Variable-Speed Wind Turbines with Doubly-Fed Induction Generators Part IV: Uninterrupted Operation Features at Grid Faults with Converter Control Coordination

Abstract

A model of variable-speed wind turbines equipped with doubly-fed induction generators (DFIG) and controlled by partial-load frequency converters described in [1,2] is applied in power stability investigations. A technical feature of uninterrupted operation at grid disturbances of large wind farms with such variable-speed wind turbines is suggested and discussed. This technical feature is based on fast re-start of the rotor converter, which blocks at grid faults. The main reactive power control is organised by the rotor converter [3]. The new part is that reactive power is controlled by the grid-side converter when the rotor converter blocks. Possible discrepancies between the results reached with the detailed representation of the frequency converter and the representation where only the rotor converter is regarded are notified and explained. The converter representation details influence on the machine current transients modelled at grid disturbances and also on damping characteristics of torsional shaft oscillations.

Damping for Wind Turbine Electrically Excited Synchronous Generators

“…According to (13) and (14), the bode plot of the closed loop torque transfer function is derived as shown in Fig. 6.…”

“…In [12], the rotation speed feedback algorithm is introduced to reduce the speed variation of the generator. Akhmatov [13] indicated that the pitch control method was not suitable to prevent mechanical resonance because its bandwidth was much lower, and the effective method was to utilize the electromagnetic torque. Hua Geng [14] compared the mechanical damping performances of three power control strategies for the PMSG.…”

Control of Grid Voltage and Power of Doubly Fed Induction Generator wind turbines during grid faults

“…[11] shows that absence or insufficient tuning of this PI controller may lead to self-excitation of the drive train system and to a risk of grid power tripping as protection against vibrations in the mechanical construction. The pitch control system is not able to damp the torsion oscillations, because of several delay mechanisms in the pitch [12]. The pitch control damps the slow frequency variations in the generator speed.…”

Grid voltage control by using DFIG during grid faults

“…The pitch control system is not able to damp the torsional oscillations, because of several delay mechanisms in the pitch [12]. The pitch control damps the slow frequency variations in the generator speed, while the damping controller is able to damp the fast oscillations in the generator speed.…”