Bidirectional llc converter synchronous rectification timing detection circuit and control method

Abstract

The application discloses a bidirectional LLC converter synchronous rectification timing detection circuit and a control method. The detection circuit comprises a first detection circuit, a second detection circuit and a control unit. The GPIO1 port of the control unit is connected with the output end of the first detection circuit. The GPIO2 port of the control unit is connected with the output end of the second detection circuit. The control unit is used for judging the comparison voltage signal capable of reflecting the current switch timing of the secondary side synchronous rectification circuit according to the current working mode of the primary side synchronous rectification circuit, the first comparison voltage signal and the second comparison voltage signal, and taking the judged comparison voltage signal as the basis of the switch timing of the secondary side synchronous rectification circuit to control the opening and closing of the corresponding synchronous rectification tube in the secondary side synchronous rectification circuit. The current phase condition of the secondary side synchronous rectification circuit is indirectly reflected through the collection of the auxiliary winding voltage signal, and the problems of high cost of sampling devices and large sampling noise of the current detection mode under the traditional low-voltage and large-current condition are ingeniously solved.

Description

Technical Field

[0001] This invention relates to the field of LLC converter technology, and in particular to a synchronous rectification timing detection circuit and control method for a bidirectional LLC converter. Background Technology

[0002] Achieving high efficiency is an important goal of power electronic converters. LLC circuits have the soft-switching characteristics of zero-voltage turn-on and zero-current turn-off, and are widely used in high-efficiency power supplies such as communication power supplies, server power supplies, power adapters, and chargers of different power ratings.

[0003] Topologies derived from LLC circuits, such as CLLC and symmetrical CLLC, achieve high efficiency while also enabling bidirectional DC / DC conversion. They are important circuit forms in the field of bidirectional power supplies for new energy, enabling charging and discharging while combining circuitry.

[0004] In low-output voltage circuits, the method of using active switches (typically power MOSFETs) instead of diodes to perform rectification and conversion on the secondary side of the transformer is called synchronous rectification. Synchronous rectification technology, combined with an LLC power resonant circuit, achieves high efficiency.

[0005] Synchronous rectification uses active switching devices (usually power MOSFETs) to replace diodes for rectification. When power current needs to flow through the original diode, the synchronous rectifier MOSFET opens its channel under the control of a drive signal, allowing the current to flow from the original diode to the MOSFET channel with a lower voltage drop. This reduces losses in the rectification stage and improves circuit efficiency. In bidirectional DC / DC converters, both the primary and secondary sides of the transformer are active switches (power MOSFETs). To reduce the current-mode rectification losses of the MOSFET body diode and prevent reverse recovery of the MOSFET body diode, synchronous rectification technology is also used.

[0006] Low-power synchronous rectification can employ a self-driven method based on the drain-prime voltage Vds of the rectifier switch (MOSFET). In higher-power LLC topologies and their derivative bidirectional CLLC circuits, as well as low-voltage, high-current LLC circuits, the timing control of the transformer secondary-side synchronous rectifier switch mainly relies on sampling the resonant current to determine the switching on and off sequence. Sampling a large-amplitude resonant current requires integrating the current sampling device into the power circuit, which complicates power circuit layout and PCB routing. Furthermore, the sampled current signal often contains glitches and noise during the switching states of the power switches, which can affect or even cause false triggering of synchronous rectification, leading to circuit failures. On the other hand, high-current sensing devices are typically expensive, especially those requiring enhanced insulation. These issues hinder the reliable and widespread use of synchronous rectification technology. Summary of the Invention

[0007] The purpose of this invention is to provide a synchronous rectification timing detection circuit and control method for a bidirectional LLC converter, aiming to solve problems such as high sampling noise in the prior art.

[0008] In a first aspect, embodiments of the present invention provide a synchronous rectification timing detection circuit for a bidirectional LLC converter. The detection circuit detects and determines a comparison voltage signal that reflects the current switching timing of the secondary-side synchronous rectification circuit, and controls the switching on and off of the corresponding synchronous rectifier diodes in the secondary-side synchronous rectification circuit. The secondary-side synchronous rectification circuit is connected to the primary-side synchronous rectification circuit via a transformer T. The detection circuit includes:

[0009] The first detection circuit has an input terminal connected to an auxiliary winding. The auxiliary winding is located on one side of the secondary coil of the transformer T. The current phase on the auxiliary winding corresponds to the current phase on the secondary coil. The first detection circuit is used to rectify, detect, compare, and process the voltage signal u2 obtained from the auxiliary winding to obtain a first comparison voltage signal u5.

[0010] The second detection circuit has its input terminal connected to the auxiliary winding. The second detection circuit is used to differentially compare the voltage signal u2 to obtain a second comparison voltage signal u7.

[0011] The control unit has its GPIO1 port connected to the output of the first detection circuit and its GPIO2 port connected to the output of the second detection circuit. The control unit is used to determine, based on the current operating mode of the primary-side synchronous rectifier circuit, the first comparison voltage signal, and the second comparison voltage signal, a comparison voltage signal that can reflect the current switching timing of the secondary-side synchronous rectifier circuit, and to use the determined comparison voltage signal as the basis for controlling the opening and closing of the corresponding synchronous rectifier tube in the secondary-side synchronous rectifier circuit.

[0012] The output terminal of the primary-side synchronous rectifier circuit is connected to the primary coil of the transformer T; the input terminal of the secondary-side synchronous rectifier circuit is connected to the secondary coil of the transformer T.

[0013] Secondly, embodiments of the present invention provide a synchronous rectification timing control method for a bidirectional LLC converter, applied to the synchronous rectification timing detection circuit of the bidirectional LLC converter, the control method comprising:

[0014] The controller acquires the current operating mode of the primary-side synchronous rectifier circuit;

[0015] The first detection circuit performs rectification, detection, and comparison processing on the voltage signal u2 across the auxiliary winding to obtain the first comparison voltage signal u5.

[0016] The second detection circuit performs differential comparison processing on the voltage signals across the auxiliary winding to obtain the second comparison voltage signal u7;

[0017] The controller determines the comparison voltage signal that reflects the current switching timing of the secondary synchronous rectifier circuit based on the current operating mode of the primary-side synchronous rectifier circuit, the first comparison voltage signal, and the second comparison voltage signal.

[0018] The controller uses the determined comparison voltage signal as the basis for controlling the switching timing of the secondary-side synchronous rectifier circuit to control the opening and closing of the corresponding synchronous rectifier tubes in the secondary-side synchronous rectifier circuit.

[0019] This invention indirectly reflects the current phase of the secondary synchronous rectifier circuit by acquiring and processing the voltage signal of the auxiliary winding. It effectively solves the problems caused by the addition of current sampling devices in the circuit in traditional current detection methods, such as difficulty in power loop layout and wiring, large noise interference of sampling signals, and high component costs.

