CN115347794A - Asymmetric half-bridge flyback converter and design method thereof - Google Patents

Asymmetric half-bridge flyback converter and design method thereof Download PDF

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CN115347794A
CN115347794A CN202210967240.3A CN202210967240A CN115347794A CN 115347794 A CN115347794 A CN 115347794A CN 202210967240 A CN202210967240 A CN 202210967240A CN 115347794 A CN115347794 A CN 115347794A
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voltage
current
transformer
capacitor
flyback converter
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姚凯
荆子琦
汤其媛
张士顺
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Nanjing University of Science and Technology
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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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • 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
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • H02M1/0058—Transistor switching losses by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero
    • 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
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
    • 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
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33571—Half-bridge at primary side of an isolation transformer
    • 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

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses an asymmetric half-bridge flyback converter and a design method thereof, which comprises the design of a main power circuit and a control circuit, and the derivation of voltage fluctuation and resonance time on a resonance capacitor. The main power circuit comprises a design of a planar transformer: the winding method adopting the PPPSSS adopts one turn of the primary side as a shielding layer to greatly reduce the coupling capacitance of the primary side and the secondary side, and meanwhile, an additional series resonance inductor is not needed to reduce the loss. Reasonable capacitance value of the resonant capacitor can be designed according to the derivation of the voltage fluctuation of the resonant capacitor, proper resonant time can be obtained according to the derivation of the resonant time so as to realize zero current turn-off of the secondary synchronous rectifier tube, and current circulation in the resonant cavity is reduced so as to improve efficiency. The invention can realize the soft switching of all the switching tubes in a wide input voltage, output voltage and power range so as to achieve high efficiency.

Description

Asymmetric half-bridge flyback converter and design method thereof
Technical Field
The invention relates to a DC-DC converter technology of an electric energy conversion device, in particular to an asymmetric half-bridge flyback converter and a design method thereof.
Background
With the widespread use of portable electronic devices, electronic device charging adapters have become a necessity. With the development of the fields of rapid charging of mobile phones and the like in recent years, higher requirements are put forward on the power and the volume of a power supply system, and charging equipment is required to have high charging speed and small volume. Meanwhile, with the increase of the power of the charging equipment, the EMI requirement of the power grid on the converter is increased increasingly, and the requirement meets the set standard of the state.
For the medium and small power switch power supply required by mobile phone fast charging mobile electronic equipment and the like, the loss is dissipated in the form of heat energy, so the requirement for the converter can be summarized as the requirement for high efficiency and high power density of the converter. At present, two common simple and practical switching power supply topologies can meet the required power requirements, one is a forward converter, and the other is a flyback converter. The energy of the forward converter can be directly transferred to the transformer, and the transformer is not used for storing the energy, so that the transformer has higher magnetizing inductance and no air gap, and the utilization rate of the transformer can be improved; and the secondary output of the transformer is subjected to LC filtering, so that the peak current on the transistor can be reduced while the output voltage ripple is reduced, and the voltage stress is reduced. Compared with a forward converter, the flyback transformer is mainly used for storing energy in the circuit operation, the application in a high-power occasion is limited, meanwhile, a secondary side of the converter does not need a filter inductor, and the flyback transformer has absolute advantages in coping with the requirements of wide voltage range input, wide voltage range output and high gain, so that the flyback transformer is an optimal choice in a low-power occasion.
The flyback converter has many problems in practical application, firstly, because the conventional flyback circuit works in a hard switching mode, high efficiency cannot be realized, secondly, in consideration of reducing cost and size, the transformer needs to be provided with an air gap to prevent magnetic flux saturation, but the leakage inductance of the transformer is increased by the measure, power loss and voltage stress of an MOS (metal oxide semiconductor) transistor are increased, and the efficiency of the converter and the stability of the circuit are reduced. In addition, the resonant peak voltage caused by the secondary winding of the converter affects the working efficiency of the transformer of the switching power supply [3] . EMI of converter in hard switching modePerformance can deteriorate, which also limits the use of flyback converters in some applications. In view of the three problems above the flyback converter, researchers have conducted a great deal of research on the flyback converter.
