Synchronous rectification circuit and method applied to bidirectional CLLC resonant converter

Abstract

The invention relates to the field of DC / DC converters, and aims to provide a synchronous rectification circuit and method applied to a bidirectional CLLC resonant converter. The synchronous rectification circuit comprises a high-speed current sampling circuit, a zero crossing point detection circuit, a timer circuit, a logic processing circuit and a driving circuit. According to the invention, the change state of the secondary side resonance current is detected, the reliable action of the switching tube is ensured according to the delay signal of the timer, and the misoperation of the switching tube possibly caused by parasitic oscillation of the circuit can be avoided. According to the method, the accuracy and reliability of synchronous rectification are improved, complex calculation is not needed, and the method has the advantages of being wide in application range and good in anti-interference performance. According to the invention, through real-time detection of the secondary side resonance current, synchronous rectification in the same period can be realized, and the conversion efficiency of the converter is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic converters and relates to a synchronous rectification circuit and a control strategy of a bidirectional CLLC resonant converter. Background Art

[0002] In the application of new energy such as distributed energy storage, DC microgrids and electric vehicles, the key issue of power conversion is how to build a bidirectional power electronic converter that can meet the requirements of bidirectional energy flow, high efficiency and high power density. Among various bidirectional isolated converters, the CLLC resonant converter based on the traditional unidirectional LLC resonant converter topology is considered to be an ideal topology because it can achieve bidirectional energy flow, soft switching and bidirectional operation.

[0003] In the traditional bidirectional CLLC resonant converter, the secondary bridge does not add a driving signal and uses its body diode for rectification. However, since the body diode often has a relatively high conduction voltage drop, it brings relatively high conduction loss, which reduces the efficiency of the converter. The synchronous rectification strategy can effectively reduce the conduction voltage drop during rectification, thereby reducing the conduction loss on the rectification side and improving the converter efficiency.

[0004] For bidirectional CLLC resonant converters, traditional synchronous rectification strategies can be divided into three categories: theoretical calculation, voltage detection, and current detection. The theoretical calculation strategy directly calculates the turn-on and turn-off time of the synchronous rectifier tube through preliminary modeling. The calculation requires accurate resonance parameters of the converter, which depends on the accuracy of preliminary modeling and has high requirements on the performance of the digital controller. It is difficult to accurately calculate the resonance process in the dynamic process. The voltage detection strategy determines the current polarity by detecting the drain-source voltage of the switch tube, and the current detection strategy directly detects the secondary side resonant current. Both strategies determine the conduction status of the secondary side rectifier tube by the polarity of the secondary side resonant current, and generate synchronous rectification drive signals accordingly. Both strategies are easily affected by circuit parasitic oscillations, causing malfunction of the synchronous rectifier tube and affecting the synchronous rectification effect.

[0005] It can be seen that the conventional synchronous rectification strategies of bidirectional CLLC resonant converters all have their own defects, which limits their application in bidirectional CLLC resonant converters. Therefore, it is necessary to improve the existing synchronous rectification technology. Summary of the invention

[0006] The object of the present invention is to provide a synchronous rectification circuit applied to a bidirectional CLLC resonant converter to overcome the deficiencies of the prior art.

[0007] The technical scheme for realizing the purpose of the present invention is as follows: a synchronous rectification circuit applied to a bidirectional CLLC resonant converter, comprising a high-speed current sampling circuit, a zero-crossing detection circuit, a timer circuit, a logic processing circuit and a drive circuit; wherein the high-speed current sampling circuit comprises a current transformer, a detection resistor and a differential amplifier circuit; the primary side of the current transformer is connected in series to the secondary side of the CLLC resonant converter, for detecting the resonant current on the secondary side of the converter; the detection resistor is connected in parallel to the secondary side of the current transformer, for converting the detected resonant current signal into a voltage signal; the differential amplifier circuit is used to amplify and offset the voltage signal at both ends of the detection resistor; the zero-crossing detection circuit is connected to the output end of the differential amplifier circuit, for generating a zero-crossing signal of the secondary resonant current; the timer circuit is connected to the output end of the zero-crossing detection circuit, and starts working in response to the zero-crossing signal; the output end of the timer circuit is respectively connected to the input end of the logic processing circuit and the input end of the drive circuit, the output signal of the timer circuit is used as the enable signal of the drive circuit, and the logic processing circuit is used to control the shutdown of the timer circuit after processing the output signal of the timer circuit.

