Energy Management Options for an Electric Vehicle with Hydraulic Regeneration System 2011-01-0868

Energy security and climate change challenges provide a strong impetus for investigating Electric Vehicle (EV) concepts. EVs link two major infrastructures, the transportation and the electric power grid. This provides a chance to bring other sources of energy into transportation, displace petroleum and, with the right mix of power generation sources, reduce CO₂ emissions. The main obstacles for introducing a large numbers of EVs are cost, battery weight, and vehicle range. Battery health is also a factor, both directly and indirectly, by introducing limits on depth of discharge. This paper considers a low-cost path for extending the range of a small urban EV by integrating a parallel hydraulic system for harvesting and reusing braking energy. The idea behind the concept is to avoid replacement of lead-acid or small Li-Ion batteries with a very expensive Li-Ion pack, and instead use a low-cost hydraulic system to achieve comparable range improvements. A Matlab/SIMULINK model was developed to simulate a baseline EV truck with a series wound DC motor and lead-acid batteries. The simulation was validated with tests at the US EPA National Vehicle and Fuel Efficiency Lab. Subsequently, the hydraulic pump/motor and accumulator models were integrated to create an EV-Hydraulic Hybrid and the simulation was used to explore tradeoffs related to improving battery health, reducing the overall energy demand, and increasing the range. Preliminary strategy was focused on maximizing the driving range, but insight obtained through the analysis of interactions in the system-enabled refinements that significantly benefit battery health without compromising electric range.