My major research interests include optimization, control, modeling, and estimation of electrical powertrain for electric, hybrid electric, and plug-in hybrid electric vehicles. In recent years, I mainly focused on the optimization and control of the battery-supercapacitor hybrid energy storage system (HESS), which has been widely used in PHEV applications. In previous publications, I showed that the energy management strategy and the component sizing of HESS should be optimized simultaneously to reduce the battery degradation and increase the system efficiency. Different HESS configurations were also compared based on the dynamic battery degradation model, which was proposed by us. Furthermore, a sliding-mode current controller and a Lyapunov function-based voltage controller were proposed to accurately control the battery/supercapacitor currents and bus voltage. For now, Prof. Heath Hofmann, Prof. Jing Sun, and I are working on the adaptive energy management strategy for over-actuated system, which can be used in HESS for simultaneous parameter identification and system optimization. In addition, I also cooperate with Pro. Minggao Ouyang and Pro. Jianqiu Li in Tsinghua University to investigate the network time-delay problem in distributed electric vehicles, the energy storage in micro-grids, and Vehicle-to-grid (V2G).