Harmonics and common mode voltage in a DFIG with two-level and three-level NPC converter using standard PWM techniques

This paper investigates harmonics performance and common mode voltage (CMV) of three-level neutral point clamped (NPC) back-to-back voltage source converter (VSC) using standard pulse width modulation (PWM) techniques for the application of doubly fed induction generator (DFIG) based wind turbine (WT) and provides a comparison with two-level back-to-back VSC. These two converter topologies are reviewed and the principle of switching instants generation methods is explained. Based on carrier based technique, phase disposition (PD) method and phase opposition disposition (POD) method for the three-level NPC converter are applied. Results show different level of harmonics performance for each different PWM type, and POD method for the three-level NPC converter produced the highest reduction of CMV. These results help in the intelligent choice of the appropriate PWM type for the DFIG application with reduction in CMV while remaining less harmonics distortion.