Multi-level DC-AC converter in variable-frequency electric motor drives

Abstract

Variable frequency motor drives (VFDs) have demonstrated remarkable potential to improve the operation and control of electric motors, along with reducing energy consumption (by electric motors) and minimizing carbon footprint. However, they can cause physical damages to the motor bearings and shaft due to common-mode voltages (CMVs) and common-mode currents (CMCs). The CMV and CMC are created due to the presence of harmonic components in the motor stator voltages when supplied by a dc-ac power converter. Multi-level power electronic converters (ML-PECs) increase voltage and power ratings while reducing harmonic distortion at low switching frequencies. Such features can be advantageous for VFDs, where CMVs and CMCs can be reduced and their damaging impacts can be minimized. This research aims to investigate the ability of 5-level and 7-level ML-PECs to reduce CMVs and CMCs in induction and permanent magnet motor VFDs, considering the impacts of switching frequency, number of levels, speed, and torque.