Current measurement of digital field oriented control

Abstract

This paper studies current measurement issues of all digital field oriented control of AC motors. The paper focuses on the effect of an antialiasing filter and also on the sampling of the fundamental components of the motor current. The antialiasing filter, which suppresses the high frequency component of the motor current, introduces cross coupling effects on the D and Q axis current regulation and limits the bandwidths of the current regulator because of its phase lag. In this paper a novel sampling technique is proposed to sample the fundamental component of the current without the antialiasing filter. It is based on the characteristic of the symmetry pulse width modulation. With this technique, the bandwidth of the current regulator can be extended to the limit given by switching frequency of the inverter and more precise torque regulation is possible.