The VFD is generally not suitable for switching back and forth between devices such as output contactors, because its control is complicated. When the motor is switched, it may cause the motor to idle, and its phase is very different from that of the variable frequency drive output. There is a relatively large impact, which will affect the life of the IGBT of the inverter. The soft starter itself is designed with these in mind, using some phase-locked loop techniques to track. So when do you need a soft starter?