The difference between inverter and soft start

Soft starters and frequency converters are two completely different applications. The frequency converter is used for speed regulation. The output not only changes the voltage but also changes the frequency. The soft starter is actually a voltage regulator. When the motor starts, the output only changes the voltage and does not change the frequency. The frequency converter has all the soft starter functions, but it is much more expensive than the soft starter and the structure is much more complicated.

The main difference between the two is:

1, soft start is to try to cut and destroy the sinusoidal waveform, it is easy, just as water flows down to the bottom;

2, the frequency converter is to do everything possible to obtain a sinusoidal waveform with adjustable frequency, it is difficult! Just as water is going to flow as high as it is difficult.

The characteristics of the inverter are:

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

2. It is an irreversible process, or impossible, because it is necessary to change the direct current into a sinusoidal AC waveform. Only the PWM widened carrier whose average voltage waveform is a sine wave can realize the frequency conversion purpose of the sinusoidal waveform;

3. The average voltage waveform is a sinusoidal PWM widened carrier, which is realized by the switching action of the full control device IGBT. The actual output of the inverter is a periodically varying rectangular wave with different widths;

4. The asynchronous motor filters out the sinusoidal waveform from the PWM widened carrier and generates a constant rotating magnetic field required for electric power;

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

Differences in technical indicators:

1. The thyristor AC voltage regulating circuit is a circuit for adjusting the thyristor alternating current waveform by adjusting the conduction angle of the thyristor to obtain an alternating current with an adjustable average voltage;

2. The AC voltage regulating circuit is applied to an automatic heating temperature control circuit, a stage dimming circuit, and the like, and the load circuit related to the average voltage is independent of the AC waveform;

3, but some people and even so-called experts put this thyristor AC voltage regulator circuit for the start of asynchronous AC motor, and its name is soft start;

4. Because the asynchronous AC motor works under the three-phase symmetrical sinusoidal AC waveform, there is a constant rotating magnetic field;

5. If the alternating current of the waveform of the sinusoidal alternating current is adjusted for the conduction angle of the thyristor by using the conduction angle of the thyristor, a constant rotating magnetic field cannot be generated;

6. This AC waveform is used for the asynchronous motor to completely destroy the starting performance of the asynchronous motor. The starting torque is low and the starting current is large. There is no soft start function that everyone imagines;

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

8, asynchronous motor self-twisting step-down start, star-delta start, water resistance step-down start, etc., step-down does not change the sinusoidal waveform, are good effective starting devices, are better than soft start;


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