Direct Virtual Torque Control of DFIG grid connection using Indirect Matrix Converter

This paper presents a new Direct Virtual Torque control (DVTC) for synchronization and grid connection of Doubly Fed Induction Generator (DFIG). DFIG is linked to the grid within the stator and rotor is fed by an Indirect Matrix Converter (IMC). Function of IMC is similar to the direct one, although it has the line and load bridges separated. IMC has low volume compare to conventional back to back converter because of elimination of dc link capacitor. The usage of four-step commutation in rectifier stage of IMC is analyzed to achieve the object of the losses´ reduction which is caused by snubber circuit. In proposed synchronization method, grid voltage is measured to calculate virtual flux and torque without needing to measure the stator voltage. For meeting equal condition between the stator voltage and grid voltage frequency and phase, the virtual torque reference is set to zero. The reference of rotor flux uses to meet equality condition between stator voltage and grid voltage magnitude. Simulations results confirm effectiveness of the fast and soft grid-connection.