CN113872448A - Fixed-frequency LLC circuit and resonant frequency tracking method thereof - Google Patents
Fixed-frequency LLC circuit and resonant frequency tracking method thereof Download PDFInfo
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- CN113872448A CN113872448A CN202111128423.8A CN202111128423A CN113872448A CN 113872448 A CN113872448 A CN 113872448A CN 202111128423 A CN202111128423 A CN 202111128423A CN 113872448 A CN113872448 A CN 113872448A
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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
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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
- H02M3/26—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes without control electrode or semiconductor devices without control electrode to produce the intermediate ac
Abstract
The invention discloses a fixed-frequency LLC circuit and a tracking method of resonant frequency thereof in the field of LLC circuits, wherein the fixed-frequency LLC circuit comprises a primary full-bridge circuit, a resonant inductor, an excitation inductor, a resonant capacitor and a rectification filter circuit; the device also comprises a voltage signal acquisition circuit, a phase difference calculation module and a phase difference calculation module, wherein the voltage signal acquisition circuit is used for acquiring bridge arm voltage and resonance capacitor voltage and sending the bridge arm voltage and the resonance capacitor voltage to the actual phase difference calculation module; the actual phase difference operation module is used for calculating the actual phase difference between the bridge arm voltage and the resonance capacitor voltage; the reference phase difference operation module is used for obtaining a reference phase difference between the bridge arm voltage and the resonance capacitor voltage through calculation when the working frequency is equal to the resonance frequency; the phase difference comparison module is used for receiving the outputs of the actual phase difference operation module and the reference phase difference operation module, comparing the actual phase difference with the reference phase difference, and outputting the comparison result to the feedback control module; the invention can adjust the working frequency of the LLC converter to track the resonant frequency and solve the problem of resonant frequency point deviation caused by circuit parameter change.
Description
Technical Field
The invention relates to the field of LLC circuits, in particular to a fixed-frequency LLC circuit and a method for tracking resonant frequency thereof.
Background
The fixed-frequency LLC converter has the advantages of fixed switching frequency, zero-voltage zero-current soft switching, good EMI (electro-magnetic interference) characteristic and the like, and is suitable for occasions with high efficiency, high power density and need of electrical isolation. In this working state, the switching frequency of the LLC converter needs to be always equal to the resonant frequency of the resonant inductor and the resonant capacitor of the isolation transformer, so that both the primary zero-voltage turn-on and the secondary zero-current turn-off can be ensured. However, in practice, due to temperature drift, aging of devices and other reasons, it is difficult to control the switching frequency to be always exactly equal to the resonant frequency, which causes "current backflow" and extra loss.
At present, the resonant frequency tracking of the fixed-frequency LLC converter is mainly realized in the following ways: 1. and directly sampling by serially connecting resistors. The method is directly connected with a sampling resistor in series in a secondary circuit to accurately acquire the zero crossing point of current to realize resonant frequency tracking, but also introduces unacceptable loss. 2. Primary side resonance current and excitation current are decoupled. The method is characterized in that a primary side extra discrete inductor is constructed to replace an excitation inductor, the excitation inductor of an isolation transformer is used for adjusting leakage inductance, namely resonance inductance, in an equal proportion, current flowing through the discrete inductor and the resonance inductor is decoupled, and accurate resonance frequency tracking can be achieved by capturing the current zero crossing point of the resonance inductor. The method needs to introduce an additional discrete inductor and a transformer for collecting the current of the resonant inductor, thereby greatly increasing the volume of the converter. 3. Frequency tracking based on fixed threshold voltage comparison. The current flowing through the rectifier tube is reflected by detecting the change of the drain-source voltage of the switch tube, and the turn-off time of the power tube is controlled by reasonably judging the voltage so as to realize the tracking of the resonant frequency. The method can only detect the fixed voltage of a specific SR, has certain limitation in application, and can still cause the increase of loss because the effective control is carried out only after the conduction of the body diode and the 'current backward flow' are detected.
In order to overcome the defects of the prior art, the applicant provides an improved scheme.
Disclosure of Invention
The invention aims to provide a fixed-frequency LLC circuit and a method for tracking the resonant frequency thereof, which can adjust the working frequency of an LLC converter in real time to track the resonant frequency and solve the problem of resonant frequency point deviation caused by circuit parameter change.