[0008] The present invention also proposes a synchronous rectification method applied to a bidirectional CLLC resonant converter, the specific steps of which are:

[0009] (1) Obtaining a scaled-down secondary-side resonant current through a current transformer;

[0010] (2) converting the detected resonant current signal into a voltage signal and amplifying and offsetting it;

[0011] (3) Compare the output of the differential operational amplifier circuit with the bias voltage to obtain a secondary side resonant current zero-crossing signal;

[0012] (4) Determine the start time of the timer based on the conduction information of the anti-parallel diode of the secondary side switch tube;

[0013] (5) Determine the turn-off time of the synchronous rectification signal of the secondary side switch tube according to the timer signal;

[0014] (6) determining the start time of the synchronous rectification signal of the secondary side switch tube and the turn-off time of the timer signal according to the primary side switch tube drive signal;

[0015] (7) In each subsequent switching cycle, the controller determines the turn-on and turn-off times of the switch tube in this cycle according to the detected secondary side current polarity and the original drive signal information in accordance with steps (1) to (6).

[0016] Preferably, the bidirectional CLLC resonant converter includes a full-bridge inverter circuit, a resonant circuit, and a full-bridge rectifier circuit connected in sequence, and the full-bridge rectifier circuit includes a fifth switch tube S5 on the secondary side, a fifth anti-parallel diode D5 on the secondary side connected in parallel with the fifth switch tube S5 on the secondary side, and a fifth parasitic capacitor C5 on the secondary side; a sixth switch tube S6 on the secondary side, a sixth anti-parallel diode D6 on the secondary side connected in parallel with the sixth switch tube S6 on the secondary side, and a sixth parasitic capacitor C6 on the secondary side; The seventh switch tube S7, the seventh anti-parallel diode D7 on the secondary side connected in parallel with the seventh switch tube S7 on the secondary side, and the seventh parasitic capacitor C7 on the secondary side; the eighth switch tube S8 on the secondary side, the eighth anti-parallel diode D8 on the secondary side connected in parallel with the eighth switch tube S8 on the secondary side, and the eighth parasitic capacitor C8 on the secondary side, the fifth switch tube S5 and the sixth switch tube S6 on the secondary side are connected in series to form a first bridge arm on the secondary side, and the seventh switch tube S7 and the eighth switch tube S8 on the secondary side are connected in series to form a second bridge arm on the secondary side;

[0017] The full-bridge inverter circuit is composed of a first primary-side switch tube S1, a first primary-side anti-parallel diode D1 connected in parallel with the first primary-side switch tube S1, and a first primary-side parasitic capacitor C1; a second primary-side switch tube S2, a second primary-side anti-parallel diode D2 connected in parallel with the second primary-side switch tube S2, and a second primary-side parasitic capacitor C2; a third primary-side switch tube S3, a third primary-side anti-parallel diode D3 connected in parallel with the third primary-side switch tube S3, and a third primary-side parasitic capacitor C3; a fourth primary-side switch tube S4, a fourth primary-side anti-parallel diode D4 connected in parallel with the fourth primary-side switch tube S4, and a fourth primary-side parasitic capacitor C4; the first primary-side switch tube S1 and the second primary-side switch tube S2 are connected in series to form a first primary-side bridge arm, and the third primary-side switch tube S3 and the fourth primary-side switch tube S4 are connected in series to form a second primary-side bridge arm.

[0018] Preferably, the output of the differential op amp circuit is biased with a DC voltage V ref By comparison, the specific method for obtaining the secondary side resonant current zero-crossing signal is:

[0019] The output of the differential op amp current is compared with the bias voltage V ref For comparison, when V c >V ref When V c =1, at this time, the fifth anti-parallel diode D5 on the secondary side connected in parallel with the fifth switch tube S5 on the secondary side and the eighth anti-parallel diode D8 on the secondary side connected in parallel with the eighth switch tube S8 on the secondary side are in the on state; when V c <V ref When V c =0, at this time, the sixth anti-parallel diode D6 on the secondary side connected in parallel with the sixth switch tube S6 on the secondary side and the seventh anti-parallel diode D7 on the secondary side connected in parallel with the seventh switch tube S7 on the secondary side are in the on state.

