The invention relates to a
power electronics control device and aims at providing an improved
continuous variable-
voltage and variable-frequency soft
starter used for a motor. The soft
starter comprises a mechanical switch K1 and a series circuit, wherein the series circuit comprises an
inverter and full-control high-frequency electronic switches Gd1 and Gd2, and the series circuit and a
capacitor C0 are connected in parallel with both ends of the output of a three-phase
diode rectifier; a series switch circuit made by connecting a full-control high-frequency
electronic switch Gd3 and a diodeDE in series is connected in parallel with both ends of the input of the
inverter; and wires respectively from the middle points of three pairs of bridge arms of the
inverter are connected with a three-phase asynchronous motor through a switch K2. The soft
starter can change frequency and
voltage continuously, so that the starting force of the motor is great while the starting current is not too great; the cost is reduced and the overload capacity is enhanced, so that the soft starter can be applicable to high-
voltage occasions; and the three functions of regulating voltage,
cutting off during failure and turning off an inverter
thyristor can be realized by using a few full-control high-frequency elements, so that the full-control high-frequency elements work at
high frequency while the
thyristor works at
low frequency.