CN111654195B - Automatic frequency tracking method of LLC resonant converter - Google Patents

Automatic frequency tracking method of LLC resonant converter Download PDF

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CN111654195B
CN111654195B CN202010592099.4A CN202010592099A CN111654195B CN 111654195 B CN111654195 B CN 111654195B CN 202010592099 A CN202010592099 A CN 202010592099A CN 111654195 B CN111654195 B CN 111654195B
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llc resonant
resonant converter
voltage
frequency tracking
frequency
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CN111654195A (en
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韦玉麒
罗全明
王芷晴
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Chongqing University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • 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

Abstract

The invention discloses an automatic frequency tracking method of an LLC resonant converter, which comprises the following steps: s1, collecting input voltage V of LLC resonant converterinAnd an output voltage Vo(ii) a S2, based on the input voltage VinAn output voltage VoCalculating a voltage gain of the LLC resonant converter according to the topology of the LLC resonant converter and the turn ratio of the LLC resonant converter; s3, when the voltage gain is smaller than 1, reducing the switching frequency to realize frequency tracking; when the voltage gain is larger than 1, the switching frequency is increased to realize frequency tracking. The automatic frequency tracking technology based on the input voltage and the output voltage can be suitable for all working modes, a high-speed and high-precision digital controller is not needed, the hardware requirement in the automatic frequency tracking process of the LLC resonant converter is reduced, the size of a detection circuit is reduced, the detection efficiency is improved, and the power loss is reduced.

