What Is The Difference Between Soft Start And Frequency Converter?

Sep 05, 2025

Soft starters and frequency converters are two completely different products for different purposes. The frequency converter is used in places where speed regulation is required, and its output not only changes the voltage but also changes the frequency at the same time; A soft starter is actually a voltage regulator used for motor starting, where the output only changes the voltage and not the frequency. The frequency converter has all the functions of a soft starter, but its price is much higher and its structure is much more complex than a soft starter.
Industrial power inverter

1, The main difference between the two is:

1. Soft start is a method of cutting and breaking sine waveforms, which is as easy as water flowing downwards;

2. The frequency converter is trying every means to obtain a sine waveform with adjustable frequency, which is difficult! It's as difficult as water flowing upwards.

2, The characteristics of a frequency converter are:

1. Regarding a frequency converter, it is a device that changes the frequency of three-phase sinusoidal alternating current;

2. Due to the irreversibility or impossibility of converting direct current into sinusoidal alternating current waveform, the frequency conversion of sinusoidal waveform can only be achieved by using PWM modulation carrier with an average voltage waveform of sine wave;

3. The average voltage waveform is a sine wave PWM modulation carrier, which is achieved through the switching action of the fully controlled IGBT device. The actual output of the frequency converter is a periodic rectangular wave with varying widths;

4. Asynchronous motors filter out sine waveforms from PWM modulated carriers and generate a constant rotating magnetic field required for electric operation;

5. And by changing the frequency, the synchronous speed of the asynchronous motor can be changed to achieve the purpose of variable frequency speed regulation of the AC motor

3, Differences in technical indicators:

1. The thyristor AC voltage regulation circuit is a circuit that adjusts the conduction angle of the thyristor, cuts the waveform of the sinusoidal AC power, and obtains AC power with adjustable average voltage;

2. This type of AC voltage regulation circuit is applied to load circuits such as automatic heating and temperature control circuits, stage dimming circuits, etc., which are independent of AC waveform and only related to average voltage;

3. But some people, even so-called experts, use this thyristor AC voltage regulation circuit for starting asynchronous AC motors and call it soft start;

4. Due to the fact that asynchronous AC motors operate under three-phase symmetrical sinusoidal AC waveforms, they have a constant rotating magnetic field;

5. If the waveform of sinusoidal AC power is cut by adjusting the conduction angle of the thyristor and used in asynchronous AC motors, a constant rotating magnetic field cannot be generated;

6. This type of communication waveform completely destroys the starting performance of asynchronous motors, with low starting torque, high starting current, and no soft start function as people imagine;

7. All soft start motors start when they are close to full voltage, with long starting time, high starting current, and greater impact on the power grid;

8. The self coupling voltage reduction starting, star delta starting, water resistance voltage reduction starting, etc. of asynchronous motors, which do not change the sine waveform during voltage reduction, are all good and effective starting devices that are superior to soft starting;