Optimal power management of plug-in HEV with intelligent transportation system

Hybrid electric vehicles (HEV) have demonstrated their capability of improving the fuel economy and emission. The plug-in HEV (PHEV), utilizing more battery power, has become a more attractive upgrade of HEV. The charge-depletion mode is more appropriate for the power management of PHEV, i.e. the state of charge (SOC) is expected to drop to a low threshold when the vehicle reaches the destination of the trip. In the past, the trip information has been considered as future information for vehicle operation and thus unavailable a priori. This situation can be changed by the current advancement of Intelligent Transportation Systems (ITS) based on the use of on-board Geographical Information Systems (GIS), Global Positioning Systems (GPS) and advanced traffic flow modeling techniques. In this paper, a new approach of optimal power management of PHEV in the charge-depletion mode is proposed with driving cycle modeling based on the historic traffic information. A dynamic programming (DP) algorithm is applied to reinforce the charge-depletion control such that the SOC drops to a specific terminal value at the final time of the cycle. The vehicle model was based on a hybrid SUV. Only fuel consumption is considered for the current stage of study. Simulation results showed significant improvement in fuel economy compared with rule-based power management. Furthermore, simulations on several driving cycles using the proposed method showed much better consistency in fuel economy compared to the rule-based control.

1. Introduction

HYBRID electric vehicle (HEV) have demonstrated its great potential in fuel economy as promising alternative means of transportation [1]–[4]. Compared to the conventional ICE powered vehicles, HEV can effectively reduce fuel consumption through downsizing the engine, energy recovery through regenerative braking. The plug-in hybrid electric vehicle (PHEV) is a new generation of HEV with higher battery capacity and the ability to be recharged from an external electric outlet [5]. Unlike the conventional HEV (known as “HEV-0”) which can sustain little purely electric range, the PHEV can sustain a longer electric range. Based on the usage of batteries with much higher capacities, PHEV can take much more advantage of the 4-times cheaper grid electricity to replace the fossil fuel. Depending on how capable the added battery pack is, the electric range may be from 10 miles to 70 miles [6]. The significant enhancement of fuel economy brought by PHEV promises a possibly shorter payback time due to the cost of adding hybrid powertrain. Such encouraging promise has attracted the significant investment on promoting PHEV technology from both government and private sectors [7].