Classification of Voltage Source Inverters
Classification of Voltage source Inverters:
Fig: Topology of 1- phase and 3-Phase VSI
- Voltage source inverters can be classified according to different criterions. They can be classified according to number of phases they output.
- Accordingly there are single-phase or three-phase inverters depending on whether they output single or three-phase voltages. It is also possible to have inverters with two or five or any other number of output phases.
- Inverters can also be classified according to their ability in controlling the magnitude of output parameters like, frequency, voltage, harmonic content etc.
- Some inverters can output only fixed magnitude (though variable frequency) voltages whereas some others are capable of both variable voltage, variable frequency (VVVF) output.
Fig: Bi-Directional controlled switch
- Output of some voltage source inverters is corrupted by significant amount of many low order harmonics like 3rd, 5th, 7th, 11th, 13th order of the desired (fundamental) frequency voltage.
- Some other inverters may be free from low order harmonics but may still be corrupted by some high order harmonics.
- Inverters used for ac motor drive applications are expected to have less of low order harmonics in the output voltage waveform, even if it is at the cost of increased high order harmonics.
- Higher order harmonic voltage distortions are, in most ac motor loads, filtered away by the inductive nature of the load itself.
- Inverters may also be classified according to their topologies. Some inverter topologies are suitable for low and medium voltage ratings whereas some others are more suitable for higher voltage applications.
- The inverters shown are two level inverters as the pole voltages may acquire either positive dc bus or negative dc bus potential. For higher voltage applications it may not be uncommon to have three level or five level inverters.