1. POWER ELECTRONICS DC-AC CONVERTERS (INVERTERS) PART 1
SITI ZARINA BINTI MD NAZIRI TMT 404 ADVANCED ENGINEERING 4

2. Content Content Concept Full-bridge Converters Half-bridge Inverters
Square-wave Inverters
Half-bridge Inverters
Introductory notes.
SOURCES: “Power Electronics”, Daniel W. Hart, Mc-Graw Hill, “Power Electronics & Drives”, Lecture Notes, Dr. Zainal Salam, UTM

3. DC-AC Converter (Inverter)
DEFINITION: Converts DC to AC power by switching the DC input voltage (or current) in a pre-determined sequence so as to generate AC voltage (or current) output.
TYPICAL APPLICATIONS: Un-interruptible power supply (UPS), Industrial (induction motor) drives, Traction, HVDC
General block diagram

4. Full-Bridge Converter
Basic circuit used to convert dc to ac
ac output is synthesized from a dc input by closing & opening switches in appropriate sequence
List of vo according to switch combinations:
Overlap of switch “on” time will result short-circuit, across dc voltage source
The time allowed for switching is called blanking time
Switches Closed
Output Voltage, vo
S1 and S2
+Vdc
S3 and S4
-Vdc
S1 and S3
S2 and S4

5. Full-Bridge Converter
S1, S2 closed
Vo = -Vdc
Vo = +Vdc
S3, S4 closed
S2, S4 closed
Vo = 0
S1, S3 closed
Vo = 0

6. Square-wave Inverter
Simplest switching scheme for full bridge converter produce a square wave output voltage
For RL load
Sum of force resources
Sum of natural resources
(S1, S2 closed)
(S3, S4 closed)
Note:
A and B are constants evaluated from initial condition m

7. Square-wave Inverter
Steady-state operation

8. Square-wave Inverter Steady-state operation
Since the square each of the current half-periods is identical, only the 1st half period need to be evaluated:
Power absorbed by load:
If switches are ideal, the power supplied must be the same as absorbed by load.
Power from a dc source:

9. Square-wave Inverter
Waveforms

10. Full-Bridge Inverter
With insulated gate bipolar transistors (IGBT) switches & feedback diodes

11. Full-Bridge Inverter With IGBT switches & feedback diodes – Operation
When IGBTs Q1 & Q2 are turned off, the load must be continuous, transferred to D3 and D4, Vo = -Vdc; effectively turning the switch path 3 & 4 before Q3 and Q4 are turned on.
IGBTs of Q3 & Q4 must be turned on before the load current decays to 0.

12. Half-bridge Inverter
The number of switches is reduce to 2, by dividing the dc source voltage into 2 parts with capacitors
Capacitors are same in value, voltage = Vdc/2
S1 closed,
Vo = -Vdc/2
S2 closed,
Vo = +Vdc/2

13. Questions/Discussions
Square-wave Inverter with RL load
Given f = 60 Hz, Vdc = 100 V, R = 10 Ohm, L = 25 mH. Determine:
An expression for load current
The power absorbed by load
The average current in dc source