The soft starter is a motor control device with motor soft start, soft stop, light-load energy saving, and multiple protection functions. It is mainly a three-phase parallel thyristor and its electronic control circuit is connected in series between the power supply and the controlled motor. By controlling the conduction angle of the three-phase parallel thyristor, the input voltage of the controlled motor can be changed according to different requirements to realize various functions.
The inverter is mainly used in places where speed is needed. Its output not only changes the voltage but also changes the frequency; the soft starter is a voltage regulator, used when the motor starts, the output only changes the voltage, not the frequency. The frequency converter has all the soft starter functions, but its price is more expensive than the soft starter, and the structure is more complicated.
The soft starter is used where the voltage is reduced to start and stop. At this time, the motor speed is unchanged; but the frequency converter is mainly used for speed regulation, where the speed is constant, and the speed is determined by the frequency. The biggest difference between the two is that the inverter can set the running frequency arbitrarily, but the soft starter only plays the role of soft start and stop.
1. Definition and function of soft starter
The soft starter is connected in series between the power supply and the controlled motor, and the internal thyristor is controlled by a microcomputer to trigger the conduction angle to achieve AC voltage regulation, so that the motor input voltage gradually rises from zero with a preset function relationship, until the end of the start. The full voltage of the motor is a soft start. In the process of soft start, the starting torque of the motor gradually increases, and the speed also gradually increases until the thyristor is fully turned on, and the motor works on the mechanical characteristics of the rated voltage to achieve a smooth start and reduce the starting current. . Avoid starting an overcurrent trip. When the motor reaches the rated number of revolutions, the start-up process ends, and the rated voltage is provided for the normal operation of the motor.
Soft starter (soft starter) is a novel motor control device that integrates motor soft start, soft stop, light-load energy saving, and multiple protection functions. It is called Soft Starter abroad. The soft starter uses a three-phase parallel thyristor as a voltage regulator, which is connected between the power supply and the motor stator. Such a circuit is a three-phase fully controlled bridge rectifier circuit.
When using the soft starter to start the motor, the output voltage of the thyristor gradually increases, and the motor gradually accelerates until the thyristor is fully turned on. The motor works on the mechanical characteristics of the rated voltage to achieve smooth starting, reduce the starting current, and avoid starting over-current tripping. When the motor reaches the rated number of revolutions, the start-up process ends, and the soft starter automatically replaces the thyristor that has completed the task with a bypass contactor to provide rated voltage for the normal operation of the motor to reduce the heat loss of the thyristor and extend the service life of the soft starter, Improve its work efficiency, and make the grid avoid harmonic pollution. The soft starter also provides a soft stop function. The soft stop is the opposite of the soft-start process. The voltage gradually decreases and the number of revolutions gradually drops to zero to avoid the torque impact caused by the free stop.
Second, the definition and function of the inverter
A converter that converts an alternating current with a fixed voltage and frequency into an alternating current with a variable voltage and frequency is called a frequency converter. Reduce the impact load caused when the motor starts, control the speed of the motor, lengthen the start time, smooth the current, achieve the purpose of soft start, and improve the efficiency of the power grid and the motor. The frequency converter is mainly used in energy-saving, through adjustment, change the output voltage, current, frequency. Generally, the speed-adjusting motor uses a frequency converter.
Three, the working principle of the inverter
The inverter is a device that converts industrial frequency power (50Hz or 60Hz) into AC power of various frequencies to realize the variable-speed operation of the motor. Among them, the control circuit completes the control of the main circuit, the rectifier circuit converts alternating current into direct current, the DC intermediate circuit smoothes and filters the output of the rectifier circuit, and the inverter circuit reverses the direct current into alternating current (and the core control circuit realizes: AC- Orthogonal process). The frequency conversion technology was born in response to the need for step-less speed regulation of AC motors.