Description

Automatic frequency tracking method of LLC resonant converter
Technical Field
The invention relates to the technical field of resonant converters, in particular to an automatic frequency tracking method of an LLC resonant converter.
Background
Nowadays, power electronic converters are moving towards high frequency, high efficiency and high power density. Among them, the LLC resonant converter is widely used in various industrial fields, including electric vehicle-mounted chargers, data center communication power supplies, and LED lighting drive circuits, because it can realize soft switching in a large input voltage and load range.
The resonant frequency of the LLC resonant converter is determined by the resonant capacitance and resonant inductance parameters in the circuit. When the LLC resonant converter operates at a frequency point greater than the resonant frequency, the switching loss of the semiconductor device increases and the secondary diode cannot achieve zero-current turn-off to lower the conversion efficiency. When the LLC resonant converter works at a point less than the resonant frequency, although the original secondary side semiconductor devices can realize soft switching, the effective value of the primary side current is increased, so that the conduction loss of a circuit is increased, and the conversion efficiency is reduced. Therefore, the optimal efficiency operating point of the LLC resonant converter is the resonant frequency operating point. Many high efficiency applications utilize the highest efficiency characteristic of LLC resonant converters at the resonant frequency operating point to achieve high efficiency power conversion. However, in actual operation, the sizes of the resonant components, i.e., the resonant inductor and the resonant capacitor, change with the influence of factors such as the operating condition and aging of the circuit, and at this time, the operating point of the LLC resonant converter deviates from the operating point with the optimal efficiency. Therefore, it has important theoretical and practical significance to implement automatic resonant frequency tracking for LLC resonant converters.
The existing LLC resonant converter automatic frequency tracking techniques mainly include the following. First, automatic frequency tracking can be achieved by detecting the length of time that the secondary side diode current is zero. However, this method is only suitable for use when the LLC resonant converter operates at a point less than the resonant frequency, and it requires a high bandwidth comparator to implement the zero current detection function. Secondly, there is a technology to realize automatic frequency tracking by detecting the harmonic content of the resonant inductor current on line, which requires a digital controller with high precision and high processing speed to realize the harmonic calculation of the resonant inductor current. Finally, there is also a technique proposed to realize automatic frequency tracking by detecting a peak point and a zero-crossing point of the resonant inductor current. Although this technique can be applied to different operating modes of an LLC resonant converter, it requires a high precision and high processing speed digital controller to implement the detection and calculation functions. In addition, the above methods require the detection of the converter current, which consumes a large amount of power and is not easy to implement.
In summary, how to reduce the hardware requirement in the automatic frequency tracking process of the LLC resonant converter, improve the detection efficiency, reduce the power loss, and be applicable to all the operating modes becomes a problem that needs to be solved urgently by those skilled in the art.
Disclosure of Invention
Aiming at the defects in the prior art, the invention discloses an automatic frequency tracking method of an LLC resonant converter, which is based on an automatic frequency tracking technology of input voltage and output voltage, can be suitable for all working modes, does not need a high-speed and high-precision digital controller, reduces the hardware requirement in the automatic frequency tracking process of the LLC resonant converter, reduces the volume of a detection circuit, improves the detection efficiency and reduces the power loss.
In order to solve the technical problems, the invention adopts the following technical scheme:
an LLC resonant converter automatic frequency tracking method, comprising:
s1, collecting LInput voltage V of LC resonant converterinAnd an output voltage Vo；
S2, based on the input voltage VinAn output voltage VoCalculating a voltage gain of the LLC resonant converter according to the topology of the LLC resonant converter and the turn ratio of the LLC resonant converter;
s3, when the voltage gain is smaller than 1, reducing the switching frequency to realize frequency tracking; when the voltage gain is larger than 1, the switching frequency is increased to realize frequency tracking.
Preferably, when the primary side of the LLC resonant converter is in an asymmetric half-bridge or stacked structure and the secondary side is in full-bridge rectification or transformer center tap rectification, the voltage gain M is calculated according to the following formula:
Figure BDA0002555993790000021
wherein N represents a turn ratio of the LLC resonant converter.
Preferably, when the LLC resonant converter is a full-bridge converter, the voltage gain M is calculated according to the following formula:
Figure BDA0002555993790000022
wherein N represents a turn ratio of the LLC resonant converter.
Preferably, when the LLC resonant converter has an asymmetric half-bridge or stacked structure on the primary side and the secondary side is voltage-doubler rectification, the voltage gain M is calculated according to the following formula:
Figure BDA0002555993790000023
wherein N represents a turn ratio of the LLC resonant converter.
Preferably, the switching step size is positively correlated with the difference between the voltage gain and the unity gain of the resonant operating point.
Preferably, when M.gtoreq.1 + Δ M2Or M is less than or equal to 1-delta M2When, Δ M2For the second frequency difference threshold, the switching adjustment step size is Δ fs 1; when M is more than or equal to 1+ delta M2 and less than or equal to 1-delta M2The switching step size is Δ fs 2.
Preferably, when 1+ Δ M1≤M≤1-ΔM1When, it is judged that the automatic frequency tracking has been achieved, Δ M1Is a first frequency difference threshold, Δ M2＞ΔM1。
Compared with the prior art, the invention has the following beneficial effects:
1. the invention can be applied to all topologies of LLC resonant converters and all working modes of LLC resonant converters.
2. The invention can realize the automatic tracking of the resonant frequency only by detecting the input voltage and the output voltage of the converter, and in practice, the input voltage and the output voltage of the converter are known, so the invention basically does not introduce any additional sampling circuit and cost.
3. The invention does not need a digital controller with high precision and high processing speed, thereby reducing the system cost. And the circuit current does not need to be detected, thereby improving the efficiency and the power density of the converter.
Drawings
For purposes of clarity, technical solutions and advantages, the present invention will be described in further detail below with reference to the accompanying drawings, in which:
