An Inverter Nonlinearity Independent Flux Observer for Direct Torque Controlled High Performance Interior Permanent Magnet Brushless AC Drives

This paper introduces a novel flux observer for direct torque controlled (DTC) interior permanent magnet brushless AC (IPM-BLAC) drives over a wide speed range including standstill. The observer takes machine nonlinearities into account and is independent of inverter nonlinearities, dead-time and armature resistance variation at steady-states since such inaccuracies are compensated quickly by measured phase currents. Magnetic saturations in the stator and rotor cores, cross-coupling effects of flux linkages of the motor and spatial harmonics in the magneto-motive force (MMF) are all considered in the novel scheme. There is no filter; hence no delays and oscillatory responses like in conventional schemes where filters are employed to prevent integrator drift issue. Superiority of the observer when compared to the state-of-the-art schemes has been illustrated by both extensive simulations and experimental results of a 10kW IPM-BLAC machine designed for traction applications.