In order to achieve the purpose, the invention provides the following technical scheme:
a fixed frequency LLC circuit comprises a primary full-bridge circuit, a resonant inductor Lr, an excitation inductor Lm, a resonant capacitor Cres and a secondary rectifying and filtering circuit; further comprising:
the voltage signal acquisition circuit is connected to the output end of the primary full-bridge circuit and two ends of the resonance capacitor Cres and is used for acquiring bridge arm voltage and resonance capacitor voltage and sending the bridge arm voltage and the resonance capacitor voltage to the actual phase difference operation module; the actual phase difference operation module is used for calculating the actual phase difference between the bridge arm voltage and the resonance capacitor voltage
A reference phase difference operation module for obtaining the reference phase difference between the bridge arm voltage Vp and the resonance capacitor voltage Vcr obtained by the parameter theory calculation of the fixed frequency LLC circuit when the working frequency fc is equal to the resonance frequency fr
A phase difference comparison module for receiving the outputs of the actual phase difference operation module and the reference phase difference operation module and comparing the actual phase difference
Phase difference from reference
The comparison result is output to a feedback control module;
and the feedback control module is used for adjusting the switching frequency of the frequency regulating LLC circuit in the next period according to the comparison result and generating control pulses corresponding to switching diodes in the primary full-bridge circuit and the rectifying and filtering circuit.
As an improved scheme of the present invention, the feedback control module includes a PI compensator, a frequency regulator, and a pulse generator, the PI compensator is configured to perform loop compensation on the fixed-frequency LLC circuit according to an output result of the phase difference comparison module, the frequency regulator is configured to determine a switching frequency adjustment amount of a next cycle, and the pulse generator is configured to generate a control pulse corresponding to a switching diode in the primary full-bridge circuit and the rectifying and filtering circuit according to the switching frequency adjustment amount.
A method for tracking the resonant frequency of a fixed-frequency LLC circuit comprises the following steps:
step 100: establishing the phase difference between the bridge arm voltage Vp, the resonance capacitor voltage Vcr and the reference when the working frequency fc of the fixed-frequency LLC circuit is equal to the resonance frequency fr
The relation between:
where θ represents the phase where the bridge arm voltage Vp lags the resonant current ir; ip represents the peak value of the excitation current; i represents a resonance current peak value; vo represents the output voltage; n represents the transformation ratio of an isolation transformer of the fixed-frequency LLC circuit; RL represents a load;
step 200: the bridge arm voltage Vp and the resonance capacitor voltage Vcr are collected in real time, and the actual phase difference between the two is calculated and obtained after digital processing
Step 300: setting an adjustment period, and periodically comparing the actual phase difference
Phase difference from reference
When the comparison result of the two is not in the preset error interval, switching diode pulses in the primary full-bridge circuit and the rectifying and filtering circuit in the next working cycle are controlled by adjusting the switching frequency;
step 400: repeating the step 100-300 until the actual phase difference
Phase difference from reference
Are equal.
As a modification of the present invention, in step 300, when
When controlling to increase the pulse frequency, when
When so, control decreases the pulse frequency.
Has the advantages that: compared with the prior art, the invention does not need to increase the volume of the LLC converter, only needs to collect bridge arm voltage and resonance capacitor voltage in the working process, adopts digital control processing, has low power consumption, can avoid generating excessive extra loss and reduces the efficiency. In addition, the invention has higher practicability, is suitable for being popularized and applied to different component type selection or parameter setting, has the same tracking method for the resonant frequency, and can not generate great influence on the technical effect.
Drawings
FIG. 1 is a schematic circuit diagram of the present invention;
FIG. 2 is a diagram illustrating a relationship between phase differences according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.
As shown in FIG. 1, a fixed frequency LLC circuit for implementing conversion of input and output power comprises a primary full bridge circuit, a resonant inductor Lr, an excitation inductor Lm, a resonant capacitor Cres and a secondary rectifying and filtering circuit. The primary full-bridge circuit comprises switching diodes V1-V4, one end of a resonant inductor Lr is connected with a first output end of the primary full-bridge circuit, the other end of the resonant inductor Lr is connected with one end of an excitation inductor Lm, and the other end of the excitation inductor Lm is connected with a second output end of the primary full-bridge circuit. In the fixed-frequency LLC circuit, two windings are arranged on the primary side of an isolation transformer, one end of a resonant capacitor Cres is connected with the non-homonymous end of a first primary winding, the other end of the resonant capacitor Cres is connected with the homonymous end of a second primary winding, and the homonymous end of the first primary winding and the non-homonymous end of the second primary winding are respectively connected with two ends of an excitation inductor Lm. The secondary side of the isolation transformer comprises two secondary windings, the rectifying and filtering circuit comprises switch diodes V5-V6, the homonymous end of the first secondary winding and the non-homonymous ends of the first switch, the second switch and the second secondary winding form a loop, the two ends of the first switch are connected with a switch diode V5 and a capacitor in parallel, and the two ends of the second switch are connected with a switch diode V6 and a capacitor in parallel.
