A Homopolar Inductor Motor/Generator and Six-step Drive Flywheel Energy Storage System Perry Tsao, Matt Senesky, Seth Sanders University of California, Berkeley Perry s thesis defense presented www-power.eecs.berkeley.edu May 15, 2003 1
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 Containment Motor Stator Bearings 2
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 Containment Motor Stator Bearings 3
Homopolar Inductor Motors (HIM) Cross-sections Top view Side view Bottom view Rotor for HIM 4
Armature Winding Construction Bladder FR4 Arm. Windings FR4 Stator Inner Bore 5
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 6
Six-Step Drive Charging (motoring) Discharging (generating) 25,000 rpm, 1kW operating point 7
Efficiency Tests 8
Efficiency Measurements 9
MEMS REPS Project Matthew Senesky Seth Sanders, Al Pisano 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 10
Design Electroplated NiFe poles allow engine rotor to be used as generator rotor Axial-flux configuration Claw pole stator made from powdered iron Side Plate Permanent Magnet Side Plate Top Plate Core Coil Toroid Pole Faces Rotor Bottom Plate 1 2 3 4 5 6 7 8 9 millimeters 11
Construction 250 m 2.4 mm Steel test rotor 2.4 mm Dr. A. Knobloch, 2003 Microfabricated Si rotor Stator pole faces cut with EDM 1 cm 2.2 mm Stator core, coil (with bobbin) and toroid. Partial stator assembly 12
Preliminary Results Open circuit voltage of 150 V/turn in 112 coil at 500 Hz Expect to improve this by factor of 4-5 13
Low-Cost Distributed Solar-Thermal-Electric Power Generation A. Der Minassians, K. H. Aschenbach, S. R. Sanders Power Electronics Research Group University of California, Berkeley
Introduction Photovoltaic (PV) technology Efficiency: up to about 15% Cost: about $5/W peak 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 Insulated Pipe Cooler Heater Stirling Engine Pump Collectors
System Efficiency Collector (nonlinear) Collector (linearized) Engine (2/3 Carnot eff.) System (overall)
Comparative Cost Analysis Cost goal set by PV is under $5/W!!! For solar-thermal-electric system Peak insolation = 800 W/m 2 System optimal efficiency = 10% ignore engine cost Cost of collector must be less than $400/m 2
Market Available Collectors Collector Model Flate Plate Collectors U [W/m 2 K] T m(opt) [ o C] sys(opt) [%] CPA STC [$/m 2 ] 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 CPC-based Collectors 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 Assumes engine achieves 2/3 Carnot, ambient is 27 º C, and engine cost is negligible Even at retail (500 m 2 qty) prices and low system efficiency, some collectors achieve costs less than $5/W
Cost Analysis: Collector Cost breakdown of commercial collector for hot water Collector Material Mass [kg/m 2 ] Specific Cost [$/kg] Cost [$/m 2 ] Low-Iron Cover Glazing 7.8 1.87 14.60 Sheet Aluminum 2.75 6.00 16.50 Sheet Copper 1.26 6.35 8.00 Fiberglass Insulation 1.2 0.83 1.00 Total 13 N/A 40.10 Based on a complete system efficiency of 6.9%... Material cost is $0.71/W; High-volume manuf. cost?
Stirling Engine: Basics Closed gas circuit Working fluid: air, hydrogen, helium Compress Displace Expand Displace Skewed phase expansion and compression spaces needed Heater / Cooler: wire screens Regenerator: woven wire screens
Stirling Engine: Losses Heater / Cooler Fluid flow friction Ineffectiveness (temperature drop) Regenerator Fluid flow friction Ineffectiveness (extra thermal load) Static heat loss (extra thermal load) Use free diaphragms as pistons = No surface friction, No leakage, No mechanical coupling!
Stirling Engine: Power Balance Leakage due to regenerator ineffectiveness (27.8 W) Leakage through regenerator housing (13.9 W) Injected heat at heater (366.9 W @ 420 K) 332.7 W 8 K temp. drop Carnot Engine 246.3 W 5 K temp. drop Rejected heat at cooler (294.6 W @ 300 K) Cooler fluid flow loss (0.9 W) 86.4 W Half regenerator fluid flow loss (5.7 W) Heater fluid flow loss (1.8 W) Half regenerator fluid flow loss (5.7 W) Output power (72.3 W) Eff.=19.7%
Stirling Engine: Multiple-Phase Expansion space (Hot) Heater (Hot) Regenerator Cooler (Cold) Compression space (Cold) Diaphragm piston Rigid Linkage Cantilever beam (spring) Diaphragm Single Stirling engine in three-phase system
Stirling Engine: Simulation
Stirling Engine: Simulation
Cost Analysis: Stirling Engine Cost for a representative 200W Stirling engine Engine Material Mass [kg] Specific Cost [$/kg] Cost [$] Cast Aluminum 4.8 5.50 26.40 Copper 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
Prototype 3-Phase Stirling Machine 29
Heater/Cooler and Regenerator 30
Conclusion Low-cost distributed solar-thermal-electricity possible with standard solar hot water collectors and low temperature Stirling heat engine Prototype experiments in progress