CN113131751B - Full-bridge LLC resonant converter resonant frequency tracking method - Google Patents

Full-bridge LLC resonant converter resonant frequency tracking method Download PDF

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CN113131751B
CN113131751B CN202110399169.9A CN202110399169A CN113131751B CN 113131751 B CN113131751 B CN 113131751B CN 202110399169 A CN202110399169 A CN 202110399169A CN 113131751 B CN113131751 B CN 113131751B
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value
resonant frequency
frequency
dead zone
deviation value
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CN113131751A (en
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赵许强
张利军
甄远伟
李海洋
祝博伟
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CRRC Qingdao Sifang Rolling Stock Research Institute Co Ltd
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CRRC Qingdao Sifang Rolling Stock Research Institute Co Ltd
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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
    • 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 for tracking the resonant frequency of a full-bridge LLC resonant converter, which comprises the following steps: configuring the controller at the bottom of the switchTriggering a controller to acquire the advance current value i of the secondary rectifier diode at the given advance time delta t before the tube is turned off at the given advance time delta tD_off(ii) a PI regulates the switching frequency f of the full-bridge LLC resonant converter, and leads the current value i of the secondary side rectifier diodeD_offControlling the resonant frequency f of LLC within a preset target rangerThe tracking of (2). The method can realize the quick tracking of the resonant frequency, the switching frequency is adjusted to the left side of the resonant frequency point and close to the resonant frequency, the resonant converter works in the optimal area, the full-bridge switching tube realizes zero voltage switching-on, and the secondary side rectifier diode has no reverse recovery problem, so that the system loss is reduced, and the system efficiency is improved. Meanwhile, the method can effectively deal with the difference of resonant frequency difference of batch products caused by the precision of resonant devices, device combination, line distribution parameters and the like and the change of resonant frequency caused by the attenuation of device parameters.

Description

Full-bridge LLC resonant converter resonant frequency tracking method
Technical Field
The invention belongs to the technical field of converters, and particularly relates to a resonant frequency tracking method of a full-bridge LLC resonant converter.
Background
The existing full-bridge LLC resonant converter mainly has two control methods: PFM frequency conversion control and PWM fixed frequency phase shift control. Whichever control method is employed requires an accurate determination of the resonant frequency point of the LLC, and it is desirable that the resonant frequency be a fixed constant. For PWM fixed-frequency shift phase control, it is necessary to set the switching frequency to the left of the resonant frequency point and close to the resonant frequency according to the determined resonant frequency point, so that the resonant converter operates in the optimum 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 resonance device can change in the long-time use process, especially the capacitance value of the resonance capacitor can be attenuated, and in addition, stray of cables and copper bars of the main circuitPresence of inductance, formulated by resonant frequency
Figure BDA0003019700710000011
It is known that the actual resonant frequency of the converter may be higher or lower than the ideal design value.
When the resonant frequency is less than the switching frequency, the secondary side rectifier diode has the problem of reverse recovery; when the resonant frequency is higher than the switching frequency, the secondary side current has longer intermittent time, the output current ripple is larger, and the phase-shifting control has a larger invalid region. Therefore, it is necessary to adjust the switching frequency according to the change of the resonant frequency so that the resonant converter operates in the optimum region. Meanwhile, when products are loaded in a large scale, it is impossible to periodically measure the resonant frequency point of the products by a manual measurement method, and a method of automatically tracking the resonant frequency in real time becomes very important.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a full-bridge LLC resonant converter resonant frequency tracking method to determine an LLC resonant frequency point and enable the switching frequency to be close to the resonant frequency.
In order to achieve the above object, the present invention provides a method for tracking resonant frequency of a full-bridge LLC resonant converter, wherein the full-bridge LLC resonant converter adopts PWM fixed-frequency shift phase control, and comprises:
configuring a controller bottom layer, triggering the controller to acquire the leading current value i of the secondary side rectifier diode at a given leading time delta t before the switching tube is switched off at the given leading time delta tD_off；
PI regulates the switching frequency f of the full-bridge LLC resonant converter, and leads the current value i of the secondary side rectifier diodeD_offControlling the resonant frequency f of LLC within a preset target rangerThe tracking of (2).
