CN113193758B - Forced resonance flyback converter and zero-voltage switch self-adaptive control method - Google Patents

Forced resonance flyback converter and zero-voltage switch self-adaptive control method Download PDF

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CN113193758B
CN113193758B CN202110490737.6A CN202110490737A CN113193758B CN 113193758 B CN113193758 B CN 113193758B CN 202110490737 A CN202110490737 A CN 202110490737A CN 113193758 B CN113193758 B CN 113193758B
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voltage
sampling
module
zero
resonance
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CN113193758A (en
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徐申
邹昊宸
聂静雨
史小雨
孙伟锋
时龙兴
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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
    • 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
    • H02M3/33515—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 digital control
    • 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
    • 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 forced resonance flyback converter and a zero-voltage switch self-adaptive control method, and belongs to the technical field of power generation, power transformation or power distribution. The flyback converter comprises a main circuit and a control circuit. The control circuit comprises a digital constant voltage multi-mode module and a zero voltage switch module. The digital constant-voltage multi-mode module is used for controlling the output voltage to be constant and comprises a double-line sampling module, a PI compensation module, a mode judgment module, a control voltage module and a switch driving module. The zero voltage switch module is used for controlling the turn-on and turn-off time of the forced resonance tube and comprises a sampling module, a zero voltage switch self-adaptive algorithm module, a forced resonance enabling module and a zero-crossing detection and switch driving module. The self-adaptive control algorithm can realize intelligent switching on and switching off of the forced resonance tube, realize zero-voltage switching in a full-voltage range, and greatly reduce switching loss and improve efficiency compared with a traditional simple control algorithm which cannot realize the zero-voltage switching accurately.

Description

Forced resonance flyback converter and zero-voltage switch self-adaptive control method
Technical Field
The invention relates to the technical field of switching power supplies, in particular to a forced resonance flyback converter and a zero-voltage switch self-adaptive control method.
Background
The flyback switching power supply is used as a digital-analog hybrid control system, and can be divided into two categories of analog control and digital control according to different implementation modes of a feedback control loop. Compared with analog control flyback switching power supplies, the digital control flyback switching power supply has the advantages of being strong in reusability, high in flexibility, convenient to monitor in real time, strong in anti-jamming capability, capable of avoiding analog signal distortion and the like. Therefore, the digital chip is widely applied to a high-end power supply with complex control, and the digital control mode is the mainstream control method of the high-frequency and high-efficiency switching power supply at present.
With the development of modern integration technology, the switching power supply device is designed and developed in a direction of being smaller and lighter. Meanwhile, theoretical analysis and practical experience show that the volume and the mass of components such as capacitors, inductors, transformers and the like used in the switching power supply are inversely proportional to the square root of the working frequency of the power supply. Therefore, the design of devices with smaller size and lighter weight inevitably requires increasing the operating frequency of the switching power supply.
However, the switching loss of the main power tube of the flyback switching power supply is larger and larger along with the increase of the operating frequency, which seriously affects the development of the switching power supply towards high frequency and high efficiency. Therefore, it is very important to reduce the switching loss of the main power tube of the flyback converter by a certain method.
The core part of the traditional flyback switching power supply is a flyback converter which adopts an optical coupler to realize the feedback and the electrical isolation of output voltage, but the current transmission ratio of the optical coupler is greatly influenced by temperature, and the sampling precision of the output voltage is influenced. In order to overcome the defect that the output voltage is fed back by the optical coupler, a primary side feedback control mode is adopted to directly sample from a primary side winding or an auxiliary winding to obtain an accurate output voltage signal, the optical coupler is removed, and meanwhile, the integration level is improved, and the cost and the power consumption are reduced.
The invention aims to realize intelligent switching-on and switching-off of a forced resonant tube by introducing a zero-voltage switch self-adaptive digital control algorithm and realize zero-voltage switching in a full-voltage range so as to overcome the defect of the conventional primary side control mode.
