LLC resonant converter and control method thereof

Abstract

The invention discloses an LLC resonant converter and a control method thereof. The LLC resonant converter comprises a first full-bridge LLC resonant converter circuit, a second full-bridge LLC resonant converter circuit, a switching tube Q1 and a switching tube Q2, wherein the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit are connected in series; a first output end of a first transformer T1 of the first full-bridge LLC resonant converter circuit is connected with an input end of a switching tube Q1, and a second output end of the first transformer T1 and a first output end of a second transformer T2 are jointly connected to a first end of an output end Vo. The second output end of a second transformer T2 of the second full-bridge LLC resonant converter circuit is connected to the input end of a switching tube Q2, and the output end of the switching tube Q2 and the output end of a switching tube Q1 are jointly connected to the second end of the output end Vo. By dividing the input high voltage and rectifying through the switching tube Q1 and the switching tube Q2, the rectifying circuit comprising the switching tube Q1 and the switching tube Q2 is a controllable rectifying circuit, the structure is simple, the reliability is high, and the rectifying efficiency is high.

Description

Technical Field

[0001] This invention belongs to the field of power electronics application technology, and specifically relates to an LLC resonant converter and its control method. Background Technology

[0002] Currently, after years of development, LLC resonant converters are widely used in electric vehicles, photovoltaics, and consumer electronics due to their simple topology and low switching losses. With increasing energy-saving requirements, many applications improve system efficiency by increasing the voltage on the grid side of the line to meet the need for low losses.

[0003] However, in such high-voltage input applications, due to the limitations of existing power devices, it is not easy to select high-frequency, high-voltage power devices in LLC resonant converters. This leads to an urgent need for an LLC resonant converter circuit that minimizes voltage stress on power devices, so as to meet the requirements of high-voltage input applications at a lower cost and with less loss.

[0004] Among various methods to reduce voltage stress on power devices, multilevel topologies are widely used in various fields. By adding diodes, the voltage stress on the switching transistor can be reduced to half of the input bus voltage. However, adding diodes as power devices inevitably introduces more losses, and the control method of the rectifier circuit, which includes diodes and switching transistors, is very complex.

[0005] To address the losses introduced by diodes, most applications employ controlled rectification to further improve efficiency. In high-current output applications, a common controlled rectification method involves adding voltage or current sensing circuitry to detect the voltage across the switching transistor. This method increases circuit complexity and is highly susceptible to interference, reducing system reliability.

[0006] In summary, how to enable high-voltage input LLC resonant converters to use power devices with low voltage stress while simultaneously having a controllable rectifier circuit, simple structure, and high reliability is a technical problem that needs to be solved.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide an LLC resonant converter and its control method, so that the rectifier circuits, including switching transistors Q1 and Q2, corresponding to the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit, are controllable rectifier circuits with simple structure, high reliability and high rectification efficiency.

[0009] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0010] The present invention provides an LLC resonant converter, including a first full-bridge LLC resonant converter circuit and a second full-bridge LLC resonant converter circuit connected in series therewith, as well as switching transistors Q1 and Q2.

[0011] The first full-bridge LLC resonant converter circuit has a first transformer T1, and the second full-bridge LLC resonant converter circuit has a second transformer T2;

[0012] The LLC resonant converter has an output terminal Vo. The first output terminal of the first transformer T1 is connected to the input terminal of the switch Q1. The second output terminal of the first transformer T1 and the first output terminal of the second transformer T2 are both connected to the first terminal of the output terminal Vo. The second output terminal of the second transformer T2 is connected to the input terminal of the switch Q2. The output terminal of the switch Q2 and the output terminal of the switch Q1 are both connected to the second terminal of the output terminal Vo.

[0013] It also includes a control module, which is connected to the control terminals of switch Q1 and switch Q2, and is used to generate drive signals to control the turn-on and turn-off of switch Q1 and switch Q2.

[0014] This invention divides the input high voltage by connecting a first full-bridge LLC resonant converter circuit and a second full-bridge LLC resonant converter circuit in series, and connects them to switching transistors Q1 and Q2 respectively. The rectification is performed by the body diodes of switching transistors Q1 and Q2, making the rectifier circuit including switching transistors Q1 and Q2 a controllable rectifier circuit with simple structure, high reliability and high rectification efficiency.

[0015] A further aspect of the present invention is that the LLC resonant converter includes a filter capacitor Co, which is connected between the first and second terminals of the output terminal Vo.

[0016] The control module controls the switching transistors Q1 and Q2 to turn on and off via drive signals, thereby charging and discharging the filter capacitor Co.

[0017] In the above scheme, charging and discharging are performed through the filter capacitor Co, which further improves the rectification efficiency and realizes that the rectifier circuit has the function of filtering.

