Frequency conversion and soft start

Variable frequency drives enable speed control over a wide range of speeds, meeting the requirements of industrial processes or aiding in energy savings. Soft starters can only address the starting issue; once starting is complete, operation continues at the rated frequency.

After soft start is complete, switch back to the contactor; if it doesn’t operate for a long time and the inverter is functioning normally, there’s no need to make this switch

First, let’s talk about starting: Variable frequency drives address the issue of electrical starting by changing the operating frequency of the power grid. They work well for large motors, providing a smooth start with minimal impact on the power grid. Soft starters, on the other hand, use thyristors to reduce voltage during startup; they require a bypass contactor, and the starting current is also around 5 times the motor’s rated current. If the soft starter is of poor quality or is used in cold northern regions, it will have difficulty starting transmission systems that rely on oil for lubrication As for operation and control: The frequency converter can adjust the speed of the motor during its operation, and it can also monitor some basic parameters of the motor. Additionally, it can communicate with other computers to enable vector control. However, for larger motors, the frequency converter requires more auxiliary components such as input reactors, output reactors, and braking resistors, which increases the cost. Soft starters can also monitor the basic operating data of the motor during its operation, but they do not have any other functions

These days, transformers have larger capacities, so soft starters are not necessary if they can be avoided; frequency conversion should also not be used unless it is strictly required by the manufacturing process, as it adds potential points of failure.

Too many frequency converters affect the quality of the power grid

The functions of an inverter include soft starting, but it also comes at a higher cost; an inverter can adjust speed by changing frequency, whereas soft starting cannot

Soft starters can only adjust voltage; they cannot adjust frequency (that is, speed)； The inverter can adjust the frequency (speed)