CN106849686A - Bicyclic fixed-frequency control method based on BUCK LLC two-stage DC/DC converters - Google Patents

Bicyclic fixed-frequency control method based on BUCK LLC two-stage DC/DC converters Download PDF

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Publication number
CN106849686A
CN106849686A CN201710146102.8A CN201710146102A CN106849686A CN 106849686 A CN106849686 A CN 106849686A CN 201710146102 A CN201710146102 A CN 201710146102A CN 106849686 A CN106849686 A CN 106849686A
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buck
llc
switching tube
converters
converter
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CN106849686B (en
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张兴
刘闯
颜瑄
赵涛
赵文广
郭华越
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Hefei University of Technology
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Hefei University of Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/338—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 in a self-oscillating arrangement
    • H02M3/3381—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 in a self-oscillating arrangement using a single commutation path
    • 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
    • H02M3/338—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 in a self-oscillating arrangement
    • H02M3/3385—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 in a self-oscillating arrangement with automatic control of output voltage or current

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

Abstract

The invention discloses a kind of bicyclic fixed-frequency control method based on BUCK LLC two-stage DC/DC converters.The switching frequency of LLC resonant converter is set to two elements resonant frequency by it, while gathering the output voltage of BUCK LLC two-stage DC/DC converters using difference channel, gathering BUCK converter inductive currents using current sensor carries out double -loop control.The gain of LLC resonant converter keeps constant in the present invention, and the output voltage of BUCK LLC two-stage DC/DC converters is adjusted by the dutycycle of double -loop control adjustment BUCK converter switches pipes.Relative to traditional monocyclic control double -loop control dynamic responding speed faster, steady-state behaviour is more preferable.Inverter power density is higher.The BUCK LLC two-stage DC/DC converter simulation models that the present invention is built, input voltage range is wider, and anti-disturbance ability is stronger, with certain engineering application value.

Description

Bicyclic fixed-frequency control method based on BUCK-LLC two-stage DC/DC converters
Technical field
It is especially a kind of to be based on BUCK-LLC two the present invention relates to a kind of double loop control of two-stage DC/DC converters The bicyclic fixed-frequency control method of level DC/DC converters.
Background technology
DC/DC converters have a wide range of applications in industrial circle, such as electric automobile and vehicle-mounted charger, the driving of LED, Direct current collecting system of generation of electricity by new energy etc..Soft switch technique is widely used in DC/DC converters, in ZVS and ZCS patterns It can reduce the interference of switching loss and EMI down.
LLC resonant converter soft switch technique can realize the ZVS of primary switch pipe, the ZCS of secondary diode.It is opened Pass frequency is higher relative to Conventional soft switch technology, and the power that converter can be significantly improved in the case of guaranteed efficiency is close Degree.But it is larger that switching tube switching frequency can be caused to fluctuate when LLC converter change range of input voltage is larger, is unfavorable for magnetic The design of element and the reduction of electromagnetic interference.And two-stage DC/DC converters can be very good to solve the above problems, become research Focus.
Therefore, people are made that various effort, document " An improved wide input vol tage buck- Boost+LLC cascaded converter [J] ", Sun X, Qiu J, Li X,《IEEE Energy Convers ion Congress and Exposi tion》,2015:A kind of 1473-1478 (" buck-boost+ for improving wide input voltage range LLC cascades code converter ",《IEEE electric energy converts meeting》, 2015 1473-1478 pages) used Boost and LLC cascade DC/DC converters, the purpose of regulation converter output, but prime are reached by adjusting the dutycycle of prime Boost It is unfavorable for the selection of rear class LLC converter metal-oxide-semiconductors using Boost converter.
Document " Boost-LLC high efficiency DC/DC converters [J] ", Shi Yuxiang, Liu Xudan, Deng Cheng,《Power electronics skill Art》, 2010,44 (8):24-26, has used the converter of BUCK-Boost and LLC cascades, and uses phase shifting control strategy, comes Ensure that LLC can realize Sofe Switch in full-load range, but Control System Design is complicated, and required component number is more, high cost.