[0018] A further aspect of the present invention is as follows: the first full-bridge LLC resonant converter circuit includes a first full-bridge circuit and a first LLC resonant network, and the second full-bridge LLC resonant converter circuit includes a second full-bridge circuit and a second LLC resonant network;

[0019] The output terminal of the first full-bridge circuit is connected to the input terminal of the first LLC resonant network, the output terminal of the first LLC resonant network is connected to the input terminal of the first transformer T1, the output terminal of the second full-bridge circuit is connected to the input terminal of the second LLC resonant network, and the output terminal of the second LLC resonant network is connected to the input terminal of the second transformer T2.

[0020] The first full-bridge circuit includes switching transistors S1 to S4, and the second full-bridge circuit includes switching transistors S5 to S8.

[0021] The control module is used to generate drive signals to control the switching transistors Q1, Q2, and S1 to S8 to turn them on and off.

[0022] In the above scheme, by using switching transistors Q1 and Q2 in conjunction with switching transistors S1 to S8 to turn them on and off, controllable rectification without detection circuitry is achieved based on the secondary current of the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit. Compared with conventional diode rectifier circuits, this reduces rectification losses, improves circuit efficiency, and the rectifier circuit structure and control method are simple, efficient, and low-cost.

[0023] A further aspect of the present invention is that the first full-bridge circuit has a first input terminal and a second input terminal, and the second full-bridge circuit has a third input terminal and a fourth input terminal;

[0024] The two ends of the voltage divider circuit are connected to the two ends of the input power supply Vi. The first input terminal of the first full-bridge circuit and the fourth input terminal of the second full-bridge circuit are respectively connected to the two ends of the voltage divider circuit. The second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are connected to the voltage divider point of the voltage divider circuit.

[0025] A further aspect of the present invention is that the first full-bridge circuit has a first output terminal and a second output terminal, and the second full-bridge circuit has a third output terminal and a fourth output terminal;

[0026] The switching transistor S1 is disposed on the bridge arm of the first full-bridge circuit connecting the first input terminal and the second output terminal; the switching transistor S4 is disposed on the bridge arm of the first full-bridge circuit connecting the first input terminal and the first output terminal; the switching transistor S6 is disposed on the bridge arm of the second full-bridge circuit connecting the fourth input terminal and the fourth output terminal; and the switching transistor S7 is disposed on the bridge arm of the second full-bridge circuit connecting the fourth input terminal and the third output terminal.

[0027] The output terminal of the switch S2 is simultaneously connected to the second input terminal of the first full-bridge circuit and the input terminal of the switch S5. The output terminal of the switch S3 is simultaneously connected to the second input terminal of the first full-bridge circuit and the input terminal of the switch S8. The input terminal of the switch S2 is connected to the second output terminal of the first full-bridge circuit, and the input terminal of the switch S3 is connected to the first output terminal of the first full-bridge circuit.

[0028] The input terminals of the switching transistors S5 and S8 are also connected to the third input terminal of the second full-bridge circuit. The output terminal of the switching transistor S5 is connected to the fourth output terminal of the second full-bridge circuit, and the output terminal of the switching transistor S8 is connected to the third output terminal of the second full-bridge circuit.

[0029] A further embodiment of the present invention is that the voltage divider circuit is provided with a first voltage equalizing capacitor Ci1 and a second voltage equalizing capacitor Ci2 connected in series.

[0030] The second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are connected together to the voltage divider point formed between the first equalizing capacitor Ci1 and the second equalizing capacitor Ci2 of the voltage divider circuit.

[0031] Preferably, the parameters of the first voltage equalizing capacitor Ci1 and the second voltage equalizing capacitor Ci2 are the same, and the parameters of the switching transistors S1 to S8 are the same.

[0032] The above scheme further reduces the voltage stress on the power devices (switching transistors S1 to S8) of the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit in series. The low-voltage power devices are available in a wide variety of models and have a lower cost.

[0033] The present invention also provides a control method for the LLC resonant converter described above, comprising:

[0034] When the control module controls the first full-bridge LLC resonant converter circuit to resonate, it controls the switching transistor Q1 to turn on.

[0035] When the control module controls the second full-bridge LLC resonant converter circuit to resonate, it controls the switch Q2 to turn on.

[0036] In the above scheme, rectification using the body diodes of switching transistors Q1 and Q2 is achieved while reducing the losses caused by the body diodes.

[0037] A further embodiment of the present invention is as follows: a first full-bridge LLC resonant converter circuit includes switching transistors S1 to S4, and a second full-bridge circuit includes switching transistors S5 to S8; the first input terminal of the first full-bridge circuit and the fourth input terminal of the second full-bridge circuit are respectively connected to the two ends of the voltage divider circuit, and the second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are jointly connected to the voltage divider point of the voltage divider circuit; switching transistor S1 is disposed on the bridge arm of the first full-bridge circuit connecting the first input terminal and the second output terminal, switching transistor S4 is disposed on the bridge arm of the first full-bridge circuit connecting the first input terminal and the first output terminal, switching transistor S6 is disposed on the bridge arm of the second full-bridge circuit connecting the fourth input terminal and the fourth output terminal, and switching transistor S7 is disposed on the bridge arm of the second full-bridge circuit connecting the fourth input terminal and the third output terminal;

[0038] Switch S1, switch S3, switch S7 and switch S5 form the first driving group, and switch S2, switch S4, switch S6 and switch S8 form the second driving group.

