Determination of maximum possible fuel economy of HEV for known drive cycle : GA based approach

Abstract

Hybrid electric vehicles (HEVs) have great potential as new alternative means of transportation. The specific benefits of HEVs, compared to conventional vehicles, include improved fuel economy and reduced emissions. Hybrid systems using a combination of an internal combustion engine and Electric motor (EM) have the potential of improving fuel economy by operating Internal Combustion Engine (ICE) in the optimum operating range and by making use of regenerative braking during deceleration This paper described a methodological approach to find out the maximum fuel economy that can be achieved by a hybrid vehicle with parallel configuration for a known drive cycle. A backward looking hybrid vehicle model is used for computation of fuel consumption. The optimization process represents a constrained nonlinear and time-varying problem that is not easily solved. Here GA approach was used to find out optimum power split between two power sources over a driving cycles that make maximum possible overall fuel economy for the given drive cycle by the vehicle. In this approach using parallel Hybrid Electric Vehicle (HEV) configuration optimization problem is formulated so as to minimize the overall fuel consumption. The whole set of Electric Motor power contribution along the drive cycle is then coded as the chromosomes. Variables are defined to find out optimum power contribution from EM and ICE. The objective function is defined to minimize weighted sum of the fuel economy and to keep the battery sac within the desired range throughout the drive cycle. These results represent the maximum fuel economy any power management system of a Hybrid Electric Vehicle with the selected HEV configuration can ever achieve and does allow a benchmark to be set against which the fuel economy is measured. It is obvious that fuel economy varies with the driving cycle and hence the result obtained from this study is valid only for the selected drive cycle. The optimum fuel economy for the selected drive cycle is compared with that of conventional vehicle