CN110289755B - DCM Buck-Flyback PFC converter with high power factor - Google Patents

DCM Buck-Flyback PFC converter with high power factor Download PDF

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CN110289755B
CN110289755B CN201910561135.8A CN201910561135A CN110289755B CN 110289755 B CN110289755 B CN 110289755B CN 201910561135 A CN201910561135 A CN 201910561135A CN 110289755 B CN110289755 B CN 110289755B
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input
buck
voltage
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CN110289755A (en
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张震
姚凯
邬程健
管婵波
李凌格
陈杰楠
马春伟
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Nanjing University of Science and Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
    • H02M1/4208—Arrangements for improving power factor of AC input
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention provides a DCM Buck-Flyback PFC converter with a high power factor. The traditional DCM Buck PFC converter adopts fixed duty ratio control, the input power factor is improved, but the input current has an inherent dead zone, the peak value of the inductive current is large, the EMI differential mode characteristic is poor, the conduction loss of a switching tube is large, and the efficiency cannot be optimized.

Description

DCM Buck-Flyback PFC converter with high power factor
Technical Field
The invention relates to an electric energy conversion device, in particular to a DCM Buck-flyback PFC converter with high power factor.
Background
A Power Factor Correction (PFC) converter can reduce input current harmonics and improve an input Power Factor, and has been widely used. The PFC converter is divided into an active mode and a passive mode, and compared with the passive mode, the active mode has the advantages of high input power factor, small size, low cost and the like.
The traditional DCM Buck PFC converter is widely applied as the DCM Buck PFC converter has the advantages of high efficiency, low output voltage, low surge current, low cost, strong short-circuit protection capability, long service life, simplicity in control, small inductance, no reverse recovery problem of a diode and the like, and can be widely applied to an AC/DC converter, but the Buck PFC converter has an inherent dead zone during working, so that the waveform distortion of the input current of the converter is serious, the PF value of the converter is reduced, the THD value of the converter is increased, the requirement of the state on the electric energy quality cannot be met, and meanwhile, the inductance current peak value is large, the EMI differential mode characteristic is poor, the conduction loss of a switch tube is large, and the efficiency cannot be optimized.
Disclosure of Invention
The invention aims to provide a DCM Buck-Flyback PFC converter with high power factor.
The technical scheme for realizing the purpose of the invention is as follows: a DCM Buck-Flyback PFC converter with high power factor comprises a main power circuit and a control circuit, wherein the main power circuit comprises an input voltage source vinThe diode rectifying circuit RB, the LC filter, the Buck circuit and the Flyback circuit share the transformer T and the primary coil inductance L of the transformer TpTransformer T secondary winding inductance LsBuck circuit switch tube QbDiode DbFreewheel diode DfwFlyback circuit switch tube QfOutput capacitance CoLoad RLd(ii) a Input voltage source vinThe output cathode of the LC filter is a reference potential zero point, and the output anode of the LC filter is respectively connected with a switching tube Q of a Buck circuitbAnd primary winding L of transformer TpIs connected with the same name end of the transformer T, and the primary coil L of the transformer TpAnd the other end of the Flyback circuit switching tube QfIs connected with one end of a switching tube QfThe other end of the switch tube Q is a reference potential zero pointbAnother terminal of (1) and a diode DbIs connected to one end of a diode DbThe other end of the transformer is respectively connected with a secondary winding L of the transformer TsOf the same name terminal and freewheeling diode DfwIs connected to one end of a secondary winding L of the transformer TsThe other end of the capacitor is simultaneously connected with an output capacitor CoAnd a load RLdIs connected to an output capacitor CoAnd a load RLdThe other end of which is a reference potentialZero point.