[0020] The first and second detection circuits detect the comparison voltage signals that reflect the current switching timing of the secondary-side synchronous rectifier circuit under different modes. Based on the comparison voltage signals, the switching timing of the secondary-side synchronous rectifier tube can be updated in each switching cycle during the operation of the converter, thereby improving the operating efficiency of the converter. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A circuit structure diagram of a bidirectional LLC converter synchronous rectification timing detection circuit (including the converter) provided for an embodiment of the present invention;

[0023] Figure 2 Waveform diagram of the converter in underresonant mode provided in an embodiment of the present invention;

[0024] Figure 3 A waveform diagram of the converter near the resonant point (resonant point mode) provided in an embodiment of the present invention;

[0025] Figure 4 Waveform diagram of the converter in overresonance mode provided in an embodiment of the present invention;

[0026] Figure 5 A flowchart illustrating a synchronous rectification timing control method for a bidirectional LLC converter provided in an embodiment of the present invention;

[0027] Figure 6 This is another flowchart illustrating the synchronous rectification timing control method for a bidirectional LLC converter provided in an embodiment of the present invention.

[0028] Figure label:

[0029] 1. Auxiliary winding; 2. Uncontrolled rectifier circuit; 3. Peak detector circuit; 4. First comparator circuit; 5. Differential voltage divider network; 6. Second comparator circuit. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0032] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0033] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0034] Several points to note regarding the attached diagram:

[0035] Figure 2 middle,

[0036] (a) represents the secondary current signal i2 and the voltage signal u2 across the auxiliary winding in the underresonant mode;

[0037] (b) shows the waveforms of voltage signals u3 and 0.5u4 in the underresonant mode;

[0038] (c) shows the waveform of the second comparison voltage signal u7 in the underresonant mode;

[0039] (d) shows the waveform of the first comparison voltage signal u5 in the underresonant mode;

[0040] Figure 3 middle,

[0041] (a) is the secondary current signal i2 near the resonance point (resonance point mode) and the voltage signal u2 across the auxiliary winding;

[0042] (b) The waveforms of voltage signals u3 and 0.5u4 near the resonance point (resonance point mode);

[0043] (c) Waveform of the first comparison voltage signal u5 near the resonance point (resonance point mode);

[0044] (d) Waveform of the second comparison voltage signal u7 near the resonance point (resonance point mode);

[0045] Figure 4 middle,

[0046] (a) represents the secondary current signal i2 and the voltage signal u2 across the auxiliary winding in over-resonance mode;

[0047] (b) shows the waveforms of voltage signals u3 and 0.5u4 in the over-resonance mode;

[0048] (c) Waveform of the first comparison voltage signal u5 in over-resonance mode;

[0049] (d) Waveform of the second comparison voltage signal u7 in over-resonance mode.

[0050] Please see Figure 1 A synchronous rectification timing detection circuit for a bidirectional LLC converter is disclosed. The detection circuit detects and determines a comparison voltage signal that reflects the current switching timing of the secondary-side synchronous rectifier circuit, and controls the switching on and off of the corresponding synchronous rectifier diodes in the secondary-side synchronous rectifier circuit. The secondary-side synchronous rectifier circuit is connected to the primary-side synchronous rectifier circuit via a transformer T. The detection circuit includes:

[0051] The first detection circuit has an input terminal connected to an auxiliary winding. The auxiliary winding is located on one side of the secondary coil of the transformer T. The current phase on the auxiliary winding corresponds to the current phase on the secondary coil. The first detection circuit is used to rectify, detect, compare, and process the voltage signal u2 obtained from the auxiliary winding to obtain a first comparison voltage signal u5.

[0052] The second detection circuit has its input terminal connected to the auxiliary winding. The second detection circuit is used to differentially compare the voltage signal u2 to obtain a second comparison voltage signal u7.

[0053] The control unit has its GPIO1 port connected to the output of the first detection circuit and its GPIO2 port connected to the output of the second detection circuit. The control unit is used to determine, based on the current operating mode of the primary-side synchronous rectifier circuit, the first comparison voltage signal, and the second comparison voltage signal, a comparison voltage signal that can reflect the current switching timing of the secondary-side synchronous rectifier circuit, and to use the determined comparison voltage signal as the basis for controlling the opening and closing of the corresponding synchronous rectifier tube in the secondary-side synchronous rectifier circuit.

[0054] The output terminal of the primary-side synchronous rectifier circuit is connected to the primary coil of the transformer T; the input terminal of the secondary-side synchronous rectifier circuit is connected to the secondary coil of the transformer T.

[0055] In this embodiment, the phase of the current in the secondary synchronous rectifier circuit is indirectly reflected by acquiring the voltage signal of the auxiliary winding, which cleverly solves the problems of high cost of additional sampling devices and high sampling noise in the traditional current detection method under low voltage and high current conditions.

[0056] The first and second detection circuits detect the comparison voltage signals that reflect the current switching timing of the secondary-side synchronous rectifier circuit under different modes. Based on the comparison voltage signals, the switching timing of the secondary-side synchronous rectifier tube can be updated in each switching cycle during the operation of the converter, thereby improving the operating efficiency of the converter.

[0057] Specifically, by combining the input comparison voltage signal information with the current operating mode of the converter, the control unit can make a comprehensive judgment, which can prevent misjudgment caused by interference.

[0058] For ease of description, the primary-side synchronous rectifier circuit will be referred to as the primary side, and the secondary-side synchronous rectifier circuit will be referred to as the secondary side.

[0059] In one embodiment, the control unit is connected to the drive circuits of the primary-side synchronous rectifier circuit and the secondary-side synchronous rectifier circuit via the ePWM unit. By sending control commands to the ePWM unit, the control unit controls the ePWM unit to issue drive signals and drive the corresponding drive circuits to control the corresponding synchronous rectifier circuits. The drive circuits are connected to the gate and source of the synchronous rectifier tubes of the primary-side synchronous rectifier circuit and the secondary-side synchronous rectifier circuit.

[0060] In one embodiment, a resistor R2 is connected in parallel with the auxiliary winding.

[0061] In one embodiment, the primary-side synchronous rectification circuit includes a first synchronous rectifier group, a second synchronous rectifier group, an inductor Lr, an inductor Lm, and a capacitor Cr, wherein the first synchronous rectifier group and the second synchronous rectifier group are connected in parallel.

[0062] The first synchronous rectifier tube group includes synchronous rectifier tubes S1 and S3 connected in series, and the second synchronous rectifier tube group includes synchronous rectifier tubes S2 and S4 connected in series. The two ends of the first synchronous rectifier tube group are respectively connected to the positive and negative terminals of the input voltage U1. One end of the inductor Lr is connected in the middle of the synchronous rectifier tubes S1 and S2. The other end of the inductor Lr is connected in series with an inductor Lm and a capacitor Cr. The capacitor Cr is connected in the middle of the synchronous rectifier tubes S3 and S4. The two ends of the inductor Lm are respectively connected to the two ends of the primary coil of the transformer T.

[0063] In one embodiment, the secondary-side synchronous rectification circuit includes a third synchronous rectifier diode group, a fourth synchronous rectifier diode group, a capacitor C0, and a resistor R1 connected in parallel.

[0064] The third synchronous rectifier tube group includes synchronous rectifier tubes S5 and S7 connected in series, and the fourth synchronous rectifier tube group includes synchronous rectifier tubes S6 and S8 connected in series. The middle of the synchronous rectifier tubes S5 and S7 is connected to one end of the transformer T, and the middle of the synchronous rectifier tubes S6 and S8 is connected to the other end of the transformer T.

