CN114244126B - Synchronous rectification method of bidirectional CLLC resonant converter - Google Patents
Synchronous rectification method of bidirectional CLLC resonant converter Download PDFInfo
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- CN114244126B CN114244126B CN202111466255.3A CN202111466255A CN114244126B CN 114244126 B CN114244126 B CN 114244126B CN 202111466255 A CN202111466255 A CN 202111466255A CN 114244126 B CN114244126 B CN 114244126B
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- 230000001360 synchronised effect Effects 0.000 title claims abstract description 51
- 238000000034 method Methods 0.000 title claims abstract description 45
- 230000002457 bidirectional effect Effects 0.000 title claims abstract description 21
- 230000010363 phase shift Effects 0.000 claims abstract description 16
- 238000005457 optimization Methods 0.000 claims abstract description 11
- 238000004364 calculation method Methods 0.000 claims abstract description 8
- 230000008569 process Effects 0.000 claims description 13
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- 238000013178 mathematical model Methods 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 7
- 239000003990 capacitor Substances 0.000 description 4
- 238000004146 energy storage Methods 0.000 description 4
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Classifications
-
- 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
- H02M3/33576—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 having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33592—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 having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
-
- 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
- H02M3/33576—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 having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33584—Bidirectional converters
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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
Abstract
The invention discloses a synchronous rectification method of a bidirectional CLLC resonant converter, which adopts a control method combining fixed phase-shift angle variable frequency control and maximum efficiency point tracking method, finds the relation between the synchronous rectification signal switching-on time of a rectifier bridge and a switching tube driving signal in an inverter bridge after adding phase-shift control, can ensure the accuracy of the switching tube switching-on time of the rectifier bridge within the full working frequency range, and automatically searches the optimal duty ratio D by the mode of maximum efficiency point tracking control optimization . According to the synchronous rectification control method, accurate modeling of the resonant converter is not needed, so that resonant elements in the resonant cavity have good parameter robustness, and the phenomenon that a circuit mathematical model is changed due to parameter errors of the resonant elements in hardware design is avoided, so that the synchronous rectification signal duty ratio calculation is wrong, and therefore the synchronous rectification control method has good anti-interference capability.
Description
Technical Field
The invention relates to the technical field of bidirectional DC-DC converters, in particular to a synchronous rectification method of a bidirectional CLLC resonant converter.
Background
Under the background of a double-carbon target, a large amount of new energy sources such as photovoltaic energy, wind power and the like are connected into a power grid, and the new energy sources generate power while reducing carbon emission, so that various unstable factors are brought to the power grid. The energy storage unit plays an important role in voltage and frequency regulation of the power grid due to the dual characteristics that the energy storage unit can be used as a load and a power supply. The bidirectional DC-DC converter is a bridge connecting the energy storage unit and the direct current micro-grid, and the performance of the bidirectional DC-DC converter directly determines the development of energy storage technology.
In recent years, among a plurality of bidirectional DC-DC converters, a bidirectional CLLC resonant converter has attracted a great deal of attention due to its advantages of having good soft switching characteristics and a wide voltage output range. The bidirectional CLLC resonant converter consists of an inverter bridge, a rectifier bridge, a high-frequency transformer and a resonant cavity. The inverter bridge and the rectifier bridge under high switching frequency usually adopt a power MOSFET or a SiC MOSFET as a power semiconductor switch, when the rectifier bridge works, under the condition that the current is not very high, the conduction voltage drop of the MOSFET anti-parallel body diode is larger than the on-state voltage drop of the MOSFET, so that if the anti-parallel body diode of the MOSFET is utilized for rectification, great on-state loss is caused, and the improvement of the working efficiency of the converter is not facilitated. This problem can be solved by operating the MOSFET on the rectifying side in synchronous rectification, further improving the efficiency of the converter. Therefore, the accurate synchronous rectification control of the bidirectional CLLC resonant converter is achieved.
