Road grade preview can benefit the hybrid electric vehicle (HEV) energy management because the energy efficiency performance degrades significantly when the battery state of charge (SOC) reaches its boundaries and the road grade has a great influence on the battery SOC balance. In reality the road grade in front may be a random variable as the future route may not always be known to the vehicle controller. This paper proposes a stochastic model predictive control (MPC) approach which does not require a determined route known in advance. The road grade is modeled as a Markov chain and all the possible future routes are considered in building the transition matrix. A large-time-scale HEV energy consumption model is built. The HEV energy management problem is formulated as a finite-horizon Markov decision process and solved using stochastic dynamic programming (SDP). Simulation results show that the proposed approach can prevent the battery SOC from reaching its boundaries and maintain good fuel efficiency by the stochastic road grade preview.

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