[0065] In one embodiment, the converter includes a primary-side full-bridge circuit (primary-side synchronous rectifier circuit), a resonant cavity, and a secondary-side full-bridge circuit (secondary-side synchronous rectifier circuit). Synchronous rectifier diodes S1-S4, D... s1 -D S4 These are the switching transistors and their body diodes in the primary-side full-bridge circuit, and the synchronous rectifier diodes S5-S8, D. S5 -D S8 These are the switching transistor and the body diode of the secondary-side full-bridge circuit, respectively. The resonant cavity circuit includes an inductor Lr, a capacitor Cr, a magnetizing inductor Lm, and a transformer T, as well as a filter capacitor C. o With load R1.

[0066] In one embodiment, the first detection circuit includes an uncontrolled rectifier circuit, a peak detection circuit, and a first comparison circuit;

[0067] The peak detection circuit includes a resistor R3, a capacitor C1, a resistor R4, and a diode D1. The resistor R3, capacitor C1, and resistor R4 are connected in parallel in sequence. The diode D1 is forward-connected between the resistor R3 and the capacitor C1. The anode of the diode D1 is connected to the positive input port of the first comparator circuit, and the cathode of the diode D1 is connected to the negative input port of the first comparator circuit.

[0068] The uncontrolled rectifier circuit is a bridge circuit. The midpoints (outputs) of the two arms of the bridge circuit are connected to the two ends of resistor R3, and the other two ends (inputs) of the bridge circuit are connected to the two ends of the auxiliary winding.

[0069] The output of the first comparator circuit is connected to the GPIO1 port of the control unit.

[0070] In this embodiment, the resistor R4 is larger and the capacitor C1 is smaller, which makes the capacitor C1 reach the peak value of the input voltage more quickly when charging, while the discharge process of the capacitor C1 is more slow, so that the resistor R4 can maintain the peak value of the input voltage better.

[0071] The auxiliary winding voltage signal u2 is sampled and passed through an uncontrolled rectifier circuit and a peak detector circuit to obtain the peak voltage signal u4 of the auxiliary winding. The voltage signal u2 of the auxiliary winding is then passed through an uncontrolled rectifier circuit to obtain the voltage signal u3. The voltage signal u3 and the voltage signal u4 have different potential reference points. The voltage signal u3 and the peak voltage signal u4 are then sent to the first comparison circuit for comparison. After conditioning, the signal is sent to the GPIO1 port of the control unit.

[0072] The first comparison circuit is comparator OA1.

[0073] In one embodiment, the second detection circuit includes a differential voltage divider network and a second comparison circuit. The two ends of the auxiliary winding are connected to the input terminals of the differential voltage divider network, the output terminals of the differential voltage divider network are connected to the positive and negative input ports of the second comparison circuit, and the output terminals of the second comparison circuit are connected to the GPIO2 port of the control unit.

[0074] In this embodiment, the sampled auxiliary winding voltage signal u2 is fed into the second comparison circuit after passing through a differential voltage divider network for comparison, and then conditioned before being sent to the GPIO2 port of the control unit.

[0075] The second comparator circuit is comparator OA2.

[0076] Understandably, the three operating modes of the converter (under-resonance mode, over-resonance mode, and resonant mode) are determined by the frequency of the switching signal, which is provided by the control unit. Therefore, the control unit can determine the current operating mode of the LLC converter. When the converter is near the resonant point (resonant mode) or operating in over-resonance mode, the current signal i2 in the secondary synchronous rectifier is continuous; when the converter is in under-resonance mode, the current signal i2 in the secondary synchronous rectifier is discontinuous.

[0077] Specifically, the zero-crossing moment of the synchronous rectifier current signal i2 on the secondary side is the standard switching moment of the synchronous rectifier on the secondary side.

[0078] Since the zero-crossing information of the current signal i2 is difficult to distinguish and identify, a comparison voltage signal that can reflect the zero-crossing information of the current signal i2 is detected and processed by the first detection circuit and the second detection circuit.

[0079] Please refer to Figure 2In the first mode: when the converter is in underresonant mode, voltage signals u3 and u4 are compared by comparator OA1 to obtain a square wave voltage signal u5 that reflects the zero-crossing information of the secondary current signal i2; at the same time, voltage signal u2 is sent to comparator OA2 after passing through a differential voltage divider network for comparison, and only voltage signal u7 that reflects the zero-crossing information of the auxiliary winding voltage signal u2 is obtained. However, the phase of voltage signal u2 at both ends of the auxiliary winding cannot accurately reflect the zero-crossing information of the secondary current signal i2 in underresonant mode. Therefore, voltage signal u5 sent to GPIO1 port in underresonant mode can reflect the switching timing of the secondary synchronous rectifier, while voltage signal u7 sent to GPIO2 port cannot reflect the switching timing of the secondary synchronous rectifier.

[0080] Please refer to Figure 3 The second mode: When the converter is near the resonant point (resonant point mode), it can be divided into two cases for discussion. The first case is when the converter is exactly at the full resonant point. Voltage signals u3 and u4 are compared by comparator OA1, and only voltage signal u5 is a series of high-level signals. At the same time, voltage signal u2 is sent to comparator OA2 after passing through the differential voltage divider network for comparison, and a square wave voltage signal u7 that can reflect the zero-crossing information of the secondary current signal i2 is obtained. This shows that the voltage phase at both ends of the auxiliary winding can accurately reflect the zero-crossing information of the secondary current at the full resonant point. Therefore, the voltage signal u7 sent to the GPIO2 port at the full resonant point can reflect the switching timing of the synchronous rectifier tube on the secondary side, while the voltage signal u5 sent to the GPIO1 port cannot reflect the switching timing of the synchronous rectifier tube on the secondary side.

[0081] When the converter is in critical resonance mode, voltage signals u3 and u4 are compared by comparator OA1. Ideally, this yields a square wave voltage signal u5 that reflects the zero-crossing information of the secondary current signal i2. Simultaneously, voltage signal u2 is compared by comparator OA2 after passing through a differential voltage divider network, yielding a square wave voltage signal u7 that basically reflects the zero-crossing information of the secondary current signal i2. In practical engineering, due to the high switching frequency and comparator speed limitations, the comparator may not be able to accurately output the voltage signal u5 after comparing voltage signals u3 and u4. In this case, voltage signal u5 remains a series of high levels. Therefore, in this situation, the voltage signal u7 sent to the GPIO2 port is used as a square wave signal reflecting the switching timing of the synchronous rectifier diodes on the secondary side.

[0082] Please refer to Figure 4The third mode: When the converter is in over-resonance mode, voltage signals u3 and u4 are compared by comparator OA1. Similar to the second mode, the resulting voltage signal u5 is a series of high-level signals. At the same time, voltage signal u2 is sent to comparator OA2 after passing through a differential voltage divider network for comparison, resulting in a square wave voltage signal u7 that reflects the zero-crossing information of the secondary current signal i2. This indicates that the voltage phase at both ends of the auxiliary winding can accurately reflect the zero-crossing information of the secondary current in over-resonance mode. Therefore, the voltage signal u7 sent to the GPIO2 port in over-resonance mode can reflect the switching timing of the secondary synchronous rectifier, while the voltage signal u5 sent to the GPIO1 port cannot reflect the switching timing of the secondary voltage synchronous rectifier.

[0083] Based on the above, after the control unit obtains the current operating mode (which can be obtained from the switching timing of the primary-side synchronous rectifier) ​​and the comparison voltage signal.