Disclosure of Invention
The invention aims to provide a zero-voltage switch self-adaptive control algorithm of a forced resonance flyback converter aiming at the defects of the background technology, and introduces a zero-voltage switch self-adaptive digital control algorithm on the basis that a forced resonance branch is applied to a primary side feedback type flyback converter, so that the intelligent connection and disconnection of a forced resonance tube are accurately realized, and the technical problem that the flyback converter cannot realize accurate zero-voltage switch in the full-voltage and full-load range by using a simple control algorithm, so that the switching loss is overlarge is solved.
The invention provides a forced resonance flyback converter and a zero voltage switch self-adaptive control method, wherein the forced resonance flyback converter comprises a main circuit, a digital constant voltage multi-mode control module and a zero voltage switch self-adaptive control module, and the digital constant voltage multi-mode control module and the zero voltage switch self-adaptive control module are respectively connected with the main circuit;
the main circuit comprises a flyback transformer, a first sampling branch circuit and a forced resonance branch circuit, wherein the first sampling branch circuit and the forced resonance branch circuit are located on the primary side of the flyback transformer, the positive current direction of the forced resonance branch circuit is opposite to the primary side current, and the forced resonance branch circuit generates a forced resonance current opposite to the positive current direction after the spontaneous resonance period of the flyback transformer is finished until the exciting current reaches a negative peak value.
The digital constant-voltage multi-mode control module is used for performing constant-voltage control on sampled primary side peak current and sampled voltage, sampling a primary side current peak value of the flyback transformer and receiving the collected knee voltage, extracting an error and control mode information of a current period from the knee voltage, generating a current period control signal according to the current period error, and generating a main switching tube driving signal following control parameters under different control modes and a forced resonance branch control signal following the primary side current peak value.
The self-adaptive control module of the zero voltage switch is used for acquiring the sampling voltage V of the first sampling branchsampCalculating the conduction time t of the resonance tube in the forced resonance branchGD1onSo that V issampVoltage peak of the main switch is Vds1Is acquired when the voltage is just reduced to 0 according to the conduction time t of the resonance tubeGD1onAnd controlling the on and off of the resonance tube so as to realize zero voltage on.
The main circuit comprises a flyback transformer, a first switching tube, a second switching tube, a third switching tube and a forced resonance capacitor. The flyback transformer comprises a primary winding, a secondary winding, a forced resonance winding and a sampling winding. The primary winding is connected with the first switching tube in series to form a primary branch, the primary branch is connected with an input power supply, and the first switching tube is connected with the input power supplyThe switch tube is a master switch tube; the secondary winding is connected with a second switching tube in series to form a secondary branch, the second switching tube is a synchronous rectifier tube, and the conduction and the disconnection of the second switching tube are controlled by a synchronous rectifier control chip. The secondary branch is connected with a load R after passing through an output filter capacitorL(ii) a A loop formed by connecting the forced resonance winding in series with a third switching tube and a forced resonance capacitor is a forced resonance branch, the third switching tube is a resonance tube, the forced resonance branch is used for realizing zero voltage switching, the loop formed by connecting the forced resonance winding in series with a first sampling resistor and a second sampling resistor is a first sampling branch, and a capacitor blocking circuit connected in parallel with the second sampling resistor is used for filtering sampling voltage; and a loop formed by the sampling winding, the third sampling resistor and the fourth sampling resistor in series is a second sampling branch.
The digital constant-voltage multi-mode module comprises a double-line sampling module, a PI compensation module, a mode judgment module, a control voltage module and a switch driving module.
The double-wire sampling module adopts a double-wire inflection point approximation sampling method, two paths of voltages with fixed difference values are used for detecting the change of the slope of the voltages at the two ends of the auxiliary winding before and after the knee voltage, the knee voltage in direct proportion to the output voltage is automatically tracked, the accurate feedback of the output voltage is realized, and the error signal of the period is obtained.
And the PI compensation module obtains the control signal of the period according to the error signal of the period. The mode judging module can judge the output load RL according to the cycle error signal and the upper cycle control signal to obtain a mode judging signal for switching different working modes.
The switch driving module changes the period (pulse frequency modulation) or the peak voltage (pulse width modulation) of the first switching tube Q1 according to the switching signal to realize the constant voltage output.
The zero voltage switch self-adaptive control module comprises a sampling module, a zero voltage switch self-adaptive algorithm module, a forced resonance enabling module and a zero-crossing detection and switch driving module.
