AC drive inverter versus soft starter

Although both devices falls under reduced voltage starting method, but soft starter can not vary the frequency. Soft starter just helps to lower the starting current and smoother the start up. Whereas AC drive inverter its much more intelligent and it has all the functions of soft starter.
If the money is not an issue and proper investigation of application, I will consider AC drive inverter instead Soft starter.

When considering differences between AC drive inverter and Soft starter: AC drive is a key element in #Energy #Efficiency (even if AC drive is a little bit costly when purchasing and of course not in all cases, it depends on the application and its required power). Means you can realize energy savings with a AC drive inverter and generally the payback doesn't exceed one year.

For motor start circuit you should consider thermal overload relay HRC fuses and contactor, the soft starter is a compact package which is includes all the mentioned equipment for starting the motor. But AC drive is a variable frequency drive it is usually apply for increase or decrease the RPM of motor.

For continuous speed control (pumps, conveyor belts, etc.) - use AC drives.  For avoiding overshoot in Amps during motor startup - use soft-starters. They're cheaper.
Even more cost-effective solution is to start several motors using only one soft-starter. But you'd need to have several contactors operate in sequence to achieve it.

If you use a AC drive inverter make sure you take into consideration the heat generated if it is mounted inside a control panel. Also the heat generated by any filters or reactors if also used.
Your suppliers' tech support can help you size the panel correctly for heat dissipation.

We build control panels for all kinds of environments and ambient temperatures such as with outdoor installations can create headaches with cooling when in direct sunlight or hot climates. However, this is not an issue with a soft starter.