CN111313714A - Full-bridge LLC resonant converter resonant frequency tracking method and system - Google Patents
Full-bridge LLC resonant converter resonant frequency tracking method and system Download PDFInfo
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- CN111313714A CN111313714A CN202010127538.4A CN202010127538A CN111313714A CN 111313714 A CN111313714 A CN 111313714A CN 202010127538 A CN202010127538 A CN 202010127538A CN 111313714 A CN111313714 A CN 111313714A
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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
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/0048—Circuits or arrangements for reducing losses
- H02M1/0051—Diode reverse recovery losses
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- 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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Abstract
The invention relates to a method and a system for tracking the resonant frequency of a full-bridge LLC resonant converter, wherein the method comprises the following steps: collecting secondary side rectifier diode current iD(ii) a Calculating the secondary side rectifier diode current iDInstantaneous value t of the off-timeDiscontinuous(ii) a Adjusting the switching frequency f of the full-bridge LLC resonant converter to make the secondary side rectifying diode current iDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous‑refRealize the resonant frequency f to LLCrThe tracking of (2). The method is carried out by adjusting the switching frequency f to the resonance frequency frAt or resonant frequency frAnd on the left side, the resonant converter works in an optimal region, the full-bridge switching tube realizes zero voltage switching-on, and the secondary rectifier diode has no reverse recovery, so that the system loss is reduced, and the system efficiency is improved. The method can effectively solve the problems of resonance frequency and theory of batch products caused by self parameter precision of resonance devices, different device combination modes, line distribution parameters and the likeThe parameter difference of the resonance frequency, the resonance frequency change caused by the attenuation of the device parameters and the like.
Description
Technical Field
The invention belongs to the field of LLC resonant converters, and particularly relates to a method and a system for tracking resonant frequency of a full-bridge LLC resonant converter.
Background
The full-bridge LLC resonant converter topology principle is shown in fig. 1, and it usually adopts frequency conversion (PFM) or fixed frequency phase shift (PWM) control method, and whichever control method is adopted, it needs to accurately determine the resonant frequency point of the converter, and it is desirable that the resonant frequency is a fixed constant, so as to control the resonant converter to work in the optimal resonant frequency region. For batch products, the resonant frequency is generally controlled within an ideal range by improving the precision of resonant devices such as resonant capacitors, resonant inductors, excitation inductors and the like, screening device combinations, optimizing device layout and wiring modes. However, the parameters of the resonant device can change in the long-time use process, especially the capacitance value of the resonant capacitor can be attenuated, and in addition, the existence of the stray inductance of the main circuit cable and the copper bar leads to the fact that the resonant frequency of the resonant converter can not be continuously and accurately obtained in the practical application process. From the resonant frequency calculation formula:
it can be known that the actual resonant frequency of the full-bridge LLC resonant converter may be higher or lower than the ideal value, frIs the resonant frequency, LrIs a resonant inductor, CrIs a resonant capacitor.
When the resonant frequency is less than the switching frequency, the secondary side rectifier diode has the problem of reverse recovery, and when the resonant frequency is greater than the switching frequency, the secondary side current has longer interrupted time, larger output current ripple and larger invalid area for phase-shifting control. In the current engineering application, real-time tracking control of the resonant frequency of the full-bridge LLC resonant converter is lacked, so that a method for tracking the resonant frequency of the full-bridge LLC resonant converter is needed.
Disclosure of Invention
The invention provides a method and a system for tracking resonant frequency of a full-bridge LLC resonant converter aiming at the LLC resonant converter, so that a controller can effectively track parameter change of the resonant frequency, and the controller can adjust the switching frequency to enable the resonant converter to work in an optimal region.
In order to achieve the above object, the present invention provides a method for tracking resonant frequency of a full-bridge LLC resonant converter, including:
collecting secondary side rectifier diode current iD；
Calculating the secondary side rectifier diode current iDInstantaneous value t of the off-timeDiscontinuous；
Adjusting the switching frequency f of the full-bridge LLC resonant converter to make the secondary side rectifying diode current iDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refRealize the resonant frequency f to LLCrThe tracking of (2).