The sampling module compares the analog quantity obtained by the digital quantity given by the zero voltage switch self-adaptive algorithm module after passing through the digital-to-analog converter with the sampling voltage to obtain a square wave signal and outputs the square wave signal to the zero voltage switch self-adaptive algorithm module, and the specific process of the zero voltage switch self-adaptive control is as follows:
after the first switch tube is switched off, energy is refracted to the secondary side branch and the forced resonance branch, the energy refracted to the secondary side enables the secondary side branch to be conducted, the primary side current is refracted to the secondary side according to ampere-turn ratio conservation, and the secondary side current is linearly reduced because the voltage at the two ends of the secondary side winding is clamped at a fixed value by the output voltage; the energy refracted to the forced resonance branch enables the freewheeling diode connected in parallel reversely on the third switching tube to be conducted, the energy is rapidly released, and the forced resonance capacitor is charged to the maximum value in the process. After the secondary side current drops to zero, the second switching tube is switched off, the output voltage loses the clamping effect on the voltage at the two ends of the secondary side winding, and the circuit enters a spontaneous resonance period, namely resonance occurs between the primary side inductor and the parasitic capacitor on the first switching tube. The third switch tube is conducted in the spontaneous resonance period, the forced resonance capacitor charges the forced resonance winding, the capacitance value of the forced resonance capacitor is large and can be approximately equal to the voltage at two ends of the capacitor, therefore, the voltage at two ends of the forced resonance winding is clamped to the maximum value by the forced resonance capacitor, the negative direction of the current of the forced resonance branch is linearly increased (the charging direction of the forced resonance capacitor is set to be positive), the third switch tube is turned off when the negative direction of the current of the forced resonance branch is increased to the maximum value, the current of the forced resonance branch is refracted to the primary side to continuously release the residual energy on the parasitic capacitor of the first switch tube, when the energy release is finished, namely the leakage source voltage of the first switch tube is equal to zero, the first switch tube is conducted to enter the next period, and at the moment, the first switch tube is conducted at zero voltage, and the switching loss is reduced.
By adopting the technical scheme, the invention has the following beneficial effects: the self-adaptive digital control algorithm based on the zero-voltage switch can realize intelligent switching on and off of the forced resonant tube and realize zero-voltage switching in the full-voltage range, and overcomes the defects of loss reduction and limited lifting efficiency of the primary side flyback topology with valley bottom conduction in high-voltage input.
Drawings
Fig. 1 is a block diagram of a system configuration of a flyback converter of the present invention.
FIG. 2 is a steady state waveform diagram of the circuit key parameters of the present invention.
Fig. 3 is a diagram of a dead band resonance waveform at zero voltage switching of the present invention.
FIG. 4 is a waveform diagram of key parameters of the adaptive digital control algorithm of the present invention.
FIG. 5 is a block flow diagram of the zero voltage switching adaptive algorithm of the present invention.
The reference numbers in the figures illustrate: q1 is the first switch tube, Q2 is the second switch tube, Q3 is the third switch tube, CFFRFor forced resonance capacitance, Np is primary winding, Ns is secondary winding, NFFRFor forced resonant winding, NZCDFor sampling the winding, CLTo output filter capacitors, RLThe first sampling resistor R1, the second sampling resistor R2 and Cz are blocking capacitors, and the third sampling resistor R3 and the fourth sampling resistor R4 are loads.
Detailed Description
In order that the invention may be more fully understood, reference will now be made to the accompanying drawings. The topology and waveform diagrams presented in the figures are preferred embodiments of the present invention, but the embodiments that can be implemented in the present application are not limited to the embodiments listed in the present application. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
The invention discloses a forced resonance flyback converter, which has a specific structure shown in figure 1.
