CN111416520B - Synchronous rectification duty ratio loss compensation method based on magnetic flux cancellation and converter - Google Patents

Synchronous rectification duty ratio loss compensation method based on magnetic flux cancellation and converter Download PDF

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CN111416520B
CN111416520B CN202010116158.0A CN202010116158A CN111416520B CN 111416520 B CN111416520 B CN 111416520B CN 202010116158 A CN202010116158 A CN 202010116158A CN 111416520 B CN111416520 B CN 111416520B
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synchronous rectification
inductance
compensator
voltage
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CN111416520A (en
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何良宗
陈嘉哲
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Xiamen University
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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
    • H02M3/33592—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 having a synchronous rectifier circuit or a synchronous freewheeling circuit 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
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0009—Devices or circuits for detecting current in a converter
    • 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
    • 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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  • Power Engineering (AREA)
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Abstract

The invention relates to a synchronous rectification duty ratio loss compensation method based on magnetic flux cancellation and an LLC resonant converter with duty ratio loss compensation. Compared with other compensation methods, the method can improve the problem of duty ratio loss of the synchronous rectification circuit by only serially connecting a coil or a turn of conducting wire in the detection loop, even without adjusting a PCB structure and only printing the conducting wire on the PCB in the implementation, and further the LLC resonant converter has the advantages of less required devices, easiness in implementation, suitability for various types of synchronous rectification controllers and the like.

Description

Synchronous rectification duty ratio loss compensation method based on magnetic flux cancellation and converter
Technical Field
The invention relates to the technical field of large-current synchronous rectification on a secondary side of a resonant DC-DC converter, in particular to a synchronous rectification duty ratio loss compensation method based on magnetic flux cancellation and an LLC resonant converter with duty ratio loss compensation.
Background
The low-voltage large-current DC-DC converter usually adopts a synchronous rectification technology to reduce the output impedance of a rectification part so as to achieve the aim of improving the efficiency of the converter. Taking the 14V converter as an example, if the diode full-wave rectification is adopted, the voltage drop of the diode is assumed to be 0.7V, and the power of the loss of the rectification part at least accounts for more than 5% of the input power under the premise of not considering the reverse recovery loss. If synchronous rectification is used and the diode is replaced by the controlled MOSFET, the on-state voltage drop generated on the MOSFET on-resistance can be reduced to below 50 mV. Then the loss of the rectifying part is only 0.3%. Therefore, the synchronous rectification technology is applied to the low-voltage high-current converter, and the efficiency of the converter can be effectively improved.
However, in the actual voltage detection type synchronous rectification application, the phenomenon of duty ratio loss often occurs. The voltage detection type synchronous rectification is realized according to the V of the MOSFETDSThe voltage (the voltage at the drain terminal versus the source terminal) determines the operating state of the MOSFET. Ideally, when the MOSFET is turned on, if the package parasitic inductance of the MOSFET is neglected, the turned-on MOSFET can be equivalently formed by only using one on-resistance RDS_ONInstead. Since it is a purely resistive branch, VDSVoltage and IDSThe currents (between drain and source) are in phase.
In general, a MOSFET is equivalent to an on-resistance R when turned onDS_ONAnd a package inductor LpackageIn series. Due to the existence of the packaging inductor, the branch circuit is a resistance-inductance type branch circuit, and the voltage phase and the current phase are firstly conducted. Thus, at this time VDSThe phase of the voltage will precede IDSThe phase of the current. When current IDSAt the beginning of descent, VDSDue to phase advance, VDSWill precede IDSZero crossing. When the synchronous rectification controller detects VDSAnd after the voltage crosses zero, the MOSFET is controlled to be switched off. And then IDSDoes not cross zero, after being turned off, IDSThe current flows through the body diode of the MOSFET, and a large amount of conduction loss is generated due to the conduction voltage drop (much larger than 50mV) of about 0.4V existing in the body diode.
On the other hand, in the application of high-current rectification, the influence of package parasitic inductance exists, and the mutual inductance of the detection loop is not negligible. According to the decoupling equivalent circuit of the synchronous rectification circuit, the mutual inductance M on the decoupled branch1And self-inductance LpackageThe series relationship, i.e., mutual inductance and self-inductance, can interfere with the normal operation of the synchronous rectification controller.