[0084] If the first comparison voltage signal u5 is a series of high levels and the converter is near the resonant point (resonant point mode) or operating in over-resonance mode, the second comparison voltage signal u7 sent from the GPIO2 port is used as the basis for the switching timing of the secondary synchronous rectifier. If the first comparison voltage signal u5 is a square wave signal and the converter is in under-resonance mode, the first comparison voltage signal u5 sent from the GPIO1 port is used as the basis for the switching timing of the secondary synchronous rectifier.

[0085] The secondary-side synchronous rectifier diodes S5 and S8 are a group with the same turn-on timing; S6 and S7 are a group with the same turn-on timing. In this application, when one group of synchronous rectifier diodes is turned on in the primary or secondary side, it can be regarded as the other group of synchronous rectifier diodes corresponding to it being turned off. Similarly, when one group of synchronous rectifier diodes is turned off, it can be regarded as the other group of synchronous rectifier diodes corresponding to it being turned on. For ease of understanding, dead time is not considered for the time being.

[0086] The diagram is labeled according to the initial setting of the primary side full-bridge current with S1 and S4 conducting.

[0087] In underresonance mode, when the current signal i2 is in the positive half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the timing of the primary-side synchronous rectifier diodes of the converter is first judged. If the primary-side synchronous rectifier diodes S1 and S4 are turned on at this time, the control unit controls the secondary-side synchronous rectifier diodes S5 and S8 to turn on. Then, when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary-side synchronous rectifier diodes S5 and S8 to turn off (that is, when the current signal i2 is in the positive half-cycle, the secondary-side synchronous rectifier diodes S5 and S8 are turned on and off sequentially within one rising edge to falling edge cycle of the first comparison voltage signal u5).

[0088] Next, when the current signal i2 enters the negative half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary synchronous rectifier diodes S6 and S7 to turn on. Then, when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary synchronous rectifier diodes S6 and S7 to turn off (that is, when the current signal i2 enters the negative half-cycle, the secondary synchronous rectifier diodes S6 and S7 are sequentially controlled to turn on and off within one cycle from the rising edge to the falling edge of the first comparison voltage signal u5).

[0089] The above describes the control logic for one complete signal cycle, combining the current signal i2 and the first comparison voltage signal u5. The timing of the synchronous rectifier tube turning on in subsequent cycles repeats the above process.

[0090] In another relative case, when the current signal i2 is in the positive half-cycle and the rising edge of the first comparison voltage signal u5 arrives, if the primary side synchronous rectifiers S2 and S3 are turned on at this time, the control unit controls the secondary side synchronous rectifiers S6 and S7 to turn on. Then, when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary side synchronous rectifiers S6 and S7 to turn off.

[0091] Next, when the current signal i2 enters the negative half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary side synchronous rectifier diodes S5 and S8 to turn on. Then, when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary side synchronous rectifier diodes S5 and S8 to turn off.

[0092] The above describes the control logic for one complete signal cycle, combining the current signal i2 and the first comparison voltage signal u5. The timing of the synchronous rectifier tube turning on in subsequent cycles repeats the above process.

[0093] Near the resonant point (resonant point mode) or in over-resonant mode, when the current signal i2 is in the positive half-cycle and the rising edge of the second comparison voltage signal u7 arrives, the timing of the primary-side synchronous rectifier diodes of the converter is first determined. If the primary-side synchronous rectifier diodes S1 and S4 are turned on at this time, the control unit controls the secondary-side synchronous rectifier diodes S5 and S8 to turn on, and the control unit controls the secondary-side synchronous rectifier diodes S6 and S7 to turn off. When the falling edge of signal u7 arrives, the control unit controls the secondary-side synchronous rectifier diodes S5 and S8 to turn off, and at the same time, the control unit controls the secondary-side synchronous rectifier diodes S6 and S7 to turn on.

[0094] The above describes the control logic for one complete signal cycle, combining the current signal i2 and the second comparison voltage signal u7. The timing of the synchronous rectifier tube turning on in subsequent cycles repeats the above process.

[0095] In another relative scenario, when the current signal i2 is in its positive half-cycle and the primary side synchronous rectifiers S2 and S3 are conducting, the control unit controls the secondary side synchronous rectifiers S6 and S7 to conduct, while simultaneously controlling the secondary side synchronous rectifiers S5 and S8 to turn off. When the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the secondary side synchronous rectifiers S6 and S7 to turn off, while simultaneously controlling the secondary side synchronous rectifiers S5 and S8 to conduct.

[0096] The above describes the control logic for one complete signal cycle, combining the current signal i2 and the second comparison voltage signal u7. The timing of the synchronous rectifier tube turning on in subsequent cycles repeats the above process.

[0097] In practice, to prevent shoot-through, a certain dead time is usually required to turn on the synchronous rectifier tubes of different bridge arms. The specific settings are based on the actual situation.

[0098] Please refer to Figure 5-6 A synchronous rectification timing control method for a bidirectional LLC converter is disclosed, applied to a synchronous rectification timing detection circuit of a bidirectional LLC converter. The control method includes:

[0099] S101, The controller obtains the current operating mode of the primary-side synchronous rectifier circuit;

[0100] S102, the first detection circuit performs rectification, detection and comparison processing on the voltage signal u2 at both ends of the auxiliary winding to obtain the first comparison voltage signal u5;

[0101] S103, the second detection circuit performs differential comparison processing on the voltage signals at both ends of the auxiliary winding to obtain the second comparison voltage signal u7;

[0102] S104, the controller determines a comparison voltage signal that reflects the current switching timing of the secondary-side synchronous rectifier circuit based on the current operating mode of the primary-side synchronous rectifier circuit, the first comparison voltage signal, and the second comparison voltage signal.

[0103] S105, the controller uses the determined comparison voltage signal as the basis for controlling the switching timing of the secondary-side synchronous rectifier circuit to control the opening and closing of the corresponding synchronous rectifier tube in the secondary-side synchronous rectifier circuit.

[0104] In this embodiment, the phase of the current in the secondary synchronous rectifier circuit is indirectly reflected by acquiring the voltage signal of the auxiliary winding, which cleverly solves the problems of high cost of additional sampling devices and high sampling noise in the traditional current detection method under low voltage and high current conditions.

[0105] The first and second detection circuits detect the comparison voltage signals that reflect the current switching timing of the secondary-side synchronous rectifier circuit under different modes. Based on the comparison voltage signals, the switching timing of the secondary-side synchronous rectifier tube can be updated in each switching cycle during the operation of the converter, thereby improving the operating efficiency of the converter.

[0106] Specifically, by combining the input comparison voltage signal information with the current operating mode of the converter, the control unit can make a comprehensive judgment, which can prevent misjudgment caused by interference.

[0107] In one embodiment, the first detection circuit includes an uncontrolled rectifier circuit, a peak detector circuit, and a first comparison circuit. The first detection circuit performs rectification, detection, and comparison processing on the voltage signal across the auxiliary winding to obtain a first comparison voltage signal.

[0108] The uncontrolled rectifier circuit processes the voltage signal u2 across the auxiliary winding to obtain the voltage signal u3.

[0109] The peak detection circuit processes the voltage signal u3 to obtain the voltage signal u4;

[0110] The first comparison circuit compares and processes the voltage signals u4 and u3 to obtain the first comparison voltage signal u5.

