A versatile method for computation of power pulsations in DFIG under grid imperfections

Highlights

Computation of power pulsations under grid imperfections.

Computing using measured stator voltages and currents.

Free from flux estimation, rotor position or machine parameters.

Accurate computation under voltage sag, dc offset, harmonics and phase jump.

Simple & straight forward method with worst case steady state error less than 3%.

Abstract

In the context of a Doubly Fed Induction Generator (DFIG) connected to the utility grid under unbalanced voltage conditions, the controller design needs to ensure additional challenges such as restricting the Total Harmonic Distortion (THD) in grid current, minimizing the pulsations in generated power, torque, dc link voltage etc. apart from facilitating the generator power control. Thus the schemes for generating reference currents for rotor converters need to incorporate a measure of power pulsations to what is required for steady state power flow control. This paper proposes a versatile scheme for computing the power pulsations in a DFIG connected to grid under unbalance voltage conditions. The active and reactive power oscillations are computed in a simple and straight forward manner using the measured stator voltage and currents in the positive d-q frame without using flux estimation. The scheme is free from flux integration or differentiation, rotor position computation and independent of machine parameters. Further, the worst case error in computation is bound within 3% considering 30% voltage dip, 7% of harmonics, ±10°phase jump or ±10% dc offset in the grid voltage. The effectiveness of the scheme is validated through PSCAD/EMTDC simulations and experimental results for a 2.3 kW DFIG test setup.

Keywords

  • Direct Power Control (DPC);
  • Doubly Fed Induction Generator (DFIG);
  • Power oscillation computation;
  • Grid imperfections

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