Impact of Background Harmonic on Filter Capacitor Reliability in Wind Turbine

Pulse width modulation converters are now used in many grid-connected application. A filter is normally inserted between the converter and the power grid to reduce the switching harmonics. Since the wind power is normally linked to the power grid through a long transmission line, the grid voltage becomes distorted and contains lower-order harmonics. By using the separated models of fundamental component, low-order, and high-order harmonics, the electrical stresses of the filter capacitor can be comprehensively evaluated. The performance of the Proportional-Integral (PI) and the Proportional-Integral-Resonant (PIR) current regulator have been analyzed with different grid distortion levels, and loading conditions. A case study of 2 MW wind power converter shows that, by using the conventional PI current control, the capacitor lifetime is considerably reduced if the background harmonic exists all year around. Nevertheless, the PIR current regulator can eliminate the additional electrical stresses of the filter capacitor caused by the background harmonic and is thereby a better solution.