In this paper, speed-sensorless vector control of parallel connected induction motor drive fed by a single inverter is reviewed. In electric locomotives a few electric motors propel the train. The speed sensor used in traction drive had ultra low resolution rotary encoder and the detection time was high. It is difficult to realize a fine antislip and re-adhesion control by using speed sensor. In order to overcome this problem, speed-sensorless vector control is implemented in the drive system of electric motor coach where the speed is estimated by an estimator (observer). Multi motor drive system is employed in traction drives where two or three induction motors are controlled by a single inverter on account of cost effectiveness, compactness and lightness. Under unbalanced load conditions, there is a difference of the rotor angular velocities among the motors and the system becomes unstable. To make the system stable under unbalanced load conditions, average and differential currents flowing into the stator windings and rotor fluxes of induction motor were considered. In addition, in the speed control loop different speed controllers were used in various literatures. The main focus of this paper is on different types of speed controllers and control techniques which are applied to make the system stable under unbalanced load conditions in parallel connected induction motor drives fed by a single inverter. Multiphase multi motors used in traction applications are also discussed.