Soft starter VS breaker VS variable frequency drive

Soft Starter is a devise where you control the voltage applied on Motor, and thus reduces the starting current of the Motor to optimum level so that not only mechanical stress on motor /load reduces but also reduces the voltage drop in system from which the subject motor is powered .The system voltage drop, Otherwise due to heavy inrush of current drawn by motor affects the starting and running performance of other motors working in the vicinity of mail motor on same system.

Breaker: Is a devise which is used to break the circuit under load condition in the event of any fault or some time even under normal condition you can use them as switch to cut off the Power.

VFD - Variable Frequency Drive -Its a device which controls the voltage and frequency both to control the speed of motor. by keeping V/F constant the motor speed can be varied from 0 to 100%,keeping torque constant.

As with VFD the starting voltage can be reduced it acts as Soft Starter also with added advantage of high starting Torque i.e with VFD the POT of motor becomes its starting torque .But in soft starter as we vary only voltage the starting torque is reduced during starting and this poses a limitation up to which starting current can be limited with Soft Starter.

In short:
Soft starter is an AC motor controller that ramps the motor up to full speed slowly and gently with less starting current over a longer (albeit limited) time, but it always results in full speed operation of the motor.
Breaker is an on-off device that protects electrical circuits from short circuits and possibly over current conditions, depending on the type of breaker that you select.
VFD is an AC motor controller that does everything that a soft starter does, but also facilitates operation at any speed between zero and maximum for the motor, for an indefinite amount of time.