The main circuit comprises a transformer, a first switch tube Q1, a second switch tube Q2, a third switch tube Q3 and a forced resonance capacitor CFFR. The transformer comprises a primary windingNp, secondary winding Ns, forced resonant winding NFFRAnd a sampling winding NZCD. The primary winding Np is connected with a first switching tube Q1 in series to form a primary branch, and the primary branch is connected with an input power supply; the secondary winding Ns is connected with the second switching tube Q2 in series to form a secondary branch circuit, and the secondary branch circuit passes through the output filter capacitor CLRear connection load RL(ii) a Forced resonance winding NFFRA third switching tube Q3 and a forced resonance capacitor CFFRThe loop formed by the series connection is a forced resonance branch circuit which is used for realizing zero voltage switching and is wound by NFFRA loop formed by connecting the first sampling resistor R1 and the second sampling resistor R2 in series is a first sampling branch circuit, and a capacitance blocking circuit connected with the second sampling resistor R2 in parallel is used for filtering the sampling voltage; sampling winding NZCDThe loop formed by the third sampling resistor R3 and the fourth sampling resistor R4 in series is a second sampling branch.
Digital constant-voltage multi-mode module with constant output controlled by control circuit and forced resonant tube Q controlled by control circuit3The self-adaptive control module of the zero voltage switch consists of two parts.
The digital constant-voltage multi-mode module comprises a double-line sampling module, a PI compensation module, a mode judgment module, a control voltage module and a switch driving module.
The double-line sampling module adopts a double-line inflection point approximation sampling method and utilizes NZCDThe slope change of the voltages at the two ends of the auxiliary winding is large before and after the knee voltage, two paths of voltages with fixed difference values are used for detecting the slope change, and the knee voltage is automatically tracked. Due to the knee voltage and the output voltage V0The output voltage is in a direct proportional relation, so that accurate feedback of the output voltage can be realized, and the error signal e (n) of the period is obtained.
The PI compensation module obtains a control signal Vc (n) of the period according to the e (n) signal of the period. The mode judging module can judge the output load according to the periodic error signal e (n) and the upper periodic control signal Vc (n-1), and obtains a mode judging signal state for switching different working modes.
The control voltage module obtains a switching signal according to the state signal and the control signal Vc (n).
The switch driving module changes the first switch tube Q according to the switch signal1Period t ofs(pulse frequency modulation) or peak voltage Vpeak(pulse width modulation) to achieve a constant voltage output. On the other hand, according to the voltage V at two ends of the primary sampling resistorCSAnd then a driving signal for controlling the connection and disconnection of the third switching tube Q3 is obtained after the zero-voltage switching self-adaptive control module is used, so that zero-voltage switching is realized.
The zero voltage switch self-adaptive control module comprises a sampling module, a zero voltage switch self-adaptive algorithm module, a forced resonance enabling module and a zero-crossing detection and switch driving module.
The sampling module is used for converting the digital quantity VSAM_MAXAnalog quantity V obtained by Digital-to-Analog Converter (DAC)sam_maxAnd the first branch sampling voltage VsampComparing to obtain a square wave signal VcompAnd outputting the output to a zero voltage switch self-adaptive algorithm module. Said digital quantity VSAM_MAXIs a sampling voltage VsampThe ideal maximum value.
Zero-voltage switch self-adaptive algorithm module Q realization3Conduction time tGD1onAnd (4) precise control.
The zero-crossing detection module is based on tGD1onAnd the moment of the first zero crossing of the converter in the spontaneous resonance phase determines whether there is sufficient time for Q in the spontaneous resonance phase of the cycle3On and off.
The forced resonance enabling module sends a signal to the switch driving module to drive the Q if enough time is available according to the judgment result of the zero-crossing detection module3On and off.
The internal structure of the sampling module is shown in fig. 1, and a zero voltage switch adaptive algorithm module gives a digital quantity VSAM_MAXAnalog quantity V obtained by Digital-to-Analog Converter (DAC)sam_maxAnd the first branch sampling voltage VsampComparing to obtain a square wave signal VcompAnd outputting the output to a zero voltage switch self-adaptive algorithm module. Zero-voltage switch self-adaptive algorithm module Q realization3Conduction time tGD1onThe detailed algorithm flow chart of the precise control is shown in fig. 5, and the following detailed analysis is performed in combination with the overall circuit and the steady state waveform, each switching cycle is divided into 5 time intervals, and the steady state waveform is shown in fig. 2.
