Analysis and filtering of common mode and shaft voltages in adjustable speed AC drives

In this paper, the effects of a variable speed drive on the motor are discussed. The most typical filtering techniques are presented. A resonant LC-circuit based filter equipped with clamping diodes is introduced in more detail. The performance of the filter and the effect of the filter neutral point connection is analyzed and verified by measurements. A coaxial instrument for measuring shaft voltage is presented. The effect of the filter and common mode voltage is investigated by shaft voltage measurements.