Nonlinear high-gain observer design for operation of SPM machine under saturation using back EMF method

This paper presents modeling, characterization and control of SPMSM under loaded conditions e.g. saturation. Determining the rotor flux position of PMAC machines under no-load is simpler since it flux and rotor position coincide. However under load condition, and in the presence of saturation in particular, the flux is comprised of two components: one due to the rotor magnets and the other due to the stator current. This fact causes the magnetic axis to shift from the rotor position, which in turn causes an error in a control algorithm that uses a conventional rotor position estimation. This paper characterizes this error through a non-linear model of the machine, as well as the finite element analysis. Design and analysis of a general position observer algorithm for PMAC machines, which accounts for saturation is presented, along with its implementation for a control method using back EMF. Simulation and experimental results validating the non-linear model of the machine, existence of the saturation induced error, and performance of the proposed observer are also given.