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PM Generator Characteristics for Oscillatory Engine Based Portable Power System

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. Sponsored by Powerix Technologies under contract to DARPA DSO. Slide 1 of 26. Overview. Introduction Research Objectives

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PM Generator Characteristics for Oscillatory Engine Based Portable Power System

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  1. 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 Sponsored by Powerix Technologies under contract to DARPA DSO Slide 1 of 26

  2. Overview • Introduction • Research Objectives • Portable Power System • Oscillatory Motion • Generator Model & Waveform Characteristics • Initial Power Estimate • Influence of Generator Parameters • Experimental Results • Conclusion Slide 2 of 26

  3. 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 Slide 3 of 26

  4. 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 Slide 4 of 26

  5. 1 2 4 3 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 Slide 5 of 26

  6. Initial Swing-engine Testing • In-chamber static combustion testing matched earlier calorimeter testing with cold-start quench losses <40% • Early testing with the swing-engine revealed significant seal failures resulting in chamber-to-chamber leakage Slide 6 of 26

  7. MICSE Summary Slide 7 of 26

  8. Oscillatory Motion Slide 8 of 26

  9. A8+ C7- B8+ A1+ C8- A1- B1+ A2- C8+ C1+ B1- SOUTH B2- A2+ NORTH A3+ 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 Slide 9 of 26

  10. FEM No Load Results Slide 10 of 26

  11. 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 FFT (Ea) FFT (Eb) FFT (Ec) Slide 11 of 26

  12. Loss Breakdown: Case 3 RLoad = 24.5 Ω Friction & Windage 5.18 W Copper 37.00 W Stray Load 5.18 W Stator Core 16.25 W Armature Reaction 36.26 W 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 Slide 12 of 26

  13. Generator Parameters • Magnet pitch to coil pitch • full pitch to maximize induced back EMF Slide 13 of 26

  14. 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 Slide 14 of 26

  15. Generator Parameters • Number of magnet poles • more poles produce “conventional shape at peak speed 60 slot 20 pole rotational 60 slot 20 pole oscillation Slide 15 of 26

  16. Generator Parameters • Number of magnet poles • more poles produce “conventional shape at peak speed 18 slot 6 pole oscillation 30 slot 10 pole oscillation Slide 16 of 26

  17. Generator Parameters • Magnet thickness • large compared to airgap, yet try not waste material 1mm magnet thickness 2mm magnet thickness Slide 17 of 26

  18. Generator Parameters • Magnet thickness • large compared to airgap, yet try not waste material 3mm magnet thickness 3.5mm magnet thickness Slide 18 of 26

  19. 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 Slide 19 of 26

  20. Swing-optimized PMAC Prototype • 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 Slide 20 of 26

  21. A B C Front Rotation Oscillation 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 Slide 21 of 26

  22. MTD-1Gx Model Validation Simulated Back EMF at 8.4Hz Measured Back EMF at 8.4Hz (MTD-1G1) Experimental Results 1 • 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 Slide 22 of 26

  23. Load Oscillatory Performance Oscillatory Power Testing • Actual power measured at frequencies up to 16Hz • Estimated power at 55Hz is >700W based on FEA simulation Slide 23 of 26

  24. Experimental Results 2 MTD-1Gx Model Validation • No load back EMF • Generator coupled directly to MICSE and operating at approximately 16Hz oscillation frequency Simulated Back EMF at 16Hz Measured Back EMF at 16Hz (MTD-1G1) Slide 24 of 26

  25. 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 Slide 25 of 26

  26. Questions Slide 26 of 26

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