CN111555626B - Control method and system of active clamp flyback converter - Google Patents

Control method and system of active clamp flyback converter Download PDF

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CN111555626B
CN111555626B CN202010381955.1A CN202010381955A CN111555626B CN 111555626 B CN111555626 B CN 111555626B CN 202010381955 A CN202010381955 A CN 202010381955A CN 111555626 B CN111555626 B CN 111555626B
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switching tube
voltage
output
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complementary energy
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CN111555626A (en
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周子焱
徐诗云
时雷雷
钱钦松
孙伟锋
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Southeast University
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Southeast 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/083—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the ignition at the zero crossing of the voltage or the current
    • 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
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • 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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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a control method and a system of an active clamp flyback converter, which adopt a working mode of combining non-complementary energy storage and complementary energy discharge in the non-complementary modeUnder the energy storage working mode, the energy of the leakage inductance is stored to the clamping capacitor, after each period, the voltage at two ends of the clamping capacitor rises, when the set threshold voltage is reached, the converter is converted into a complementary energy release working mode from a non-complementary energy storage working mode, after the complementary energy release working mode works for one period, the converter jumps to the non-complementary energy storage mode again, under the condition of not losing the duty ratio, the ZVS of the main switch tube and the clamping switch tube is realized, and meanwhile, the root mean square value I of the primary side current in each period is reducedrms。

Description

Control method and system of active clamp flyback converter
Technical Field
The invention relates to a switching power supply, in particular to a control method and a control system of an active clamp flyback converter.
Background
In the application of small power converters, a flyback converter is one of the commonly adopted topologies. In the actual working process, due to the existence of leakage inductance, a clamping circuit is often needed for the flyback converter. In recent years, an active clamp flyback converter can realize leakage inductance energy recovery and soft switching, so that the working frequency and the efficiency are greatly improved, and the active clamp flyback converter gradually becomes a solution for improving the power density, the switching frequency and the efficiency of a small-power converter.
In general, designers typically design an active clamp flyback converter in a continuous operation mode under low input voltage conditions and employ a complementary control strategy, and a circuit in this operation state can realize all switching tubes ZVS (zero voltage switching). And because of the complementary type drive, the clamping switch tube is always in a conducting state in the working process of the clamping circuit, and the reverse recovery problem of the body diode can not occur. In addition, the conducting time of the clamping switch tube is long, so that the current change slope in the circuit is small, and the EMI performance is good. As the input voltage increases, or the output power decreases, the circuit enters an intermittent mode of operation. If a complementary control strategy is still adopted in the intermittent working mode, although ZVS of all switching tubes can be realized, the primary side excitation current and the leakage inductance current of the transformer are reversely increased after the secondary side output clamp is lost.
In view of the above situation, a non-complementary Control strategy is gradually developed, and a Novel non-complementary Control strategy of an Active Clamp Flyback converter is proposed in the document a Novel non-complementary Active Clamp Flyback Control Technique. As shown in fig. 1, the topology of the active-clamp flyback converter is not as good as that of the conventional synchronous rectification active-clamp flyback converter, and only the control strategy is innovative. A conventional non-complementary control strategy is shown in FIG. 2, where IsIs the current of the secondary side, IpRepresenting the current through the transformer, wherein the dotted line represents the magnetizing current, VdsVoltage across the main switching tube, VgswIs the driving waveform of the main switching tube, VgsaFor clamping the driving waveform of the switching tube, VgsrThe driving waveform of the switching tube is rectified synchronously.
As shown in fig. 2: at t0At the moment, the main switch tube is disconnected, the clamping switch tube and the synchronous rectification switch tube are not switched on, the leakage inductance and the excitation inductance charge an output capacitor of the main switch tube, the output capacitor of the clamping switch tube discharges, and when the voltage at two ends of the main switch tube rises to enable a body diode of the clamping switch tube to be switched on, namely t1At the moment, the synchronous rectification switch tube is conducted, t1～t2During the time period, the leakage inductance charges the clamping capacitor, the excitation inductance is clamped by the secondary side at the same time, energy is coupled to the secondary side, and the energy t2At the moment, the leakage inductance energy is completely transmitted, t2～t3Only the synchronous rectifier switch tube is conducted, and at the moment, the excitation inductor continuously transmits energy to the secondary side, and at t3At the moment, the energy of the excitation inductor is completely transmitted, the clamping switch tube is opened, the clamping capacitor and the transformer form a loop, part of energy on the clamping capacitor is coupled to the secondary side and resonates with the leakage inductor at the same time, t4At the moment, the clamping switch tube and the synchronous rectification switch tube are turned off, the leakage inductance discharges the output capacitor of the main switch tube at the moment, and the output capacitor of the clamping switch tube is charged until t5At the moment, the output capacitor of the main switching tube is completely discharged to realize ZVS of the main switching tube, and at the moment, the main switching tube is opened, and the power supply excites the excitation inductor, thereby formingOne complete cycle.