Furthermore, the control circuit comprises an output voltage sampling circuit, an output voltage feedback control circuit, a sawtooth wave comparison and switching tube driving circuit, an input voltage comparison circuit and a logic switching circuit; sampling resistor R in output voltage sampling circuit1And R2After being connected in series with the output voltage V of the main power circuitoThe sampling output end of the output voltage sampling circuit is connected with the input end of the output voltage feedback control circuit, and the positive input end of the output voltage feedback control circuit is connected with the reference voltage VrefThe positive input end and the reverse input end of the sawtooth wave comparison and switch tube driving circuit are respectively connected with the output end of the output voltage feedback control circuit and the triangular wave, the positive input end of the input voltage comparison circuit is connected with the positive output end of the LC filter of the main power circuit through a divider resistor, and the reverse input end of the input voltage comparison circuit is connected with the critical voltage VboundaryTwo AND gate input ends of the logic switch circuit are connected with the output end of the sawtooth wave comparison and switch tube driving circuit, and a second AND gate ANDgate in the logic switch circuit2The other input end of the first and-gate is connected with the output end of the input voltage comparison circuit through an inverting amplifier, and the second and-gate ANDgate2As an output signal V of the control circuitd_fAnd is connected with the switch tube Q of Flyback circuit in the main power circuitfThe gate pole of the switch tube Q is connected to drive the switch tube QfWorking, first AND gate ANDgate in logic switch circuit1The other input terminal of the first AND gate is connected with the output terminal of the input voltage comparison circuit, and the first AND gate ANDgate1As an output signal V of the control circuitd_bWith switching tube Q of Buck circuit in main power circuitbThe gate pole of the switch tube Q is connected to drive the switch tube QbAnd (6) working.
Furthermore, the switch tube driving chip can be an integrated IC circuit of UC3843, UC3844 or UC3525 type, an output end of the sawtooth wave comparison circuit of the sawtooth wave comparison and switch tube driving circuit is connected with the switch tube driving chip through an RS trigger, and a fourteenth sum of the switch tube driving chip is a pin which is connected with an eighth diode D through an eighth diode D respectively8And seventh diodePipe D7As the output signal of the sawtooth wave comparison and switch tube driving circuit; an amplifier IC 1-IC 6 used in the output voltage feedback control circuit selects one type of operational amplifier from TL074, TL072, LM358 and LM 324; the voltage comparator in the sawtooth wave comparison and switch tube driving circuit and the input voltage comparison circuit is one of LM324, LM358, UA741, TL081, LM339 and LM 393; the RS trigger in the sawtooth wave comparison and switch tube driving circuit is one of the types of RS triggers 74LS71, 74LS279, 74HC279 and 74279; the AND gate in the logic switch circuit is an integrated AND gate circuit of one of 7408, 7409, 7411 and 7415 types.
According to the DCM Buck-Flyback PFC converter with the high power factor, due to the fact that an integrated Buck-Flyback topology is adopted, the PF value can be improved to be close to 1 in the whole wide input voltage range of 90-264 VAC, and the DCM Buck-Flyback PFC converter with the high power factor has the advantages of being high in input power factor, small in output voltage ripple, small in input current harmonic content and the like.
The invention is further described below with reference to the accompanying drawings.
Drawings
Fig. 1 is a schematic diagram of a DCM Buck PFC converter main circuit.
FIG. 2 is a waveform diagram of the inductor current and the switching tube current of the DCM Buck PFC converter.
FIG. 3 is a graph of input current waveform (v) for DCM Buck PFC converter at different output voltagesin＝110VAC)。
Fig. 4 is a plot of the power factor PF of the DCM Buck PFC converter over a wide input voltage range.
Fig. 5 is a schematic diagram of a DCM Buck-Flyback PFC converter main circuit.
Fig. 6 shows waveforms of primary and secondary side inductor current and switching tube current of the transformer of the DCM Buck-Flyback PFC converter.
FIG. 7 is a graph of the turns ratio n of the DCM Buck-flyback PFC transformer versus the power factor PF at different output voltages over a wide range of input voltages, where (a) is shown at 90VAC, (b) is shown at 110VAC, (c) is shown at 220VAC, and (d) is shown at 264 VAC.
FIG. 8 is a graph of power factor PF as a function of input voltage, where the sum (a) is VoSchematic under 70, (b) is VoSchematic diagram under 80, (c) is V o90, (d) is VoSchematic under 100.
Fig. 9 is a plot of power factor PF at an optimal turn ratio in combination with output voltage over a wide range of input voltages.
FIG. 10 is a graph of the critical inductance over a wide input voltage range: (a) the Buck converter is shown in a schematic diagram, and the (b) is a Flyback converter schematic diagram.
