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 V_dc / 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 – V_dc / 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 180⁰ phase 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

Resistive load

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

R – L load

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

Mode 1 ( t₁ < t < t₂ )

• The load receives V_dc / 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 – V_dc / 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 + V_dc / 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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