A fault ride-through circuit with a variable frequency transformer (VFT) and a control method thereof are provided, and the control method comprises: pretreating acquired voltages of grids, a voltage of a stator interface and a voltage of a rotor interface to obtain a rotor voltage DC component and a rotor voltage DC component; testing and treating a voltage frequency of a first grid and a voltage frequency of a second grid; carrying out a reference voltage calculation for a stator voltage DC component, a rotor voltage DC component, the voltage frequencies of the first grid and the second grid to obtain a positive voltage reference value of the first PWM convertor and the second PWM convertor; and processing the voltage reference values to obtain the switch signals for controlling the first PWM convertor and the second PWM convertor.

A fault ride-through circuit with a variable frequency transformer (VFT) and a control method thereof are provided, and the control method comprises: pretreating acquired voltages of grids, a voltage of a stator interface and a voltage of a rotor interface to obtain a rotor voltage DC component and a rotor voltage DC component; testing and treating a voltage frequency of a first grid and a voltage frequency of a second grid; carrying out a reference voltage calculation for a stator voltage DC component, a rotor voltage DC component, the voltage frequencies of the first grid and the second grid to obtain a positive voltage reference value of the first PWM convertor and the second PWM convertor, and processing the voltage reference values to obtain the switch signals for controlling the first PWM convertor and the second PWM convertor.

A frequency converter includes: a primary winding 12 in which a plurality of windings on which a polyphase alternating voltage is applied are arranged periodically along a particular direction; a secondary winding 22 which is magnetically coupled to the primary winding 12 and in which a plurality of windings are arranged along the particular direction with a repetition period different from the primary winding 12; and a frequency modulation part 3 which is arranged on a magnetic path between the primary winding 12 and the secondary winding 22 and in which a plurality of magnetic materials 31 are arranged periodically. Then, the pitch of the plurality of magnetic materials 31 and the winding arrangement period of the primary winding 12 and the secondary winding 22 are different from each other so that an alternating voltage having a frequency different from the frequency of the polyphase alternating voltage is induced in the secondary winding 22.

A frequency converter includes: a primary winding 12 in which a plurality of windings on which a polyphase alternating voltage is applied are arranged periodically along a particular direction; a secondary winding 22 which is magnetically coupled to the primary winding 12 and in which a plurality of windings are arranged along the particular direction with a repetition period different from the primary winding 12; and a frequency modulation part 3 which is arranged on a magnetic path between the primary winding 12 and the secondary winding 22 and in which a plurality of magnetic materials 31 are arranged periodically. Then, the pitch of the plurality of magnetic materials 31 and the winding arrangement period of the primary winding 12 and the secondary winding 22 are different from each other so that an alternating voltage having a frequency different from the frequency of the polyphase alternating voltage is induced in the secondary winding 22.