CN114244126A - Synchronous rectification method of bidirectional CLLC resonant converter - Google Patents
Synchronous rectification method of bidirectional CLLC resonant converter Download PDFInfo
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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
- 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
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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
- 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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Abstract
The invention discloses a synchronous rectification method of a bidirectional CLLC resonant converter, which adopts a control method combining fixed phase-shift angle frequency conversion control and a maximum efficiency point tracking method, finds the relation between the turn-on time of a synchronous rectification signal of a rectifier bridge after phase-shift control and a driving signal of a switching tube in an inverter bridge, can ensure the accuracy of the turn-on time of the switching tube of the rectifier bridge in the full working frequency range, and automatically searches for the optimal duty ratio D in a maximum efficiency point tracking control modeoptimization. The synchronous rectification control method does not need to carry out accurate modeling on the resonant converter, can enable the resonant elements in the resonant cavity to have good parameter robustness, and avoids the phenomenon that the duty ratio of a synchronous rectification signal is calculated wrongly due to the change of a circuit mathematical model caused by the parameter errors of the resonant elements during hardware design, so that the synchronous rectification control method has good anti-jamming 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, new energy such as photovoltaic energy, wind power and the like is connected to a power grid in large quantity, and various unstable factors are brought to the power grid while carbon emission is reduced by new energy power generation. The energy storage unit plays an important role in voltage regulation and frequency modulation of a power grid due to the dual characteristics of the energy storage unit which 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 microgrid, and the performance of the bidirectional DC-DC converter directly determines the development of an energy storage technology.
In recent years, among many bidirectional DC-DC converters, a bidirectional CLLC resonant converter has attracted much attention because of its advantages of good soft switching characteristics and wide voltage output range. The bidirectional CLLC resonant converter consists of four parts, namely 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, and when the rectifier bridge works, the conduction voltage drop of the inverse parallel diode of the MOSFET is larger than the on-state voltage drop of the MOSFET under the condition that the current is not very high, so that if the inverse parallel diode of the MOSFET is used for rectification, great on-state loss is caused, and the improvement of the working efficiency of the converter is not facilitated. If the MOSFET on the rectifying side is operated in a synchronous rectification state, the problem can be solved, and the efficiency of the converter is further improved. Therefore, the realization of accurate synchronous rectification control of the bidirectional CLLC resonant converter has important research significance.
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 the synchronous rectification signal is calculated by accurate time domain modeling, simplifies the control process and improves the operation efficiency of the converter.
In order to achieve the purpose, the invention provides the following technical scheme: a synchronous rectification method of a bidirectional CLLC resonant converter comprises the following steps:
fmin≤fs＜0.95fr，State1
0.95fr≤fs≤1.05fr，State2
1.05fr＜fs≤fmax，State3 (1)
wherein in the formula (1), fminIs the minimum switching frequency, f, in the switching frequency rangemaxIs the maximum switching frequency in the switching frequency range.
Step 3, selecting a phase shift angle
The circuit operates in a fixed phase-shifting angle frequency conversion control mode; phase shift angle
Is shown in formula (2), wherein
tdead＝100ns；
Step 5, the low-voltage side rectifier controls soft start operation through synchronous rectification, and a switch S is equal to 1; the specific process is as follows: the duty cycle starts from 0 and is in steps deltaD within each switching periodsoftstartIncrease to Dsoftstart_finalWherein D issoftstart_finalCalculated according to equation (4), Δ DsoftstartObtaining according to the formula (5); t issoftstartFor synchronous rectification of soft start time, T is taken heresoftstart＝50ms， Dsoftstart_finalIs T ═ TsoftstartDuty ratio of time switching tube Q5 to switching tube Q8:
Dsoftstart_final＝Dbasisstate2 or State3 (4)
Note TstepFor the calculation of the step size by the controller, take T as an example of a controller with a clock frequency of 150MHzstep16.667ns, soft start step Δ DsoftstartThe calculation formula of (2) is as follows:
step 6, when D ═ Dsoftstart_finalWhen synchronous rectification soft start is finished, and the switch S is 2, the maximum efficiency point tracking control is started to be carried out on the low-voltage side rectifier;
step 7, obtaining a switching signal V from the switching tube Q5 to the switching tube Q8 according to the duty ratio Dgs5To Vgs8(ii) a Conduction time t of low-voltage side switch tube Q5 and switch tube Q8onIs the falling edge of the high side switch tube Q3; conduction time t of low-voltage side switch tube Q6 and switch tube Q7onIs the falling edge of the high side switch Q4.
Preferably, the specific steps of 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), UoAnd IoRespectively, an output side DC voltage and a DC current, UinAnd IinAn input side direct voltage and a direct current, respectively.