Under this mode, the ZVS of main switch pipe can be fine realization, but there is some drawbacks simultaneously: clamping switch tube at t1～t2The diode is disconnected in a time period, the clamping capacitor is charged through the body diode, diode conduction loss is generated, the reverse recovery characteristic of the body diode is poor generally, the reverse recovery current of the body diode of the clamping switch tube is increased due to the rapid current change rate, and the service life of the device is also influenced due to the reverse recovery of the body diode. t is t3～t4During this time, the circulating energy on the primary circuit is too great, resulting in a higher ground Irms(root mean square value of primary current) resulting in greater conduction losses.
The Novel non-complementary Control strategy proposed in the article "A Novel non-complementary Active Clamp feedback Control Technique" is shown in FIG. 3. all variables in FIG. 3 have no different meanings from those shown in FIG. 2, except that t1～t2The clamp switch tube is conducted in a time period, so that the conduction loss of a body diode in the clamp switch tube is reduced, and t3～t4In the time period, the synchronous rectification switch tube is disconnected, the clamping switch tube is switched on, the main switch tube is disconnected, and the exciting inductor and the leakage inductor are simultaneously discharged through the clamping tube, so that IpThe rate of descent is reduced, thereby achieving a reduction in IrmsThe effect of (1). But the drawbacks are also evident, the energy transferred to the secondary side per cycle is reduced and due to IpThe falling rate is reduced, and the time for resetting the clamp capacitor is required to be more, so that the duty ratio of the main switching tube is reduced in each period, and the loss of the duty ratio can reduce the load capacity of the whole system.
In summary, although the non-complementary control strategy solves the problem of reverse surge of the conventional complementary active clamping flyback circuit in which the high input voltage enters the discontinuous working mode after the primary side exciting current and the leakage inductance current of the transformer lose the secondary side output clamping, the non-complementary control strategy also has some problems, namely, the energy transmitted from the primary side to the secondary side is reduced, and the duty ratio is lost, so that the load carrying capacity of the non-complementary control strategy is reduced.
Disclosure of Invention
Based on the problems in the prior art, the invention provides a control method and a control system for an active clamp flyback converter, in particular to a control method and a control system combining non-complementary and complementary synchronous rectification, which can reduce the root mean square value I of primary side current in each period while realizing ZVS of a main switching tube and a clamp switching tube under the condition of not losing duty ratiormsThereby improving the working efficiency of the whole converter.
In order to achieve the purpose, the invention adopts the following technical scheme: a control method of an active clamp flyback converter is based on a circuit topology of the active clamp flyback converter and comprises an input voltage source Vin, a main switching tube Sw, a clamp switching tube Sa, a clamp capacitor Cclamp, a synchronous rectification switching tube Sr, a leakage inductance Lr of a transformer on the primary side, an excitation inductance Lm of the transformer, an output filter capacitor Co, a load R and an output voltage Vo, wherein the clamp capacitor Cclamp and the clamp switching tube Sa are connected in series to form a clamp circuit;
the method is characterized in that: the energy storage and complementary energy release combined working mode is adopted, the energy of the leakage inductance Lr is stored to the clamping capacitor Cclamp in the non-complementary energy storage working mode, after the non-complementary energy storage working mode is completed by one period, the voltage at two ends of the clamping capacitor Cclamp is increased, when the voltage at the drain end of the main switching tube Sw reaches the set threshold voltage Vth, the converter is converted into the complementary energy release working mode from the non-complementary energy storage working mode, and the converter jumps to the non-complementary energy storage mode again after the complementary energy release working mode works for one period;
the non-complementary energy storage operating mode comprises the following steps:
s1, firstly, the main switch tube Sw is switched on, the clamping switch tube Sa and the synchronous rectification switch tube Sr are switched off, and the voltage source Vin stores energy to the excitation inductor Lm;
s2, after the conduction time of the main switching tube Sw, the main switching tube Sw is turned off, the excitation inductor Lm and the leakage inductor Lr charge the junction capacitor of the main switching tube Sw in the dead time, the junction capacitor of the clamping switching tube Sa and the synchronous rectification switching tube Sr is discharged, and the voltage of the leakage end of the main switching tube Sw rises;
s3, after dead time, the clamp switch tube Sa and the synchronous rectification switch tube Sr are conducted, the remaining energy of the leakage inductance Lr is stored in the clamp capacitor Ccclamp, meanwhile, the energy of the primary side excitation inductance Lm is transmitted to the secondary side, at the moment, the voltage Vds of the drain end of the main switch tube Sw is detected and compared with the set threshold voltage Vth, if Vds > Vth, the complementary energy releasing working mode is jumped to after the working cycle is finished, otherwise, the next working cycle is still in the non-complementary energy storing working mode;
s4, when the leakage inductance current is close to 0, the clamping switch tube Sa is turned off to prevent the current of the clamping capacitor Ccclamp from reversing, the excitation inductor Lm continues to transmit energy to the secondary side, and meanwhile, the secondary side current is detected, and when the excitation current of the secondary side passes through zero, the synchronous rectification switch tube Sr is triggered to be turned off;
s5, in the dead time after the synchronous rectification switch tube Sr is turned off and before the main switch tube Sw is turned on, the clamping switch tube Sa is turned on, and reverse excitation is carried out on the excitation inductor Lm and the leakage inductor Lr to prepare for the main switch tube Sw to realize a zero-voltage switch ZVS;
s6, turning off the clamp switching tube Sa after the on time of the clamp switching tube Sa; then the main switching tube Sw is switched on to realize ZVS; completing one working cycle of the non-complementary energy storage working mode.