FIG. 11 is a diagram of a transformer primary and secondary side inductor peak current waveform of a DCM Buck-Flyback converter.
Fig. 12 is a graph of the effective value of the primary inductor current of a transformer over a wide input voltage range.
Fig. 13 is a graph of the effective value of the secondary side inductor current of the transformer over a wide input voltage range.
Fig. 14 is a comparison of Buck and Buck-Flyback converter power factor PF.
FIG. 15 is a comparison of the 3, 5, and 7 harmonic content of Buck and Buck-Flyback converter input currents.
Fig. 16 is a comparison of the output voltage waveforms of the Buck and Buck-Flyback converters over half the power frequency cycle.
Fig. 17 is a comparison of the voltage ripple magnitude of the Buck and Buck-Flyback converters over a wide input voltage range.
FIG. 18 is a plot of the critical inductance values of the Buck and Buck-Flyback converters.
Fig. 19 is a plot of the peak inductor current for the Buck and Buck-Flyback converters.
Fig. 20 is a graph of the effective value of the inductor current of the Buck-Flyback converter.
Fig. 21 is a schematic circuit diagram of the DCM Buck-Flyback converter with high power factor according to the present invention.
Main symbol names in the above figures: v. ofinSupply voltage iinInput current, RB-rectifier bridge, vg-rectified output voltage, iLbInductor current, Lb-inductance, Qb-switching tube, QfSwitching tube, Db-diode, DfwDiodes, T-transformers, LpPrimary winding inductance, L, of a transformersSecondary winding inductance of transformer, CoOutput filter capacitance, IoOutput current, RLd-load, VoOutput voltage, VrefReference voltage, v, of feedback control of output voltageEAOutput voltage feedback controlled error voltage signal output, VboundaryCritical voltage, t-time, ω -input voltage angular frequency, VmInput voltage peak value, vd_f-switching tube QfV drive voltage ofd_b-switching tube QbD-duty cycle, fs-converter switching frequency, PF-power factor.
Detailed Description
Fig. 1 is a BuckPFC converter main circuit. The following assumptions were made: (1) all devices are ideal elements; (2) the output voltage ripple is very small compared to its dc amount; (3) the switching frequency is much higher than the input voltage frequency.
Fig. 2 shows waveforms of inductor current and switching tube current in one switching cycle of the DCM BuckPFC converter. When Q isbWhen conducting, DfwCut-off, inductance LsVoltage across vg－VoCurrent of i thereofLsStarting from zero with (v)g－Vo)/LsIs linearly increased, vgLoad supply and energy storage capacitor CoAnd (5) supplying power. When Q isbWhen turned off, iLsBy DfwFollow current, at this time LsThe voltage across is-Vo，iLsWith Vo/LsIs decreased, and iLsMay drop to zero before a new period begins.
Without loss of generality, define the input AC voltage vinThe expression of (a) is:
vin＝Vm sinθ (1)
wherein VmAnd theta is the amplitude and phase angle of the input AC voltage, respectively。
In half power supply cycle 0, pi]In, the rectified input voltage vgSame as the input voltage, i.e.
vg＝vin＝Vm sinθ (2)
In one switching cycle, the inductance LsPeak value of current iLs_pkIs composed of
Figure BDA0002108309260000041
Wherein DQbIs a switching tube QbDuty ratio, fsIs the switching frequency.
In each switching cycle, LsThe volt-second area of both ends is balanced, i.e.
Figure BDA0002108309260000051
Wherein VoTo output a voltage, DDfwbThe duty cycle corresponding to the inductor current dropping to zero.