The prior art mainly has three main categories of solutions to duty cycle loss: firstly, the detected V is detected by utilizing the characteristic of self-carried delay of the RC networkDSThe voltage first passes through a first-stage RC filter, and the delay generated by the RC filter is used for compensating M1And LpackageThe advance of generation. However, since the RC network also causes the synchronous rectifier to be turned on in a delayed manner at the turn-on time (the delayed time is called turn-on delay, and similar turn-off is advanced, and the turn-on delay also causes duty ratio loss), an improved RC Filter, Zero-cross Noise Filter, abbreviated as ZCNF, is proposed by the liuyanfei task group of the university of queen canada. The ZCNF filter can complete the compensation of the lost duty ratio on the premise of not generating the turn-on delay. The drawback is that ZCNF requires more than 2 resistors, more than 1 capacitor plus at least 1 diode, which increases hardware cost. At the same time, to ensure compensating network operating timingThe voltage drop of the selected diode must be consistent with that of the body diode of the MOSFET, and the selection difficulty of the device is greatly increased.
Secondly, the external compensation inductor is utilized to generate compensation voltage, and the voltage is superposed on V with error after being reversed by an inverter arranged in the chipDSThe voltage. If the inductance value of the compensation inductor is consistent with the inductance value of the parasitic inductor, the generated voltage is the same as the error voltage on the parasitic inductor, and the generated voltage is reversed through the reverser to be used as the compensation voltage. The method is integrated on a synchronous rectification controller NCP4303 of the company Anson, and has the defects that an external excitation inductor is connected with a MOSFET in series, and the current flowing through the inductor is IDSAnd therefore the inductance will bring about conduction losses. On the other hand, the inductance is required to be an ideal inductance having a small parasitic resistance. Otherwise, the voltage drop generated on the parasitic resistor may cause the turn-off threshold voltage of the synchronous rectification controller to be increased, so that the compensation is opposite.
And thirdly, providing a grid driving signal with variable amplitude by using an adaptive driving control strategy through a synchronous rectification controller. When I isDSWhen larger, increase the gate voltage, when IDSThe gate voltage is reduced for smaller, by applying a suitable gate voltage to make VDSThe absolute value of the voltage is maintained at around 50mV throughout the MOSFET conduction period. The synchronous rectification controller TEA1995T of Enzhipu corporation applies the method, and the defect is that the driving capability of the self-adaptive grid driving is weak, so that the method is not suitable for being applied to a large-current synchronous rectification application occasion requiring multiple parallel pipes.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a synchronous rectification duty ratio loss compensation method based on magnetic flux cancellation, and an LLC resonant converter with duty ratio loss compensation, solves the problem that a synchronous rectifier tube in a secondary synchronous rectification circuit in the LLC converter is turned off in advance, and improves the efficiency of the converter.
The technical scheme of the invention is as follows:
a synchronous rectification duty cycle loss compensation method based on magnetic flux cancellation utilizes a magnetic flux cancellation principle to introduce mutual inductance into a voltage detection loop of a synchronous rectification controller, generate specific induced electromotive force, cancel error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop, and compensate loss of a synchronous rectification duty cycle.
Preferably, the turn-off time sequence of the synchronous rectifier tube is adjusted by utilizing a magnetic flux cancellation principle and matching with the synchronous rectifier controller; according to the electromagnetic induction law, an alternating magnetic field generated by a secondary winding of a transformer of an isolation converter is coupled through a compensator, and an induced electromotive force satisfying the following relation is generated:
Voffset＝-IDS(jwM1+jwLpackage)；
wherein, IDSFor current between drain and source of MOSFET of synchronous rectifier tube, M1Self-inductance L of voltage detection loop for synchronous rectification controller1Secondary leakage inductance L with transformer2Coupling inductance, L, produced by mutual inductancepackageIs parasitic inductance in a synchronous rectifier MOSFET.