[0111] In this embodiment, the auxiliary winding voltage signal u2 is sampled and passed through an uncontrolled rectifier circuit and a peak detector circuit in sequence to obtain the peak voltage signal u4 of the auxiliary winding. The voltage signal u2 of the auxiliary winding is then passed through an uncontrolled rectifier circuit to obtain the voltage signal u3. The voltage signal u3 and the voltage signal u4 have different potential reference points. The voltage signal u3 and the peak voltage signal u4 are then sent to the first comparison circuit for comparison. After conditioning, the voltage signal u3 is sent to the GPIO1 port of the control unit.

[0112] In one embodiment, the second detection circuit includes a differential voltage divider network and a second comparison circuit. The second detection circuit performs differential comparison processing on the voltage signal across the auxiliary winding to obtain a second comparison voltage signal, including:

[0113] The differential voltage divider network processes the voltage signal u2 across the auxiliary winding to obtain the voltage signal u6.

[0114] The second comparison circuit receives the voltage signal u6 and performs comparison processing to obtain the second comparison voltage signal u7.

[0115] In this embodiment, the sampled auxiliary winding voltage signal u2 is fed into the second comparison circuit after passing through a differential voltage divider network for comparison, and then conditioned before being sent to the GPIO2 port of the control unit.

[0116] In one embodiment, the controller determines a comparison voltage signal that reflects the current switching timing of the secondary-side synchronous rectifier circuit based on the current operating mode of the primary-side synchronous rectifier circuit, a first comparison voltage signal, and a second comparison voltage signal, including:

[0117] Obtain the switching timing of the primary-side synchronous rectifier circuit;

[0118] Determine whether the current operating mode is under-resonance mode, over-resonance mode, or resonant point mode;

[0119] If the current operating mode is underresonance mode, determine whether the first comparison voltage signal u5 is a square wave signal;

[0120] If the first comparison voltage signal u5 is a square wave signal, then it is determined that the first comparison voltage signal u5 can reflect the current switching timing of the secondary side synchronous rectifier circuit.

[0121] In this embodiment, the operating mode and the first comparison voltage signal u5 are used to determine the comparison voltage signal that can reflect the current switching timing of the secondary side synchronous rectifier circuit.

[0122] In one embodiment, the controller determines a comparison voltage signal that reflects the current switching timing of the secondary-side synchronous rectifier circuit based on the current operating mode of the primary-side synchronous rectifier circuit, a first comparison voltage signal, and a second comparison voltage signal, including:

[0123] If the current operating mode is over-resonance mode or resonant point mode (the converter operates near the resonant point), determine whether the first comparison voltage signal u5 consists of a series of high levels;

[0124] If the first comparison voltage signal u5 consists of a series of high levels, then the second comparison voltage signal u7 is determined to reflect the current switching timing of the secondary-side synchronous rectifier circuit.

[0125] In this embodiment, the operating mode and the first comparison voltage signal u5 are used to determine the comparison voltage signal that can reflect the current switching timing of the secondary side synchronous rectifier circuit.

[0126] In one embodiment, the primary-side synchronous rectifier circuit includes a first synchronous rectifier diode group and a second synchronous rectifier diode group, an inductor Lr, an inductor Lm, and a capacitor Cr connected in parallel.

[0127] The first synchronous rectifier tube group includes synchronous rectifier tubes S1 and S3 connected in series, and the second synchronous rectifier tube group includes synchronous rectifier tubes S2 and S4 connected in series. The two ends of the first synchronous rectifier tube group are respectively connected to the positive and negative terminals of the input voltage U1. One end of the inductor Lr is connected in the middle of the synchronous rectifier tubes S1 and S2. The other end of the inductor Lr is connected in series with an inductor Lm and a capacitor Cr. The capacitor Cr is connected in the middle of the synchronous rectifier tubes S3 and S4. The two ends of the inductor Lm are respectively connected to the two ends of the primary coil of the transformer T.

[0128] The controller uses the determined comparison voltage signal as the basis for controlling the switching timing of the secondary-side synchronous rectifier circuit to control the opening and closing of the corresponding synchronous rectifier tubes in the secondary-side synchronous rectifier circuit, including:

[0129] Obtain the secondary coil current signal i2 of the transformer T;

[0130] If it is determined that the first comparison voltage signal u5 can reflect the current switching timing of the secondary side synchronous rectifier circuit, then it is determined whether the current signal i2 is in the positive half-cycle;

[0131] If the current signal i2 is in the positive half-cycle, then determine whether the synchronous rectifier tubes S1 and S4 are in the conducting state.

[0132] First positive cycle processing step 1: If the synchronous rectifier tubes S1 and S4 are in the on state, when the rising edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn on, and when the falling edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn off.

[0133] When the current signal i2 enters the negative half-cycle and the rising edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn on; when the falling edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn off.

[0134] Return to step 1 of the first positive cycle processing.

[0135] In this embodiment, under the underresonant mode, when the current signal i2 is in the positive half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the timing of the primary-side synchronous rectifier of the converter is first judged. If the primary-side synchronous rectifiers S1 and S4 are turned on at this time, the control unit controls the secondary-side synchronous rectifiers S5 and S8 to turn on. Then, when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary-side synchronous rectifiers S5 and S8 to turn off (that is, when the current signal i2 is in the positive half-cycle, the secondary-side synchronous rectifiers S5 and S8 are turned on and off sequentially within a period from the rising edge to the falling edge of the first comparison voltage signal u5).

[0136] Next, when the current signal i2 enters the negative half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary synchronous rectifier diodes S6 and S7 to turn on. Then, when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary synchronous rectifier diodes S6 and S7 to turn off (that is, when the current signal i2 enters the negative half-cycle, the secondary synchronous rectifier diodes S6 and S7 are sequentially controlled to turn on and off within one cycle from the rising edge to the falling edge of the first comparison voltage signal u5).

[0137] After completing the above steps, the process will return to the first positive cycle and repeat step 1.

[0138] The current signal i2 can be obtained through a current sensor.

[0139] In one embodiment, the step of determining whether the current signal i2 is in the positive half-cycle if it is determined that the first comparison voltage signal u5 can reflect the current switching timing of the secondary-side synchronous rectifier circuit includes:

[0140] If the current signal i2 is in the negative half-cycle, then determine whether the synchronous rectifier tubes S2 and S3 are in the on state;

[0141] First negative cycle processing step 1: If the synchronous rectifier tubes S2 and S3 are in the on state, then when the rising edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn on, and when the falling edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn off.

[0142] When the current signal i2 enters the positive half-cycle and the rising edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn on; when the falling edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn off.

[0143] Return to step 1 of the first negative cycle processing.

[0144] In this embodiment, the situation is the same as the previous embodiment, except for the logical changes caused by different half-cycle judgments.

[0145] In one embodiment, determining whether the synchronous rectifier diodes S1 and S4 are in a conducting state if the current signal i2 is in the positive half-cycle includes:

[0146] First positive cycle processing step 2: If the synchronous rectifier tubes S1 and S4 are in the off state (which can be regarded as the synchronous rectifier tubes S2 and S3 being turned on), then when the rising edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to be turned on, and when the falling edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to be turned off.

[0147] When the current signal i2 enters the negative half-cycle and the rising edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn on; when the falling edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn off.