The fixed-frequency LLC circuit needs to track the resonant frequency, and further comprises a voltage signal acquisition circuit, an actual phase difference operation module, a reference phase difference operation module, a phase difference comparison module and a feedback control module.
The voltage signal acquisition circuit is connected to the output end of the primary full-bridge circuit and two ends of the resonant capacitor Cres, and is used for acquiring bridge arm voltage Vp and resonant capacitor voltage Vcr and sending the bridge arm voltage Vp and resonant capacitor voltage Vcr to the actual phase difference operation module;
the actual phase difference operation module is used for calculating the actual phase difference between the bridge arm voltage and the resonance capacitor voltage
A reference phase difference operation module for obtaining the reference phase difference between the bridge arm voltage Vp and the resonance capacitor voltage Vcr obtained by the parameter theory calculation of the fixed frequency LLC circuit when the working frequency fc is equal to the resonance frequency fr
A phase difference comparison module for receiving the outputs of the actual phase difference operation module and the reference phase difference operation module and comparing the actual phase difference
Phase difference from reference
The comparison result is output to a feedback control module;
the feedback control module comprises a PI compensator, a frequency regulator and a pulse generator, the PI compensator is used for performing loop compensation on the LLC converter according to an output result of the phase difference comparison module, the frequency regulator is used for determining a switching frequency adjustment quantity of the next period, and the pulse generator is used for generating control pulses corresponding to switching diodes in the primary full-bridge circuit and the rectifying and filtering circuit according to the switching frequency adjustment quantity.
The actual phase difference operation module, the reference phase difference operation module, the phase difference comparison module and the feedback control module can realize the specific calculation process through a DSP, an FPGA, a singlechip and the like, and the circuit structure of the voltage signal acquisition circuit is not limited. The detailed implementation of the method is detailed in the prior art and is not described too much here.
The method for tracking the resonant frequency of the fixed-frequency LLC circuit comprises the following steps:
step 100: as shown in FIG. 2, for the fixed frequency LLC circuit shown in FIG. 1, when the operating frequency fc is equal to the resonance frequency fr, the phase difference between the bridge arm voltage Vp and the resonance current ir
The phase of the resonant capacitor voltage Vcr lags the phase of the resonant current ir determined by the magnetizing inductance Lm
Assuming that the phase of the bridge arm voltage lagging resonant current is theta, im is exciting current, Ip is peak value of exciting current, the reference phase difference operation module can theoretically establish exciting inductance Lm, bridge arm voltage Vp, resonant capacitor voltage Vcr and reference phase difference according to parameters of the LLC circuit
The relation between:
wherein I represents a resonance current peak; vo represents the output voltage; n represents the transformation ratio of an isolation transformer of the fixed-frequency LLC circuit; RL denotes a load.
Step 200: the voltage signal acquisition circuit acquires the bridge arm voltage Vp and the resonance capacitor voltage Vcr in real time, the bridge arm voltage Vp and the resonance capacitor voltage Vcr can be converted into voltage signals suitable for digital processing through circuits such as an isolation operational amplifier, and an actual phase difference between the bridge arm voltage Vp and the resonance capacitor voltage Vcr can be calculated and acquired through a method such as a phase-locked loop through an actual phase difference operation module
Step 300: setting an adjustment period, actual phase differences may be periodically compared by the phase difference comparison module at intervals of 1 or more duty cycles
Phase difference from reference
When the circuit parameters influence the resonance frequency, i.e. the reference phase difference
When changed, the actual phase difference
Phase difference from reference
When the comparison result of the two is not in the preset error interval, the feedback control module controls the pulse of the switching diodes V1-V6 in the next working period by adjusting the switching frequency. The error interval is generally set according to the actual situation, for example, it can be set
If it is judged that
If the difference value is not in the preset error interval, the feedback control module controls the pulse frequency to be increased, and according to the formula, the value theta is reduced at the moment, the actual phase difference is gradually reduced until the difference value between the actual phase difference and the reference phase difference is in the preset error interval; on the contrary, if judged
And if the difference value is not in the preset error interval, the feedback control module controls to reduce the pulse frequency, at the moment, the pulse period is increased, the theta value is increased, and the actual phase difference is increased
Gradually increasing; when the difference value is within the error interval, the pulse frequency is not changed. The error interval is used as an allowable value to prevent the switching frequency from being frequently changed.
Step 400: repeating the step 100 and 300, the feedback control continuously adjusts the operating frequency of the circuit until the actual phase difference
Phase difference from reference
Equal, when the switching frequency equals the new resonance frequency, the circuit enters a new steady state.
