LLC resonant converter
Through the series full-bridge LLC resonant converter circuit and controllable rectification technology, the problem of the LLC resonant converter is difficult to select low voltage stress under high voltage input, achieving efficient and reliable rectification effect, reducing circuit complexity and loss.
Patent Information
- Application Number
- CN202421971905.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-14
- Publication Date
- 2025-07-29
- Estimated Expiration
- 2034-08-14
AI Technical Summary
It is difficult to select low voltage stress power devices in high voltage input applications, resulting in complex rectification circuits, low reliability and high losses, especially in large current output occasions, which are difficult to meet the needs of efficient and controllable rectification.
The first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit are used to rectify through the body diodes of the switch tubes Q1 and Q2, and charge and discharge with the filter capacitor Co to realize controllable rectification, simplify the circuit structure and improve the rectification efficiency.
It realizes the application of power devices with low voltage stress, and has high reliability and high rectification efficiency, which reduces losses and simplifies circuit design, making it suitable for promotion and use.
Smart Images
Figure CN223168235U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of power electronics applications, and particularly relates to an LLC resonant converter. Background Art
[0002] At present, after years of development, LLC resonant converters are widely used in electric vehicles, photovoltaics, consumer electronics and other applications due to their simple topological structure and low switching losses. With the improvement of energy-saving requirements, in many applications, in order to improve the efficiency of the system, the voltage on the line network side is mostly increased to meet the demand 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 and high-voltage-resistant power devices in LLC resonant converters, resulting in an urgent need for a circuit of an LLC resonant converter with a smaller voltage stress on the power device to meet the requirements of high-voltage input applications at a lower cost and loss.
[0004] Among various ways to reduce the voltage stress on power devices, multi-level topological structures are widely used in various fields, and the voltage stress borne by the switching tube can be reduced to half of the input bus voltage by adding diodes. However, the added diodes as power devices will inevitably bring more losses, and the control method of the rectifier circuit including diodes and switching tubes is very complex.
[0005] To cope with the losses brought by diodes, most applications will adopt controlled rectification to further improve efficiency. In applications with large current output, the common controlled rectification method is to detect the voltage of the switching tube by adding voltage or current detection lines to achieve controlled rectification. This method will increase the complexity of the circuit and is very vulnerable to interference, reducing the reliability of the system.
[0006] In summary, how to enable a high-voltage input LLC resonant converter to use low-voltage stress power devices while its rectifier circuit is a controlled rectifier circuit with simple structure and high reliability is a technical problem to be solved at present.
[0007] In view of this, the present utility model is specifically proposed. Summary of the Utility Model
[0008] The technical problem to be solved by the present utility model is to overcome the deficiencies of the prior art and provide an LLC resonant converter, so that the rectifier circuit including switching tube Q1 and switching tube Q2 corresponding to the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit is a controlled rectifier circuit with simple structure, high reliability and high rectification efficiency.
[0009] The basic concept of the technical solution adopted by the present utility model to solve the above technical problem is:
[0010] The utility model provides an LLC resonant converter, which 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 a switching transistor Q1 and a switching transistor 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 switching transistor Q1. The second output terminal of the first transformer T1 and the first output terminal of the second transformer T2 are commonly connected to the first end of the output terminal Vo. The second output terminal of the second transformer T2 is connected to the input terminal of the switching transistor Q2. The output terminal of the switching transistor Q2 and the output terminal of the switching transistor Q1 are commonly connected to the second end of the output terminal Vo.
[0013] In the utility model, the input high voltage is divided by the series-connected first full-bridge LLC resonant converter circuit and second full-bridge LLC resonant converter circuit, and is respectively connected to the switching transistor Q1 and the switching transistor Q2. Rectification is performed through the body diodes of the switching transistor Q1 and the switching transistor Q2, so that the rectification circuit including the switching transistor Q1 and the switching transistor Q2 is a controllable rectification circuit, and has a simple structure, high reliability and high rectification efficiency.
