Nonlinear high-gain observer design for operation of SPMS machine under saturation

This paper presents modeling, characterization and control of SPMSM under loaded conditions i.e. saturation. Determining the rotor flux position of PMAC machines under no-load is relatively trivial since it is directly related to the rotor position. However under loaded condition, 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 any control algorithm that uses a conventional rotor position estimation. In other words, the rotor flux position under loaded operating conditions is dependent on both rotor position and stator currents. 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 control algorithm for the PMAC machines which accounts for the saturation is presented, along with its implementation for a specific high frequency injection method for sensor control of PMAC machine. 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.