In the non-complementary energy storage working mode, the switching waveforms of the main switching tube Sw and the clamping switching tube Sa are not complementary waveforms; in the complementary discharging working mode, the switching waveforms of the main switching tube Sw and the clamping switching tube Sa are complementary waveforms.
A control system for realizing the control method of the active clamp flyback converter is characterized in that: the method comprises the steps that a control system consisting of a peak current sampling circuit, a drain-source voltage sampling circuit, an output current detection circuit, an output voltage isolation sampling circuit, a control logic circuit and a grid electrode driving circuit is arranged to form a closed loop with an active clamping flyback converter topology; the peak current sampling circuit samples a peak current Ics when the main switching tube Sw is switched on through a sampling resistor Rcs, the drain-source voltage sampling circuit samples the drain end voltage of the main switching tube Sw and reduces the drain end voltage in an equal proportion to a magnitude Vds which can be identified by the control logic circuit, the output current detection circuit obtains an output current Io by detecting the voltage at two ends of the synchronous rectification switching tube Sr in the conduction time period of the synchronous rectification switching tube Sr, the peak current Ics, the drain end voltage Vds after the equal proportion reduction, the output current Io and the output voltage Vo obtained by the output voltage isolation sampling circuit are all connected to the control logic circuit, the output of the control logic circuit is connected with a grid driving circuit, and the grid driving circuit outputs three control signals Vswsa, Vg and Vgs which are respectively correspondingly connected with the grids of the main switching tube Sw, the clamping switching tube Sa and the synchronous rectification switching tube Sr.
The control logic circuit comprises a comparator A, a non-complementary energy storage controller, a complementary energy release controller and a PWM grid signal generation module, wherein the positive input end of the comparator A is connected with a drain end voltage Vds output by a drain-source voltage sampling circuit, the negative input end of the comparator A is connected with a set threshold voltage Vth, the output of the comparator A is respectively connected with the input ends of the non-complementary energy storage controller and the complementary energy release controller, the non-complementary energy storage controller is further provided with three input ends of peak current Ics, output current Io and output voltage Vo, the output of the non-complementary energy storage controller and the output of the complementary energy release controller are respectively connected with the PWM grid signal generation module, and three grid logic signals output by the PWM grid signal generation module generate corresponding three control signals Vgsa, Vgsw and Vgsr through a grid driving circuit.
The non-complementary energy storage controller comprises a compensation network, a comparator B, a comparator C, a trigger A, a trigger B, a timer A and an OR gate, wherein two input ends of the compensation network are respectively connected with a reference voltage Vref and an output voltage Vo, the compensation network outputs a reference current Iref to be connected with a positive input end of the comparator B, a peak current Ics to be connected with a negative input end of the comparator B, and the output of the comparator B is connected with a reset end of the trigger A
Figure GDA0003482906610000041
Set terminal of trigger A
Figure GDA0003482906610000042
The output end of the OR gate is connected, and the output end Q of the trigger A outputs a gate logic signal Vgsw; gate logicThe signals Vgsr and Vgsa are respectively connected with two input ends of the OR gate; output terminal of flip-flop A
Figure GDA0003482906610000043
Set terminal connected with trigger B
Figure GDA0003482906610000044
Reset terminal of trigger B
Figure GDA0003482906610000045
The output end of the comparator C is connected, the positive input end of the comparator C is connected with the output current Io, the negative input end of the comparator C is grounded, the output end Q of the trigger B outputs a grid logic signal Vgsr and is connected with the input end of the timer A, and the timer A outputs a grid logic signal Vgsa.
The complementary discharging controller comprises a timer B, an inverter A and an inverter B, wherein the input of the timer B is connected with the output of the comparator A, and the timer B outputs a grid logic signal Vgsw, a grid logic signal Vgsa is output through the inverter A, and a grid logic signal Vgsr is output through the inverter B.
