Common-mode voltage status in three-level five-phase inverter

Abstract

The common-mode voltage (CMV) is one of the main reasons for the flow of bearing currents in induction motors (IM). This mainly leads to the bearing failure and causes severe problems. The CMV is one of the major issues in NPC inverters. It causes rise of bearing current in motor, which leads to damage and shortens the lifetime of the motor. In addition, the CMV can also be the cause for increases in electromagnetic interference issues. In this work three-level five-phase inverter (TL-FPI) is used for the study of CMV elimination because TL-FPI offers more voltage vectors than its two-level counterpart. The space vector pulse width modulation (SVPWM) technique is developed for the elimination of CMV, only those switching states are selected which give zero CMV. The selection of TL-FPI is based on availability of those voltage vectors which eliminate the CMV. There are two types of voltage vectors available in TL-FPI, via vertex and nonvertex voltage vectors. These vertex voltage vectors do not eliminate CMV, whereas non-vertex voltage vectors eliminate CMV. There are forty non-vertex voltage vectors along with one zero voltage vector available to eliminate the CMV. In this work two different methods are presented. In first method large and zero voltage vectors are selected to get CMV elimination and maximum DC link. In second method large, medium and zero voltage vectors are selected to get elimination of CMV and x-y stator plane. Both the simulation and experimental results are given to validate the methods.