The difference between the inverter and the soft inverter:

The inverter device : 

A device used to control the speed of AC motors from the moment they are turned on to the moment they are stopped, through their normal operating period, and the need for it is related to the desire to change the load speed and not the capacity and size of the motor.

The device controls the speed of the motor by changing the voltage and frequency of the wave applied to the motor coils and this is done by converting the AC voltage feeding the device into DC voltage by means of a unified Rectifier IC and electrolytic capacitors and then converting it to an AC frequency wave through a group of transistors - usually the Insulated type Gate Bipolar Transistor IGBT - This group is the so-called Inverter IC- This wave can be controlled in its effective voltage value and its frequency by controlling the rate and method of ignition of these transistors until we get the required speed. Sometimes the Rectifier IC and the Inverter IC are separate and sometimes they are combined into a single IC known as IGBT Module.

As a result of changing both the voltage and frequency of the wave applied to the motor, the torque is almost constant, and the ampere drawn by the motor does not exceed the rated ampere of the motor Rated Current even when the starting rotation is started.

The inverter controls the operation of the motor in the same way as its normal control in the case of normal operation, where it gradually raises the voltage and frequency from zero until it reaches the programmed initial speed or the required speed, Reference Speed, within a percentage of time called the acceleration time.

As well as the process of stopping the motor, it gradually reduces the voltage and frequency from the value it is at the moment of the stop request until it reaches zero within a percentage of time called the acceleration time that has been determined and programmed in advance.

This percentage is 100% if the initial operating speed is the maximum speed or the current speed at the moment of the request to stop is the maximum speed. The device is programmed to the rated values ​​of the voltage, frequency and ampere of the motor. The device can be programmed to raise the motor speed above the rated speed - we have 50 Hz in Egypt - but this will be at the expense of torque, as the voltage cannot be increased above the rated value. Also, the inverter will not be able to output a voltage value higher than the feeding, and therefore the 380 motor cannot be run on the 220 inverter. If it is, the determination will be weaker.

Soft starter:

A device that softly operates large and medium-capacity motors to reduce the starting current, which is high when the motor is directly running through a contactor, for example, and gradually raises the load speed from zero to maximum speed. It is the best alternative to Star Delta circuits, especially in large capacities and the need for it is related to the capacity of the motor. And upon completion of the motor straightening, it operates an internal contactor and turns into a normal contactor.

It can also be used to gradually stop the pregnancy to protect it.

The device performs its task in smooth rectification and stopping by applying the supply voltage gradually from a certain value of the Starting Voltage to the value of the voltage during the start time period by using a thyristor for each phase and controlling the degree of ignition of it Until it reaches 100%. In all cases, the wave has the same frequency as the feeding wave. Both devices are connected to the motor in one of the star connections or delta connections to the contactor, according to the motor’s voltage, other than the star-delta circuit, from which the motor must be 6 terminals.

Both devices are equipped with protection from Over Load (Over Current) and short circuit, and they are caused by the motor and motor temperature - according to the design.
The 3-phase inverter is sufficient for it only two phases to operate it, as in all cases, this voltage will be converted to DC, and it will be cut off.

As for the soft starter, 3 phases are required to operate it, as each phase is segmented and this segmentation is passed as it is.