From formulas (2) and (4):
Figure BDA0002108309260000052
according to the formulas (3) and (5), the switching tube Q flowing in one switching period can be obtainedbThe average value of (a) is:
Figure BDA0002108309260000053
then at [ theta ]0,(-θ0]In the middle, the average value of the input current of the Buck converter is as follows:
Figure BDA0002108309260000054
due to the fact thatBuck converter only at input voltage vinAbove a threshold voltage value, so that the input current iinComprises the following steps:
Figure BDA0002108309260000055
the input power can be found by combining equation (1) and equation (8) as follows:
Figure BDA0002108309260000056
assuming 100% converter efficiency, the input power is equal to the output power, i.e. Pin＝PoThe duty ratio D can be obtainedQbExpression (c):
Figure BDA0002108309260000057
the input power factor can be calculated from equations (1) and (8) as:
Figure BDA0002108309260000058
v can be made according to formulas (8) - (11)inAt 110VAC, the DCM Buck PFC converter corresponds to an input current waveform plot at different output voltages and a power factor PF plot over a wide input voltage range, as shown in fig. 3 and 4, respectively. As can be seen from the figure, the input current waveform has a dead zone, resulting in a low power factor, and therefore, a new method is required to eliminate the dead zone of the input current and increase the power factor value.
Fig. 5 is a DCM Buck-Flyback PFC converter main circuit. The following assumptions were made: (1) all devices are ideal elements; (2) the output voltage ripple is very small compared to its dc amount; (3) the switching frequency is much higher than the input voltage frequency.
FIG. 6 shows waveforms of the switching tube current and the primary and secondary side inductor current of the transformer in one switching period in DCM. When the instantaneous value of the input voltage is less than the critical voltage value, QfOn, QbOff, DfwInductance L of primary coil of cut-off transformerpVoltage across vg－VoCurrent of i thereofLpStarting from zero with (v)g－Vo)/LpIs linearly increased, vgLoad supply and energy storage capacitor CoAnd (5) supplying power. When Q isfWhen turned off, iLsBy DfwFollow current, the secondary coil inductance L of the transformer at this timesThe voltage across is-Vo，iLsWith Vo/LsIs decreased, and iLsMay drop to zero before a new period begins. When the instantaneous value of the input voltage is greater than the critical voltage value, QbOn, QfOff, D on, DfwInductance L of secondary coil of cut-off transformersVoltage across vg－VoCurrent of i thereofLsStarting from zero with (v)g－Vo)/LsIs linearly increased, vgLoad supply and energy storage capacitor CoAnd (5) supplying power. When Q isbWhen turned off, iLsBy DfwFollow current, the secondary coil inductance L of the transformer at this timesThe voltage across is-Vo，iLsWith Vo/LsIs decreased, and iLsMay drop to zero before a new period begins.
When the instantaneous value of the input voltage is smaller than the critical voltage value, the converter works in a Flyback state, and the peak value i of the inductive current of the primary end of the transformer is within one switching periodLp_pkIs composed of
Figure BDA0002108309260000061
Wherein DQbfIs a switching tube QfDuty ratio, fsIs the switching frequency.
In each switching cycle, the primary winding L of the transformerpThe volt-second area of both ends is balanced, i.e.
Figure BDA0002108309260000062
Wherein VoTo output a voltage, DDfwfThe duty ratio corresponding to the fact that the current of the secondary end of the transformer is reduced to zero.
From formulas (2) and (13):
Figure BDA0002108309260000063
according to the equations (12) and (14), the flow through the switching tube Q in one switching cycle can be obtainedfThe average value of (a) is:
Figure BDA0002108309260000071
is then at [0, theta ]0]And [ (-) theta0,(]The average value of the input current of the converter is as follows:
Figure BDA0002108309260000072
when the instantaneous value of the input voltage is larger than the critical voltage value, the converter works in a Buck state, and the analysis conclusion is shown in the first section.
Thus, the input current iinComprises the following steps:
Figure BDA0002108309260000073
wherein
Figure BDA0002108309260000074
The average value P of the input power of the converter in a half cycle can be obtained by the formula (1) and the formula (13)inComprises the following steps:
Figure BDA0002108309260000075
assuming a converter efficiency of 100%, the input power is equal to the output power. The duty ratio D can be obtained from equation (14)Qbf：
Figure BDA0002108309260000076
The PF value can be obtained from equations (17) and (18) by the following expression:
Figure BDA0002108309260000077
wherein Irms_bfIs the effective value of the input current.
Combining (20) and converter parameters, a plot of turn ratio n as a function of PF value can be made for a wide range of input voltages at different output voltages, as shown in fig. 7 (a-d). The optimal turn ratios n of the 90VAC,110VAC,220VAC and 264VAC input voltages to the 70VDC,80VDC,90VDC and 100VDC output voltages can be observed.
