CN111682769B - Self-adaptive synchronous rectification digital control method of active clamp forward converter - Google Patents

Self-adaptive synchronous rectification digital control method of active clamp forward converter Download PDF

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CN111682769B
CN111682769B CN202010559535.8A CN202010559535A CN111682769B CN 111682769 B CN111682769 B CN 111682769B CN 202010559535 A CN202010559535 A CN 202010559535A CN 111682769 B CN111682769 B CN 111682769B
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switching tube
synchronous rectification
current
inductor
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CN111682769A (en
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孙尧
许国
路正美
刘福临
韩华
王辉
粟梅
刘永露
熊文静
但汉兵
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Central South 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
    • 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
    • H02M3/33507—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 with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—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 with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • 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
    • H02M1/0048—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 provides an active clamping forward converter and a self-adaptive synchronous rectification digital control method, which comprises the following steps that 1, a CPU (central processing unit) is used for controlling a controller to generate two groups of complementary PWM (pulse width modulation) signals with dead zones; step 2, inputting two groups of complementary PWM signals with dead zones into a driving circuit; and 3, outputting two groups of complementary PWM signals with dead zones into four paths of driving signals by the driving circuit, and correspondingly inputting the four paths of driving signals into grid terminals of the main switching tube, the auxiliary switching tube, the first synchronous rectification switching tube and the second synchronous rectification switching tube by the driving circuit respectively. When the active clamping forward converter works in a light-load intermittent working mode, the time for reducing the current in the filter inductor to zero can be accurately calculated through the DSP, the driving signal of the first synchronous rectification switching tube is closed in a self-adaptive mode, the current in the filter inductor is effectively prevented from flowing reversely in the follow current process, and the transmission efficiency and the reliability of the active clamping forward converter are improved.

Description

Self-adaptive synchronous rectification digital control method of active clamp forward converter
Technical Field
The invention relates to the technical field of power electronics, in particular to a self-adaptive synchronous rectification digital control method of an active clamp forward converter.
Background
Dc switching power supplies are widely used as power supplies for various electronic devices and electric appliances, and have been rapidly developed in recent years. Because the integration level of the electronic device is continuously increased, the functions are stronger and stronger, and the size is smaller and smaller, a novel power supply with small size, light weight, high efficiency and good performance is urgently needed, and powerful power is provided for the development of the switching power supply technology.
High transfer efficiency is important to improve power density of the power supply, while Zero Voltage Switching (ZVS) of the power devices improves the efficiency of the converter by reducing losses. The active clamping forward converter as a soft switching circuit has the advantages of high switching frequency, small switching loss, high efficiency, small EMI noise, small switching stress and the like, and is paid attention and paid attention by scholars at home and abroad.
Compared with the traditional forward converter, the active clamping forward converter is additionally provided with the active clamping circuit on the primary side, so that the soft switching of a primary side power switch can be realized, and the rectification loss of a switching tube becomes an important link for limiting the improvement of the power efficiency at the moment. In order to reduce the rectification loss of the secondary side switching tube, a synchronous rectification technology is adopted, and a special power MOSFET with extremely low on-state resistance is used for replacing a Schottky diode, so that the efficiency of a power supply can be greatly improved. However, the existing active clamp forward scheme mostly uses analog control, the pulse width of the secondary side drive of the synchronous rectification is the same as that of the voltage on the primary side transformer, and the defects are brought to light-load operation: when the circuit works under the intermittent condition, the MOSFET provides a reverse path for current. During the dead time, the reverse current may raise the junction capacitance voltage of the switch, the switch tube may be damaged due to the high back voltage, and the negative power generated by the reverse current may reduce the efficiency of the forward converter.
Disclosure of Invention
The invention provides a self-adaptive synchronous rectification digital control method of an active clamp forward converter, and aims to solve the problems that when a traditional converter is in light load, the efficiency of the converter is reduced due to damage and backflow caused by overhigh back pressure of a switching tube.
In order to achieve the above object, an embodiment of the present invention provides an active clamp forward converter including:
a power source;
the active clamping circuit comprises a clamping capacitor and an auxiliary switching tube, wherein the first end of the clamping capacitor is electrically connected with the positive end of the power supply, and the drain end of the auxiliary switching tube is electrically connected with the second end of the clamping capacitor;
a first end of the resonant inductor is electrically connected with a first end of the clamping capacitor;
the first end of the excitation inductor is electrically connected with the second end of the resonance inductor, and the second end of the excitation inductor is electrically connected with the source end of the auxiliary switching tube;
the first end of the primary side of the transformer is electrically connected with the first end of the excitation inductor, and the second end of the primary side of the transformer is electrically connected with the second end of the excitation inductor;
the drain end of the main switching tube is electrically connected with the second end of the excitation inductor, and the source end of the main switching tube is electrically connected with the negative end of the power supply;
the synchronous rectification circuit comprises a first synchronous rectification switching tube and a second synchronous rectification switching tube, wherein the drain end of the first synchronous rectification switching tube is electrically connected with the first end of the secondary side of the transformer, the drain end of the second synchronous rectification switching tube is electrically connected with the second end of the secondary side of the transformer, and the source end of the second synchronous rectification switching tube is electrically connected with the source end of the first synchronous rectification switching tube;
the output filter circuit comprises a filter inductor and a filter capacitor, wherein the first end of the filter inductor is electrically connected with the drain end of the first synchronous rectification switch tube, the first end of the filter capacitor is electrically connected with the second end of the filter inductor, and the second end of the filter capacitor is electrically connected with the source end of the first synchronous rectification switch tube;
and the first end of the output resistor is electrically connected with the first end of the filter capacitor, and the second end of the output resistor is electrically connected with the second end of the filter capacitor.
