Control model design to limit DC-link voltage during grid fault in a dfig variable speed wind turbine

Cajethan M. Nwosu – Cosmas U. Ogbuka – Stephen E. Oti

   This paper presents a control model design capable of inhibiting the phenomenal rise in the DC-link voltage during grid-fault condition in a variable speed wind turbine. Against the use of power circuit protection strategies with inherent limitations in fault ride-through capability, a control circuit algorithm capable of limiting the DC-link voltage rise which in turn bears dynamics that has direct influence on the characteristics of the rotor voltage especially during grid faults is here proposed. The model results so obtained compare favorably with the simulation results as obtained in a MATLAB/SIMULINK environment. The generated model may therefore be used to predict near accurately the nature of DC-link voltage variations during fault given some factors which include speed and speed mode of operation, the value of damping resistor relative to half the product of inner loop current control bandwidth and the filter inductance.

Keywords: active damping, DC-link voltage, virtual resistor, control loop bandwidth

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