Fundamentals of Regenerative Braking

One of the most important features of electric vehicles (EVs), hybrid electric vehicles (HEVs), and fuel cell vehicles (FCVs) is their ability to recover significant amounts of braking energy. The electric motors in EVs, HEVs, and FCVs can be controlled to operate as generators to convert the kinetic or potential energy of vehicle mass into electric energy that can be stored in the energy storage and then reused. A successfully designed braking system for a vehicle must always meet the distinct demand of quickly reducing vehicle speed and maintaining vehicle direction controllable by the steering wheel. The former requires the braking system to be able to supply sufficient braking torque on all wheels. The latter requires proper braking force distribution on all wheels, as discussed in Chapter 2. One of the most important features of electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV) is their ability to recover significant amounts of braking energy. In EVs, HEVs, and FCVs, mechanical friction braking systems must coexist with electrical regenerative braking. Braking energy distribution over vehicle speed in typical urban drive cycles is useful information for the design and control of a regenerative brake system. The chapter introduces two configurations of hybrid brake systems and their corresponding design and control principles. One is the parallel hybrid brake system, which has a simple structure and control and retains all the major components of conventional brakes. The other is a fully controllable hybrid brake system, which can fully control the braking force for each individual wheel, thus greatly enhancing the vehicle's braking performance on all types of roads. The chapter discusses two typical control strategies; one emphasizes the braking performance and the other the maximum regenerative braking energy recovery.