In order to observe the influence of the turn ratio on the power factor under different output voltages in a wide input voltage range more obviously, a functional graph of the power factor PF and the input voltage is drawn in a graph of FIG. 8. Considering that 110VAC and 220VAC are nominal input voltages, we select the blue curve from fig. 8 as the basis for determining the optimal turn ratio, so that the optimal turn ratio at which n is 1.42, n is 1.52, n is 1.65 and n is 1.80 is selected as Vo is 70, Vo is 80, Vo is 90 and Vo is 100V, at which the converter can obtain the maximum power factor value.
Based on the above analysis, we can plot the power factor curve for the optimal turn ratio in combination with the output voltage over the wide input voltage range of fig. 9. It can be seen that under the combination of the optimal turn ratio and the output voltage, the power factor of the DCMBuck-Flyback PFC converter can be guaranteed to be above 0.956 in all cases, and the power factor approaches 1 as the input voltage increases.
In order to make the converter operate in DCM, the inductor current needs to be reduced to 0 before the light-emitting tube is turned on, and the duty ratio of the Buck converter needs to satisfy the following formula:
Figure BDA0002108309260000081
substituting formula (5) into formula (21):
Figure BDA0002108309260000082
by substituting equation (19) for equation (22), the critical inductance of the secondary winding of the transformer is:
Figure BDA0002108309260000083
the critical inductance value curve in the wide input voltage range of the Buck converter is made according to equation (23), as shown in fig. 10 (a).
For a Flyback converter, in order to operate the converter in DCM, the duty cycle needs to satisfy the following formula:
Figure BDA0002108309260000084
substituting formula (14) into formula (24):
Figure BDA0002108309260000085
by substituting equation (19) for equation (25), the critical inductance of the secondary winding of the transformer is:
Figure BDA0002108309260000091
the Flyback converter can be constructed from the equation (26) by plotting the critical inductance of the secondary winding of the transformer over a wide input voltage range, as shown in fig. 10 (b).
In order to make the converter work normally, the minimum inductance value of the secondary winding of the transformer operating in Buck and Flyback states needs to be guaranteed to be the same.
According to the equations (3), (12) and (19), the DCM Buck-Flyback converter peak inductor current waveform can be obtained as shown in fig. 11. It can be seen from the figure that the peak current decreases with increasing output voltage.
When the switch tube is in a conducting state, the current passing through the switch tube Q can be calculatedbAnd a switching tube QfEffective value of current:
Figure BDA0002108309260000092
Figure BDA0002108309260000093
when the switch tube is in the off state, the current flowing through the freewheeling diode D can be calculatedfwEffective value of (c):
Figure BDA0002108309260000094
Figure BDA0002108309260000095
when opening the light pipe QfWhen the transformer is in a conducting state, the effective value of the inductance flowing through the primary end coil of the transformer can be calculated:
Figure BDA0002108309260000097
when opening the light pipe QfIn the off state, QbIn on and off states, canTo calculate the effective value of the inductance flowing through the secondary coil of the transformer:
Figure BDA0002108309260000096
the waveforms of the effective values of the primary and secondary windings of the transformer can be respectively made according to the expressions (27) to (32), namely, the waveforms of fig. 12 and fig. 13.
The power factors PF of the conventional DCM Buck converter and the DCMBuck-Flyback converter can be compared according to equations (1), (11) and (20), as shown in fig. 14. As can be seen from the figure, the power factor of the DCM Buck-Flyback converter is greatly improved compared to the conventional DCM Buck converter, especially at high input voltages with PF values close to 1.
Fourier analysis is carried out on the input current waveform of the DCM Buck-Flyback converter to obtain the input current waveform
Figure BDA0002108309260000101
As can be seen from fig. 15, the 3 rd order, 5 th order and 7 th order harmonic contents of the DCM Buck converter all meet the national standard requirements, while the 3 rd order, 5 th order and 7 th order harmonic contents of the conventional DCM Buck converter do not meet the national standard requirements, and particularly at low input voltages, the 3 rd order, 5 th order and 7 th order harmonic contents are very high.