In order to reduce the voltage stress and voltage spike of the flyback converter, a passive RCD absorption circuit is usually adopted in a quasi-resonant circuit (QR), so that residual energy in leakage inductance is consumed, and the efficiency improvement of the flyback converter is limited. An active clamp flyback circuit (ACF) can effectively utilize energy in leakage inductance through a clamp capacitor, but the development and application of a flyback converter are still restricted by the problem of high voltage stress of a switching tube.
Disclosure of Invention
The invention aims to overcome the defects of the background technology and provides an asymmetric half-bridge flyback converter and a design method thereof, so that the converter can meet the requirements of wide input and wide output (input 90VAC-220VAC, output 5V-15V, 5A), the efficiency is as high as possible, and the power density is as high as possible.
The invention adopts the following technical scheme for realizing the aim of the invention:
an asymmetric half-bridge flyback converter includes a main power circuit including V B For the bus voltage of the AC input voltage via a rectifier bridge and an input filter capacitor, S 1 、S 2 For the primary side switching tube, a GaN device is adopted, and since the GaN device does not have a body diode but has a third quadrant, the GaN device uses the same S in a schematic diagram 1 、S 2 The parallel diode represents its third quadrant in order to describe the freewheeling process. The transformer model can be equivalent to leakage inductance L r Excitation inductance of L m With an ideal transformer having a turn ratio of n:1, C r Is a resonant capacitor, Q 1 Is a secondary side synchronous rectifier tube, C o To output capacitance, R o Is a load.
A design method of an asymmetric half-bridge flyback converter is used for the asymmetric half-bridge flyback converter and comprises the following steps:
step A: analyzing leakage inductance current i under each mode according to working modes of the converter Lr And two ends of resonance capacitorVoltage v Cr An equation;
and B: obtaining an upper pipe S according to the volt-second balance of the excitation inductance 1 Duty ratio of
Figure BDA0003794438750000021
Step C: the output current is obtained according to the integral of the input power
Figure BDA0003794438750000022
Wherein I Lmmax And I Lmmin Respectively positive and negative peak currents of the exciting inductor. It is specifically calculated as
Figure BDA0003794438750000023
Wherein t is off The upper tube turn-off time;
step D: the secondary current can be approximately regarded as a half sine wave, and the average value of the secondary current in one period is equal to the output current I o The secondary side peak current can be obtained
Figure BDA0003794438750000024
Step E: input capacitance C in Is dependent on the minimum effective value V of the alternating voltage inrms_min And a minimum capacitor voltage V B_min Input filter capacitance value of
Figure BDA0003794438750000025
Step F: maximum turn ratio obtained by setting maximum duty ratio according to upper tube
Figure BDA0003794438750000026
Synchronous rectifier tube Q according to secondary side 1 Minimum turn ratio for withstand voltage
Figure BDA0003794438750000027
Thus, obtaining the turn ratio n of the transformer;
step G: designing a transformer according to the effective area A of the magnetic core e And the magnetic flux density variable Delta BNumber of turns of secondary winding of transformer
Figure BDA0003794438750000028
Thus, the number of turns N of the primary side of the transformer is obtained p And a core air gap size δ;
step H: since the secondary current is approximately half a sine wave, the waveform is equal to I o Has a crossing point on the waveform of t A1 And t A2 Obtaining the output capacitor according to the requirement of the ripple amplitude delta U of the output voltage
Figure BDA0003794438750000031
Preferably, the voltage fluctuation valley value on the resonance capacitor is t in FIG. 1 1 The voltage value of the resonance capacitor at the moment is
Figure BDA0003794438750000032
In the formula
Figure BDA0003794438750000033
The peak value of the voltage fluctuation on the resonant capacitor, i.e. t in FIG. 1 5 The voltage value of the resonance capacitor at the moment is
Figure BDA0003794438750000034
In the formula
Figure BDA0003794438750000035
Figure BDA0003794438750000036
Preferably, top tube off, i.e. bottom tube on time t off The dead time is ignored, the dead time is matched with the resonance time to the greatest extent, so that the circulation current in the resonance cavity is reduced, meanwhile, the secondary side synchronous rectifier tube is turned off at zero current, and the resonance time is
Figure BDA0003794438750000037
In the formula
Figure BDA0003794438750000038
Preferably, a planar transformer design is adopted, and a PPPSSS winding method is adopted to design a shielding layer by using a single turn of a primary coil and a resonant capacitor C r The positive electrode has the same potential, so that the coupling capacitors between the original secondary side are coupled to a potential with small fluctuation, common mode noise can be effectively reduced, and meanwhile, additional series resonance inductors are not needed to reduce loss.
