Efficiency improvement of a sliding-mode controlled induction motor by flux removal

A method to calculate a trajectory for the rotor flux is presented. This trajectory corresponds to an electromagnetic transition of the induction motor which links without any discontinuities, or electromagnetic transients, to the preceding and the succeeding steady state of the motor. The way the trajectory is presented differs from the known field-oriented control, but the result can be translated into the field-oriented d- and q-components of the stator current. Cost functions are derived to calculate the optimal shape of the rotor flux trajectory to achieve the lowest power peak. The shape of the trajectory is calculated for the sliding-mode positon drive. An experimental induction motor position drive was built using the sliding mode control technique. The sliding mode is equipped with a band around the sliding line for which the torque and rotor flux are zero. When the rotor axis moves inside this band, all electrical power, copper, and iron losses are avoided. During the experiments, an energy loss of 42% resulted as compared with the standard sliding-mode control