A solar battery charging module by means of Limit-Cycle MPPT control

The objective of this paper is to develop a power converter module that charges a battery with solar power, and the design technique at the product level is introduced to realize a compact size and light weight. The main circuit is a buck-boost chopper so that it can cover wide range of charging voltage. The MPPT control is realized by a very simple algorithm of Limit-Cycle MPPT (LCMPPT) proposed by authors previously. All control functions are implemented in digital algorithm and a HITACHI H8 microprocessor is used for the control. In addition to the battery, a load can be directly connected also, which is automatically disconnected in the case of detecting a low voltage condition of the battery. RS-232C port is also available for observing the internal variables such as input/output voltages and currents through a PC. An example of obtained test results showing the relations of output power versus input/output voltages and efficiency are given. The efficiency is about 70-72% in a wide range of output power.