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## 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**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**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**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)**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.**Single-phase full bridge VSI**Operation principle**Quantitative analysis**Fourier series extension of output voltage Magnitude of output voltage fundamental component Effective value of output voltage fundamental component**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**5.3Current 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.**Single-phase bridge CSI**Parallel Resonant Inverter**5.4 Multiple- inverter connections and multi-level inverters**• Series connection of 2 single- phase VSIs