Description

This paper proposes a switching angle controller (SAC) and an automatic generation controller (AGC) for the doubly-fed induction generator (DFIG) to control the frequency of DFIG-based wind power penetrated power systems (WPPSs). The concept of virtual rotor angle of the DFIG is defined. The virtual rotor angle is controlled by the SAC in a bang-bang manner such that the active power of the DFIG is regulated to provide frequency support to the external power grids. The output of the SAC is also used for the control of pitch angle to offer a short-term regulation of the mechanical power input to the DFIG, and the long-term control of the mechanical power input is achieved with the AGC. Small-signal analysis is undertaken to verify the effectiveness of the SAC and the AGC. Simulation studies are carried out in a two-machine power system and a modified Kundur four-machine two-area power system, respectively. The frequency support performance of DFIGs having different control configurations is investigated. Modal analysis is undertaken to evaluate the effect of the SAC and the AGC in providing additional damping to the rotor oscillation modes of the modified Kundur four-machine two-area power system.