I) switching mode 1[ t3, t4]
At time t3, the main power transistor Q1 is turned on, i.e. GD0 is 1, and Q1 drain-source voltage VdsThe voltage across the primary winding is clamped to the rectified DC voltage V of the AC input to be 0DCSo primary side current iPLinearly rising, and the current in the other winding circuit is 0, so the exciting current iMagAlso rises linearly and at time i of t4MagUp to a maximum value. Peak current of primary side IpeakAnd a direct current VDCPrimary side excitation inductance LpAnd Q1Conduction time tGD0onThe relationship (c) is shown in the formula (1).
Figure GDA0003504572480000061
Wherein R isCSAnd VpeakThe primary sampling resistor and the peak voltage at two ends of the primary sampling resistor are respectively.
II) switching mode 2[ t4, t5]
At the time of t4, the main power tube Q1 is turned off, GD0 is 0, and the parasitic capacitance C on Q1OSSIs rapidly charged to the maximum value and clamped, the primary side current iPRapidly drops to 0 and the voltage polarity at the same name terminal becomes positive. A secondary side loop: the synchronous rectifier Q2 is conducted, and the voltage across the secondary winding is clamped at V0(neglecting the Q2 conduction voltage drop), so the secondary current drops linearly, the excitation current drops linearly and the clamp voltage V0Refraction to the primary side results in VdsIs clamped to (V)DC+V0·NP/NS). Forced resonance branch circuit: since the inductor current can not suddenly change and Q3 is not conducted, the resonance current i is forcedffrThe fast release is achieved by a freewheeling diode connected in anti-parallel with Q3, as shown in fig. 1, during which the resonant capacitor C is forcedFFRIs charged to a maximum value, CFFRThe upper plate voltage of (2) is positive.
III) switching mode 3[ t5, t1] time period
At time t5, the secondary current drops to 0, the synchronous rectifier Q2 is turned off, and the output voltage V is0The voltage at the two ends of the secondary winding is not clamped, the converter enters a spontaneous resonance period, and the excitation inductor LPAnd Q1 parasitic capacitance COSSResonance occurs, Q1 drain-source voltage VdsIs a direct voltage V on the primary side loopDCThe superimposed amplitude is (V)0·NP/NS) Of a resonance period T of
Figure GDA0003504572480000071
IV) [ t1, t2] time period
At the time t1, the Q3 tube is conducted to force the resonant capacitor CFFRDischarging to the forced resonance winding in the current direction i in FIG. 1ffrThe reverse direction of (1); and because of the forced resonance capacitance CFFRThe capacitance value is large and can be approximated as that two ends of the forced resonance winding are VCFFRClamping, so that the excitation current increases inversely linearly at t2Reaches a peak value i at the momentffr(t2) Calculating the available iffr(t2)，
Figure GDA0003504572480000072
(ignore t)1Time iffrInitial value of (1). Wherein, tGD1on is Q3Conducting time; l isFFRIs an equivalent excitation inductance of a forced resonance winding, which is equal to the primary excitation inductance LpIn a relationship of
Figure GDA0003504572480000073
V) [ t2, t3] time period
t2Time Q3And the converter is switched off and enters a dead zone. Forced resonant tank current iffr(t2) Refracted to the primary side as a current ip(t2) According to the law of conservation of ampere-turn ratio and iffr(t2) Can obtain t2Time primary side current ip(t2) The formula (c) of (a),
Figure GDA0003504572480000074
wherein the negative sign indicates the current direction and ipThe opposite direction is shown in fig. 1. Due to a negative current i refracted to the primary sidep(t2) Larger, Q can be1Parasitic capacitance CossMost of the energy left on the rotor is released to the exciting inductance LpTherefore V isds1And rapidly decreases. If at the dead time end time CossCan just be completely released, then at t3Time Vds1Can be lowered to 0, at which point Q is turned on1And the converter enters the next working period, namely zero voltage conduction is realized.
