Zero Torque Control for EV Coasting Considering Cross-Coupling Inductance

Abstract

Coasting is a deceleration driving mode not recurring to an active braking while sustaining rolling as much as possible. In an electric vehicle (EV), coasting should be realized in theory by letting the $q$ -axis current set to zero. However, unintentional braking takes place at high speeds when the gas pedal is tapped off. The reason is that negative torque is developed even when the $q$ -axis current is equal to zero. Such a braking reduces the coasting distance. To prevent undesirable braking, positive $q$ -axis current is often utilized in practice. In this paper, we focus on a braking torque component caused by a cross-coupling inductance $L_{qd}$ . It is produced only by the $d$ -axis current, and is normally small. However, its magnitude becomes noticeable in a deep field-weakening region. As a curing method, it is suggested to shift the angle of the reference frame clockwise. The magnitude of compensation angle is derived analytically using two different methods. The proposed compensation method was demonstrated by simulation and experiments.