A Low-Cost Battery-Balancing Auxiliary Power Module With Dual-Active Half Bridge Links and Coreless Transformers
Weizhong Wang, Youssef Fahmy, Matthias Preindl
Abstract
Redistributive balancing brings many benefits to electric vehicles, such as increased range and more uniform cell degradation. Despite previous analyses suggesting a 17%–36% extension of battery lifetime, the cost of such systems has prevented the technology from being adopted in practice. This study proposes a simplified topology for battery-balancing auxiliary power modules (BB-APMs) with reduced magnetic material to achieve cost-friendly solutions without sacrificing functionality or balancing modes. The proposed system consists of a dual-active half bridge, halving the number of switches needed compared with the conventional dual-active bridge (DAB). In addition, the transformer core material is removed and a coreless transformer is used to provide isolation and energy transfer. Both the changes reduce the cost of redistributive balancing. The topological modeling differs from cored transformer circuits as the coupling of the coreless transformer is weaker. The coupling coefficient is now used in an updated model that includes transformer currents and output powers. These, along with the balancing modes, are analyzed and then experimentally verified. The proposed models can guide the selection of MOSFETs and the design of the coreless transformer. An analytic projection shows up to a 22% cost reduction compared with similar topologies.