Publication - IEEE Transactions on Power Electronics
We are happy to share that an article, documenting our supercapacitor interfacing innovations within the framework of the project, and titled ‘Design optimization of dual active bridge converter for supercapacitor application’, was accepted for publication in the journal, IEEE Transactions on Power Electronics, on 4th May 2024.
In the project, supercapacitors are employed as energy storage owing to their distinct characteristics compared to other forms of energy storage. These unique properties present opportunities to optimize the remaining electrical system to extract power from a supercapacitor as efficiently as possible. Since the system to extract power from the supercapacitors is a balance-of-plant, keeping its size as low as possible improves the attractiveness of the solution.
A power electronic interface (PEI), is used to extract electric power from a supercapacitor and feed it to the larger electrical system. Supercapacitor storage is formed of a number of smaller, individual supercapacitors, called cells, each of which operates at a maximum voltage of a few volts. These cells can be “stacked up” to form a supercapacitor stack that then operates at a higher voltage level, although this “stacking” is limited by other considerations. To interface the stack to a DC system operating at a few hundred volts, the power electronic interface of the stack needs to provide a voltage boost, while maintaining a high power-conversion efficiency.
Certain power converter topologies, such as the dual active bridge, facilitate a large voltage boost at a high efficiency, and can hence be used as a power electronic interface for the supercapacitor. However, the widely varying terminal voltage of the supercapacitor complicates the design of the dual active bridge. In particular, operating the dual active bridge over a wide voltage range on one of its ports leads to an increased power loss in the converter.
In our paper, we address this problem considering a new indicator of efficiency, that reflects the overall efficiency of the supercapacitor discharge process. This efficiency indicator is maximized using an algorithm that searches for the design of the dual active bridge that corresponds to a peak of the overall efficiency. The process is thus automatic; we show that this algorithm is guaranteed to locate the single efficiency peak in the space of all possible circuit designs of the dual active bridge.
The design strategy for the dual-active-bridge-based power electronic interface is executed in the paper and compared to an existing design of the dual active bridge for a supercapacitor application. For the operating conditions used in the paper, the proposed design method proposed achieves a ~25% experimental reduction in losses over the supercapacitor discharge duration. This results both in a higher overall efficiency of the supercapacitor system, and, since less energy is lost (dissipated), leads to a more compact (smaller) supercapacitor stack. The lower losses also imply that a smaller cooling system is required for the supercapacitor and its interface, which leads to a further reduction in the size of the overall system.