An effective method of regenerative braking for electric vehicles

Batteries are commonly used as the power source of plug-in electric vehicles. Low efficiency in a battery is responsible for the low-mileage of electric vehicles. Improving battery efficiency can be done by harvesting the energy wasted during braking, which is commonly called as regenerative braking. The braking energy is to be used to recharge the battery. However, this braking method is not implementable in some conditions, including the conditions when the battery is full, when the vehicle speed is very slow, and when the desired braking currents exceed the converter capability. Therefore, mechanical braking is also still required. This paper proposes a simple but effective technique to deal with the problems found so far in the regenerative braking implementation. The fuzzy-logic theory is implemented to control the sharing proportion between the use of regenerative and electric brakings using one single brake-lever. To improve the current response of electric braking, the proportional-integral control method is used. Being compared to the widely used braking techniques, the method proposed and explored through simulation in this paper offers double advantages, which is increasing the battery efficiency as well as the driving comfort and practicality. The implementation of the method can extend the battery life because the energy regeneration is adapted to the state-of-charge and charging capability of the battery so that the battery can be maintained not to be overcharged.