Preferably, the secondary rectifier diode current i is calculatedDInstantaneous value t of the off-timeDiscontinuousThe method comprises the following steps:
for collected secondary side rectifying diode current iDPerforming first-order low-pass filtering, and calculating the current value i of the secondary side rectifier diode after filteringD-filter；
Judging the current value i of the secondary side rectifier diode after filteringD-filterWhether the current value is less than a given target value of the rectifier diode or not, if the current value is less than the target value, the current value i of the secondary side rectifier diode is filteredD-filterIf the current is less than the target value of the given rectifier diode, the current i of the secondary rectifier diode is determinedDThe value is 0, and the secondary side rectifier diode is in an intermittent state;
calculating the current i of the secondary side rectifier diode by a timing counting methodDSecondary rectifier diode current i at 0DInstantaneous value t of the off-timeDiscontinuous。
Preferably, the switching frequency f of the full-bridge LLC resonant converter is adjusted to enable the secondary side to rectify the diode current iDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refThe method comprises the following steps:
calculating the secondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-ref；
Rectifying the diode current i with the secondary sideDInstantaneous value t of the off-timeDiscontinuousSecondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-refSecondary side rectifier diode current iDOff-time compensation value t ofCompensateFor input variables of PI controller, with switching frequency f and initial switching frequency f0PI modulation is carried out for the output variable of the PI controller, the switching frequency f is adjusted, and the secondary side rectifying diode current i is causedDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-ref。
Preferably, the secondary rectifier diode current i is calculatedDReference value t of on-off timeDiscontinuous-refThe method comprises the following steps:
according to the formula:
determining secondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-ref；
Wherein: d is the phase-shifted full-bridge duty cycle, tDead-zoneIs the PWM dead time.
The invention also provides a system for tracking the resonant frequency of the full-bridge LLC resonant converter, which comprises:
the secondary side current sensor is arranged at the front end of the output filter capacitor of the resonant converter and used for collecting the current of the secondary side rectifier diode;
and the main control unit is connected with the secondary side current sensor and the LLC resonant converter and used for calculating the instantaneous value of the interrupted time of the secondary side rectifier diode current and adjusting the switching frequency of the full-bridge LLC resonant converter to enable the instantaneous value of the interrupted time of the secondary side rectifier diode current to be equal to the reference value of the interrupted time of the secondary side rectifier diode current, so that the LLC resonant frequency is tracked.
Preferably, the main control unit includes:
a filtering unit: for rectifying diode current i on secondary side of collectionDPerforming first-order low-pass filtering, and calculating the current value of the secondary side rectifier diode after filtering;
a secondary side rectifier diode intermittent state determination unit: the secondary side rectifier diode current value detection circuit is used for judging whether the current value of the secondary side rectifier diode after filtering is smaller than a given rectifier diode target value or not, and if the current value of the secondary side rectifier diode after filtering is smaller than the given rectifier diode target value, determining that the current of the secondary side rectifier diode is 0 and the secondary side rectifier diode is in an intermittent state;
instantaneous value of on-off time calculation unit: the method is used for calculating the instantaneous value of the on-off time of the secondary side rectifier diode current when the secondary side rectifier diode current is 0 by a timing counting method.
Preferably, the main control unit further includes:
discontinuous time reference value calculation unit: the reference value of the break-make time of the current of the secondary side rectifier diode is calculated;
a PI controller: the method is used for performing PI modulation by taking the instantaneous value of the on-off time of the secondary side rectifying diode current, the reference value of the on-off time of the secondary side rectifying diode current and the compensation value of the on-off time of the secondary side rectifying diode current as input variables of a PI controller and taking the switching frequency and the initial switching frequency as output variables of the PI controller, and adjusting the switching frequency to enable the instantaneous value of the on-off time of the secondary side rectifying diode current to be equal to the reference value of the on-off time of the secondary side rectifying diode current.
Preferably, the main control unit adopts a high main frequency controller.
Compared with the prior art, the invention has the advantages and positive effects that:
the invention provides a method for tracking the resonant frequency of a full-bridge LLC resonant converter, which collects the current i of a secondary side rectifier diodeDCalculating the secondary side rectifier diode current iDInstantaneous value t of the off-timeDiscontinuousAdjusting the switching frequency f of the full-bridge LLC resonant converter to make the secondary side rectifying diode currentiDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refCan realize the resonant frequency f of LLCrThe tracking of (2). Adjusting the switching frequency f to a resonant frequency frAt or resonant frequency frAnd on the left side, the resonant converter works in an optimal region, the full-bridge switching tube realizes zero voltage switching-on, and the secondary rectifier diode has no reverse recovery problem, so that the system loss is reduced, and the system efficiency is improved. The method can effectively solve the problem of parameter difference between the resonant frequency of batch products and the resonant frequency of theoretical design caused by the self parameter precision of the resonant devices, different device combination modes, line distribution parameters and the like, can simultaneously solve the resonant frequency change caused by device parameter attenuation, and has strong practicability. Meanwhile, the invention also provides a corresponding full-bridge LLC resonant converter resonant frequency tracking system according to the method.
