Nine-Switch-Converter-based DFIG Wind Power System and its dynamic port-current assigned approach for Low Voltage Riding Through (LVRT)

This paper proposes a Doubly-Fed Induction Generator (DFIG) Wind Power System, which is driven by the novel Nine-Switch Converter (NSC). Considering the switches in the NSC are shared by two three-phase ports, a new adapted control method is proposed to flexibly control and fully use of the current capacity of the switches. With the proposed method, the current capacity of the switches is designed to satisfy the normal condition, however at the beginning of Low Voltage Riding Through (LVRT), more current can be assigned to the rotor-side port to demagnetize the undesired flux, and during LVRT, more current can also be assigned to the grid-side port to provide the maximal reactive power to help gird voltage recovery. The proposed system and adapted control method ensure the rating capacity of the switches can be fully used in any conditions, and no extra capacity margin is required. Considering the traditional back-to-back converter requires not only twelve switches, but also extra capacity margin or additional auxiliary circuit to realize LVRT, the proposed NSC-based system is more cost-efficient.