In high - demanding ac drives as for example traction applications, usually, an encoder or speedsensor is needed on the rotorshaft. Replacing this sensor with speed estimation may result in lower costs and maintenance demands due to one less critical component in the system. By estimating the speed instead of measuring it is called sensorless control. The topic in this book is senorless control adopted on the induction machine (IM). Research in the area sensorless control is wide and especially control problems at low speed has been an interesting problem to solve. In this book the focusing topic is 0 Hz crossover problems, which occurs as the machine alters between motoring and regenerating drive. As sensorless control method a rotorflux estimator is adopted in a vector controlled scheme by the so - called voltage model (VM). The VM design is used for estimating the frequency by measured stator voltages and currents. The analysis here mainly considers parameter variations and instability problems, which are two important reasons for control problems at low speed. The proposed final method shows good performance both by linear and nonlinear analysis methods.