Efficient SMPS Circuit for SPV Battery Charger

[HIZIBIZI]

Hi guys,
I hv found that at that low duty cycle and so high an input voltage, design is messy. Hence I hv opted for a lower voltage solar array. I am fabricating the prototype as follows, -
I/p voltage - 81 Volts peak, that is six 170 Wp modules, connected three in series, two strings in parallel, total 1020 Wp, Vmax - 72 Volts, Imax - 14.18 Amps.
Battery bank - 4 x 12v/180 ah batteries in series. Nominal voltage - 48 Volts, peak charging voltage - 64 volts, minimum duty ratio - 0.61.

I am using two buck converters interleaved. As for push - pull or other isolated topologies, an extra magnetic element (assuming the switching and conduction losses of the single switch and diode of the buck converter is equally distributed in the two switches and two diodes of these topologies) should add extra losses. However, doing is believing. First I will go with this prototype (there is no turning back, as I hv already fabricated the control and drive card). Then we shall look into the alternatives.

Anyway, Thanks again for all the suggestions.

 

[Warpspeed]

Sounds like a good plan.

 

[William I. Behen]

I agree that 95% is tough, even with synchronous rectification. You will definitely want a true PWM switching converter which means one or more power inductors. A relatively low switcing frequency will mean better efficiency and will make driving the FETs' Gates easier. Paralleling FETs is not very hard, and increases efficiency. Remember that low fs means larger inductance values, and bigger wire for lower copper losses also translates to physically large parts. Multiple converters would ease this situation, as no one magnetic part was inordinately big/heavy.

Do you require isolation? This would have some influence on the converter topology you use (buck, boost, etc.)

Also remember that a solar panel produces substantial power only in a certain region of output voltage and current! At max voltage or max current, not much power is generated. Often a "conditioner" is used to keep the array at/near this point....

 

[William I. Behen]

As a P.S. to my previous comment, look up MPPT in Wikipeida for a good explanation!