Preferably, the compensator has a self-inductance L3And secondary leakage inductance L of transformer2Coupling inductance M generated by mutual inductance3，M3The magnitude of the sensitivity value satisfies the following relation:
M1-M3+Lpackage＝0。
preferably, the compensator is inDSBefore the current drops to zero, the current passes through a coupling inductor M3The generated negative induced voltage is compensated by the parasitic inductance LpackageAnd self-inductance L of the voltage detection loop1The generated positive error voltage enables the synchronous rectification controller to accurately detect the current zero crossing point and generate a turn-off signal without duty ratio loss.
Preferably, said duty cycle loss is caused by a parasitic inductance LpackageOr a coupling inductor M1The generated error voltage causes the synchronous rectification controller to generate a turn-off signal in advance to cause the MOSFET of the synchronous rectification tube to be in IDSThe current is turned off in advance when not passing zero; after MOSFET of synchronous rectifier is turned off, IDSThe current passes throughThe body diode of the step rectifier MOSFET freewheels, generating losses.
Preferably, the compensator is a coil or a lead wire with one turn or a printed lead wire on a PCB, one end of the compensator is connected with the drain electrode of the synchronous rectifier MOSFET, and the other end of the compensator is connected with the synchronous rectifier controller.
Preferably, the compensator is connected in series in the voltage detection loop for providing the compensation voltage.
Preferably, the synchronous rectification controller and the synchronous rectification tube are connected in series through a pair of voltage detection lines to form a voltage detection loop; the synchronous rectification controller has at least one pair of voltage detection pins for detecting V of synchronous rectification MOSFETDSA voltage; one pin is connected with the source electrode of the synchronous rectifier tube MOSFET, and the other pin is connected with the drain electrode of the synchronous rectifier tube MOSFET.
An LLC resonant converter with duty cycle loss compensation comprises an input voltage source, a controllable switch network, an LLC resonant network, a transformer, a synchronous rectification unit provided with a compensator, a filter capacitor and a load; the synchronous rectification unit comprises a synchronous rectification controller and a synchronous rectification MOSFET; based on the synchronous rectification duty ratio loss compensation method, mutual inductance is introduced into a voltage detection loop of a synchronous rectification controller through a compensator, specific induced electromotive force is generated, error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop is offset, and synchronous rectification duty ratio loss is compensated.
Preferably, the compensator is externally arranged on the synchronous rectification unit and is connected in series in a voltage detection loop of the synchronous rectification controller.
The invention has the following beneficial effects:
according to the synchronous rectification duty ratio loss compensation method based on magnetic flux cancellation and the LLC resonant converter with duty ratio loss compensation, mutual inductance is introduced into a voltage detection loop of a synchronous rectification controller by utilizing a magnetic flux cancellation principle, a specific induced electromotive force is generated, an error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop is offset, the problem that a synchronous rectification tube in a secondary synchronous rectification circuit in the LLC converter is turned off in advance is solved, and the efficiency of the converter is improved. Compared with other compensation methods, the method can improve the problem of duty ratio loss of the synchronous rectification circuit by only serially connecting a coil or a turn of conducting wire in the detection loop, even without adjusting a PCB structure and only printing the conducting wire on the PCB in the implementation, and further the LLC resonant converter has the advantages of less required devices, easiness in implementation, suitability for various types of synchronous rectification controllers and the like.
Drawings
Fig. 1 is a circuit schematic of an LLC resonant converter in accordance with the invention;
FIG. 2 is a circuit schematic of a synchronous rectification unit;
FIG. 3 is a schematic diagram of an equivalent circuit with synchronous rectification unit decoupling;
FIG. 4 is a duty cycle loss diagram;
FIG. 5 is a circuit schematic of a synchronous rectification unit with a compensator;
fig. 6 is a schematic of a decoupled equivalent circuit of a synchronous rectification circuit with a compensator.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
In order to solve the problems in the prior art, the invention provides a synchronous rectification duty cycle loss compensation method based on magnetic flux cancellation and an LLC resonant converter with duty cycle loss compensation.
The synchronous rectification duty cycle loss compensation method based on the magnetic flux cancellation introduces mutual inductance into a voltage detection loop of a synchronous rectification controller by utilizing the magnetic flux cancellation principle, generates specific induced electromotive force, cancels error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop, and compensates the loss of the synchronous rectification duty cycle.
