25 June 2017

Parallel Inverter OR Parallel Inverter With Feedback Diodes

working of parallel inverter



Mode 1
  • The load current flows through path +Vdc – L – c – a – SCR T1 – Vdc when the SCR T1 is turned on. 
  • This will generate flux and resulting emf in the transformer primary winding ac and bc. 
  • The charging of capacitor is done up to 2Vdc voltage due to these induced emf. 
  • The polarity of capacitor C is done in the figure B. 
  • The maximum voltage withstand capability of the SCR T2 is 2Vdc
  • The induced emf in the transformer secondary is 2Vdc as there is unity turns ratio between half primary and secondary winding
  • This will result flow of current through load.

Mode 2
  • When the SCR T2 is turned on, the SCR T1 is turned off due to capacitor reverse voltage 2Vdc applied across it. 
  • As the SCR T2 is turned on, the load current flows through path +Vdc – L – c – b – SCR T2 – Vdc and discharging of capacitor is done through SCR T2. 
  • The charging of capacitor again done with – 2Vdc voltage. 
  • The current flows during this interval are in reverse direction as that of when SCR T1 is turned on. 
  • The SCR T1 again turned on when it receives gate pulse and SCR T2 is in off condition during this interval. 
  • The waveform of the output voltage become rectangular due to alternately switching of SCR T1 and SCR T2. 
waveform of parallel inverter


Parallel inverter with feedback diodes
  • When load is inductive, the load current becomes out of phase with load voltage and direction of load current reverses with respect to load voltage.  
  • The stored energy during this interval feeds back through diodes D1 and D2. 
  • The circuit diagram of parallel inverter with feedback diodes is shown in the figure C.
parallel inverter with feedback diodes


  • When SCR T1 is turned on, flow of current through path + Vdc – c – a – SCR T1 – L – Vdc (-).  
  • The flux generated in the transformer primary winding ac and bc due to this current. 
  • This will result in 2Vdc voltage induced in the transformer primary winding. 
  • The charging of capacitor polarity is shown in the figure D. 
  • When SCR T2 is switched on, the SCR T1 is turned off due to reverse voltage of capacitor and capacitor discharges through path C – g – SCR T2 – L – D1 – d – a – f – C. 
  • The stored energy of capacitor transfers to load via transformer upper side primary winding. 
  • When SCR T2 is turned on, the current flows through path + Vdc – c – b – SCR T2 – L – Vdc(-) and capacitor again charges with voltage – 2Vdc
  • The capacitor again discharges through path C – f – SCR T1 – L – D2 – e – b – g – C when SCR T1 is again turned on. 
  • This will result in stored energy of capacitor transfer to load via transformer lower side primary winding.

working of parallel inverter with feedback diodes

Advantages

Disadvantages
  • The parallel inverter is useful only when load is fixed. (The output waveform changes due to change in load )
  • The inverter does not useful for higher power for fixed value of inductor L and capacitor C.
  • The design of inverter is done for fixed voltage.