Disclosure of Invention
The invention aims to provide a synchronous rectification control method applied to a bidirectional CLLC resonant converter. The method overcomes the problem that the traditional hardware detection circuit brings additional loss, also avoids the defect of poor parameter robustness when accurate time domain modeling calculation is performed on synchronous rectification signals, simplifies the control process, and improves the operation efficiency of the converter.
In order to achieve the above purpose, the present invention provides the following technical solutions: a synchronous rectification method of a bidirectional CLLC resonance converter comprises the following steps:
step 1, obtaining the switching frequency f of a circuit in a voltage control loop s The method comprises the steps of carrying out a first treatment on the surface of the Sampling the output voltage V of the low-side rectifier o Will be measured value V o And a given value V oref The difference is made, and then the voltage control quantity V is output through a voltage controller control The voltage control adopts a PI controller, wherein the voltage control quantity V control The working switching frequency f of the circuit is generated after passing through the voltage-controlled oscillator s ；
Step 2, according to the working switching frequency f s And the formula (1) judges the working state of the circuit according to the switching frequency f s The circuit operation State is divided into a far resonance frequency under resonance State which is marked as State1, a State near the resonance frequency which is marked as State2 and a far resonance frequency over resonance State which is marked as State3, and the frequency ranges of the three operation states are as follows:
f min ≤f s ＜0.95f r ，State1
0.95f r ≤f s ≤1.05f r ，State2
1.05f r ＜f s ≤f max ，State3 (1)
wherein in formula (1), f min For the minimum switching frequency in the switching frequency range, f max Is the maximum switching frequency within the switching frequency range.
Step 3, selecting phase shift angleThe circuit operates in a fixed phase angle variable frequency control mode; phase shift angle->The selection range of (2) is shown in formula (2), wherein +.>t dead ＝100ns；
When f s ＜f r
When f s ＞f r (2)
Step 4, according to the phase shift angleAnd equation (3) calculating the duty ratio D generated by phase shifting basis ； D basis The calculation formula of (2) is as follows:
when->
When->
Step 5, the low-voltage side rectifier synchronously rectifies and controls soft start operation, and a switch S=1; the specific process is as follows: the duty cycle is started from 0 with a step size DeltaD in each switching period softstart Increase to D softstart_final Wherein D is softstart_final According to formula (4), ΔD softstart Obtaining according to a formula (5); t (T) softstart For synchronous rectification soft start time, T is taken here softstart ＝50ms， D softstart_final For t=t softstart Duty ratio of the time switching transistor Q5 to the switching transistor Q8:
D softstart_final ＝D basis state2 or State3 (4)
T-shaped memory step Calculating step length for the controller, taking T as an example of the controller with the clock frequency of 150MHz step 16.667ns, soft start step Δd softstart The calculation formula of (2) is as follows:
step 6, when d=d softstart_final When the synchronous rectification soft start is finished, the switch S=2 starts to carry out maximum efficiency point tracking control on the low-voltage side rectifier;
step 7, obtaining the switching signals V of the switching tubes Q5 to Q8 according to the duty ratio D gs5 To V gs8 The method comprises the steps of carrying out a first treatment on the surface of the Switching-on time t of low-voltage side switching tube Q5 and switching tube Q8 on Is the falling edge of the high-voltage side switching tube Q3; switching tube Q6 at low voltage side and switching tube Q7 at conduction time t on Is the falling edge of the high side switching tube Q4.
Preferably, the specific steps of the step 6 are as follows: the specific process is as follows:
step 6.1, calculating the working efficiency eta of the circuit according to the formula (6):
in the formula (6), U o And I o Respectively, is output side DC voltage and DC current, U in And I in The input side dc voltage and dc current, respectively.
