EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Ern on November 25, 2016, 08:40:18 am
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I haven't done it with a buck-boost converter, but I have done a simple boost MPPT stage. After a certain amount of screwing around, we found that the easiest move was to just drive the stage with fixed PWM duty cycle (D = Vin_ref / Vout) and let the dynamics take care of themselves. Remember that the PV panel is current limited. For extra credit, you can do some more complicated maths to encompass Discontinuous Conduction Mode (DCM) operation.
Your PV panel appears to have an open circuit voltage of 18V. I would suggest that you use a simple buck converter. LT makes some which have (approximate) MPPT built in (http://cds.linear.com/docs/en/lt-journal/LTJournal-V20N4-02-df-LT3652-Jay_Celani.pdf (http://cds.linear.com/docs/en/lt-journal/LTJournal-V20N4-02-df-LT3652-Jay_Celani.pdf)), which would be easier to manipulate than a generic converter. Alternatively, you can place a discrete MOSFET, diode and gate driver, directly controlled by a micro controller PWM pin.
Also don't forget about transients! I suggest your buck stage input have a 30V TVS diode and use 45V devices. (Note TVS diodes clamp voltages to around 1.3x - 1.5x their rated voltage.)
FYI, your PV panel model is pretty crude, and may give misleading results.