[0039] The control module inputs complementary drive signals with a duty cycle of less than 50% to the first drive group and the second drive group to control the two drive groups to not be turned on at the same time;

[0040] During the time the first drive group is turned on, the control switch Q1 is turned on for a first set duration, and during the time the second drive group is turned on, the control switch Q2 is turned on for a second set duration.

[0041] In the above scheme, the current flowing to the switching transistors Q1 and Q2 in the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit is in the same direction. This reduces the voltage stress on the power devices of the full-bridge LLC resonant converter circuit while allowing the switching transistors Q1 and Q2 to be connected in parallel to the output terminal Vo.

[0042] A further aspect of the present invention is as follows: the control module controls the first drive group to be turned on and the second drive group to be turned off, and when only the resonant capacitor Cr1 and the resonant inductor Lr1 of the first LLC resonant network participate in the resonance, the first LLC resonant network is controlled to be turned off through the control terminal of the switch Q1 and the control terminal of the switch Q2, and the current passes through the body diodes of the switch Q1 and the switch Q2.

[0043] In the above scheme, the body diodes of switching transistors Q1 and Q2 are used more effectively for rectification.

[0044] A further aspect of the present invention is as follows: when the control module controls the first drive group to be turned on, and when the resonant capacitor Cr1, resonant inductor Lr1 and excitation inductor Lm1 of the first LLC resonant network all participate in the resonance, the control terminal of the switch Q1 is used to control its conduction.

[0045] When the control module controls the second drive group to turn on, and the resonant capacitor Cr2, resonant inductor Lr2 and excitation inductor Lm2 of the second LLC resonant network all participate in resonance, the control terminal of the switch Q2 is controlled to turn on.

[0046] In the above scheme, it is ensured that the large resonant current will not be lost by the body diode of switch Q1 and the body diode of switch Q2.

[0047] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0048] 1. The high voltage input is divided by the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit connected in series, and then connected to the switching transistors Q1 and Q2 respectively. The rectification is performed by the body diodes of the switching transistors Q1 and Q2, so that the rectifier circuit including the switching transistors Q1 and Q2 is a controllable rectifier circuit with high reliability and high rectification efficiency.

[0049] 2. The circuit structure of this invention is simple, the effect is significant, and it is suitable for widespread use.

[0050] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0051] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0052] Figure 1 This is a block diagram of an LLC resonant converter circuit according to the present invention;

[0053] Figure 2 This is a schematic diagram of an LLC resonant converter circuit according to the present invention;

[0054] Figure 3 This is a waveform timing diagram of an LLC resonant converter according to the present invention when the first resonant frequency is less than the switching frequency and the second resonant frequency.

[0055] In the diagram: 11. First full-bridge circuit; 12. Second full-bridge circuit; 21. First LLC resonant network; 22. Second LLC resonant network; 3. Rectifier circuit.

[0056] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0058] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0059] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0060] This invention provides an LLC resonant converter and its control method. The high voltage input is divided by a first full-bridge LLC resonant converter circuit and a second full-bridge LLC resonant converter circuit connected in series and connected to switching transistors Q1 and Q2 respectively. The rectifier is rectified by the body diodes of switching transistors Q1 and Q2, so that the rectifier circuit 3 including switching transistors Q1 and Q2 is a controllable rectifier circuit 3 with simple structure, high reliability and high rectification efficiency.

[0061] Example 1

[0062] like Figures 1 to 2As shown, this embodiment provides an LLC resonant converter, including a first full-bridge LLC resonant converter circuit and a second full-bridge LLC resonant converter circuit connected in series therewith. The first output terminal of the first transformer T1 of the first full-bridge LLC resonant converter circuit is connected to the input terminal of the switch Q1. The second output terminal of the first transformer T1 is connected to the first output terminal of the second transformer T2 of the second full-bridge LLC resonant converter circuit and to the second terminal of the output terminal Vo. The second output terminal of the second transformer T2 is connected to the input terminal of the switch Q2. The output terminal of the switch Q2 is connected to the output terminal of the switch Q1 and to the first terminal of the output terminal Vo. The LLC resonant converter rectifies the first and second full-bridge LLC resonant converter circuits at least through the body diodes of the switch Q1 and the switch Q2. A control module is connected to the control terminals of the switches Q1 and Q2 and is used to generate drive signals to control the turn-on and turn-off of the switches Q1 and Q2.

[0063] In this embodiment, the high voltage input is divided by a first full-bridge LLC resonant converter circuit and a second full-bridge LLC resonant converter circuit connected in series, and then connected to the switching transistors Q1 and Q2 respectively. The rectification is performed by the body diodes of the switching transistors Q1 and Q2, so that the rectifier circuit 3 including the switching transistors Q1 and Q2 is a controllable rectifier circuit 3, with simple structure, high reliability and high rectification efficiency.