Document " Improved Power Qual ity Buck-Boost Converter fed LLC Resonant Converter for Induction Heater ", Bhim Singh, Rahul Pandey,《2016IEEE6th Internat ional Conference on Power Systems(ICPS)》, IEEE, 2016:The 1-6 (" use with LLC resonant converter Applied in electric heating sensing in the buck-Boost converters for improving power quality ",《The 6th International Power system of IEEE in 2016 System meeting (ICPS)》, 2016 page 1 to 6).Employed for prime One Buck-Boost converter body and rear class LLC converters and separated The method of independent control, is unfavorable for the stability of whole system, and antijamming capability is not strong.
Document " Buck+ half-bridge LLC multiplication of voltage resonance two-stage type DC/DC converters ", Zhang Jinwei, Zhou Dongfang, Li Jianbing, Zheng Yang Bravely,《The big journal of information engineering》, 2012.06.009.Monocyclic control method is employed for two-stage DC/DC converters, system is rung Answer speed slow, antijamming capability is not also improved.
In sum, prior art fails to solve the problems with of two-stage DC/DC converters simultaneously：
1st, two-stage DC/DC changer systems stability is poor, and external interference resistance is weak.
2nd, Control System Design is complicated, is unfavorable for engineer applied in practice.
3rd, two-stage DC/DC converters input voltage regulation narrow range, is unfavorable for applying in wide range input voltage.
4th, control system response speed is slow, is unfavorable for the quick response of output voltage.
The content of the invention
The technical problem to be solved in the present invention is the limitation for overcoming above-mentioned various technical schemes, for BUCK-LLC two-stages The control strategy of DC/DC converters, using bicyclic fixed-frequency control strategy, its control performance is relative to traditional monocyclic control strategy Faster, steady-state behaviour is more preferable for dynamic responding speed.Using this control method two-stage DC/DC converters input voltage range compared with Width, anti-disturbance ability is stronger, with certain engineering application value.
It is solve technical problem of the invention, the invention provides a kind of based on BUCK-LLC two-stage DC/DC converters Bicyclic fixed-frequency control method.
Circuit topological structure involved in the present invention is two-layer configuration, and prime BUCK converters include DC input voitage Vin、 Switching tube S1, switching tube S2, inductance LBUCK, output capacitance Cin；Rear class LLC converters include switching tube Q1, switching tube Q2, switch Pipe Q3, switching tube Q4, resonant inductance Lr, resonant capacitance Cr, high frequency transformer T, diode DR1, diode DR2, output capacitance C0、 Output load resistance R0；
The colelctor electrode connection input voltage V of switching tube S1inPositive pole, the hair of the colelctor electrode connecting valve pipe S1 of switching tube S2 Emitter-base bandgap grading, the emitter stage connection DC input voitage V of switching tube S2inNegative pole, the inductance L of BUCK convertersBUCKOne end connection is opened The emitter stage of pipe S1 and the intersection point of switching tube S2 colelctor electrodes are closed, the other end connects the output capacitance C of BUCK convertersinPositive pole, The output capacitance C of BUCK convertersinNegative pole connection input voltage VinThe intersection point of negative pole and switching tube S2 emitter stages；
LLC converter switches pipes Q1 and Q3 head and the tail are connected, i.e. the colelctor electrode connection LLC converter input capacitances of switching tube Q1 CinPositive pole, the emitter stage of the colelctor electrode connecting valve pipe Q1 of switching tube Q3, switching tube Q3 emitter stage connection BUCK converters Output capacitance CinNegative pole；LLC converter switches pipes Q2 and Q4 head and the tail are connected, i.e. the colelctor electrode connection BUCK of switching tube Q2 becomes The output capacitance C of parallel operationinPositive pole, the colelctor electrode of the emitter stage connecting valve pipe Q4 of switching tube Q2, the emitter stage of switching tube Q4 Connection LLC converter input capacitances CinNegative pole；Switching tube Q1 emitter stages are drawn as A with the intersection point of switching tube Q3 colelctor electrodes Point, switching tube Q2 emitter stages are drawn as B points with the