Speed and rotor position estimation of the PMSM by cascaded sliding mode observers with single and double compound manifolds

The paper presents a method to estimate the EMFs and the speed of the permanent magnet synchronous motor (PMSM). The method uses only the measured voltages and currents of the motor; estimation is done using cascaded sliding mode (SM) observers. A first observer estimates the EMFs of the motor in the stationary reference frame; these are obtained by filtering the manifolds of the SM observer. The EMFs are passed to a second SM observer that estimates the speed and re-estimates the EMFs. The method is applicable in sensorless speed controlled PMSM drives where the EMFs are used to obtain the rotor position angle and the estimated speed is used for feedback. The paper discusses the EMF observer - this is a SM design that uses simple manifolds. Then, two versions of the speed observer are presented: the first design uses a single compound manifold; the second uses two manifolds. For both speed observers, the estimated speed of the PMSM is obtained by filtering the switching manifolds of the observer. The theoretical developments are supported with simulations.