Soft starter used for continuous frequency conversion and voltage transformation of motor

Abstract

The invention relates to control equipment of power electronics and aims to provide a soft starter used for continuous frequency conversion and voltage transformation of the motor. The soft starter comprises a mechanical switch K1 which is connected with a three-phase electric network power supply, and further comprises a series circuit which consists of an inverter and a fully-controlled high-frequency electronic switch Kd, wherein the series circuit and a capacitor C0 are connected to two output terminals of a three-phase diode rectifier bridge in parallel; the mechanical switch K1 is connected to an input terminal of the three-phase diode rectifier bridge; in the inverter, three pairs of bridge arms are formed by six sets of thyristors Th1,1' to Th6,6'; each pair of bridge arms consist of two anti-parallel thyristors; and the center point of an upper bridge arm and a lower bridge arm of each of the three pairs of bridge arms leads a lead out respectively and is connected to a three-phase asynchronous motor through a mechanical switch K4. In the soft starter used for continuous frequency conversion and voltage transformation of the motor, three functions of regulating voltage, switching off an inverter thyristor, and switching off the main circuit when protection is needed can be simultaneously realized by using only one fully-controlled electronic switch Kd. Simultaneously, due to the adoption of the thyristor inverter, the soft starter has the advantages of simple and reliable circuit, low cost, and great use flexibility.

Description

technical field [0001] The invention relates to a power electronic control device, more specifically, the invention relates to a soft starter for continuous frequency conversion and voltage conversion of electric motors. Background technique [0002] In the current industrial production and operation, because the current of the large motor is too large when it is started, it is difficult for the power grid to bear, so it is often necessary to add a set of soft starters. The commonly used soft starter is actually a set of step-down devices composed of thyristors. As the voltage decreases, although the starting current can be reduced, the starting torque is also greatly reduced, and it is difficult to start for heavier loads. It is best to reduce the frequency while reducing the voltage, because reducing the frequency can increase the magnetic field of the motor, thereby increasing the torque. From the perspective of reducing the impact on the power grid and improving the st...

AI Technical Summary

Problems solved by technology

Although the different connection methods of thyristors will produce several levels of different frequencies, because the number of levels is too small, it often cannot meet the requirements of soft start.

Therefore, sometimes expensive frequency converters have to be used instead of starters

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