Impacts of rotor current control targets on DC-link capacitor lifetime in DFIG-based wind turbine during grid voltage unbalance

In doubly-fed induction generator (DFIG)-based wind turbines, the DC-link capacitor of the back-to-back (B2B) converters is one of the components that tend to fail most often. The equivalent resistance of electrolytic capacitors is frequency dependent and presents higher values in the low-frequency range. Therefore, additional low-frequency ripple current components will stress the DC-link capacitor and reduce its lifetime. Under unbalanced grid voltage conditions, the conventional vector control strategy of the rotor side converter may be replaced by flexible multi-objective control strategies, leading to different low-frequency harmonics in DC-link capacitor current. Therefore, in this paper the differences between the different control targets with respect to overall RMS current, additional low-frequency ripple current and temperature are analyzed by means of simulations for a 2 MW DFIG wind turbine.


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