Current amplification problem in Solar charge controller

solar charge controller

Dear Guys,

I have developed a solar charge controller, using MPPT algo. It actually charges the battery in three stages :

Stage 1 => Bulk charge using MPPT
Stage 2 => Constant Voltage charging without MPPT
Stage 3 => Trickling, when the battery is fully charged


When i connect 12V battery to 42V(no load voltage) panel it trackes the maximum point, and at the Max Power point the panel voltage drops to 26v and 4 amp max current, and the buck converter amplifies the current upto 7A and the battery voltage is 12.8v.
When i connect 42v panel directly to 12v battery it gives 3A current and drops voltage to 13v
It is a good response of the Charger as it gives Amplified current.

But the problem arises when i connect 12V battery to 21V(no load voltage) panel it tracks the maximum point, and at the Max Power point the panel voltage drops to 13v and 5 amp max current.
When i connect 21v panel directly to 12v battery it gives 6A current and drops voltage to 12.8v
It is not a good response as it doesn't amplify the current. And it is useless for 21v panel to charge 12v battery.

I want to launch this charger as a product in the market but its response for 21v panel is quit disappointed.

I am unable how to amplify the current ?

Regards,
Iftikhar Abid