Current Source Inverter ( CSI )

  • The voltage source inverter is one in which output voltage remains constant and it does not depends upon type of load. 
  • The voltage across load is kept constant by connecting large capacitor at the input side of the inverter. 
  • The current source inverter is one in which output current remains constant with respect to type of load.  
  • An inductor of suitable value is placed in series with DC voltage source.


  • The DC input voltage in the current source inverter is supplied through rectifier bridge/controlled rectifier bridge or DC chopper.  
  • The LC filter is connected at the input in order to get ripple free current.  
  • The function of the inductor L is to decrease the ripple current whereas the capacitor C is to reduce source impedance. 
  • The power flow from supply to load and vice versa is possible at different power factor due to low impedance of DC supply. 
  • The current source inverter is either load commutated or force commutated
  • The current source inverter is load commutated if the load power factor is leading whereas it must be force commutated if the load power factor is lagging. 
  • The current source inverter can be used for the speed control of induction motor in which variation of load torque occurs. 
  • There is additional diode requires for feeding the reactive power back to the supply when inductive load is used.


  • There are converter grade thyristor used in the current source inverter which has reverse blocking voltage capability. 
  • The converter grade thyristor should have withstand capacity of high voltage spike during commutation.

  • The commutation capability depends upon the load current and this will limit the operating frequency.
  • Sluggish performance and stability problem at light load and high frequency

  • Induction heating
  • Speed control of AC motor
  • Starting of synchronous motor
  • To compensate lagging reactive power

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