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As the penetration of large-scale grid-connected wind farms increasing year by year, low voltage ride-through (LVRT) capability has been an extremely important criterion for grid-connected wind farms required by many countries to improve power quality at grid fault. A new dynamic voltage restorer (DVR) topology based on modular multilevel converters (MMC) is proposed in this paper to improve LVRT capability of wind farms. Related control strategies and pulse width modulation (PWM) method are also proposed, to keep wind farm terminal voltage normal and voltages of MMC fly-capacitors in balance during voltage sag period; a special energy sharing topology is applied on DC sides of the device, three phase DC bus voltages can kept in balance through the given control strategy. PSCAD/EMTDC simulations are carried out to prove the effectiveness of the proposed technique and some related conclusions and comments are summarized.
Date of Conference: 25-28 Oct. 2012