Abstract：Low frequency transmission was adopted in the sending end of wind power farm，in order to reduce

line impedance and charging current of distributed capacitance，improve the static stability limit and transmission

capacity. Compared with using flexible DC converter valves to send power and connect to grid，modular multi-level

matrix converter（M3C）variable frequency valve was adopted to connect power grid in the receiving end，in order

to omit the converter valve in the sending end and save cost. In the wind power low frequency transmission system，when power frequency grid fault occurred，active power transmission capability was dropped severely，the voltage of low frequency side can hardly respond instantly，and wind turbines had mechanical inertia，braking resistors in low frequency side of M3C were switched on to consume the redundant power of wind power farm，injecting reactive power to the power frequency fault point at the same time. When low frequency bus fault occurred，wind power converters ran to fault ride-through mode，low frequency side of M3C was converted to current source mode from voltage source mode，injecting the reactive power to support voltage. At last，330 MV·A M3C model was built in Matlab/Simulink，the effectiveness of fault ride through strategy of low frequency transmission system was validated.

      Key words：modular multi-level matrix converter（M3C）；power frequency fault ride through；low frequency

fault ride through