Preferably, the upper tube of the primary switch tube is selected from GS-065-011-1-L of GaN Systems, the lower tube is selected from GS66508B of GaN Systems, the secondary synchronous rectifier tube is selected from BSC093N15NS5 of British Rabdosia, and the magnetic core is selected from PC95EL25X8.6-Z of TDK; the control chip adopts XDPS2201 chip of England flying company.
Compared with the prior art, the technical scheme adopted by the invention has the following beneficial effects:
1. the invention provides an asymmetric half-bridge flyback converter and a design method thereof, wherein random frequency is selected in the range of two switching frequency changes in each control period to randomize the switching frequency, so that the harmonic dispersion effect of a random SVPWM method can be improved under the condition of a narrow switching frequency change range, and the electromagnetic interference is further inhibited.
2. The invention provides an asymmetric half-bridge flyback converter and a design method thereof, which can realize zero-voltage switching (ZVS) of a primary side switching tube and zero-current switching (ZCS) of a secondary side synchronous rectifier tube in the range of wide input voltage, output voltage and output power.
3. The invention provides an asymmetric half-bridge flyback converter and a design method thereof, and provides a novel magnetic shielding technical method for designing a planar transformer of the asymmetric half-bridge flyback converter, wherein a primary side one-turn winding is used as a shielding layer to greatly reduce a primary side coupling capacitor and a secondary side coupling capacitor, so that the converter meets the requirements of EN 55022B.
4. The invention provides an asymmetric half-bridge flyback converter and a design method thereof, which reduce the alternating current impedance of a transformer by adopting a mixed copper thickness mode and improve the efficiency and the power density of the converter.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a key waveform of a converter during one switching cycle;
fig. 2 is a main circuit of an asymmetric half-bridge flyback converter;
FIG. 3 is a diagram of the operating mode of the converter;
FIG. 4 is a schematic diagram of a PPPSSS winding process;
FIG. 5 is a cross-sectional view of a transformer winding;
fig. 6 is a spatial structure diagram of a transformer winding.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
1. The working principle of the asymmetric half-bridge flyback converter is as follows:
fig. 1 shows a key waveform of the converter in a switching cycle, which includes an upper tube driving signal, a lower tube driving signal, a resonant current and an excitation current, a secondary side current, and a half-bridge midpoint voltage in sequence from top to bottom, fig. 2 is a main circuit of an asymmetric half-bridge flyback converter, and fig. 3 shows a working mode diagram of the converter.
Mode 1: t is t 1 ～t 2 Stage S 1 Opening, S 2 And closing. Current increase in the transformer, resonant capacitance C r Both devices can store energy with increasing voltage. Secondary diode D 1 Is reverse biased so that no energy is transferred to the secondary side.
Mode 2: t is t 2 ～t 3 Stage, switch tube S 1 And S 2 Are all off. Primary side current supply S 1 Charging the parasitic capacitance of the S-bridge and simultaneously charging the S-bridge 2 Is discharged at t 3 Time S 1 And S 2 Ends the charging and discharging process of the parasitic capacitance of (1), S 2 The voltage drop across is zero and is S 2 The body diode turn-on of (1) provides a condition.
