Speed, Rotor Position and Load Torque Estimation of the PMSM using an Extended Dynamic Model and Cascaded Sliding Mode Observers

The paper presents a method to estimate the rotor position, speed and load torque of the PMSM drive. The estimation is done using cascaded sliding mode observers (SMOs) and uses an extended dynamic model of the PMSM. A first SMO is constructed based on the current equations of the motor and estimates the EMFs; these are used to calculate the rotor position angle. The EMFs are also fed in a second SMO that estimates the speed and the load torque of the PMSM drive. The paper presents the design and analysis of the observers. In order to obtain accurate estimates, both observers are implemented using the second order sliding mode approach. It is shown that the estimates of the speed and torque are accurate both during transient and at steady-state. The method can be used in a sensorless PMSM implementation if an estimate of the load torque is available, this allows to improve the response of the speed loop. The theoretical findings are supported with simulations.