voltage source inverter and current source inverter

Difference between Inverters: VSI vs CSI

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In this article we are study about the difference between voltage source inverter (VSI) and current source inverter (CSI).

What Is Inverter?

An inverter, is a power electronics device which used to convert fixed DC (Direct Current) into controlled AC (Alternating Current)”. Here, Controlled AC means we controlled two parameter of AC signal Frequency and Amplitude.

Inverter

In other words, the inverter is a static device. It can convert one form of electrical energy into other forms of electrical energy. But it cannot generate electrical power.

Inverter takes DC input power from the batteries and converts into AC output power at the time of the power failure or power cutoff.

In inverter we use some power semiconductor switching devices like IGBT, MOSFET, GTO because these devices having self-commutation property.

A power inverter used in the power system network to convert bulk DC power to AC power. i.e., It used at the receiving end of HVDC transmission lines. This inverter is known as a grid-tie inverter.

Classification Of Inverter

Inverters are mainly classified into two types:

  1. VSI (Voltage Source Inverter)
  2. CSI (Current Source Inverter)

What Is VSI (Voltage Source Inverter)?

In voltage source inverter (VSI) input voltage is kept constant. VSI is fed from a DC voltage source having negligible or zero impedance.

So, to make a VSI we connect a DC source in parallel with large capacitor that maintained Input voltage constant. In case of VSI an output voltage is independent of load. Here, the waveform of the load current as well as its magnitude depends upon the nature of load impedance.

Voltage Source Inverter

A voltage source inverter is fed by a stiff DC voltage or constant DC voltage is called Voltage Source Inverter (VSI) or Voltage Fed Inverter (VFI).

In Voltage Source Inverter (VSI) we use power semiconductor switching devices in the circuit like Power BJT, Power MOSFET, IGBT having self-commutation properties.

VSI drives are more efficient than CSI designs. This is because in VSI drives we use IGBT switching devices that is more efficient than the GTO or SGCT devices used in CSI versions. 

What Is CSI (Current Source Inverter)?

In current source inverter (CSI) input current is kept constant. CSI is fed with adjustable current source from a DC voltage source of high impedance.

VSI can be converted into CSI, by connecting large series inductance that maintained input current constant. In CSI output current is independent of load. Here, the magnitude of output voltage and its waveform depends upon the nature of the load impedance.

Current Source Inverter

A Current Source Inverter is fed by a stiff current source or constant current source is also called Current Source Inverter (CSI) or Current Fed Inverter (CFI).

In Current Source Inverter (CSI) we use Thyristor as a semiconductor switching device.

Below circuit diagram help you to understand about the difference between VSI and CSI.

VSI Circuit Diagram
CSI Circuit Diagram

Difference between Voltage Source Inverter (VSI) and Current Source Inverter (CSI)

VSI (Voltage Source Inverter)CSI (Current Source Inverter)
1. In voltage source inverter input voltage is kept constant.1. In current source inverter input current is kept constant.
2. VSI is fed from a DC voltage source having small or negligible impedance.2. CSI is fed with adjustable current source from a DC voltage source of high impedance.
3. DC source in parallel with large capacitor.3. VSI can be converted into CSI, By connecting large series inductance.
4.Input voltage is maintained constant.4. The input current is constant but adjustable.
5. An output voltage is independent of load.5. An output current is independent of load
6. The waveform of the load current as well as its magnitude depends upon the nature of load impedance.6. The magnitude of output voltage and its waveform depends upon the nature of the load impedance.
7. VSI has slow response than CSI. 7. CSI has fast response than VSI.
8. VSI requires feedback diodes8. The CSI does not require any feedback diodes.
9. The commutation circuit is complicated. It uses current commutation.9. Commutation circuit is simple as it contains only capacitors. It uses voltage commutation.
10. Power BJT, Power MOSFET, IGBT with self commutation can be used in the circuit.10. Thyristors are Used.
11. In VSI diodes are connected in parallel.11. In CSI diodes are connected in series.
12. PWM technique is used.12. PWM technique is not used.

FAQ’s (Frequently Asked Questions)

What are the main differences between VSI and CSI?

In voltage source inverter (VSI) input voltage is kept constant. VSI is fed from a DC voltage source having negligible or zero impedance. In current source inverter (CSI) input current is kept constant. CSI is fed with adjustable current source from a DC voltage source of high impedance.
A VSI can also be operated in current-controlled mode, and similarly a CSI can also be operated in the voltage control mode.

What are the advantages of VSI?

The advantages of VSI are; (i) It has a small size. (ii) Its output voltage waveform does not depend on the type of load.

What are the advantages of VSI over CSI?

VSI drives are more efficient than CSI designs. This is because in VSI drives we use IGBT switching devices that is more efficient than the GTO or SGCT devices used in CSI versions. 

What is voltage source inverter?

In voltage source inverter (VSI) input voltage is kept constant. VSI is fed from a DC voltage source having negligible or zero impedance.
So, to make a VSI we connect a DC source in parallel with large capacitor that maintained Input voltage constant. In case of VSI an output voltage is independent of load. Here, the waveform of the load current as well as its magnitude depends upon the nature of load impedance.

What is current source inverter?

In current source inverter (CSI) input current is kept constant. CSI is fed with adjustable current source from a DC voltage source of high impedance.
VSI can be converted into CSI, by connecting large series inductance that maintained input current constant. In CSI output current is independent of load. Here, the magnitude of output voltage and its waveform depends upon the nature of the load impedance.


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