Power Management for an Electrified Bus

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The Ohio State University

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Transit buses are the most important form of public transportation, and there is a continuing effort to make them more fuel efficient to reduce their economic and environmental footprint. One means of improving the fuel economy of buses is by replacing fuel consumed to power the vehicle and its accessory loads with electricity. This can be accomplished by way of hybrid powertrains (hybrid-electric buses are a common sight today), and by managing the accessory loads in a more efficient manner. The focus of the research carried out in this project pertains to the increasing electrification of buses. This electrification has created a high demand for additional electrical energy to power accessory loads such as air conditioning, and air compressors. Conventional buses use multiple alternators to supply the additional energy. In this project we explore the possibility of using a single, larger electrical generator and an optimal power management strategy to service the accessory loads more efficiently. An important step in the process of developing a power management strategy is to develop efficiency models of each of the subsystems to be managed. Efficiency models are developed to understand the power consumption of fans, air conditioners, air compressors, and power steering pumps, and these models are incorporated into a computational model that includes the engine and all of its loads. The mathematical and computational models developed will make it possible to increase the overall efficiency of a bus by enabling the design of optimal power management strategies. Results of simulations show that while there isn’t a difference in fuel economy between a conventional and electrified bus, adding regenerative breaking can increase fuel economy by 13%. Buses are high mileage vehicles, so increases in fuel efficiency are extremely important and make large differences in the amount of fuel used. This reduces the economic and environmental impact of buses.



Automotive, Accessory Loads, Hybrid, Electrified