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1、Power Electronics,Chapter 5 DC to DC Converters (Choppers),Outline,5.1 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 converters,5.1.1 Buck converter (Step-down con
2、verter)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 converter,5.1 Basic DC to DC converters,IntroductionBuck converter,SPDT switch changes dc component,Switch output voltage waveform,Duty cycle D: 0
3、 D 1,complement D:D = 1 - D,Dc component of switch output voltage,Fourier analysis: Dc component = average value,Insertion of low-pass filter to remove switching harmonics and pass only dc component,Basic operation principle of buck converter,Buck converter with ideal switch,Realization using power
4、MOSFET and diode,Thought process in analyzing basic DC/DC converters,Basic 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 volt
5、age waveform during different switching statesQuantitative analysis according to inductor volt-second balance or capacitor charge balance,Actual output voltage waveform of buck converter,Buck convertercontaining practicallow-pass filter,Actual output voltagewaveform,v(t) = V + vripple(t),The small r
6、ipple approximation,v(t) = 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 1,Inductor
7、 voltage and currentsubinterval 2: switch in position 2,Inductor voltage and current waveforms,Determination of inductor current ripple magnitude,Inductor current waveform during start-up transient,The principle of inductor volt-second balance: Derivation,Inductor volt-second balance:Buck converter
8、example,The principle of capacitor charge balance: Derivation,Boost converter example,Boost converter analysis,Subinterval 1: switch in position 1,Subinterval 2: switch in position 2,Inductor voltage and capacitor current waveforms,Inductor volt-second balance,Conversion ratio M(D) ofthe boost conve
9、rter,Determination of inductor current dc component,Continuous-Conduction-Mode (CCM) and Discontinuous-Conduction-Mode (DCM) of buck,Power,Electronics,28,Continuous-Conduction-Mode (CCM) and Discontinuous-Conduction-Mode (DCM) of boost,29,Power,Electronics,5.2 Composite DC/DC converters and connecti
10、on of multiple DC/DC converters,5.2.1 A current-reversible chopper5.2.2 Bridge chopper (H-bridge DC/DC converter)5.2.3 Multi-phase multi-channel DC/DC converters,5.2.1 A current reversible chopper,31,Power,Electronics,Can be considered as a combination of a Buck and a Boost Can realize two-quadrant
11、( I & II) operation of DC motor: forward motoring, forward braking,Bridge 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
12、 due to multi-channel paralleling. Ripple 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 structure
13、Necessary isolation between input and outputIn 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 rectifie
14、rs,Classification of isolated DC to DC converters,Isolated DC to DCconverters,Single-ended converters Forward converter Flyback converter,Double-ended converters Half bridge Push-pull Full bridge,According to whether transformer current is uni-direction or bi-directional,5.3.1 Forward converter,Simp
15、le, low costUni-polar transformer current, low power applications,5.3.2 Flyback converter,Simple, low costUni-polar transformer current, low power applications,5.3.3 Half bridge converter,Cost higher than forward and flyback converterBi-polar transformer current, up to several kilowatts,5.3.4 Push-p
16、ull converter,Cost higher than forward and flyback converterCenter-tapped transformer,5.3.5 Full-bridge converter,Cost is even higherBi-polar transformer current, up to several hundreds of kilowatts,5.3.6 Rectifier circuits in the isolated DC to DC converters,Full-wave rectifier,Full-bridge rectifie
17、r,Synchronous rectifier,5.3.7 Configuration of switching power supply,Linear power supply,42,Regulated DC output,Line frequencyAC input,Inverter,Filter,Transformer,DC,High frequencyAC,Rectifier,Rectifier,Filter,AC,High frequency,Isolation,Indirect DC to DC converter,Switching power supply,Power Elec
18、tronics,Chapter 6 AC to AC Converters( AC Controllers and Frequency Converters ),Classification of AC to AC converters,Power,Electronics,44,Classification of AC controllers,AC controller,Phase control: AC voltage controller(Delay angle control),Integral cycle control: AC power controller,PWM control
19、: AC chopper(Chopping control),On/off switch: electronic AC switch,PWM: Pulse Width Modulation,Classification of frequency converters,Frequency converter(Cycloconverter),Phase control: thyristor cycloconverter(Delay angle control),PWM control: matrix converter(Chopping control),Power,Electronics,Cyc
20、loconverter is sometimes referred to in a broader senseany ordinary AC to AC converterin a narrower sensethyristor cycloconverter,46,Outline,6.1 AC voltage controllers6.2 Other AC controllers 6.3 Thyristor cycloconverters6.4 Matrix converters,6.1 AC voltage controllers,6.1.1 Single-phase AC voltage
21、controller6.1.2 Three-phase AC voltage controllerApplicationsLighting controlSoft-start of asynchronous motorsAdjustable speed drive of asynchronous motorsReactive power control,6.1.1 Single-phase AC voltage controller,The phase shift range (operation range of phase delay angle):0 a p,Resistive load