intersection point of switching tube Q4 colelctor electrodes；The resonant inductance L of LLC convertersrOne end Connection A points, the primary side positive pole on other end connection high frequency transformer T sides, the negative pole connection LLC converters of high frequency transformer T primary sides Resonant capacitance CrOne end, LLC converter resonant capacitances CrThe other end connection B points；High frequency transformer T secondary is taken out with center Head, centre cap connection LLC output capacitances C0Negative pole, high frequency transformer T secondary cathode connecting diodes DR1Positive pole, high frequency Transformer T secondary negative pole connection diode DR2Positive pole, diode DR1Negative pole and diode DR2Negative pole be connected；Diode DR1Negative pole and diode DR2The intersection point connection LLC converter output capacitances C of negative pole0Positive pole；Load resistance R0Positive pole connects LLC Converter output capacitance C0Positive pole, load resistance R0Negative pole meets LLC converter output capacitances C0Negative pole；Load resistance two ends Voltage U0It is the output voltage of LLC converters；
This control method is included to BUCK-LLC two-stages DC/DC converters output voltage and BUCK converter inductive currents Sampling, key step is as follows：
Step 1, calculates the resonant frequency f of LLC converters resonant inductance and resonant capacitancer, its expression formula is as follows：
Wherein, LrIt is the resonant inductance of LLC converters, CrIt is the resonant capacitance of LLC converters；
Step 2, set LLC converter switches pipes Q1, switching tube Q2, switching tube Q3, switching tube Q4 switching frequency fs as The resonant frequency f that step 1 is obtainedr, the output voltage U of BUCK-LLC two-stage DC/DC converters is gathered using difference channel0, profit BUCK converter inductive currents i is gathered with current sensorBUCK；
Step 3, the output voltage U of the two-stage DC/DC converters that step 2 is obtained0With given two-stage DC/DC converters Output voltage reference value U0-refSubtract each other and obtain voltage-regulation error e rrV, voltage-regulation error e rrV is obtained by pi regulator To BUCK converter inductive currents iBUCKReference signal iBUCK-ref,
ErrV=U0-U0_ref
iBUCK_ref=KpverrV+Kiv ∫ errVdt
Wherein Kpv is the proportionality coefficient of voltage error pi regulator, and Kiv is the integral coefficient of voltage error pi regulator, t It is the time of integration.
Step 4, the BUCK converter inductive currents i for first obtaining step 3BUCKReference signal iBUCK-refAdopted with step 2 The BUCK converter inductive currents i that sample is obtainedBUCKSubtract each other and obtain current regulation error errI, then by current regulation error ErrI is by pi regulator, the modulation wave signal to obtaining the driving of BUCK converter switches pipe after pi regulator output signal amplitude limit Temp,
ErrI=iBUCK-iBUCK_ref
Temp=KpierrI+Kii ∫ errIdt
Wherein Kpi is the proportionality coefficient of current error pi regulator, and Kii is the integral coefficient of current error pi regulator, t It is the time of integration；
Step 5, modulation wave signal temp and the triangular wave carrier that step 4 is obtained is compared, when modulation wave signal width Value exports high level when being more than triangular carrier amplitude, and low level is exported when modulation wave signal amplitude is less than triangular carrier amplitude, When modulation wave signal amplitude is equal to triangular carrier amplitude, output level keeps constant, it is hereby achieved that BUCK converter switches The drive signal EPWM1 and EPWM2 of pipe S1 and switching tube S2.
Preferably, the switching tube Q1 of the LLC converters in step 2, switching tube Q2, switching tube Q3, switching tube Q4 are fixation The opened loop control of frequency and dutycycle.
Preferably, in step 5 BUCK converter drive signals EPWM1 and EPWM2 is complementary, i.e. BUCK converter switches pipe The complementary conductings of S1 and S2.
Preferably, the frequency of step 5 intermediate cam carrier wave is BUCK converter switches frequencies, and triangular carrier amplitude becomes for BUCK Parallel operation DC input voitage Vin。
The present invention is relative to the beneficial effect of prior art：
1st, LLC resonant converter switching frequency is fixed, and magnetic core element design is relatively easy to.
