Introduction toPower ElectronicsChapter 1Advanced Power ElectronicsWhat is Power Electronics? Power + Electronics 電力電子 Power conversion by processing electricpower to expected voltage, current and /or frequency with semiconductor devices High frequency >20kHz Rapidly developed since 80s Applications Industrial, commercial and residentialpurposes Electrical vehicles, aerospace and spacetechnologiesApplications of Power Electronics Switched Mode Power Supplies(SMPS) Steady and regulated output voltage / current Applications of SMPS Low voltage high current DC power supplies Battery chargers Welding machines with over 100A Aerospace power systems Several KV power supplies for radar systems,cathode rayApplications of Power Electronics Switched Mode Power Supplies (SMPS) Closed loop control for regulating output Pulse-width-modulation (PWM), frequency modulation or phasemodulation controlInputPower High FrequencyConverterOutputPowerLoadSwitchingControlCircuitExternalControlSignalsGateSignalVoltage /Current Control ICs (Unitrode,Maxim) Microprocessors DSPs Range of operationconcernedApplications of Power Electronics Inverters AC current or mainly voltage output DC/AC converters or inverters DC input Applications of Inverters AC power supplies AC drives Induction heating Electronic ballastsApplications of Power Electronics Waveform Shaping & EMIControl Systems Shaping input / output and voltage /current Applications of Waveform Shaping Switched-mode amplifiers Harmonic waveform generationsystem Applications of EMI Control Power factor correction rectifiers Active filtersApplications of Power Electronics Uninterruptible Power Supplies With DC/DC converter of chargingand discharging battery With Inverter for AC output Motor Drives Choppers for brush-type DC motors Variable speed drives (VSD) forinduction motors Converters for brushless DC motors Converters for switched reluctancemotorsPower Components Energy Storage Components Inductors, capacitors, transformers Active Switching Devices MOSFET, IGBT Thyristors (SCR), Gate turn-off thyristors (GTO) Bipolar Junction Transistors (BJT) Passive Switching Devices(Power Diodes) General purpose diodes Ultra-fast recovery diodes Schottky barrier diodesWhy high frequency? Small size and light weight Inductors CapacitorsPL EL fS LIL 2 fS1 2 PC EC fS CVC 2 fS1 2 EnergyStorageDeviceENERGYINENERGYOUTCharacteristics of Active Switching Devices Symbol of Active Switching Devices ThyristorBJTMOSFETGTOIGBT GateAnodeCathodeCollectorEmitterBaseGateDrainSourceGateAnodeCathodeGateCollectorEmitter Thyristor / Silicon Controlled Rectifier(SCR) Developed in 1960s Switched on by a short injecting gate current pulse Firing or Triggering Switched off when reverse biased Ratings up to 5kV and 4000A Very high power applications Around 2V on-state voltage Slow response fS < 1kHz Force commutation necessaryCharacteristics of Active Switching Devices Bipolar Junction Transistor (BJT) Controlled by base current On and off only Linear region avoid Ratings up to 1kV and 4000A Very high power applications On-state voltage >1V fS < 5kHz Faster than thyristors Slower than MOSFET and IGBT Rarely usedCharacteristics of Active Switching DevicesN P NBC E MOSFET Metal Oxide Silicon Field Effect Transistor Developed in early 1980s Controlled by gate-to-source voltage (Vgs) Gate Signal, 10V to 18V, typically 15V Ratings up to 1000V and 2000A High current low voltage applications SMPS, battery chargers Very fast response fS < 1MHz, higher for soft-switching Bidirectional and resistive conduction characteristicsCharacteristics of Active Switching Devices Gate Turn-off Thyristor (GTO) Developed in mid 1980s Similar to thyristor Switched on by a injecting shortgate current pulse Switched off by reverse biased Switched off by a high and shortreverse current pulse Ratings up to 4.5kV and 3000A High power applications On-state voltage 2V to 3V Response faster than thyristors fS < 2kHzCharacteristics of Active Switching Devices IGBT Insulated Gate Bipolar Transistor Developed in late 1980s Combination of MOSFET and BJT Controlled by gate-to-emitter voltage (Vge) Same as MOSFET Ratings up to 3500V and 2000A Medium to high power applications up to 200kW Popular in Motor drives On-state voltage 1.7V to 3V Fast response Typically fS < 40kHz, faster for some modelsCharacteristics of Active Switching Devices Comparing to Signal Diodes More complicated structure Much higher V and I ratings Used in power processing Lower frequency response Higher on-state voltage (forwardvoltage, VF)Characteristics of Power Diodes+ P N+ + Forward Bias Low forward voltage drop(forward voltage, VF) Temp related 0.2V to 3V Decreasing with temp increase Typical VF provided in datasheetCharacteristics of Power DiodesVFIratedIVVBRReverseBiasBreakdownReverseLeakageCurrentForward Bias Reverse Bias Reverse leakage current µA to mA Increasing with increaseof junction temp, Tj Increasing with increaseof reverse voltage, VRCharacteristics of Power Diodes Junction Capacitance Diode as a capacitor inreverse bias Junction capacitancebetween anode and cathode Parasitic oscillations caused Solved by resonantconverter techniques Acting as resonantcomponent Decreasing with theincrease of reverse voltageCharacteristics of Power DiodesCJForward Recovery of Power DiodesVFtIF10% t90%Vfr 100% 110%tfr During the change from reversebias to forward bias Forward voltage, VF, increasingand back to normal Affecting high current and highvoltage systems Not affecting low power systemsReverse Recovery of Power DiodesIF VFtrrIRM VRMtQ1 Q2iF diF /dtvFVR During the change fromforward bias to reverse bias Conducting for a period Minority carriers remaining inp-n junction Ignoring in 0.4A Up to 500kHzSignalI/P O/PVCCNon-floating Gate Drive CircuitRGSignal ZGSDRIRGS Gate / emitter connected to ground RG Limiting charging current ofjunction capacitor Damping swing of vgs 8 to 33Ω suggested RGS Speeding up discharging of junction capacitor 1kΩ to 10kΩ ZGS Suppressing vgs transient voltage Voltage rating = peak output voltage of DRIFloating Gate Drive Circuits Gate / emitterconnected to ground Small pulse 1:1transformer Electrical isolationRGD RGS1:1ZGSC1 C2SignalDRITXp C1 filtering DC component of O/P of DRI Vdri /2 to –Vdri /2 C2 recovering the voltage from DC to AC square wave Vdri to 0Floating Gate Drive CircuitsRGSignal RGS ZGSOPREIsolated DCPower Supply+ –RA DRI Optocoupler Electrical Isolation Very low power isolated DC power supply Powering OP and DRIConduction Characteristicand Conduction Losses ForwardVoltage Diodes IGBTs BJTs Thyristors DevicesConductionEquivalent CircuitConductionLossDiodeThyristorIGBT VFiaVFIaConduction Characteristicand Conduction Losses Resistive Inductors Capacitors MOSFETs DevicesConduction EquivalentCircuitConduction LossMOSFETInductorCapacitor ia Rdsia RESRia RESRIa(rms)2RdsIa(rms)2RESRCooling Devices Most power losses of devices converted into heat Heat dissipation for long lifetime of devices Too small surface area to flow heat to surrounding mediumCooling Devices Air convection cooling Low to medium power Heat sink Finned aluminium Increasing surface area Decreasing thermal resistance Fan Increasing air flowHeat SinkDeviceFinsNatural air Convection cooling The change of temp of deviceT Tj Ta PlossRjc Rch Rha
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