A critical study of modulation techniques for three level Diode Clamped Voltage Source Inverter for grid connection of WECS

This paper presents a critical study of modulation strategies for three level Diode Clamped Voltage Source Inverter (DCVSI) for grid connected wind turbine. The survey is carried out on two types of modulation techniques popularly used in three level DCVSI, viz. Sinusoidal PWM and Space vector PWM. Purpose of the survey is to critically analyze and identify the problems associated with existing DCVSI used in grid connection. It is observed from the study that the three level DCVSI suffers from narrow pulse width and capacitor voltage imbalance, which would be more predominant with higher rated wind turbine. Further this problem results in inefficient performance of DCVSI, there by affecting the power quality. The study also reveals that the existing modulation techniques, even though popular in drive application, fail to meet the present requirements of grid connection. Observations from the study will be of much use to investigators, to develop modulation strategies to overcome the said problems for grid connection of wind turbines. This study is part of research project entitled "Development of FPGA-DSP Controlled Multilevel Inverter Interface for Grid Connection of Wind Turbine Generators" funded by All India Council Technical Education (AICTE), New Delhi, India.