Preferably, the bottom layer of the controller is configured, and the controller is triggered to acquire the leading current value i of the secondary side rectifier diode at a given leading time delta t before the switching tube is switched offD_offThe method comprises the following steps:
the counting period of the driving of the switching tube is calculated as follows:
Figure BDA0003019700710000021
wherein f isCPUTo count the clock frequency;
setting a first comparison value CMPA driven by the switch tube as follows:
CMPA＝TBPRD×D (2)
when a counting register driven by a configuration switch tube counts to a first comparison value CMPA, level change is carried out, and the switch tube is controlled to be switched from an on state to an off state;
d is the duty ratio of a driving signal of the switching tube;
determining a second comparison value CMPB of the switching tube drive for a given lead time Δ t from the first comparison value CMPA as:
CMPB＝CMPA-Δt×fCPU (3)
when a counting register driven by a configuration switch tube counts to a second comparison value CMPB, a trigger controller acquires the leading current value i of a secondary rectifier diode at a given leading time delta tD_off。
Preferably, if the resonant frequency frGreater than the switching frequency f, the resonant current iLrIs equal to the excitation current iLmLeading current value i of secondary side rectifier diodeD_offTo 0, the switching frequency f is increased to track the resonant frequency.
Preferably, if the resonant frequency frLess than the switching frequency f, the resonant current iLrGreater than the exciting current iLmLeading current value i of secondary side rectifier diodeD_offAbove 0, the switching frequency f is reduced to track the resonant frequency.
Preferably, PI regulates the switching frequency f of the full-bridge LLC resonant converter, and leads the current value i of the secondary side rectifier diodeD_offThe method for tracking the LLC resonant frequency is controlled within a preset target range and comprises the following steps:
setting leading current reference value i of secondary side rectifier diodeD_off_ref；
Giving upper and lower limit values of a dead zone, and determining a dead zone range;
leading current reference value i of secondary side rectifying diodeD_off_refLeading current value i of secondary side rectifier diodeD_offThe deviation value error0 is subjected to dead zone nonlinear processing, so that the corrected deviation value error after the dead zone nonlinear processing meets the dead zone range, and the leading current value i of the secondary side rectifier diode is adjustedD_offControlling the temperature within a preset target range;
at an initial switching frequency f0The corrected deviation value error is subjected to PI regulation and then output to obtain a switching frequency f;
according to the formulas (1) - (3), further modifying the bottom layer of the controller, tracking the resonant frequency of the next period, and determining the final stable value of the switching frequency f as the resonant frequency f of the LLC resonant converterr。
Preferably, if the deviation value error0 meets the dead zone range, the corrected deviation value error after dead zone nonlinear processing is performed on the deviation value error0 is 0;
if the deviation value error0 is smaller than the given dead zone lower limit value, increasing the corrected deviation value error after dead zone nonlinear processing is carried out on the deviation value error0 to be within the dead zone range;
and if the deviation value error0 is larger than the given dead zone upper limit value, reducing the corrected deviation value error after dead zone nonlinear processing is carried out on the deviation value error0 to be within a dead zone range.
Preferably, if the deviation value error0 is smaller than the given dead zone lower limit value, the corrected deviation value error is the sum of the deviation value error0 and the dead zone lower limit value;
if the deviation value error0 is greater than the given upper dead band limit, the corrected deviation value error is the difference between the deviation value error0 and the upper dead band limit.
Compared with the prior art, the invention has the advantages and positive effects that:
the method for tracking the resonant frequency of the full-bridge LLC resonant converter provided by the invention triggers the controller to acquire the super of the secondary side rectifier diode at the given advance time delta t before the switching tube is switched off by configuring the bottom layer of the controllerFront current value iD_off(ii) a Then, the switching frequency f of the full-bridge LLC resonant converter is regulated through PI, and the leading current value i of the secondary side rectifier diode is adjustedD_offAnd controlling the LLC resonant frequency within a preset target range to realize the tracking of the LLC resonant frequency. The method can realize the quick tracking of the resonant frequency, the switching frequency is adjusted to the left side of the resonant frequency point and close to the resonant frequency, the resonant converter works in the optimal area, the full-bridge switching tube realizes zero voltage switching-on, and the secondary side rectifier diode has no reverse recovery problem, so that the system loss is reduced, and the system efficiency is improved. Meanwhile, 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 capacitance, resonance inductance, excitation inductance 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.