The first end of the output resistor is electrically connected with the first end of the control circuit, the second end of the control circuit is electrically connected with the gate terminal of the main switching tube, the third end of the control circuit is electrically connected with the gate terminal of the auxiliary switching tube, the fourth end of the control circuit is electrically connected with the gate terminal of the second synchronous rectification switching tube, the fifth end of the control circuit is electrically connected with the gate terminal of the first synchronous rectification switching tube, the control circuit comprises a controller, a PWM (pulse width modulation) modulator, a self-adaptive control duty ratio calculation module and a driving circuit, the controller adopts a DSP (digital signal processor) as a core, and the driving circuit is used for generating a driving signal.
The main switch tube, the auxiliary switch tube, the first synchronous rectification switch tube and the second synchronous rectification switch tube respectively comprise a body diode and a parasitic junction capacitor of a drain source electrode which are connected in an anti-parallel mode.
The embodiment of the invention also provides a self-adaptive synchronous rectification digital control method of the active clamp forward converter, which comprises the following steps:
step 1, a CPU controls a controller to generate two groups of complementary PWM signals with dead zones;
step 2, inputting two groups of complementary PWM signals with dead zones into a driving circuit;
step 3, the driving circuit outputs two groups of complementary PWM signals with dead zones into four paths of driving signals, and the driving circuit correspondingly inputs the four paths of driving signals into grid terminals of a main switching tube, an auxiliary switching tube, a first synchronous rectification switching tube and a second synchronous rectification switching tube respectively;
step 4, judging whether the active clamping forward converter works in a light-load intermittent working mode;
step 5, calculating the time t for the current in the filter inductor to drop to zero when the active clamping forward converter works in a light-load discontinuous working modes。
Wherein the step 1, the step 2 and the step 3 specifically include:
the primary side driving signals PWM1 and PWM2 of the active clamping positive laser are generated by modulating a control signal obtained by PI regulation of error voltage generated by negative feedback of output voltage, and the pulse rising edge of a secondary side driving signal PWM3 of the active clamping positive laser is used for fixing time tdLagging behind the rising edge of the pulse of the primary side driving signal PWM1, the falling edge of the pulse of the secondary side driving signal PWM3 is fixed for a fixed time tdThe soft switching of the second synchronous rectification switching tube is realized in advance of the falling edge of the primary side driving signal PWM1 pulse, and the rising edge of the secondary side driving signal PWM4 pulse of the active clamping forward circuit is used for fixing the time tdLagging behind the rising edge of the primary side driving signal PWM2 pulse, realizing the soft switch of the first synchronous rectification switch tube, and the pulse width of the secondary side driving signal PWM4 of the active clamping normal shock circuit is determined by the zero-crossing time of the inductive current calculated by the CPU.
Wherein, the step 4 specifically comprises:
whether the active clamping forward device works in a light-load intermittent working mode is judged according to the following formula:
Figure GDA0003000826270000031
wherein L isfRepresenting filter inductance, fsIndicating the switching frequency, v, of the switching tubeoRepresenting the output voltage, d representing the duty cycle of the main switching tube drive signal, IpThe average value of the switching period of the primary side current obtained by sampling the primary side current is shown, and n represents the transformation ratio of the transformer.
Wherein, the step 5 specifically comprises:
in the first stage, the main switch tube is turned off at the time t0～t1Forward power transfer, input voltage applied to primary side of transformer, current increase in filter inductorLarge, resonant inductor current increases as follows:
Figure GDA0003000826270000041
wherein L iskRepresenting the resonant inductance, LmRepresenting excitation inductance, ik(t) represents the current in the resonant inductor, t represents the conduction time of the main switching tube, VinRepresents an input voltage;
Figure GDA0003000826270000042
wherein ik(t1) Represents t1Time of day resonant inductor current, LkRepresenting the resonant inductance, LmIndicating exciting inductance, VinRepresenting the input voltage, d representing the duty cycle of the main switching tube drive signal, TsRepresents a switching cycle;
t1-t0＝d*Ts (4)
wherein, t0Indicates the on-time of the main switch tube, t1Indicating the turn-off time of the main switching tube, TsRepresenting the switching period and d the duty cycle.
