7/15/2020 Designed MPPT

A project log for solar powered boat

low-cost methods to power boats from solar power

sean-depagniersean d'epagnier 08/29/2020 at 18:560 Comments

I have designed and built my own working MPPT.   A few notable differences:
a) free software and hardware design.  <github link>
b) all ceramic capacitors.  This slightly increases efficiency as electrolytic capacitors are often a weak link and also eventually fail
c) buck/boost design allow either higher or lower voltage of battery vs panel.
d) components rated for up to 48 volt system (60 volt mosfets)
e) voltage and current monitoring on both input and output.  This allows the unit to calculate it's own conversion efficiency and display this information
f) high-efficiency regulators to power the 3.3v logic as well as the 10v needed for gate drive.   This keeps quiecent power consumption around 5 milliamps even powering the backlight of the lcd.

I had not used the stm32 series microprocessors before, so this seemed like a good opportunity to learn.  I can use floating point calculations with no noticeable performance penalty even running at only 8mhz.   I have used the stm32duino environment as working with registers directly on this processor is very complex compared to the avr I am more familiar with.   Despite this I needed to anyway for the pwm output to achieve the variable deadtime needed in driving the mosfets.   I have achieved variable deadtime in the past using timer interrupts on avr series, but this limits the overal maximum frequency to around 20khz.

The design uses a basic buck converter, however it can be reversed and act as a boost converter as well.  So there is not a solar or battery specific side, but a high and low voltage side.  The parts cost approximately $12 in small quantities.