Drawings
FIG. 1 is a schematic diagram of a full-bridge LLC resonant converter topology with an additional secondary current sensor;
FIG. 2 shows the leading current value i of the secondary rectifier diodeD_offCollecting a schematic diagram;
FIG. 3 is a waveform of a secondary side rectifier diode when the resonant frequency is greater than the switching frequency;
FIG. 4 shows the resonance frequency frThe waveform of the secondary side rectifier diode is less than the switching frequency f;
FIG. 5 is a block diagram of a resonant frequency tracking method;
FIG. 6 shows simulation results at an initial switching frequency of 15 kHz;
FIG. 7 shows simulation results at an initial switching frequency of 26 kHz;
FIG. 8 is a simulated waveform with the switching frequency stabilized to 22.26 kHz;
fig. 9 is a simulated waveform when the switching frequency settles to 22.26 kHz.
Detailed Description
The following further describes embodiments of the present invention with reference to the accompanying drawings.
The invention provides a method for tracking the resonant frequency of a full-bridge LLC resonant converter, wherein the full-bridge LLC resonant converter adopts PWM fixed frequency shift phase control, and the method comprises the following steps:
(1) configuring a controller bottom layer, triggering the controller to acquire the advance current value i of the secondary side rectifier diode at a given advance time delta t before the switch tube is turned off at the given advance time delta tD_off. The method specifically comprises the following steps:
the counting period of the driving of the switching tube is calculated as follows:
Figure BDA0003019700710000061
wherein, fCPUTo count the clock frequency;
setting a first comparison value CMPA driven by the switch tube as follows:
CMPA＝TBPRD×D (2)
when a counting register driven by a configuration switch tube counts to a first comparison value CMPA, level change is carried out, and the switch tube is controlled to be switched from an on state to an off state;
d is the duty ratio of a driving signal of the switching tube;
determining a second comparison value CMPB of the switching tube drive for a given lead time Δ t from the first comparison value CMPA as:
CMPB＝CMPA-Δt×fCPU (3)
when a counting register driven by a configuration switch tube counts to a second comparison value CMPB, a trigger controller acquires the leading current value i of a secondary rectifier diode at a given leading time delta tD_off。
(2) If the resonant frequency frGreater than the switching frequency f, the resonant current iLrIs equal to the excitation current iLmLeading current value i of secondary side rectifier diodeD_offTo be 0, the switching frequency f needs to be increased to track the resonant frequency. If the resonant frequency frLess than the switching frequency f, the resonant current iLrGreater than the exciting current iLmLeading current value i of secondary side rectifier diodeD_offAbove 0, the switching frequency f needs to be lowered to track the resonant frequency. Therefore, the switching frequency f of the full-bridge LLC resonant converter is regulated through PI, and the secondary side of the LLC resonant converter is rectified by the secondary side of the LLC resonant converterFront current value iD_offAnd controlling the LLC resonant frequency within a preset target range to realize the tracking of the LLC resonant frequency. The method specifically comprises the following steps:
setting the leading current reference value i of the secondary side rectifier diodeD_off_refGiving upper and lower limit values of the dead zone, and determining the range of the dead zone;
② leading current reference value i of secondary side rectifying diodeD_off_refLeading current value i of secondary side rectifier diodeD_offThe deviation value error0 is subjected to dead zone nonlinear processing, so that the corrected deviation value error after the dead zone nonlinear processing meets the dead zone range, and the leading current value i of the secondary side rectifier diode is adjustedD_offAnd controlling within a preset target range. Namely:
if the deviation value error0 meets the dead zone range, the corrected deviation value error after dead zone nonlinear processing is carried out on the deviation value error0 is 0;
if the deviation value error0 is smaller than the given dead zone lower limit value, increasing the correction deviation value error after dead zone nonlinear processing is carried out on the deviation value error0 to the dead zone range, namely, taking the correction deviation value error as the sum of the deviation value error0 and the dead zone lower limit value;
if the deviation value error0 is greater than the given dead zone upper limit value, the corrected deviation value error after dead zone nonlinear processing is performed on the deviation value error0 is reduced to be within the dead zone range, and the corrected deviation value error can be taken as the difference between the deviation value error0 and the dead zone upper limit value.
