Direct Power Control of DFIG With Constant Switching Frequency and Improved Transient Performance

This paper proposes a new direct power control (DPC) strategy for a doubly fed induction generator (DFIG)-based wind turbine system. The required rotor control voltage, which eliminates active and reactive power errors within each fixed time period, is directly calculated based on stator flux, rotor position, and active and reactive powers and their corresponding errors. No extra power or current control loops are required, simplifying the system design, and improving transient performance. Constant converter switching frequency is achieved that eases the design of the power converter and the ac harmonic filter. Rotor voltage limit during transients is investigated, and a scheme is proposed that prioritizes the active and reactive power control such that one remains fully controlled while the error of the other is reduced. The impact of machine parameter variations on system performance is investigated and found negligible. Simulation results for a 2 MW DFIG system demonstrate the effectiveness and robustness of the proposed control strategy during variations of active and reactive power, machine parameters, and wind speed

I. Nomenclature

Stator flux, rotor angles in the stationary frame.

Phase angle between the rotor and stator flux vectors.

Synchronous, rotor, slip angular frequency.

Stator, rotor flux vectors.

Stator, rotor current vectors.

Mutual inductance.

Stator, rotor leakage inductance.

Stator, rotor self-inductance.

Stator, rotor resistance.

Stator active and reactive power.

Stator, rotor voltage vectors.

Superscripts

Synchronous reference frame.

Rotor reference frame.

Reference value.

^

Conjugate complex.

Subscripts –

– axis.

Stator, rotor.

Synchronous – axis.