[0020] Preferably, the specific method for determining the start time of the timer according to the conduction information of the anti-parallel diode of the secondary side switch tube is:

[0021] When the resonant current passes through zero, the signal is V c =1 becomes V c = 0, that is, at the moment t1 when the secondary side resonant current changes from positive to zero, the timer t in the start timer circuit is triggered. clk1 ; The resonant current zero-crossing signal is V c =0 becomes V c = 1, that is, at the moment t2 when the secondary side resonant current changes from negative to zero, the timer t in the start timer circuit is triggered. clk2 .

[0022] Preferably, the specific method for determining the turn-off time of the synchronous rectification signal of the secondary-side switch tube according to the timer signal is:

[0023] The zero-crossing point t1 when the resonant current changes from positive to zero is the timer signal t clk1 At the start time, the fifth and eighth switches on the secondary side are turned off, and the timer signal t clk1 During the timing period, the fifth and eighth switches on the secondary side are kept in the off state; the zero-crossing point t2 when the resonant current changes from negative to zero is the timer signal t clk2 At the start time, the sixth and seventh switches on the secondary side are turned off, and the timer signal t clk2 During the timing period, the sixth and seventh switches on the secondary side are kept closed.

[0024] Preferably, the specific method for determining the turn-on time of the synchronous rectification signal of the secondary-side switch tube and the turn-off time of the timer signal according to the primary-side switch tube driving signal is:

[0025] The original driving signals of the fifth switch tube S5 and the eighth switch tube S8 on the secondary side are consistent with the driving signals of the first switch tube S1 and the fourth switch tube S4 on the primary side; the original driving signals of the sixth switch tube S6 and the seventh switch tube S7 on the secondary side are consistent with the driving signals of the second switch tube S2 and the third switch tube S3 on the primary side; when the turn-on signal of the sixth and seventh switch tubes on the secondary side arrives, that is, at time t3, the timer t is turned off. clk1 When the turn-on signal of the fifth and eighth switches on the secondary side arrives, that is, at time t4, the timer t is turned off. clk2 .

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention is constructed using an analog circuit, has a rapid control response, can implement synchronous rectification operation within the same cycle, and thus achieve better synchronous rectification effects under various working conditions.

[0028] (2) The present invention does not require complex calculations and can avoid the uncertainty caused by circuit parasitic oscillations, thereby improving the feasibility and reliability of synchronous rectification.

[0029] (2) The synchronous rectification current of the present invention is decoupled from the closed-loop control of the converter, and the synchronous rectification is controlled separately, which does not increase the complexity of the closed-loop control of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The specific implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0031] Figure 1 It is a circuit diagram of a bidirectional CLLC resonant converter of a controlled object of the present invention.

[0032] Figure 2 This is the second circuit diagram of the controlled object bidirectional CLLC resonant converter of the present invention.

[0033] Figure 3 It is the third circuit diagram of the controlled object bidirectional CLLC resonant converter of the present invention.

[0034] Figure 4 It is a basic principle diagram of the bidirectional CLLC resonant converter synchronous rectification circuit proposed in the present invention.

[0035] Figure 5 It is a theoretical waveform diagram of the bidirectional CLLC resonant converter synchronous rectification strategy proposed in the present invention when the converter operates in the under-resonance mode. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0037] Figure 1 , Figure 2 , Figure 3The bidirectional CLLC resonant converter as a controlled object is shown, and the bidirectional CLLC resonant converter includes a full-bridge inverter circuit, a resonant circuit, and a full-bridge rectifier circuit connected in sequence. The full-bridge rectifier circuit includes a fifth switch tube S5 on the secondary side, a fifth anti-parallel diode D5 on the secondary side connected in parallel with the fifth switch tube S5 on the secondary side, and a fifth parasitic capacitor C5 on the secondary side; a sixth switch tube S6 on the secondary side, a sixth anti-parallel diode D6 on the secondary side connected in parallel with the sixth switch tube S6 on the secondary side, and a sixth parasitic capacitor C5 on the secondary side; a seventh switch tube S7 on the secondary side, a seventh anti-parallel diode D7 on the secondary side connected in parallel with the seventh switch tube S7 on the secondary side, and a seventh parasitic capacitor C7 on the secondary side; an eighth switch tube S8 on the secondary side, an eighth anti-parallel diode D8 on the secondary side connected in parallel with the eighth switch tube S8 on the secondary side, and an eighth parasitic capacitor C8 on the secondary side; the fifth switch tube S5 on the secondary side and the sixth switch tube S6 on the secondary side are connected in series to form a first bridge arm on the secondary side, and the seventh switch tube S7 on the secondary side and the eighth switch tube S8 on the secondary side are connected in series to form a second bridge arm on the secondary side;

