Improved braking performance of an electric vehicle by integrating plug braking with regenerative braking.

With the increase in demand for green energy, new technologies are evolved to improve energy efficiency. One of the methods to improve energy efficiency in electric vehicles and hybrid electric vehicles is regenerative braking. As regeneration is not effective during low speeds, hydraulic braking is being used along with regenerative braking. Different control algorithms are proposed in literature for proper selection between the two types of braking. The hydraulic braking system consists of multiple pistons that provide equal distribution of braking force on the wheels. However, this can be directly achieved by providing necessary braking torque on the shaft by applying dissipative braking at low speeds using an auxiliary motor parallel to the traction motor. In this thesis, a method is proposed where two induction motors are used, one as the traction motor and other as an auxiliary motor to demonstrate braking phenomenon. Plug braking of auxiliary motor is integrated with regenerative braking of main motor by coupling both the shafts of the two motors. The advantage of this method is that force is directly acting on the shaft and hence equal braking force is distributed on all the wheels, even at low speeds. The auxiliary motor can also be used for propulsion according to the torque demand and peak regeneration current can be counteracted by the plugging current thus limiting the battery current to its range. The disadvantage is that some amount energy is dissipated during plugging for small duration at low speeds. A transient analysis implementing vector control of induction machine is performed in Matlab and the results show good braking performance.