Creative usage of stator flux linkage to fast brake electric vehicles

Abstract

Kinetic energy has to be rapidly transferred or dissipated in order to quickly brake an electric vehicle. In electric vehicles, a finite amount of kinetic energy can be transferred to the battery. Motor braking capability is fundamentally limited by the maximum charging rate and the state-of-charge of the battery. This paper presents a methodology to manipulate system losses such that the additional kinetic energy can also be dissipated in the motor and the inverter, eventually in the cooling system. To do this, stator flux linkage is dynamically varying while torque control accuracy is not compromised. The achieved additional torque can assist to brake electric vehicles faster with fully-charged batteries, as well as in emergency situations. The maximum braking torque is affected by the current limit, DC bus voltage and the peak power that energy storage system can absorb. Analytical and experimental evaluation is provided to quantitatively examine the additional braking torque.