Asynchronous motor soft starter based on single-chip microcomputer

Abstract

The invention relates to an asynchronous motor soft starter based on a single-chip microcomputer. The asynchronous motor soft starter comprises a main loop and a control loop, wherein the main loop and the control loop are connected with a three-phase power supply; the main loop consists of three groups of anti-parallel thyristors, a bypass contactor and a current transformer; the control loop consists of the single-chip microcomputer, a power supply circuit connected with the single-chip microcomputer, a voltage synchronization signal detection circuit, a pulse trigger circuit for generating a thyristor gate trigger signal, a current detection circuit, a voltage detection circuit, an LCD (Liquid Crystal Display) display and keyboard circuit, a contactor control circuit, a state output circuit and a protection circuit; the single-chip microcomputer is connected with the three groups of anti-parallel thyristors through the pulse trigger circuit; the current transformer is connected with the current detection circuit and a three-phase asynchronous motor. The asynchronous motor soft starter is convenient and easy to operate, and can run stably and reliably in time according to the change of motor load on the premise of meeting the starting torque requirement and reducing the starting current of the asynchronous motor.

Description

technical field [0001] The invention relates to the technical field of soft start, in particular to a soft starter for an asynchronous motor based on a single-chip microcomputer. Background technique [0002] AC asynchronous motors, especially three-phase squirrel-cage asynchronous motors, are widely used in agricultural production, factories and mines, transportation, In the defense industry and in various fields of people's daily life. However, there are many problems in the startup process. [0003] At present, the starting methods commonly used by asynchronous motors include full-voltage direct starting and reduced-voltage starting. The advantage of full-voltage direct starting is that the starting equipment and operation are the simplest, and the starting torque is larger than that of step-down starting; its disadvantage is that the inrush current generated during starting is 2 to 7 times its rated current, which will cause: ( 1) The instantaneous drop and violent fl...

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Problems solved by technology

The advantage of full-voltage direct starting is that the starting equipment and operation are the simplest, and the starting torque is larger than that of step-down starting; its disadvantage is that the inrush current generated during starting is 2 to 7 times its rated current, which will cause: ( 1) The instantaneous drop and violent fluctuation of the grid voltage will affect the normal operation of other motors or electrical equipment on the same network; (2) The impact current will cause the local temperature of the motor to rise, and the motor will overheat when it is started frequently, reducing the service life of the motor; (3) The mechanical impulse generated will accelerate the wear of mechanical transmission parts; (4) The impact current will also interfere with the normal operation of electrical instruments in the form of electromagnetic waves and other hazards

[0004] The traditional step-down starting methods include stator series resistance or reactance starting, autotransformer starting and Yanbian triangle starting, etc. These starting methods have the following disadvantages: (1) The starting equipment is large in size and high in cost; (2) It belongs to step regulation, The starting voltage cannot be adjusted linearly, continuously and smoothly, and its starting characteristics are not ideal; (3) The starting current cannot be limited within a certain range, and the secondary impact current caused by switching cannot be eliminated; (4) The contact relay control cannot Realize frequent repeated starts; (5) Heavy maintenance workload

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