Testing and Analysis of Three Plug-in Hybrid Electric Vehicles

Current-production hybrid electric vehicles (HEVs) have shown a measurable improvement in fuel economy, in comparison with conventional vehicles, by using the internal combustion engine in a more efficient operating region, which therefore reduces petroleum consumption. These HEVs operate with a charge-sustaining control strategy. Plug-in HEVs (PHEVs) show the potential to further decrease petroleum consumption by operating in a charge-depletion control strategy, in which the energy stored in the battery pack in used during normal driving and recharged through stationary, off-board vehicle charging. This charge-depletion strategy uses more electrical energy to propel the vehicle, which displaces more petroleum. This paper discusses the testing and analysis of a Hymotion Prius PHEV, an Energy CS Prius PHEV, and a Renault Kangoo PHEV. Fuel economy, electrical energy usage, emissions, and powertrain controls were measured and analyzed by using the four-wheel-drive chassis dynamometer facility at Argonne National Laboratory. All three vehicles have rather large battery packs (from 5 to 9 kWh), which are required for the charge-depletion operation. The Kangoo is an electric vehicle with a range-extending gasoline engine/generator set. The two Prius PHEV variants operate in EV mode at high states of charge (SOCs) to maximize the benefit of the charge-depletion control strategy. By maximizing the charge-depletion rate for maximum petroleum displacement, other characteristics are compromised, including emissions, as a result of infrequent engine operation and diminished engine operating efficiency because the battery is not recharged while the vehicle is driven, reducing engine load. This maximum charge-depletion operation in a power-split hybrid, although not optimized, can serve as a benchmark for future research on PHEVs to study the effects of a charge-depletion control strategy on battery sizing and battery life, real-world cost, charging, controls optimization, and powertrain configurations.