Thirdly, at the initial switching frequency f0The corrected deviation value error is subjected to PI regulation and then output to obtain a switching frequency f;
according to the formulas (1) - (3), further modifying the bottom layer of the controller, tracking the resonant frequency of the next period, and determining the final stable value of the switching frequency f as the resonant frequency f of the LLC resonant converterr。
The following describes the above-mentioned resonant frequency tracking method in detail with reference to the full-bridge LLC resonant converter shown in fig. 1:
output filter capacitor C of LLC resonant converterfThe front end is additionally provided with a secondary side current sensor, as shown in figure 1, for collectingCurrent i of secondary side rectifier diodeD；
To trigger the controller AD to collect at a given lead time Δ t before the switching transistor Q1 turns off, the lead current value i of the secondary rectifier diode at that time is collectedD_offThe bottom layer of the controller needs to be configured, and the specific principle is as shown in fig. 2:
taking a DSP controller as an example, assume that EPWM1A is used as a driving source of switching tube Q1, and count register TBCTR performs count-up counting, and if the count clock frequency is fCPUThen, the counting period is:
Figure BDA0003019700710000081
wherein, fCPUTo count the clock frequency;
setting a first comparison value CMPA driven by the switch tube as follows:
CMPA＝TBPRD×D
wherein, D is the duty cycle of the driving signal of the switching tube, and the duty cycle of the driving signal of the switching tube Q1 is 50%.
The drive source EPWM1A configuring the switching tube Q1 is set to 1 when the count register TBCTR is equal to 0 and is greater than CMPA and is set to 0, so that the count register TBCTR counts up to the moment of the first comparison value CMPA (e.g. t of FIG. 2)3Moment), the level of the EPWM1A is changed from 1 to 0, namely, the switching tube Q1 is switched from an on state to an off state at the moment;
determining a second comparison value CMPB of the switching tube drive for a given lead time Δ t from the first comparison value CMPA as:
CMPB＝CMPA-Δt×fCPU
continuously configuring the bottom layer of the DSP controller, triggering DAP ADC to collect when the TBCTR of the counting register is equal to a second comparison value CMPB, wherein the current value of the secondary side rectifier diode collected by the DSP ADC is the delta t moment before the switching tube Q1 is turned off (for example, t moment in fig. 2)2Leading current value i of time secondary side rectifier diodeD_offWhere Δ t is a very small value.
In the embodiment, the switching frequency f of the full-bridge LLC resonant converter is adjusted through the PI controller, and the auxiliary converterLeading current value i of side rectifier diodeD_offControlling within a small range to finish the control of LLC resonant frequency frThe tracking of (2). Referring to fig. 3 to 5, specifically:
when the resonant frequency frAt a higher time, i.e. resonant frequency frIs higher than the current switching frequency f, when the switching tube Q1 is turned off, the LLC is in the resonant inductor LrResonant capacitor CrAnd excitation inductance LmA resonance phase when a resonance current iLrIs equal to the excitation current iLmThe secondary rectifier diode current is 0, i.e. iD_offTo be 0, as shown in fig. 3, the switching frequency f needs to be increased to track the resonant frequency. When the resonant frequency frPartial, i.e. resonant frequency frIs less than the current switching frequency f, and when the switching tube Q1 is turned off, the LLC is in the resonant inductor LrAnd a resonance capacitor CrA resonance phase when a resonance current iLrGreater than the exciting current iLmThe secondary rectifier diode current is very large, i.e. iD_offIn order to track the resonant frequency, the switching frequency f needs to be lowered, as shown in fig. 4.
Therefore, as shown in fig. 5, the switching frequency f of the full-bridge LLC resonant converter is adjusted by the PI controller, specifically:
setting the leading current reference value i of the secondary side rectifier diodeD_off_refGet iD_off_refAt a very small value, when the switch tube Q1 is turned off (t in FIG. 2)3At time), the current of the secondary rectifier diode drops to just 0.