[0014] A further solution of the utility model is that the LLC resonant converter includes a filter capacitor Co, and the filter capacitor Co is connected between the first end and the second end of the output terminal Vo;
[0015] The control module controls the conduction and cutoff of the switching transistor Q1 and the switching transistor Q2 through drive signals, so that the filter capacitor Co is charged and discharged.
[0016] In the above solution, charging and discharging are performed through the filter capacitor Co, further improving the rectification efficiency and realizing the filtering function of the rectification circuit.
[0017] A further solution of the utility model is 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;
[0018] 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. The output terminal of the second LLC resonant network is connected to the input terminal of the second transformer T2;
[0019] The first full-bridge circuit includes switching transistors S1 to S4, and the second full-bridge circuit includes switching transistors S5 to S8.
[0020] In the above solution, by the cooperation of switching transistors Q1 and Q2 with switching transistors S1 to S8 for conduction and cutoff, controllable rectification without detecting the line is realized according to the secondary-side current of the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit. Compared with the conventional diode rectification circuit, the rectification loss is reduced, the circuit efficiency is improved, and the rectification circuit structure and control method are simple, efficient and low-cost.
[0021] A further solution of the present utility model is that: the switching transistors Q1, Q2, and the switching transistors S1 to S8 are all MOS transistors with body diodes.
[0022] A further solution of the present utility model 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;
[0023] Both ends of a voltage-dividing circuit are connected to both 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 both ends of the voltage-dividing circuit, and the second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are commonly connected to the voltage-dividing point of the voltage-dividing circuit.
[0024] A further solution of the present utility model 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;
[0025] 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. 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;
[0026] 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. 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;
[0027] 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.
[0028] A further solution of the present utility model is that the voltage-dividing circuit is provided with a series-connected first voltage-sharing capacitor Ci1 and a second voltage-sharing capacitor Ci2.
[0029] The second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are commonly connected to a voltage-dividing point formed between the first voltage-sharing capacitor Ci1 and the second voltage-sharing capacitor Ci2 of the voltage-dividing circuit.
[0030] In the above solution, the voltage stress of 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 is further reduced. The types of power devices with low voltage are rich and the cost is low.
[0031] A further solution of the present utility model is that the parameters of the first voltage-sharing capacitor Ci1 and the second voltage-sharing capacitor Ci2 are the same, and the parameters of the switching transistors S1 to S8 are the same.
[0032] In the above solution, it is further ensured that the voltage division of the first voltage-sharing capacitor Ci1 and the second voltage-sharing capacitor Ci2 can be automatically balanced, and the output current values of the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit are close.
[0033] A further solution of the present utility model is that the first LLC resonant network includes a resonant inductor Lr1, an exciting inductor Lm1 and a resonant capacitor Cr1, and the second LLC resonant network includes a resonant inductor Lr2, an exciting inductor Lm2 and a resonant capacitor Cr2.
[0034] The first output terminal of the first full-bridge circuit is connected to one end of the resonant inductor Lr1, the second output terminal of the first full-bridge circuit is connected to one end of the resonant capacitor Cr1, and the other end of the resonant inductor Lr1 and the other end of the resonant capacitor Cr1 are connected to both ends of the exciting inductor Lm1.
[0035] The third output terminal of the second full-bridge circuit is connected to one end of the resonant inductor Lr2, the fourth output terminal of the second full-bridge circuit is connected to one end of the resonant capacitor Cr2, and the other end of the resonant inductor Lr2 and the other end of the resonant capacitor Cr2 are connected to both ends of the exciting inductor Lm2.
[0036] A further solution of the present utility model is that both ends of the first transformer T1 are connected to both ends of the exciting inductor Lm1. The first output end of the first transformer T1 and the end connected to the resonant inductor Lr1 are of the same name, and the second output end of the first transformer T1 and the end connected to the resonant capacitor Cr1 are of opposite names.
[0037] Both ends of the second transformer T2 are connected to both ends of the exciting inductor Lm1. The first output end of the second transformer T2 and the end connected to the resonant inductor Lr2 are of the same name, and the second output end of the second transformer T2 and the end connected to the resonant capacitor Cr2 are of opposite names.
