Optimal control of hybrid electric vehicles based on Pontryagin's minimum principle

A number of strategies for the power management of hybrid electric vehicles (HEVs) are proposed in the literature. A key challenge is to achieve near-optimality while keeping the methodology simple. The Pontryagin's minimum principle (PMP) is suggested as a viable real-time strategy. In this brief, the global optimality of the principle under reasonable assumptions is described from a mathematical viewpoint. Instantaneous optimal control with an appropriate equivalent parameter for battery usage is shown to be possibly a global optimal solution under the assumption that the internal resistance and open-circuit voltage of a battery are independent of the state-of-charge (SOC). This brief also demonstrates that the optimality of the equivalent consumption minimization strategy (ECMS) results from the close relation of ECMS to the optimal-control-theoretic concept of PMP. In static simulation for a power-split hybrid vehicle, the fuel economy of the vehicle using the control algorithm proposed in this brief is found to be very close - typically within 1% - to the fuel economy through global optimal control that is based on dynamic programming (DP). �� 2006 IEEE.Manuscript received May 03, 2009; revised February 15, 2010; accepted June 15, 2010. Manuscript received in final form July 20, 2010. Date of publication August 23, 2010; date of current version August 17, 2011. Recommended by Associate Editor C. Bohn. This work was supported in part by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) under KRF-2007-612-D00081 and by Korea Ministry of Knowledge Economy for the development project of industry core technologies under 0420-20090041