What is the difference between a soft start and a variable frequency start?
Installing a soft starter makes the motor start when the current does not rush up to several times the rated current of the motor, its current will rise smoothly until the motor runs normally, the inverter is a soft start function, and may be in the motor running speed regulation, and its speed regulation is to change the frequency of the motor, so that it can start a role of energy saving. Production quality now in the domestic are making mature, general occasions with domestic can be.
     1, frequency:
　　Soft starter output frequency is fixed for the power frequency, the frequency is not adjustable; frequency converter is adjustable output frequency.
     2、Voltage:
　　Soft starters control the output voltage by controlling the silicon controlled (or other power electronic components) conduction angle, the output voltage slowly rises from 0V to the rated voltage; the voltage of the inverter is adjustable.
      3. In terms of motor speed:
　　Soft starters cannot adjust the motor speed; inverters can adjust the motor to run at any speed. The power module inside the inverter is an insulated gate bipolar transistor to suit the frequency of the motor for a long time; and most soft starters currently use silicon controlled components, set the start time and initial voltage and other parameters through the setup interface, once the start-up is complete (to the working frequency) immediately after jumping off the soft start circuit, the bypass contactor sucks in and accesses the working frequency operation.
　　Soft start is only called this in low-voltage systems, high-voltage motors are currently used more liquid resistance starter (cabinet), commonly known as "water resistance". The function is almost the same, but the principle is not the same. The former through the thyristor voltage regulation current-limited start, the latter through the resistance voltage regulation current-limited start.
     The main purpose of the soft starter is to change the starting torque, reduce the impact on the grid and reduce the impact on machinery and equipment when the motor is started, so it is clear that the soft start must be based on the motor's starting torque T and other influencing parameters to build a control function relationship. The inverter, on the other hand, focuses on speed regulation, so it must be based on the functional relationship between the motor's speed and the power supply frequency.
     2. The inverter can realize the work of the soft starter, but the soft starter cannot realize the work of the inverter, because the soft starter cannot regulate the speed, it is based on adjusting the voltage to adjust the starting torque; the soft starter is equipped with negative voltage feedback in the device in order to realize the motor to maintain a high starting torque, which enhances the hardness of the mechanical characteristics of the motor.
     3. Although both frequency converters and soft starters have motor protection and soft stop functions, the amount of harmonics generated by frequency converters is greater than that of soft starters.