In the dead zone phase, Q1Parasitic capacitance CossRelease energy to excitation inductance LpCan also be regarded as LpAnd CossResonance occurs. Thus, the voltage Vds1Has a waveform of an input DC voltage VDCSuperimposing an amplitude of VmA sine wave. Amplitude VmAnd a forced resonance tube Q3On-time t ofGD1onRelated to, as shown in formula (2)
Figure GDA0003504572480000081
When t is3Time CossJust after all the residual energy is released, the efficiency of the converter can be optimized. FIG. 3 is a graph of the dead band resonance waveform (t) when zero voltage switching can be achieved2-t3I.e., dead time). As can be seen from the figure, when the amplitude V is largemIs equal to the input DC voltage VDCThe bottom of the resonance valley is exactly 0. Thus, let V in formula (2)DCIs equal to VmCan obtain t when the zero voltage is conductedGD1onThe theoretical formula (2) is shown in (3).
Figure GDA0003504572480000082
Realize zero electricityVoltage on except for control Q3Conduction time t of the tubeGD1onIn addition, the dead time t needs to be controlleddeadTo turn on Q when the resonance just reaches the valley1The next switching cycle is entered. According to the B point coordinate (t) in FIG. 330) the dead zone phase V can be obtainedds1The formula of the waveform of (a) is,
Figure GDA0003504572480000083
then coordinate the point A (t)2，VDC+V0·NPS) To obtain tdeadThe theoretical formula is shown in (4).
Figure GDA0003504572480000084
Finally, the down-converter switching period t is controlled by the constant frequencysWhen known, then by the formula (t)s-tGD1on-tdead) To obtain Q3The moment of conduction of the tube (i.e. t)1Value of (d).
Peak voltage V can be obtained by the above digital constant voltage multi-mode modulepeakThen V can be obtained according to the formula (1)DCQ can be obtained from the values of (3) and (4)3Tube lead-through time tGD1onAnd a dead time tdeadThe theoretical value of (1). However, in practice, the effect of zero-voltage switching is influenced by a plurality of factors, the main factor is the current ipResonance in the spontaneous resonance phase, which results in t1Time ipInitial value is not 0 and VDCThe change of the resonance position with the change of the load causes ip(t1) Since the initial value is difficult to calculate, t is calculated in equation (3)GD1onWhile neglecting ip(t1) Is started. In addition VDCSampling accuracy, capacitance CFFRThe equivalent series resistance of (2) also affects the zero voltage switch implementation. As can be seen from the above, and tdeadIn contrast, tGD1onThe theoretical and actual values of (c) are far apart. Therefore, the pair t is mainly considered in the zero-voltage switch adaptive algorithmGD1onAnd (4) adjusting.
Adaptive algorithm for zero voltage switchA detailed algorithm flow diagram is shown in fig. 5. Wherein, scount is pair VcompCount the number of counts obtained as 1; t is tGD1ONIs t in the algorithmGD1onThe number of counts.
Firstly, the peak voltage V at two ends of a primary side sampling resistorpeakTo obtain a voltage VDCThen according to tGD1onIs given to tGD1onAssigning an initial value;
judgment VDCWith or without change, if VDCIf it is changed, t is newly pairedGD1onAssigning an initial value;
if VDCIf no change, judging whether scount (n) is 1; wherein scount (n) is for VcompCount the number of counts obtained as 1;
if scount (n) is 0, the digital quantity V is setSAM_MAXToo large, i.e. representing the digital quantity V in FIG. 4sam_maxAnd VsampNo intersection), so the digital quantity V is converted into a digital quantity VSAM_MAXSubtracting 1 and returning to the re-sampling peak value; if scount (n) is greater than 1, a digital quantity V is indicatedSAM_MAXToo small, thus reducing the digital quantity VSAM_MAXAdd 1 and return to resampling VsampA voltage peak; if 1, it means sampling VsampVoltage peak value, at this moment, finishing sampling;
judging whether scount (n) is 1 in the dead zone tdeadInternally sampling, if so, indicating tGD1onIs larger (as shown in FIG. 4 (a)) because at tdeadWhen dead time is not over Vds1Having fallen to 0, V is known from the analysis of the above principle sectionds1Premature drop to 0 means that the capacitance C is presentFFRConsuming too much energy, also affecting converter efficiency, so Q will be3Count value t of on-timeGD1ONSubtracting 1 and returning to the resample peak.
