Analysis of an irradiance adaptative PV based battery floating charger

In a system composed of a PV cell, a converter and a resistive load, the MPPT techniques are done on the output of the PV cell and not on the load level. This study considers a battery as load and considers its state of charge and take into consideration that empty battery need more current than a fully charged one and therefore the MPPT is not useful in this case, but a smart system able to manage the battery current based on different irradiance levels. For a fixed voltage output of the DC/DC converter, the current risks to reach its maximum when the battery is totally empty which is caused by the big difference of potential between the converter and the battery voltages. Whereas in a fully charged battery, the difference of potential between the charger and the battery is zero and therefore no need to search for the MPP in this case. The study treats first the modeling of an open loop DC/DC buck converter and then a modeling of the converter in a closed loop with a PID controller. Also, it proposes the use of a microcontroller with three different circuit designs and algorithms to manage the current and the voltage together depending on the battery state of charge. The final design is called a PV based battery floating charger that increase the lifetime of the battery by controlling the converter output voltage with respect to the consumed current, the available PV current and the converter Mosfet tolerated current.