Although the present description is described in terms of embodiments, not every embodiment includes only a single embodiment, and such description is for clarity only, and those skilled in the art should be able to integrate the description as a whole, and the embodiments can be appropriately combined to form other embodiments as will be understood by those skilled in the art.
Therefore, the above description is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application; all changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Claims (4)
1. A fixed frequency LLC circuit comprises a primary full-bridge circuit, a resonant inductor Lr, an excitation inductor Lm, a resonant capacitor Cres and a secondary rectifying and filtering circuit; the isolation transformer is characterized in that a first primary winding and a second primary winding are arranged on the primary side of the isolation transformer, one end of a resonant capacitor Cres is connected with a non-homonymous end of the first primary winding, the other end of the resonant capacitor Cres is connected with a homonymous end of the second primary winding, and the homonymous end of the first primary winding and the non-homonymous end of the second primary winding are respectively connected with two ends of an excitation inductor Lm; further comprising:
the voltage signal acquisition circuit is connected to the output end of the primary full-bridge circuit and two ends of the resonance capacitor Cres and is used for acquiring bridge arm voltage and resonance capacitor voltage and sending the bridge arm voltage and the resonance capacitor voltage to the actual phase difference operation module; the actual phase difference operation module is used for calculating the actual phase difference between the bridge arm voltage and the resonance capacitor voltage
A reference phase difference operation module for obtaining the reference phase difference between the bridge arm voltage Vp and the resonance capacitor voltage Vcr obtained by the calculation according to the hardware parameter theory of the fixed frequency LLC circuit when the working frequency fc is equal to the resonance frequency fr
A phase difference comparison module for receiving the outputs of the actual phase difference operation module and the reference phase difference operation module and comparing the actual phase difference
Phase difference from reference
The comparison result is output to a feedback control module;
and the feedback control module is used for adjusting the switching frequency of the frequency regulating LLC circuit in the next period according to the comparison result and generating control pulses corresponding to switching diodes in the primary full-bridge circuit and the rectifying and filtering circuit.
2. The fixed frequency LLC circuit of claim 1, wherein the feedback control module comprises a PI compensator, a frequency regulator and a pulse generator, the PI compensator is used for performing loop compensation on the fixed frequency LLC circuit according to the output result of the phase difference comparison module, the frequency regulator is used for determining the switching frequency adjustment amount of the next period, and the pulse generator is used for generating control pulses corresponding to the switching diodes in the primary full bridge circuit and the rectifying and filtering circuit according to the switching frequency adjustment amount.
3. A method for tracking the resonant frequency of a fixed-frequency LLC circuit is characterized by comprising the following steps:
step 100: establishing the phase difference between the bridge arm voltage Vp, the resonance capacitor voltage Vcr and the reference when the working frequency fc of the fixed-frequency LLC circuit is equal to the resonance frequency fr
The relation between:
where θ represents the phase where the bridge arm voltage Vp lags the resonant current ir; ip represents the peak value of the excitation current; i represents a resonance current peak value; vo represents the output voltage; n represents the transformation ratio of an isolation transformer of the fixed-frequency LLC circuit; RL represents a load;
step 200: the bridge arm voltage Vp and the resonance capacitor voltage Vcr are collected in real time, and the actual phase difference between the two is calculated and obtained after digital processing
Step 300: setting an adjustment period, and periodically comparing the actual phase difference
Phase difference from reference
When the comparison result of the two is not in the preset error interval, switching diode pulses in the primary full-bridge circuit and the rectifying and filtering circuit in the next working cycle are controlled by adjusting the switching frequency;
step 400: repeating the step 100-300 until the actual phase difference
Equal to the reference phase difference
4. A method for tracking the resonant frequency of a fixed frequency LLC circuit as claimed in claim 3, wherein in step 300, when
When controlling to increase the pulse frequency, when
When so, control decreases the pulse frequency.
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| CN202111128423.8A CN113872448A (en) | 2021-09-26 | 2021-09-26 | Fixed-frequency LLC circuit and resonant frequency tracking method thereof |
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| CN202111128423.8A CN113872448A (en) | 2021-09-26 | 2021-09-26 | Fixed-frequency LLC circuit and resonant frequency tracking method thereof |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114583932A (en) * | 2022-04-29 | 2022-06-03 | 茂睿芯（深圳）科技有限公司 | Control circuit and control method for LLC resonant converter |
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2021
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114583932A (en) * | 2022-04-29 | 2022-06-03 | 茂睿芯（深圳）科技有限公司 | Control circuit and control method for LLC resonant converter |
| CN114583932B (en) * | 2022-04-29 | 2022-07-26 | 茂睿芯（深圳）科技有限公司 | Control circuit and control method for LLC resonant converter |
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