[0064] Furthermore, the rectifier circuit includes a filter capacitor Co, whose two ends are connected to the first and second terminals of the output terminal Vo. The control module controls the switching transistors Q1 and Q2 to turn on and off via drive signals, causing the filter capacitor Co to charge and discharge. Charging and discharging the filter capacitor Co further improves the rectification efficiency, thus enabling the rectifier circuit 3 to perform a filtering function.

[0065] Understandably, compared to the secondary current waveform of a single-channel LLC resonant converter circuit, the secondary current waveform of the series-connected LLC resonant converter circuit in this embodiment shows that the output currents of the two LLC resonant converter circuits are the same, enabling automatic current sharing. Therefore, the current sharing circuit in rectifier circuit 3 can be omitted, further reducing design complexity and circuit cost.

[0066] Furthermore, the first full-bridge LLC resonant converter circuit includes a first full-bridge circuit 11 and a first LLC resonant network 21, and the second full-bridge LLC resonant converter circuit includes a second full-bridge circuit 12 and a second LLC resonant network 22; the output terminal of the first full-bridge circuit 11 is connected to the input terminal of the first LLC resonant network 21, the output terminal of the first LLC resonant network 21 is connected to the input terminal of the first transformer T1, the output terminal of the second full-bridge circuit 12 is connected to the input terminal of the second LLC resonant network 22, and the output terminal of the second LLC resonant network 22 is connected to the input terminal of the second transformer T2; the first full-bridge circuit 11 includes switches S1 to S4, and the second full-bridge circuit 12 includes switches S5 to S8; the control module is used to generate drive signals to control the switching transistors Q1, Q2, and S1 to S8 to turn on and off. By using switching transistors Q1 and Q2 in conjunction with switching transistors S1 to S8 to turn them on and off, controllable rectification without the need for detection circuits is achieved based on the secondary currents of the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit. The circuit structure and control method are simple, efficient, and low in cost.

[0067] Furthermore, the first full-bridge circuit has a first input terminal and a second input terminal, and the second full-bridge circuit has a third input terminal and a fourth input terminal; the two ends of the voltage divider circuit are connected to the two ends of the input power supply Vi, the first input terminal of the first full-bridge circuit 11 and the fourth input terminal of the second full-bridge circuit 12 are respectively connected to the two ends of the voltage divider circuit, and the second input terminal of the first full-bridge circuit 11 and the third input terminal of the second full-bridge circuit 12 are connected together to the voltage dividing point of the voltage divider circuit.

[0068] Furthermore, the first full-bridge circuit has a first output terminal and a second output terminal, and the second full-bridge circuit has a third output terminal and a fourth output terminal; the switching transistor S1 is disposed on the bridge arm of the first full-bridge circuit connecting the first input terminal and the second output terminal, the switching transistor S4 is disposed on the bridge arm of the first full-bridge circuit connecting the first input terminal and the first output terminal, the switching transistor S6 is disposed on the bridge arm of the second full-bridge circuit connecting the fourth input terminal and the fourth output terminal, and the switching transistor S7 is disposed on the bridge arm of the second full-bridge circuit connecting the fourth input terminal and the third output terminal; the output terminal of the switching transistor S2 is simultaneously connected to... The second input terminal of the first full-bridge circuit and the input terminal of the switching transistor S5 are connected together. The output terminal of the switching transistor S3 is simultaneously connected to the second input terminal of the first full-bridge circuit and the input terminal of the switching transistor S8. The input terminal of the switching transistor S2 is connected to the second output terminal of the first full-bridge circuit, and the input terminal of the switching transistor S3 is connected to the first output terminal of the first full-bridge circuit. The input terminals of the switching transistors S5 and S8 are also connected to the third input terminal of the second full-bridge circuit. The output terminal of the switching transistor S5 is connected to the fourth output terminal of the second full-bridge circuit, and the output terminal of the switching transistor S8 is connected to the third output terminal of the second full-bridge circuit.

[0069] Furthermore, the voltage divider circuit includes a first voltage-equalizing capacitor Ci1 and a second voltage-equalizing capacitor Ci2 connected in series; the second input terminal of the first full-bridge circuit 11 and the third input terminal of the second full-bridge circuit 12 are connected to the voltage divider point formed between the first voltage-equalizing capacitor Ci1 and the second voltage-equalizing capacitor Ci2 in the voltage divider circuit; preferably, the parameters of the first voltage-equalizing capacitor Ci1 and the second voltage-equalizing capacitor Ci2 are the same, and the parameters of the switching transistors S1 to S8 are the same. This further reduces the voltage stress on the power devices (switching transistors S1 to S8) of the series-connected first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit, and provides a wide variety of low-voltage power devices at a lower cost.

[0070] It is understandable that when the switching transistors Q1 and / or Q2 are NMOS transistors, their input terminal is the drain, their output terminal is the source, and their control terminal is the gate.

[0071] It is understandable that the drive signal output by the control module is a PWM signal, which uses PFM modulation to control the LLC resonant converter in order to meet the gain required by the load connected to the output Vo.