Step 6.2, when the resonant converter works at State1 and State3, the duty ratio D is shown as the formula (7):
D＝Dlast+ΔDMEPT (7)
delta D in formula (7)MEPTFor maximum efficiency point tracking the step length of the change of the duty ratio in the control, DlastSynchronous rectification duty cycle for the previous switching cycle, DlastHas an initial value of Dsoftstart_final(ii) a If the operating efficiency η increases after executing equation (7), then equation (7) continues to be executed until D ═ DoptimizationAt a time of rest, DoptimizationAs shown in fig. 3, represents the optimal duty cycle of the synchronous rectification process; when the resonant converter is operating at State2, the duty cycle D is as shown in equation (8):
D＝Dsoftstart_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 interrupted state in the full working frequency range, ensures that the opening time of the synchronous rectification signal has a strict corresponding relation with the driving signal of the inversion side, greatly increases the accuracy of the synchronous rectification driving impulse, 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.
The synchronous rectification control method does not need to carry out accurate modeling on the resonant converter, can enable the resonant element in the resonant cavity to have good parameter robustness, and avoids the problem that the duty ratio of the synchronous rectification signal is calculated wrongly due to the change of a circuit mathematical model caused by the parameter error of the resonant element during hardware design, so that the synchronous rectification control method has good anti-jamming capability.
Drawings
FIG. 1 is a circuit diagram of a bidirectional CLLC resonant converter according to the present invention;
fig. 2 is a diagram of implementation steps of a bidirectional CLLC resonant converter synchronous rectification control method in a forward energy flow mode;
fig. 3 is a waveform diagram of an example of the synchronous rectification strategy when the bidirectional CLLC resonant converter proposed in the present invention flows forward energy from the high-voltage side to the low-voltage side; FIG. 3(a) is the driving pulse waveform of the switching tube when the high-voltage side inverter bridge is phase-shifted; fig. 3(b), (c) and (d) show the theoretical waveforms of the low-voltage side resonant current at State1, State2 and State3, respectively, and the waveforms of the synchronous rectification signal proposed by the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1-3, the present invention provides a technical solution: a synchronous rectification method of a 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 consists of a switching tube Q1, a switching tube Q2, a switching tube Q3 and a switching tube Q4, and a primary side resonant inductor L is connected to the midpoint of a bridge arm in seriesr1And primary side resonance capacitor Cr1And is connected to the primary side of a high-frequency transformer T, where LmThe primary side equivalent excitation inductance of the high-frequency transformer. A low-voltage side single-phase bridge is formed by the switching tube Q5, the switching tube Q6, the switching tube Q7 and the switching tube Q8, and the middle point of a bridge arm is connected in series with a secondary side resonance inductor Lr2And secondary side resonance capacitor Cr2And is connected to the secondary side of the high frequency transformer T. Vdc_highIs a high side DC voltage, Vdc_lowIs a low-side direct-current voltage. Cf1Is a high-side filter capacitor, Cf2Is a low-voltage side filter capacitor. The switching tubes Q1 to Q8 are power MOSFETs or SiCSMOSFETs.
The bidirectional CLLC resonant converter can operate in a forward energy flow mode and a reverse energy flow mode. When in a forward energy flow mode, 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 energy flow mode, the 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 angle variable frequency control and a maximum efficiency point tracking method, finds the relation between the switching-on time of a synchronous rectification signal of a rectifier bridge after phase shift control and a driving signal of a switching tube in an inverter bridge, can ensure the accuracy of the switching-on time of the switching tube of the rectifier bridge in the full working frequency range, and automatically finds the optimal duty ratio D by the maximum efficiency point tracking control methodoptimization。
The synchronous rectification control method of the rectifier bridge is described by taking a forward energy flow mode as an example. Fig. 2 is a schematic diagram of the proposed synchronous rectification control method in the forward energy flow mode of the present invention. Obtaining a voltage control quantity V from a voltage control loopcontrol，VcontrolSwitching frequency f acting on high-voltage side inverter bridge of voltage-controlled oscillator output resonant convertersAdding a phase shift angle
And then driving signals Vgs1, Vgs2, Vgs3 and Vgs4 from the high-voltage side inverter bridge switching tube Q1 to the switching tube Q4 are obtained respectively. The method for generating the driving signals from the switching tube Q5 to the switching tube Q8 of the low-voltage side rectifier bridge is as follows: firstly, the falling edges of the driving signals Vgs3 and Vgs4 of the high-voltage side 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 Q8onAnd the starting conduction time of the low-voltage side switch tube Q6 and the switch tube Q7. Secondly, from a given phase shift angle
