Low frequency sensorless field oriented control of an induction machine fed by a direct matrix converter

The main open problem in sensorless Field Oriented Control is to achieve orientation at very low frequency due to the low back-EMF signal, affecting the capability of any observer structure to estimate flux and speed. This problem is worsen by the converter non-linearities, like voltage drop and dead-time in VSI, that become significant at low frequency. This problem restricts the sensorless operation of nay drive to medium and high frequencies. On the other hand, Matrix Converters have received increasing attention recently and their benefits are still being studied. One of this benefits is the capability to synthesize better sinusoidal voltages, having an almost linear behaviour when controlled with four step commutation. Furthermore, the small commutation error of the four step commutation strategy has been characterized in literature and can be compensated. In this paper, the low speed performance of a sensorless vector controlled Matrix Converter drive is studied experimentally and the effects of the compensation of the device voltage drop and commutation error is evaluated. The well known extended Kalman filter (EKF) structure is used as state observer.