Wherein, the step 5 further comprises:
in the second stage, the main switch tube is turned off at the time t1-initial commutation time t2The voltage resonance of the main switch tube junction capacitor rises to the input voltage VinAs follows:
Figure GDA0003000826270000043
wherein L iskRepresenting the resonant inductance, LmRepresenting excitation inductance, ik(t) represents the current in the resonant inductor, VinRepresenting the input voltage uc1(t) represents the main switch junction capacitance voltage;
Figure GDA0003000826270000044
wherein, C1Representing the main switch junction capacitance, uc1(t) represents the main switch junction capacitance voltage, ik(t) represents the current in the resonant inductor;
substituting formula (6) for formula (5) and substituting the calculation result t of formula (3)1Moment of resonance inductor current ik(t1) As follows:
t1and (3) obtaining the following result when the capacitor voltage of the main switch tube junction is zero:
Figure GDA0003000826270000051
wherein u isc1(t) represents the main switch junction capacitance voltage, VinRepresenting the input voltage, ωrDenotes the resonant frequency, C1Indicating the main switch junction capacitance, LkRepresenting the resonant inductance, LmRepresenting the excitation inductance, d the duty cycle, TsDenotes the switching period, IpRepresenting the average current value obtained by sampling the primary current;
Figure GDA0003000826270000052
wherein, ω isrDenotes the resonant frequency, LkRepresenting the resonant inductance, C1Representing the main switch tube junction capacitance;
substituting formula (8) for formula (7) to let uc1(t)＝VinThe time for the second stage is obtained as follows:
Figure GDA0003000826270000053
wherein, t2Indicating the secondary commutation initial time, t1Indicating the moment of main switching tube turn-off, omegarRepresenting the resonant frequency, VinWhich is representative of the input voltage, is,C1representing the main switch junction capacitance, d representing the duty cycle, TsDenotes the switching period, IpRepresenting the average current value obtained by sampling the primary current;
the current in the filter inductor is as follows:
Figure GDA0003000826270000054
wherein ilf(t2) Filter inductance current, V, representing the initial moment of secondary side commutationinRepresenting the input voltage, voRepresents the output voltage, LfRepresenting filter inductance, t2Indicating the secondary commutation initial time, t0And the time when the main switching tube is switched on is shown.
Wherein, the step 5 further comprises:
third stage, commutation initial time t2Time t when the current in the filter inductor drops to zero3The secondary freewheel, the current in the filter inductor drops, as follows:
Figure GDA0003000826270000055
wherein ilf(t2) The filter inductance current, v, representing the initial moment of secondary commutationoRepresents the output voltage, LfRepresenting filter inductance, t3Representing the moment, t, at which the current in the filter inductor drops to zero2Representing the initial moment of secondary side commutation;
time t for current in filter inductor to drop to zerosAs follows:
Figure GDA0003000826270000061
wherein, tsRepresenting the time, t, for the current in the filter inductor to drop to zero0Indicates the on-time of the main switch tube, t1Indicating the turn-off time of the main switching tube, t2Display pairInitial time of edge commutation, t3Representing the moment when the current in the filter inductor drops to zero, d represents the duty cycle, TsDenotes the switching period, VinRepresenting the input voltage, ωrDenotes the resonant frequency, C1Representing the main switch tube junction capacitance, n representing the transformer transformation ratio, IpRepresenting the average value, v, of the switching period of the primary current sampled from the primary currentoRepresents the output voltage; and the driving of the first synchronous rectification switching tube is closed at the zero-crossing moment of the current in the filter inductor, so that the self-adaptive control of synchronous rectification is realized.
The scheme of the invention has the following beneficial effects:
the adaptive synchronous rectification digital control method of the active clamp forward converter according to the above embodiment of the present invention, when the active clamping forward converter works in a light-load discontinuous mode, the time for reducing the current in the filter inductor to zero can be accurately calculated through the DSP of the controller, the drive of the first synchronous rectification switch tube is closed at the current zero-crossing moment in the filter inductor through the digital control signal, the reduction of the efficiency of the converter caused by the negative power is prevented, the transmission efficiency and the reliability of the active clamping forward converter in the light-load intermittent mode are improved, the condition that the junction capacitor of the first synchronous rectification switching tube is charged by the reverse current can not occur in the dead time, the condition that the first synchronous rectification switch tube is damaged due to overhigh back pressure is avoided, and digital control is adopted, so that the design of the converter is more flexible, and various protections are more sensitive.
Drawings
FIG. 1 is a flow chart of the present invention;
fig. 2 is a specific circuit schematic diagram of the active clamp forward converter of the present invention;
FIG. 3 is a schematic diagram of the waveform of the present invention (1);
FIG. 4 is a schematic diagram of the waveform of the present invention (2);
FIG. 5 is a control diagram of the present invention.
[ description of reference ]
1-a power supply; 2-a clamping capacitor; 3-auxiliary switching tube; 4-resonant inductance; 5-excitation inductance; 6-a transformer; 7-main switching tube; 8-a first synchronous rectification switching tube; 9-a second synchronous rectification switching tube; 10-a filter inductance; 11-a filter capacitance; 12-output resistance; 13-control circuit.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
The invention provides a self-adaptive synchronous rectification digital control method of an active clamp forward converter, aiming at the problems that the efficiency of the converter is reduced due to damage and backflow caused by overhigh back pressure of a switching tube when the existing converter is in light load.
