Soft start ingress is actually a stageless decompression start. When asynchronous motor changes the supply voltage, the critical rotation of its mechanical characteristics is constant, but the critical torque is reduced more.
As a result, the starting torque is significantly reduced when starting at low pressure, as shown in Figure a. After the realization of variable frequency speed, because the inverter has a variety of compensation functions and vector control functions, the mechanical characteristics of the motor will be greatly improved, can ensure that there is a large starting torque, as shown in Figure b.
Figure Soft Start and Variable Frequency Start
a) Soft starting machinery characteristics
b) b) variable frequency starting machinery characteristics
1. The inverter is used where the speed adjustment is needed, and the output of the drive not only changes the voltage but also changes the frequency at the same time.
2. The soft starter is actually a regulator, which protects the motor, and the soft starter output only changes the voltage and does not change the frequency when the motor buck starts.
3. The drive has all the functions of the soft starter, but its structure is complex and the price is much more expensive than the soft starter.
4. The inverter is used to control the use of electrical equipment by adjusting the frequency, which can be adjusted and started, such as the inverter pump for industrial use. Soft start basicaway is by changing the resistance in the circuit, so that the current from small to large, such a way to start high-power motor, used to reduce the high-power motor direct start to the grid caused fluctuations, or cause some unimportant load unloading trouble.