[0038] The full-bridge inverter circuit is composed of a first primary-side switch tube S1, a first primary-side anti-parallel diode D1 connected in parallel with the first primary-side switch tube S1, and a first primary-side parasitic capacitor C1; a second primary-side switch tube S2, a second primary-side anti-parallel diode D2 connected in parallel with the second primary-side switch tube S2, and a second primary-side parasitic capacitor C2; a third primary-side switch tube S3, a third primary-side anti-parallel diode D3 connected in parallel with the third primary-side switch tube S3, and a third primary-side parasitic capacitor C3; a fourth primary-side switch tube S4, a fourth primary-side anti-parallel diode D4 connected in parallel with the fourth primary-side switch tube S4, and a fourth primary-side parasitic capacitor C4; the first primary-side switch tube S1 and the second primary-side switch tube S2 are connected in series to form a first primary-side bridge arm, and the third primary-side switch tube S3 and the fourth primary-side switch tube S4 are connected in series to form a second primary-side bridge arm.

[0039] The resonant circuit of the CLLC resonant converter has three structures, one symmetrical structure and two asymmetrical structures. Figure 1 The symmetrical structure of the resonant circuit is shown, and the resonant circuit includes a first resonant inductor L on the primary side. r1 , the first resonant capacitor C on the primary side r1 , the second resonant inductor L on the secondary side r2 , the second resonant capacitor C on the secondary side r2 and a transformer with a turns ratio of n:1; a first resonant inductor L on the primary side r1 With the first resonant capacitor C on the primary side r1 Connected in series to the primary side of the transformer; the second resonant inductor L on the secondary side r2 The second resonant capacitor C r2 Connected in series on the secondary side of the transformer; Figure 2 , Figure 3 The asymmetric structure of the resonant circuit is shown. Figure 2In the asymmetric structure shown, the resonant circuit includes a first resonant inductor L on the primary side. r1 , the first resonant capacitor C on the primary side r1 , the second resonant capacitor C on the secondary side r2 And the transformer with a turns ratio of n:1, the first resonant inductor L on the primary side r1 With the first resonant capacitor C on the primary side r1 Connected in series to the primary side of the transformer; the second resonant capacitor C on the secondary side r2 Connected in series on the secondary side of the transformer; Figure 3 In the asymmetric structure shown, the resonant circuit includes a first resonant capacitor C on the primary side. r1 , the second resonant inductor L on the secondary side r2 , the second resonant capacitor C on the secondary side r2 And a transformer with a turns ratio of n:1; the first resonant capacitor C on the primary side r1 Connected in series to the primary side of the transformer; the second resonant inductor L on the secondary side r2 The second resonant capacitor C r2 Connected in series on the secondary side of the transformer.

[0040] Figure 4 This is the basic principle diagram of the bidirectional CLLC resonant converter synchronous rectification circuit proposed in the present invention. Figure 4 In: The proposed bidirectional CLLC resonant converter synchronous rectification circuit consists of a high-speed current sampling circuit, a zero-crossing detection circuit, a timer circuit, a logic processing circuit and a drive circuit; it is characterized in that a current transformer is connected in series on the secondary side of the CLLC resonant cavity, and the secondary side of the current transformer is connected to the detection resistor, the differential amplifier circuit, the zero-crossing detection circuit, the timer circuit, and the logic processing circuit in sequence; the timer circuit is connected to the enable pin of the bidirectional CLLC resonant converter driver chip.