[0038] In the above solution, it is further ensured that the current directions flowing from the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit to the output terminal Vo are the same.
[0039] After adopting the above technical solution, the present utility model has the following beneficial effects compared with the prior art.
[0040] 1. The input high voltage is divided by the series-connected first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit, and is respectively connected to the switching transistors Q1 and Q2. Rectification is performed through the body diodes of the switching transistors Q1 and Q2, so that the rectification circuit including the switching transistors Q1 and Q2 is a controllable rectification circuit with high reliability and high rectification efficiency.
[0041] 2. The circuit structure of the present utility model is simple, the effect is remarkable, and it is suitable for popularization and use.
[0042] The following further describes in detail the specific implementation manners of the present utility model with reference to the accompanying drawings. Description of the Drawings
[0043] As a part of the present utility model, the accompanying drawings are used to provide a further understanding of the present utility model. The schematic embodiments and descriptions thereof are used to explain the present utility model, but do not constitute an improper limitation to the present utility model. Obviously, the accompanying drawings in the following description are only some embodiments. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts. In the drawings:
[0044] Figure 1 is a principle block diagram of an LLC resonant converter circuit of the present utility model;
[0045] Figure 2 is a schematic circuit diagram of an LLC resonant converter circuit of the present utility model;
[0046] Figure 3It is a waveform timing diagram of an LLC resonant converter of the present utility model when the first resonant frequency is less than the switching frequency and less than the second resonant frequency.
[0047] In the figure: 11, the first full-bridge circuit; 12, the second full-bridge circuit; 21, the first LLC resonant network; 22, the second LLC resonant network; 3, the rectifier circuit.
[0048] It should be noted that these drawings and text descriptions are not intended to limit the scope of the concept of the present utility model in any way, but to illustrate the concept of the present utility model to those skilled in the art by referring to specific embodiments. Detailed implementation manners
[0049] To make the objectives, technical solutions and advantages of the embodiments of the present utility model clearer, the technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. The following embodiments are used to illustrate the present utility model but are not intended to limit the scope of the present utility model.
[0050] In the description of the present utility model, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present utility model.
[0051] In the description of the present utility model, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.
[0052] The present utility model provides an LLC resonant converter, which divides the input high voltage through a series-connected first full-bridge LLC resonant converter circuit and a second full-bridge LLC resonant converter circuit, and is respectively connected to the switching transistor Q1 and the switching transistor Q2. The rectifier circuit 3 including the switching transistors Q1 and Q2 is a controllable rectifier circuit 3, and has a simple structure, high reliability, and high rectification efficiency.
[0053] Embodiment 1
[0054] Such as Figures 1 to 2As shown in the figure, this embodiment provides an LLC resonant converter, which includes 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 switching transistor 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 is also connected 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 switching transistor Q2. The output terminal of the switching transistor Q2 is connected to the output terminal of the switching transistor Q1 and is also connected to the first terminal of the output terminal Vo. The LLC resonant converter rectifies the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit at least through the body diodes of the switching transistor Q1 and the switching transistor Q2. A control module is connected to the control terminals of the switching transistor Q1 and the switching transistor Q2 and is used to generate drive signals for controlling the conduction and cutoff of the switching transistor Q1 and the switching transistor Q2.
[0055] In this embodiment, the input high voltage is divided by the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit connected in series, and they are respectively connected to the switching transistor Q1 and the switching transistor Q2. Rectification is performed through the body diodes of the switching transistor Q1 and the switching transistor Q2, so that the rectification circuit 3 including the switching transistor Q1 and the switching transistor Q2 is a controllable rectification circuit 3, with a simple structure, high reliability, and high rectification efficiency.
[0056] Furthermore, the rectification circuit has a filter capacitor Co, and both ends of the filter capacitor Co are connected to the first terminal and the second terminal of the output terminal Vo. The control module controls the conduction and cutoff of the switching transistor Q1 and the switching transistor Q2 through the drive signals, causing the filter capacitor Co to charge and discharge. By charging and discharging the filter capacitor Co, the rectification efficiency is further improved, and the rectification circuit 3 realizes the function of filtering.
