In this context, it's a feature name (not a product class name), and a meaningless meta-feature name. It's just that customers are calling motor controller manufacturers: "but does this have a soft start?" Instead of explaining: "In context of current-regulated (torque-limiting) motor controllers, there is no concept of 'soft start' at all, soft starting is an implicit side effect in limiting torque in all other edge cases (startup being only one) too", they found out it's easier to write "built-in soft start" to stop stupid questions.
There is a learning opportunity here for me! I don't really understand what you are saying in the above paragraph when you imply that soft starting isn't even a real thing in current-regulated controllers.
To my mind, a soft start is when the motor increases its speed from 0rpm to its normal running speed over a controlled period of time. Imagine a chart with time along the x axis, motor speed along the y axis, and the required speed vs time curve is plotted on the graph. It is the
motor speed that is of primary interest, rather than the motor torque. Of course the torque determines the rate of speed increase, and the torque is controlled by the current in the motor. So obviously controlling the current controls the acceleration of the motor.
As I see it, though, the current isn't the thing of primary interest - it's the motor speed. So I envisage a control circuit whereby the instantaneous speed of the motor is monitored (NOT the motor current), and the current is adjusted in real time to give the required motor speed at every point in the start-up curve. Depending on the load on the motor, different soft starts might require different current ramps in order to achieve the wanted speed ramp.
This sounds to me like a distinct function that does not automatically "fall out" of a constant current controller. It requires a couple of extra things: a speed feedback from the motor; and an internal representation of the required start-up curve.
Obviously a constant current controller has the
potential to provide a soft start just by limiting the current in the motor. But surely when you want a
specific start-up curve you need the extras I've described in the above paragraph. The controller
might have the facility for a speed/time start-up curve to be stored internally and invoked at motor start-up, but equally it might rely on external circuitry to do that and send the appropriate control signals to the motor controller.
Now, I'm an amateur and a hobbyist, so I might be completely wrong about all of this. If so, could you explain a bit more about your thinking behind your statement?
Thank you! I always appreciate people taking the time to teach us beginners.