1、Power ElectronicsChapter 5 DC to DC Converters (Choppers)Outline5.1 Basic DC to DC converters5.2 Composite DC/DC converters and connection of multiple DC/DC converters5.3 Isolated DC to DC converters (Indirect DC to DC converters )5.1 Basic DC to DC converters5.1.1 Buck converter (Step-down converte

2、r)5.1.2 Boost converter (Step-up converter)5.1.3 Buck-Boost converter (Step-down/step- up converter) and Cuk converter5.1.4 Sepic converter and Zeta converter5.1 Basic DC to DC convertersIntroductionBuck converterSPDT switch changes dc componentSwitch output voltage waveformDuty cycle D: 0 D 1comple

3、ment D:D = 1 - DDc component of switch output voltageFourier analysis: Dc component = average valueInsertion of low-pass filter to remove switching harmonics and pass only dc componentBasic operation principle of buck converterBuck converter with ideal switchRealization using power MOSFET and diodeT

4、hought process in analyzing basic DC/DC convertersBasic operation principle (qualitative analysis)How does current flow during different switching statesHow is energy transferred during different switching statesVerification of small ripple approximationDerivation of inductor voltage waveform during

5、 different switching statesQuantitative analysis according to inductor volt-second balance or capacitor charge balanceActual output voltage waveform of buck converterBuck convertercontaining practicallow-pass filterActual output voltagewaveformv(t) = V + vripple(t)The small ripple approximationv(t)

6、= V + vripple(t)In a well-designed converter, the output voltage ripple is small. Hence, the waveforms can be easily determined by ignoring the ripple:Buck converter analysis:inductor current waveform Inductor voltage and currentsubinterval 1: switch in position 1Inductor voltage and currentsubinter

7、val 2: switch in position 2Inductor voltage and current waveformsDetermination of inductor current ripple magnitudeInductor current waveform during start-up transientThe principle of inductor volt-second balance: DerivationInductor volt-second balance:Buck converter example The principle of capacito

8、r charge balance: DerivationBoost converter exampleBoost converter analysisSubinterval 1: switch in position 1Subinterval 2: switch in position 2Inductor voltage and capacitor current waveformsInductor volt-second balanceConversion ratio M(D) ofthe boost converterDetermination of inductor current dc

9、 componentContinuous-Conduction-Mode (CCM) and Discontinuous-Conduction-Mode (DCM) of buckEV+-MRLVDioEMuoiGPowerElectronics28Continuous-Conduction-Mode (CCM) and Discontinuous-Conduction-Mode (DCM) of boost29PowerElectronics5.2 Composite DC/DC converters and connection of multiple DC/DC converters5.

10、2.1 A current-reversible chopper5.2.2 Bridge chopper (H-bridge DC/DC converter)5.2.3 Multi-phase multi-channel DC/DC converters5.2.1 A current reversible chopper31PowerElectronics Can be considered as a combination of a Buck and a Boost Can realize two-quadrant ( I & II) operation of DC motor: forwa

11、rd motoring, forward brakingBridge chopper (H-bridge chopper) Can be considered as the combination of two current-reversible choppers. Can realize 4-quadrant operation of DC motor.Multi-phase multi-channel DC/DC converter Current output capability is increased due to multi-channel paralleling. Rippl

12、e in the output voltage and current is reduced due to multi- channel paralleling. Ripple in the input current is reduced due to multi-phase paralleling.5.3 Isolated DC to DC converters (Indirect DC to DC converters )Reasons to use indirect DC to DC structureNecessary isolation between input and outp

13、utIn some cases isolated multiple outputs are neededThe ratio of input and output voltage is far away from 1Power semiconductor devices usually usedInverter part: Power MOSFETs, IGBTsRectifier part: Fast recovery diodes, Schottky diodes, Synchronous rectifiersInverterTransformerRectifierFilterDC inp

14、utACACDC outputHigh frequencyIsolationClassification of isolated DC to DC convertersIsolated DC to DCconvertersSingle-ended converters Forward converter Flyback converterDouble-ended converters Half bridge Push-pull Full bridgeAccording to whether transformer current is uni-direction or bi-direction

15、al 5.3.1 Forward converterSimple, low costUni-polar transformer current, low power applications5.3.2 Flyback converterSimple, low costUni-polar transformer current, low power applications5.3.3 Half bridge converterCost higher than forward and flyback converterBi-polar transformer current, up to seve

16、ral kilowatts5.3.4 Push-pull converterCost higher than forward and flyback converterCenter-tapped transformer5.3.5 Full-bridge converterCost is even higherBi-polar transformer current, up to several hundreds of kilowatts5.3.6 Rectifier circuits in the isolated DC to DC convertersFull-wave rectifierF

17、ull-bridge rectifierSynchronous rectifier5.3.7 Configuration of switching power supplyLinear power supply42Regulated DC outputLine frequencyAC inputInverterFilterTransformerDCHigh frequencyACRectifierRectifierFilterACHigh frequencyIsolationIndirect DC to DC converterLine frequencyAC inputRectifierFi

18、lterSeries PassRegulatorTransformerDCRegulated DC outputLine frequencyIsolationSwitching power supplyPower ElectronicsChapter 6 AC to AC Converters( AC Controllers and Frequency Converters )Classification of AC to AC convertersSame frequencyvariable magnitudeAC powerAC powerVariable frequencyAC powe

19、rAC controllersFrequency converters(Cycloconverters)AC to AC convertersPowerElectronics44Classification of AC controllersAC controllerPhase control: AC voltage controller(Delay angle control)Integral cycle control: AC power controllerPWM control: AC chopper(Chopping control)On/off switch: electronic

