Dc-link capacitance reduction in a high power medium voltage modular wind power converter

With the increasing power rating of large multi-MW wind turbines, medium voltage power conversion is preferred in terms of high power density, reduced current level and reduced cable and switchgear cost. This paper has presented a multilevel high power converter topology suitable for 10kV, 10MW wind power conversion. A special investigation has been given to the reduction of the large dc-link capacitor of the converter, which is expensive, bulky and not reliable. The grid-side (transformer secondary side) inverter is actively controlled to compensate the single-phase pulsating power from the generator (H-bridge) side. Therefore, less dc-link capacitor is needed to smooth the low-frequency power ripple. The proposed method does not affect grid power quality, albeit introducing harmonic current in the transformer secondary side. The impact of the proposed control strategy on the converter and transformer current rating and thermal performance has also been analysed and simulated. The control scheme has been experimentally validated in a single converter cell.