As shown in fig. 1 to 5, an embodiment of the present invention provides an active-clamp forward converter including: a power supply 1; the active clamping circuit comprises a clamping capacitor 2 and an auxiliary switching tube 3, wherein a first end of the clamping capacitor 2 is electrically connected with a positive end of the power supply 1, and a drain end of the auxiliary switching tube 3 is electrically connected with a second end of the clamping capacitor 2; a resonant inductor 4, wherein a first end of the resonant inductor 4 is electrically connected with a first end of the clamping capacitor 2; the first end of the excitation inductor 5 is electrically connected with the second end of the resonance inductor 4, and the second end of the excitation inductor 5 is electrically connected with the source end of the auxiliary switching tube 3; a first end of a primary side of the transformer 6 is electrically connected with a first end of the excitation inductor 5, and a second end of the primary side of the transformer 6 is electrically connected with a second end of the excitation inductor 5; a main switching tube 7, wherein a drain end of the main switching tube 7 is electrically connected with a second end of the excitation inductor 5, and a source end of the main switching tube 7 is electrically connected with a negative end of the power supply 1; the synchronous rectification circuit comprises a first synchronous rectification switching tube 8 and a second synchronous rectification switching tube 9, wherein the drain end of the first synchronous rectification switching tube 8 is electrically connected with the first end of the secondary side of the transformer 6, the drain end of the second synchronous rectification switching tube 9 is electrically connected with the second end of the secondary side of the transformer 6, and the source end of the second synchronous rectification switching tube 9 is electrically connected with the source end of the first synchronous rectification switching tube 8; the output filter circuit comprises a filter inductor 10 and a filter capacitor 11, wherein a first end of the filter inductor 10 is electrically connected with a drain end of the first synchronous rectification switch tube 8, a first end of the filter capacitor 11 is electrically connected with a second end of the filter inductor 10, and a second end of the filter capacitor 11 is electrically connected with a source end of the first synchronous rectification switch tube 8; and a first end of the output resistor 12 is electrically connected with a first end of the filter capacitor 11, and a second end of the output resistor 12 is electrically connected with a second end of the filter capacitor 11.
The first end of the output resistor 12 is electrically connected to the first end of the control circuit 13, the second end of the control circuit 13 is electrically connected to the gate terminal of the main switching tube 7, the third end of the control circuit 13 is electrically connected to the gate terminal of the auxiliary switching tube, the fourth end of the control circuit 13 is electrically connected to the gate terminal of the second synchronous rectification switching tube 9, the fifth end of the control circuit 13 is electrically connected to the gate terminal of the first synchronous rectification switching tube 8, the control circuit 13 includes a controller, a PWM modulator, an adaptive control duty ratio calculation module and a driving circuit, the controller uses a DSP as a core, and the driving circuit is used for generating a driving signal.
The main switching tube 7, the auxiliary switching tube 3, the first synchronous rectification switching tube 8 and the second synchronous rectification switching tube 9 all include parasitic junction capacitors of anti-parallel body diodes and drain source electrodes.
The adaptive synchronous rectification digital control method of the active clamp forward converter according to the above embodiment of the present invention, the control circuit 13 is mainly composed of a controller taking a DSP as a core, a PWM modulator, a self-adaptive control duty ratio calculation module and a drive circuit for generating a drive signal, wherein under the control of a CPU, two groups of complementary PWM signals with dead zones are generated in the PWM modulator and are respectively a PWM1 signal, a PWM2 signal, a PWM3 signal and a PWM4 signal, the PWM modulator outputs the PWM1 signal, the PWM2 signal and the PWM3 signal to a driving circuit, the PWM4 signal is input to the driving circuit after passing through an adaptive control duty ratio calculation module, and the driving circuit provides driving voltage for the main switching tube 7, the auxiliary switching tube 3, the second synchronous rectification switching tube 9 and the first synchronous rectification switching tube 8 after voltage enhancement of the received PWM1 signal, the PWM2 signal, the PWM3 signal and the PWM4 signal.
The embodiment of the invention also provides a self-adaptive synchronous rectification digital control method of the active clamp forward converter, which comprises the following steps: step 1, a CPU controls a controller to generate two groups of complementary PWM signals with dead zones; step 2, inputting two groups of complementary PWM signals with dead zones into a driving circuit; step 3, the driving circuit outputs two groups of complementary PWM signals with dead zones into four paths of driving signals, and the driving circuit correspondingly inputs the four paths of driving signals into grid ends of a main switching tube 7, an auxiliary switching tube 3, a first synchronous rectification switching tube 8 and a second synchronous rectification switching tube 9 respectively; step 4, judging whether the active clamping forward converter works in a light-load intermittent working mode; step 5, calculating the time t for the current in the filter inductor 10 to drop to zero when the active clamping forward converter works in a light-load discontinuous working modes。
In the adaptive synchronous rectification digital control method of the active clamp forward converter according to the above embodiment of the present invention, in the light load discontinuous mode of the active clamp forward converter, when the main switching tube 7 is turned off, the resonant inductor 4 and the magnetizing inductor 5 resonate with the junction capacitor of the main switching tube 7, when the voltage of the junction capacitor of the main switching tube 7 rises to the input voltage level, the first synchronous rectification switching tube 8 and the second synchronous rectification switching tube 9 commutate, the body diode of the second synchronous rectification switching tube 9 is turned on, and then the second synchronous rectification switching tube 9 is turned on to realize zero voltage turn-on, so as to provide a freewheeling path, the time t when the current in the filter inductor 10 drops to zero is accurately calculated by the DSP of the controller, as shown in formula (12), the driving of the second synchronous rectification switching tube 9 is turned off at the zero crossing time of the current in the inductor filter 10, the condition that the current in the filter inductor 10 is over negative is prevented, and the self-adaptive control of synchronous rectification is realized.
