Direct torque control of machine side multilevel converter for variable speed wind turbines

Nowadays, wind turbine capacities are increasing rapidly. New capacities of 5 MW wind turbines now exist and yet are still increasing continuously, especially for offshore wind turbines. Generation voltage has been increased to comply with the new power. MLC (Multilevel converter) is used to decrease switching voltage to an acceptable level. In this paper, diode clamped three level, as well as, four level converters with DTC (direct torque controller) for the machine side converter with PI (proportional integral) controller is used. This technique enhances the performance of the induction generator torque, current, flux, speed, active and reactive power during start up and wind speed variations. Moreover the THD (total harmonic distortion) is decreased compared with the classical two levels converter without the need of using complex controllers. The simulation is done using Matlab/Simulink SimPowerSystems for the 5 MW wind turbine. (C) 2015 Elsevier Ltd. All rights reserved.