A Homopolar Inductor Motor/Generator and Six-step Drive Flywheel Energy Storage System

1. 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

2. Flywheel Energy Storage System Motor Stator Flywheel Rotor Bearings Containment • Prototype design goals • 30 kW (40 hp) • 15 s discharge • 500 kJ (140 W-hr) • 1 kW/kg (30 kg, 66 lbs.) Integrated Flywheel

3. Flywheels Motor Stator Flywheel Rotor Bearings Containment • Integrated flywheel • Single-piece solid steel rotor • Combines energy storage and electromagnetic rotor • Motor housing provides • Vacuum containment • Burst containment Integrated Flywheel

4. Homopolar Inductor Motors (HIM) Rotor for HIM

5. Armature Winding Construction Bladder FR4 Arm. Windings FR4 Stator Inner Bore

6. 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

7. Six-Step Drive Charging (motoring) Discharging (generating) 25,000 rpm, 1kW operating point

8. Efficiency Tests

9. Efficiency Measurements

10. 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 Matthew SeneskySeth Sanders, Al Pisano Concept Unit Engine/ Generator Package Generator

11. Design Top Plate Side Plate Core Coil Permanent Magnet Toroid Pole Faces Side Plate Rotor Bottom Plate 1 2 3 4 5 6 7 8 9 millimeters • Electroplated NiFe poles allow engine rotor to be used as generator rotor • Axial-flux configuration • Claw pole stator made from powdered iron

12. Construction 2.4 mm 2.4 mm Dr. A. Knobloch, 2003 250 m Steel test rotor Microfabricated Si rotor Stator pole faces cut with EDM 1 cm 2.2 mm Partial stator assembly Stator core, coil (with bobbin) and toroid.

13. Preliminary Results • Open circuit voltage of 150V/turn in 112 coil at 500 Hz • Expect to improve this by factor of 4-5

14. 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

15. 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

16. 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)

17. Representative Diagram

18. System Efficiency Collector (nonlinear) Collector (linearized) Engine (2/3 Carnot eff.) System (overall)

19. Comparative Cost Analysis Cost goal set by PV is under $5/W !!! For solar-thermal-electric system… Peak insolation = 800 W/m2 System optimal efficiency = 10% ignore engine cost Cost of collector must be less than $400/m2

20. 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

21. Cost Analysis: Collector Cost breakdown of commercial collector for hot water Based on a complete system efficiency of 6.9%... Material cost is $0.71/W; High-volume manuf. cost?

22. 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

23. 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!

24. Stirling Engine: Power Balance

25. Stirling Engine: Multiple-Phase

26. Stirling Engine: Simulation

27. Stirling Engine: Simulation

28. Cost Analysis: Stirling Engine Cost for a representative 200W Stirling engine Engine cost is $0.31/W System cost: about $1/W

29. Prototype 3-Phase Stirling Machine

30. Heater/Cooler and Regenerator

31. Conclusion • Low-cost distributed solar-thermal-electricity possible with standard solar hot water collectors and low temperature Stirling heat engine • Prototype experiments in progress