Wherein the steps 1, 2 and 3 specifically include: the primary side driving signals PWM1 and PWM2 of the active clamping positive laser are generated by modulating a control signal obtained by PI regulation of error voltage generated by negative feedback of output voltage, and the pulse rising edge of a secondary side driving signal PWM3 of the active clamping positive laser is used for fixing time tdLagging behind the rising edge of the pulse of the primary side driving signal PWM1, the falling edge of the pulse of the secondary side driving signal PWM3 is fixed for a fixed time tdThe soft switching of the second synchronous rectification switching tube 9 is realized in advance of the falling edge of the primary side driving signal PWM1 pulse, and the rising edge of the secondary side driving signal PWM4 pulse of the active clamping normal shock circuit is used for fixing the time tdLagging behind the rising edge of the primary side driving signal PWM2 pulse, realizing the soft switch of the first synchronous rectification switch tube 8, and the pulse width of the secondary side driving signal PWM4 of the active clamping normal shock circuit is determined by the zero-crossing time of the inductive current calculated by the CPU.
Wherein, the step 4 specifically comprises: whether the active clamping forward device works in a light-load intermittent working mode is judged according to the following formula:
Figure GDA0003000826270000091
wherein L isfRepresenting the filter inductance 10, fsIndicating the switching frequency, v, of the switching tubeoRepresenting the output voltage, d representing the duty cycle of the drive signal of the main switching tube 7, IpThe average value of the switching period of the primary current obtained by sampling the primary current is shown, and n represents the transformation ratio of the transformer 6.
Wherein, the step 5 specifically comprises: in the first stage, the main switch tube 7 is turned off at the time t0～t1In forward power transmission, the input voltage is applied to the primary side of the transformer 6, the current in the filter inductor 10 increases, and the current in the resonant inductor 4 increases, as follows:
Figure GDA0003000826270000092
wherein L iskRepresenting the resonant inductance 4, LmRepresenting exciting inductance 5, ik(t) represents the current in the resonant inductor 4, t represents the conduction time of the main switching tube 7, VinRepresents an input voltage;
Figure GDA0003000826270000101
wherein ik(t1) Represents t1Time of day resonant inductor current, LkRepresenting the resonant inductance, LmIndicating exciting inductance, VinRepresenting the input voltage, d representing the duty cycle of the main switching tube drive signal, TsRepresents a switching cycle;
t1-t0＝d*Ts (4)
wherein, t0Indicates the on-time of the main switch tube, t1Indicating the turn-off time of the main switching tube, TsRepresenting the switching period and d the duty cycle.
Wherein, the step 5 further comprises: in the second stage, the main switch tube 7 is turned off at the time t1-initial commutation time t2The voltage resonance of the main switch tube junction capacitor rises to the input voltage VinAs follows:
Figure GDA0003000826270000102
wherein L iskRepresenting the resonant inductance 4, LmRepresenting exciting inductance 5, ik(t) represents the current in the resonant inductor 4, VinRepresenting the input voltage uc1(t) represents the main switch junction capacitance voltage;
Figure GDA0003000826270000103
wherein, C1Representing the main switch junction capacitance, uc1(t) represents the main switch junction capacitance voltage, ik(t) represents the current in the resonant inductor 4;
substituting formula (6) for formula (5) and substituting the calculation result t of formula (3)1Moment of resonance inductor current ik(t1) As follows:
t1and (3) obtaining the following result when the capacitor voltage of the main switch tube junction is zero:
Figure GDA0003000826270000104
wherein u isc1(t) represents the main switch junction capacitance voltage, VinRepresenting the input voltage, ωrDenotes the resonant frequency, C1Indicating the main switch junction capacitance, LkRepresenting the resonant inductance 4, LmIndicating the excitation inductance 5, d the duty cycle, TsDenotes the switching period, IpRepresenting the average current value obtained by sampling the primary current;
Figure GDA0003000826270000105
wherein, ω isrDenotes the resonant frequency, LkRepresenting resonant inductance 4, C1Representing the main switch tube junction capacitance;
substituting formula (8) for formula (7) to let uc1(t)＝VinThe time for the second stage is obtained as follows:
Figure GDA0003000826270000111
wherein, t2Indicating the secondary commutation initial time, t1Indicating the moment of main switching tube turn-off, omegarRepresenting the resonant frequency, VinRepresenting the input voltage, C1Representing the main switch junction capacitance, d representing the duty cycle, TsDenotes the switching period, IpRepresenting the average current value obtained by sampling the primary current;
the current in the filter inductor 10 is as follows:
Figure GDA0003000826270000112
wherein ilf(t2) Current, V, of filter inductor 10 representing initial time of secondary side commutationinRepresenting the input voltage, voRepresents the output voltage, LfRepresenting the filter inductance 10, t2Indicating the secondary commutation initial time, t0Indicating the moment when the main switching tube 7 is switched on.
