Abstract: Low voltage ride through capability is one of the most challenging requirements to the wind power generation unit in the operating instruction for wind farms all around the world. The performance of the wind power generation unit in the course of the low voltage ride through and the magnitude of the current not only relates to type of the failure, but also to the phase of power grid voltage while the fault occurs. To research and measure the low voltage ride-through performance of wind power generation unit under the most serious failure situation, adopting AC contactless switch an impedance form based power network voltage asymmetrical sag generator was developed to absorb the overvoltage at both ends of insulated gate bipolar transistor (abbr. IGBT) by the absorbing circuit composed by resistance-capacitance-diode (abbr. RCD), besides, the phase angle of power network voltage was computed by the improved arctangent function and the single-chip microcomputer was used as the controller. Experiment results show that the developed device can fairly accurately simulate the fault of power network voltage asymmetrical sag at the given phase angle of power network, and it possesses such advantages as simple in structure, convenient to achieve, relative low manufacturing cost and good practicability.