What is Current Source Inverter, Working, Diagram, Principle

The induction motor speed can be controlled by varying the supply frequency and the mainly used ins squirrel cage induction motor and the variable frequency control allows good running and stable performance to be obtained from a squirrel cage induction motor

Its specialized to maintaining the free operation such as underground and under water installations and this applications involving explosive and contaminated environments such as in mines and the chemical industry.

The variable frequency AC drive application are

Pumps, fans, blowers, compressor, conveyors, machine tool etc.,

The power semi conductors devices such as power transistors, power MOSFETs, IGBTs and GTOs with maintain to improve ratings and characteristics general purpose medium and high power variable frequency drives are available. The cost of the equipment is less compared to the dc drives. The variable frequency conversion system classified as

  • Voltage source inverter
  • Current source inverter
  • Cycloconverter

Current Source Inverter fed AC Drives

The voltage source inverter the output voltage is controlled by the input voltage. So the input voltage is kept constant but the output current depends upon the nature of load. In the current source inverter the input current in maintained constant because it can be adjusted. A large value of inductance is connected in series with voltage source and its act as a constant current source and the output voltage waveform is depending upon the load impedance.


The variable current and variable frequency control method and this circuit consists of 3phase controlled bridge rectifier inductor Ld and inverter due to the 3phase ac voltage is converted into variable dc by using 3phase controlled bridge rectifier. This dc voltage is converted into dc current source by passing through a large inductor in series with voltage source.

The inverter frequency is controlled by varied and the triggering of the inverter circuit SCRs and the output of the inverter is variable current variable frequency which is used to control the speed of the motor. The current is controlled during the acceleration periods to the controller circuit is used to varying the firing angle of the controlled rectifier. Due to controlled rectifier the main futures are that forced commutation is not required but the drawbacks is poor power factor at low load.

The current source inverter consists of a three phase diode rectifier, dc chopper, inductor Ld and inverter three phase diode bridge rectifier is used to convert fixed ac to fixed dc voltage and this output voltage is fed to the dc chopper and its convert fixed dc into variable dc voltage by connecting inductor and its convert dc voltage in to dc current. The constant frequency which is used to control the speed of the motor. The dc chopper voltage is control by controller circuit. The futures of the CSI is power factor is high. The demerits of this need to the force commutation

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