Grading variable-frequency soft starting device

The utility model provides a grading variable-frequency soft starting device which gradually increases the voltage in a starting process and correspondingly increases the frequency to meet grid frequency from low to high so as to improve staring torque and reduce staring current. The device comprises a control unit, a voltage synchronizing signal acquisition unit, a current zero-crossing signal acquisition unit and a thyristor soft starting unit, wherein the voltage synchronizing signal acquisition unit and the current zero-crossing signal acquisition unit are respectively connected with the control unit which is connected with the thyristor soft starting unit. The device realizes smooth frequency-increasing soft starting, reduces starting impact and starting current, increases starting torque, and can enable a motor to smoothly start under full load. The grading variable-frequency soft starting adopts a main circuit structure of the traditional thyristor soft starting, and only thetriggering order and the control method of a thyristor are changed, therefore, the device does not increase the cost, is superior to the traditional thyristor soft starting, and realizes the soft starting performance similar to that of a frequency converter.