Sensorless speed estimation in induction motor drives

A new approach is proposed in the present paper to perform an indirect speed estimation on sensorless field oriented induction motor drives. It is based on the injection of a suitable high frequency current test signal, that causes a small oscillation of the rotor flux angular frequency and the generation of a zero sequence stator voltage component. The motor speed can be expressed as a function of only the ripple generated on the rotor flux angular frequency and stator current components. Therefore, the amplitude of the ripple on the rotor flux angular frequency is directly measured from the frequency of the zero sequence voltage component and used to indirectly estimate the rotor speed in any operating conditions, including no load and zero stator frequency. Speed estimation according to the proposed approach is fully insensitive to motor parameter variations, features a large bandwidth and can be used on either IFOC, DFOC and DTC sensorless schemes.