Improved Series Inverter [Type 1]

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Improved Series Inverter [Type 1]
Circuit Diagram of Series Inverter :
  • One of the major disadvantages of the basic series inverter circuit is the limitation on its maximum output frequency.
  • This can be overcome by the improved series circuit shown in Figure A. The output frequency can be increased by turning on SCR2 even before SCR1 is turned off.

Modified Series Inverter :

Configuration
Figure A

Mode 1
Figure B

Mode 2
Figure C

Operation of Series Inverter :

  • The inductors L1, and L2 have same inductance and are closely coupled.
  • Therefore when SCR1 is fired and current i starts flowing, the potential across L1 will be +ve with a polarity as shown in figure B.
  • The capacitor C1 charges with polarity shown in Figure B through SCR1, L1 and load.
  • The induced voltage in inductance L2 will reverse bias SCR2.
  • The important feature of this circuit is that SCR2 can be turned on even before the load current has reached zero or before SCR, has been turned off.
  • Therefore the output frequency can be greater than the ringing frequency of L1, C1 resonant circuit. Thus frequency range of the inverter is increased.
  • Suppose that SCR2 is turned on before SCR1 has been turned off. At the instant of firing SCR2 the voltage on G will be slightly less than (V + ec) with a polarity as shown in Figure B the load voltage and current will be close to zero. (ec+, is the voltage on the capacitor C1) Vc = V + ec.
  • Therefore a voltage equal to Vc. minus the load voltage will appear across L2 with a polarity shown in Figure B.
  • Since L1, is closely coupled to L2 same voltage appears across L1.
  • Thus cathode potential of SCR1 will be higher than its anode voltage and therefore SCR1 will be turned off due to application of reverse voltage across it as soon as SCR2 is turned ON.
  • A similar operation will take place if SCR1 is triggered before SCR2 is turned off.
  • There is no danger of short circuiting the input power supply due to the inclusion of the closely coupled reactors L1, and L2, in the circuit.
  • Only the first disadvantage of basic series inverter has been eliminated but all the other drawbacks remain as they are.

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