[0057] It can be understood that, compared with the secondary side current waveform of a single LLC resonant converter circuit, for the secondary side current waveform obtained by the series-topology LLC resonant converter circuit in this embodiment, the output currents of the two LLC resonant converter circuits are the same, and automatic current sharing can be achieved. Therefore, the current sharing circuit in the rectification circuit 3 can be omitted, further reducing the design difficulty and circuit cost.
[0058] 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 end of the first full-bridge circuit 11 is connected to the input end of the first LLC resonant network 21, the output end of the first LLC resonant network 21 is connected to the input end of the first transformer T1, the output end of the second full-bridge circuit 12 is connected to the input end of the second LLC resonant network 22, and the output end of the second LLC resonant network 22 is connected to the input end of the second transformer T2; the first full-bridge circuit 11 includes switching transistors S1 to S4, and the second full-bridge circuit 12 includes switching transistors S5 to S8; the control module is configured to generate drive signals for controlling the conduction and cutoff of the switching transistors Q1, Q2, and S1 to S8. By cooperating the switching transistors Q1 and Q2 with the switching transistors S1 to S8 for conduction and cutoff, controllable rectification without detecting the line is achieved according to the secondary side current of the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit, and the circuit structure and control method are simple, efficient, and low-cost.
[0059] Furthermore, the first full-bridge circuit has a first input end and a second input end, and the second full-bridge circuit has a third input end and a fourth input end; both ends of a voltage dividing circuit are connected to both ends of the input power supply Vi, the first input end of the first full-bridge circuit 11 and the fourth input end of the second full-bridge circuit 12 are respectively connected to both ends of the voltage dividing circuit, and the second input end of the first full-bridge circuit 11 and the third input end of the second full-bridge circuit 12 are commonly connected to the voltage dividing point of the voltage dividing circuit.
[0060] Further, 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 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 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 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 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 connected to both the second input terminal of the first full-bridge circuit and the input terminal of the switching transistor S5, the output terminal of the switching transistor S3 is connected to both 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 further 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.
[0061] Further, the voltage dividing circuit is provided with a series-connected first voltage-sharing capacitor Ci1 and a second voltage-sharing capacitor Ci2; 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 a voltage dividing point formed between the first voltage-sharing capacitor Ci1 and the second voltage-sharing capacitor Ci2 of the voltage dividing circuit; further, the parameters of the first voltage-sharing capacitor Ci1 and the second voltage-sharing capacitor Ci2 are the same, and the parameters of the switching transistors S1 to S8 are the same. The voltage stress of 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 is further reduced, and the types of low-voltage power devices are rich and the cost is low.
[0062] Further, the switching transistors Q1, Q2, and the switching transistors S1 to S8 are all MOS transistors with body diodes. It can be understood that when the switching transistor Q1 and / or the switching transistor Q2 is an NMOS transistor, its input terminal is the drain, the output terminal is the source, and the control terminal is the gate.
[0063] It can be understood that the driving signal output by the control module is a PWM signal to control the LLC resonant converter in a PFM modulation mode to meet the gain required by the load connected to the output terminal Vo.
[0064] Further, the first LLC resonant network includes a resonant inductor Lr1, an exciting inductor Lm1, and a resonant capacitor Cr1, and the second LLC resonant network includes a resonant inductor Lr2, an exciting inductor Lm2, and a resonant capacitor Cr2; a first output terminal of the first full-bridge circuit is connected to one end of the resonant inductor Lr1, a second output terminal of the first full-bridge circuit is connected to one end of the resonant capacitor Cr1, and the other end of the resonant inductor Lr1 and the other end of the resonant capacitor Cr1 are connected to both ends of the exciting inductor Lm1; a third output terminal of the second full-bridge circuit is connected to one end of the resonant inductor Lr2, a fourth output terminal of the second full-bridge circuit is connected to one end of the resonant capacitor Cr2, and the other end of the resonant inductor Lr2 and the other end of the resonant capacitor Cr2 are connected to both ends of the exciting inductor Lm2.
