## 11 June 2017

### Single Phase Half wave Inverter

• The power circuit diagram for the single phase half bridge inverter is shown in the figure A.
• The SCR triggering circuit and commutation circuit is not shown for simplicity.

The SCR T1 is turned on for time 0 ≤ t ≤ T/2 times. This is shown in the figure C.
• The load receives Vdc / 2 voltage from upper DC voltage source.
• The SCR T1 is turned off and SCR T2 is turned on at time t = T/2.
• The load receives – Vdc / 2 voltage from lower half supply source during time T/2 ≤ t ≤ T time.
• Each SCR gate receives gate pulse at frequency f = 1/T. There is 180phase displacement between two SCR gate signals.
• The frequency of the output voltage is equal to 1/T and it is controlled by time period T.

### Effect of type of load on output waveform

• The load voltage and load current waveform do not have any phase displacement when the resistive load is connected at the output.

The working of the single phase half bridge inverter is explain as follows

#### Mode 1 ( t1 < t < t2 )

• The load receives Vdc / 2 voltage when the SCR T1 is turned on and load current increases slowly and exponentially.
• The load voltage and load current polarity becomes equal when SCR T1 is turned off. The energy stored in the load during this interval.

#### Mode 2 ( t2 < t < t3 )

• The flow of inductive load current continues to flow when SCR T1 is turned off. The direction of load voltage reverses.
• The load current flows through conduction of lower half diode D2. The stored energy of load feedback to lower half.

#### Mode 3 ( t3 < t < t4 )

• The load current becomes zero and SCR T2 is turned on during this interval.
• The voltage across load becomes – Vdc / 2.  The load current becomes maximum negative at the end of this period ( t4 time ).

#### Mode 4 ( t4 < t < t5 )

• The SCR T2 is turned off at time t4 but the load current continues to flow due to inductive load.
• The voltage across load becomes equal to + Vdc / 2.
• The load current flows through upper half portion due to conduction of diode D1.
• The energy stored of load feedback to upper part of the supply source.
• The power flows from supply to load and vice versa. The main disadvantage of the single phase half bridge inverter is that it requires three wire DC supplies.

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