Calculating the duty ratio D generated by phase shiftbasis. Further, according to an operation state (x is 1, 2, 3) of the circuit, corresponding synchronous rectification control is performed. In FIG. 2, the single-pole double-throw switch is marked as S, and when T is less than TsoftstartWhen S is 1, carrying out a soft start process of synchronous rectification control; when T > TsoftstartAnd when S is 2, searching for the optimal duty ratio of the switching tube of the synchronous rectifier bridge based on the maximum efficiency point tracking control. Finally, the switching tubes Q5 to Q8 carry out synchronous rectification control with the optimal duty ratio;
taking the forward energy flow mode as an example, the complete steps of the control strategy proposed by the present invention are as follows:
fmin≤fs＜0.95fr，State1
0.95fr≤fs≤1.05fr，State2
1.05fr＜fs≤fmax，State3 (1)
step 3, selecting a phase shift angle
The circuit operates in a fixed phase-shifting angle frequency conversion control mode; phase shift angle
Is shown in formula (2), wherein
tdead＝100ns；
Step 5, the low-voltage side rectifier synchronous rectification controls the soft start operation, and at the moment, a switch S in the graph 2 is equal to 1; the specific process is as follows: the duty cycle starts from 0 and is in steps deltaD within each switching periodsoftstartIncrease to Dsoftstart_finalWherein D issoftstart_finalCalculated according to equation (4), Δ DsoftstartSolving according to a formula (5); t issoftstartFor synchronous rectification soft start time, T is taken heresoftstart＝50ms，Dsoftstart_finalIs T ═ TsoftstartThe duty ratio of the time switching tube Q5 to the switching tube Q8 is as follows:
Dsoftstart_final＝Dbasisstate2 or State3 (4)
Note TstepFor the calculation of the step size by the controller, take T as an example of a controller with a clock frequency of 150MHzstep16.667ns, soft start step Δ DsoftstartThe calculation formula of (2) is as follows:
step 6, when D ═ Dsoftstart_finalWhile, at the same timeAnd (3) finishing the step rectification soft start, wherein the switch S is 2 at the moment, and starting to carry out maximum efficiency point tracking control on the low-voltage side rectifier, wherein the specific process is as follows:
step 6.1, calculating the working efficiency of the circuit according to the formula (6):
step 6.2, when the resonant converter works at State1 and State3, the duty ratio D is shown as the formula (7):
D＝Dlast+ΔDMEPT (7)
delta D in formula (7)MEPTFor maximum efficiency point tracking the step length of the change of the duty ratio in the control, DlastSynchronous rectification duty cycle for the previous switching cycle, DlastHas an initial value of Dsoftstart_final(ii) a If the operating efficiency η increases after executing equation (7), then equation (7) continues to be executed until D ═ DoptimizationAt a time of rest, DoptimizationAs shown in fig. 3, represents the optimal duty cycle of the synchronous rectification process; when the resonant converter is operating at State2, the duty cycle D is as shown in equation (8):
D＝Dsoftstart_final (8)
step 7, obtaining a switching signal V from the switching tube Q5 to the switching tube Q8 according to the duty ratio Dgs5To Vgs8(ii) a Description of the drawings: conduction time t of low-voltage side switch tube Q5 and switch tube Q8onIs the falling edge of the high-side switch tube Q3; conduction time t of low-voltage side switch tube Q6 and switch tube Q7onIs the falling edge of the high side switching tube Q4.
FIG. 3 is a waveform diagram of an example of the synchronous rectification strategy for the forward energy flow from the high-side to the low-side of the bidirectional CLLC resonant converter proposed in the present invention, wherein (a) is the driving pulse of the high-side switch tube, and the switch tube Q1 is ahead of the switch tube Q4
The switch tube Q1 and the switch tube Q2 are conducted complementarily, and the switch isThe tube Q3 and the switch tube Q4 are conducted complementarily, and a dead time T is added between the upper switch tube and the lower switch tube of the same bridge armsIs a switching cycle. (b) The low-voltage side resonant current and synchronous rectification signal waveforms of the converter when operating at State1 are shown, and the driving pulse signals of the switching tube Q6 and the switching tube Q7 are mirror-inverted on the time axis in order to visually observe the positions of the driving pulses. Wherein Vgs58Is the driving signal of the low-voltage side switch tube Q5 and the switch tube Q8, Vgs67Is the driving signal of the switch tube Q6 and the switch tube Q7 ilrsFor low side resonant current, TMEPTFor the duration of the maximum efficiency point tracking process, D in State1 Statesoftstart_finalLess than optimal duty cycle Doptimization，t＝TsoftstartAnd carrying out maximum efficiency point tracking control according to the efficiency. (c) The graph shows the theoretical waveform of the converter when operating at State2, with the duty cycle of the synchronous rectification signal increased to Dsoftstart_finalIn this state, T ═ TsoftstartTime Dsoftstart_final＝DoptimizationAnd then maximum efficiency point tracking control is not performed. (d) The converter is shown operating in State3, which is similar to State1, Dsoftstart_finalLess than optimal duty cycle DoptimizationMaximum efficiency point tracking control is performed.
