Hybrid Electric Vehicles, 2nd Edition

3HEV Fundamentals

3.1 Introduction

Hybrid electric vehicles (HEVs) have been discussed along with their rationale in Chapter 2. As noted there, HEVs are vehicles that combine an internal combustion engine (ICE) with an electrical traction system. A hybrid vehicle should contain at least two sources of energy storage devices, such as battery, gasoline tank, or hydrogen tank. Based on the energy storages devices, there should also be corresponding power conversion sources, such as ICE or electric motor, within the vehicle to convert the energy into mechanical power. The end result is that the mechanical power to the wheels can potentially (but does not necessarily have to) come from multiple (at least two) sources. The main benefit of hybrid vehicle architecture is that it allows advantage to be taken of the best operating points of the sources (i.e. source characteristics) in terms of efficiency for delivering a certain amount of power, and matching the source characteristics to the load characteristics to achieve the best overall efficiency when delivering a particular load power. Advantages offered by HEVs are:

• operating the IC engine operation at its best operating point in the engine efficiency map
• efficiency improvement through regenerative braking, which allows braking energy to be returned to some energy storage element
• less engine idling
• improved fuel economy, automatically leading to reduced emission of greenhouse gases
• reduced fossil fuel consumption
• limited amount of ...