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.

single phase half wave inverter












         
  • 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 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.

operation-of-single-phase-half-wave-bridge-inverter.png

               














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 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.