Based on the synchronous rectification duty ratio loss compensation method, the invention also provides an LLC resonant converter with duty ratio loss compensation, as shown in fig. 1, comprising an input voltage source UiControllable switchA network (in this embodiment, including high-low side switching tubes S1, S2), and an LLC resonant network (including a resonant capacitor C)rResonant capacitor LpResonant capacitor Lr) Transformer T1A synchronous rectification unit with a compensator (one end of the compensator is connected with the drain electrode of the synchronous rectification MOSFET, the other end of the compensator is connected with the synchronous rectification controller), a filter capacitor CoutLoad RL(ii) a The synchronous rectification unit comprises a synchronous rectification controller and synchronous rectification MOSFETs (in the embodiment, the synchronous rectification unit comprises two synchronous rectification units, namely two synchronous rectification controllers and two synchronous rectification transistors SR1 and SR 2); mutual inductance is introduced into a voltage detection loop of the synchronous rectification controller through the compensator, specific induced electromotive force is generated, error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop is offset, and loss of a synchronous rectification duty ratio is compensated. In this embodiment, the compensator is connected in series in the voltage detection loop for providing the compensation voltage.
In the invention, a synchronous rectification controller and a synchronous rectification tube are connected in series through a pair of voltage detection lines to form a voltage detection loop; the synchronous rectification controller has at least one pair of voltage detection pins for detecting V of synchronous rectification MOSFETDSVoltage (voltage of drain versus source); one pin is connected with the source electrode of the synchronous rectifier tube MOSFET, and the other pin is connected with the drain electrode of the synchronous rectifier tube MOSFET.
The invention utilizes the principle of magnetic flux cancellation and is matched with a synchronous rectification controller to adjust the turn-off time sequence of a synchronous rectification tube; coupling of transformer T by isolating converter by compensator according to law of electromagnetic induction1The secondary winding generates an alternating magnetic field and an induced electromotive force which satisfies the following relation:
Voffset＝-IDS(jwM1+jwLpackage)；
wherein, IDSFor current between drain and source of MOSFET of synchronous rectifier tube, M1Self-inductance L of voltage detection loop for synchronous rectification controller1And transformer T1Secondary side leakage inductance L2Coupling inductance, L, produced by mutual inductancepackageIs parasitic inductance in a synchronous rectifier MOSFET.
In the synchronous rectification unit, as shown in fig. 2, an inductor L1、L2Respectively, parasitic inductances on the conductors of the voltage detection loop and the transformer T1Leakage inductance of the secondary side. Self-inductance L of voltage detection loop due to synchronous rectification controller1And transformer T1Secondary side leakage inductance L2There is a coupling relationship, i.e. the coupling inductance is produced by the mutual inductance, denoted M1For representing inductance L1And L2The interaction between them. Use of AC current source for equivalent transformer T1The primary part and the inverter circuit part are used for simplifying analysis. For high frequency currents, the filter capacitor CoutIs approximately 0, so that it can be considered that the filter capacitance C is a high frequency current rippleoutShort-circuited load RLAnd is shown in dashed lines.
By decoupling the mutual inductance in the synchronous rectification unit shown in fig. 2, it can be seen that V detected by the synchronous rectification controller is shown in fig. 3DSThe voltage satisfies the following relationship:
Figure BDA0002391565010000061
wherein, VSR1Voltage is IDSThe voltage drop produced when current flows through the synchronous rectifier MOSFET is due in part to the on-resistance RDS_ONAnother part is the parasitic inductance L due to the packagepackageAnd (4) generating. Among the commonly used synchronous rectification controllers, there is a V of the synchronous rectification controllerDSThe input impedance of the voltage input end is very large, taking the synchronous rectification controller NCP4303 as an example, under the condition that 200V bias voltage is applied to the D end and the S end of the controller, the I flowing into the chip2The current is only 1uA, corresponding to an equivalent input impedance of 200M Ω. Due to I2<<IDSIt can therefore be approximated that the self-inductance L on the voltage detection loop1And a coupling inductor M1The resulting pressure drop is 0. Further, VDSThe voltages can be simplified to the following relationship:
VDS＝IDS(jwM1+jwLpackage+RDS_ON)。
from the above formula, VDSThe voltage being parasitic mutual inductance (i.e. coupling inductance M)1) Parasitic inductance LpackageAnd an on-resistance RDS_ONThe sum of the voltages on. Wherein the coupling inductance M1And parasitic inductance LpackageThe resulting voltage will result in a detected VDSThe phase of the voltage leading IDSThe phase of the current, in turn, increases the off current threshold.