[0148] Return to step 2 of the first positive cycle processing.

[0149] In this embodiment, the situation is the opposite of the previous embodiment. When the current signal i2 is in the positive half-cycle and the rising edge of the first comparison voltage signal u5 arrives, if the primary side synchronous rectifiers S2 and S3 are turned on at this time, the control unit controls the secondary side synchronous rectifiers S6 and S7 to turn on. Then, when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary side synchronous rectifiers S6 and S7 to turn off.

[0150] Next, when the current signal i2 enters the negative half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary side synchronous rectifier diodes S5 and S8 to turn on. Then, when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the secondary side synchronous rectifier diodes S5 and S8 to turn off.

[0151] After completing the above steps, the process will return to the first positive cycle and repeat step 2.

[0152] In one embodiment, determining whether the synchronous rectifier diodes S2 and S3 are in a conducting state if the current signal i2 is in the negative half-cycle includes:

[0153] First negative cycle processing step 2: If the synchronous rectifier tubes S2 and S3 are in the off state, when the rising edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn on, and when the falling edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn off.

[0154] When the current signal i2 enters the positive half-cycle and the rising edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn on; when the falling edge of the voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn off.

[0155] Return to step 2 of the first negative cycle processing.

[0156] In this embodiment, the situation is the same as the previous embodiment, except for the logical changes caused by different half-cycle judgments.

[0157] In one embodiment, the primary-side synchronous rectifier circuit includes a first synchronous rectifier diode group and a second synchronous rectifier diode group, an inductor Lr, an inductor Lm, and a capacitor Cr connected in parallel.

[0158] The first synchronous rectifier tube group includes synchronous rectifier tubes S1 and S3 connected in series, and the second synchronous rectifier tube group includes synchronous rectifier tubes S2 and S4 connected in series. The two ends of the first synchronous rectifier tube group are respectively connected to the positive and negative terminals of the input voltage U1. One end of the inductor Lr is connected in the middle of the synchronous rectifier tubes S1 and S2. The other end of the inductor Lr is connected in series with an inductor Lm and a capacitor Cr. The capacitor Cr is connected in the middle of the synchronous rectifier tubes S3 and S4. The two ends of the inductor Lm are respectively connected to the two ends of the primary coil of the transformer T.

[0159] The controller uses the determined comparison voltage signal as the basis for controlling the switching timing of the secondary-side synchronous rectifier circuit to control the opening and closing of the corresponding synchronous rectifier tubes in the secondary-side synchronous rectifier circuit, including:

[0160] If it is determined that the second comparison voltage signal u7 can reflect the current switching timing of the secondary side synchronous rectifier circuit, then it is determined whether the current signal i2 is in the positive half-cycle;

[0161] If the current signal i2 is in the positive half-cycle, then determine whether the synchronous rectifier tubes S1 and S4 are in the conducting state.

[0162] First positive cycle processing step 3: If the synchronous rectifier tubes S1 and S4 are in the on state, when the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn on, and when the falling edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn off.

[0163] When the current signal i2 enters the negative half-cycle and the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn on; when the falling edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn off.

[0164] Return to step 3 of the first positive cycle processing.

[0165] In this embodiment, near the resonant point (resonant point mode) or in over-resonant mode, when the current signal i2 is in the positive half-cycle and the rising edge of the second comparison voltage signal u7 arrives, the timing of the primary-side synchronous rectifier diodes of the converter is first determined. If the primary-side synchronous rectifier diodes S1 and S4 are turned on at this time, the control unit controls the secondary-side synchronous rectifier diodes S5 and S8 to turn on, and the control unit controls the secondary-side synchronous rectifier diodes S6 and S7 to turn off. When the falling edge of signal u7 arrives, the control unit controls the secondary-side synchronous rectifier diodes S5 and S8 to turn off, and at the same time, the control unit controls the secondary-side synchronous rectifier diodes S6 and S7 to turn on.

[0166] After completing the above steps, the process will return to the first positive cycle and repeat step 3.

[0167] In one embodiment, the step of determining whether the current signal i2 is in the positive half-cycle if it is determined that the first comparison voltage signal u7 can reflect the current switching timing of the secondary-side synchronous rectifier circuit includes:

[0168] If the current signal i2 is in the negative half-cycle, then determine whether the synchronous rectifier tubes S2 and S3 are in the on state;

[0169] First negative cycle processing step 3: If the synchronous rectifier tubes S2 and S3 are in the on state, when the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn on, and when the falling edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn off.

[0170] When the current signal i2 enters the positive half-cycle and the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn on; when the falling edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn off.

[0171] Return to step 3 of the first negative cycle processing.

[0172] In this embodiment, the situation is the same as the previous embodiment, except for the logical changes caused by different half-cycle judgments.

[0173] In one embodiment, determining whether the synchronous rectifier diodes S1 and S4 are in a conducting state if the current signal i2 is in the positive half-cycle includes:

[0174] First positive cycle processing step 4: If the synchronous rectifier tubes S1 and S4 are in the off state, when the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn on, and when the falling edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn off.

[0175] When the current signal i2 enters the negative half-cycle and the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn on; when the falling edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn off.

[0176] Return to step 4 of the first positive cycle processing.

[0177] In this embodiment, the situation is the opposite of the previous embodiment. When the current signal i2 is in the positive half-cycle and the primary side synchronous rectifiers S2 and S3 are turned on, the control unit controls the secondary side synchronous rectifiers S6 and S7 to turn on, while simultaneously controlling the secondary side synchronous rectifiers S5 and S8 to turn off. When the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the secondary side synchronous rectifiers S6 and S7 to turn off, while simultaneously controlling the secondary side synchronous rectifiers S5 and S8 to turn on.

[0178] After completing the above steps, the process will return to the first positive cycle processing step 4 and repeat.

[0179] In one embodiment, determining whether the synchronous rectifier diodes S2 and S3 are in a conducting state if the current signal i2 is in the negative half-cycle includes:

[0180] First negative cycle processing step 4: If the synchronous rectifier tubes S2 and S3 are in the off state, when the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn on, and when the falling edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn off.

[0181] When the current signal i2 enters the positive half-cycle and the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn on; when the falling edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier tubes S5 and S8 to turn off.

[0182] Return to step 4 of the first negative cycle processing.

[0183] In this embodiment, the situation is the same as the previous embodiment, except for the logical changes caused by different half-cycle judgments.

[0184] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A synchronous rectification timing detection circuit for a bidirectional LLC converter, characterized in that, The detection circuit is used to detect and determine a comparison voltage signal that reflects the current switching timing of the secondary-side synchronous rectifier circuit, and to control the switching on and off of the corresponding synchronous rectifier diodes in the secondary-side synchronous rectifier circuit. The secondary-side synchronous rectifier circuit is connected to the primary-side synchronous rectifier circuit through a transformer T. The detection circuit includes: The first detection circuit has an input terminal connected to an auxiliary winding. The auxiliary winding is located on one side of the secondary coil of the transformer T. The current phase on the auxiliary winding corresponds to the current phase on the secondary coil. The first detection circuit is used to rectify, detect, compare, and process the voltage signal u2 obtained from the auxiliary winding to obtain a first comparison voltage signal u5. The second detection circuit has its input terminal connected to the auxiliary winding. The second detection circuit is used to differentially compare the voltage signal u2 to obtain a second comparison voltage signal u7. The control unit has its GPIO1 port connected to the output of the first detection circuit and its GPIO2 port connected to the output of the second detection circuit. The control unit is used to determine, based on the current operating mode of the primary-side synchronous rectifier circuit, the first comparison voltage signal, and the second comparison voltage signal, a comparison voltage signal that can reflect the current switching timing of the secondary-side synchronous rectifier circuit, and to use the determined comparison voltage signal as the basis for controlling the opening and closing of the corresponding synchronous rectifier tube in the secondary-side synchronous rectifier circuit. The output terminal of the primary-side synchronous rectifier circuit is connected to the primary coil of the transformer T; the input terminal of the secondary-side synchronous rectifier circuit is connected to the secondary coil of the transformer T.