FIG. 1 is a flow chart of an embodiment of an automatic frequency tracking method of an LLC resonant converter disclosed by the invention;
FIG. 2 is a schematic diagram of a voltage gain curve of the LLC resonant converter under different circuit parameters;
FIG. 3 is a schematic diagram of the frequency tracking process of the present invention when the LLC resonant converter operates at a point less than the resonant frequency;
FIG. 4 is a schematic diagram of the frequency tracking process of the present invention when the LLC resonant converter operates at a point greater than the resonant frequency;
FIG. 5 is a schematic diagram of a variable step size adjustment strategy according to the present invention;
fig. 6 is a flowchart of another embodiment of an automatic frequency tracking method for an LLC resonant converter disclosed in the present invention.
FIG. 7 is an experimental waveform diagram when the LLC resonant converter operates at less than the resonant frequency point;
FIG. 8 is an experimental waveform diagram when the LLC resonant converter operates at a point greater than the resonant frequency;
fig. 9 is an experimental waveform diagram when the LLC resonant converter resonant capacitance value changes.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, the present invention discloses an automatic frequency tracking method for an LLC resonant converter, comprising:
s1, collecting input voltage V of LLC resonant converterinAnd an output voltage Vo；
S2, based on the input voltage VinAn output voltage VoCalculating a voltage gain of the LLC resonant converter according to the topology of the LLC resonant converter and the turn ratio of the LLC resonant converter;
s3, when the voltage gain is smaller than 1, reducing the switching frequency to realize frequency tracking; when the voltage gain is larger than 1, the switching frequency is increased to realize frequency tracking.
Fig. 2 is a voltage gain curve of an LLC resonant converter under different circuit parameters. It can be seen that when the LLC resonant converter operates at the resonant operating point, its voltage gain is 1. Therefore, the present invention realizes the automatic tracking of the resonant frequency according to the characteristic of the LLC resonant converter.
When the LLC resonant converter operates at less than the resonant frequency point, this is shown in fig. 3 at point a. At this time, the calculated voltage gain is greater than 1, and in order to make the voltage gain equal to 1, the voltage gain can be reduced by increasing the switching frequency. At this time, the LLC resonant converter may operate at the B point, and finally the LLC resonant converter may operate at the C point, that is, the resonant frequency operation point we want.
Similarly, when the LLC resonant converter operates at a frequency greater than the resonant frequency point, it is shown as point E in fig. 4. At this time, the calculated voltage gain is less than 1, and the voltage gain can be increased by lowering the switching frequency, and finally the converter is adjusted to the resonant frequency operating point C.
In specific implementation, when the primary side of the LLC resonant converter is in an asymmetric half-bridge or stacked structure and the secondary side is in full-bridge rectification or transformer center tap rectification, the voltage gain M is calculated according to the following formula:
Figure BDA0002555993790000041
wherein N represents a turn ratio of the LLC resonant converter.
In specific implementation, when the LLC resonant converter is a full-bridge converter, the voltage gain M is calculated according to the following formula:
Figure BDA0002555993790000042
wherein N represents a turn ratio of the LLC resonant converter.
In specific implementation, when the primary side of the LLC resonant converter is in an asymmetric half-bridge or stacked structure and the secondary side is voltage-doubler rectification, the voltage gain M is calculated according to the following formula:
Figure BDA0002555993790000043
wherein N represents a turn ratio of the LLC resonant converter.
The method can be applied to all LLC resonant converter topologies, and only corresponding changes are needed to be made on the gain calculation formula.
In specific implementation, the switching adjustment step length is positively correlated with the difference between the voltage gain and the unit gain of the resonant operating point.
In specific implementation, when M is more than or equal to 1+ delta M2Or M is less than or equal to 1-delta M2When, Δ M2For the second frequency difference threshold, the switching adjustment step size is Δ fs 1; when 1+ Δ M2≤M≤1-ΔM2The switching step size is Δ fs 2.
As shown in fig. 5, in order to increase the tracking speed of the resonant frequency, the present invention adopts a step-size-variable method. When the calculated voltage gain is far from the unity gain, i.e., the operation regions 1 and 5, the step size of the frequency conversion is large. And when the working point is closer to the resonance working point, the step length of frequency conversion is smaller, so that accurate frequency tracking is realized.
When embodied, 1+ Δ M1≤M≤1-ΔM1When, it is judged that the automatic frequency tracking has been achieved, Δ M1Is a first frequency difference threshold, Δ M2＞ΔM1。
In the present invention,. DELTA.M1，ΔM2And the values of Δ fs1 and Δ fs2 mainly depend on the requirement of the system for frequency tracking speed. If the system requires faster tracking speed, Δ M2The value should be such that 1+ Δ M2And 1-. DELTA.M2Around 1, and Δ M1Larger values should be taken to make the system reach steady state faster, and the values of Δ fs1 and Δ fs2 should be larger to accelerate the tracking speed. On the contrary, if the system has a high requirement on the tracking accuracy, the values should be selected in the opposite direction.
FIG. 6 is a flow chart of an embodiment of the present invention, in which the input voltage V of the LLC resonant converter is first collectedinAnd an output voltage Vo(ii) a Based on the input voltage VinAn output voltage VoCalculating a voltage gain of the LLC resonant converter according to the topology of the LLC resonant converter and the turn ratio of the LLC resonant converter; when 1+ Δ M1≤M≤1-ΔM1When the operation is finished, other operations are not carried out; when the voltage gain M is greater than or equal to 1+ Δ M1Then, it is judged whether M is greater than or equal to 1+ Δ M2If so, increasing the switching frequency by Δ fs1, otherwise, increasing the switching frequency by Δ fs 2; when M is less than or equal to 1- Δ M1When M is less than or equal to 1- Δ M, it is judged whether M is less than or equal to 1- Δ M2If yes, the switching frequency is reduced by delta fs1, otherwise, the switching frequency is reduced by delta fs2Low switching frequency.
As shown in fig. 7 to 9, fig. 7 and 8 illustrate that, by using the method disclosed in the present invention, the LLC resonant converter can realize automatic frequency tracking when operating in two operating regions, i.e., less than the resonant frequency and more than the resonant frequency;
fig. 9 illustrates that the proposed scheme also performs well in tracking frequency when circuit parameters change. The tracking time is about 200ms, and the tracking can be faster.
Finally, it is noted that the above-mentioned embodiments illustrate rather than limit the invention, and that, while the invention has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (4)