The invention has the advantages and obvious effects that: the control method and the system combining the non-complementary energy storage and the complementary energy discharge can reduce the root mean square value I of the primary side current in each period while realizing ZVS of the main switching tube and the clamping switching tube under the condition of not losing the duty ratiormsThereby improving the working efficiency of the whole converter.
Drawings
Fig. 1 is a schematic diagram of a typical active clamp synchronous rectification flyback converter circuit of the prior art;
FIG. 2 is a waveform diagram of key signals of a typical non-complementary mode active clamp synchronous rectification flyback converter of the prior art;
FIG. 3 is a waveform diagram of a key signal of a non-complementary Control strategy proposed in "A Novel non-complementary Active Clamp Flyback Control Technique";
FIG. 4 is a control system schematic of the present invention;
FIG. 5 is a waveform diagram of a key signal of the control method of the present invention;
FIG. 6 is a circuit configuration of the control system of the present invention;
FIG. 7 is a non-complementary energy storage controller configuration in the control system of the present invention;
FIG. 8 is a complementary discharge controller structure in the control system of the present invention.
Detailed Description
The energy storage and discharge integrated circuit adopts a working mode combining non-complementary energy storage and complementary energy discharge, the energy of a leakage inductor Lr is stored to a clamping capacitor Cclamp in the non-complementary energy storage working mode, after the non-complementary energy storage working mode finishes one period, the voltage at two ends of the clamping capacitor Cclamp rises, when the voltage of the drain end of a main switching tube Sw reaches a set threshold voltage Vth, a converter is converted into a complementary energy discharge working mode from the non-complementary energy storage working mode, and the converter jumps to the non-complementary energy storage mode again after the complementary energy discharge working mode works for one period;
the non-complementary energy storage operating mode comprises the following steps:
s1, firstly, the main switch tube Sw is switched on, the clamping switch tube Sa and the synchronous rectification switch tube Sr are switched off, and the voltage source Vin stores energy to the excitation inductor Lm;
s2, after the conduction time of the main switching tube Sw, the main switching tube Sw is turned off, the excitation inductor Lm and the leakage inductor Lr charge the junction capacitor of the main switching tube Sw in the dead time, the junction capacitor of the clamping switching tube Sa and the synchronous rectification switching tube Sr is discharged, and the voltage of the leakage end of the main switching tube Sw rises;
s3, after dead time, the clamp switch tube Sa and the synchronous rectification switch tube Sr are conducted, the remaining energy of the leakage inductance Lr is stored in the clamp capacitor Ccclamp, meanwhile, the energy of the primary side excitation inductance Lm is transmitted to the secondary side, at the moment, the voltage Vds of the drain end of the main switch tube Sw is detected and compared with the set threshold voltage Vth, if Vds > Vth, the complementary energy releasing working mode is jumped to after the working cycle is finished, otherwise, the next working cycle is still in the non-complementary energy storing working mode;
s4, when the leakage inductance current is close to 0, the clamping switch tube Sa is turned off to prevent the current of the clamping capacitor Ccclamp from reversing, the excitation inductor Lm continues to transmit energy to the secondary side, and meanwhile, the secondary side current is detected, and when the excitation current of the secondary side passes through zero, the synchronous rectification switch tube Sr is triggered to be turned off;
s5, in the dead time after the synchronous rectification switch tube Sr is turned off and before the main switch tube Sw is turned on, the clamping switch tube Sa is turned on, and reverse excitation is carried out on the excitation inductor Lm and the leakage inductor Lr to prepare for the main switch tube Sw to realize a zero-voltage switch ZVS;
s6, turning off the clamp switching tube Sa after the on time of the clamp switching tube Sa; then the main switching tube Sw is switched on to realize ZVS; completing one working cycle of the non-complementary energy storage working mode.
Non-complementary working energy storage mode: the switching waveforms of the main switching tube Sw and the clamping switching tube Sa are not complementary waveforms, and the clamping capacitor Cclamp is charged in each period, so that the voltages at two ends of the clamping capacitor Cclamp rise, and the voltage at the drain end of the main switching tube Sw rises. The method comprises the following specific steps:
(1) the main switching tube Sw is connected with the clamping switching tube Sa and is disconnected with the synchronous rectification switching tube Sr, the voltage source Vin stores energy to the excitation inductor Lm, the main switching tube Sw is disconnected, the excitation inductor Lm and the leakage inductor Lr charge the junction capacitor of the main switching tube Sw and discharge the junction capacitor of the clamping switching tube Sa and the synchronous rectification switching tube Sr, the voltage of the leakage end of Sw rises, the clamping switching tube Sa is switched on to store the rest leakage inductor energy to the clamping capacitor Ccclamp, meanwhile, the synchronous rectification switching tube Sr is switched on to transmit the energy of the primary side excitation inductor to the secondary side, and the clamping switching tube Sa is disconnected when the leakage inductor energy is transmitted.