20、 AC switchPWM: Pulse Width ModulationClassification of frequency convertersFrequency converter(Cycloconverter)Phase control: thyristor cycloconverter(Delay angle control)PWM control: matrix converter(Chopping control)PowerElectronicsCycloconverter is sometimes referred to in a broader senseany ordin

21、ary AC to AC converterin a narrower sensethyristor cycloconverter46Outline6.1 AC voltage controllers6.2 Other AC controllers 6.3 Thyristor cycloconverters6.4 Matrix converters6.1 AC voltage controllers6.1.1 Single-phase AC voltage controller6.1.2 Three-phase AC voltage controllerApplicationsLighting

22、 controlSoft-start of asynchronous motorsAdjustable speed drive of asynchronous motorsReactive power control6.1.1 Single-phase AC voltage controllerThe phase shift range (operation range of phase delay angle):0 a pResistive loadPowerElectronicsRu1uoioVT1VT2Ou1uoiouVTwtOwtOwtOwt49RMS value of output

23、voltageRMS value of output currentRMS value of thyristor currentPower factor of the circuitResistive load, quantitative analysis(6-1)(6-2)(6-3)(6-4)Inductive (Inductor-resistor) load, operation principleThe phase shift range: a pRu1uoioVT1VT2Differential equationSolutionConsidering io=0 when wt=a+q

24、We haveInductive load, quantitative analysisThe RMS value of output voltage, output current, and thyristor current can then be calculated. (6-5)(6-6)(6-7)Inductive load, when a The circuit can still work.The load current will be continuous just like the thyristors are short-circuit, and the thyristo

25、rs can no longer control the magnitude of output voltage. The start-up transient will be the same as the transient when a RL load is connected to an AC source at wt =a (a ).Start-up transientHarmonic analysisThere is no DC component and even order harmonics in the current.The current waveform is hal

26、f-wave symmetric.The higher the number of harmonic ordinate, the lower the harmonic content. a = 90 is when harmonics is the most severe. The situation for the inductive load is similar to that for the resistive load except that the corresponding harmonic content is lower and is even lower as is inc

27、reasing. PowerElectronicsCurrent harmonics for the resistive load060120180Fundamental357a/( )In/I*/%20406080100546.1.2 Three-phase AC voltage controllerClassification of three-phase circuitsY connectionLine-controlled connectionBranch-controlled connectionNeutral-point-controlled connection3-phase 3

28、-wire Y connection AC voltage controllerFor a time instant, there are 2 possible conduction states:Each phase has a thyristor conducting. Load voltages are the same as the source voltages.There are only 2 thyristors conducting, each from a phase. The load voltages of the two conducting phases are ha

29、lf of the corresponding line to line voltage, while the load voltage of the other phase is 0.nnabcuaubuciaUa0VT5VT3VT6VT4VT2VT13-phase 3-wire Y connection AC voltage controllerResistive load, 0 a 60 a4p32p35p3p302puaouauab2uac2t1t2t3VT1VT3VT6VT4VT6VT2VT5VT5VT13-phase 3-wire Y connection AC voltage c

30、ontrollerResistive load, 60 a 90 ap4p32p35p3p302puaouauab2uac2t1t2t3VT5VT1VT3VT4VT6VT2VT6VT53-phase 3-wire Y connection AC voltage controllerResistive load, 90 a 0, io0: V1 charging, V3 freewheeling0, io0: V4 charging, V2 freewheeling0: V3 charging, V1 freewheeling0, io0: V2 charging, V4 freewheelin

31、g6.3 Thyristor cycloconverters (Thyristor AC to AC frequency converter)Another namedirect frequency converter (as compared to AC-DC-AC frequency converter which is discussed in Chapter 8)Can be classified into single-phase and three-phase according to the number of phases at output6.3.1 Single-phase

32、 thyristor-cycloconverter6.3.2 Three-phase thyristor-cycloconverter6.3.1 Single-phase thyristor-cycloconverterCircuit configuration and operation principleZPNuoOuoaP=0aP=p2aP=p2wtOutput voltageAverage output voltageSingle-phase thyristor-cycloconverterModes of operationtttttOOOOOuo,iouoiot1t2t3t4t5u

33、ouPuNuoiPiNRectificationInversionBlockingPNInversionBlockingRectificationSingle-phase thyristor-cycloconverterTypical waveformsCalculation methodFor the rectifier circuitFor the cycloconverter outputEquating (6-15) and (6-16)ThereforeCosine wave-crossing methodModulation methods for firing delay ang

34、lePrinciple of cosine wave-crossing method(6-15)(6-16)(6-17)(6-18)Calculated results for firing delay angleOutput voltage ratio (Modulation factor)g = 0g = 0.1a/()Output voltage phase anglew 0 t12015018030609000.10.20.30.80.91.00.80.20.30.91.0p2p2p23pInput and output characteristicsMaximum output fr

35、equency: 1/3 or 1/2 of the input frequency if using 6-pulse rectifiersInput power factorHarmonics in the output voltage and input current are very complicated, and both related to input frequency and output frequency.0.80.60.40.20g =1.0Input displacement factorLoad power factor (lagging)Load power f

36、actor (leading)01.00.80.60.40.200.80.60.40.20.80.60.40.26.3.2 Three-phase thyristor-cycloconverterThe configuration with common input lineThree-phase thyristor-cycloconverterThe configuration with star-connected outputThree-phase thyristor-cycloconverterTypical waveforms200t/msOutput voltageInput cu

37、rrent with3-phase output 200t/ms200t/msInput current withSingle-phase output 000Input and output characteristicsThe maximum output frequency and the harmonics in the output voltage are the same as in single-phase circuit.Input power factor is a little higher than single-phase circuit. Harmonics in the input current is a little lower than the