The instantaneous output voltage value of the output end capacitor is expressed as
Figure BDA0002108309260000102
The output voltage ripples of the DCM Buck converter and the DCM Buck-Flyback converter can be calculated according to the following formula
Figure BDA0002108309260000103
When in use
Figure BDA0002108309260000104
While the output capacitor is charged, while
Figure BDA0002108309260000105
Time out, the output capacitor is discharged, theta1,θ2,θ3,andθ4Respectively a traditional DCM Buck converter and a DCM Buck-Flyback converter
Figure BDA0002108309260000106
Phase angle at 1. The output voltage waveforms of both converters within half the power frequency period can be plotted according to equation (34), as shown in fig. 16. The ripple magnitude of the output voltage of the two converters can be plotted according to equation (35) over a wide input voltage range, as shown in fig. 17. As can be seen from the figure, the output voltage ripple of the DCM Buck-Flyback converter is greatly reduced compared to the conventional Buck converter.
According to equation (21) and combining equations (5) and (10), the critical inductance equation of the DCM Buck converter is as follows:
Figure BDA0002108309260000107
fig. 18 shows the critical inductance value curves of the DCM Buck converter and the DCM Buck-Flyback converter from equation (36). Under the condition of considering the allowance, the critical inductance value of the DCM Buck converter is 33uH which is smaller than the critical inductance value of 40uH of the DCM Buck-Flyback converter, and the critical inductance value can be improved to a certain extent by the converter provided by the invention.
According to equations (3) and (10), and with reference to fig. 11, the inductor current peak curves of the DCMBuck converter and the DCM Buck-Flyback converter at an input voltage of 110VAC can be plotted, as shown in fig. 19. As can be seen from the figure, the peak value of the inductor current of the DCM Buck-Flyback converter is greatly reduced compared with the conventional DCMBuck converter, and the overall peak envelope is closer to sine, so that the power factor of the DCM Buck-Flyback converter is greatly improved.
The effective value expression of the inductive current of the Buck converter is as follows:
Figure BDA0002108309260000111
by substituting equations (3), (5) and (10) into equation (37) and referring to fig. 13, the effective value curves of the inductor current of the two converters shown in fig. 20 can be prepared. The DCM Buck-Flyback converter has a small current effective value. Therefore, in the DCM Buck-Flyback converter, the loss of the main components is much smaller than that of the Buck converter.
Referring to fig. 21, the high power factor DCM Buck-Flyback converter of the present invention comprises a main power circuit (1) and a control circuit, wherein the main power circuit (1) comprises an input voltage source vinThe diode rectifying circuit RB, the LC filter, the Buck circuit and the Flyback circuit share the transformer T, and the primary coil inductance L of the transformer TpInductance L of secondary winding of transformer TsBuck circuit switch tube QbDiode DbFreewheel diode DfwFlyback circuit switch tube QfOutput capacitance CoLoad RLdIn which a voltage source v is inputinThe output cathode of the LC filter is a reference potential zero point, and the output anode of the LC filter is connected with a switching tube Q of the Buck circuit at the same timebAnd primary winding L of transformer TpIs connected with the same name end of the transformer T, and the primary coil L of the transformer TpAnd the other end of the Flyback circuit switching tube QfIs connected with one end of a switching tube QfThe other end of the switch tube Q is a reference potential zero pointbAnother terminal of (1) and a diode DbIs connected to one end of a diode DbThe other end of the transformer is simultaneously connected with a secondary winding L of the transformer TsOf the same name terminal and freewheeling diode DfwIs connected to one end of a secondary winding L of the transformer TsThe other end of the capacitor is simultaneously connected with an output capacitor CoAnd a load RLdIs connected to an output capacitor CoAnd a load RLdThe other end of the reference potential zero Buck inductor LbThe other end of the capacitor is simultaneously connected with an output capacitor CoAnd a load RLdIs connected to an output capacitor CoAnd a load RLdAnd the other end of the same is a reference potential zero point.