(2) During the turn-off period of the main switching tube Sw, the current of the secondary side is detected through the secondary side current detection circuit, the zero-crossing time of the current of the secondary side is detected, the synchronous rectification switching tube Sr is turned off at the moment, the clamping switching tube Sa is turned on, and the clamping capacitor Cclamp resonates with the excitation inductor Lm and the leakage inductor Lr to form a negative current capable of realizing ZVS (zero voltage switching) of the main switching tube Sw.
(3) After a period of dead time, the main switching tube Sw realizes ZVS, the main switching tube Sw is turned on, and the non-complementary energy storage mode completes one period.
Complementary work release work mode: the switching waveforms of the main switching tube Sw and the clamping switching tube Sa are complementary waveforms, the duty ratio of the main switching tube Sw is small compared with a non-complementary working energy release mode, and in the working mode, the clamping capacitor Cclamp is discharged and coupled to the secondary side in one period, so that the voltage at two ends of the clamping capacitor Cclamp is reduced, and meanwhile, the voltage at the drain end of the main switching tube Sw is reduced. The method comprises the following specific steps:
(1) the main switching tube Sw switches on the clamping switching tube Sa and switches off the synchronous rectification switching tube Sr, the voltage source Vin stores energy to the excitation inductor Lm, the main switching tube Sw is switched off, the excitation inductor Lm and the leakage inductor Lr charge the junction capacitor of the main switching tube Sw, the clamp switching tube Sa and the junction capacitor of the synchronous rectification switching tube Sr are discharged, the voltage of the drain end of the main switching tube Sw rises, the clamping switching tube Sa is switched on to store the rest leakage inductor energy to the clamping capacitor Cclamp, and the clamping switching tube Sa is switched on to transmit the energy of the primary excitation inductor to the secondary side.
(2) And turning off the clamping switch tube Sa and the synchronous rectification switch tube Sr, stopping discharging of the clamping capacitor Ccclamp, realizing ZVS of the main switch tube Sw by the negative current formed by the leakage inductance and the excitation inductance at the same time, then turning on the main switch tube Sw, and switching from the complementary energy release working mode to the non-complementary energy storage working mode.
The converter charges the clamp capacitor under a plurality of periods of non-complementary energy storage working modes, so that the energy stored in the clamp capacitor under each period is increased, the voltage of the drain end of the main switching tube Sw is compared with the set threshold voltage Vth when the main switching tube Sw is switched off and the Sa is switched on under the non-complementary working mode, if the voltage of the drain end of the main switching tube Sw is greater than the set threshold voltage Vth, the converter is switched to a complementary working energy release mode after the non-complementary energy storage working period, and the converter is switched to the non-complementary energy storage working mode after the complementary energy release working mode is finished.
The non-complementary energy storage mode is switched to the complementary energy release mode, and then the complementary energy release mode is switched to the non-complementary energy storage mode after working for a period, and the switching stage is shown in fig. 5.
The non-complementary energy storage working mode states are as follows:
0～t0: the main switch tube Sw is conducted, the clamping switch tube Sa is synchronousThe rectifier switch tube Sr is disconnected, and the power supply excites the magnetizing inductor and the leakage inductor, and has
Figure GDA0003482906610000071
The magnetizing inductance and the leakage inductance current increase linearly.
t0～t1: in fig. 5, it is shown by amplification that the dead time is actually very small, at which time the main switching tube Sw is turned off, the leakage inductance and the magnetizing inductance charge the output capacitor of the main switching tube Sw and discharge the output capacitor of the clamping switching tube Sa, and at this stage, the voltage V across the main switching tube SwdsApproximately linear rise, when rising to about Vin+VcAnd the body diode of the clamp switch tube Sa is switched on.
t1～t2: turning on the clamping switch tube Sa and the synchronous rectification switch tube Sr, at the stage VdsThe secondary side clamps the magnetizing inductor, the magnetizing inductor transfers energy to the secondary side through the magnetic core, simultaneously, the leakage inductor charges the clamping capacitor Ccclamp through the clamping switch tube Sa, the leakage inductor current is approximately linearly reduced at the stage, and the magnetizing inductor is clamped by the secondary side through the secondary side
Figure GDA0003482906610000072
The linearity decreases.
t2～t3: at t2At the moment, the leakage current is close to 0, the clamping switch tube Sa is turned off, and only the magnetizing inductor transmits energy to the secondary side at the stage.
t3～t4: at t3At the moment, the energy of the magnetizing inductor is completely coupled to the secondary side, the synchronous rectification switch tube Sr is closed, the clamping switch tube Sa is opened, the magnetizing inductor and the leakage inductor are reversely charged through the clamping capacitor Cclamp, and preparation is made for the main switch tube Sw to realize ZVS. At this stage, the clamp capacitor Cclamp is not completely reset, and only partial energy is released to realize ZVS of the main switching tube Sw, which should satisfy
Figure GDA0003482906610000073
Where Im _ is the negative current required for zero voltage switching of the main switching tube Sw, Csw is the equivalent junction capacitance, and Vds is the main switchThe voltage at the two ends of the tube Sw, Lm is the inductance value of the excitation inductance.
t4～t5: at t4At time, the clamp switch tube Sa is turned off at t4～t5Within a time period. In the process, after the output capacitance of the main switching tube Sw is reduced to 0, the leakage inductance and the follow current of the magnetizing inductance are realized through the body diode, and the ZVS of the main switching tube Sw is realized.
t5At the moment, the main switch tube is switched on to complete a period.
