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Soft starter, in fact, is a motor control device with motor soft start, soft stop, light load energy saving and a variety of protection functions. It is mainly a three-phase anti parallel thyristor and its electronic control circuit connected in series between the power supply and the controlled motor. By controlling the conduction angle of the three-phase anti parallel thyristor, the input voltage of the controlled motor will change according to different requirements to achieve various functions.


Inverter, which is mainly used in the need of speed regulation, its output not only changes the voltage but also changes the frequency; The soft starter is actually a voltage regulator. When the motor is started, the output only changes the voltage, not the frequency. The frequency converter manufacturers emphasize that the frequency converter has all the functions of soft starter, but its price is more expensive than soft starter, and its structure is more complex.


The soft starter is used in the place where the voltage is reduced to start and stop, when the motor speed remains unchanged; But the frequency converter is mainly used for speed control, constant voltage place, the speed is determined by the frequency. Inverter manufacturers believe that the biggest difference between the two is that the inverter can set the operating frequency arbitrarily, but the soft starter only plays the role of soft start and soft stop.


Definition and function of soft starter


The soft starter is connected in series between the power supply and the controlled motor. The thyristor triggering conduction angle inside the soft starter is controlled by the microcomputer to realize the AC voltage regulation. The input voltage of the motor increases gradually from zero with a preset function until the end of the start, giving the motor full voltage, which is called soft start. In the process of soft start, the starting torque and speed of the motor increase gradually, Until the thyristor is fully turned on, the motor works on the mechanical characteristics of rated voltage to realize smooth starting and reduce starting current. Avoid starting over-current trip. When the motor reaches the rated speed, the start-up process ends, and the rated voltage is provided for the normal operation of the motor.


Soft starter (soft starter) is a new motor control device which integrates soft start, soft stop, light load energy saving and multiple protection functions. The soft starter uses three-phase anti parallel thyristor as voltage regulator, which is connected between the power supply and the motor stator. This kind of circuit is like three-phase full control bridge rectifier circuit. When the soft starter is used to start the motor, the output voltage of the thyristor increases gradually, and the motor accelerates gradually until the thyristor is fully connected. The motor works on the mechanical characteristics of the rated voltage to realize smooth start, reduce the starting current and avoid starting over-current trip. When the motor reaches the rated speed and the starting process is over, the soft starter automatically replaces the thyristor with the bypass contactor to provide the rated voltage for the normal operation of the motor, so as to reduce the heat loss of the thyristor, prolong the service life of the soft starter, improve its working efficiency, and avoid the harmonic pollution of the power grid. Soft starter also provides soft stop function, soft stop and soft start process is opposite, the voltage gradually decreases, the number of revolutions gradually drops to zero, to avoid the torque impact caused by free stop.


major function


Overload protection function: the soft starter introduces current control loop, so it can track and detect the change of motor current at any time. By adding the setting of overload current and inverse time control mode, the overload protection function is realized. When the motor is overloaded, the thyristor is turned off and the alarm signal is sent out.


Open phase protection function: when working, the soft starter can detect the change of three-phase line current at any time. Once the current is cut off, it can make open phase protection response.


Overheat protection function: detect the temperature of the thyristor radiator through the internal thermal relay of the soft starter. Once the radiator temperature exceeds the allowable value, automatically turn off the thyristor and send out an alarm signal.


Function of measuring circuit parameters: when the motor is working, the detector in the soft starter always monitors the running state of the motor, and sends the monitored parameters to the CPU for processing. The CPU analyzes, stores and displays the monitored parameters. Therefore, the motor soft starter also has the function of measuring circuit parameters.


Other functions: through the combination of electronic circuits, other interlocking protection can be realized in the system.


Definition and function of frequency converter


The converter that transforms the alternating current with constant voltage and frequency into alternating current with variable voltage and frequency is called frequency converter. It can reduce the impact load caused by motor starting, control the motor speed, lengthen the starting time, smooth the current change, achieve the purpose of soft starting, and improve the efficiency of power grid and motor at the same time. In fact, the frequency converter is mainly used in energy saving, by adjusting, changing the output voltage, current, frequency. Generally, the motor of speed adjustment calculation uses frequency converter.


Working principle of frequency converter


The frequency converter is the equipment that transforms the power frequency power (50 Hz or 60 Hz) 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 AC into DC, the DC intermediate circuit smoothes the output of the rectifier circuit, and the inverter circuit reverses DC into AC (and the core control circuit realizes the process of AC-DC-AC). Frequency conversion technology is born to meet the needs of stepless speed regulation of AC motor