[0041] Figure 1 The resonant frequency f of the CLLC resonant converter shown in r1 The calculation formula is as follows:

[0042]

[0043] When C r2 =n 2 C r1 , n 2 L r2 =L r1 hour, Figure 1 The resonant frequency f of the CLLC resonant converter shown in r1 The calculation formula is as follows:

[0044]

[0045] Figure 2The resonant frequency f of the asymmetric CLLC resonant converter shown in r2 The calculation formula is as follows:

[0046]

[0047] Figure 3 The resonant frequency f of the asymmetric CLLC resonant converter shown in r3 The calculation formula is as follows:

[0048]

[0049] When the converter operating frequency f s <f r When the converter operates in the sub-resonant mode, the converter operates in the sub-resonant mode; when the converter operating frequency f s =f r When the converter operates in quasi-resonant mode, the converter operates in quasi-resonant mode; when the converter operating frequency f s >f r In order to ensure the reliable operation of the synchronous rectification of the secondary side switch tube, the timing period of the timer is equal to the minimum operating frequency f of the converter. smin , maximum operating frequency f smax and the converter resonant frequency f r The timing period of the timer is T tclk The following conditions should be met:

[0050]

[0051] The converter needs to control the switch tube on the primary side according to the input and output voltage, current and other signals. Taking the forward working mode as an example, the driving signals applied by the controller to the four switches on the primary side are all square wave signals with a duty cycle of 50%, among which the driving signals of the first switch tube S1 and the second switch tube S2 on the primary side are completely complementary, and the driving signals of the third switch tube S3 and the fourth switch tube S4 on the primary side are completely complementary, and the driving signals of the first switch tube S1 and the fourth switch tube S4 on the primary side are in phase, and the primary bridge outputs a square wave voltage with a duty cycle of 50% and positive and negative symmetry applied to the resonant cavity. The controller changes the frequency of the output voltage of the primary bridge by changing the frequency of the primary bridge driving signal, and changes the impedance of the resonant cavity to adjust the output voltage or current. In the absence of synchronous rectification, the secondary bridge is always in an uncontrolled state during this process, and only uses its body diode for rectification. When synchronous rectification is applied, the secondary bridge is applied with a suitable drive signal so that its channel is turned on when the body diode starts to conduct, current flows through the channel, and is turned off when the channel current passes zero. Synchronous rectification has relatively strict requirements on the turn-on and turn-off time of the switch tube.

[0052] Taking the converter working in sub-resonant mode as an example, combined with Figure 5 , the specific synchronous rectification control strategy process proposed by the present invention is:

[0053] Step 1: Obtain the scaled-down resonant current through the current transformer. Use the current transformer connected in series on the secondary side to detect the resonant current on the secondary side and obtain the resonant current on the secondary side; record the resonant current on the secondary side as i Lr2 , the turns ratio of the primary and secondary coils of the current transformer is 1:N, and the detected current signal is

[0054] Step 2: Convert the detected resonant current signal into a voltage signal and amplify and offset it. The detected current signal is converted into a voltage signal through a detection resistor, and the voltage signal is amplified through a differential amplifier circuit. The detection resistor is R sense , the gain of the amplifier circuit is k, and the DC voltage bias is V ref , the processed voltage signal is V sense =kR sense i sense +V ref ;

[0055] Step 3: Compare the output of the differential op amp circuit with the bias voltage to obtain the zero-crossing signal of the secondary-side resonant current and obtain the conduction information of the anti-parallel diode of the secondary-side switch. In the bidirectional CLLC resonant converter, the polarity of the secondary-side resonant current determines the conduction of the anti-parallel diode of the secondary-side switch. Compare the output of the differential op amp current with the bias voltage V ref Compare and output the resonant current zero-crossing signal V c When V c >V ref When V c =1, at this time, the fifth anti-parallel diode D5 on the secondary side connected in parallel with the fifth switch tube S5 on the secondary side and the eighth anti-parallel diode D8 on the secondary side connected in parallel with the eighth switch tube S8 on the secondary side are in the on state; when V c <V ref When V c =0, at this time, the sixth anti-parallel diode D6 on the secondary side connected in parallel with the sixth switch tube S6 on the secondary side and the seventh anti-parallel diode D7 on the secondary side connected in parallel with the seventh switch tube S7 on the secondary side are in the on state.