In the above-described operation mode, the clamp capacitor Cclamp is charged every cycle.
The complementary discharge mode states are as follows:
t5～t6: in the time period, the main switching tube Sw is turned on, the clamping switching tube Sa and the synchronous rectification switching tube Sr are turned off, the power supply excites the leakage inductance and the magnetizing inductance, and the current linearly increases. Compared with the first operating state, the time period is shorter, and ZVS of the clamping switching tube Sa can be realized at the same time.
t6～t7: in the time period, the main switching tube Sw is closed, the leakage inductance and the magnetizing inductance charge the output capacitor of the main switching tube Sw, the output capacitor of the clamping switching tube Sa is discharged, and the voltage at two ends of the main switching tube Sw rises to about Vin+VcZVS of the clamp switching tube Sa is realized.
t7～t8: in the time period, the main switching tube Sw is closed, the clamping switching tube Sa and the synchronous rectification switching tube Sr are conducted, at the moment, the magnetizing inductor transmits energy to the secondary side in a coupling mode, the leakage inductor resonates with the clamping inductor, and in the time period, the leakage inductor resonates with the clamping capacitor to reset the energy stored in the capacitor in the previous period.
t8～t9: in the time period, the clamping switch tube Sa and the synchronous rectification switch tube Sr are turned off, at the moment, the leakage inductance resonates with the output capacitor of the main switch tube Sw, the absolute value of the current of the leakage inductance is reduced, the voltage at two ends of the main switch tube Sw is reduced, and the main switch is realizedZVS for tube Sw.
t9～t10: at t9At time, the energy of the leakage inductance and the magnetizing inductance flows back to the power supply at t10At that time, the next control state is started.
t10～t11: the main switch tube Sw is conducted, the clamping switch tube Sa is disconnected with the synchronous rectification switch tube Sr, and the power supply excites the magnetizing inductor and the leakage inductor
Figure GDA0003482906610000081
The magnetizing inductance and the leakage inductance current increase linearly. And repeatedly entering a non-complementary conduction energy storage mode.
As shown in fig. 4, the control system for implementing the control method of the active clamp flyback converter includes a peak current sampling circuit, a drain-source voltage sampling circuit, an output current detection circuit, an output voltage isolation sampling circuit, a control logic circuit, and a gate driving circuit, and forms a closed loop with the topology of the active clamp flyback converter. The peak current sampling circuit, the drain-source voltage sampling circuit, the output current detection circuit, the output voltage isolation sampling circuit and the gate drive circuit are all known circuits.
As shown in fig. 6, the control logic circuit includes two different controllers as well as a comparator a and a PWM signal generation block. The output end of the comparator A is connected with the enabling ends of the non-complementary energy storage controller and the complementary energy release controller, the high level of the non-complementary energy storage controller is effective, and the converter is controlled to work in a non-complementary energy storage working mode; the complementary discharging controller is effective in low level and controls the converter to work in a complementary discharging working mode. At the end of each working period, the comparator A compares the signal Vds sampled by the drain-source voltage sampling circuit with a set threshold voltage Vth, and judges whether the system is switched from the non-complementary energy storage working mode to the complementary energy release working mode.
As shown in fig. 7, the non-complementary energy storage controller includes a compensation network, a comparator B, a comparator C, a flip-flop a, a flip-flop B, an or gate, and a timer a. The compensation network is for realizing the closed loop stability and dynamic response speed required by the switching power supply, and two types of compensation networks and three types of compensation networks are generally used, which are already the existing mature technologies and are not described herein again. Wherein the falling edge of timer a triggers to generate a constant pulse width signal.
The non-complementary energy storage controller outputs a voltage signal Vo and a peak current signal Ics, and the duty ratio of a grid signal of the main switching tube is adjusted through closed-loop feedback of the peak current, so that the output voltage of the converter is stably controlled. The collected voltage output signal Vo is compared with a set reference voltage Vref to generate a peak current reference signal after passing through a compensation network, a current signal Ics sampled by a peak current sampling circuit is compared with a signal Iref in a comparator B to generate a gate signal Vgsw logic signal for controlling a main switching tube Sw, when Ics is less than Iref, the main switching tube Sw keeps the original state, and when Ics is greater than Iref, the main switching tube Sw is switched off through a trigger, so that when a load or an input voltage changes, the on-time of the main switching tube Sw can be controlled through peak current feedback, and stable voltage output is realized.
