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Published byLeslie Casey Modified over 9 years ago
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To develop a small scale solar powered system that will power a DC load, which incorporates power management techniques, DC-DC conversion and a user interface.
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Renewable energy source Non-polluting Reliable Can work anywhere sun is shining No major mechanical parts Relatively no maintenance Noise Free Last decades
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Solar Panel DC-DC Converter Load Controller Back-up Battery
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Silicon cells combined in series or parallel Converts solar energy into electricity Cell Technologies › Copper Indium Selenide (CIS) and Amorphous › Monocrystalline and Polycrystalline Current varies with cell size and light intensity
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Rp Rs IphD Id Vo Ip
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Peak Power of 10 Watts Vmpp = 15.6 V Impp = 0.64 A Shell ST10 Voc = 22.9 V Isc = 0.77 A The solar panel was tested with different resistances under a constant light source + - V
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Two MPPT algorithms were considered: Incremental Conductance Method › By comparing incremental conductance with instantaneous conductance. Perturb & Observe Method › By periodically perturbing the PV array voltage and comparing the output power with that of the previous cycle. The operating point oscillates around the MPP since the system is continuously perturbed.
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Algorithm was implemented using LabVIEW Solar panel read via a NI-USB 6009 The voltage was measured across a high power resistor to read current Duty cycle output on NI USB 6009 digital output line Start Set Duty Out Read V, I P_new = V*I P_new > P_old Duty = Duty(-) Duty = Duty(+) P_old P_new
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Used to implement P&O algorithm › ‘G’ programming Also used to generate a user interface through the front panel › Waveforms showing voltage and current of solar panel › Numeric indicator showing power › Duty cycle displayed › ‘Stop’ button to end program
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Data acquisition tool Read data in, and generate digital signals out Does not have a hardware counter, cannot generate digital outputs at high frequencies Solution M series
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DC-DC converter needed for two reasons › To implement the MPPT algorithm › To bring the DC voltage to an acceptable level to power the load Buck converter was chosen and designed
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The most important components are the inductor and capacitor Use Vo = DVi to deduce ideal duty cycle range (0.3 – 0.5) Using both of these values for D, and the ΔI equation two values for the inductor were calculated (2.8 mH & 1.6 mH) Using the Δ V equation the capacitor value was determined (21.3 μF)
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Vin 2.2 mH 22 uF LOADLOAD + - + - D PWM
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Solar panels only generate power when there sun available Storage element is recommended Various rechargeable battery cell chemistries › Lead Acid › Nickel-Cadmium › Nickel-Metal-Hydride › Lithium Ion
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Up to 99% efficiencies Highest weight to energy ratio Average voltage of one Li-ion cell is 3.6- 3.7 Volts A Li-ion battery pack with a capacity of 4 AH would be enough to store all energy generated on the longest day of the year at maximum power Safety issues
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Overvoltage Over discharging can cause short circuit Battery packs usually include protective circuit › Limits input voltage › Limits discharge voltage Li-ion charger IC is recommended to implement charging profile
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Initially it was thought a mobile phone charging algorithm would have to implemented Research showed that the charging algorithm is employed on the phone To prove this, a commercial Nokia car cigarette lighter charger was disassembled A ‘ma34063a’ DC-DC converter was found To charge a mobile an appropriate constant voltage is needed, along with some circuitry protection
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Solar cell equivalent circuit, characteristics and various cell technologies Maximum power point tracking techniques LabVIEW – ‘G’ programming and user interface DC-DC converter design including choosing appropriate components and simulation in Pspice Rechargeable Batteries
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