Presentation on theme: "Chapter 4 DC to AC Converters ( Inverters )"— Presentation transcript:
1 Chapter 4 DC to AC Converters ( Inverters ) Power ElectronicsChapter DC to AC Converters ( Inverters )
2 Applications of Inverters Conversion of electric power from DC type energy sources to AC type loadBatteryPhotovoltaic cell (Solar cell)Fuel cellAs a part of composite converterAC-DC-AC frequency converter (for AC motor drive)AC-DC-AC constant-voltage constant-frequency converter (for uninterruptable power supplies)AC-DC-AC Converters for induction heatingAC-DC-AC-DC switching power supplies
3 Outline 4.1 Commutation 4.2 Voltage source inverters 4.3 Current source inverters4.4 Multiple-inverter connections and multi-level inverters
4 4.1 Commutation types Basic operation principle of inverters LoadS1234iouUdA classification of invertersSquare-wave inverters (are discussed in this chapter)PWM inverters ( will be discussed in Chapter 6)The concept of commutation
5 4 types of commutation Device commutation: Fully-controlled devices: GTO, IGBT, MOSFETLine commutation Phase-controlled rectifierPhase-controlled AC controllerThyristor cycloconverterLoad commutationForced commutation
6 Load commutation Condition: Load current is leading load voltage Application: capacitive load, synchronous motor
8 Another classification of commutations 4 types of CommutationsFor fully-controlled devicesDevice commutationSelf-commutationForced commutationLine commutationFor thyristorsExternalcommutationLoad commutation
9 2 classes of inverters Voltage Source Inverter (VSI) Current Source Inverter(CSI)
10 4.2 Voltage source inverter (VSI) +-CRLUdV1234VDuoiFeaturesDC 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)
11 Single-phase half bridge VSI UdiouV12VDuoUmit123456VVDG1G2The 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.
12 Single-phase full bridge VSI oUmit123456VVDG1,4G2,3Operation principle+V3VD3VD1CV1RiLUoduV2oVDVD42V4-The magnitude of output square-wave voltage is Ud.The effective value of output voltage (or fundamental output voltage) can be changed by changing Ud.
13 Single-phase full bridge VSI Quantitative analysisFourier series extension of output voltageMagnitude of output voltage fundamental componentEffective value of output voltage fundamental component(4-1)(4-2)(4-3)
14 Single-phase full bridge VSI Output voltage control by phase-shift+-CRLUdV1234VDuoi
15 Inverter with center-tapped transformer —push-pull inverter
16 Dead time (blanking time) to avoid “shoot through” Three-phase VSI180o conductionDead time (blanking time) to avoid “shoot through”
17 Basic equations to obtain voltage waveforms Three-phase VSIBasic equations to obtain voltage waveformsFor line voltageFor phase voltage of the load
18 Three-phase VSI Quantitative analysis Fourier series extension of output line-to-line voltageMagnitude of output voltage (line-to-line) fundamental componentEffective value of output voltage (line-to-line) fundamental component(4-8)(4-10)(4-11)
19 4.3 Current source inverter (CSI) FeaturesDC side is constant current, high impedance (current source, or large inductor)AC side current is quasi square 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.
20 Single-phase bridge CSI Parallel Resonant InverterACRLdIVT1234TT3T4uoiSwitching frequency is a little higher than the resonant frequency so that the load becomes capacitive and load current is leading voltage to realize load commutation.
26 Multi-level Inverters Ways to deal with higher voltage and achieve better waveformSeries connection of multiple convertersSeries connection of multiple switch devicesMajor type of multi-level invertersNeutral point clamped multi-level inverterFlying-capacitor multi-level inverterCascade H-bridge( series connected H-bridges)In broad sense, previously discussed series connection of multiple inverters is also called multi-level inverter.In narrow sense, only NPC and FC structures are called multi-level inverters.