And the Vgsr logic signal and the Vgsa logic signal are connected into an OR gate, and if and only if the Vgsr logic signal and the Vgsa logic signal are both in a low level, the trigger A triggers the main switching tube Sw to output a high level signal so as to control the conduction of the main switching tube Sw. Wherein the Q end of the trigger B outputs a Vgsw logic signal, and the output end of the other end outputs a synchronous rectifier switch tube connected to the set end of the trigger B
Figure GDA0003482906610000091
Reset terminal of trigger B
Figure GDA0003482906610000092
And is connected to the output signal of the comparator C. The output current Io obtained by sampling of the output current detection circuit is compared with zero, and when the output current Io drops to zero and is output low level, a falling edge triggers the trigger B, so that the Vgsr logic signal is controlled to be converted from high level to low level. The Vgsr logic signal is connected into a timer A, the falling edge triggers the timer, a Vgsa logic signal with constant pulse width is output, the clamping switch tube is conducted in the time, and the Vgsr logic signal resonates with the excitation inductor through the clamping capacitor, so that the Vgsr logic signal is obtainedAnd realizing ZVS of the main switching tube Sw.
As shown in fig. 8, the complementary discharging controller comprises a timer B and two inverters, wherein the rising edge of the timer B triggers and outputs a constant pulse width signal. The input end of the timer B is connected with the output end of the comparator A, the output of the timer B is a Vgsw logic signal, the output end of the timer B is also respectively connected with the inverter A and the inverter B, the inverter A outputs a Vgsa logic signal, and the inverter B outputs a Vgsr logic signal.
When the complementary energy release controller starts to work, the main switching tube Sw with fixed time is switched on to positively excite the excitation inductor, then the main switching tube Sw is switched off, the clamping switching tube Sa with constant time and the synchronous rectification switching tube Sr are switched on, and the energy stored in the clamping inductor is released. And turning off the complementary energy release controller and turning on the non-complementary energy storage controller, thereby circulating.

Claims (7)

1. A control method of an active clamp flyback converter is based on a circuit topology of the active clamp flyback converter and comprises an input voltage source Vin, a main switching tube Sw, a clamp switching tube Sa, a clamp capacitor Cclamp, a synchronous rectification switching tube Sr, a leakage inductance Lr of a transformer on the primary side, an excitation inductance Lm of the transformer, an output filter capacitor Co, a load R and an output voltage Vo, wherein the clamp capacitor Cclamp and the clamp switching tube Sa are connected in series to form a clamp circuit;
the method is characterized in that: the energy storage and complementary energy release combined working mode is adopted, the energy of the leakage inductance Lr is stored to a clamping capacitor Cclamp in the non-complementary energy storage working mode, after the non-complementary energy storage working mode finishes one period, the voltage at two ends of the clamping capacitor Cclamp rises, when the voltage sampling value of the drain end of a main switching tube Sw reaches a set threshold voltage Vth, a converter is converted into a complementary energy release working mode from the non-complementary energy storage working mode, and the converter jumps to the non-complementary energy storage mode again after the complementary energy release working mode works for one period;
the non-complementary energy storage operating mode comprises the following steps:
s1, firstly, the main switch tube Sw is switched on, the clamping switch tube Sa and the synchronous rectification switch tube Sr are switched off, and the voltage source Vin stores energy to the excitation inductor Lm;
s2, after the conduction time of the main switching tube Sw, the main switching tube Sw is turned off, the excitation inductor Lm and the leakage inductor Lr charge the junction capacitor of the main switching tube Sw in the dead time, the junction capacitor of the clamping switching tube Sa and the synchronous rectification switching tube Sr is discharged, and the voltage of the leakage end of the main switching tube Sw rises;
s3, after dead time, the clamp switch tube Sa and the synchronous rectification switch tube Sr are conducted, the rest energy of the leakage inductance Lr is stored in the clamp capacitor Ccclamp, meanwhile, the energy of the primary side excitation inductance Lm is transmitted to the secondary side, at the moment, the voltage of the leakage end of the main switch tube Sw is detected to obtain a sampling value Vds of the voltage of the leakage end, the sampling value Vds is compared with the set threshold voltage Vth, if Vds > is Vth, the complementary energy releasing working mode is jumped to after the working period is finished, otherwise, the non-complementary energy storing working mode is still set in the next working period;
s4, when the leakage inductance current is close to 0, the clamping switch tube Sa is turned off to prevent the current of the clamping capacitor Ccclamp from reversing, the excitation inductor Lm continues to transmit energy to the secondary side, and meanwhile, the secondary side current is detected, and when the excitation current of the secondary side passes through zero, the synchronous rectification switch tube Sr is triggered to be turned off;
s5, in the dead time after the synchronous rectification switch tube Sr is turned off and before the main switch tube Sw is turned on, the clamping switch tube Sa is turned on, and reverse excitation is carried out on the excitation inductor Lm and the leakage inductor Lr to prepare for the main switch tube Sw to realize a zero-voltage switch ZVS;
s6, turning off the clamp switching tube Sa after the on time of the clamp switching tube Sa; then the main switching tube Sw is switched on to realize ZVS; completing one working cycle of the non-complementary energy storage working mode.
