Soft starters and frequency converters are two completely different products. Inverter is used in the need for speed control, the output will not only change the voltage but also change the frequency; soft starter is actually a regulator, which is used when the motor starts, the output changes only the voltage is not Change the frequency.
1, thyristor AC voltage regulator circuit, by adjusting the thyristor conduction angle and chopped sinusoidal AC waveform, and then get the average voltage adjustable AC circuit;
2, this exchange voltage regulator circuit, used in automatic heating temperature control circuit, stage dimming circuit and some other AC waveform has nothing to do with only the average voltage load circuit;
3, but some people even some so-called experts to the thyristor AC voltage regulator circuit for asynchronous AC motor start, and its name is called soft-start;
4, due to asynchronous AC motor, is a three-phase symmetrical sinusoidal AC waveform to work, only a constant rotating magnetic field;
5, if by adjusting the thyristor conduction angle and chopped sinusoidal alternating current waveform AC asynchronous motor, it will not produce a constant rotating magnetic field;
6, this exchange waveform for the induction motor will destroy the complete induction motor starting performance, will make the starting torque smaller, starting current becomes larger, there is no we imagine the soft-start function;
7, all the soft-start motor, are close to full pressure when it started, the longer the start, start the current, the greater the impact on the power grid;
8, the asynchronous motor buck-start from the lotus root, delta start and water resistance step-down start, etc., buck does not change the sine wave, are good and effective start-up equipment, are better than the soft start;
1) About frequency changer, it is a kind of equipment that changes the frequency of three-phase sinusoidal alternating current;
2) Since it is an irreversible process to convert DC into sinusoidal AC waveform, it is impossible to realize the purpose of frequency conversion of sinusoidal waveform by PWM widening the carrier whose average voltage waveform is sinusoidal.
3) The average voltage waveform is sinusoidal wave PWM widened carrier, through the full control device IGBT switch to achieve;
4) The asynchronous motor filters out the sinusoidal waveform from the PWM modulated carrier and generates a constant rotating magnetic field required by the motor.
5) Change the synchronous motor speed by changing the frequency, in order to achieve the greatest difference between the purpose of AC motor speed control is:
① soft-start is trying to cut the sabotage waveform, it is easy, just as simple as the flow of water to the lower;
② inverter is to do everything possible to obtain a sine wave of adjustable frequency, it is difficult! It is as difficult as the water flows to the top.