[0072] In one specific implementation of this embodiment, such as Figure 2As shown, the switching transistors S1 to S8, Q1, and Q2 are NMOS transistors. The resonant inductor Lr1, magnetizing inductor Lm1, and resonant capacitor Cr1 of the first LLC resonant network 21 are connected in series. The two ends of the magnetizing inductor Lm1 are connected in parallel to the input terminal of the first isolation transformer T1. One end of the resonant inductor Lr1 is the first input terminal of the first LLC resonant network 21, which is connected between the source of the switching transistor S4 and the drain of the switching transistor S3. One end of the resonant capacitor Cr1 is the second input terminal of the first LLC resonant network 21, which is connected between the source of the switching transistor S1 and the drain of the switching transistor S2. The resonant inductance Lr2, magnetizing inductance Lm2, and resonant capacitor Cr2 of the second LLC resonant network 22 are configured in the same way as the first LLC resonant network 21 described above. The first input terminal of the second LLC resonant network 22 is connected between the source of the switch S8 and the drain of the switch S7, and the second input terminal is connected between the source of the switch S5 and the drain of the switch S6.

[0073] Furthermore, the parameters of the first LLC resonant network 21 and the second LLC resonant network 22 are the same, that is, the resonant inductance Lr1 of the first LLC resonant network 21 and the resonant inductance Lr2 of the second LLC resonant network 22 have the same inductance, the resonant capacitance Cr1 of the first LLC resonant network 21 and the resonant capacitance Cr2 of the second LLC resonant network 22 have the same capacitance, the parameters of the first isolation transformer T1 and the second isolation transformer T2 are the same, and the magnetizing inductance Lm1 of the first LLC resonant network 21 and the inductance Lm2 of the second LLC resonant network 22 have the same inductance.

[0074] In this embodiment, the input high voltage is divided by a first full-bridge LLC resonant converter circuit and a second full-bridge LLC resonant converter circuit connected in series, and then connected to switching transistors Q1 and Q2 respectively. The rectification is performed by the body diodes of switching transistors Q1 and Q2, making the rectifier circuit 3 including switching transistors Q1 and Q2 a controllable rectifier circuit with simple structure, high reliability, and high rectification efficiency. The circuit structure of this embodiment is simple, the effect is significant, and it is suitable for widespread use.

[0075] Example 2

[0076] like Figures 1 to 3 As shown, this embodiment provides a control method for an LLC resonant converter as described in Embodiment 1, including: when the first full-bridge LLC resonant converter circuit resonates, the control module controls the switch Q1 to turn on; when the second full-bridge LLC resonant converter circuit resonates, the control module controls the switch Q2 to turn on. This achieves rectification using the body diodes of switches Q1 and Q2 while reducing losses caused by the body diodes.

[0077] Furthermore, the first full-bridge LLC resonant converter circuit includes switches S1 to S4, and the second full-bridge circuit 12 includes switches S5 to S8; the first input terminal of the first full-bridge circuit 11 and the fourth input terminal of the second full-bridge circuit 12 are connected to the two ends of the input power supply Vi, and a voltage divider circuit is set to connect the two ends of the input power supply Vi; the second input terminal of the first full-bridge circuit 11 and the third input terminal of the second full-bridge circuit 12 are connected to the voltage divider circuit; the switches S1 and S4 connected to the first end of the input power supply Vi are connected to the second full-bridge circuit 12. A first driving group is formed by a parallel connection of switch S3, a switch S7 connected to the second terminal of the input power supply Vi, and a switch S5 connected in parallel with switch S7. A second driving group is formed by switches S2, S4, S6, and S8. The control module inputs complementary driving signals with a duty cycle less than 50% to the first and second driving groups, controlling them to not conduct simultaneously. During the time the first driving group is on, the control module controls the conduction time of switch Q1 to a set duration, and during the time the second driving group is on, it controls the conduction time of switch Q2 to a set duration. Therefore, the current flow to switches Q1 and Q2 in the first and second full-bridge LLC resonant converter circuits is the same, reducing the voltage stress on the power devices of the full-bridge LLC resonant converter circuit while allowing switches Q1 and Q2 to be connected in parallel to the output terminal Vo.

[0078] It is understood that the control module inputs PWM drive signals to the first drive group and the second drive group, generating controllable rectified signals Vsr1 and Vsr2 respectively. The controllable rectified signal Vsr1 is delayed by time ta before the PWM drive signal of the first drive group turns on, and is delayed by time tb before the PWM drive signal of the first drive group turns off. The controllable rectified signal Vsr2 is delayed by time ta before the PWM drive signal of the second drive group turns on, and is delayed by time tb before the PWM drive signal of the second drive group turns off. The time ta and time tb can be optimized according to actual usage. The values ​​of the time ta and time tb are related to the current required by the load connected to the output terminal Vo and the required circuit efficiency of the LLC resonant converter.

[0079] Furthermore, the control module controls the first drive group to turn on and the second drive group to turn off. When only the resonant capacitor Cr1 and the resonant inductor Lr1 of the first LLC resonant network participate in resonance, the first LLC resonant network is turned off through the control terminals of switch Q1 and switch Q2, and the current flows through the body diodes of switch Q1 and switch Q2. This better utilizes the body diodes of switch Q1 and switch Q2 for rectification.