[0056] Step 4: Determine the start time of the timer based on the conduction information of the anti-parallel diode of the secondary switch tube. The resonant current zero-crossing signal is generated by V c =1 becomes V c = 0, that is, the moment t1 when the secondary side resonant current changes from positive to zero, triggering the opening of the fifth and eighth switch tube timers t clk1 ; The resonant current zero-crossing signal is V c=0 becomes V c = 1, that is, at the moment t2 when the secondary side resonant current changes from negative to zero, the sixth and seventh switch tube timers t clk2 .

[0057] Step 5: The driving circuit determines the turn-off time of the synchronous rectification signal of the secondary side switch tube according to the timer signal. clk1 With t clk2 The opening time is the cut-off time of the anti-parallel diode of the secondary switch tube. The zero-crossing point t1 when the resonant current changes from positive to zero is the timer signal t clk1 At the moment of generation, the fifth and eighth switches on the secondary side are turned off, and the timer signal t clk1 During the timing period, the fifth and eighth switches on the secondary side are kept in the off state; the zero-crossing point t2 when the resonant current changes from negative to zero is the timer signal t clk2 At the moment of generation, the sixth and seventh switches on the secondary side are turned off, and the timer signal t clk2 During the timing period, the sixth and seventh switch tubes on the secondary side are kept in a closed state.

[0058] Step 6: The logic circuit determines the start time of the synchronous rectification signal of the secondary switch tube and the turn-off time of the timer signal according to the primary switch tube driving signal. The turn-on time of the secondary side fifth anti-parallel diode D5 connected in parallel with the secondary side fifth switch tube S5 and the secondary side eighth anti-parallel diode D8 connected in parallel with the secondary side eighth switch tube S8 is consistent with the turn-on time of the primary side first switch tube S1 and the primary side fourth switch tube S4; the turn-on time of the secondary side sixth anti-parallel diode D6 connected in parallel with the secondary side sixth switch tube S6 and the secondary side seventh anti-parallel diode D7 connected in parallel with the secondary side seventh switch tube S7 is consistent with the turn-on time of the primary side second switch tube S2 and the primary side third switch tube S3. The original drive signals of the fifth switch tube S5 and the eighth switch tube S8 on the secondary side can be consistent with the drive signals of the first switch tube S1 and the fourth switch tube S4 on the primary side; the original drive signals of the sixth switch tube S6 and the seventh switch tube S7 on the secondary side can be consistent with the drive signals of the second switch tube S2 and the third switch tube S3 on the primary side. When the turn-on signal of the sixth and seventh switches on the secondary side arrives, that is, at time t3, the timer t is turned off. clk1 When the signal of the fifth and eighth switch tubes on the secondary side arrives, that is, at time t4, the timer t is turned off. clk2 .

[0059] Step 7: In each subsequent switching cycle, the controller determines the turn-on and turn-off times of the switch tube in this cycle according to the detected secondary side current polarity and the original drive signal information.

[0060] Finally, it should be noted that the above are only several specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there may be many variations. For example, the strategy proposed in the present invention can be used to implement synchronous rectification control of other types of resonant converters, and can also be applied to other purposes such as converter protection and closed-loop control. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered to be within the scope of protection of the present invention.

Claims

1. A synchronous rectification circuit for a bidirectional CLLC resonant converter, characterized in that: It includes a high-speed current sampling circuit, a zero-crossing detection circuit, a timer circuit, a logic processing circuit and a drive circuit; wherein the high-speed current sampling circuit includes a current transformer, a detection resistor and a differential amplifier circuit; the primary side of the current transformer is connected in series to the secondary side of the CLLC resonant converter to detect the resonant current on the secondary side of the converter; the detection resistor is connected in parallel to the secondary side of the current transformer to convert the detected resonant current signal into a voltage signal; the differential amplifier circuit is used to amplify and offset the voltage signal at both ends of the detection resistor; the zero-crossing detection circuit is connected to the output end of the differential amplifier circuit to generate a zero-crossing signal of the secondary resonant current; the timer circuit is connected to the output end of the zero-crossing detection circuit and starts working in response to the zero-crossing signal; the output end of the timer circuit is respectively connected to the input end of the logic processing circuit and the input end of the drive circuit, the output signal of the timer circuit is used as the enable signal of the drive circuit, and the logic processing circuit is used to control the shutdown of the timer circuit after processing the output signal of the timer circuit.

