An Introduction to Inverter Circuit

1. Inverter
Dr. Sarmista Sengupta
Asst. Prof., Dept. of ECE
Techno Main Salt Lake

2. • An Inverter is basically a converter that converts DC-AC
power.
• The word “inverter” in the context of power electronics
denotes a class of power conversion circuits that
operates from a dc voltage source or a dc current
source and converts it into ac voltage or current.
• The primary source of input power may be utility ac
voltage supply that is converted, to dc by an ac to dc
converter and then inverted back to ac using an
inverter.
• The final output may be of a different frequency and
magnitude than the input ac of the utility supply.
• Typical Applications such as Un-interruptible Power
Supply (UPS), Industrial (induction motor) drives,
Traction, HVDC.

3. Self oscillating and driven inverter
Transistor inverters can either be self oscillating, or driven
by a separate oscillator. In the self oscillating type, the
transformer itself provides the positive feedback required
to cause oscillation. However, loading and transformer
design will affect operation to a certain degree. Where
frequency stability is important, the inverter requires a
separate oscillator to drive the switching transistors.

4. Classification of driven inverter
• Voltage-source inverter (VSI) or Voltage-fed
inverters (VFI)
– Stiff dc voltage source at the input (A stiff voltage
source reliably produces the intended voltage as load
currents change.)
• Current-source inverter (CSI) or Current-fed
inverter (CFI)
– Stiff dc current source at the input (A “stiff” current is
a current source with a very high (or
infinite) source impedance. In other words,
the current decreases very little (or not at all) as
the voltage increases.)

5. Single Phase VSI
• Single phase half-bridge inverter

6. Working Principle
Drawback: 3-wire DC supply

7. Single Phase VSI
• Single phase full-bridge inverter

8. Working Principle

9. CSI and VSI brief comparison
• In VSI, input voltage is maintained constant and the
amplitude of the output voltage does not depend upon
the load.
• Waveform of load current and its magnitude depends
upon the nature of the load impedance (R,RL etc.).
• In CSI, input current is constant but adjustable.
• The amplitude of output current from CSI is
independent of the load.
• However, the magnitude of output voltage and its
waveform output from CSI is dependent upon the
nature of the load.
• A CSI does not require feedback diodes, whereas these
are required in VSI.

10. CSI: Converts input DC current to
output AC current
• The DC input to CSI is obtained from a fixed
voltage AC source, through a controlled
rectifier bridge, or through a diode bridge and
a chopper.
• To make current input to CSI almost ripple
free, L-filter is used before CSI.

11. CSI: Applications

12. Single phase CSI

13. Working Principle

14. Series and Parallel inverters

15. Series and Parallel inverters