Identification of Moment of Inertia in Sensorless PMSM drive at Quasi Stand-Still

Permanent Magnet Synchronous Motors (PMSMs) have been increasingly employed in many industrial applications recently, thanks to their high-power density, high torque-to-inertia ratio, and high efficiency. State and parameter estimations of PMSM are a key factor that influences the performance improvement and efficiency of the motor control systems. High-performance and reliable operation of PMSM drive demands the precise identification of electrical and mechanical parameters. Identification of the mechanical parameters, such as moment of inertia and viscous friction coefficient are critical for design of the speed-loop controller.In this paper, a technique for identifying the moment of inertia of a PMSM with attached load is proposed, which operates at quasi stand-still operation (i.e. small rotor movement) and does not exploit position measurement (i.e. suitable to sensorless drives). A current vector with constant amplitude and varying angle is imposed to the stator, causing a mechanical oscillation with limited rotor movement, which in turn generates a back-EMF signal. By processing the inverter voltage reference, the inertia is identified based on estimated oscillation period. A mathematical model is developed to approximately describe the generated back-EMF under this peculiar condition. Simulation and experimental results provided on a PMSM confirm the validity of the proposed method.