2nd, LLC resonant converter is operated at resonant frequency, and operating efficiency is higher.
3rd, bicyclic fixed-frequency control method causes converter response speed faster, and stability is more preferable.
4th, at resonant frequency, its gain is not influenceed LLC by load change, and anti-disturbance ability is stronger.
5th, the input voltage range that BUCK-LLC two-stages DC/DC converters are allowed is wider.
Brief description of the drawings
Fig. 1 is BUCK-LLC two-stages DC-DC converter topological structure of the invention.
Fig. 2 is the double -loop control block diagram that the present invention is used for BUCK-LLC two-stages DC-DC converter.
Fig. 3 is LLC resonant converter switching tube Q1 both end voltages u in the present inventiondsAnd ugsSimulation waveform.
Fig. 4 is the voltage u of LLC resonant converter A, B point-to-point transmission in the present inventionABSimulation waveform.
Fig. 5 is LLC resonant converter resonant inductance L in the present inventionrElectric current iLrWith flow through transformer T excitation inductance currents iLmSimulation waveform.
Fig. 6 is the driving voltage u at BUCK converter switches pipe S1 and S2 two ends in the present invention when input voltage is 60Vgs Simulation waveform.
Fig. 7 is the BUCK-LLC 2 stage converter output voltages U in the present invention when input voltage is 60V0Simulation waveform
Fig. 8 is the driving voltage u at BUCK converter switches pipe S1 and S2 two ends in the present invention when input voltage is 30Vgs Simulation waveform.
Fig. 9 is the BUCK-LLC 2 stage converter output voltages U in the present invention when input voltage is 30V0Simulation waveform
Specific embodiment
The present invention is described in further detail below in conjunction with the accompanying drawings.
Fig. 1 is circuit topology figure of the invention, it may be seen that circuit topological structure involved in the present invention is two-stage knot Structure, prime BUCK converters include DC input voitage Vin, switching tube S1, switching tube S2, inductance LBUCK, output capacitance Cin；Afterwards Level LLC converters include switching tube Q1, switching tube Q2, switching tube Q3, switching tube Q4, resonant inductance Lr, resonant capacitance Cr, high frequency Transformer T, diode DR1, diode DR2, output capacitance C0, output load resistance R0。
The colelctor electrode connection input voltage V of switching tube S1inPositive pole, the hair of the colelctor electrode connecting valve pipe S1 of switching tube S2 Emitter-base bandgap grading, the emitter stage connection DC input voitage V of switching tube S2inNegative pole, the inductance L of BUCK convertersBUCKOne end connection is opened The emitter stage of pipe S1 and the intersection point of switching tube S2 colelctor electrodes are closed, the other end connects the output capacitance C of BUCK convertersinPositive pole, The output capacitance C of BUCK convertersinNegative pole connection input voltage VinThe intersection point of negative pole and switching tube S2 emitter stages；LLC is converted Device switching tube Q1 and Q3 head and the tail are connected, i.e. the colelctor electrode connection LLC converter input capacitances C of switching tube Q1inPositive pole, switching tube The emitter stage of the colelctor electrode connecting valve pipe Q1 of Q3, the emitter stage of switching tube Q3 connects the output capacitance C of BUCK convertersinIt is negative Pole；LLC converter switches pipes Q2 and Q4 head and the tail are connected, i.e. the colelctor electrode of switching tube Q2 connects the output capacitance C of BUCK convertersin Positive pole, the colelctor electrode of the emitter stage connecting valve pipe Q4 of switching tube Q2, the emitter stage connection LLC converters input of switching tube Q4 Electric capacity CinNegative pole；The intersection point of switching tube Q1 emitter stages and switching tube Q3 colelctor electrodes is drawn as A points, switching tube Q2 emitter stages with The intersection point of switching tube Q4 colelctor electrodes is drawn as B points；The resonant inductance L of LLC convertersrOne end connects A points, and other end connection is high The primary side positive pole on frequency power transformer T sides, the negative pole connection LLC converter resonant capacitances C of high frequency transformer T primary sidesrOne end, LLC Converter resonant capacitance CrThe other end connection B points；High frequency transformer T secondary carries centre cap, and LLC is defeated for centre cap connection Go out electric capacity C0Negative pole, high frequency transformer T secondary cathode connecting diodes DR1Positive pole, high frequency transformer T secondary negative pole connection Diode DR2Positive pole, diode DR1Negative pole and diode DR2Negative pole be connected；Diode DR1Negative pole and diode DR2It is negative The intersection point connection LLC converter output capacitances C of pole0Positive pole；Load resistance R0Positive pole connection LLC converter output capacitances C0's Positive pole, load resistance R0Negative pole meets LLC converter output capacitances C0Negative pole；The voltage U at load resistance two ends0It is LLC converters Output voltage.
