Bandwidth oriented proportional-integral controller design for back-to-back power converters in DFIG wind turbine system

The Doubly-Fed Induction Generator (DFIG) system currently occupies close to 50% of the wind energy market. The vector control is the proven and state-of-the-art solution for its back-to-back power converters by using the dual-loop controller design: the inner current and the outer voltage/power. This paper focuses on the modelling of power converters and the parameters design of PI controller. According to the Bode plots, the relationship among the switching frequency, inner loop bandwidth, and outer loop bandwidth can be found. At least one tenth difference between them is necessary for the sake of either the switching harmonic mitigation or the fully decouple of the dual loops. The procedure to design bandwidth for the grid-side converter and the rotor-side converter are thoroughly addressed and explained on a real-scale 2 MW and a down-scaled 7.5 kW DFIG systems. On the basis of the relationship between the controller bandwidth and the rise time, the theoretically designed bandwidth is able to be verified in both the simulation and the experiment.