Ultracapacitor-Battery Hybrid Energy Storage System Based on the Asymmetric Bidirectional <italic>Z </italic>-Source Topology for EV

TLDR

The conventional symmetry assumption in Z‑source topology impedance analysis does not hold for the proposed HESS configuration. This paper proposes an ultracapacitor–battery hybrid energy storage system for electric vehicles based on an asymmetric bidirectional Z‑source topology. The design uses the Z‑source converter’s buck/boost function to harness UC energy without a battery converter, models the asymmetric power distribution, introduces a frequency‑dividing coordinated control, and estimates battery peak current. Compared with a conventional two‑stage design, the HESS can be integrated into the traction inverter, improving performance and reducing cost, and its steady‑state and transient traction/regenerative responses were validated by simulation and experiment.

Abstract

This paper proposes an ultracapacitor (UC)-battery hybrid energy storage system (HESS) for electric vehicle based on asymmetric bidirectional Z-source topology. Compared with the conventional two-stage design, the HESS can be incorporated into the traction inverter system, leading to better performance and lower cost. The UC energy can be effectively utilized due to the buck/boost characteristic in the Z-source converter; meanwhile, the battery converter gets eliminated in this case. The assumption about the symmetry in the Z-source topology impendence network states for the conventional analysis no longer applies to the proposed HESS configuration. The asymmetric characteristic related with the uneven power distribution of UCs and battery is mathematically excavated in detail. The frequency dividing coordinated control is proposed to exploit the advantages of UCs and battery. The battery peak current estimation is then investigated. Finally, the steady performance and transient response in both traction and regenerative modes are verified by simulation and experimental results.