A new method of compensating harmonic currents for wind power generation systems with the soft starter using a hybrid active filter

This paper proposes a new method of compensating harmonic currents for wind power generation systems with the soft starter using a hybrid active filter. The hybrid active filter consists of single-tuned LC and small-rated active filters. The single-tuned LC filter absorbs the harmonic current while behaving as a phase-leading capacitor for the fundamental component. The small-rated active filter improves the compensation characteristics of the passive filter under the soft start of the constant-speed wind turbine. The required rating of the active filter can be reduced because the active filter does not supply the fundamental reactive current. The basic principle of the proposed compensation method is discussed, and then confirmed by digital computer simulation using PSCAD/EMTDC. Simulation results demonstrate that the waveform of the source current becomes sinusoidal under the soft start. The required rating of the active filter is about 8.5% of the induction generator rating. A new calculation method of THD with the detrending algorithm is proposed for the transient state. The THD of the source current is about 7.3% using the hybrid active filter.