Ultracapacitor-Battery Hybrid Energy Storage System Based on the Asymmetric Bi-Directional Z-Source Topology for EV

  • This work proposes an ultracapacitor-battery hybrid energy storage system (HESS) for electric vehicle (EV) based on asymmetric bi-directional 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 ultracapacitor (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 details. 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.


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