Soft Starter Functioning

You've got the correct concept but the wrong units. A soft starter gradually increases the current through the stator windings not the voltage. This current is modulated by using a Pulse Width Modulation technique of the voltage applied to the inductive stator windings through the three thyristors (one per stator phase winding). Don't forget that the current through an inductor will follow the differential equation of V=Ldi/dt. Now the minimum current "start" condition will change significantly depending on the motor size and the driven mechanical load. This is why all of the soft starters I've seen have user select able settings for starting conditions.

Sorry, no. All a soft starter can technically control is the RMS voltage. By taking a feedback loop of current, you can control current by modulating the voltage.

The softstarter makes use of the fact that when the motor voltage is low during start, the starting current and starting Torque is also low. The motor voltage is regulated with a printed circuit board

During the first part of the start the voltage to the motor is so low that it is only able to adjust the play between the gear wheels or stretching driving belts or chains etc. In other words, eliminating unnecessary jerks during the start. Gradually, the voltage and the torque increase so that the machinery starts to accelerate.

Thyristors are semi-conducting components connected in an anti-parallel fashion and placed in two or three phases of the main circuit. They regulate (by increasing or decreasing) the level of voltage during start and the stop ramp, as described in the picture Above. During a continuous run the thyristors are conducting fully.

Off (non blue portion) : Thyristor is non-conducting

On (blue portion): Thyristor is conducting

Start: The thyristors let part of the voltage through at the beginning and then increase it, according to the set ramp time for the start.

Stop: The thyristors are fully conducting and when soft stopping, they decrease the voltage according to the set ramp time for stop.