If not at tdeadIf sampling is done, there are two cases of fig. 4(b) and 4 (c). Will VSAM_MAX(n) subtracting a fixed voltage difference value DeltaV to obtain a digital quantity V of (n +1) periodSAM_MAX(n +1), obtaining an analog quantity V by DACsam_maxThen is further reacted with VsampComparing to obtain VcompCount value scount (n +1) of 1. Then, whether scount (n +1) is 1 or not is judgedIs in the dead zone tdeadInternal mining: if not, the waveform is too large at the bottom of the valley as shown in FIG. 4(b), and zero-voltage switching is not realized, therefore t is setGD1ONAdding 1 and returning to the re-sampling peak value; if so, the waveform achieves zero voltage switching as shown in FIG. 4(c), at which time accurate Q is obtained3Conduction time tGD1on. And (5) finishing the self-adaptive algorithm and jumping out of the loop.
The forced resonance enabling module is according to tGD1onAnd the moment of the first zero crossing of the converter in the spontaneous resonance phase determines whether there is sufficient time for Q in the spontaneous resonance phase of the cycle3On and off. If enough time is available, the forced resonance enabling module sends a signal to the switch driving module to drive the Q3To achieve precise control of the turn on and turn off of Q3.
The foregoing is a more detailed description of the invention, taken in conjunction with the specific preferred embodiments thereof, and it is not intended that the invention be limited to these specific embodiments, as many variations of the embodiments of the invention are possible without departing from the spirit or scope of the invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (3)

1. A forced resonance flyback converter is characterized by comprising a main circuit, a digital constant voltage multi-mode control module and a zero voltage switch self-adaptive control module, wherein the digital constant voltage multi-mode control module and the zero voltage switch self-adaptive control module are respectively connected with the main circuit;
the main circuit comprises a flyback transformer, a first sampling branch positioned on the primary side of the flyback transformer and a forced resonance branch positioned on the primary side of the flyback transformer, wherein the positive current direction of the forced resonance branch is opposite to the primary side current, and the forced resonance branch generates a forced resonance current opposite to the positive current direction after the spontaneous resonance period of the flyback transformer is finished until the exciting current reaches a negative peak value;
the flyback transformer comprises a primary winding, a secondary winding, a forced resonance winding and a sampling winding; the primary winding is connected with the first switch tube in seriesA primary side branch is formed after the first switching tube is connected with the input power supply, and the first switching tube is a main switching tube; the secondary winding is connected with a second switching tube in series to form a secondary branch, and the second switching tube is a synchronous rectifier tube; the secondary side branch is connected with a load after passing through an output filter capacitor; a loop formed by connecting the forced resonance winding in series with a third switching tube and a forced resonance capacitor is a forced resonance branch, the third switching tube is a resonance tube, the forced resonance branch is used for realizing zero voltage switching, and a loop formed by connecting the forced resonance winding in series with a first sampling resistor and a second sampling resistor is a first sampling branch; the voltage of the middle node of the first sampling resistor and the second sampling resistor in the first sampling branch circuit is filtered to obtain a sampling voltage Vsamp(ii) a A loop formed by connecting the sampling winding with the third sampling resistor and the fourth sampling resistor in series is a second sampling branch circuit;
the digital constant-voltage multi-mode control module is used for sampling a primary current peak value of the flyback transformer, receiving the collected knee voltage, extracting an error of a current period and control mode information from the knee voltage, generating a current period control signal according to the current period error and generating a main switching tube driving signal following control parameters under different control modes;
the self-adaptive control module of the zero voltage switch is used for acquiring the sampling voltage V of the first sampling branchsampCalculating the conduction time t of the resonance tube in the forced resonance branchGD1onSo that V issampThe voltage peak value of the main switch tube is obtained when the drain-source voltage of the main switch tube is just reduced to zero according to the conduction time t of the resonance tubeGD1onControlling the on and off of the resonance tube specifically comprises the following processes:
by sampling the peak voltage V at two ends of the resistor at the primary sidepeakTo obtain a voltage VDC，VDCInputting a direct current voltage for a primary side;
according to tGD1onIs given to tGD1onAssigning an initial value;
judgment VDCWith or without change, if VDCIf it is changed, t is newly pairedGD1onAssigning an initial value;
if VDCIf no change, judging whether scount (n) is 1; wherein scount (n) is for VcompCount the number of counts obtained as 1;
digital quantity V to be setSAM_MAXAnalog quantity V obtained after passing through digital-to-analog convertersam_maxAnd a sampling voltage VsampComparing to obtain a square wave signal Vcomp(ii) a Said digital quantity VSAM_MAXIs a sampling voltage VsampA digital quantity corresponding to the ideal maximum value;
if scount (n) is 0, it means that the digital quantity V is setSAM_MAXIs too large, so the digital quantity VSAM_MAXSubtract 1 and return to resampling VsampVoltage peak value of (d); if scount (n) is greater than 1, a digital quantity V is indicatedSAM_MAXToo small, thus reducing the digital quantity VSAM_MAXAfter adding 1, return to re-sampling VsampA voltage peak; if 1, it means sampling VsampVoltage peak value, at this moment, finishing sampling;
judging whether scount (n) is 1 in the dead zone tdeadInternally harvesting;
if yes, indicating the conduction time t of the resonance tubeGD1onIs larger because at tdeadThe drain-source voltage V of the first switch tube when the dead time is not overds1Has fallen to 0 and thus has turned on the resonator tube for a time tGD1onIs counted value tGD1ONSubtract 1 and return to resampling VsampA voltage peak;
if not in the dead zone tdeadSampling to, convert the digital quantity VSAM_MAX(n) subtracting a fixed voltage difference value DeltaV to obtain a digital quantity V of (n +1) periodSAM_MAX(n +1), obtaining an analog quantity V by DACsam_maxThen is further reacted with VsampComparing to obtain VcompA count value scount (n +1) of 1;
judging whether scount (n +1) is 1 or not in the dead zone tdeadInternal mining: if not, the step t is carried outGD1ONAdding 1 and returning to the re-sampling peak value;
if yes, zero voltage switching is realized, and accurate resonant tube conduction time t is obtainedGD1on(ii) a The self-adaptive algorithm is finished, and a loop is jumped out;
according to tGD1onIs determined in the period by the time of the first zero crossing point of the converter in the spontaneous resonance stageAnd if the time is enough, the forced resonance enabling module sends a signal to the switch driving module to drive the resonance tube to be switched on and off.
2. A flyback converter as claimed in claim 1, wherein the conduction time t of the resonant tube in the forced resonant branch is tGD1onThe theoretical calculation formula is
Figure DEST_PATH_IMAGE001
Realizing zero voltage conduction except controlling the conduction time t of the resonant tubeGD1onIn addition, the dead time t needs to be controlleddead，tdeadTheoretical formula is
Figure 235509DEST_PATH_IMAGE002
Wherein Lp is excitation inductance, COSSIs the parasitic capacitance of the main switch tube, NpsIs the turn ratio of primary and secondary windings of the flyback transformer, VDCFor primary side input of DC voltage, V0Is the output voltage of the flyback converter.
3. The flyback converter according to claim 1, wherein the zero-voltage-switch adaptive control module comprises a sampling module, a zero-voltage-switch adaptive algorithm module, a forced resonance enabling module and a zero-crossing detection module;
the sampling module is used for converting the digital quantity VSAM_MAXAnalog quantity V obtained after passing through digital-to-analog convertersam_maxThe sampling voltage V of the first sampling branchsampComparing to obtain a square wave signal VcompOutputting the signal to a zero voltage switch self-adaptive algorithm module;
zero-voltage switch self-adaptive algorithm module for realizing resonant tube conduction time tGD1onThe accurate control of the control;
the zero-crossing detection module is used for detecting the conduction time t of the resonance tubeGD1onJudging whether enough time is available for switching on and off the resonant tube in the spontaneous resonance stage of the period at the moment of the first zero crossing point of the converter in the spontaneous resonance stage;
and the forced resonance enabling module sends a signal to the switch driving module to drive the resonance tube to be switched on and off if enough time is available according to the judgment result of the zero-crossing detection module.
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CN111525801A (en) * 2020-04-15 2020-08-11 东南大学 Flyback converter and control method for realizing zero-voltage switch
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