In step 6.2, when the resonant converter operates in State1 and State3, the duty ratio D is as shown in formula (7):
D＝D last +ΔD MEPT (7)
ΔD in equation (7) MEPT D for the step length of the change of the duty ratio in the maximum efficiency point tracking control last Synchronous rectification duty cycle for last switching period, D last Initial value of D softstart_final The method comprises the steps of carrying out a first treatment on the surface of the If the work efficiency η increases after the execution of the formula (7), the execution of the formula (7) is continued until d=d optimization Stop at time D optimization As shown in fig. 3, an optimal duty cycle of the synchronous rectification process is represented; when the resonant converter is operating at State2, the duty cycle D is as shown in equation (8):
D＝D softstart_final (8)。
compared with the prior art, the invention has the following beneficial effects:
the synchronous rectification control method ensures that the resonant current of the rectification side of the resonant converter is in an intermittent state within the full working frequency range, ensures that the switching-on time of the synchronous rectification signal and the driving signal of the inversion side have a strict corresponding relation, greatly increases the accuracy of synchronous rectification driving pulse, avoids the problem of efficiency reduction caused by the distortion of the resonant current of the rectification side due to the error of the starting time of the synchronous rectification signal, and improves the reliability.
According to the synchronous rectification control method, accurate modeling of the resonant converter is not needed, so that resonant elements in the resonant cavity have good parameter robustness, and the phenomenon that a circuit mathematical model is changed due to parameter errors of the resonant elements in hardware design is avoided, so that the duty ratio of a synchronous rectification signal is calculated incorrectly, and therefore the synchronous rectification control method has good anti-interference capability.
Drawings
FIG. 1 is a circuit diagram of a bi-directional CLLC resonant converter according to the present invention;
FIG. 2 is a diagram of steps in implementing a synchronous rectification control method of a bi-directional CLLC resonant converter in a forward energy flow mode according to the present invention;
FIG. 3 is a waveform diagram of an example of a synchronous rectification strategy for a bidirectional CLLC resonant converter according to the present invention when forward energy flows from a high voltage side to a low voltage side; fig. 3 (a) is a driving pulse waveform of a switching tube when the high-voltage side inverter bridge is phase-shifted; fig. 3 (b), (c) and (d) are the theoretical waveforms of the low-voltage side resonant current and the synchronous rectification signal waveforms provided by the invention when State1, state2 and State3 are respectively.
Detailed Description
Technical aspects of embodiments of the present invention will be clearly and fully described in the following description of the embodiments of the present invention with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, are intended to fall within the scope of the present invention.
Referring to fig. 1-3, the present invention provides a technical solution: the synchronous rectification method of the bidirectional CLLC resonant converter comprises the bidirectional CLLC resonant converter, wherein the bidirectional CLLC resonant converter consists of an inverter bridge, a rectifier bridge, a high-frequency transformer and a resonant cavity, a high-voltage side single-phase bridge is formed by a switching tube Q1, a switching tube Q2, a switching tube Q3 and a switching tube Q4, and the midpoint of a bridge arm is connected in series with a primary side resonant inductor L r1 And primary side resonance capacitor C r1 And is connected to the primary side of the high-frequency transformer T, where L m Is the primary side equivalent excitation inductance of the high-frequency transformer. The switching tube Q5, the switching tube Q6, the switching tube Q7 and the switching tube Q8 form a low-voltage side single-phase bridge together, and the middle point of the bridge arm is connected in series with the secondary side resonance inductance L r2 And a secondary sideResonance capacitor C r2 And is connected with the secondary side of the high-frequency transformer T. V (V) dc_high Is a high-voltage side direct current voltage, V dc_low Is a low-side direct-current voltage. C (C) f1 Is a high-voltage side filter capacitor C f2 Is a low-side filter capacitor. The switching transistors Q1 to Q8 are power MOSFETs or sicmosfets.
The bi-directional CLLC resonant converter can operate in a forward energy flow mode and a reverse energy flow mode. When the energy flows in the forward direction, energy flows from the direct-current high-voltage side to the direct-current low-voltage side, the switching tube Q1, the switching tube Q2, the switching tube Q3 and the switching tube Q4 form an inverter bridge, and the switching tube Q5, the switching tube Q6, the switching tube Q7 and the switching tube Q8 form a rectifier bridge; when the energy flows in the reverse direction, energy flows from the direct-current low-voltage side to the direct-current high-voltage side, the switching tube Q5, the switching tube Q6, the switching tube Q7 and the switching tube Q8 form an inverter bridge, and the switching tube Q1, the switching tube Q2, the switching tube Q3 and the switching tube Q4 form a rectifier bridge.