And secondly, giving upper and lower limit values of the dead zone and determining the range of the dead zone. To avoid the fluctuation of the switching frequency, the reference value i of the leading current of the secondary rectifier diode is neededD_off_refLeading current value i of secondary side rectifier diodeD_offThe deviation value error0 is subjected to dead zone nonlinear processing, so that the corrected deviation value error after the dead zone nonlinear processing meets the dead zone range, and the leading current value i of the secondary side rectifier diode is adjustedD_offAnd controlling within a preset target range. Namely:
if the deviation value error0 meets the dead zone range, the corrected deviation value error after dead zone nonlinear processing is carried out on the deviation value error0 is 0;
if the deviation value error0 is smaller than the given dead zone lower limit value, the corrected deviation value error after dead zone nonlinear processing is carried out on the deviation value error0 is increased to the range of the dead zone, and the corrected deviation value error can be taken as the sum of the deviation value error0 and the dead zone lower limit value in actual design;
if the deviation value error0 is greater than the given dead zone upper limit value, the corrected deviation value error after dead zone nonlinear processing is performed on the deviation value error0 is reduced to be within a dead zone range, and the corrected deviation value error can be a difference value between the deviation value error0 and the dead zone upper limit value in actual design.
Thirdly, at the initial switching frequency f0The corrected deviation value error is subjected to PI regulation and then output to obtain a switching frequency f;
fourthly, according to the formulas (1) to (3), the bottom layer of the controller is further modified, the resonant frequency tracking of the next period is carried out, and the final stable value of the switching frequency f is determined to be the resonant frequency f of the LLC resonant converterr。
In practical application, the resonant frequency tracking must be started when the full-bridge phase-shift duty ratio is sufficiently large (for example, greater than 98%), and the switching frequency f will be stabilized on the left side of the resonant frequency of the LLC resonant converter and close to the resonant frequency, that is, the optimal operating region, because the dead zone of the switching tube and the duty ratio cannot be full.
The resonant frequency tracking method of the present application is verified in a specific embodiment as follows:
a simulation model of a certain 25kW full-bridge LLC resonant converter is built under the Simulink environment, and the resonant frequency tracking method provided by the application is verified. Actual resonance frequency f of LLC resonant converterr22.97kHz, 0.5us of dead time of a switching tube, 0.5us of delta t, iD_off_refThe frequency is 5A, the upper and lower limit values of a dead zone of the current error dead zone nonlinear processing are +/-2A, and the resonant frequency tracking is started when the duty ratio of the phase-shifted full-bridge is more than or equal to 98%. As a result of the simulation, as shown in fig. 6, 7, 8, and 9, the initial switching frequency f was 15kHz and 26kHz, respectively, and the resonant frequency tracking started at 0.6 time, and the resonant frequency tracking was completed within 0.5s, and the switching was startedThe off frequency converged to 22.26kHz, and the simulation achieved fast tracking of the resonant frequency, with the switching frequency close to and to the left of the resonant frequency point. The resonance current is close to sine, the current of the secondary side rectifier diode is naturally reduced to 0, and the rectifier diode has no reverse recovery problem.
In summary, according to the full-bridge LLC resonant converter resonant frequency tracking method provided by the present invention, by configuring the controller bottom layer, the controller is triggered to acquire the leading current value i of the secondary side rectifier diode at the given leading time Δ t before the switching tube is turned off at the given leading time Δ tD_off(ii) a Then, the switching frequency f of the full-bridge LLC resonant converter is regulated through PI, and the leading current value i of the secondary side rectifier diode is adjustedD_offAnd controlling the LLC resonant frequency within a preset target range to realize the tracking of the LLC resonant frequency. The method can realize the quick tracking of the resonant frequency, the switching frequency is adjusted to the left side of the resonant frequency point and close to the resonant frequency, the resonant converter works in the optimal area, the full-bridge switching tube realizes zero voltage switching-on, and the secondary side rectifier diode has no reverse recovery problem, so that the system loss is reduced, and the system efficiency is improved. Meanwhile, 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 capacitance, resonance inductance, excitation inductance 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.
The above description is only a preferred embodiment of the present invention, and not intended to limit the present invention in other forms, and any person skilled in the art may apply the above modifications or changes to the equivalent embodiments with equivalent changes, without departing from the technical spirit of the present invention, and any simple modification, equivalent change and change made to the above embodiments according to the technical spirit of the present invention still belong to the protection scope of the technical spirit of the present invention.