Modality 3: t is t 3 ～t 4 Stage, switch tube S 1 And S 2 Are all closed, S 2 The body diode of (1) clamps the voltage. Primary side of transformer and capacitor C r With the same voltage. S 2 The voltage across (2) is the turn-on voltage of the body diode.
Modality 4: t is t 4 ～t 5 Stage, in ZVS state S 1 Closing, S 2 Open, secondary side voltage equals to C on capacitor r Divided by the turns ratio. Current begins to flow through Q 1 The energy in the capacitor, transformer is transferred to the output. Since the LC resonant cavity is composed of L r The leakage inductance of the transformer and the resonance capacitance, and the secondary side current is a sine wave determined by the resonance period of the two devices. The primary current is the sum of the excitation current plus the secondary reflected current. The current in the resonant cavity is still positive and mainly composed of a transformer T 1 Driven by exciting inductor and flowing into resonant capacitor C r And further charging.
Mode 5: t is t 5 ～t 6 A phase is a continuation of the previous phase. S 1 Off, S 2 Open, energy still transferred to secondary side but with the resonant tank current and voltage reversed in direction, by resonant capacitor C r A voltage is provided. Resonance capacitorThe energy of the transformer is not only transferred to the secondary side, but also contributes to the magnetizing current T of the transformer 1 At S 2 Turn on to decrease to a negative value.
Modality 6: t is t 6 ～t 7 A stage in which the secondary current is finally reduced to zero, and the primary current continues to be reduced after resonating to zero, for S 1 Body diode turn-on provides sufficient negative current to realize S 1 The zero voltage turns on.
Modality 7: t is t 7 ～t 8 Stage, switch tube S 1 And S 2 Are all off. Primary side current supply S 2 Charging the parasitic capacitance of the S-bridge and simultaneously charging the S-bridge 1 Is discharged at t 8 Time S 2 And S 1 Ends the charging and discharging process of the parasitic capacitance of (1), S 1 The voltage drop across is zero and is S 1 The body diode turn-on of (1) provides a condition. .
Modality 8: t is t 8 ～t 9 Stage in which the switch S 1 And S 2 Are all off. S 1 Is turned on as S 1 The zero voltage turn-on provides a condition.
Modality 9: t is t 9 ～t 10 Stage, similar to the first stage, under ZVS conditions, S 1 Opening, S 2 Off, but the current in the transformer cavity is still negative, which means that excess energy in the cavity will be fed back to the input.
2. Designing circuit parameters:
step A: analyzing leakage inductance current i under each mode according to working modes of the converter Lr And the voltage v at two ends of the resonant capacitor Cr And (4) an equation.
And B: obtaining an upper pipe S according to the volt-second balance of the excitation inductance 1 Duty ratio of
Figure BDA0003794438750000051
And C: the output current is obtained according to the integral of the input power
Figure BDA0003794438750000052
In which I Lmmax And I Lmmin Respectively positive and negative peak currents of the excitation inductor. It is specifically calculated as
Figure BDA0003794438750000053
Wherein t is off The upper tube turn-off time.
Step D: the secondary current can be approximately regarded as a half sine wave, and the average value of the secondary current in one period is equal to the output current I o Secondary side peak current can be obtained
Figure BDA0003794438750000061
Step E: input capacitance C in Is dependent on the minimum effective value V of the alternating voltage inrms_min And a minimum capacitor voltage V B_min . An input filter capacitance value of
Figure BDA0003794438750000062
Step F: maximum turn ratio obtained by setting maximum duty ratio according to upper tube
Figure BDA0003794438750000063
According to the secondary side synchronous rectifier Q 1 Minimum turn ratio for withstand voltage
Figure BDA0003794438750000064
The transformer turn ratio n is determined in this way.