Drawings
FIG. 1 is a schematic diagram of a full-bridge LLC resonant converter topology;
FIG. 2 is a flow chart of a method for tracking the resonant frequency of the full-bridge LLC resonant converter according to the invention;
FIG. 3 is a schematic diagram of a full-bridge LLC resonant converter topology with an additional secondary current sensor according to an embodiment of the present invention;
FIG. 4 shows the resonance frequency frA full-bridge LLC resonant converter oscillogram when the switching frequency f is less than the switching frequency f;
FIG. 5 shows the resonant frequency frWhen the switching frequency f is greater than the full-bridge LLC resonant converter oscillogram;
FIG. 6 is a block diagram of a resonant frequency tracking control using PI control;
FIG. 7 is a graph of simulation results (initial switching frequency 15kHz) using the resonant frequency tracking method of the present invention;
FIG. 8 is a graph of simulation results (initial switching frequency 26kHz) using the resonant frequency tracking method of the present invention;
fig. 9 is a block diagram of a full-bridge LLC resonant converter resonant frequency tracking system.
Detailed Description
In order to make the technical solutions of the present invention better understood by those skilled in the art, the technical solutions in the embodiments of the present invention will be clearly described below with reference to the drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The terms "comprises" and "comprising," and any variations thereof, in the description and claims of this invention and the above-described drawings are intended to cover non-exclusive inclusions. For example, a process, method, or system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus. Furthermore, the terms "first," "second," and "third," etc. are used to distinguish between different objects and are not used to describe a particular order.
An embodiment of the present invention provides a method for tracking a resonant frequency of a full-bridge LLC resonant converter, as shown in fig. 2, which includes the following steps:
(1) collecting secondary side rectifier diode current iD；
The method specifically comprises the following steps: referring to FIG. 3, a filter capacitor C is provided at the output of the resonant converterfA secondary current sensor is additionally arranged at the front end to measure the current i of a secondary rectifier diodeD. The controller needs to have a higher system frequency to realize the secondary side rectifying diode current iDHigh-speed acquisition. Therefore, in the embodiment, a high-main-frequency DSP or FPGA controller can be adopted to acquire the current i of the secondary side rectifier diode at a high speedDFor example, to achieve 1% tracking accuracy, the AD acquisition frequency is set to be 4MHz or higher, taking the resonant frequency of 20kHz as an example.
(2) Calculating the secondary side rectifier diode current iDInstantaneous value t of the off-timeDiscontinuous；
The method specifically comprises the following steps: for preventing secondary side rectifying diode currentiDThe collection includes noise interference, and the collected secondary side rectifier diode current iDPerforming first-order low-pass filtering, and calculating the current value i of the secondary side rectifier diode after filteringD-filter；
Judging the current value i of the secondary side rectifier diode after filteringD-filterWhether the current value is less than a given target value of the rectifier diode or not, if the current value is less than the target value, the current value i of the secondary side rectifier diode is filteredD-filterIf the current is less than the target value of the given rectifier diode, the current i of the secondary rectifier diode is determinedDThe value is 0, and the secondary side rectifier diode is in an intermittent state;
calculating the secondary side rectifier diode current i by a method of software counting timing or programmable counter/timer timing countingDSecondary rectifier diode current i at 0DInstantaneous value t of the off-timeDiscontinuous。
(3) Adjusting the switching frequency f of the full-bridge LLC resonant converter to make the secondary side rectifying diode current iDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refRealize the resonant frequency f to LLCrThe tracking of (2).
The method specifically comprises the following steps:
the principle of resonant frequency tracking will be explained in two cases:
① at resonant frequency frWhen the frequency is less than the switching frequency f, the bridge arm pair tube is conducted simultaneously with the resonant current i in the periodLrAnd an excitation current iLmAre not equal. Referring to FIGS. 3 and 4, uQ1、uQ2、uQ3、uQ4Respectively, the driving signals of the switching tubes Q1, Q2, Q3 and Q4. t is t1At the moment, the switching tubes Q1 and Q4 are simultaneously conducted, and then LrAnd CrResonance, resonant current iLrGreater than the exciting current iLmThe secondary diode D1 is conducted, the primary side transmits energy to the load, the exciting inductor is clamped by the output voltage, and the exciting current iLmLinear increase; t is t2At the moment, due to the resonant frequency frLess than the switching frequency f, so that the resonant current i is now presentLrIs still greater than the exciting current iLmThe switching tube Q1 is turned off, and then the resonant current iLrIs pulled down rapidly; t is t3Time of day, resonant current iLrIs equal to the excitation current iLmThe secondary diode D1 turns off, but due to the sudden change in current, it causes a reverse recovery problem, after which Lr、CrAnd LmResonating; t is t4At this time, the switching tubes Q2 and Q3 are turned on simultaneously, and enter the next half of the switching period, which is not described in detail herein.
