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## 19/06/2017

### Single Phase Full Bridge Inverter

• The power circuit diagram for the single phase full bridge inverter is shown in the figure A.
• The SCR triggering circuit and commutation circuit is not shown for simplicity.
• There are two wire DC supply source, four freewheeling diodes and four SCRs used in this inverter.
• The SCR T1 and SCR T2 are turned on at same time whose frequency is f = 1/T. Similarly the SCR T3 and SCR T4 are turned on simultaneously.
• There is 1800 phase difference between positive group of SCRs ( SCR T1 and SCR T2 ) and negative group of SCRs ( SCR T3 and SCRT4 ).

The working of single phase full bridge inverter is explain as follows
Mode 1
• The load voltage becomes to + Vdc when SCR T1 and SCR T2 are turned on at same time.
• Therefore the load current flows through path (+)Vdc – SCR T1 – load – SCR T2 – Vdc(-).
• The load current and load voltage becomes positive during this period therefore the power flows from supply to load.

Mode 2
• The polarity of voltage across load changes due to inductive load and as soon as the SCR T1 and SCR T2 are turned off in this mode.
• As the diode D3 and D4 conduct, the load current flows through path diode D3 – (+)Vdc – Vdc(-) – diode D4.
• The power flows from load to supply during this mode.

Mode 3
• The SCR T1 and SCR T2 are turned off whereas SCR T3 and SCR T4 are turned on during this mode.
• The voltage across load becomes – Vdc and current flows through path (+)Vdc – SCR T3 – load – SCR T4 – Vdc(-).
• The power flows through supply to load as the load voltage and load current both are negative during this period.

Mode 4
• The polarity of voltage across load changes as the SCR T3 and SCR T4 are turned off in this mode.
• The load current flows through path diode D1 – (+)Vdc – Vdc(-) – diode D2 – load due to conduction of freewheeling diode D1 and D2.
• The power flows from load to supply as the direction of load current reverses during this mode.
• The output voltage of the single phase full bridge inverter is double to that of single phase half bridge inverter.