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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 andSix-step Drive Flywheel Energy Storage
System
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Flywheel 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 Stator
BearingsContainment
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Flywheels
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 Stator
BearingsContainment
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Homopolar Inductor Motors (HIM)
Side view
Top view
Bottom view
Cross-sections
Rotor for HIM
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Armature Winding Construction
Bladder
FR4Arm. WindingsFR4
Stator InnerBore
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Six-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 Drive
Charging(motoring)
Discharging(generating)
25,000 rpm, 1kW operating point
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Efficiency Tests
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Efficiency Measurements
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MEMS 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 SeneskySeth Sanders, Al Pisano
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Design 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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Construction
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 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 Solar-Thermal-Electric Power Generation
A. Der Minassians, K. H. Aschenbach,
S. R. Sanders
Power Electronics Research GroupUniversity of California, Berkeley
Introduction 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 Plan Solar-Thermal Collection Low-concentration non-imaging collector Low maintenance Low cost: sheet metal, glass cover, plumbing Proven technology Low 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 Diagram
Stirling EngineInsulated Pipe
Collectors
Pump
Heater
Cooler
System Efficiency
Collector (linearized)Engine (2/3 Carnot eff.)
System (overall)
Collector (nonlinear)
Comparative Cost Analysis
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 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
[$/W]
Thermo Dynamics G Series 74 5.247 79 3.9 194 6.27
Arcon HT 79 3.796 101 5.8 142 3.07
AOSOL CPC 1.5X 75 4.280 90 4.7 158 4.16
SOLEL CPC 2000 1.2X 91 4.080 106 6.9 193 3.49
Flate Plate Collectors
CPC-based Collectors
Cost Analysis: CollectorCost breakdown of commercial collector for hot water
Collector Material Mass [kg/m2] Specific Cost [$/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 $0.71/W;High-volume manuf. cost?
Based on a complete system efficiency of 6.9%...
Stirling Engine: Basics
Closed gas circuit Working fluid: air, hydrogen, helium Compress – Displace – Expand – Displace
Skewed phase expansion and compression spaces needed
Heater / Cooler: wire screens Regenerator: woven wire screens
Stirling Engine: Losses Heater / CoolerFluid flow frictionIneffectiveness (temperature drop)
RegeneratorFluid flow frictionIneffectiveness (extra thermal load)Static heat loss (extra thermal load)
Use “free” diaphragms as pistons = No surface friction, No leakage, No mechanical coupling!
CarnotEngine
Rejected heat atcooler
(294.6 W @ 300 K)246.3 W
5 K temp. drop332.7 W
8 K temp. drop
Injected heat atheater
(366.9 W @ 420 K)
86.4 WCoole
r fluid
flow lo
ss (0.
9 W)
Half regenerator
fluid flow loss
(5.7 W)
Heater fluid
flow loss (1.8 W)Half regenerator
fluid flow loss (5.7 W)
Leakage throughregenerator housing
(13.9 W)
Leakage due toregenerator ineffectiveness
(27.8 W)
Output power(72.3 W)
Eff.=19.7%
Stirling Engine: Power Balance
Expansion space (Hot)Heater (Hot)RegeneratorCooler (Cold)Compression space (Cold)Diaphragm pistonRigid LinkageCantilever beam (spring)Diaphragm
Single Stirling engine in three-phase system
Stirling Engine: Multiple-Phase
Stirling Engine: Simulation
Stirling Engine: Simulation
Cost Analysis: Stirling EngineCost for a representative 200W Stirling engine
Engine Material Mass [kg] Specific Cost [$/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/W
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Prototype 3-Phase Stirling Machine
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Heater/Cooler and Regenerator
Conclusion
Low-cost distributed solar-thermal-electricity possible with standard solar hot water collectors and low temperature Stirling heat engine
Prototype experiments in progress