The invention adopts a control method combining fixed phase-shift angle variable frequency control and maximum efficiency point tracking method, finds the relation between the synchronous rectification signal switching-on time of the rectifier bridge and the switching tube driving signal in the inverter bridge after adding phase-shift control, can ensure the accuracy of the switching tube switching-on time of the rectifier bridge in the full working frequency range, and automatically searches the optimal duty ratio D by the mode of maximum efficiency point tracking control optimization 。
The synchronous rectification control method of the rectifier bridge will be described by taking a forward energy flow mode as an example. Fig. 2 is a schematic diagram of the synchronous rectification control method provided in the forward energy flow mode of the present invention. Obtaining the voltage control quantity V by a voltage control loop control ，V control Switching frequency f acting on high-side inverter bridge of voltage-controlled oscillator output resonant converter s Adding phase shift angleAnd driving signals Vgs1, vgs2, vgs3 and Vgs4 of the high-voltage side inverter bridge switching tubes Q1 to Q4 are obtained respectively. The driving signal generation method of the switching tube Q5 to the switching tube Q8 of the low-voltage side rectifier bridge is as follows: first, from the high-pressure sideThe falling edges of the driving signals Vgs3 and Vgs4 of the inverter bridge switching tube Q3 and the switching tube Q4 respectively obtain the starting conduction time t of the low-voltage side switching tube Q5 and the switching tube Q8 on And the starting conduction time of the low-voltage side switching tube Q6 and the switching tube Q7. Second, by a given phase shift angle +.>Calculating the duty ratio D generated by phase shift basis . Furthermore, corresponding synchronous rectification control is performed according to different running states Statex (x=1, 2, 3) of the circuit. The single pole double throw switch is shown as S in FIG. 2 when T < T softstart When s=1, a soft start process of synchronous rectification control is performed; when T > T softstart When s=2, the synchronous rectifier switching tube optimal duty ratio based on the maximum efficiency point tracking control is searched. Finally, the switching tubes Q5 to Q8 perform synchronous rectification control with the optimal duty ratio;
taking a forward energy flow mode as an example, the complete steps of the control strategy provided by the invention are as follows:
step 1, obtaining the switching frequency f of a circuit in a voltage control loop s The method comprises the steps of carrying out a first treatment on the surface of the Sampling the output voltage V of the low-side rectifier o Will be measured value V o And a given value V oref The difference is made, and then the voltage control quantity V is output through a voltage controller control The voltage control adopts a PI controller, wherein the voltage control quantity V control The working switching frequency f of the circuit is generated after passing through the voltage-controlled oscillator s ；
Step 2, according to the working switching frequency f s And the formula (1) judges the working state of the circuit according to the switching frequency f s The circuit operation State is divided into a far resonance frequency under resonance State which is marked as State1, a State near the resonance frequency which is marked as State2 and a far resonance frequency over resonance State which is marked as State3, and the frequency ranges of the three operation states are as follows:
f min ≤f s ＜0.95f r ，State1
0.95f r ≤f s ≤1.05f r ，State2
1.05f r ＜f s ≤f max ，State3 (1)
step 3, selecting phase shift angleThe circuit operates in a fixed phase angle variable frequency control mode; phase shift angle->The selection range of (2) is shown in formula (2), wherein +.>t dead ＝100ns；
When f s ＜f r
When f s ＞f r (2)
Step 4, according to the phase shift angleAnd equation (3) calculating the duty ratio D generated by phase shifting basis ； D basis The calculation formula of (2) is as follows:
when->
When->