The loss of duty cycle is caused by parasitic inductance LpackageOr a coupling inductor M1The generated error voltage causes the synchronous rectification controller to generate a turn-off signal in advance to cause the MOSFET of the synchronous rectification tube to be in IDSThe current is turned off in advance when not passing zero; after MOSFET of synchronous rectifier is turned off, IDSCurrent freewheels through the body diode of the synchronous rectifier MOSFET, creating losses. As shown in fig. 4, since the synchronous rectification controller is detecting VDSAfter the voltage crosses zero, a turn-off signal is generated and sent to the synchronous rectifier MOSFET; therefore, if V without compensation is adoptedDSThe voltage signal is directly used to generate the driving signal, which results in an early turn-off of the synchronous rectifier MOSFET, i.e. a loss of duty cycle. After MOSFET of synchronous rectifier is turned off, IDSCurrent will freewheel through the body diode of the synchronous rectifier MOSFET, resulting in a large amount of conduction losses.
As shown in fig. 5, the compensator is externally disposed on the synchronous rectification unit and is connected in series in the voltage detection loop of the synchronous rectification controller. In this embodiment, an external coil is used as a compensator and is connected in series to a voltage detection loop. The compensator has self-inductance L3Transformer T1Secondary side leakage inductance L2Self-inductance L with compensator3There is a coupling relation between them, transformer T1Secondary side leakage inductance L2Self-inductance L with compensator3The coupling inductance, denoted M, being generated by mutual inductance3. Wherein M is3Can be changed by changing the transformer T1Secondary side leakage inductance L2Self-inductance L with compensator3End of same nameThe position is adjusted. At the same time, the self-inductance L of the voltage detection loop1Self-inductance L with compensator3There is also a coupling relation between them, the self-inductance L of the voltage detection loop1Self-inductance L with compensator3The coupling inductance, denoted M, being generated by mutual inductance2。
Decoupling the mutual inductance in the synchronous rectification unit shown in fig. 5, as shown in fig. 6, can obtain a coupled inductance M3Is decoupled at IDSThe branch through which the current flows, and the parasitic inductance LpackageCoupled inductor M1And an on-resistance RDS_ONIn a serial relationship. Thus, the coupling inductance M can be made by inserting an external compensator of suitable size3Satisfies the following relationship:
M1-M3+Lpackage＝0。
compensator inDSBefore the current drops to zero, the current passes through a coupling inductor M3The generated negative induced voltage is compensated by the parasitic inductance LpackageAnd self-inductance L of the voltage detection loop1The generated positive error voltage enables the synchronous rectification controller to accurately detect the current zero crossing point and generate a turn-off signal without duty ratio loss. I.e. by introducing a coupling inductance M3And the whole branch circuit is converted into a pure resistive branch circuit, and the pure resistive branch circuit meets the relation of voltage and current in the same phase. Therefore, the problem of duty ratio loss can not be caused by detecting the voltage on the branch circuit as the trigger signal of the synchronous rectification controller.
Due to parasitic parameters (i.e. coupling inductance M generated by mutual inductance present in the voltage detection loop1) Generally small, and in practice, the compensator may be implemented as a coil or wire of one turn, or as a section of printed wiring on a PCB, sufficient to generate a coupling inductance M of the order nH3. Compared with other compensation methods, the method can solve the problem of duty ratio loss at the turn-off time of the synchronous rectification circuit only by serially connecting a turn of coil in the voltage detection loop or even without adjusting a PCB structure, and has the advantages of less required devices, easiness in implementation, suitability for various types of synchronous rectification controllers and the like.
