Accurate inverter error compensation and related self-commissioning scheme in sensorless induction motor drives

The inverter non-linear effects limit the performance of Sensorless Field Oriented Control (SFOC) of Induction Motor (IM) drives. When no direct voltage measurement is available and the reference voltages are used instead, the problem relies in the non-linear error that affects the motor back-EMF estimation. The back-EMF signals are fundamental for estimating the motor flux in most of SFOC schemes, either oriented on the stator flux or on the rotor flux. Many methods have been proposed for compensating such non-linearities (IGBT dead-time and on-state voltage drops) by means of the digital control algorithm. In many references the compensation relies on an inverter model based on the signum function of the motor phase currents. In the considered cases, the identification of the compensation parameters is performed off-line, often with additional processing tasks. Very few schemes are integrated into the control code of the IM drive. The goal of the paper is to present a model of the inverter non-linear effects that is more accurate than the signum-based one, and the related self-identification method. The proposed inverter model can be identified directly by the digital controller at the drive start-up with no extra measures other than the motor phase currents and dc-link voltage. After the commissioning session, the compensation does not require to be tuned furthermore and is robust against temperature detuning. The identification is based on the feedback signal of the closed-loop flux observer in dc current conditions. The experimental results, presented here for a rotor flux oriented SFOC IM drive for home appliances, demonstrate the feasibility of the proposed solution.