Abstract
To achieve asymmetric fault ride-through (FRT), it is crucial to limit the overcurrent for both the grid-forming modular multilevel converter (MMC) and the grid side converters (GSCs) of wind turbines. Compared with the MMC, GSCs enable better system stability when providing negative sequence paths, while the overcurrent can occur due to the negative sequence current. To address this issue, a negative sequence overcurrent suppression method is proposed, which introduces a negative sequence voltage proportional current control in each GSC. The redistribution of negative sequence currents is achieved in the manner that each GSC (filter included) is equivalent to a resistor with resistance determined by the proportional coefficient. Through this control, the negative sequence current can be evenly distributed so that the overcurrent can be effectively suppressed. Finally, simulations are performed in MATLAB/Simulink to verify the validity of the proposed negative sequence overcurrent suppression method.
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