Wherein, the step 5 further comprises: third stage, commutation initial time t2Time t at which the current in the filter inductor 10 drops to zero3The secondary freewheel, the current in the filter inductor 10 drops, as follows:
Figure GDA0003000826270000113
wherein ilf(t2) Current, v, of filter inductor 10 representing the initial moment of commutation at secondary sideoRepresents the output voltage, LfRepresenting the filter inductance 10, t3Represents the moment, t, at which the current in the filter inductor 10 drops to zero2Representing the initial moment of secondary side commutation;
time t for the current in the filter inductor 10 to drop to zerosAs follows:
Figure GDA0003000826270000114
wherein, tsRepresents the time, t, for the current in the filter inductor 10 to drop to zero0Indicates the time t of the main switch tube 7 being turned on1Indicating the moment of switching-off of the main switching tube 7, t2Indicating the secondary commutation initial time, t3Represents the time when the current in the filter inductor 10 drops to zero, d represents the duty cycle, TsDenotes the switching period, VinRepresenting the input voltage, ωrDenotes the resonant frequency, C1Representing the main switch junction capacitance, n representing the transformer 6 transformation ratio, IpRepresenting the average value, v, of the switching period of the primary current sampled from the primary currentoRepresenting output voltage(ii) a And the driving of the first synchronous rectification switching tube 8 is closed at the current zero-crossing moment in the filter inductor 10, so that the self-adaptive control of synchronous rectification is realized.
The adaptive synchronous rectification digital control method of the active clamp forward converter according to the above embodiment of the present invention, as shown in fig. 5, specifically includes the following steps: in the light-load discontinuous mode of the active clamp forward converter, the main switching tube 7 is conducted to transmit power, the current in the filter inductor 10 is increased, after the main switching tube 7 is turned off, the main switching tube junction capacitor resonates with the excitation inductor 5 and the resonant inductor 4, the current in the filter inductor 10 continues to rise, and after the voltage of the main switching tube junction capacitor rises to the input voltage level, the first synchronous rectification switching tube 8S on the secondary side4And the second synchronous rectification switching tube 9S3Current conversion is carried out, and the first synchronous rectification switching tube 8S4The body diode of (1) is turned on, the current in the filter inductor 10 starts to decrease, and the first synchronous rectification switch tube 8S4The time from the current in the filter inductor 10 to zero is calculated through a DSP of the controller, and when the current in the filter inductor 10 is reduced to zero, the first synchronous rectification switch tube 8S is closed4The current reversal is prevented, and the condition that the current flows negatively in the filter inductor 10 is prevented.
The adaptive synchronous rectification digital control method of the active clamp forward converter according to the embodiment of the invention has the following working process: the active clamping forward converter works under the condition of light load, t0At the moment, the main switch tube 7 is switched on, the auxiliary switch tube 3 is switched off, the input voltage is applied to two ends of the primary side of the transformer 6, and the exciting current ikStarting from a certain value to increase linearly, the second synchronous rectification switch tube 9 is conducted, the body diode of the second synchronous rectification switch tube 9 is conducted first, the second synchronous rectification switch tube 9 is driven to come later, power is transmitted to the secondary side of the transformer 6, and t1At the moment, the main switch tube 7 is turned off, the exciting current and the load current converted to the primary side of the transformer 6 charge the main switch tube junction capacitor, and the voltage of the main switch tube junction capacitor is fastFast rise, t2At the moment, when the voltage of the main switch tube junction capacitor is charged to the input voltage, the voltage at two ends of the primary side of the transformer 6 is zero, at the moment, the first synchronous rectification switch tube 8 and the second synchronous rectification switch tube 9 at the secondary side are subjected to commutation, the first synchronous rectification switch tube 8 and the second synchronous rectification switch tube 9 are simultaneously conducted to cause the voltage at two ends of the secondary side of the transformer 6 to be clamped to zero, the excitation inductor 5 can be equivalent to a current source, at the moment, the main switch tube junction capacitor and the resonance inductor 4 begin to resonate, the voltage of the main switch tube junction capacitor continues to rise, and t is2And after the moment, the output voltage is reversely applied to the two ends of the filter inductor 10, so that the current in the filter inductor 10 is reduced, the time t for reducing the current in the filter inductor 10 to be zero is accurately calculated by a DSP (digital signal processor) of the controller, the first synchronous rectification switch tube 8 is turned off, the reverse of the filter current is prevented, and the operation has no influence on the working mode of the primary side of the active clamping forward converter. When the voltage of the main switch tube junction capacitor rises to the level of the sum of the input voltage and the voltage of the clamping capacitor 2, the body diode of the auxiliary switch tube 3 starts to be conducted, and the back voltage of the clamping capacitor 2 starts to be applied to the two ends of the transformer 6. And when the back voltage of the clamping capacitor 2 reduces the resonant current to be equal to the exciting current, the current conversion of the first synchronous rectification switch tube 8 and the second synchronous rectification switch tube 9 on the secondary side is finished. The primary coil of the transformer 6 is acted by reverse clamping voltage to reduce exciting current, the auxiliary switch tube 3 is opened before the exciting current is reduced to zero, the exciting current starts to reverse after being reduced to zero, the auxiliary switch tube 3 is turned off, the main switch tube junction capacitor resonates with the exciting inductor 5 and the resonant inductor 4, the main switch tube junction capacitor starts to discharge due to the reverse exciting current, when the voltage of the main switch tube junction capacitor drops to an input voltage level, the first synchronous rectification switch tube 8 and the second synchronous rectification switch tube 9 on the secondary side of the transformer 6 start to convert current, the exciting inductor 5 is clamped into a current source, the main switch tube junction capacitor resonates with the resonant inductor 4 to enable the voltage of the main switch tube junction capacitor to drop to zero, and the body diode of the main switch tube 7 starts to convert currentAnd conducting the follow current and waiting for the next period.
