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Human Energy Storage for Off-Grid Use

Human Energy Storage for Off-Grid Use. ECE 445 Spring 2009 Project #5 Scott Aderhold Shruti Sharma Chris Graca. Introduction. Off-grid source of electricity Exercise with benefit of harnessing otherwise wasted energy. Power for on demand or stored for later use.

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Human Energy Storage for Off-Grid Use

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  1. Human Energy Storage for Off-Grid Use ECE 445 Spring 2009 Project #5 Scott Aderhold Shruti Sharma Chris Graca

  2. Introduction • Off-grid source of electricity • Exercise with benefit of harnessing otherwise wasted energy. • Power for on demand or stored for later use. • Clean source of electricity

  3. Features • Compatible with a variety of bicycles • Output:120V-AC, 60Hz • Simple Operation • Compact and Portable • Battery voltage display

  4. System

  5. Bicycle Interface

  6. Generator Currie Technologies PMDC Motor model no. XYD-6D • 24V DC • Rated Speed: 2600 RPM • Rated Current: 22 A • Rated Power: 350 W

  7. Bike Stand Bell Motivator Mag Indoor Bicycle Trainer • Dual adjustment locking mechanism • Foldable and compact • Adjustment for varying wheel sizes

  8. Calculations Road bike circumference: 2.096m Generator shaft circumference: 0.35908m Generator speed: 800 RPM

  9. Calculations Typical drivetrain losses= 5% Normal force= 70 N Rolling resistance= 0.07 Number of tires=1 Generator efficiency= 95% Bike speed=3.44m/s Generator output=95W

  10. Testing and Results

  11. Testing and Results

  12. Testing and Results

  13. Recommendations • Hook up motor to dynamometer to do better testing and get more motor characteristics.

  14. Buck-Boost ConverterTheory • Output voltage determined by duty ratio and input voltage • Transfer of Energy between inductor and capacitor • Switching frequency higher than time constant • Inverted Output voltage Image from http://en.wikipedia.org/wiki/Buck-boost_converter

  15. Buck-Boost ConverterInitial Design and Modifications • Correct Concept but with errors in chip selection and layout • Original PWM could not reach desired pulse widths • High Side switching not diagnosed as problem • Non-IC Design correct

  16. Buck-Boost ConverterModifications • Changed PWM chip to UC2843 • Allowed for pulse width to vary to desired ranges • Accounted for high side switching • Isolated grounds of PWM from the converter ground

  17. Buck-Boost ConverterEnd Design • Snubber Circuit • Additional Capacitors to • reduce ESR • Capacitor Across DC input • to reduce high frequency • ripple • PMOS to account for high • side switching problems • Inductor needed large • wiring in order to handle • Iout + Iin sized currents

  18. Buck-Boost ConverterResults Efficiency higher than 1 can be attributed to ripple current for 20 volt input • More tests should be done with varying • loads • Circuit • Tests should also be done with generator • Ripple was not measured and skews the • results

  19. Buck-BoostWhy High Side switching can be bad • NMOSs create less losses (smaller capacitance and internal resistance) • Vgs > 2*Vth (In Power FETs) • Vgs > 10 + Vs (Rule of thumb) • High side can be very large, requiring Vg of up to 25 volts (in this design) • In PMOS, Vgs < Vs – 10 to turn off, allowing for lower Vgate • Vgs limits of volts Vgs

  20. Buck-BoostFuture Work • PMOS should be changed to NMOSs with high side gate drivers • Possible change to a Flyback or Push Pull converter. • Isolation available • No need for high side drivers • The transformer might get excessively large in order to handle large currents. • Implement feedback control

  21. InverterTheory • Reverse of a full-wave rectifier • Uses switches to change polarity of voltage on load • Implemented with FETs and a PWM chip Image from http://en.wikipedia.org/wiki/Buck-boost_converter

  22. InverterInitial Design • Design very similar to Stirling Engine group from last semester • Wiring was a little incorrect, but only slight modifications had to be made

  23. InverterResults • Problems with High side switching (Again) • Output of PWM was as expected (quasi sine wave) Dead-time can be adjusted

  24. InverterFuture Work • Implement High Side switches • Possible change to Flyback or push-pull converter to reduce transformer size

  25. Battery Lead Acid battery MODEL – PSH-1280 F2 12 Volts 8 Amp Hr. 36 Watts per Cell Charge rate 600mA at 12V Charging time = 8000/600 =13.33 hours

  26. Battery Charger • Three Stage process • STAGE 1 – BULK CHARGE • 10.5 Volts to 15 Volts • STAGE 2- ABSORPTION CHARGE • 14.2 Volts – 15.5 Volts • STAGE 3- FLOAT CHARGE • 13.02Volts – 13.2 Volts

  27. Charger Schematic • Precision Voltage Source • Temperature Sensor with negative temperature Coefficient of -8mV per degree Celsius • Large Power Diode • LM350 – 3 pin Voltage Regulator • 1.2 V to 33 V output range • Adjust Pin function

  28. Testing and Results • Applied different voltages ranging from 10V to 15V through the circuit • Charged for 14V and above • Input current 0.3 A • Output current 0.205 A • Power = VI • Input Power 4.2 Watts • Output Power 2.46 Watts • Efficiency 58.57%

  29. 12 V Lead Acid Monitor

  30. Display Schematic • Dot Mode • Input voltage of 12.65 V- Led 10 lights up • Led 1 lights up at 11.89 V • Entire circuit uses 10 mA • Led Brightness Adjustable

  31. Transformer • Obtained core from the Power lab • Step Up Transformer • Toroid • Primary Side 12V • Secondary Side 120 V • Turns Ratio 1:10 • Windings

  32. Testing and Results • Open Circuit Test • Connected the low side of the transformer to a function generator • High side was left open • For 1.9 V it stepped to 13.6V • For 2.2 V it stepped to 38.4 V • Flow of Flux

  33. Simulations

  34. Recommendations • Use a higher capacity battery for testing instead of a smaller battery. • Laminated Core for Transformer • Current Limiter Circuit • Numeric Display • Use PQ core instead of toroid geometry.

  35. Estimated Overall Efficiency • Mechanical to Generator Electrical Output 77.4% • Buck-Boost Efficiency • Measured approximately 98% but actual is more likely to be lower, 80% • Battery Charger Efficiency 55% • Overall Efficiency: 77.4*80*55 = 34.5%

  36. Ethical Considerations • Safety is primary concern • High currents in Inductor • Overcharge protection is a must for Lead Acid batteries • Possible overheating if not more cooling added

  37. Summary • Overall efficiency of 34.5% to the battery • Use dynamometer for testing of motor • Implement high side switching • Feedback is a must on final design • Possibly switch to flyback or push-pull converter • Use a higher capacity battery for testing instead of a smaller battery. • Laminated Core for Transformer • Current Limiter Circuit • Numeric Display • Use PQ core instead of toroid geometry.

  38. Acknowledgments A special thank you to: • Professor Gary R. Swenson • Professor Patrick Lyle Chapman • Professor Philip T. Krein • Professor Peter W Sauer • Kevin James Colravy • Ali Bazzi • Andy Friedl • Zuhaib Sheikh

  39. Questions and Comments?

  40. Buck-Boost CalculationsInductor and Capacitance • Assumed 350W input and 24v max input • Voltage ripple of 1% (.148v) • Current ripple of 10% of Iout • Final equations:

  41. Flyback Converter • Provides Isolation • Output is dependent on transformer turns ratio and Pulse width • Same function as buck boost • Provides Isolation from output and low side switching

  42. Output waveforms

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