The DCM Buck-flyback PFC converter with the high power factor is characterized in that a control circuit comprises an output voltage sampling circuit (2), an output voltage feedback control circuit (3), a sawtooth wave comparison and switching tube driving circuit (4), an input voltage comparison circuit (5) and a logic switching circuit (6), wherein a sampling resistor R in the output voltage sampling circuit (2) is connected with a sampling resistor R1And R2After being connected in series with the output voltage V of the main power circuit (1)oThe sampling output end F of the output voltage sampling circuit (2) is connected with the end A of the output voltage feedback control circuit (3); the positive input end of the output voltage feedback control circuit (3) and the reference voltage VrefConnecting; the positive input end and the negative input end of the sawtooth wave comparison and switch tube driving circuit (4) are respectively connected with the output end B of the output voltage feedback control circuit and the triangular wave; the positive input end of the input voltage comparison circuit (5) is connected with the positive output end of the LC filter of the main power circuit (1) through a divider resistor, and the reverse input end is connected with the critical voltage VboundaryConnecting; the input ends of two AND gates of the logic switch circuit (6) are connected with the output end Q of the sawtooth wave comparison and switch tube driving circuit (4), wherein the AND gate ANDgate2The other input end of the first and second voltage-difference detection circuits is connected with the output end E of the input voltage comparison circuit (5) through an inverting amplifier and then connected with an AND gate ANDgate2As an output signal V of the control circuitd_fWith the switching tube Q of the Flyback circuit in the main power circuit (1)fThe gate pole of the switch tube Q is connected to drive the switch tube QfWorking AND gate ANDgate1Is connected with the output end E of the input voltage comparison circuit (5) and is connected with an AND gate ANDgate1As an output signal V of the control circuitd_bWith the switching tube Q of the Buck circuit in the main power circuit (1)bThe gate pole of the switch tube Q is connected to drive the switch tube QbAnd (6) working.
The output end C of the sawtooth wave comparison circuit of the sawtooth wave comparison and switch tube driving circuit (4) is connected with a switch tube driving chip through an RS trigger, and the output end of the switch tube driving chip14 and output 11 are respectively connected via a diode D8And a diode D7As the output signal of the sawtooth wave comparison and switching tube driving circuit (4), the switching tube driving chip can be an integrated IC (integrated circuit) of UC3843, UC3844 or UC 74279, the amplifier IC 1-IC 6 used in the output voltage feedback control circuit (3) can be an operational amplifier of TL074, TL072, LM358, LM324 and the like, the voltage comparators in the sawtooth wave comparison and switching tube driving circuit (4) and the input voltage comparison circuit (5) can be voltage comparators of LM324, LM358, UA741, TL081, LM339, LM393 and the like, the RS flip-flops in the sawtooth wave comparison and switching tube driving circuit (4) can be RS flip-flops of 74LS71, 74LS279, 74HC279, 74279 and the like, and the and gates in the logic switching circuit (6) can be integrated circuits of 7408, 7409, 7411, 7415 and the like.
In summary, the high power factor DCM Buck-Flyback converter of the present invention combines the Buck topology with the Flyback topology, so that the Flyback circuit operates when the input voltage is lower than the critical voltage value, and the Buck circuit operates when the input voltage is higher than the critical voltage value, thereby eliminating the dead zone of the input current of the Buck circuit in the DCM mode, so that the input current is close to a sine wave having the same phase as the input voltage, and meanwhile, the present invention designs the optimum turn ratio and the output voltage of the Buck-Flyback, so as to increase the PF value to be close to 1 in the whole wide input voltage range of 90-264 VAC. In addition, compared with the traditional constant duty ratio control converter only comprising a Buck circuit, the Buck-Flyback circuit topology further has the advantages of small output voltage ripple, small conduction loss of a switching tube, reduction of required diode stress and the like.

