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Limited battery power and poor engine efficiency at cold temperature results in low plug in hybrid vehicle (PHEV) fuel economy and high emissions. Quick rise of battery temperature is not only important to mitigate lithium plating and thus preserve battery life, but also to increase the battery power limits so as to fully achieve fuel economy savings expected from a PHEV. Likewise, it is also important to raise the engine temperature so as to improve engine efficiency (therefore vehicle fuel economy) and to reduce emissions. One method of increasing the temperature of either component is to maximize their usage at cold temperatures thus increasing cumulative heat generating losses. Since both components supply energy to meet road load demand, maximizing the usage of one component would necessarily mean low usage and slow temperature rise of the other component. Thus, a natural trade-off exists between battery and engine warm-up.

Significant amount of energy is lost in frequent braking, automatic transmission and engine idling for a conventional engine powered passenger car while driving in cities. In this paper, a mild hybrid vehicle drive train has been introduced. It uses a small electric motor with floating stator, called TRANSMOTOR and small and a battery pack. The transmotor functions as a generator, engine starter, frictionless clutch (electric torque coupler), regenerative braking and propelling. The mild hybrid drive train can effectively reduce the urban-driving fuel consumption by regenerative braking, eliminate of energy losses in conventional automatic transmission and engine idling. The drive train can use low voltage system (42V for example), due to the low electric power rating, and is more similar to conventional drive train than full hybrid vehicle. Therefore, less effort is needed to evolve it from conventional vehicles.

A fuel cell/battery hybrid system for an electric vehicle was characterized under simulated driving conditions. The fuel cell is a 72 cell stack with 270 cm2 per cell of active electrode area. It has a continuous output of 1500 Watts and a peak power of 3000 Watts operating on hydrogen and atmospheric pressure air. The batteries are a tubular flooded lead-acid type. Seven 6 volt modules were connected in series with each module having a normal capacity of 205 Ahr. The fuel cell battery hybrid system was laboratory tested using a variable load battery cycler to simulate electric vehicle operation over a Modified Simplified Federal Urban Driving Schedule (MSFUDS). The fuel cell/battery hybrid operated successfully under steady state and dynamic conditions with the performance of the fuel cell only slightly degraded under the dynamic conditions of MSFUDS compared to steady state operation.

A empirically based mathematical model of a lead-acid battery for use in the Texas A&M University's Electrically Peaking Hybrid (ELPH) computer simulation is presented. The battery model is intended to overcome intuitive difficulties with currently available models by employing direct relationships between state-of-charge, voltage, and power demand. The model input is the power demand or load. Model outputs include voltage, an instantaneous battery efficiency coefficient and a state-of-charge indicator. A time and current dependent voltage hysteresis is employed to ensure correct voltage tracking inherent with the highly transient nature of a hybrid electric drivetrain.

This paper discusses a new computer simulation tool, V-Elph, which extends the capabilities of previous modeling and simulation efforts by facilitating in-depth studies of any type of hybrid or all electric configuration or energy management strategy through visual programming and by creating components as hierarchical subsystems which can be used interchangeably as embedded systems. V-Elph is composed of detailed models of four major types of components: electric motors, internal combustion engines, batteries, and vehicle dynamics which can be integrated to simulate drive trains having all electric, series hybrid, and parallel hybrid configurations. V-Elph was written in the Matlab/Simulink graphical simulation language and is portable to most computer platforms. A simulation study of a sustainable, electrically-peaking hybrid-electric vehicle was performed to illustrate the applicability of V-Elph to hybrid and electric vehicle design.