Advanced Power Electronics | My Assignment Tutor

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 deviceT  Tj  Ta  PlossRjc  Rch  Rha 


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