Control of a Back-to-Back Two-Level/Five-Level Grid Connection of a Wind Turbine

This paper proposes a new Space Vector Modulation (SVM) technique to control the grid-side inverter for improving the output power quality of a Doubly-Fed Induction Generator (DFIG) based Wind Energy Conversion System (WECS). A five-level Cascaded H-Bridge Inverter (CHBI) was used to connect the DFIG to the grid. The SVM algorithm enables controlling of the DFIG inverter which improves the quality of the output power by reducing the Total Harmonic Distortion (THD) of the generated currents and power ripples. However, the multi-level inverter has a major drawback, the even-order harmonics production, which can be overcame by controlling the five-level CHBI using this novel SVM technique generalized to N-level. The paper further presents the mechanism of this algorithm and a method to deduce the trajectories from the sequences, enabling reduction of the time and number of commutations, a better performance among several possible trajectories, and reduction of the THD rate of the DFIG output currents.