Step 5, the low-voltage side rectifier synchronous rectification controls the soft start operation, and the switch s=1 in fig. 2; the specific process is as follows: the duty cycle is started from 0 with a step size DeltaD in each switching period softstart Increase to D softstart_final Wherein D is softstart_final According to formula (4), ΔD softstart Solving according to a formula (5); t (T) softstart For synchronous rectification soft start time, T is taken here softstart ＝50ms，D softstart_final For t=t softstart Duty ratio of the time switching transistor Q5 to the switching transistor Q8:
D softstart_final ＝D basis state2 or State3 (4)
T-shaped memory step Calculating step length for the controller, taking T as an example of the controller with the clock frequency of 150MHz step 16.667ns, soft start step Δd softstart The calculation formula of (2) is as follows:
step 6, when d=d softstart_final At this time, the synchronous rectification soft start is finished, and at this time, the switch s=2 starts to perform maximum efficiency point tracking control on the low-voltage side rectifier, and the specific process is as follows:
step 6.1, calculating the working efficiency of the circuit according to the formula (6):
in step 6.2, when the resonant converter operates in State1 and State3, the duty ratio D is as shown in formula (7):
D＝D last +ΔD MEPT (7)
ΔD in equation (7) MEPT D for the step length of the change of the duty ratio in the maximum efficiency point tracking control last Synchronous rectification duty cycle for last switching period, D last Initial value of D softstart_final The method comprises the steps of carrying out a first treatment on the surface of the If the working efficiency eta increases after the execution of the formula (7), the execution of the formula (7) is continued untilD＝D optimization Stop at time D optimization As shown in fig. 3, an optimal duty cycle of the synchronous rectification process is represented; when the resonant converter is operating at State2, the duty cycle D is as shown in equation (8):
D＝D softstart_final (8)
step 7, obtaining the switching signals V of the switching tubes Q5 to Q8 according to the duty ratio D gs5 To V gs8 The method comprises the steps of carrying out a first treatment on the surface of the Description: switching-on time t of low-voltage side switching tube Q5 and switching tube Q8 on Is the falling edge of the high-voltage side switching tube Q3; switching tube Q6 at low voltage side and switching tube Q7 at conduction time t on Is the falling edge of the high side switching tube Q4.
FIG. 3 is a waveform diagram of an embodiment of a synchronous rectification strategy for forward energy flow from high side to low side of a bidirectional CLLC resonant converter according to the present invention, wherein (a) is a driving pulse of a high side switching tube, and wherein switching tube Q1 leads switching tube Q4 by an angleThe switching tube Q1 and the switching tube Q2 are complementarily conducted, the switching tube Q3 and the switching tube Q4 are complementarily conducted, a dead time is added between the upper switching tube and the lower switching tube of the same bridge arm, and T is the same s Is a switching period. (b) In the figure, the low-voltage side resonant current and the synchronous rectification signal waveform when the converter is operated at State1 are shown, and the driving pulse signals of the switching transistor Q6 and the switching transistor Q7 are mirror-inverted on the time axis in order to visually observe the positions of the driving pulses. Wherein V is gs58 Is the driving signal of the low-voltage side switching tube Q5 and the switching tube Q8, V gs67 I is the driving signal of the switching tube Q6 and the switching tube Q7 lrs Is low-voltage side resonance current, T MEPT For the duration of the maximum efficiency point tracking process, D in State1 State softstart_final Less than the optimal duty cycle D optimization ，t＝T softstart And when the maximum efficiency point tracking control is performed according to the efficiency. (c) The diagram is the theoretical waveform of the converter when working at State2, the duty ratio of the synchronous rectification signal is increased to D softstart_final In this state t=t softstart Time D softstart_final ＝D optimization AfterwardsThe maximum efficiency point tracking control is no longer performed. (d) The diagram shows the converter operating in State3, which is similar to State1, D softstart_final Less than the optimal duty cycle D optimization Maximum efficiency point tracking control is performed.