2. The synchronous rectification timing detection circuit for a bidirectional LLC converter according to claim 1, characterized in that: The primary-side synchronous rectifier circuit includes a first synchronous rectifier diode group, a second synchronous rectifier diode group, an inductor Lr, an inductor Lm, and a capacitor Cr, wherein the first synchronous rectifier diode group and the second synchronous rectifier diode group are connected in parallel. The first synchronous rectifier tube group includes synchronous rectifier tubes S1 and S3 connected in series, and the second synchronous rectifier tube group includes synchronous rectifier tubes S2 and S4 connected in series. The two ends of the first synchronous rectifier tube group are respectively connected to the positive and negative terminals of the input voltage U1. One end of the inductor Lr is connected in the middle of the synchronous rectifier tubes S1 and S3. The other end of the inductor Lr is connected in series with an inductor Lm and a capacitor Cr. The capacitor Cr is connected in the middle of the synchronous rectifier tubes S2 and S4. The two ends of the inductor Lm are respectively connected to the two ends of the primary coil of the transformer T.

3. The synchronous rectification timing detection circuit for a bidirectional LLC converter according to claim 1, characterized in that: The secondary-side synchronous rectifier circuit includes a third synchronous rectifier diode group, a fourth synchronous rectifier diode group, a capacitor C0, and a resistor R1 connected in parallel. The third synchronous rectifier tube group includes synchronous rectifier tubes S5 and S7 connected in series, and the fourth synchronous rectifier tube group includes synchronous rectifier tubes S6 and S8 connected in series. The middle of the synchronous rectifier tubes S5 and S7 is connected to one end of the transformer T, and the middle of the synchronous rectifier tubes S6 and S8 is connected to the other end of the transformer T.

4. The synchronous rectification timing detection circuit for a bidirectional LLC converter according to claim 1, characterized in that: The first detection circuit includes an uncontrolled rectifier circuit, a peak detector circuit, and a first comparison circuit; The peak detection circuit includes a resistor R3, a capacitor C1, a resistor R4, and a diode D1. The resistor R3, capacitor C1, and resistor R4 are connected in parallel in sequence. The diode D1 is forward-connected between the resistor R3 and the capacitor C1. The anode of the diode D1 is connected to the positive input port of the first comparator circuit, and the cathode of the diode D1 is connected to the negative input port of the first comparator circuit. The uncontrolled rectifier circuit is a bridge circuit. The midpoints of the two arms of the bridge circuit are respectively connected to the two ends of the resistor R3, and the other two ends of the bridge circuit are respectively connected to the two ends of the auxiliary winding. The output of the first comparator circuit is connected to the GPIO1 port of the control unit.

5. The synchronous rectification timing detection circuit for a bidirectional LLC converter according to claim 1, characterized in that: The second detection circuit includes a differential voltage divider network and a second comparison circuit. The two ends of the auxiliary winding are connected to the input terminal of the differential voltage divider network, the output terminal of the differential voltage divider network is connected to the positive and negative input ports of the second comparison circuit, and the output terminal of the second comparison circuit is connected to the GPIO2 port of the control unit.

6. A synchronous rectification timing control method for a bidirectional LLC converter, characterized in that, The control method applied to the synchronous rectification timing detection circuit of the bidirectional LLC converter according to any one of claims 1-5 includes: The control unit acquires the current operating mode of the primary-side synchronous rectifier circuit; The first detection circuit performs rectification, detection, and comparison processing on the voltage signal u2 across the auxiliary winding to obtain the first comparison voltage signal u5. The second detection circuit performs differential comparison processing on the voltage signals across the auxiliary winding to obtain the second comparison voltage signal u7; The control unit determines the comparison voltage signal that reflects the current switching timing of the secondary synchronous rectifier circuit based on the current operating mode of the primary-side synchronous rectifier circuit, the first comparison voltage signal, and the second comparison voltage signal. The control unit uses the determined comparison voltage signal as the basis for controlling the switching timing of the secondary-side synchronous rectifier circuit to control the opening and closing of the corresponding synchronous rectifier tubes in the secondary-side synchronous rectifier circuit.

7. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 6, characterized in that, The first detection circuit includes an uncontrolled rectifier circuit, a peak detector circuit, and a first comparison circuit. The first detection circuit performs rectification, detection, and comparison processing on the voltage signal across the auxiliary winding to obtain a first comparison voltage signal, including: The uncontrolled rectifier circuit processes the voltage signal u2 across the auxiliary winding to obtain the voltage signal u3. The peak detection circuit processes the voltage signal u3 to obtain the voltage signal u4; The first comparison circuit compares and processes the voltage signals u4 and u3 to obtain the first comparison voltage signal u5.

8. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 6, characterized in that, The second detection circuit includes a differential voltage divider network and a second comparison circuit. The second detection circuit performs differential comparison processing on the voltage signal across the auxiliary winding to obtain a second comparison voltage signal, including: The differential voltage divider network processes the voltage signal u2 across the auxiliary winding to obtain the voltage signal u6. The second comparison circuit receives the voltage signal u6 and performs comparison processing to obtain the second comparison voltage signal u7.

9. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 6, characterized in that, The control unit determines, based on the current operating mode of the primary-side synchronous rectifier circuit, the first comparison voltage signal, and the second comparison voltage signal, a comparison voltage signal that reflects the current switching timing of the secondary-side synchronous rectifier circuit, including: Obtain the switching timing of the primary-side synchronous rectifier circuit; Determine whether the current operating mode is under-resonance mode, over-resonance mode, or resonant point mode; If the current operating mode is underresonance mode, determine whether the first comparison voltage signal u5 is a square wave signal; If the first comparison voltage signal u5 is a square wave signal, then it is determined that the first comparison voltage signal u5 can reflect the current switching timing of the secondary side synchronous rectifier circuit.

10. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 9, characterized in that, The control unit determines, based on the current operating mode of the primary-side synchronous rectifier circuit, the first comparison voltage signal, and the second comparison voltage signal, a comparison voltage signal that reflects the current switching timing of the secondary-side synchronous rectifier circuit, including: If the current operating mode is over-resonance mode or resonant point mode, determine whether the first comparison voltage signal u5 consists of a series of high levels; If the first comparison voltage signal u5 consists of a series of high levels, then the second comparison voltage signal u7 is determined to reflect the current switching timing of the secondary-side synchronous rectifier circuit.

11. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 9, characterized in that, The primary-side synchronous rectifier circuit includes a first synchronous rectifier diode group and a second synchronous rectifier diode group, an inductor Lr, an inductor Lm, and a capacitor Cr connected in parallel. The first synchronous rectifier tube group includes synchronous rectifier tubes S1 and S3 connected in series, and the second synchronous rectifier tube group includes synchronous rectifier tubes S2 and S4 connected in series. The two ends of the first synchronous rectifier tube group are respectively connected to the positive and negative terminals of the input voltage U1. One end of the inductor Lr is connected in the middle of the synchronous rectifier tubes S1 and S3. The other end of the inductor Lr is connected in series with an inductor Lm and a capacitor Cr. The capacitor Cr is connected in the middle of the synchronous rectifier tubes S2 and S4. The two ends of the inductor Lm are respectively connected to the two ends of the primary coil of the transformer T. The secondary-side synchronous rectifier circuit includes a third synchronous rectifier tube group, a fourth synchronous rectifier tube group, a capacitor C0, and a resistor R1 connected in parallel; the third synchronous rectifier tube group includes synchronous rectifier tubes S5 and S7 connected in series, the fourth synchronous rectifier tube group includes synchronous rectifier tubes S6 and S8 connected in series, the middle of synchronous rectifier tubes S5 and S7 is connected to one end of the transformer T, and the middle of synchronous rectifier tubes S6 and S8 is connected to the other end of the transformer T; The control unit uses the determined comparison voltage signal as the basis for controlling the switching timing of the secondary-side synchronous rectifier circuit to control the opening and closing of the corresponding synchronous rectifier tubes in the secondary-side synchronous rectifier circuit, including: Obtain the secondary coil current signal i2 of the transformer T; If it is determined that the first comparison voltage signal u5 can reflect the current switching timing of the secondary side synchronous rectifier circuit, then it is determined whether the current signal i2 is in the positive half-cycle; If the current signal i2 is in the positive half-cycle, then determine whether the synchronous rectifier tubes S1 and S4 are in the conducting state. First positive cycle processing step 1: If the synchronous rectifier S1 and S4 are in the on state, when the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier S5 and S8 to turn on, and when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier S5 and S8 to turn off. When the current signal i2 enters the negative half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier diodes S6 and S7 to turn on; when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier diodes S6 and S7 to turn off. Return to step 1 of the first positive cycle processing.

12. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 11, characterized in that, If it is determined that the first comparison voltage signal u5 can reflect the current switching timing of the secondary-side synchronous rectifier circuit, then determining whether the current signal i2 is in the positive half-cycle includes: If the current signal i2 is in the negative half-cycle, then determine whether the synchronous rectifier tubes S2 and S3 are in the on state; First negative cycle processing step 1: If the synchronous rectifier S2 and S3 are in the on state, when the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier S6 and S7 to turn on, and when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier S6 and S7 to turn off. When the current signal i2 enters the positive half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn on; when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn off. Return to step 1 of the first negative cycle processing.

13. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 11, characterized in that, If the current signal i2 is in the positive half-cycle, determining whether the synchronous rectifier diodes S1 and S4 are in the on state includes: First positive cycle processing step 2: If the synchronous rectifier tubes S1 and S4 are in the off state, when the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn on, and when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn off. When the current signal i2 enters the negative half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn on; when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn off. Return to step 2 of the first positive cycle processing.

14. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 12, characterized in that, If the current signal i2 is in the negative half-cycle, determining whether the synchronous rectifier diodes S2 and S3 are in the on state includes: First negative cycle processing step 2: If the synchronous rectifier tubes S2 and S3 are in the off state, when the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn on, and when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier tubes S6 and S7 to turn off. When the current signal i2 enters the positive half-cycle and the rising edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn on; when the falling edge of the first comparison voltage signal u5 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn off. Return to step 2 of the first negative cycle processing.

15. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 10, characterized in that, The primary-side synchronous rectifier circuit includes a first synchronous rectifier diode group and a second synchronous rectifier diode group, an inductor Lr, an inductor Lm, and a capacitor Cr connected in parallel. The first synchronous rectifier tube group includes synchronous rectifier tubes S1 and S3 connected in series, and the second synchronous rectifier tube group includes synchronous rectifier tubes S2 and S4 connected in series. The two ends of the first synchronous rectifier tube group are respectively connected to the positive and negative terminals of the input voltage U1. One end of the inductor Lr is connected in the middle of the synchronous rectifier tubes S1 and S3. The other end of the inductor Lr is connected in series with an inductor Lm and a capacitor Cr. The capacitor Cr is connected in the middle of the synchronous rectifier tubes S2 and S4. The two ends of the inductor Lm are respectively connected to the two ends of the primary coil of the transformer T. The control unit uses the determined comparison voltage signal as the basis for controlling the switching timing of the secondary-side synchronous rectifier circuit to control the opening and closing of the corresponding synchronous rectifier tubes in the secondary-side synchronous rectifier circuit, including: If it is determined that the second comparison voltage signal u7 can reflect the current switching timing of the secondary side synchronous rectifier circuit, then it is determined whether the current signal i2 is in the positive half-cycle; If the current signal i2 is in the positive half-cycle, then determine whether the synchronous rectifier tubes S1 and S4 are in the conducting state. First positive cycle processing step 3: If the synchronous rectifier S1 and S4 are in the on state, when the rising edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier S5 and S8 to be turned on, and when the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier S5 and S8 to be turned off. When the current signal i2 enters the negative half-cycle and the rising edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier diodes S6 and S7 to turn on; when the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier diodes S6 and S7 to turn off. Return to step 3 of the first positive cycle processing.

16. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 15, characterized in that, If it is determined that the second comparison voltage signal u7 can reflect the current switching timing of the secondary-side synchronous rectifier circuit, then determining whether the current signal i2 is in the positive half-cycle includes: If the current signal i2 is in the negative half-cycle, then determine whether the synchronous rectifier tubes S2 and S3 are in the on state; First negative cycle processing step 3: If the synchronous rectifier S2 and S3 are in the on state, when the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier S6 and S7 to turn on, and when the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier S6 and S7 to turn off. When the current signal i2 enters the positive half-cycle and the rising edge of the voltage signal u7 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn on; when the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn off. Return to step 3 of the first negative cycle processing.

17. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 15, characterized in that, If the current signal i2 is in the positive half-cycle, determining whether the synchronous rectifier diodes S1 and S4 are in the on state includes: First positive cycle processing step 4: If the synchronous rectifier S1 and S4 are in the off state, when the rising edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier S6 and S7 to turn on, and when the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier S6 and S7 to turn off. When the current signal i2 enters the negative half-cycle and the rising edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn on; when the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn off. Return to step 4 of the first positive cycle processing.

18. The synchronous rectification timing control method for a bidirectional LLC converter according to claim 16, characterized in that, If the current signal i2 is in the negative half-cycle, determining whether the synchronous rectifier diodes S2 and S3 are in the on state includes: First negative cycle processing step 4: If the synchronous rectifier S2 and S3 are in the off state, when the rising edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier S6 and S7 to turn on, and when the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier S6 and S7 to turn off. When the current signal i2 enters the positive half-cycle and the rising edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn on; when the falling edge of the second comparison voltage signal u7 arrives, the control unit controls the synchronous rectifier diodes S5 and S8 to turn off. Return to step 4 of the first negative cycle processing.

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