Reducing Peak Battery Currents in Hybrid Electric Vehicles Using an Ultracapacitor as a Secondary Energy Storage System

Open Access
Author:
Jadwin, Michael Seving
Area of Honors:
Engineering Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Michael T Lanagan, Thesis Supervisor
  • Corina Stefania Drapaca, Honors Advisor
Keywords:
  • battery
  • hybrid
  • electric vehicle
  • ultracapacitor
  • battery degradation
  • simulink
  • stateflow
  • simulation
Abstract:
The increasing demand for the electrification of vehicles has led automotive manufacturers to produce more models of fully electric and hybrid electric cars. Many of these vehicles use a battery as the sole energy storage system (ESS), which reduces the amount of fuel consumed. Batteries also recover kinetic energy, through regenerative breaking, that dissipates in typical internal combustion (IC) vehicles. A current issue with battery electric vehicles (BEVs) and hybrid electric vehicles (HEVs) is the significant cost and limited lifetime of the battery. In automotive applications, a battery is subject to high current magnitudes either in sharp regenerative breaking or acceleration demands. These large currents are detrimental to the battery and speed up the degradation process, which lowers the capacity, power, and overall efficiency of the battery. A viable solution to this problem is using an ultracapacitor incorporated with the battery so that the vehicle has two ESSs. Because of the high specific power of an ultracapacitor relative to that of a battery, the ultracapacitor can act as a current buffer to the battery to help limit its peak current demands. A standalone Simulink model of a dual ESS HEV from Autonomie is adapted to represent a typical HEV to confirm the reduction in battery current. Using five selected drive cycles, simulations run on two different models confirm under which driving conditions each configuration excels. In conclusion, the optimal sizing of the ultracapacitor is calculated to determine the minimum size of ultracapacitor so that it can still adequately reduce battery current peaks.