2 How MPPT and VINDPM Works on Solar Battery Chargers

To extract the MPP from a solar panel, a MPPT algorithm is used. One good way is to use the Fractional Open Circuit Voltage (FOCV) technique. In this method, the solar battery charger input voltage is regulated to a percentage of the open circuit voltage (OCV) of the solar panel. This OCV is the output voltage of the solar panel under a no load condition [4]. During normal sunlight conditions this ratio, also known as a K-factor, is typically between 75% to 85%. Another method is to regulate the input voltage to a fixed value. All of the Solar Battery Chargers presented here work by using one of these two algorithms. The following sections detail how specifically each charger achieves MPPT operation.

Using MPPT requires input voltage regulation, also known as VINDPM (Input Voltage Dynamic Power Management). VINDPM activates when the battery charger requires more output power than the input can handle which starts to lower the input voltage. By selecting the appropriate VINDPM setting, the charge current will reduce under VINDPM to prioritize the system load and to prevent the input voltage from dropping below the VINDPM value. The VINDPM setting is determined by external resistor divider or I²C setting. The combination of choosing the desired K-factor from the OCV and regulating with VINDPM to the target input voltage presents a clear MPPT solution.