Relevant PSIM simulation softwares electric parameter when the present invention is implemented sets as follows：BUCK converter DC input voitages VinIt is 60V, BUCK converter inductance LBUCKIt is 1.5mH, BUCK converter switches frequencies 20KHz.LLC converter resonant inductances Lr It is 10uH, LLC converter resonant capacitances CrIt is 220nF, LLC converter switches pipes Q1, switching tube Q2, switching tube Q3, switching tube Q4 switching frequencies are 70KHz, and dutycycle is 50%, and transformer voltage ratio is 3:1:1.
Control method of the invention is included to BUCK-LLC two-stages DC/DC converters output voltage and BUCK converter inductance The sampling of electric current, key step is as follows：
Step 1, calculates the resonant frequency f of LLC converters resonant inductance and resonant capacitancer, its expression formula is as follows：
Wherein, LrIt is the resonant inductance of LLC converters, CrIt is the resonant capacitance of LLC converters.
Step 2, set the switching tube Q1 of LLC converters, switching tube Q2, switching tube Q3, switching tube Q4 as fixed frequency and The opened loop control of dutycycle, switching frequency fs is resonant frequency fr.As shown in Fig. 2 switching tube switching frequency is in the present invention 100KHz, dutycycle is 50%.The output voltage U of BUCK-LLC two-stage DC/DC converters is gathered using difference channel0, utilize Current sensor collection BUCK converter inductive currents iBUCK。
Step 3, the output voltage U of the two-stage DC/DC converters that step 2 is obtained0With given two-stage DC/DC converters Output voltage reference value U0-refSubtract each other and obtain voltage-regulation error e rrV, voltage-regulation error e rrV is obtained by pi regulator To BUCK converter inductive currents iBUCKReference signal iBUCK-ref, expression is as follows：
ErrV=U0-U0_ref
iBUCK_ref=KpverrV+Kiv ∫ errVdt
Wherein Kpv is the proportionality coefficient of voltage error pi regulator, is in this embodiment 0.5；Kiv is adjusted for voltage error PI The integral coefficient of device is saved, is in this embodiment 0.01；T is the time of integration.
Step 4, the BUCK converter inductive currents i for first obtaining step 3BUCKReference signal iBUCK-refAdopted with step 2 The BUCK converter inductive currents i that sample is obtainedBUCKSubtract each other and obtain current regulation error errI, then by current regulation error ErrI is by pi regulator, the modulation wave signal to obtaining the driving of BUCK converter switches pipe after pi regulator output signal amplitude limit Temp, expression is as follows：
ErrI=iBUCK-iBUCK_ref
Temp=KpierrI+Kii ∫ errIdt
Wherein Kpi is the proportionality coefficient of current error pi regulator, is in the present invention 23.674；Kii is current error The integral coefficient of pi regulator, is in the present invention 2.26064.
