Chapter 5 DC to AC Converters

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Chapter 5 DC to AC Converters

• Outline
• 5.1 Commutation
• 5.2 Voltage source inverters
• 5.3 Current source inverters
• 5.4 Multiple- inverter connections and multi-
  level inverters

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5.1 Commutation types

• Basic operation principle of inverters
• A classification of inverters
• Square- wave inverters (are discussed in this
  chapter)
• PWM inverters ( will be discussed in Chapter 6)
• The concept of commutation

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• 4 types of commutation
• 1)Device commutation
• Fully- controlled devices GTO, IGBT, MOSFET
• 2)Line commutation
• Phase- controlled rectifier,Phase- controlled AC
  controller,
• Thyristor cycloconverter
• 3)Load commutation
• 4)Forced commutation

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• (1) Load commutation

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• (2) Forced commutation (capacitance commutation)

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• Another classification of commutations

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• 2 classes of inverters

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5.2 Voltage source inverter (VSI)

• Features
• DC side is constant voltage, low impedance
  (voltage source, or bulk cap)
• AC side voltage is square wave or quasi- square
  wave.
• AC side current is determined by the load.
• Anti- parallel diodes are necessary to provide
  energy feedback path.
• (freewheeling diodes , feedback diodes)

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• Single-phase half bridge VSI
• The current conducting path is determined by the
  polarity of load voltage and load current. (This
  is true for analysis of many power electronics
  circuits.)
• The magnitude of output square- wave voltage is
  Ud/2.

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• Single-phase full bridge VSI
• Operation principle

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• Quantitative analysis
• Fourier series extension of output voltage
• Magnitude of output voltage fundamental component
  
• Effective value of output voltage fundamental
  component

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• Output voltage control by phase-shift

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• Inverter with center- tapped transformerpush-pull
  inverter

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• Three-phase VSI

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• Basic equations to obtain voltage

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• Quantitative analysis
• Fourier series extension of output line- to- line
  voltage
• Magnitude of output voltage (line- to- line)
  fundamental component
• Effective value of output voltage (line- to-
  line) fundamental component

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5.3 Current source inverter (CSI)

• Features
• DC side is constant current , high impedance
  (current source, or large inductor)
• AC side current is quasis-quare wave. AC side
  voltage is determined by the load.
• No anti-parallel diodes are needed. sometimes
  series diodes are needed to block reverse voltage
  for other power semiconductor devices.

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• Single-phase bridge CSI
• Parallel Resonant Inverter

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• Three- phase self-commutated CSI

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• Three- phase force- commutated CSI

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• Three- phase load-commutated CSI

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5.4 Multiple- inverter connections and
multi-level inverters

• Series connection of 2 single- phase VSIs

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• Series connection of 2 3- phase VSIs

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• Multi-level Inverters 3- level inverter