The above description is directed to the implementation of a synchronous rectification strategy when a bidirectional CLLC resonant converter is in forward energy flow from the high-voltage side to the low-voltage side. When the bidirectional CLLC resonant converter reversely flows, the implementation process of the synchronous rectification strategy is also applicable, only the rectification 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 appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in 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 is characterized by comprising the following steps:
step 1, obtaining the switching frequency f of the circuit in a voltage control loops(ii) a Sampling the output voltage V of a low side rectifieroWill measure the value VoWith a given value VorefMaking difference, and outputting voltage control quantity V by voltage controllercontrolThe voltage control adopts PI controller, wherein the voltage control quantity VcontrolGenerating the operating switching frequency f of the circuit after passing through a voltage-controlled oscillators；
Step 2, according to the working switching frequency fsAnd formula (1) determining the operating state of the circuit according to the switching frequency fsThe operating states of the circuit are divided into a far resonant frequency under-resonance State recorded as State1, a State near the resonant frequency recorded as State2 and a far resonant frequency over-resonance State recorded as State3, and the frequency ranges of the three operating states are as follows:
fmin≤fs＜0.95fr，State1
0.95fr≤fs≤1.05fr，State2
1.05fr＜fs≤fmax，State3 (1)
wherein in the formula (1), fminIs the minimum switching frequency, f, in the switching frequency rangemaxIs the maximum switching frequency within the switching frequency range;
step 3, selecting a phase shift angle
The circuit operates in a fixed phase-shifting angle frequency conversion control mode; phase shift angle
Is shown in formula (2), wherein
tdead＝100ns；
Step 4, according to the phase shift angle
And equation (3) calculating the duty cycle D resulting from the phase shiftbasis；DbasisThe calculation formula of (2) is as follows:
Step 5, the low-voltage side rectifier controls soft start operation through synchronous rectification, and a switch S is equal to 1; the specific process is as follows: the duty cycle starts from 0 and is in steps deltaD within each switching periodsoftstartIncrease to Dsoftstart_finalWherein D issoftstart_finalCalculated according to equation (4), Δ DsoftstartSolving according to a formula (5); t issoftstartFor synchronous rectification of soft start time, T is taken heresoftstart＝50ms，Dsoftstart_finalIs T ═ TsoftstartDuty ratio of time switching tube Q5 to switching tube Q8:
Dsoftstart_final＝Dbasisstate2 or State3 (4)
Note TstepFor the calculation of the step size by the controller, take T as an example of a controller with a clock frequency of 150MHzstep16.667ns, soft start step Δ DsoftstartThe calculation formula of (2) is as follows:
step 6, when D ═ Dsoftstart_finalWhen synchronous rectification soft start is finished, and the switch S is 2, the maximum efficiency point tracking control is started to be carried out on the low-voltage side rectifier;
step 7, obtaining a switching signal V from the switching tube Q5 to the switching tube Q8 according to the duty ratio Dgs5To Vgs8(ii) a Conduction time t of low-voltage side switch tube Q5 and switch tube Q8onThe falling edge of the high-side switch tube Q3; conduction time t of low-voltage side switch tube Q6 and switch tube Q7onIs the falling edge of the high side switching tube Q4.
2. The synchronous rectification method of the bidirectional CLLC resonant converter according to claim 1, wherein 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), UoAnd IoRespectively, an output side DC voltage and a DC current, UinAnd IinThe input side direct current voltage and the input side direct current are respectively;
step 6.2, when the resonant converter works at State1 and State3, the duty ratio D is as shown in formula (7):
D＝Dlast+ΔDMEPT (7)
formula (7)Middle Delta DMEPTFor maximum efficiency point tracking the step length of the change of the duty ratio in the control, DlastSynchronous rectification duty cycle for the previous switching cycle, DlastHas an initial value of Dsoftstart_final(ii) a If the operating efficiency η increases after executing equation (7), then equation (7) continues to be executed until D ═ DoptimizationAt a time of rest, DoptimizationAs shown in fig. 3, represents the 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＝Dsoftstart_final (8)。
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| CN202111466255.3A CN114244126B (en) | 2021-12-03 | 2021-12-03 | Synchronous rectification method of bidirectional CLLC resonant converter |
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