1. An LLC resonant converter automatic frequency tracking method is characterized by comprising the following steps:
s1, collecting input voltage V of LLC resonant converterinAnd an output voltage Vo；
S2, based on the input voltage VinAn output voltage VoCalculating a voltage gain M of the LLC resonant converter according to the topology of the LLC resonant converter and the turn ratio of the LLC resonant converter;
s3, when the voltage gain M is smaller than 1, reducing the switching frequency to realize frequency tracking; when the voltage gain M is larger than 1, increasing the switching frequency to realize frequency tracking;
the switching adjustment step length is positively correlated with the difference value between the voltage gain M and the unit gain of the resonance working point;
when M is more than or equal to 1+ delta M2Or M is less than or equal to 1-delta M2When, Δ M2For the second frequency difference threshold, the switching adjustment step size is Δ fs 1; when 1+ Δ M2≤M≤1-ΔM2The switching step is Δ fs 2;
when 1+ Δ M1≤M≤1-ΔM1When, it is judged that the automatic frequency tracking has been achieved, Δ M1Is a first frequency differenceDifferent threshold, Δ M2＞ΔM1。
2. The method according to claim 1, wherein when the LLC resonant converter has an asymmetric half-bridge or stacked structure on its primary side and a full-bridge rectifier or transformer center tap rectifier on its secondary side, the voltage gain M is calculated according to the following formula:
Figure FDA0003349943700000011
wherein N represents a turn ratio of the LLC resonant converter.
3. The method of automatic frequency tracking of an LLC resonant converter as claimed in claim 1, wherein when said LLC resonant converter is a full-bridge converter, the voltage gain M is calculated according to the following equation:
Figure FDA0003349943700000012
wherein N represents a turn ratio of the LLC resonant converter.
4. The method for automatic frequency tracking of LLC resonant converter as claimed in claim 1, wherein when said LLC resonant converter is in asymmetric half-bridge or stacked structure at primary side and voltage-doubling rectification at secondary side, the voltage gain M is calculated according to the following formula:
Figure FDA0003349943700000013
wherein N represents a turn ratio of the LLC resonant converter.
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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102843133A (en) * 2012-08-30 2012-12-26 西安欣创电子技术有限公司 Method for quickly and automatically adjusting resonant frequency of voltage-controlled oscillator
CN107342688A (en) * 2016-04-29 2017-11-10 华为技术有限公司 A kind of resonant power converter and its frequency tracking method
KR20180004655A (en) * 2016-07-04 2018-01-12 숭실대학교산학협력단 Hybrid full-bridge llc converter and control method thereof
CN111222228A (en) * 2019-12-27 2020-06-02 科华恒盛股份有限公司 Method for controlling working frequency of LLC (logical Link control) and terminal equipment
CN111313714A (en) * 2020-02-28 2020-06-19 中车青岛四方车辆研究所有限公司 Full-bridge LLC resonant converter resonant frequency tracking method and system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102843133A (en) * 2012-08-30 2012-12-26 西安欣创电子技术有限公司 Method for quickly and automatically adjusting resonant frequency of voltage-controlled oscillator
CN107342688A (en) * 2016-04-29 2017-11-10 华为技术有限公司 A kind of resonant power converter and its frequency tracking method
KR20180004655A (en) * 2016-07-04 2018-01-12 숭실대학교산학협력단 Hybrid full-bridge llc converter and control method thereof
CN111222228A (en) * 2019-12-27 2020-06-02 科华恒盛股份有限公司 Method for controlling working frequency of LLC (logical Link control) and terminal equipment
CN111313714A (en) * 2020-02-28 2020-06-19 中车青岛四方车辆研究所有限公司 Full-bridge LLC resonant converter resonant frequency tracking method and system

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