The document discusses three phase voltage source inverters. It begins by introducing inverters and their use in converting DC to AC power. It then classifies inverters as voltage source or current source. The main topic is the three phase voltage source inverter, which converts DC to three phase AC power using six switches in three arms delayed by 120 degrees. The inverter can operate in 180 degree or 120 degree conduction modes, which determine the output phase and line voltages. Applications of three phase inverters include DC power utilization, UPS, induction heating, variable frequency drives, and electric vehicle drives.

1. THREE PHASE VOLTAGE
SOURCE INVERTER
Kongunadu College of Engineering and Technology Three Phase VSI
Contents:
Inverter Introduction
classification
Three phase Voltage source inverter
180 degree conduction mode
120 degree conduction mode
Applications
References

2. INTRODUCTION
 An inverter refers to a power electronic device that converts power in
DC form to AC form at the required frequency and voltage output.
 The ideal output of an inverter is a sinusoidal waveform. Such a
wave gives continuous flow of power. But the output from the circuit
is generally not ideal. It gives output in the form of square wave,
quasi-square wave or PWM.
 The conversion of DC power to AC power can be done using two
approaches. Both do conversion in two steps.
 In the first approach, a low voltage DC power is converted into
high voltage DC power and then in the second step this high
voltage DC power is converted to AC power.
 In the second approach, a low voltage DC power is converted to
low voltage AC power and then this output is stepped up to high
voltage AC power.
Kongunadu College of Engineering and Technology Three phase VSI

3. classification
 Voltage Source Inverter (VSI) − The voltage source inverter
has stiff DC source voltage that is the DC voltage has limited
or zero impedance at the inverter input terminals.
 Current Source Inverter (CSI) − A current source inverter is
supplied with a variable current from a DC source that has high
impedance. The resulting current waves are not influenced by
the load.
Kongunadu College of Engineering and Technology Three phase VSI

4. Three phase voltage source inverter
Kongunadu College of Engineering and Technology Three phase VSI

5. Cont…
 A three-phase inverter converts a DC input into a three-phase
AC output. Its three arms are normally delayed by an angle of
120° so as to generate a three-phase AC supply. The inverter
switches each has a ratio of 50% and switching occurs after
every T/6 of the time T (60° angle interval). The switches S1
and S4, the switches S2 and S5 and switches S3 and S6
complement each other.
 The two types of inverters above have two modes of
conduction − 180° mode of conduction and 120° mode of
conduction.
Kongunadu College of Engineering and Technology Three phase VSI

6. 180 degree mode of conduction
The load voltages are gives as follows;
 VAN = V/3,
 VBN = −2V/3,
 VCN = V/3
The line voltages are given as follows;
 VAB = VAN − VBN = V,
 VBC = VBN − VCN = −V,
 VCA = VCN − VAN = 0
Kongunadu College of Engineering and Technology Three phase VSI

7. Cont…
Kongunadu College of Engineering and Technology Three phase VSI

8. 120 degree mode of conduction
 Phase voltages = Line voltages
 VAB = V
 VBC = −V/2
 VCA = −V/2
Kongunadu College of Engineering and Technology Three phase VSI

9. Cont…
Kongunadu College of Engineering and Technology Three phase VSI

10. Applications
 Dc power source utilization
 Un interruptible power supplies
 Induction heating
 Variable frequency drive
 Electrical vehicle drive
Kongunadu College of Engineering and Technology Three phase VSI

11. References
 M.H.Rashid, ‘Power Electronics: Circuits, Devices and
Applications’, Pearson, PHI Third Edition, New Delhi, 2004.
 P.S.Bimbra “Power Electronics” Khanna Publishers, third
Edition, 2003.
 https://www.tutorialspoint.com/power_electronics/power_elect
ronics_types_of_inverters.htm
 https://www.theengineeringprojects.com/2016/10/introduction-
inverters.html
Kongunadu College of Engineering and Technology Three phase VSI