[0065] In a specific implementation manner of this embodiment, as Figure 2 shown, the switching transistors S1 to S8, the switching transistor Q1, and the switching transistor Q2 are NMOS transistors. The resonant inductor Lr1, the exciting inductor Lm1, and the resonant capacitor Cr1 of the first LLC resonant network 21 are connected in series in sequence. Both ends of the exciting inductor Lm1 are connected in parallel to the input end of the first isolation transformer T1. One end of the resonant inductor Lr1 is the first input end of the first LLC resonant network 21, and the first input end is connected between the source electrode of the switching transistor S4 and the drain electrode of the switching transistor S3. One end of the resonant capacitor Cr1 is the second input end of the first LLC resonant network 21, and the second input end is connected between the source electrode of the switching transistor S1 and the drain electrode of the switching transistor S2. The arrangement of the resonant inductor Lr2, the exciting inductor Lm2, and the resonant capacitor Cr2 of the second LLC resonant network 22 is the same as that of the first LLC resonant network 21 described above. The first input end of the second LLC resonant network 22 is connected between the source electrode of the switching transistor S8 and the drain electrode of the switching transistor S7, and the second input end is connected between the source electrode of the switching transistor S5 and the drain electrode of the switching transistor S6.
[0066] Further, the parameters of the first LLC resonant network 21 and the second LLC resonant network 22 are the same, that is, the inductance of the resonant inductor Lr1 of the first LLC resonant network 21 is the same as the inductance of the resonant inductor Lr2 of the second LLC resonant network 22, the capacitance value of the resonant capacitor Cr1 of the first LLC resonant network 21 is the same as the capacitance value of the resonant capacitor Cr2 of the second LLC resonant network 22, the transformer parameters of the first isolation transformer T1 and the second isolation transformer T2 are the same, and the inductance of the exciting inductor Lm1 of the first LLC resonant network 21 is the same as the inductance of Lm2 of the second LLC resonant network 22.
[0067] Further, both ends of the first transformer T1 are connected to both ends of the exciting inductor Lm1. The first output terminal of the first transformer T1 and the end where it is connected to the resonant inductor Lr1 are of the same name. The second output terminal of the first transformer T1 and the end where it is connected to the resonant capacitor Cr1 are of opposite names. Both ends of the second transformer T2 are connected to both ends of the exciting inductor Lm1. The first output terminal of the second transformer T2 and the end where it is connected to the resonant inductor Lr2 are of the same name. The second output terminal of the second transformer T2 and the end where it is connected to the resonant capacitor Cr2 are of opposite names. This further ensures that the current directions flowing from the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit to the output terminal Vo are the same.
[0068] In this embodiment, the input high voltage is divided by the series-connected first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit, and they are respectively connected to the switching transistors Q1 and Q2. Rectification is performed through the body diodes of the switching transistors Q1 and Q2, so that the rectification circuit 3 including the switching transistors Q1 and Q2 is a controllable rectification circuit, with a simple structure, high reliability, and high rectification efficiency. The circuit structure of this embodiment is simple, with remarkable effects, and is suitable for popularization and use.
[0069] Embodiment 2
[0070] As Figures 1 to 3 shown, this embodiment provides a control method for applying the LLC resonant converter described in Embodiment 1, including: when the control module controls the first full-bridge LLC resonant converter circuit to resonate, controlling the switching transistor Q1 to conduct; when the control module controls the second full-bridge LLC resonant converter circuit to resonate, controlling the switching transistor Q2 to conduct. While realizing rectification using the body diodes of the switching transistors Q1 and Q2, the losses brought by the body diodes are reduced.
