Comparison of Inverters: VSI vs CSI
Comparison of Inverters: VSI vs CSI
This post will discuss about the difference between Voltage Source Inverter and Current Source Inverter.
Before proceeding further we will get the introduction about them.
What is meant by Inverter?
The Inverter is the power electronic circuit, which converts the DC voltage into AC voltage. The DC source is normally a battery or output of the controlled rectifier.
- The output voltage waveform of the inverter can be square wave, quasi-square wave or low distorted sine wave.
- The output voltage can be controlled with the help of drives of the switches.
- The pulse width modulation techniques are most commonly used to control the output voltage of inverters. Such inverters are called as PWM inverters.
- The output voltage of the inverter contain harmonics whenever it is not sinusoidal.
- These harmonics can be reduced by using proper control schemes.
What are the various types of Inverters?
Inverters can be broadly classified into two types. They are
- Voltage Source Inverter (VSI)
- Current Source Inverter (CSI)
When the DC voltage remains constant, then it is called Voltage Source Inverter(VSI) or Voltage Fed Inverter (VFI).
When input current is maintained constant, then it is called Current Source Inverter (CSI) or Current Fed Inverter (CFI).
Some times, the DC input voltage to the inverter is controlled to adjust the output. Such inverters are called Variable DC Link Inverters. The inverters can have single phase or three-phase output.
- A voltage source inverter(VSI) is fed by a stiff DC voltage, whereas a current source inverter is fed by a stiff current source.
- A voltage source can be converted to a current source by connecting a series inductance and then varying the voltage to obtain the desired current.
- A VSI can also be operated in current-controlled mode, and similarly a CSI can also be operated in the voltage control mode.
- The inverters are used in variable frequency ac motor drives, uninterrupted power supplies, induction heating, static VAR compensators, etc.
The following table gives us the comparative study between VSI and CSI
|VSI is fed from a DC voltage source having small or negligible impedance.||CSI is fed with adjustable current from a DC voltage source of high impedance.|
|Input voltage is maintained constant||The input current is constant but adjustable.|
|Output voltage does not dependent on the load||The amplitude of output current is independent of the load.|
|The waveform of the load current as well as its magnitude depends upon the nature of load impedance.||The magnitude of output voltage and its waveform depends upon the nature of the load impedance.|
|VSI requires feedback diodes||The CSI does not require any feedback diodes.|
|The commutation circuit is complicated||Commutation circuit is simple as it contains only capacitors.|
|Power BJT, Power MOSFET, IGBT, GTO with self commutation can be used in the circuit.||They cannot be used as these devices have to withstand reverse voltage.|
DO YOU KNOW???
Do you know about Inductors?
A component called an inductor is used when the property of inductance is required in a circuit. The basic form of an inductor is simply a coil of wire.
Factors which affect the inductance of an inductor include:
(i) the number of turns of wire—the more turns, the higher the inductance.
(ii) the cross-sectional area of the coil of wire—the greater the cross-sectional area the higher the inductance.
(iii) the presence of a magnetic core—when the coil is wound on an iron core, the same current sets up a more concentrated magnetic fi eld and the inductance is increased.
(iv) the way the turns are arranged—a short thick coil of wire has a higher inductance than a long thin one.