At this time, the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refThe determination is as follows:
tDiscontinuous-ref＝tD+tDead-zone
wherein: d is the phase-shifted full-bridge duty cycle, tDead-zoneIs the PWM dead time.
If the resonant frequency f is to be realizedrWhen Q1 is desired to be turned off, the secondary side rectifying diode current iDJust beginning to make contact, i.e. LrAnd CrEnd of resonance, Lr、CrAnd LmStarting resonance, i.e. desiring the secondary-side rectifying diode current iDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refI.e. tDiscontinuous＝tDiscontinuous-ref. Resonant frequency frWhen the frequency is less than the switching frequency f, the secondary side rectifier diode current iDInstantaneous value t of the off-timeDiscontinuousLess than secondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-refI.e. tDiscontinuous<tDiscontinuous-refTo track the resonant frequency, the switching frequency f needs to be reduced.
② at resonant frequency frWhen the frequency is greater than the switching frequency f, the bridge arm pair tube is conducted simultaneously with the resonant current i in the periodLrIs equal to the excitation current iLm. Referring to FIGS. 3, 5, t1At the moment, the switching tubes Q1 and Q4 are simultaneously conducted, and then LrAnd CrResonance, resonant current iLrGreater than the exciting current iLmThe secondary diode D1 is conducted, the primary side transmits energy to the load, the exciting inductor is clamped by the output voltage, and the exciting current iLmLinear increase; t is t2At the moment, due to the resonant frequency frGreater than the switching frequency f, before the switching tube Q1 is turned off, the resonant current iLrIs equal to the excitation current iLmThe secondary diode D1 turns off current naturally zero-crossing without reverse recovery problem, then Lr、CrAnd LmResonating; t is t3At the moment, the switching tube Q1 is turned off, and the resonant current iLrIs still equal to the excitation current iLm，Lr、CrAnd LmContinuing to resonate, and turning off a switching tube Q1; t is t4At this time, the switching tubes Q2 and Q3 are turned on simultaneously, and enter the next half of the switching period, which is not described in detail herein. Resonant frequency frWhen the frequency is greater than the switching frequency f, the secondary side rectifier diode current iDInstantaneous value t of the off-timeDiscontinuousGreater than secondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-refI.e. tDiscontinuous>tDiscontinuous-refTo track the resonant frequency, the switching frequency f needs to be increased.
Through the analysis, in the embodiment, the switching frequency f of the full-bridge LLC resonant converter can be adjusted by adopting the PI controller, and the current i of the secondary side rectifier diodeDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refI.e. tDiscontinuous＝tDiscontinuous-refThe control block diagram is shown in fig. 6. I.e. rectifying the diode current i with the secondary sideDInstantaneous value t of the off-timeDiscontinuousSecondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-refSecondary side rectifier diode current iDOff-time compensation value t ofCompensateFor input variables of PI controller, with switching frequency f and initial switching frequencyf0PI modulation is carried out for the output variable of the PI controller, the switching frequency f is adjusted, and the secondary side rectifying diode current i is causedDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-ref. In practical design, the secondary side rectifier diode current iDOff-time compensation value t ofCompensateCan be 0 or a small positive number according to the requirement, so that the switching frequency f can be adjusted to the resonance frequency point frAnd near the resonant frequency point. Phase-shifted full-bridge duty cycle D and PWM dead time tDead-zoneThe tracking precision is influenced, the larger the duty ratio D is, the dead time tDead-zoneThe smaller the tracking accuracy, the closer the switching frequency f is to the resonance frequency fr. In the actual design, the dead time t should be minimizedDead-zoneAt the same time, resonant frequency tracking may be initiated when the duty cycle D is greater than 0.98.
The effect of the resonant frequency tracking method provided by the invention is verified by taking a certain 25kW full-bridge LLC resonant converter as an example.