[0071] Further, the first full-bridge LLC resonant converter circuit includes switching transistors S1 to S4, and the second full-bridge circuit 12 includes switching transistors 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 both ends of the input power supply Vi. A voltage-dividing circuit for connecting both ends of the input power supply Vi is provided, 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 to the voltage-dividing circuit; the switching transistor S1 connected to the first end of the input power supply Vi, the switching transistor S3 in parallel with the switching transistor S1, the switching transistor S7 connected to the second end of the input power supply Vi, and the switching transistor S5 in parallel with the switching transistor S7 are used as the first driving group, and the switching transistors S2, S4, S6, and S8 are used as the second driving group; a control module inputs complementary driving signals with a duty cycle less than 50% to the first driving group and the second driving group to control their non-simultaneous conduction; the control module controls the switching transistor Q1 to conduct for a set duration during the time when the first driving group is controlled to conduct, and controls the switching transistor Q2 to conduct for a set duration during the time when the second driving group is controlled to conduct. Therefore, it is ensured that the current flowing through the switching transistors Q1 and Q2 from the first full-bridge LLC resonant converter circuit and the second full-bridge LLC resonant converter circuit has the same direction, reducing the voltage stress of the power devices in the full-bridge LLC resonant converter circuit, and enabling the switching transistors Q1 and Q2 to be connected in parallel to the output terminal Vo after being connected in parallel.
[0072] It can be understood that the PWM driving signals input by the control module to the first driving group and the second driving group generate controllable rectification signals Vsr1 and Vsr2 respectively following them. Among them, the controllable rectification signal Vsr1 is delayed by a time ta to turn on with respect to the PWM driving signal of the first driving group, and is advanced by a time tb to turn off with respect to the PWM driving signal of the first driving group. The controllable rectification signal Vsr2 is delayed by a time ta to turn on with respect to the PWM driving signal of the second driving group, and is advanced by a time tb to turn off with respect to the PWM driving signal of the second driving group. The time ta and the time tb can be optimized according to the actual usage situation. The magnitudes of the time ta and the time tb are related to the magnitude of the current required by the load connected to the output terminal Vo and the circuit efficiency of the required LLC resonant converter.
[0073] Further, when the control module controls the first driving group to conduct and the second driving group to turn off, and only the resonant capacitor Cr1 and the resonant inductor Lr1 of the first LLC resonant network participate in resonance, the control terminals of the switching transistor Q1 and the switching transistor Q2 are used to control their turn-off, and the current passes through the body diodes of the switching transistor Q1 and the switching transistor Q2. The body diodes of the switching transistor Q1 and the switching transistor Q2 are better utilized for rectification.
[0074] Further, when the control module controls the first driving group to conduct, and the resonant capacitor Cr1, resonant inductor Lr1, and exciting inductor Lm1 of the first LLC resonant network 21 all participate in resonance, the control switch Q1 is controlled to conduct; when the control module controls the second driving group to conduct, and the resonant capacitor Cr2, resonant inductor Lr2, and exciting inductor Lm2 of the second LLC resonant network 22 all participate in resonance, the control switch Q2 is controlled to conduct. Therefore, it is ensured that the large resonant current will not be lost due to the body diodes of the switch Q1 and the switch Q2.
[0075] 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 parameters of the first full-bridge circuit and the second full-bridge circuit are the same, the parameters of the first LLC resonant network and the second LLC resonant network are the same, and the parameters of the first isolation transformer T1 and the second isolation transformer T2 are the same. Therefore, 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.
[0076] The first resonant frequency is represented by fr1, that is:
[0077]
[0078] The second resonant frequency is represented by fr2, that is:
[0079]
[0080] The first resonant frequency of the first resonant network is the same as the first resonant frequency of the second resonant network.
[0081] Among them, f r2 <f r1 .
[0082] 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, the resonant frequency f r1 and the 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 converters in the three modes are slightly different. In this embodiment, f r1 <fs<f r2is described, and its timing diagram is shown in Figure 3 , which contains a total of 5 modes, specifically:
[0083] Mode 1, in the t0 - t1 stage: Control the second drive group to turn off and the first drive group to conduct with zero voltage. Specifically, at t0, the switching tubes of the second drive group turn off. 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 diodes of the switching tubes of the first drive group, making the voltage across the switching tubes of the first drive group zero, preparing for zero - voltage conduction. During the period from t0 to t1, in this stage, the switching tubes of the first drive group conduct with zero voltage. At this time, the voltage across each resonant network is half of the input voltage Vi. The first resonant current Ir1 and the second resonant current Ir2 slowly increase to 0, and Ir1 is equal to Ir2. The body diode of the secondary - side switching tube Q1 conducts. At this time, the secondary - side voltage of the transformer is the output voltage, and at this time, the resonant capacitor and the resonant inductor start to resonate.
