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Solar Power Converter

Solar Power Converter. Senior Design Project David Kline, Jet-Sun Lin, Ting-Hau Ho. Goals of the Project. Create an efficient means to collect, convert, and store solar energy in a battery Create a monitoring and switching circuit to control charging/discharging cycles

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Solar Power Converter

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  1. Solar Power Converter Senior Design Project David Kline, Jet-Sun Lin, Ting-Hau Ho

  2. Goals of the Project • Create an efficient means to collect, convert, and store solar energy in a battery • Create a monitoring and switching circuit to control charging/discharging cycles • Convert stored energy from battery to a 120V(ac) output

  3. Overview

  4. Stage 1. Solar Panel • Obtained from Prof. Krein • In direct sunlight: • Voc=22.2 V • Isc=300mA • Resulting in power output of 6.66W • Incident power expected=260W (based on 0.2m2 panel and 1300W/m2 solar constant) • Efficiency=2.56%

  5. Stage 2. DC Step-Down • Design Based on MaximMAX724 • PWM Regulated LC circuit • Converts 14.25-24+ V tosteady 13.8V (adjustable via turnpot) up to 5A • Original design based on Maxim MAX830 scrapped due to pinout/size considerations

  6. Stage 2. DC-Step Down • Steady Voltage over entire range of solar panel inputs (14.25-24+ V) • Efficiency: 76%

  7. Stage 3. Monitor & Switch

  8. Stage 3. Monitor & Switch • Relay-based design using Magnecraft W60HE1S-12DC and W60HE2S-12DC • Original voltage monitor design based on Maxim MAX8215 scrapped • Final Voltage Monitoring Circuit based on LM741CN op-amps • Monitoring Circuit is adjustable with turnpot • Precision up to 0.01V

  9. Stage 3. Monitor & Switch • 13V Voltage Monitor switches at Vbatt=12.98V

  10. Stage 3. Monitor & Switch • Voltage monitor A (11 V) (Green LED): • V (battery) >11V: connect DC/AC converter with battery. • V (battery) <11V: disconnect DC/AC converter from battery.

  11. Stage 3. Monitor & Switch • Voltage monitor B (13 V) (Red LED): • V (battery) >13V: disconnect solar converter from battery. • V (battery) <13V: connect solar converter with battery.

  12. Stage 4. Battery • Genesis EP Series G12V26Ah10EP Lead-Acid • Original design based on current monitoring • Voltage across terminals varies during charging cycle • Discharge reversal electro-chemical process

  13. Stage 4. Battery

  14. Stage 5. DC/AC Inverter • PWM Process • Compare 60Hz sine wave to 75kHz triangle wave resulting in PWM signal driving MOSFETs

  15. Stage 5. DC/AC Inverter • ICL8038 generating 60Hz sine wave • Vpp=2.55-3.0V (depending on Vbatt) • DC offset of ½ Vbatt • SG3525 generating 75kHz triangle wave • Vpp=3.0V • DC offset of 1.5V • The two waveforms are required to be on same scale, so a coupling circuit was added

  16. Stage 5. DC/AC Inverter • SG3525 provides 2 outputs to drive the 2 complementary MOSFET pairs • A MIC4424 MOSFET driver amplifies the PWM signal and provides a high-impedance output to the MOSFETs

  17. Stage 5. DC/AC Inverter • Full-Bridge inverter driven by PWM

  18. Stage 5. DC/AC Inverter • Current must flow through load • Current must never be allowed to flow directly through a single leg to ground • Low drain to source resistance of MOSFET causes very high current to flow and damages MOSFET • PWM timing is important to prevent burn-out

  19. Stage 5. DC/AC Inverter • MOSFETs have switching time of 72ns • SG3525 was set to provide “dead time” of 1.2μs • Inverter output stepped up using a 10:117V transformer

  20. Results & Analysis • Able to obtain VOC=110Vac(rms) • With load connected, Vout=0.34Vac(rms) • Transformer is likely becoming saturated and cannot provide the necessary voltage and current

  21. Results & Analysis • 80% Efficiency on DC/AC Inverter for most loads • Overall Efficiency of Converter: 60.8%

  22. Questions?

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