Speed and load torque observer for rotating machines

For the sensorless control of a rotating machine the estimation of speed is required. A speed encoder is undesirable in a drive because it creates cost and reliability problems, and sometimes it also requires shaft extension and mounting arrangements. Traditional methods for estimation of speed include approximate derivatives and numerical differentiations. In this paper a solution to the speed observer problem for a general rotating machine is provided. The speed observer is designed following the Immersion and Invariance technique and it is shown to be globally convergent. Simulation results to compare the proposed observer with the approximate differentiation approach are presented.