2. A synchronous rectification method applied to a bidirectional CLLC resonant converter, characterized in that: The specific steps are: (1) Obtaining a scaled-down secondary-side resonant current through a current transformer; (2) converting the detected resonant current signal into a voltage signal and amplifying and offsetting it; (3) Compare the output of the differential operational amplifier circuit with the bias voltage to obtain a secondary side resonant current zero-crossing signal; (4) Determine the start time of the timer based on the conduction information of the anti-parallel diode of the secondary side switch tube; (5) Determine the turn-off time of the synchronous rectification signal of the secondary side switch tube according to the timer signal; (6) determining the start time of the synchronous rectification signal of the secondary side switch tube and the turn-off time of the timer signal according to the primary side switch tube drive signal; (7) In each subsequent switching cycle, the turn-on and turn-off times of the switch tube of this cycle are determined according to steps (1) to (6) based on the detected secondary side current polarity and the original drive signal information.

3. The synchronous rectification method applied to the bidirectional CLLC resonant converter according to claim 2, characterized in that: The bidirectional CLLC resonant converter includes a full-bridge inverter circuit, a resonant circuit, and a full-bridge rectifier circuit connected in sequence. The full-bridge rectifier circuit includes a fifth switch tube S5 on the secondary side, a fifth anti-parallel diode D5 on the secondary side connected in parallel with the fifth switch tube S5 on the secondary side, and a fifth parasitic capacitor C5 on the secondary side; a sixth switch tube S6 on the secondary side, a sixth anti-parallel diode D6 on the secondary side connected in parallel with the sixth switch tube S6 on the secondary side, and a sixth parasitic capacitor C6 on the secondary side; a seventh switch tube S7 on the secondary side, a seventh anti-parallel diode D7 on the secondary side connected in parallel with the seventh switch tube S7 on the secondary side, and a seventh parasitic capacitor C7 on the secondary side; an eighth switch tube S8 on the secondary side, an eighth anti-parallel diode D8 on the secondary side connected in parallel with the eighth switch tube S8 on the secondary side, and an eighth parasitic capacitor C8 on the secondary side. The fifth switch tube S5 on the secondary side and the sixth switch tube S6 on the secondary side are connected in series to form a first bridge arm on the secondary side, and the seventh switch tube S7 on the secondary side and the eighth switch tube S8 on the secondary side are connected in series to form a second bridge arm on the secondary side; The full-bridge inverter circuit is composed of a first primary-side switch tube S1, a first primary-side anti-parallel diode D1 connected in parallel with the first primary-side switch tube S1, and a first primary-side parasitic capacitor C1; a second primary-side switch tube S2, a second primary-side anti-parallel diode D2 connected in parallel with the second primary-side switch tube S2, and a second primary-side parasitic capacitor C2; a third primary-side switch tube S3, a third primary-side anti-parallel diode D3 connected in parallel with the third primary-side switch tube S3, and a third primary-side parasitic capacitor C3; a fourth primary-side switch tube S4, a fourth primary-side anti-parallel diode D4 connected in parallel with the fourth primary-side switch tube S4, and a fourth primary-side parasitic capacitor C4; the first primary-side switch tube S1 and the second primary-side switch tube S2 are connected in series to form a first primary-side bridge arm, and the third primary-side switch tube S3 and the fourth primary-side switch tube S4 are connected in series to form a second primary-side bridge arm.

4. The synchronous rectification method applied to a bidirectional CLLC resonant converter according to claim 3, characterized in that: The output of the differential op amp circuit is biased with a DC voltage V ref By comparison, the specific method for obtaining the secondary side resonant current zero-crossing signal is: The output of the differential op amp current is compared with the bias voltage V ref For comparison, when V c >V ref When V c =1, at this time, the fifth anti-parallel diode D5 on the secondary side connected in parallel with the fifth switch tube S5 on the secondary side and the eighth anti-parallel diode D8 on the secondary side connected in parallel with the eighth switch tube S8 on the secondary side are in the on state; when V c <V ref When V c =0, at this time, the sixth anti-parallel diode D6 on the secondary side connected in parallel with the sixth switch tube S6 on the secondary side and the seventh anti-parallel diode D7 on the secondary side connected in parallel with the seventh switch tube S7 on the secondary side are in the on state.