[0084] Mode 2: In the t1 - t2 stage, the first drive group remains conducting. The resonant capacitors and resonant inductors of the first LLC resonant network 21 and the second LLC resonant network 22 resonate, and the magnetizing inductors do not participate in the resonance. The first resonant current and the second resonant current increase sinusoidally. Specifically, the first resonant current Ir1 and the second resonant current Ir2 remain equal and slowly increase sinusoidally from 0. The body diode of the secondary - side rectifier tube Q1 remains conducting, and the current slowly increases. The resonant network remains in series resonance in this stage, that is, the resonant inductor Lr1 and the resonant capacitor Cr1 of the first LLC resonant network 21 resonate, and the resonant inductor Lr2 and the resonant capacitor Cr2 of the second LLC resonant network 22 resonate, and the magnetizing inductors Lm1 and Lm2 do not participate in the resonance.
[0085] Mode 3: In the t2 - t3 period, control the first drive group to remain conducting. The magnetizing inductors of the first LLC resonant network 21 and the second LLC resonant network 22 participate in the resonance, and 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 t2, the PWM drive signal input by the control module to the control terminal of the NMOS tube Q1 is inverted to a high - level signal, and the NMOS tube Q1 is controlled to conduct until t3.
[0086] Mode Four: During the time period from t3 to t4, control the first drive group to remain conducting, the first resonant current and the second resonant current decrease, and remain greater than the corresponding first exciting inductance current and second exciting inductance current. Specifically, at t3, the PWM drive signal input by the control module to the control terminal of NMOS transistor Q1 is inverted 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 exciting inductance current Im1, the second resonant current Ir2 is greater than the second exciting inductance current Im2, and the primary side of the first full-bridge LLC resonant converter circuit continues to transfer energy to the secondary side. The current flows through the body diode of NMOS transistor Q1 to achieve rectification.
[0087] Mode Five: During the time period from t4 to t5, when the first resonant current is equal to the first exciting inductance current and the second resonant current is equal to the second exciting inductance current, control the first drive group to remain conducting for a set duration and then turn off, and the primary side circuit of the first LLC resonant network 21 does not transfer energy to the secondary side circuit. Specifically, at t4, the first resonant current Ir1 is equal to the first exciting inductance current Im1, the second resonant current Ir2 is equal to the second exciting inductance current Im2, the primary side of the first full-bridge LLC resonant converter circuit does not transfer energy to the secondary side, NMOS transistor Q1 turns off with zero current, and the first drive group remains conducting. This stage has a short time and the primary side current remains unchanged. At t5, the first drive group is disconnected, and both the first resonant current Ir1 and the second resonant current Ir2 are greater than 0.
[0088] The working principle of the LLC resonant converter in the second half of the working cycle is symmetric to that of the first half of the above-mentioned Modes One to Five.
[0089] It should be noted that Figure 3 In, the first four rows are the PWM waveform diagrams received by the control terminals of the corresponding switching transistors, the fifth row is the waveform diagrams of the resonant current and the exciting inductance current, and the sixth row is the output waveform diagrams of switching transistors Q1 and Q2. From Figure 3 it can be seen that the first LLC resonant network 21 and the second LLC resonant network 22 work independently of each other and do not affect each other.
[0090] Specifically, the working process of the rectifier circuit 3 is as follows: In Mode 1, both the switching transistor Q1 and the switching transistor 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 start to change, the body diode of the switching transistor Q1 conducts, and the current IQ1 gradually increases; in Mode 2, control both the switching transistor Q1 and the switching transistor Q2 to be turned off, and the body diode of the switching transistor Q1 remains conducting; in Mode 3, control the switching transistor Q1 to conduct, so that the current IQ1 flows through Q1 and no longer flows through its body diode; in Mode 4, control the switching transistor Q1 of the rectifier filter circuit to be turned off, and the body diode of the switching transistor Q1 conducts; in Mode 5, control the first drive group to conduct for a set duration and then turn off, and the body diode of the switching transistor Q1 turns off with zero current.
