Many people can’t distinguish between frequency converters and soft starters. Here’s a detailed explanation:

What is a frequency converter?

A frequency converter is a converter that transforms AC power with a fixed voltage and frequency into AC power with a variable voltage and frequency. It’s mainly used in applications requiring speed control; its output changes both voltage and frequency. A soft starter, on the other hand, is essentially a voltage regulator used during motor starting. Its output only changes the voltage, not the frequency. Frequency converter manufacturers emphasize that they possess all the functions of a soft starter, but they are more expensive and have a more complex structure.

What is a soft starter?

A soft starter is connected in series between the power supply and the controlled motor. A microcomputer controls the internal thyristor conduction angle to achieve AC voltage regulation, gradually increasing the motor input voltage from zero according to a preset function until the start-up is complete, providing the motor with full voltage – this is soft starting. During soft starting, the motor’s starting torque and speed gradually increase until the thyristors are fully conducting, and the motor operates at its rated voltage mechanical characteristics, achieving smooth starting and reducing starting current. This avoids overcurrent tripping during startup. The starting process ends when the motor reaches its rated speed, providing the rated voltage for normal motor operation.

So, what is the main difference between a frequency converter and a soft starter?

A frequency converter is used where speed regulation is required. Its output changes both voltage and frequency simultaneously.

A soft starter is essentially a voltage regulator, providing protection for the motor. When used for reduced-voltage starting, the soft starter output only changes the voltage, not the frequency.