Step G: designing a transformer according to the effective area A of the magnetic core e And the number of secondary turns of the transformer can be obtained by the variable Delta B of the magnetic flux density
Figure BDA0003794438750000065
Thus, the number of turns N of the primary side of the transformer is obtained p And core air gap size δ.
Step H: since the secondary current approximates a half sine wave, its waveform is equal to I o Has an intersection point t on the waveform A1 And t A2 Obtaining the output capacitor according to the requirement of the ripple amplitude Delta U of the output voltage
Figure BDA0003794438750000066
3. Reference of voltage fluctuation value on the resonance capacitor:
the valley of the voltage fluctuation on the resonant capacitor, i.e. t in FIG. 1 1 The voltage value of the resonance capacitor at the moment is
Figure BDA0003794438750000067
In the formula
Figure BDA0003794438750000068
The peak value of the voltage fluctuation on the resonant capacitor, i.e. t in FIG. 1 5 The voltage value of the resonance capacitor at the moment is
Figure BDA0003794438750000069
In the formula
Figure BDA00037944387500000610
Figure BDA00037944387500000611
4. Designing the opening time of the lower pipe:
upper tube turn-off, i.e. lower tube turn-on time t off The dead time is ignored, and the dead time is matched with the resonance time as much as possible so as to reduce the circulation current in the resonance cavity and simultaneously turn off the secondary side synchronous rectifier tube at zero current. A resonance time of
Figure BDA0003794438750000071
In the formula
Figure BDA0003794438750000072
5. Designing a planar transformer:
in order to improve the power density, a planar transformer design is adopted, and the winding mode of the six-layer planar transformer mainly comprises a PPPSSS winding method and a PSPSPS winding method. The cross-sectional view and the spatial structure view of the winding of the transformer by PSPSPS winding are shown in fig. 5 (a) and fig. 6 (a), respectively. The winding method can cause a plurality of coupling capacitors C to exist between the primary side and the secondary side PS Common mode noise passes through C PS The common mode noise is relatively large. The PPPSSS winding principle diagram is shown in fig. 4, and the sectional view and the space structure diagram of the transformer winding are shown in fig. 5 (b) and fig. 6 (b), respectively. The winding method uses a single turn of a primary coil to design the primary coil into a shielding layer and a resonant capacitor C r The positive electrode has the same potential, so that the coupling capacitors between the original secondary side are coupled to a potential with small fluctuation, and the common mode noise can be effectively reduced.
The parameters of both windings at the same inductance were measured by LCR with an excitation inductance of 55 muh, as shown in table 1. Through measurement, the primary side coupling capacitance and the secondary side coupling capacitance of the PPPSSS winding method are far smaller than those of the PSPSPS winding method, and inductance impedance and alternating current impedance are not changed greatly, so that common mode noise can be effectively reduced on the premise of not influencing efficiency. Meanwhile, leakage inductance is increased, and extra series resonance inductance is avoided, so that the efficiency is improved, and the power density is increased.
Figure BDA0003794438750000073
TABLE 1
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (6)

1. An asymmetric half-bridge flyback converter, comprising: includes a main power circuit including V B For the bus voltage of the AC input voltage via a rectifier bridge and an input filter capacitor, S 1 、S 2 For the primary side switching tube, a GaN device is adopted, and since the GaN device does not have a body diode but has a third quadrant, the GaN device uses the same S in a schematic diagram 1 、S 2 The parallel diode represents its third quadrant in order to describe the freewheeling process. The transformer model can be equivalent to leakage inductance L r Excitation inductance of L m With an ideal transformer having a turn ratio of n:1, C r Is a resonant capacitor, Q 1 Is a secondary side synchronous rectifier tube, C o As an output capacitance, R o Is a load.