Step 5, setting BUCK converter drive signals EPWM1 and EPWM2 is complementary, i.e. BUCK converter switches pipe S1 and open The complementary conductings of pipe S2 are closed, modulation wave signal temp and the triangular wave carrier that step 4 is obtained are compared, when modulation wave signal width Value exports high level when being more than triangular carrier amplitude, and low level is exported when modulation wave signal amplitude is less than triangular carrier amplitude, When modulation wave signal amplitude is equal to triangular carrier amplitude, output level keeps constant, it is hereby achieved that BUCK converter switches The drive signal EPWM1 and EPWM2 of pipe S1 and switching tube S2.
In the present embodiment, the frequency of triangular carrier is BUCK converter switches frequencies, is 20KHz in the present embodiment.Three The amplitude of angle carrier wave is the input voltage of BUCK-LLC two-stage DC/DC converters, i.e. BUCK converters DC input voitage Vin, It is 60V in the present invention.
Fig. 3 is LLC converter switches pipe Q1 voltages udsAnd ugsSimulation waveform waveform, as can be seen from the figure switching tube Driving voltage ugsWith the voltage u at switching tube two endsdsWithout intersecting, the function of Sofe Switch is realized.U in Fig. 4ABFor LLC is converted The square-wave voltage of device inversion output.LLC converters exciting current and resonance current can be seen that LLC converters work from Fig. 5 At resonant inductance and resonant capacitance two elements resonant frequency.It can be seen that when input voltage is dropped to by 60V in Fig. 6,7,8,9 During 30V, by adjusting the dutycycle of BUCK converter switches pipes, BUCK-LLC two-stage DC/DC converters can be still caused Output voltage keeps stabilization, by lab diagram it can be seen that BUCK-LLC two-stages DC/DC inverter control methods proposed by the present invention With input voltage regulation ability wider.

Claims (4)

1. it is a kind of to be based on the BUCK-LLC bicyclic fixed-frequency control methods of two-stage DC/DC converters, it is characterised in that involved in the present invention Circuit topological structure is two-layer configuration, and prime BUCK converters include DC input voitage Vin, switching tube S1, switching tube S2, electricity Sense LBUCK, output capacitance Cin；Rear class LLC converters include switching tube Q1, switching tube Q2, switching tube Q3, switching tube Q4, resonance electricity Sense Lr, resonant capacitance Cr, high frequency transformer T, diode DR1, diode DR2, output capacitance C0, output load resistance R0；
The colelctor electrode connection input voltage V of switching tube S1inPositive pole, the transmitting of the colelctor electrode connecting valve pipe S1 of switching tube S2 Pole, the emitter stage connection DC input voitage V of switching tube S2inNegative pole, the inductance L of BUCK convertersBUCKOne end connecting valve The emitter stage of pipe S1 and the intersection point of switching tube S2 colelctor electrodes, the other end connect the output capacitance C of BUCK convertersinPositive pole, The output capacitance C of BUCK convertersinNegative pole connection input voltage VinThe intersection point of negative pole and switching tube S2 emitter stages；
LLC converter switches pipe Q1 and switching tube Q3 head and the tail are connected, i.e. the colelctor electrode connection LLC converter input electricity of switching tube Q1 Hold CinPositive pole, the emitter stage of the colelctor electrode connecting valve pipe Q1 of switching tube Q3, switching tube Q3 emitter stage connection BUCK conversion The output capacitance C of deviceinNegative pole；LLC converter switches pipes Q2 and Q4 head and the tail are connected, i.e. the colelctor electrode connection BUCK of switching tube Q2 The output capacitance C of converterinPositive pole, the colelctor electrode of the emitter stage connecting valve pipe Q4 of switching tube Q2, the transmitting of switching tube Q4 Pole connects LLC converter input capacitances CinNegative pole；Switching tube Q1 emitter stages are drawn as A with the intersection point of switching tube Q3 colelctor electrodes Point, switching tube Q2 emitter stages are drawn as B points with the intersection point of switching tube Q4 colelctor electrodes；The resonant inductance L of LLC convertersrOne end Connection A points, the primary side positive pole on other end connection high frequency transformer T sides, the primary side negative