An observer design for the flux of line start permanent magnet synchronous motors

The flux generated by permanent magnets is essential to the performance of the line start permanent magnet synchronous motor (LSPMSM), especially during the start-up operation. The permanent magnet is degraded with operating time due to the demagnetization phenomenon, which is principally caused by the armature magnetic field interaction and operating temperature. In the motor model, the permanent magnet flux is important since it directly affects the electromagnetic torque. This paper introduces an observer design that is aimed at estimating the permanent magnet flux of the LSPMSM from the measurement of stator currents. First, derived from the mathematical equations of the motor in the dq0 reference frame, a set of equations in state variables of stator currents, magnetic fluxes and rotor angular frequency is considered. Equations of the fluxes are analyzed with the introduction of a new flux variable that allows designing open loops to estimate the fluxes from the stator currents. Moreover, a system of equations only in the state variables of stator currents and permanent magnet flux is formulated in order to design a flux observer, which is with a constant gain. Simulation results confirm the efficiency and robustness of the designed observer.