Question

Give the circuit analysis of current source inverter with resistive load. What are the main difference between voltage source inverter and current source inverter?

Answer 1

Current source inverter (CSI):

In current source inverter, the output current is independent of load. The input current of current source inverter is constant. Current source converter converts DC input current to AC output current. Output AC frequency depends on triggering of SCRs. The input to the current source inverter is the current source which is obtained by connecting large inductor in series with a voltage source. The switches (i.e. SCRs) of current source must be able to block reverse voltage. The diodes are connected in series to each switch to block reverse voltage. Current source inverter does not require freewheeling diode, this reduces the size and weight of current source inverter.

Difference between Voltage Source Inverter (VSI) and Current Source Inverter (CSI) is as follows:

Voltage Source Inverter (VSI)	Current Source Inverer (CSI)
In voltage source inverter input voltage is kept constant.	In current source inverter input current is kept constant.
An output voltage is independent of load.	The output current is independent of load.
VSI required feedback diode.	CSI does not require feedback diode.
Commutation circuit of VSI is complicated as compare to CSI.	Commutation circuit of CSI is simple as compare to VSI. Only diodes and capacitors are required for commutation.
BJT, MOSFET, IGBT, and GTO with self-commutation can be used in VSI.	BJT, MOSFET, IGBT, and GTO cannot be used in current source inverter because these devices have to withstand large reverse voltage.
Output current changes with load.	Output voltage changes with load.
Voltage source inverter requires capacitor in parallel.	Current source inverter require large reactor at output stage.
VSI has a slow response than CSI.	CSI has a faster response than VSI.
Voltage source inverter uses current commutation.	Current source inverter uses voltage commutation.
In VSI diodes are connected in parallel.	In CSI diodes are connected in series.