[0091] In this embodiment, the PWM drive signals of the power switching transistors of the LLC resonant converter are easy to implement. Each of its switching transistors can achieve zero-voltage turn-on, and the withstand voltage is one-half of the input voltage. At the same time, the voltages on the voltage-sharing capacitors can be automatically balanced, making it suitable for high-voltage input applications and capable of easily improving the power density and efficiency of the power supply at low cost.
[0092] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art of this patent, without departing from the scope of the technical solution of the present invention, can make some changes or modifications using the technical content prompted above into equivalent embodiments of equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution 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 a switching transistor Q1 and a switching transistor 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 switching transistor Q1. The second output terminal of the first transformer T1 and the first output terminal of the second transformer T2 are commonly connected to the first end of the output terminal Vo. The second output terminal of the second transformer T2 is connected to the input terminal of the switching transistor Q2. The output terminal of the switching transistor Q2 and the output terminal of the switching transistor Q1 are commonly connected to the second end of the output terminal Vo.
2. The LLC resonant converter according to claim 1, characterized in that, It includes a filter capacitor Co, and the filter capacitor Co is connected between the first end and the second end of the output terminal Vo.
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.
4. An LLC resonant converter according to claim 3, characterized in that, The switching transistors Q1, Q2, and S1 to S8 are all MOS transistors with body diodes.
5. A 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; Both ends of a voltage dividing circuit are connected to both 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 both ends of the voltage dividing circuit. The second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are commonly connected to the voltage dividing point of the voltage dividing circuit.
6. The LLC resonant converter according to claim 5, wherein, 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. 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. 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.
7. The LLC resonant converter according to claim 6, wherein The voltage-dividing circuit is provided with a series-connected first voltage-sharing capacitor Ci1 and a second voltage-sharing capacitor Ci2; The second input terminal of the first full-bridge circuit and the third input terminal of the second full-bridge circuit are commonly connected to the voltage-dividing point formed between the first voltage-sharing capacitor Ci1 and the second voltage-sharing capacitor Ci2.
8. A LLC resonant converter according to claim 7, characterized in that, The parameters of the first voltage-sharing capacitor Ci1 and the second voltage-sharing capacitor Ci2 are the same, and the parameters of the switching transistors S1 to S8 are the same.
9. An LLC resonant converter according to claim 6, wherein The first LLC resonant network includes a resonant inductor Lr1, an exciting inductor Lm1, and a resonant capacitor Cr1. The second LLC resonant network includes a resonant inductor Lr2, an exciting inductor Lm2, and a resonant capacitor Cr2; The first output terminal of the first full-bridge circuit is connected to one end of the resonant inductor Lr1. The second output terminal of the first full-bridge circuit is connected to one end of the resonant capacitor Cr1. The other end of the resonant inductor Lr1 and the other end of the resonant capacitor Cr1 are connected to both ends of the exciting inductor Lm1; The third output terminal of the second full-bridge circuit is connected to one end of the resonant inductor Lr2. The fourth output terminal of the second full-bridge circuit is connected to one end of the resonant capacitor Cr2. The other end of the resonant inductor Lr2 and the other end of the resonant capacitor Cr2 are connected to both ends of the exciting inductor Lm2.
10. A LLC resonant converter according to claim 9, characterized in that, Both ends of the first transformer T1 are connected to both ends of the exciting inductor Lm1. The first output terminal of the first transformer T1 and the end connected to the resonant inductor Lr1 are of the same name. The second output terminal of the first transformer T1 and the end connected to the resonant capacitor Cr1 are of opposite names; Both ends of the second transformer T2 are connected to both ends of the exciting inductor Lm1. The first output terminal of the second transformer T2 and the end connected to the resonant inductor Lr2 are of the same name. The second output terminal of the second transformer T2 and the end connected to the resonant capacitor Cr2 are of opposite names.