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What is VFD or Soft starter




so what excatly is a VFDs. it stands for variable frequency drives,

they are use for running AC motor at varing frequencies or for ramping up motor speed in order to achieve a smooth startup.


It works by adjusting the frequency of the drives which inturn increase the speeds of the drives..

the VFD have three main components,

the the rectifier the filter and a inverter.

the rectifier act like diode, the incoming AC voltage will be converted to DC voltage.

the converted DC voltage will be further smoothened by the filter using Capacitors.

finally, the inverter will convert the DC voltage back to AC voltage which can be varied in hartz.

the hartz will be used to drive the motor to specific speed knowns as rpm.







a typical soft starter triac consists of 6 back taristors or scr placed in parallel configuration to start the motors.

the main aim of this drive is to limit the in rush currents to the motors.

a tyristor is made up of three part, the logic gate, the anode and cathode.

when internal pulse is applied to it gate, it allows current to flows from anode to cathode which will be sent to an electric motor.

when the pulses applied to the gate is interrupted, the current flowing the cathode from the anode will be interrupted and the scr will be in off states.

the pulse are sent at ramp time,this way, current is applied to the motor at very reduce amount, this will allow the motor to start slowly.

this reduces mechanical stress that might be generated as a result of sudden startup.

when the motor reaches full speed, the soft starter will behave as other starting method mentioned earlier.





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