5. The synchronous rectification method applied to the bidirectional CLLC resonant converter according to claim 3, characterized in that: The specific method for determining the start time of the timer based on the conduction information of the anti-parallel diode of the secondary side switch tube is: When the resonant current passes through zero, the signal is V c =1 becomes V c = 0, that is, at the moment t1 when the secondary side resonant current changes from positive to zero, the timer t in the start timer circuit is triggered. clk1 ; The resonant current zero-crossing signal is V c =0 becomes V c = 1, that is, at the moment t2 when the secondary side resonant current changes from negative to zero, the timer t in the start timer circuit is triggered. clk2 .

6. The synchronous rectification method applied to the bidirectional CLLC resonant converter according to claim 5, characterized in that: The specific method for determining the turn-off time of the synchronous rectification signal of the secondary side switch tube according to the timer signal is: The zero-crossing point t1 when the resonant current changes from positive to zero is the timer signal t clk1 At the start time, the fifth and eighth switches on the secondary side are turned off, and the timer signal t clk1 During the timing period, the fifth and eighth switches on the secondary side are kept in the off state; the zero-crossing point t2 when the resonant current changes from negative to zero is the timer signal t clk2 At the start time, the sixth and seventh switches on the secondary side are turned off, and the timer signal t clk2 During the timing period, the sixth and seventh switch tubes on the secondary side are kept in a closed state.

7. The synchronous rectification method applied to a bidirectional CLLC resonant converter according to claim 5, characterized in that: The specific method for determining the start time of the synchronous rectification signal of the secondary side switch tube and the turn-off time of the timer signal according to the primary side switch tube drive signal is: The original driving signals of the fifth switch tube S5 and the eighth switch tube S8 on the secondary side are consistent with the driving signals of the first switch tube S1 and the fourth switch tube S4 on the primary side; the original driving signals of the sixth switch tube S6 and the seventh switch tube S7 on the secondary side are consistent with the driving signals of the second switch tube S2 and the third switch tube S3 on the primary side; when the turn-on signal of the sixth and seventh switch tubes on the secondary side arrives, that is, at time t3, the timer t is turned off. clk1 When the turn-on signal of the fifth and eighth switches on the secondary side arrives, that is, at time t4, the timer t is turned off. clk2 .

8. The synchronous rectification method applied to a bidirectional CLLC resonant converter according to claim 3, characterized in that: The resonant circuit is any one of the following three structures, which are: The resonant circuit includes a first resonant inductor L on the primary side. r1 , the first resonant capacitor C on the primary side r1 , the second resonant inductor L on the secondary side r2 , the second resonant capacitor C on the secondary side r2 and a transformer with a turns ratio of n:1; a first resonant inductor L on the primary side r1 With the first resonant capacitor C on the primary side r1 Connected in series to the primary side of the transformer; the second resonant inductor L on the secondary side r2 The second resonant capacitor C r2 Connected in series on the secondary side of the transformer; Alternatively, the resonant circuit includes a first resonant inductor L on the primary side r1 , the first resonant capacitor C on the primary side r1 , the second resonant capacitor C on the secondary side r2 And the transformer with a turns ratio of n:1, the first resonant inductor L on the primary side r1 With the first resonant capacitor C on the primary side r1 Connected in series to the primary side of the transformer; the second resonant capacitor C on the secondary side r2 Connected in series on the secondary side of the transformer; Alternatively, the resonant circuit includes a first resonant capacitor C on the primary side r1 , the second resonant inductor L on the secondary side r2 , the second resonant capacitor C on the secondary side r2 And a transformer with a turns ratio of n:1; the first resonant capacitor C on the primary side r1 Connected in series to the primary side of the transformer; the second resonant inductor L on the secondary side r2 The second resonant capacitor C r2 Connected in series on the secondary side of the transformer.

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