INTRODUCTIONThe White House announced new fuel efficiency standards for trucks, buses, and other heavy duty vehicles in August 2011. Within the standards, vehicles manufactured between 2014 and 2018 are required to reduce their fuel consumption and greenhouse gas emissions by 10% to 20%. HEVs are considered as the most promising short-term solutions in reducing the fuel consumption [1,2]. By exploiting the capacity of a storage system installed aboard, HEVs can achieve better fuel economy and lower exhaust emissions than traditional powertrain vehicles. In a HEV, an electrical path is added to the powertrain such that part of the vehicle kinetic energy and exhaust gas energy can be captured by the electrical machines, and be used to recharge the battery. The energy assisted by the electrical machines also helps downsizing the internal combustion engine (ICE), resulting in better fuel efficiency and lower heat loss [3]. Since electrical machines provide faster boosting torque than mechanical systems, HEVs offer the improved launching performance and the reduced overall rated power comparing with traditional ICE vehicles.A key issue in developing HEVs is the coordination of multiple energy flow of both fuel path and electrical path, that is the management of the power distribution in parallel paths to minimize the fuel consumption, while satisfying the constraints of power demand and battery SOC [4]. The energy management strategies, also called supervisory control strategies, can be grouped into three categories: rulebased control strategies [5,6,7], optimization-based control strategies [8,9,10], and real-time control strategies [11,12,13]. In the rule-based control strategies, the rules are designed using heuristics, human expertise, or mathematical models. Although the control approaches can offer improvement on energy efficiency, it is clear that they do not guarantee an optimal result in all conditions. Using the optimization-based control strategies, the global optimum solution can be found by performing the optimization over a fixed drive cycle. Unfortunately, the global optimization approach is noncasual in nature, because the prior knowledge of the future driving information is required. The real-time optimization strategies manage the energy flow online, where the most well-known approach is the ECMS. The ECMS realizes the real-time optimization by minimizing an instantaneous cost function, so behaves as a closed-loop controller. The equivalent fuel consumption is defined as the extra energy which is offered by the battery and is effected by both the engine operating condition and the supervisory control action. It is assumed that the variation of battery SOC will be compensated in the
Real-Time Optimal Energy Management of Heavy Duty Hybrid Electric VehiclesDezong Zhao and Richard StobartLoughborough University
ABSTRACTThe performance of energy flow management strategies is essential for the success of hybrid electric vehicles (HEVs), which are considered amongst the most promising solutions for impro...