2. A design method of an asymmetric half-bridge flyback converter is used for the asymmetric half-bridge flyback converter and is characterized by comprising the following steps:
step A: analyzing leakage inductance current i under each mode according to working modes of the converter Lr And the voltage v at two ends of the resonant capacitor Cr An equation;
and B, step B: obtaining an upper pipe S according to the volt-second balance of the excitation inductance 1 Duty ratio of
Figure FDA0003794438740000011
And C: the output current is obtained according to the integral of the input power
Figure FDA0003794438740000012
Wherein I Lmmax And I Lmmin Respectively positive and negative peak currents of the exciting inductor. It is specifically calculated as
Figure FDA0003794438740000013
Wherein t is off The upper tube turn-off time;
step D: the secondary side current can be approximately regarded as a half sine wave, and the secondary side current in one periodThe average value of the current being equal to the output current I o The secondary side peak current can be obtained
Figure FDA0003794438740000014
Step E: input capacitance C in Is dependent on the minimum effective value V of the alternating voltage inrms_min And a minimum capacitor voltage V B_min Input filter capacitance value of
Figure FDA0003794438740000015
Step F: maximum turn ratio obtained by setting maximum duty ratio according to upper tube
Figure FDA0003794438740000016
According to the secondary side synchronous rectifier Q 1 Minimum turn ratio for withstand voltage
Figure FDA0003794438740000017
Thus, obtaining the turn ratio n of the transformer;
g: designing a transformer according to the effective area A of the magnetic core e And the number of turns of the secondary side of the transformer can be obtained by the variable Delta B of the magnetic flux density
Figure FDA0003794438740000018
Thus, the number of turns N of the primary side of the transformer is obtained p And a core air gap size δ;
step H: since the secondary current is approximately half a sine wave, the waveform is equal to I o Has an intersection point t on the waveform A1 And t A2 Obtaining the output capacitor according to the requirement of the ripple amplitude delta U of the output voltage
Figure FDA0003794438740000019
3. The design method of an asymmetric half-bridge flyback converter according to claim 2, wherein: the valley of the voltage fluctuation on the resonant capacitor, i.e. t in FIG. 1 1 The voltage value of the resonance capacitor at the moment is
Figure FDA0003794438740000021
In the formula
Figure FDA0003794438740000022
The peak value of the voltage fluctuation on the resonant capacitor, i.e. t in FIG. 1 5 The voltage value of the resonance capacitor at the moment is
Figure FDA0003794438740000023
In the formula
Figure FDA0003794438740000024
Figure FDA0003794438740000025
4. The design method of the asymmetric half-bridge flyback converter according to claim 2, wherein: upper tube turn-off, i.e. lower tube turn-on time t off The dead time is ignored, the dead time is matched with the resonance time to the greatest extent, so that the circulation current in the resonance cavity is reduced, meanwhile, the secondary side synchronous rectifier tube is turned off at zero current, and the resonance time is
Figure FDA0003794438740000026
In the formula
Figure FDA0003794438740000027
5. The method of claim 2The design method of the asymmetric half-bridge flyback converter is characterized by comprising the following steps: the planar transformer is designed by PPPSSS winding method, and the primary coil is designed into a shielding layer and a resonant capacitor C by using a single turn of the primary coil r The positive pole is at the same potential, so that the coupling capacitors between the original secondary sides are coupled to a potential with small fluctuation, common mode noise can be effectively reduced, and meanwhile, additional series resonance inductors are not needed to reduce loss.
6. The design method of the asymmetric half-bridge flyback converter according to claim 2, wherein: the upper tube of the primary side switch tube is selected from GS-065-011-1-L of GaN Systems, the lower tube is selected from GS66508B of GaN Systems, the secondary side synchronous rectifier tube is selected from BSC093N15NS5 of England flying company, and the magnetic core is selected from PC95EL25X8.6-Z of TDK; the control chip adopts XDPS2201 chip of the England flying company.
CN202210967240.3A 2022-08-12 2022-08-12 Asymmetric half-bridge flyback converter and design method thereof Pending CN115347794A (en)

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