Sensorless position control of permanent magnet drives

Permanent magnet motor drives require absolute position information so that individual phase currents can be modulated in synchronism with the rotor. The eradication of such sensors has been the subject of many publications. This paper describes the principles and implementation of a new algorithm for combined flux-linkage and position estimation in permanent magnet motors. The algorithm uses the machine's flux-linkage versus current versus position characteristic and thus is able to take account of machine nonlinearities. The position estimator utilises the characteristic in a generalised nonintrusive estimation scheme, which is effective over the whole range of operating conditions. The paper shows implementation of the observer as embedded code in a DSP based drive system. All experimental results show for the first time the closed loop, sensorless, performance of the algorithm under steady state and transient conditions.