The above description is directed to the synchronous rectification strategy implementation of a bi-directional CLLC resonant converter when forward energy flows from the high voltage side to the low voltage side. When the bidirectional CLLC resonant converter flows in reverse energy, the synchronous rectification strategy implementation process is also applicable, except that the rectifier bridge is arranged on the high-voltage side and consists of a switching tube Q1, a switching tube Q2, a switching tube Q3 and a switching tube Q4, and the inverter bridge is arranged on the low-voltage side and consists of a switching tube Q5, a switching tube Q6, a switching tube Q7 and a switching tube Q8.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (2)
1. A synchronous rectification method of a bidirectional CLLC resonant converter, comprising the steps of:
step 1, obtaining the switching frequency f of a circuit in a voltage control loop s The method comprises the steps of carrying out a first treatment on the surface of the Sampling the output voltage V of the low-side rectifier o Will be measured value V o And a given value V oref The difference is made, and then the voltage control quantity V is output through a voltage controller control The voltage control adopts a PI controller, wherein the voltage control quantity V control The working switching frequency f of the circuit is generated after passing through the voltage-controlled oscillator s ；
Step 2, according to the working switching frequency f s And the formula (1) judges the working state of the circuit according to the switching frequency f s The circuit operation State is divided into a far resonance frequency under resonance State which is marked as State1, a State near the resonance frequency which is marked as State2 and a far resonance frequency over resonance State which is marked as State3, and the frequency ranges of the three operation states are as follows:
f min ≤f s ＜0.95f r ，State1
0.95f r ≤f s ≤1.05f r ，State2
1.05f r ＜f s ≤f max ，State3 (1)
wherein in formula (1), f min For the minimum switching frequency in the switching frequency range, f max Is the maximum switching frequency in the switching frequency range;
step 3, selecting phase shift angleThe circuit operates in a fixed phase angle variable frequency control mode; phase shift angle->The selection range of (2) is shown in formula (2), wherein +.>t dead =100 ns, primary side resonance inductance L r1 The primary side resonance capacitance is C r1 ；
When f s ＜f r
When f s ＞f r (2)
Step 4, according to the phase shift angleAnd equation (3) calculating the duty ratio D generated by phase shifting basis ；D basis The calculation formula of (2) is as follows:
when->
When->
Step 5, the low-voltage side rectifier synchronously rectifies and controls soft start operation, and a switch S=1; the specific process is as follows: the duty cycle is started from 0 with a step size DeltaD in each switching period softstart Increase to D softstart_final Wherein D is softstart_final According to formula (4), ΔD softstart Solving according to a formula (5); t (T) softstart For synchronous rectification soft start time, T is taken here softstart ＝50ms，D softstart_final For t=t softstart Duty ratio of the time switching transistor Q5 to the switching transistor Q8:
D softstart_final ＝D basis state2 or State3 (4)
T-shaped memory step Calculating step length for the controller, taking T as an example of the controller with the clock frequency of 150MHz step 16.667ns, soft start step Δd softstart The calculation formula of (2) is as follows:
step 6, when d=d softstart_final When the synchronous rectification soft start is finished, the switch S=2 starts to carry out maximum efficiency point tracking control on the low-voltage side rectifier;
step 7, according to the duty cycleD obtaining the switching signals V of the switching tubes Q5 to Q8 gs5 To V gs8 The method comprises the steps of carrying out a first treatment on the surface of the Switching-on time t of low-voltage side switching tube Q5 and switching tube Q8 on Is the falling edge of the high-voltage side switching tube Q3; switching tube Q6 at low voltage side and switching tube Q7 at conduction time t on Is the falling edge of the high side switching tube Q4.
2. The synchronous rectification method of a bidirectional CLLC resonant converter of claim 1, wherein said step 6 comprises the specific steps of: the specific process is as follows:
step 6.1, calculating the working efficiency eta of the circuit according to the formula (6):
in the formula (6), U o And I o Respectively, is output side DC voltage and DC current, U in And I in Respectively input side direct current voltage and direct current;
in step 6.2, when the resonant converter operates in State1 and State3, the duty ratio D is as shown in formula (7):
D＝D last +ΔD MEPT (7)
ΔD in equation (7) MEPT D for the step length of the change of the duty ratio in the maximum efficiency point tracking control last Synchronous rectification duty cycle for last switching period, D last Initial value of D softstart_final The method comprises the steps of carrying out a first treatment on the surface of the If the work efficiency η increases after the execution of the formula (7), the execution of the formula (7) is continued until d=d optimization Stop at time D optimization Representing an optimal duty cycle of the synchronous rectification process; when the resonant converter operates at State2, the duty cycle D is as shown in equation (8):
D＝D softstart_final (8)。
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