FPGA-based Li-battery-series charger with energy recycling considered

In this paper, a main circuit, a buck converter, together with an auxiliary circuit, bidirectional buck converter, is used to charge two Li batteries connected in series. By doing so, such an auxiliary circuit takes two roles in executing equalization between the two Li batteries. One role, together with the main circuit, to charge the second battery whose low-level terminal is connected to the ground. The other is to pump some charge energy back into the input so as to execute energy recycling. The main circuit is controlled in the constant current mode or in the constant voltage mode, depending on the voltage across the two Li batteries, whereas the auxiliary circuit is always controlled in the constant voltage mode. Some experimental results, based on a Cyclone II FPGA chip used as a control kernel, are provided to verify the proposed topology.