Keywords: sensorless control, permanent magnet synchronous motors, PMSM, induction motors, rotor position estimation, rotor flux angle estimation, sliding mode control, observer design, speed estimation, simulation
Sensorless observers with speed estimate for direct field orientation of induction motor and PMSM drives
The paper discusses the problem of sensorless rotor position/rotor flux angle estimation for the permanent magnet synchronous motor (PMSM) and for the induction motor (IM) and presents a family of sensorless observer designs that use a speed estimate. In sensorless field–oriented AC drive control, it is typical to measure the motor's voltages and currents and to estimate the other quantities of interest: speed, fluxes (or EMFs) and the field orientation angle. The simultaneous estimation of these quantities is possible, however, the methods available are rather complicated and the accuracy is often questionable, especially under parameter variations. The paper proposes a sequential estimation approach which is much simpler: first, estimate the drive's speed; then, use this speed estimate along with the measurements to estimate the states of the motor model and to obtain the field orientation angle. A family of observers for the IM and the PMSM is presented - these are constructed using the respective motor models in the stationary reference frame. The observers are developed assuming that the speed estimate obtained is different from the real speed; it is shown that despite this inaccuracy, with special gain designs, the correct field orientation angle is obtained. The estimators are based on sliding mode and/or non–linear Lyapunov design methods. They can be directly used in sensorless field–oriented drives that do not require the magnitude of the flux. The theoretical developments are supported with simulations and with experimental tests.