1、Applications of InvertersConversion 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

2、power supplies)AC-DC-AC Converters for induction heatingAC-DC-AC-DC switching power suppliesOutline4.1 Commutation4.2 Voltage source inverters4.3 Current source inverters4.4 Multiple-inverter connections and multi-level inverters 4.1 Commutation typesA classification of invertersSquare-wave inverter

3、s (are discussed in this chapter)PWM inverters ( will be discussed in Chapter 6)The concept of commutationBasic operation principle of invertersLoadS1S2S3S4iouoUd4 types of commutation Device commutation: Fully-controlled devices: GTO, IGBT, MOSFET Line commutation Phase-controlled rectifier Phase-c

4、ontrolled AC controller Thyristor cycloconverter Load commutation Forced commutationLoad commutation Condition: Load current is leading load voltage Application: capacitive load, synchronous motor Forced commutation (capacitance commutation)Direct-CoupledWith Coupling-InductorAnother classification

5、of commutationsSelf-commutationDevice commutationForced commutationLine commutationLoad commutation4 types of CommutationsExternal commutationFor fully-controlled devicesFor thyristors2 classes of invertersVoltage Source Inverter (VSI)Current Source Inverter (CSI)4.2 Voltage source inverter (VSI) DC

6、 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)+-CRLUdV1V2V3V4VD1VD2VD3VD

7、4uoioFeaturesSingle-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.)-RLUdiouoV1V2VD1VD2Ud2Ud2The magnitude of output square-wave voltage is Ud/2.uoUmiot1t2t3t4t5t6V1V2V1V2

8、VD1VD2VD1VD2UG1UG2 Single-phase full bridge VSIOperation principle+-CRLUdV1V2V3V4VD1VD2VD3VD4uoio 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.uoUmiot1t2t3t4t5t6V1V2V1V2VD1VD2VD1VD2UG1,4UG2,3VD4

9、VD3VD4VD34343VVVVFourier series extension of output voltageMagnitude of output voltage fundamental component Effective value of output voltage fundamental component Single-phase full bridge VSIQuantitative analysis(4-1)(4-2)(4-3) Single-phase full bridge VSI Output voltage control by phase-shift+-CR

10、LUdV1V2V3V4VD1VD2VD3VD4uoioInverter with center-tapped transformerpush-pull inverter Three-phase VSI 180o conduction Dead time (blanking time) to avoid “shoot through” Three-phase VSIBasic equations to obtain voltage waveformsFor line voltageFor phase voltage of the loadThree-phase VSIFourier series

11、 extension of output line-to-line voltageMagnitude of output voltage (line-to-line) fundamental component Effective value of output voltage (line-to-line) fundamental componentQuantitative analysis(4-8)(4-10)(4-11)4.3 Current source inverter (CSI) DC side is constant current, high impedance (current

12、 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.FeaturesSingle-phase bridge CSIParallel Resonant Inverte

13、r ACRLLdIdVT1VT2VT3VT4LT1LT2LT3LT4uoio Switching 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.Three-phase self-commutated CSI 120o conductionThree-phase force-commutated CSIThree-phase loa

14、d-commutated CSI4.4 Multiple-inverter connections and multi-level invertersSeries connection of 2 single-phase VSIsSeries connection of 2 3-phase VSIsMulti-level InvertersWays 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