Cascade control of single input multi output buck converter for synchronous charging applications of battery/ultracapacitor hybrid energy storage systems

In the near future, seeing more than one energy storage device in mobile device power systems will be possible. Although Lithium-ion (Li-ion) battery cells in today's technology stand out with their high energy density and superior cell voltage advantages, they suffer from limited cycle lives. When high-power density ultracapacitors (UC) are combined with battery cells, a highly efficient hybrid power system can be created. However, since the cell voltages and power densities of these two energy storage devices are not equal, both the charge voltages and charge currents will be different from each other. This study proposes a single-input, multi-output cascade buck converter structure to charge battery and ultracapacitor cells synchronously. Converter parameters are calculated according to the charge powers of energy storage devices, and a cascade controller structure is designed for separate control of charge currents and cell voltages. The proposed synchronous charging system is tested using two different procedures: continuous current (CC) mode, where reference currents are closely monitored, and continuous voltage (CV) mode, where the charge voltage is limited. According to the results obtained, it was observed that the proposed system closely followed the reference currents in a short time of 6ms with a slight overshoot rate of approximately 8% in all tests.