In the adaptive synchronous rectification digital control method of the active clamp forward converter according to the above embodiment of the present invention, when the active clamp forward converter operates in the light load discontinuous mode, through the adaptive synchronous rectification control method, the time for the current in the filter inductor 10 to decrease to zero can be accurately calculated by the DSP of the controller, the driving signal of the first synchronous rectification switch tube 8 is adaptively turned off, so that the current in the filter inductor 10 is effectively prevented from flowing reversely in the freewheeling process, the situation that the reverse voltage breaks down the first synchronous rectification switch tube 8 due to the fact that the current of the filter inductor 10 flowing reversely in the dead time charges the first synchronous rectification switch tube 8 and the reverse voltage is too high due to the charging of the first synchronous rectification switch tube 8 is avoided, and the situation that the negative power generated by the reverse current reduces the transmission efficiency of the active clamp forward converter in the light load discontinuous mode is also avoided, the synchronous rectification of the secondary side of the active clamp forward converter is more stable, and the transmission efficiency and reliability of the active clamp forward converter are improved.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (3)

1. An adaptive synchronous rectification digital control method of an active clamp forward converter, the active clamp forward converter comprising:
a power source;
the active clamping circuit comprises a clamping capacitor and an auxiliary switching tube, wherein the first end of the clamping capacitor is electrically connected with the positive end of the power supply, and the drain end of the auxiliary switching tube is electrically connected with the second end of the clamping capacitor;
a first end of the resonant inductor is electrically connected with a first end of the clamping capacitor;
the first end of the excitation inductor is electrically connected with the second end of the resonance inductor, and the second end of the excitation inductor is electrically connected with the source end of the auxiliary switching tube;
the first end of the primary side of the transformer is electrically connected with the first end of the excitation inductor, and the second end of the primary side of the transformer is electrically connected with the second end of the excitation inductor;
the drain end of the main switching tube is electrically connected with the second end of the excitation inductor, and the source end of the main switching tube is electrically connected with the negative end of the power supply;
the synchronous rectification circuit comprises a first synchronous rectification switching tube and a second synchronous rectification switching tube, wherein the drain end of the first synchronous rectification switching tube is electrically connected with the first end of the secondary side of the transformer, the drain end of the second synchronous rectification switching tube is electrically connected with the second end of the secondary side of the transformer, and the source end of the second synchronous rectification switching tube is electrically connected with the source end of the first synchronous rectification switching tube;
the output filter circuit comprises a filter inductor and a filter capacitor, wherein the first end of the filter inductor is electrically connected with the drain end of the first synchronous rectification switch tube, the first end of the filter capacitor is electrically connected with the second end of the filter inductor, and the second end of the filter capacitor is electrically connected with the source end of the first synchronous rectification switch tube;
a first end of the output resistor is electrically connected with a first end of the filter capacitor, and a second end of the output resistor is electrically connected with a second end of the filter capacitor;
the first end of the output resistor is electrically connected with the first end of a control circuit, the second end of the control circuit is electrically connected with the gate terminal of the main switching tube, the third end of the control circuit is electrically connected with the gate terminal of the auxiliary switching tube, the fourth end of the control circuit is electrically connected with the gate terminal of the second synchronous rectification switching tube, the fifth end of the control circuit is electrically connected with the gate terminal of the first synchronous rectification switching tube, the control circuit comprises a controller, a PWM (pulse width modulation) modulator, a self-adaptive control duty ratio calculation module and a driving circuit, the controller adopts a DSP (digital signal processor) as a core, and the driving circuit is used for generating a driving signal;
the main switch tube, the auxiliary switch tube, the first synchronous rectification switch tube and the second synchronous rectification switch tube respectively comprise parasitic junction capacitors of anti-parallel body diodes and drain-source electrodes;
the self-adaptive synchronous rectification digital control method of the active clamp forward converter comprises the following steps:
step 1, a CPU controls a controller to generate two groups of complementary PWM signals with dead zones;
step 2, inputting two groups of complementary PWM signals with dead zones into a driving circuit;
step 3, the driving circuit outputs two groups of complementary PWM signals with dead zones into four paths of driving signals, and the driving circuit correspondingly inputs the four paths of driving signals into grid terminals of a main switching tube, an auxiliary switching tube, a first synchronous rectification switching tube and a second synchronous rectification switching tube respectively;
step 4, judging whether the active clamping forward converter works in a light-load intermittent working mode;
step 5, calculating the time t for the current in the filter inductor to drop to zero when the active clamping forward converter works in a light-load discontinuous working modes；
The step 5 specifically includes:
in the first stage, the main switch tube is turned off at the time t0～t1Forward power transfer, with an input voltage applied to the primary side of the transformer, the current in the filter inductor increases and the resonant inductor current increases as follows:
Figure FDA0003017996140000021
wherein L iskRepresenting the resonant inductance, LmRepresenting excitation inductance, ik(t) represents the current in the resonant inductor, t represents the conduction time of the main switching tube, VinRepresents an input voltage;
