A study on the control loop design of non-isolated configurations for hybrid storage systems

This work focuses on the control strategies for different configurations of Non-Isolated Hybrid Energy Storage Systems. Basic strategies are proposed, studied and compared. Parting from the standard parallel connection of bidirectional boost converter in hybrid storage systems, a comparison with alternate topologies is presented. These alternative schemes overcome the problems that arise in the original configuration due the high mismatch in voltage ratings of the individual storage systems. A strategy to design the control loops of the resulting Hybrid Energy Storage System is proposed, studied, simulated and experimentally implemented on a 1.5 kW demonstrator. The control strategy is implemented in the standard bidirectional boost converter approach and also in the series-parallel connection of the storage units. The reported results show how the proposed control strategy applied to the series parallel connection presents a good performance in terms of dynamic and steady state operation.