Inverters

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Inverters

  1. 1. InvertersInverters take dc from a battery (etc) and convert it electronically to ac power. Revision 01 1
  2. 2. Revision 01 2
  3. 3. Block diagram of and inverter AC OutDC In Switches Transformer Rectifier Filter DC Out DC to AC Output is sampled to adjust switching for voltage regulation Revision 01 3
  4. 4. Inverter OPERATION• Inverters are classified by their ac output waveform. – Square wave – Modified sine wave – True sine wave Revision 01 4
  5. 5. Inverter operationSine Wave Square Wave Modified Square Wave Revision 01 5
  6. 6. Inverter operation• Most smaller inverters are either square wave (cheap) or modified square wave. Revision 01 6
  7. 7. Inverter operationBy closing and opening the switch rapidly, a square wave supply tothe transformer is achieved. This used to be done mechanically witha “vibrator”. (Yeah! I know…) Revision 01 7
  8. 8. Inverter operationThe switches close in turn, producing a pseudo-AC in the primary.Not that rectification is centre-tapped, full wave, with an L filter. Revision 01 8
  9. 9. Inverter operationHere the rectifier is a full wave, bridge, with L filter. Revision 01 9
  10. 10. Inverter operationA single winding is used here on the primary, with the switchesclosing is sequence to provide AC to the primary. Revision 01 10
  11. 11. Vibrator Vibrator Here is what one looks like. Inside are vibrating mechanical contact points that oscillate and generate a low voltage AC signal from the DC voltage applied to it from the battery. The AC signal then feeds a transformer where the voltage is increased. AC Out Revision 01 11
  12. 12. Revision 01 12
  13. 13. Square waves• Cheap• Very poor regulation• Produce large amounts of RFI• Very rough AC• Large amounts of harmonics• Often used for small appliances eg; fluro lightsVery few but the very cheapest inverters any more are square wave. A square wave inverter will run simple things like tools with universal motors with no problem - but not much else. These are seldom seen any more except in small, very cheap or very old inverters. Revision 01 13

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