Coordinated control for the series grid side converter-based DFIG at subsynchronous operation

Abstract

Connecting the Grid Side Converter of Doubly Fed Induction Generators (DFIG) in series presents some advantages compared to the traditional parallel connection. The series converter acts as a Dynamic Voltage Restorer, improving the DFIG capability to deal with disturbances in the grid, specially symmetric and asymmetric faults. However, a drawback of this scheme is to control the power during subsynchronous speeds. For this operating condition, the stator voltage should be higher than the grid voltage, which may result in machine saturation. This paper proposes a control strategy for the series-based DFIG to avoid the need of the stator voltage from being higher than the grid voltage. The proposed solution for this issue is based on phase shifts of the voltages and currents and a coordinated control, considering several wind turbines, to achieve a unity power factor at the point of common coupling of the wind farm. The proposed solution overcomes the saturation problem, as it does not depend on the stator voltage magnitude variation. The validation is performed by computational simulations using the MatLab Simulink environment.