2. The method of controlling an active-clamp flyback converter according to claim 1, wherein: in the non-complementary energy storage working mode, the switching waveforms of the main switching tube Sw and the clamping switching tube Sa are not complementary waveforms.
3. The method of controlling an active-clamp flyback converter according to claim 1, wherein: in the complementary discharging working mode, the switching waveforms of the main switching tube Sw and the clamping switching tube Sa are complementary waveforms.
4. A control system for implementing the control method of the active-clamp flyback converter of claim 1, characterized in that: the method comprises the steps that a control system consisting of a peak current sampling circuit, a drain-source voltage sampling circuit, an output current detection circuit, an output voltage isolation sampling circuit, a control logic circuit and a grid electrode driving circuit is arranged to form a closed loop with an active clamping flyback converter topology; the peak current sampling circuit samples a peak current Ics when the main switching tube Sw is switched on through a sampling resistor Rcs, the drain-source voltage sampling circuit samples the drain end voltage of the main switching tube Sw and reduces the drain end voltage in an equal proportion to a magnitude Vds which can be identified by the control logic circuit, the output current detection circuit obtains an output current Io by detecting the voltage at two ends of the synchronous rectification switching tube Sr in the conduction time period of the synchronous rectification switching tube Sr, the peak current Ics, the drain end voltage Vds after the equal proportion reduction, the output current Io and the output voltage Vo obtained by the output voltage isolation sampling circuit are all connected to the control logic circuit, the output of the control logic circuit is connected with a grid driving circuit, and the grid driving circuit outputs three control signals Vgsw, Vgsa and Vgsr which are respectively correspondingly connected with the grids of the main switching tube Sw, the clamping switching tube Sa and the synchronous rectification switching tube Sr.
5. The control system for realizing the control method of the active-clamp flyback converter according to claim 4, wherein: the control logic circuit comprises a comparator A, a non-complementary energy storage controller, a complementary energy release controller and a PWM grid signal generation module, wherein the positive input end of the comparator A is connected with a drain end voltage Vds output by a drain-source voltage sampling circuit, the negative input end of the comparator A is connected with a set threshold voltage Vth, the output of the comparator A is respectively connected with the input ends of the non-complementary energy storage controller and the complementary energy release controller, the non-complementary energy storage controller is further provided with three input ends of peak current Ics, output current Io and output voltage Vo, the output of the non-complementary energy storage controller and the output of the complementary energy release controller are respectively connected with the PWM grid signal generation module, and three grid logic signals output by the PWM grid signal generation module generate corresponding three control signals Vgsa, Vgsw and Vgsr through a grid driving circuit.
6. The control system for implementing the control method of the active-clamp flyback converter according to claim 5, wherein: the non-complementary energy storage controller comprises a compensation network, a comparator B, a comparator C, a trigger A, a trigger B, a timer A and an OR gate, wherein two input ends of the compensation network are respectively connected with a reference voltage Vref and an output voltage Vo, the compensation network outputs a reference current Iref to be connected with a positive input end of the comparator B, a peak current Ics to be connected with a negative input end of the comparator B, and the output of the comparator B is connected with a reset end of the trigger A
Figure FDA0003489795370000021
Set terminal of trigger A
Figure FDA0003489795370000022
The output end of the OR gate is connected, and the output end Q of the trigger A outputs a gate logic signal Vgsw; the grid logic signals Vgsr and Vgsa are respectively connected with two input ends of the OR gate; output terminal of flip-flop A
Figure FDA0003489795370000023
Set terminal connected with trigger B
Figure FDA0003489795370000024
Reset terminal of trigger B
Figure FDA0003489795370000025
The output end of the comparator C is connected, the positive input end of the comparator C is connected with the output current Io, the negative input end of the comparator C is grounded, the output end Q of the trigger B outputs a grid logic signal Vgsr and is connected with the input end of the timer A, and the timer A outputs a grid logic signal Vgsa.
7. The control system for implementing the control method of the active-clamp flyback converter according to claim 5, wherein: the complementary discharging controller comprises a timer B, an inverter A and an inverter B, wherein the input of the timer B is connected with the output of the comparator A, the timer B outputs a grid logic signal Vgsw and outputs a grid logic signal Vgsa through the inverter A, and the grid logic signal Vgsw outputs a grid logic signal Vgsr through the inverter B.
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