A simulation model is set up under the Simulink environment, and the actual resonant frequency f of the full-bridge LLC resonant converterr22.97kHz, PWM dead time 0.5us, and compensation quantity tCompensateAnd the duty ratio of the phase-shifted full bridge is 0.3us, and the resonance frequency tracking is started when the duty ratio of the phase-shifted full bridge is equal to 1.
As shown in fig. 7 and 8, the simulation results show that the initial switching frequency f is 15kHz and 26kHz, and the resonant frequency tracking is started when the initial switching frequency f is 0.6, the tracking of the resonant frequency is completed within 0.5s, the switching frequency converges to 22.12kHz, the simulation realizes the fast tracking of the resonant frequency, and the switching frequency is close to the resonant frequency and is located on the left side of the resonant frequency point.
Therefore, in summary, the resonant frequency tracking method of the full-bridge LLC resonant converter provided by the invention collects the current i of the secondary side rectifier diodeDCalculating the secondary side rectifier diode current iDInstantaneous value t of the off-timeDiscontinuousAdjusting the switching frequency f of the full-bridge LLC resonant converter to make the secondary side rectifying diode current iDInstantaneous value of the off-timetDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refCan realize the resonant frequency f of LLCrThe tracking of (2). Adjusting the switching frequency f to a resonant frequency frAnd the resonant converter works in an optimal region at the left side of a resonant frequency point, the full-bridge switching tube realizes zero voltage switching-on, and the secondary rectifier diode has no reverse recovery problem, so that the system loss is reduced, and the system efficiency is improved. The method can effectively deal with the difference of resonance frequency difference of batch products caused by the precision of resonance devices such as resonance capacitors, resonance inductors, excitation inductors and the like, device combination, line distribution parameters and the like, and can deal with the resonance frequency change caused by the attenuation of device parameters, thereby having strong practicability.
Meanwhile, the invention also provides a corresponding full-bridge LLC resonant converter resonant frequency tracking system according to the method, as shown in fig. 9, specifically:
a secondary side current sensor arranged at the front end of the output filter capacitor of the resonant converter and used for collecting the current i of the secondary side rectifier diodeD；
The main control unit is connected with the secondary side current sensor and the LLC resonant converter and used for calculating the current i of the secondary side rectifier diodeDInstantaneous value t of the off-timeDiscontinuousAdjusting the switching frequency f of the full-bridge LLC resonant converter to make the secondary side rectifying diode current iDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refRealize the resonant frequency f to LLCrThe tracking of (2).
Wherein, the main control unit includes:
a filtering unit: for rectifying diode current i on secondary side of collectionDPerforming first-order low-pass filtering, and calculating the current value i of the secondary side rectifier diode after filteringD-filter；
A secondary side rectifier diode intermittent state determination unit: used for judging the current value i of the secondary side rectifier diode after filteringD-filterWhether less than a given target value for the rectifier diode, if so, the filtered pairSide rectifier diode current value iD-filterIf the current is less than the target value of the given rectifier diode, the current i of the secondary rectifier diode is determinedDThe value is 0, and the secondary side rectifier diode is in an intermittent state;
instantaneous value of on-off time calculation unit: for calculating secondary-side rectifier diode current i by means of a timed counting methodDSecondary rectifier diode current i at 0DInstantaneous value t of the off-timeDiscontinuous。
Discontinuous time reference value calculation unit: for calculating the secondary rectifier diode current iDReference value t of on-off timeDiscontinuous-ref；
A PI controller: for rectifying diode current i with secondary sideDInstantaneous value t of the off-timeDiscontinuousSecondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-refSecondary side rectifier diode current iDOff-time compensation value t ofCompensateFor input variables of PI controller, with switching frequency f and initial switching frequency f0PI modulation is carried out for the output variable of the PI controller, the switching frequency f is adjusted, and the secondary side rectifying diode current i is causedDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-ref。
Claims (8)
1. A method for tracking resonant frequency of a full-bridge LLC resonant converter is characterized by comprising the following steps:
collecting secondary side rectifier diode current iD；
Calculating the secondary side rectifier diode current iDInstantaneous value t of the off-timeDiscontinuous；
Adjusting the switching frequency f of the full-bridge LLC resonant converter to make the secondary side rectifying diode current iDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refRealize the resonant frequency f to LLCrThe tracking of (2).
