Holger Jedtberg

Back-to-back converters for wind turbine systems feature capacitors in the dc-link to maintain a stable voltage and to decouple a generator from the electric grid. The electrolytic capacitors are typically chosen for their advantages; a higher energy density and a higher capacitance at lower costs. Long-term field experiences and recorded failure data revealed that the capacitors are one of the most frequent failure reasons for the wind turbine system. The current profile of the capacitors is highly responsible for this degradation, since it determines the dissipated power of the capacitor. This paper analyzes the actual current profile in the dc-link capacitor of a back-to-back converter for wind turbine application. A power converter is also designed to generate sinusoidal current at arbitrary frequency and arbitrary dc bias voltage for testing purposes. The experimental results confirm that the proposed power converter enables us to derive the correlation between the current frequency and the temperature variation of capacitor.