pole connection LLC converters of high frequency transformer T Resonant capacitance CrOne end, LLC converter resonant capacitances CrThe other end connection B points；High frequency transformer T secondary is taken out with center Head, centre cap connection LLC output capacitances C0Negative pole, high frequency transformer T secondary cathode connecting diodes DR1Positive pole, high frequency Transformer T secondary negative pole connection diode DR2Positive pole, diode DR1Negative pole and diode DR2Negative pole be connected；Diode DR1Negative pole and diode DR2The intersection point connection LLC converter output capacitances C of negative pole0Positive pole；Load resistance R0Positive pole connects LLC Converter output capacitance C0Positive pole, load resistance R0Negative pole meets LLC converter output capacitances C0Negative pole；Load resistance two ends Voltage U0It is the output voltage of LLC converters；
This control method includes adopting BUCK-LLC two-stages DC/DC converters output voltage and BUCK converter inductive currents Sample, key step is as follows：
Step 1, calculates the resonant inductance of LLC converters and the resonant frequency f of resonant capacitancer, its expression formula is as follows：
f r = 1 2 π L r · C r
Wherein, LrIt is the resonant inductance of LLC converters, CrIt is the resonant capacitance of LLC converters；
Step 2, sets LLC converter switches pipes Q1, switching tube Q2, switching tube Q3, the switching frequency fs of switching tube Q4 as step 1 The resonant frequency f for obtainingr, the output voltage U of BUCK-LLC two-stage DC/DC converters is gathered using difference channel0, using electric current Sensor collection BUCK converter inductive currents iBUCK；
Step 3, the output voltage U of the two-stage DC/DC converters that step 2 is obtained0It is defeated with given two-stage DC/DC converters Go out voltage reference value U0-refSubtract each other and obtain voltage-regulation error e rrV, voltage-regulation error e rrV is obtained by pi regulator BUCK converter inductive currents iBUCKReference signal iBUCK-ref,
ErrV=U0-U0_ref
iBUCK_ref=KpverrV+Kiv ∫ errVdt
Wherein Kpv is the proportionality coefficient of voltage error pi regulator, and Kiv is the integral coefficient of voltage error pi regulator, and t is product Between timesharing.
Step 4, the BUCK converter inductive currents i for first obtaining step 3BUCKReference signal iBUCK-refSampled with step 2 The BUCK converter inductive currents i for arrivingBUCKSubtract each other and obtain current regulation error errI, then by current regulation error errI By pi regulator, the modulation wave signal to obtaining the driving of BUCK converter switches pipe after pi regulator output signal amplitude limit Temp,
ErrI=iBUCK-iBUCK_ref
Temp=KpierrI+Kii ∫ errIdt
Wherein Kpi is the proportionality coefficient of current error pi regulator, and Kii is the integral coefficient of current error pi regulator, and t is product Between timesharing；
Step 5, modulation wave signal temp and the triangular wave carrier that step 4 is obtained is compared, when modulation wave signal amplitude is big High level is exported when triangular carrier amplitude, low level is exported when modulation wave signal amplitude is less than triangular carrier amplitude, work as tune Output level keeps constant when ripple signal amplitude processed is equal to triangular carrier amplitude, it is hereby achieved that BUCK converter switches pipes S1 With the drive signal EPWM1 and EPWM2 of switching tube S2.
2. according to claim 1 based on the BUCK-LLC bicyclic fixed-frequency control methods of two-stage DC/DC converters, its feature exists In the switching tube Q1 of the LLC converters in step 2, switching tube Q2, switching tube Q3, switching tube Q4 are fixed frequency and dutycycle Opened loop control.
3. according to claim 1 based on the BUCK-LLC bicyclic fixed-frequency control methods of two-stage DC/DC converters, its feature exists In BUCK converter the drive signals EPWM1 and EPWM2 in step 5 are complementary, i.e. BUCK converter switches pipe S1 and switching tube S2 Complementation conducting.
4. according to claim 1 based on the BUCK-LLC bicyclic fixed-frequency control methods of two-stage DC/DC converters, its feature exists In the frequency of step 5 intermediate cam carrier wave is BUCK converter switches frequencies, and triangular carrier amplitude is input into for BUCK converters direct current Voltage Vin。
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