Comparison of a linear and a non-linear state observer for sensorless control of PM machines

This paper presents two different state observers for position-sensorless control of permanent magnet synchronous machines (PMSMs). Both methods improve the angular rotor position and determine the machine speed of a back electromotive force (back-EMF) model [1]. The Arctan observer calculates the electrical rotor position from real and imaginary flux-linkage components with a common arctangent function. A novel observer with non-linear feedback coefficients, called Sin/Cos observer, omits this calculation and improves the quality of the position information. Dynamic measurements on an outer rotor traction machine [2] verify the characteristics of the presented observer techniques.