[0080] Further, when the control module controls the first drive group to conduct and the resonant capacitor Cr1, resonant inductor Lr1, and magnetizing inductor Lm1 of the first LLC resonant network 21 all participate in resonance, it controls the switch Q1 to conduct; when the control module controls the second drive group to conduct and the resonant capacitor Cr2, resonant inductor Lr2, and magnetizing inductor Lm2 of the second LLC resonant network 22 all participate in resonance, it controls the switch Q2 to conduct. Therefore, it is ensured that a large resonant current will not be lost due to the body diodes of the switch Q1 and the switch Q2.

[0081] In a specific implementation manner of this embodiment, the working principle and control logic of the LLC resonant converter are as follows: The input voltage Vi and output voltage Vo of the LLC resonant converter are stable direct currents. Since the first full-bridge circuit and the second full-bridge circuit have the same parameters, the first LLC resonant network and the second LLC resonant network have the same parameters, and the first isolation transformer T1 and the second isolation transformer T2 have the same parameters, the first resonant frequency of the first resonant network is the same as the first resonant frequency of the second resonant network, and the second resonant frequency of the first resonant network is the same as the second resonant frequency of the second resonant network.

[0082] The first resonant frequency is represented by fr1, that is:

[0083]

[0084] The second resonant frequency is represented by fr2, that is:

[0085]

[0086] The first resonant frequency of the first resonant network is the same as the first resonant frequency of the second resonant network.

[0087] where, f r2 <f r1 .

[0088] In actual use, the switching frequency fs of the first full-bridge circuit and the second full-bridge circuit is set to be greater than the first resonant frequency f r1 , so as to ensure that the power tubes S1 to S8 of the first full-bridge circuit and the second full-bridge circuit operate in the soft-switching state. According to the magnitude relationship between the switching frequency fs, resonant frequency f r1 and resonant frequency f r2 , the LLC resonant converter can operate in three different modes, that is, f r2 < fs < f r1 , fs = f r1 , f r1 < fs. The working principles of the converter in the three modes are slightly different. In this embodiment, f r1 < fs < f r2For further explanation, please refer to the timing diagram. Figure 3 It contains 5 modes, specifically:

[0089] In Mode 1, during the t0-t1 phase: the second drive group is turned off, and the first drive group is turned on with zero voltage. Specifically, at time t0, the switch of the second drive group is turned off, and the first resonant current Ir1 of the first LLC resonant network 21 and the second resonant current Ir2 of the second LLC resonant network 22 are both less than 0. Ir1 and Ir2 continue to flow through the body diode of the switch of the first drive group, making the voltage on the switch of the first drive group zero, preparing for zero-voltage turn-on. During the t0-t1 period, the switch of the first drive group is turned on with zero voltage. At this time, the voltage on each resonant network is half of the input voltage Vi. The first resonant current Ir1 and the second resonant current Ir2 gradually increase to 0, and Ir1 and Ir2 are equal. The body diode of the secondary switch Q1 is turned on, and the secondary voltage of the transformer is the output voltage. At this time, the resonant capacitor and resonant inductor begin to resonate.

[0090] Mode 2: During the t1 to t2 phase, the first drive group remains on. The resonant capacitors and resonant inductors of the first LLC resonant network 21 and the second LLC resonant network 22 resonate, while the magnetizing inductor does not participate in the resonance. The first and second resonant currents increase sinusoidally. Specifically, the first resonant current Ir1 and the second resonant current Ir2 remain equal and gradually increase sinusoidally from 0. The body diode of the secondary rectifier Q1 remains on, and the current gradually increases. During this phase, the resonant networks maintain series resonance; that is, the resonant inductor Lr1 of the first LLC resonant network 21 resonates with the resonant capacitor Cr1, and the resonant inductor Lr2 of the second LLC resonant network 22 resonates with the resonant capacitor Cr2. The magnetizing inductors Lm1 and Lm2 do not participate in the resonance.

[0091] Mode 3: During the period from t2 to t3, the first drive group is kept on, and the magnetizing inductors of the first LLC resonant network 21 and the second LLC resonant network 22 participate in resonance. The first resonant current and the second resonant current are respectively greater than the corresponding first magnetizing inductor current and second magnetizing inductor current. Specifically, the first resonant current Ir1 is greater than the first magnetizing inductor current Im1, and the second resonant current Ir2 is greater than the second magnetizing inductor current Im2. At time t2, the PWM drive signal input from the control module to the control terminal of NMOS transistor Q1 flips to a high-level signal, controlling NMOS transistor Q1 to conduct until time t3.

