Step DriveSix-Step Drive
Six-step– PWM impractical at max speed (6.7 kHz)– Lower switching losses– Field winding compensates for fixed voltage
Potential problems– Harmonic currents– Harmonic rotor core losses
Controlled by adjusting armature inductance
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Six-Step DriveSix-Step Drive
Charging (motoring)
Discharging (generating)
25,000 rpm, 1kW operating point
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Efficiency TestsEfficiency Tests
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Efficiency MeasurementsEfficiency Measurements
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MEMS REPS ProjectMEMS REPS Project
MEMS Rotary Engine Power System
Concept– Replace conventional batteries
with rotary engine and generator plus fuel
Specifications– Goal is to provide 10-100mW– Need ~10% system efficiency
with octane fuel to beat batteries
Engine/ Generator Package
Concept Unit
Generator
Matthew SeneskyMatthew SeneskySeth Sanders, Al PisanoSeth Sanders, Al Pisano
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DesignDesign Electroplated
NiFe poles allow engine rotor to be used as generator rotor
Axial-flux configuration
Claw pole stator made from powdered iron
Toroid
Core
Pole Faces
Rotor
Coil
Permanent Magnet
1 2 3 4 5 6 7 8 9millimeters
Bottom Plate
Top Plate
Side Plate
Side Plate
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ConstructionConstruction
Stator pole faces cut with EDM
Stator core, coil (with bobbin) and toroid.
250 m
2.2 mmPartial stator assembly
Steel test rotor Microfabricated Si rotor
1 cm
2.4 mm2.4 mmDr. A. Knobloch, 2003
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Preliminary ResultsPreliminary Results Open circuit voltage of 150V/turn in 112 coil at 500 Hz Expect to improve this by factor of 4-5
Low-Cost Distributed Low-Cost Distributed Solar-Thermal-Electric Solar-Thermal-Electric Power GenerationPower Generation
A. Der Minassians, K. H. Aschenbach,
S. R. Sanders
Power Electronics Research GroupUniversity of California, Berkeley
IntroductionIntroduction Photovoltaic (PV) technology
– Efficiency: up to about 15%– Cost: about $5/Wpeak
– Materials cost: about $5/W (with a low profit margin)– Cost reduction limited by cost of silicon area– No alternative for small-scale off-grid applications
Technology similar to PV but at lower cost would see widespread acceptance
View is that unit cost ($/W) is paramount Many untapped siting opportunities
Possible PlanPossible Plan Solar-Thermal Collection
Low-concentration non-imaging collector Low maintenance Low cost: sheet metal, glass cover, plumbing Proven technology Low temperatureLow temperature
Thermal-Electric Conversion Stirling heat engine: Theoretically achieves Carnot
efficiency, can achieve large fraction of Carnot eff. Low cost: Bulk metal and plastic Linear electric generator (high efficiency & low cost)
Representative DiagramRepresentative Diagram
Stirling EngineInsulated Pipe
Collectors
Pump
Heater
Cooler
System EfficiencySystem Efficiency
Collector (linearized)Engine (2/3 Carnot eff.)
System (overall)
Collector (nonlinear)
Comparative Cost AnalysisComparative Cost Analysis
Cost goal set by PV is under $5/W !!!Cost goal set by PV is under $5/W !!!
Peak insolation = 800 W/m2
System optimal efficiency = 10%
ignore engine cost
Cost of collector must be less than $400/m2
For solar-thermal-electric system…
Market Available CollectorsMarket Available Collectors
Assumes engine achieves 2/3 Carnot, ambient is 27 ºC, and engine cost is negligible
Even at retail (500 m2 qty) prices and low system efficiency, some collectors achieve costs less than $5/W
Collector Model
U
[W/m2K]T m(opt)
[oC]
sys(opt)
[%]CPA STC
[$/m2]CPW sys
[$/W]
Thermo Dynamics G Series 74 5.247 79 3.9 194 6.27
Arcon HT 79 3.796 101 5.8 142 3.07
AOSOL CPC 1.5X 75 4.280 90 4.7 158 4.16
SOLEL CPC 2000 1.2X 91 4.080 106 6.9 193 3.49
Flate Plate Collectors
CPC-based Collectors
Cost Analysis: CollectorCost Analysis: CollectorCost breakdown of commercial collector for hot water
Collector Material Mass [kg/m2] Specific Cost [$/kg] Cost [$/m2]Low-Iron Cover Glazing 7.8 1.87 14.60
Sheet Aluminum 2.75 6.00 16.50Sheet Copper 1.26 6.35 8.00
Fiberglass Insulation 1.2 0.83 1.00Total 13 N/A 40.10
Material cost is $0.71/W;High-volume manuf. cost?
Based on a complete system efficiency of 6.9%...
Stirling Engine: BasicsStirling Engine: Basics
Closed gas circuitWorking fluid: air, hydrogen, heliumCompress – Displace – Expand – Displace
Skewed phase expansion and compression spaces neededHeater / Cooler: wire screensRegenerator: woven wire screens
Stirling Engine: LossesStirling Engine: LossesHeater / Cooler
Fluid flow frictionIneffectiveness (temperature drop)
RegeneratorFluid flow frictionIneffectiveness (extra thermal load)Static heat loss (extra thermal load)
Use “free” diaphragms as pistons = No surface friction, No leakage, No mechanical coupling!
CarnotEngine
Rejected heat atcooler
(294.6 W @ 300 K)246.3 W
5 K temp. drop332.7 W
8 K temp. drop
Injected heat atheater
(366.9 W @ 420 K)
86.4 W
Leakage throughregenerator housing
(13.9 W)
Leakage due toregenerator ineffectiveness
(27.8 W)
Output power(72.3 W)
Eff.=19.7%
Stirling Engine: Power BalanceStirling Engine: Power Balance
E xpansion space (H ot)H eater (H ot)R egeneratorC ooler (C old)C om pression space (C old)D iaphragm pis tonR igid L inkageC antilever beam (spring)D iaphragm
Single S tirling engine in three-phase system
Stirling Engine: Multiple-PhaseStirling Engine: Multiple-Phase
Stirling EngineStirling Engine:: Simulation Simulation
Stirling EngineStirling Engine:: Simulation Simulation
Cost Analysis: Stirling EngineCost Analysis: Stirling EngineCost for a representative 200W Stirling engine
Engine Material Mass [kg] Specific Cost [$/kg] Cost [$]Cast Aluminum 4.8 5.50 26.40Copper Wire 3.5 10.00 35.00
Total 8.3 N/A 61.40
Engine cost is $0.31/W
System cost: about $1/WSystem cost: about $1/W
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Prototype 3-Phase Stirling MachinePrototype 3-Phase Stirling Machine
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Heater/Cooler and RegeneratorHeater/Cooler and Regenerator
ConclusionConclusion Low-cost distributed solar-thermal-
electricity possible with standard solar hot water collectors and low temperature Stirling heat engine
Prototype experiments in progress
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