Claims (5)

1. A full-bridge LLC resonant converter resonant frequency tracking method is characterized in that the full-bridge LLC resonant converter adopts PWM fixed frequency shift phase control, and the method comprises the following steps:
configuring a controller bottom layer, triggering the controller to acquire the leading current value i of the secondary side rectifier diode at a given leading time delta t before the switching tube is switched off at the given leading time delta tD_off；
PI regulates the switching frequency f of the full-bridge LLC resonant converter, and leads the current value i of the secondary side rectifier diodeD_offControlling the resonant frequency f of LLC within a preset target rangerTracking of (2);
the PI adjusts the switching frequency f of the full-bridge LLC resonant converter, and leads the current value i of the secondary rectifying diodeD_offThe method for tracking the LLC resonant frequency is controlled within a preset target range and comprises the following steps:
setting leading current reference value i of secondary side rectifier diodeD_off_ref；
Giving upper and lower limit values of a dead zone, and determining a dead zone range;
leading current reference value i of secondary side rectifying diodeD_off_refLeading current value i of secondary side rectifier diodeD_offThe deviation value error0 is subjected to dead zone nonlinear processing, so that the corrected deviation value error after the dead zone nonlinear processing meets the dead zone range, and the leading current value i of the secondary side rectifier diode is adjustedD_offControlling the temperature within a preset target range;
at an initial switching frequency f0The corrected deviation value error is subjected to PI regulation and then output to obtain a switching frequency f;
according to the formulas (1) - (3), further modifying the bottom layer of the controller, tracking the resonant frequency of the next period, and determining the final stable value of the switching frequency f as the resonant frequency f of the LLC resonant converterr；
The method comprises the steps that a controller bottom layer is configured, the controller is triggered to collect the leading current value i of a secondary side rectifier diode at a given leading time delta t before a switching tube is turned off at the given leading time delta tD_offThe method comprises the following steps:
the counting period of the driving of the switching tube is calculated as follows:
Figure FDA0003607752100000021
wherein, fCPUTo count the clock frequency;
setting a first comparison value CMPA of the switch tube driving as follows:
CMPA＝TBPRD×D (2)
when a counting register driven by a configuration switch tube counts to a first comparison value CMPA, level change is carried out, and the switch tube is controlled to be switched from an on state to an off state;
d is the duty ratio of a driving signal of the switching tube;
determining a second comparison value CMPB of the switching tube drive for a given lead time Δ t according to the first comparison value CMPA as:
CMPB＝CMPA-Δt×fCPU (3)
when a counting register driven by a configuration switch tube counts to a second comparison value CMPB, a trigger controller acquires the leading current value i of a secondary rectifier diode at a given leading time delta tD_off。
2. The full-bridge LLC resonant converter resonant frequency tracking method according to claim 1, wherein if the resonant frequency f isrGreater than the switching frequency f, the resonant current iLrIs equal to the excitation current iLmLeading current value i of secondary side rectifier diodeD_offTo 0, the switching frequency f is increased to track the resonant frequency.
3. The full-bridge LLC resonant converter resonant frequency tracking method according to claim 2, wherein if the resonant frequency f isrLess than the switching frequency f, the resonant current iLrGreater than the exciting current iLmLeading current value i of secondary side rectifier diodeD_offAbove 0, the switching frequency f is lowered to track the resonant frequency.
4. The method for tracking the resonant frequency of the full-bridge LLC resonant converter according to claim 3, wherein if the deviation value error0 meets the dead zone range, the corrected deviation value error after dead zone nonlinear processing of the deviation value error0 is set to 0;
if the deviation value error0 is smaller than the given dead zone lower limit value, increasing the corrected deviation value error after dead zone nonlinear processing is carried out on the deviation value error0 to be within the dead zone range;
and if the deviation value error0 is larger than the given dead zone upper limit value, reducing the corrected deviation value error after dead zone nonlinear processing is carried out on the deviation value error0 to be within a dead zone range.
5. The full-bridge LLC resonant converter resonant frequency tracking method according to claim 4, characterized in that:
if the deviation value error0 is smaller than the given dead zone lower limit value, correcting the deviation value error to be the sum of the deviation value error0 and the dead zone lower limit value;
if the deviation value error0 is greater than the given upper dead band limit, the corrected deviation value error is the difference between the deviation value error0 and the upper dead band limit.
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CN114844362B (en) * 2022-04-26 2023-02-03 深圳信息职业技术学院 Control circuit and method of resonant converter
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