[0092] Mode 4: During the period from t3 to t4, the first drive group is kept on, the first resonant current and the second resonant current decrease, and remain greater than the corresponding first magnetizing inductor current and second magnetizing inductor current. Specifically, at time t3, the PWM drive signal input from the control module to the control terminal of NMOS transistor Q1 flips to a low level signal, causing NMOS transistor Q1 to turn off. At this time, the first resonant current Ir1 is greater than the first magnetizing inductor current Im1, and the second resonant current Ir2 is greater than the second magnetizing inductor current Im2. The primary side of the first full-bridge LLC resonant converter circuit continues to transfer energy to the secondary side, and the current flows through the body diode of NMOS transistor Q1 to achieve rectification.

[0093] Mode 5: During the period from t4 to t5, when the first resonant current equals the first magnetizing inductor current and the second resonant current equals the second magnetizing inductor current, the first drive group is controlled to remain on for a set time and then turned off. The primary circuit of the first LLC resonant network 21 does not transfer energy to the secondary circuit. Specifically, at time t4, the first resonant current Ir1 equals the first magnetizing inductor current Im1, and the second resonant current Ir2 equals the second magnetizing inductor current Im2. The primary side of the first full-bridge LLC resonant converter circuit does not transfer energy to the secondary side, the NMOS transistor Q1 is turned off with zero current, and the first drive group remains on. This stage is relatively short, and the primary current remains unchanged. At time t5, the first drive group is turned off, and both the first resonant current Ir1 and the second resonant current Ir2 are greater than 0.

[0094] The working principle of the LLC resonant converter in the second half of the working cycle is symmetrical to that of the first half of the working cycle of modes one to five mentioned above.

[0095] It should be noted that, Figure 3 In the diagram, the first four rows show the PWM waveforms received at the control terminals of the corresponding switching transistors; the fifth row shows the waveforms of the resonant current and the magnetizing inductor current; and the sixth row shows the output waveforms of switching transistors Q1 and Q2. Figure 3 As can be seen from this, the first LLC resonant network 21 and the second LLC resonant network 22 operate independently and do not affect each other.

[0096] Specifically, the operation of rectifier circuit 3 is as follows: In mode one, both switches Q1 and Q2 are turned off. When the first resonant current of the first LLC resonant network 21 and the second resonant current of the second LLC resonant network 22 begin to change, the body diode of switch Q1 is turned on, and the current IQ1 gradually increases. In mode two, both switches Q1 and Q2 are turned off, and the body diode of switch Q1 remains on. In mode three, switch Q1 is turned on, so that the current IQ1 flows through Q1 and no longer flows through its body diode. In mode four, switch Q1 of the rectifier filter circuit is turned off, and the body diode of switch Q1 is on. In mode five, the first drive group is turned off after being on for a set time, and the body diode of switch Q1 is turned off with zero current.

[0097] In this embodiment, the PWM drive signal of the power switching transistors of the LLC resonant converter is easy to implement. Each of its switching transistors can achieve zero-voltage turn-on and has a withstand voltage of half the input voltage. At the same time, the voltage on the voltage equalizing capacitor can be automatically balanced, making it suitable for high-voltage input applications. It can easily and cost-effectively improve the power density and efficiency of the power supply.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An LLC resonant converter, characterized in that, It includes a first full-bridge LLC resonant converter circuit and a second full-bridge LLC resonant converter circuit connected in series therewith, as well as switching transistors Q1 and Q2; The first full-bridge LLC resonant converter circuit has a first transformer T1, and the second full-bridge LLC resonant converter circuit has a second transformer T2; The LLC resonant converter has an output terminal Vo. The first output terminal of the first transformer T1 is connected to the input terminal of the switch Q1. The second output terminal of the first transformer T1 and the first output terminal of the second transformer T2 are both connected to the first terminal of the output terminal Vo. The second output terminal of the second transformer T2 is connected to the input terminal of the switch Q2. The output terminal of the switch Q2 and the output terminal of the switch Q1 are both connected to the second terminal of the output terminal Vo. It also includes a control module, which is connected to the control terminals of switch Q1 and switch Q2, and is used to generate drive signals to control the turn-on and turn-off of switch Q1 and switch Q2.

2. The LLC resonant converter according to claim 1, characterized in that, Includes a filter capacitor Co, which is connected between the first and second terminals of the output terminal Vo; The control module controls the switching transistors Q1 and Q2 to turn on and off via drive signals, thereby charging and discharging the filter capacitor Co.

3. An LLC resonant converter according to claim 1 or 2, characterized in that, The first full-bridge LLC resonant converter circuit includes a first full-bridge circuit and a first LLC resonant network, and the second full-bridge LLC resonant converter circuit includes a second full-bridge circuit and a second LLC resonant network. The output terminal of the first full-bridge circuit is connected to the input terminal of the first LLC resonant network, the output terminal of the first LLC resonant network is connected to the input terminal of the first transformer T1, the output terminal of the second full-bridge circuit is connected to the input terminal of the second LLC resonant network, and the output terminal of the second LLC resonant network is connected to the input terminal of the second transformer T2. The first full-bridge circuit includes switching transistors S1 to S4, and the second full-bridge circuit includes switching transistors S5 to S8. The control module is used to generate drive signals to control the switching transistors Q1, Q2, and S1 to S8 to turn them on and off.