Claims (2)

1. A DCM Buck-Flyback PFC converter with high power factor is characterized by comprising a main power circuit (1) and a control circuit, wherein the main power circuit (1) comprises an input voltage source vinThe diode rectifying circuit RB, the LC filter, the Buck circuit and the Flyback circuit share the transformer T and the primary coil inductance L of the transformer TpTransformer T secondary winding inductance LsBuck circuit switch tube QbDiode DbFreewheel diode DfwFlyback circuit switch tube QfOutput capacitance CoLoad RLd(ii) a Wherein
Input voltage source vinIs connected with the input port of the RB rectifying circuit,
the output port of the RB rectifying circuit is connected with the input port of the LC filter,
the output cathode of the LC filter is a reference potential zero point,
the output positive pole of the LC filter is respectively connected with a Buck circuit switch tube QbAnd primary winding L of transformer TpThe same-name ends of the two terminals are connected,
transformer T primary winding LpAnd the other end of the Flyback circuit switching tube QfIs connected with one end of a switching tube QfThe other end of the first electrode is a reference potential zero point,
switch tube QbAnother terminal of (1) and a diode DbOne end of the two ends of the connecting rod is connected,
diode DbThe other end of the transformer is respectively connected with a secondary winding L of the transformer TsOf the same name terminal and freewheeling diode DfwOne end of the two ends of the connecting rod is connected,
transformer T secondary winding LsThe other end of the capacitor is simultaneously connected with an output capacitor CoAnd a load RLdIs connected to an output capacitor CoAnd a load RLdThe other end of the reference potential zero point is a reference potential zero point;
the control circuit comprises an output voltage sampling circuit (2), an output voltage feedback control circuit (3), a sawtooth wave comparison and switching tube driving circuit (4), an input voltage comparison circuit (5) and a logic switching circuit (6);
sampling resistor R in output voltage sampling circuit (2)1And R2After being connected in series with the output voltage V of the main power circuit (1)oAre connected in parallel and are connected in parallel,
the sampling output end of the output voltage sampling circuit (2) is connected with the input end of the output voltage feedback control circuit (3),
the positive input end of the output voltage feedback control circuit (3) and the reference voltage VrefThe connection is carried out in a connecting way,
the positive input end and the reverse input end of the sawtooth wave comparison and switch tube driving circuit (4) are respectively connected with the output end of the output voltage feedback control circuit (3) and the triangular wave,
the positive input end of the input voltage comparison circuit (5) is connected with the positive output end of the LC filter of the main power circuit (1) through a divider resistor,
the reverse input terminal of the input voltage comparison circuit (5) and the critical voltage VboundaryThe connection is carried out by connecting the two parts,
the input ends of two AND gates of the logic switch circuit (6) are connected with the output end of the sawtooth wave comparison and switch tube driving circuit (4),
a second AND gate ANDgate in the logic switch circuit (6)2The other input end of the input voltage comparator circuit (5) is connected with the output end of the input voltage comparator circuit through an inverting amplifier,
second AND gate ANDgate2As an output signal V of the control circuitd_fAnd is connected with a switch tube Q of a Flyback circuit in the main power circuit (1)fThe gate pole of the switch tube Q is connected to drive the switch tube QfIn the working process, the operation is carried out,
first AND gate ANDgate in logic switch circuit (6)1Is connected to the output of the input voltage comparison circuit (5),
first AND gate ANDgate1As an output signal V of the control circuitd_bWith the switching tube Q of the Buck circuit in the main power circuit (1)bThe gate pole of the switch tube Q is connected to drive the switch tube QbAnd (6) working.
2. The converter according to claim 1, wherein the switching tube driver chip is selected from an integrated circuit of UC3843, UC3844 or UC3525, an output terminal of the saw-tooth comparison circuit of the saw-tooth comparison and switching tube driver circuit (4) is connected to the switching tube driver chip through an RS flip-flop, and a fourteenth node of the switching tube driver chip is connected to a pin through an eighth diode D8And a seventh diode D7As the output signal of the sawtooth wave comparison and switch tube driving circuit (4);
an amplifier IC 1-IC 6 used in the output voltage feedback control circuit (3) selects one type of operational amplifier from TL074, TL072, LM358 and LM 324;
the voltage comparators in the sawtooth wave comparison and switch tube driving circuit (4) and the input voltage comparison circuit (5) are voltage comparators of one type selected from LM324, LM358, UA741, TL081, LM339 and LM 393;
the RS trigger in the sawtooth wave comparison and switch tube driving circuit (4) is one type of RS trigger selected from 74LS71, 74LS279, 74HC279 and 74279;
the AND gate in the logic switch circuit (6) is an integrated AND gate circuit of one type of 7408, 7409, 7411 and 7415.
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