Difference between soft starter and frequency converter

Difference between soft starter and frequency converter

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

Frequency converter, which is mainly used in places where speed regulation is required, whose 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 without changing the frequency. The frequency converter manufacturer emphasized that the frequency converter has all the functions of soft starter, but its price is more expensive than the 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, at which time the motor speed remains unchanged; However, the frequency converter is mainly used for speed regulation. In places with constant voltage, the speed is determined by the frequency. The inverter manufacturer believes 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 microcomputer controls its internal thyristor trigger conduction angle to achieve AC voltage regulation, so that the motor input voltage gradually rises from zero in a preset functional relationship until the end of starting. The motor is given full voltage, which is called soft starting. During the soft starting process, the motor starting torque gradually increases, and the speed gradually increases until the thyristor is fully connected, The motor works on the mechanical characteristics of rated voltage to achieve smooth starting and reduce starting current. Avoid starting overcurrent tripping. When the motor reaches the rated speed, the starting process is completed and the rated voltage is provided for the normal operation of the motor.
Soft starter (soft starter) is a new motor control device that integrates motor soft start, soft stop, light load energy saving and multiple protection functions. It is called Soft Starter abroad. Soft starter uses three-phase anti parallel thyristor as voltage regulator, which is connected between power supply and motor stator. This 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 gradually increases, and the motor gradually accelerates until the thyristor is fully connected. The motor works on the mechanical characteristics of the rated voltage to achieve smooth starting, reduce the starting current, and avoid starting overcurrent tripping. When the motor reaches the rated speed and the starting process is over, the soft starter automatically replaces the completed thyristor with a bypass contactor to provide rated voltage for the normal operation of the motor, so as to reduce the heat loss of the thyristor, extend the service life of the soft starter, improve its working efficiency, and avoid harmonic pollution of the power grid. The soft starter also provides the soft stop function. The soft stop process is opposite to the soft start process. The voltage gradually decreases and the number of revolutions gradually decreases to zero to avoid torque impact caused by free stop.
major function 
Overload protection function: the soft starter introduces a current control loop, so it can track and detect the change of motor current at any time. By adding overload current setting and inverse time limit control mode, the overload protection function is realized. When the motor is overloaded, the thyristor is turned off and an alarm signal is sent.
Phase loss protection function: during operation, the soft starter can detect the change of three-phase line current at any time, and make phase loss protection reaction once the current is cut off.
Overheat protection function: the temperature of the thyristor radiator is detected through the thermal relay inside the soft starter. Once the radiator temperature exceeds the allowable value, the thyristor is automatically turned off and an alarm signal is sent.
Parameter function of measuring circuit: when the motor is working, the detector in the soft starter monitors the motor's operating state all the time, and sends the monitored parameters to the CPU for processing, and 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 protections can also be realized in the system.
Definition and function of frequency converter
The converter that converts the AC with fixed voltage and frequency into AC with variable voltage and frequency is called frequency converter. Reduce the impact load caused by motor starting, control the motor speed, lengthen the starting time, flatten the current, achieve the purpose of soft starting, and improve the efficiency of power grid and motor. In fact, the frequency converter is mainly used for energy saving. Through regulation, the output voltage, current and frequency can be changed. Generally, frequency converter is used for speed regulating motor.
Working principle of frequency converter
Frequency converter is a device that converts power frequency power supply (50Hz or 60Hz) into AC power supply of various frequencies to realize variable speed operation of motor. Among them, the control circuit controls the main circuit, the rectifier circuit converts the AC to DC, the DC intermediate circuit filters the output of the rectifier circuit smoothly, and the inverter circuit reverses the DC to AC (and the core control circuit realizes: the AC-DC-AC process). The frequency conversion technology was born to meet the needs of stepless speed regulation of AC motors


Difference between soft starter and frequency converter