Soft starter and frequency converter are two completely different products. Frequency converter is used in the place where speed regulation is needed, 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 and does not change the frequency. Frequency converter has all the functions of soft starter, but its price is much more expensive than soft starter and its structure is much more complicated.

1、 The main difference between the two

1. Soft start is to try to cut and destroy the sine wave, which is very easy, just as the water flows to the low place;

2. It is very difficult to obtain the frequency adjustable sinusoidal waveform by all means, just as the water flows to the high place.

2、 Characteristics of frequency converter

1. About frequency converter, it is a kind of equipment that changes the frequency of three-phase sinusoidal alternating current;

2. Because it is an irreversible process or impossible to convert DC into sinusoidal AC waveform, only PWM width modulated carrier whose average voltage waveform is sine wave can realize the purpose of frequency conversion of sinusoidal waveform;

3. The average voltage waveform is a PWM carrier wave of sine wave, which is realized by the switching action of IGBT. The output of inverter is actually rectangular wave with different width;

4. The sinusoidal waveform is filtered from PWM carrier wave and the constant rotating magnetic field is produced;

5. And by changing the frequency of asynchronous motor to change the synchronous speed, to achieve the purpose of AC motor frequency control.

3、 Differences in technical indicators

1. The thyristor AC voltage regulating circuit is a circuit which can obtain the adjustable average voltage by adjusting the conduction angle of thyristor and chopping the waveform of sinusoidal alternating current;

2. This kind of AC voltage regulating circuit is used in the load circuit which has nothing to do with the AC waveform but only relates to the average voltage;

3. However, some people even the so-called experts use this kind of thyristor AC voltage regulating circuit for the starting of asynchronous AC motor, which is called soft starting;

4. Because asynchronous AC motor works in three-phase symmetrical sinusoidal AC waveform, it has a constant rotating magnetic field;

5. If the AC motor is applied to the induction motor by adjusting the conduction angle of the thyristor and chopping the sinusoidal AC waveform, a constant rotating magnetic field cannot be generated;

6. When the AC waveform is used in asynchronous motor, the starting performance of asynchronous motor is completely destroyed. The starting torque is low and the starting current is large, so there is no soft start function imagined by everyone;

7. All soft start motors are started when they are close to the full voltage. The starting time is long and the starting current is large, which has a greater impact on the power grid;

8. The self coupling step-down start-up, star delta start-up, water resistance step-down start-up and so on are good and effective start-up equipment, which are better than soft start-up.