The above examples are provided only for illustrating the present invention and are not intended to limit the present invention. Changes, modifications, etc. to the above-described embodiments are intended to fall within the scope of the claims of the present invention as long as they are in accordance with the technical spirit of the present invention.

Claims (9)

1. A synchronous rectification duty cycle loss compensation method based on magnetic flux cancellation is characterized in that a magnetic flux cancellation principle is utilized, and a synchronous rectification controller is matched to adjust the turn-off time sequence of a synchronous rectification tube; according to the electromagnetic induction law, an alternating magnetic field generated by a secondary winding of a transformer of an isolation converter is coupled through a compensator, and an induced electromotive force satisfying the following relation is generated:
Voffset＝-IDS(jwM1+jwLpackage)；
wherein, IDSFor current between drain and source of MOSFET of synchronous rectifier tube, M1Self-inductance L of voltage detection loop for synchronous rectification controller1Secondary leakage inductance L with transformer2Coupling inductance, L, produced by mutual inductancepackageParasitic inductance in MOSFET of synchronous rectifier tube;
introducing mutual inductance into a voltage detection loop of the synchronous rectification controller, generating specific induced electromotive force, offsetting error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop, and compensating loss of a synchronous rectification duty ratio;
one end of the compensator is connected with the drain electrode of the synchronous rectifier MOSFET, and the other end of the compensator is connected with the synchronous rectifier controller.
2. The method of claim 1, wherein the compensator has a self-inductance L3And secondary leakage inductance L of transformer2Coupling inductance M generated by mutual inductance3，M3The magnitude of the sensitivity value satisfies the following relation:
M1-M3+Lpackage＝0。
3. the flux cancellation based synchronous rectification duty cycle loss compensation method of claim 2, wherein the compensator is at IDSBefore the current drops to zero, the current passes through a coupling inductor M3The generated negative induced voltage is compensated by the parasitic inductance LpackageAnd self-inductance L of the voltage detection loop1The generated positive error voltage enables the synchronous rectification controller to accurately detect the current zero crossing point and generate a turn-off signal without duty ratio loss.
4. The method of claim 3, wherein the duty cycle loss is compensated for by a parasitic inductance LpackageOr a coupling inductor M1The generated error voltage causes the synchronous rectification controller to generate a turn-off signal in advance to cause the MOSFET of the synchronous rectification tube to be in IDSThe current is turned off in advance when not passing zero; after MOSFET of synchronous rectifier is turned off, IDSCurrent freewheels through the body diode of the synchronous rectifier MOSFET, creating losses.
5. The method of any of claims 2 to 4, wherein the compensator is a one-turn coil or wire, one end of the compensator is connected to the drain of the synchronous rectifier MOSFET, and the other end of the compensator is connected to the synchronous rectifier controller.
6. The method of flux cancellation based synchronous rectification duty cycle loss compensation according to claim 5, wherein the compensator is connected in series in the voltage detection loop for providing the compensation voltage.
7. The flux cancellation based synchronous rectification duty cycle loss compensation method according to claim 1, wherein the synchronous rectification controller and the synchronous rectification tube are connected in series through a pair of voltage detection lines to form a voltage detection loop; the synchronous rectification controller has at least one pair of voltage detection pins for detecting V of synchronous rectification MOSFETDSVoltage of(ii) a One pin is connected with the source electrode of the synchronous rectifier tube MOSFET, and the other pin is connected with the drain electrode of the synchronous rectifier tube MOSFET.
8. An LLC resonant converter with duty cycle loss compensation is characterized by comprising an input voltage source, a controllable switch network, an LLC resonant network, a transformer, a synchronous rectification unit provided with a compensator, a filter capacitor and a load; the synchronous rectification unit comprises a synchronous rectification controller and a synchronous rectification MOSFET; the synchronous rectification duty cycle loss compensation method based on any one of claims 1 to 7, wherein mutual inductance is introduced into a voltage detection loop of a synchronous rectification controller through a compensator, a specific induced electromotive force is generated, an error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop is offset, and the synchronous rectification duty cycle loss is compensated.
9. The LLC resonant converter with duty cycle loss compensation of claim 8, wherein the compensator is external to the synchronous rectification unit and is connected in series in a voltage detection loop of the synchronous rectification controller.
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