W. Staffler, M. Schrödl:
"Sensorless Control of PM synchronous machines in the whole speed range using a novel load torque observer and a combined INFORM / EMF-Model";
Talk: International Conference on Power Electronics and Intelligent Motion (PCIM), Nürnberg, Germany; 05-04-2010 - 05-06-2010; in: "International Exhibition&Conference for Power Electronics Intelligent Motion Power Quality", (2010), 1 - 7.

The paper describes an extended mechanical observer structure in combination with an enhanced voltage
model for sensorless control of permanent magnet synchronous machines (PMSM) working stable in the
whole speed range. Depending on the speed range, two different feedback structures are used. The paper
shows the structure and stability analysis in the low speed range. The mechanical observer estimates rotor
speed, rotor angular position and load torque. It is stabilized by INFORM measurements. The observer
output stabilizes the back EMF model even at standstill and low speed. Hence, a highly dynamic change
from low speed range to high speed range is guaranteed. Furthermore, the estimated load torque is
considered at the speed controller output as a disturbance compensation. Hence, the speed controller can
be implemented as a simple proportional element without steady-state deviation at load.