22、,Power,Electronics,49,RMS value of output voltageRMS value of output currentRMS value of thyristor currentPower factor of the circuit,Resistive load, quantitative analysis,(6-1),(6-2),(6-3),(6-4),Inductive (Inductor-resistor) load, operation principle,The phase shift range: a p,Differential equation
23、SolutionConsidering io=0 when wt=a+q We have,Inductive load, quantitative analysis,The 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 thy
24、ristors are short-circuit, and the thyristors 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 transient,Harmonic analysis,There is no DC component and even order harmon
25、ics in the current.The current waveform is half-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 harmoni
26、c content is lower and is even lower as is increasing.,Power,Electronics,Current harmonics for the resistive load,54,6.1.2 Three-phase AC voltage controller,Classification of three-phase circuits,Y connection,Line-controlled connection,Branch-controlled connection,Neutral-point-controlled connection
27、,3-phase 3-wire Y connection AC voltage controller,For 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 ph
28、ases are half of the corresponding line to line voltage, while the load voltage of the other phase is 0.,3-phase 3-wire Y connection AC voltage controller,Resistive load, 0 a 60,3-phase 3-wire Y connection AC voltage controller,Resistive load, 60 a 90,3-phase 3-wire Y connection AC voltage controlle
29、r,Resistive load, 90 a 150,6.2 Other AC controllers,6.2.1 Integral cycle controlAC power controller6.2.2 Electronic AC switch6.2.3 Chopping controlAC chopper,6.2.1 Integral cycle control AC power controller,Circuit topologies are the same as AC voltage controllers. Only the control method is differe
30、nt.Load voltage and current are both sinusoidal when thyristors are conducting.,Spectrum of the current in AC power controller,There is NO harmonics in the ordinary sense. There is harmonics as to the control frequency. As to the line frequency, these components become fractional harmonics.,6.2.2 El
31、ectronic AC switch,Circuit topologies are the same as AC voltage controllers. But the back-to-back thyristors are just used like a switch to turn the equipment on or off.,6.2.3 Chopping controlAC chopper,Principle of chopping controlThe mean output voltage over one switching cycle is proportional to
32、 the duty cycle in that period. This is also called Pulse Width Modulation (PWM).AdvantagesMuch better output waveforms, much lower harmonicsFor resistive load, the displacement factor is always 1.,Waveforms when the load is pure resistor,AC chopper,Modes of operation0, io0: V1 charging, V3 freewhee
33、ling0, io0: V3 charging, V1 freewheeling0, io0: V2 charging, V4 freewheeling,6.3 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
34、and three-phase according to the number of phases at output6.3.1 Single-phase thyristor-cycloconverter6.3.2 Three-phase thyristor-cycloconverter,6.3.1 Single-phase thyristor-cycloconverter,Circuit configuration and operation principle,Z,P,N,u,o,Single-phase thyristor-cycloconverter,Modes of operatio
35、n,Single-phase thyristor-cycloconverter,Typical waveforms,Calculation methodFor the rectifier circuitFor the cycloconverter outputEquating (6-15) and (6-16)ThereforeCosine wave-crossing method,Modulation methods for firing delay angle,Principle of cosine wave-crossing method,(6-15),(6-16),(6-17),(6-
36、18),Calculated results for firing delay angle,Output voltage ratio (Modulation factor),Input and output characteristics,Maximum output frequency: 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
37、 both related to input frequency and output frequency.,6.3.2 Three-phase thyristor-cycloconverter,The configuration with common input line,Three-phase thyristor-cycloconverter,The configuration with star-connected output,Three-phase thyristor-cycloconverter,Typical waveforms,200,t,/,ms,Output voltag
38、e,Input current with3-phase output,200,t,/,ms,200,t,/,ms,Input current withSingle-phase output,0,0,0,Input and output characteristics,The 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 c
39、ircuit. Harmonics in the input current is a little lower than the single-phase circuit due to the cancellation of some harmonics among the 3 phases. To improve the input power factor:Use DC bias or 3k order component bias on each of the 3 output phase voltages,Features and applications,FeaturesDirec
40、t frequency conversionhigh efficiencyBidirectional energy flow, easy to realize 4-quadrant operationVery complicatedtoo many power semiconductor devicesLow output frequencyLow input power factor and bad input current waveformApplicationsHigh power low speed AC motor drive,6.4 Matrix converter,Circui
41、t configuration,a),b),Matrix converter,Usable input voltage,a) Single-phase input voltage,b) Use 3 phase voltages to construct output voltage,c) Use 3 line-line voltages to construct output voltage,Features,Direct frequency conversionhigh efficiencyCan realize good input and output waveforms, low ha
42、rmonics, and nearly unity displacement factorBidirectional energy flow, easy to realize 4-quadrant operationOutput frequency is not limited by input frequencyNo need for bulk capacitor (as compared to indirect frequency converter)Very complicatedtoo many power semiconductor devicesOutput voltage magnitude is a little lower as compared to indirect frequency converter.,
