Regenerative Braking is a type of electrical braking system.
In shunt Motors,when running in general normal condition .Now if due to,say,hauling load,speed increases above normal due to increase in speed the induced emf will increase and if it exceeds the line voltage,the machine will start supplying current to the line,thus have tendency to prevent any further increase in speed.(i.e.,when back emf E>V,therefore,armature current become negative.The motor drive,then acts generator which provides the braking torque.)
Mazda recently introduced a new regenerative braking system that powers the car�s electrical functions as the vehicle brakes. The system is called i-ELOOP � or �Intelligent Energy Loop". I believe it is a unique technology that makes an internal combustion automobile behaves in a manner comparable to a hybrid.I've read the article here:New Mazda regenerative braking system to roll out