4. An LLC resonant converter according to claim 3, characterized in that, The first full-bridge circuit has a first input terminal and a second input terminal, and the second full-bridge circuit has a third input terminal and a fourth input terminal; The two ends of the voltage divider circuit are connected to the two ends of the input power supply Vi. The first input terminal of the first full-bridge circuit and the fourth input terminal of the second full-bridge circuit are respectively connected to the two ends of the voltage divider circuit. The second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are connected to the voltage divider point of the voltage divider circuit.

5. An LLC resonant converter according to claim 4, characterized in that, The first full-bridge circuit has a first output terminal and a second output terminal, and the second full-bridge circuit has a third output terminal and a fourth output terminal; The switching transistor S1 is disposed on the bridge arm of the first full-bridge circuit connecting the first input terminal and the second output terminal; the switching transistor S4 is disposed on the bridge arm of the first full-bridge circuit connecting the first input terminal and the first output terminal; the switching transistor S6 is disposed on the bridge arm of the second full-bridge circuit connecting the fourth input terminal and the fourth output terminal; and the switching transistor S7 is disposed on the bridge arm of the second full-bridge circuit connecting the fourth input terminal and the third output terminal. The output terminal of the switch S2 is simultaneously connected to the second input terminal of the first full-bridge circuit and the input terminal of the switch S5. The output terminal of the switch S3 is simultaneously connected to the second input terminal of the first full-bridge circuit and the input terminal of the switch S8. The input terminal of the switch S2 is connected to the second output terminal of the first full-bridge circuit, and the input terminal of the switch S3 is connected to the first output terminal of the first full-bridge circuit. The input terminals of the switching transistors S5 and S8 are also connected to the third input terminal of the second full-bridge circuit. The output terminal of the switching transistor S5 is connected to the fourth output terminal of the second full-bridge circuit, and the output terminal of the switching transistor S8 is connected to the third output terminal of the second full-bridge circuit.

6. An LLC resonant converter according to claim 5, characterized in that, The voltage divider circuit is equipped with a first voltage equalizing capacitor Ci1 and a second voltage equalizing capacitor Ci2 connected in series. The second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are connected together to the voltage divider point formed between the first equalizing capacitor Ci1 and the second equalizing capacitor Ci2. Preferably, the parameters of the first voltage equalizing capacitor Ci1 and the second voltage equalizing capacitor Ci2 are the same, and the parameters of the switching transistors S1 to S8 are the same.

7. A control method for an LLC resonant converter as described in any one of claims 1 to 6, characterized in that, include: When the control module controls the first full-bridge LLC resonant converter circuit to resonate, it controls the switching transistor Q1 to turn on. When the control module controls the second full-bridge LLC resonant converter circuit to resonate, it controls the switch Q2 to turn on.

8. The control method for an LLC resonant converter according to claim 7, characterized in that, The first full-bridge LLC resonant converter circuit includes switches S1 to S4, and the second full-bridge circuit includes switches S5 to S8. The first input terminal of the first full-bridge circuit and the fourth input terminal of the second full-bridge circuit are respectively connected to the two ends of the voltage divider circuit. The second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are connected to the voltage divider point of the voltage divider circuit. Switch S1 is disposed on the bridge arm of the first full-bridge circuit that connects the first input terminal and the second output terminal, switch S4 is disposed on the bridge arm of the first full-bridge circuit that connects the first input terminal and the first output terminal, switch S6 is disposed on the bridge arm of the second full-bridge circuit that connects the fourth input terminal and the fourth output terminal, and switch S7 is disposed on the bridge arm of the second full-bridge circuit that connects the fourth input terminal and the third output terminal. Switch S1, switch S3, switch S7 and switch S5 form the first driving group, and switch S2, switch S4, switch S6 and switch S8 form the second driving group. The control module inputs complementary drive signals with a duty cycle of less than 50% to the first drive group and the second drive group to control the two drive groups to not be turned on at the same time; During the time the first drive group is turned on, the control switch Q1 is turned on for a first set duration, and during the time the second drive group is turned on, the control switch Q2 is turned on for a second set duration.

9. The control method for an LLC resonant converter according to claim 8, characterized in that, The control module controls the first drive group to be turned on and the second drive group to be turned off. When only the resonant capacitor Cr1 and the resonant inductor Lr1 of the first LLC resonant network participate in the resonance, the first LLC resonant network is turned off by controlling the control terminals of the switch Q1 and the switch Q2. The current passes through the body diodes of the switch Q1 and the switch Q2.

10. The control method for an LLC resonant converter according to claim 8, characterized in that, When the control module controls the first drive group to be turned on, and the resonant capacitor Cr1, resonant inductor Lr1 and excitation inductor Lm1 of the first LLC resonant network all participate in the resonance, the control terminal of the switch Q1 is controlled to be turned on. When the control module controls the second drive group to turn on, and the resonant capacitor Cr2, resonant inductor Lr2 and excitation inductor Lm2 of the second LLC resonant network all participate in resonance, the control terminal of the switch Q2 is controlled to turn on.

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