Feedback Control of Doubly-Fed Generator Connected to Current Source Converter

Doubly-fed induction generator (DFIG) system supplied by current source converter (CSC) is considered in this article. The DFIG can work in two independent modes: AC grid connection and stand-alone mode. The DFIG is connected to the ac grid directly through its stator and the CSC links the rotor side. In this mode, the active and reactive powers of the DFIG must be controlled. This article proposes two control system structures for the DFIG working in the generator mode. Both control structures are based on nonlinear transformations but on different state-feedback control variables. The selection of the variables is similar to the input-output linearization but more complicated due to the CSC and "voltage control" involved. Both proposed control structures ensure independent control of the active and reactive powers with different accuracies; as evidenced in the simulation and experimental results. The proposed approach can be named by voltage control of the DFIG because the control variables are the voltage in the dc-link and the angular speed of the output current vector from the inverter. For both proposed control structures, the current in the dc-link is not a constant value, but depends on the dynamic states and values of the controlled powers; thus, it varies accordingly. The proposed control strategy can be applied to low- and high-power DFIG systems. Simulation and experimental results from a 2-kW generator validate theoretical propositions.