2. The full-bridge LLC resonant converter resonant frequency tracking method according to claim 1, wherein a secondary side rectifier diode current i is calculatedDInstantaneous value t of the off-timeDiscontinuousThe method comprises the following steps:
for collected secondary side rectifying diode current iDPerforming first-order low-pass filtering, and calculating the current value i of the secondary side rectifier diode after filteringD-filter；
Judging the current value i of the secondary side rectifier diode after filteringD-filterWhether the current value is less than a given target value of the rectifier diode or not, if the current value is less than the target value, the current value i of the secondary side rectifier diode is filteredD-filterIf the current is less than the target value of the given rectifier diode, the current i of the secondary rectifier diode is determinedDThe value is 0, and the secondary side rectifier diode is in an intermittent state;
calculating the current i of the secondary side rectifier diode by a timing counting methodDSecondary rectifier diode current i at 0DInstantaneous value t of the off-timeDiscontinuous。
3. The full-bridge LLC resonant converter resonant frequency tracking method according to claim 1 or 2, wherein the switching frequency f of the full-bridge LLC resonant converter is adjusted to make the secondary side rectifying diode current iDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-refThe method comprises the following steps:
calculating the secondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-ref；
Rectifying the diode current i with the secondary sideDInstantaneous value t of the off-timeDiscontinuousSecondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-refSecondary side rectifier diode current iDOff-time compensation value t ofCompensateFor input variables of PI controller, with switching frequency f and initial switching frequency f0PI modulation is carried out for the output variable of the PI controller, the switching frequency f is adjusted,rectifying the secondary side with a diode current iDInstantaneous value t of the off-timeDiscontinuousEqual to the secondary side rectifying diode current iDReference value t of on-off timeDiscontinuous-ref。
4. The full-bridge LLC resonant converter resonant frequency tracking method according to claim 3, wherein a secondary side rectifier diode current i is calculatedDReference value t of on-off timeDiscontinuous-refThe method comprises the following steps:
according to the formula:
determining secondary side rectifier diode current iDReference value t of on-off timeDiscontinuous-ref；
Wherein: d is the phase-shifted full-bridge duty cycle, tDead-zoneIs the PWM dead time.
5. A full-bridge LLC resonant converter resonant frequency tracking system, which adopts the full-bridge LLC resonant converter resonant frequency tracking method of any one of claims 1-4, characterized by comprising:
the secondary side current sensor is arranged at the front end of the output filter capacitor of the resonant converter and used for collecting the current of the secondary side rectifier diode;
and the main control unit is connected with the secondary side current sensor and the LLC resonant converter and used for calculating the instantaneous value of the interrupted time of the secondary side rectifier diode current and adjusting the switching frequency of the full-bridge LLC resonant converter to enable the instantaneous value of the interrupted time of the secondary side rectifier diode current to be equal to the reference value of the interrupted time of the secondary side rectifier diode current, so that the LLC resonant frequency is tracked.
6. The full-bridge LLC resonant converter resonant frequency tracking system of claim 5, wherein said master control unit comprises:
a filtering unit: for secondary side of collectionRectifying diode current iDPerforming first-order low-pass filtering, and calculating the current value of the secondary side rectifier diode after filtering;
a secondary side rectifier diode intermittent state determination unit: the secondary side rectifier diode current value detection circuit is used for judging whether the current value of the secondary side rectifier diode after filtering is smaller than a given rectifier diode target value or not, and if the current value of the secondary side rectifier diode after filtering is smaller than the given rectifier diode target value, determining that the current of the secondary side rectifier diode is 0 and the secondary side rectifier diode is in an intermittent state;
instantaneous value of on-off time calculation unit: the method is used for calculating the instantaneous value of the on-off time of the secondary side rectifier diode current when the secondary side rectifier diode current is 0 by a timing counting method.
7. The full-bridge LLC resonant converter resonant frequency tracking system of claim 6, wherein said master control unit further comprises:
discontinuous time reference value calculation unit: the reference value of the break-make time of the current of the secondary side rectifier diode is calculated;
a PI controller: the method is used for performing PI modulation by taking the instantaneous value of the on-off time of the secondary side rectifying diode current, the reference value of the on-off time of the secondary side rectifying diode current and the compensation value of the on-off time of the secondary side rectifying diode current as input variables of a PI controller and taking the switching frequency and the initial switching frequency as output variables of the PI controller, and adjusting the switching frequency to enable the instantaneous value of the on-off time of the secondary side rectifying diode current to be equal to the reference value of the on-off time of the secondary side rectifying diode current.
8. The full-bridge LLC resonant converter resonant frequency tracking system according to any of claims 5 to 7, wherein said master control unit employs a high master frequency controller.
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