A new dual series-connected Nine-Switch Converter topology for a twelve-phase induction machine wind energy system

This paper introduces a new transformerless converter topology for Multiphase-Based Wind Energy Conversion Systems (WECSs). In this topology, a twelve-phase induction generator is integrated to the grid using dual Nine-Switch Converters (NSCs) connected in series forming a high voltage cascaded dc-link. For this generator phase number, this topology reduces the total number of semiconductor devices in the machine side converter by 25% than conventional topologies, where four three-phase two-level voltage source converters are typically needed. Moreover, it offers a high ac-dc boosting capability, which facilities a transformerless system operation. The twelve-phase induction generator can be regarded as dual symmetrical six-phase windings with a spatial displacement of 30°. Therefore, each NSC controls each six-phase winding set. The dc-link midpoint balancing is achieved based on controlling the (x-y) current components of the two winding groups. The proposed topology and its control system are analyzed and simulated under different operating cases using MATLAB/SIMULINK.