Control strategies have been developed for hybrid electric vehicles (HEV) that minimize fuel consumption while satisfying a charge sustaining constraint. Since one of the components of an HEV is typically the ubiquitous internal combustion engine, tailpipe emissions must also be considered. This paper uses shortest-path stochastic dynamic programming (SP-SDP) to address the minimization of a weighted sum of fuel consumption and tailpipe emissions for an HEV equipped with a dual mode electrically variable transmission (EVT) and a catalytic converter. The shortest path formulation of SDP is chosen to directly address the charge sustaining requirement. Using simple methods, an SP-SDP solution required more than eight thousand hours. Using linear programming and duality, an SP-SDP problem is solved in about three hours on a desktop PC. The resulting time-invariant feedback controller reduces tailpipe emissions by more than 50% when compared to a popular baseline controller.
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