Figure FDA0003017996140000022
wherein ik(t1) Represents t1Time of day resonant inductor current, LkRepresenting the resonant inductance, LmIndicating exciting inductance, VinRepresenting the input voltage, d representing the duty cycle of the main switching tube drive signal, TsRepresents a switching cycle;
t1-t0＝d*Ts (3)
wherein, t0Indicates the on-time of the main switch tube, t1Indicating the turn-off time of the main switching tube, TsRepresenting the switching period, d representing the duty cycle;
the step 5 further comprises:
in the second stage, the main switch tube is turned off at the time t1-initial commutation time t2The voltage resonance of the main switch tube junction capacitor rises to the input voltage VinAs follows:
Figure FDA0003017996140000031
wherein L iskRepresenting the resonant inductance, LmRepresenting excitation inductance, ik(t) represents the current in the resonant inductor, VinRepresenting the input voltage uc1(t) represents the main switch junction capacitance voltage;
Figure FDA0003017996140000032
wherein, C1Representing the main switch junction capacitance, uc1(t) represents the main switch junction capacitance voltage, ik(t) represents the current in the resonant inductor;
substituting formula (5) for formula (4), and substituting the calculation result t of formula (2)1Moment of resonance inductor current ik(t1) As follows:
t1and (3) obtaining the following result when the capacitor voltage of the main switch tube junction is zero:
Figure FDA0003017996140000033
wherein u isc1(t) represents the main switch junction capacitance voltage, VinRepresenting the input voltage, ωrDenotes the resonant frequency, C1Indicating the main switch junction capacitance, LkRepresenting the resonant inductance, LmRepresenting the excitation inductance, d the duty cycle, TsDenotes the switching period, IpThe average value of the switching period of the primary current obtained by sampling the primary current is represented;
Figure FDA0003017996140000034
wherein, ω isrDenotes the resonant frequency, LkRepresenting the resonant inductance, C1Representing the main switch tube junction capacitance;
substituting formula (7) for formula (6) to let uc1(t)＝VinThe time for the second stage is obtained as follows:
Figure FDA0003017996140000035
wherein, t2Indicating the secondary commutation initial time, t1Indicating the moment of main switching tube turn-off, omegarRepresenting the resonant frequency, VinRepresenting the input voltage, C1Representing the main switch junction capacitance, d representing the duty cycle, TsDenotes the switching period, IpRepresenting the average current value obtained by sampling the primary current;
the current in the filter inductor is as follows:
Figure FDA0003017996140000041
wherein ilf(t2) Filter inductance current, V, representing the initial moment of secondary side commutationinRepresenting the input voltage, voRepresents the output voltage, LfRepresenting filter inductance, t2Indicating the secondary commutation initial time, t0Representing the opening time of a main switching tube;
the step 5 further comprises:
third stage, commutation initial time t2Time t when the current in the filter inductor drops to zero3The secondary freewheel, the current in the filter inductor drops, as follows:
Figure FDA0003017996140000042
wherein ilf(t2) The filter inductance current, v, representing the initial moment of secondary commutationoRepresents the output voltage, LfRepresenting filter inductance, t3Representing the moment, t, at which the current in the filter inductor drops to zero2Representing the initial moment of secondary side commutation;
time t for current in filter inductor to drop to zerosAs follows:
Figure FDA0003017996140000043
wherein, tsRepresenting the time, t, for the current in the filter inductor to drop to zero0Indicates the on-time of the main switch tube, t1Indicating the turn-off time of the main switching tube, t2Indicating the secondary commutation initial time, t3Representing the moment when the current in the filter inductor drops to zero, d represents the duty cycle, TsDenotes the switching period, VinRepresenting the input voltage, ωrDenotes the resonant frequency, C1Representing the main switch tube junction capacitance, n representing the transformer transformation ratio, IpRepresenting the average value, v, of the switching period of the primary current sampled from the primary currentoRepresents the output voltage; in the filterAnd the drive of the first synchronous rectification switching tube is closed at the zero-crossing moment of the current in the inductor, so that the self-adaptive control of synchronous rectification is realized.
2. The adaptive synchronous rectification digital control method of the active-clamp forward converter according to claim 1, wherein the steps 1, 2 and 3 specifically include:
the primary side driving signals PWM1 and PWM2 of the active clamping forward converter are generated by modulating a control signal obtained by PI regulation of error voltage generated by negative feedback of output voltage, and the pulse rising edge of a secondary side driving signal PWM3 of the active clamping forward converter is used for fixing time tdLagging behind the rising edge of the pulse of the primary side driving signal PWM1, the falling edge of the pulse of the secondary side driving signal PWM3 is fixed for a fixed time tdLeading the falling edge of the primary side driving signal PWM1 pulse to realize the soft switching of the second synchronous rectification switching tube, and fixing the time t by the rising edge of the secondary side driving signal PWM4 pulse of the active clamping forward converterdLagging behind the rising edge of the primary side driving signal PWM2 pulse, realizing the soft switch of the first synchronous rectification switch tube, and the pulse width of the secondary side driving signal PWM4 of the active clamping forward converter is determined by the zero-crossing time of the inductive current calculated by the CPU.
3. The adaptive synchronous rectification digital control method of the active-clamp forward converter according to claim 1, wherein the step 4 specifically comprises:
whether the active clamping forward converter works in a light-load discontinuous working mode is judged according to the following formula:
Figure FDA0003017996140000051
wherein L isfRepresenting filter inductance, fsIndicating the switching frequency, v, of the switching tubeoRepresenting the output voltage, d representing the duty cycle of the main switching tube drive signal, IpRepresenting the average of the switching period of the primary current sampled from the primary currentThe value n represents the transformer transformation ratio.
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