Gain-adjustable LLC resonant converter

Abstract

The utility model provides a gain-adjustable LLC resonant converter, which comprises a primary side and a secondary side, the secondary side comprises a full-bridge circuit, the high sides of two bridge arms of the full-bridge circuit are both provided with diodes, and the low sides of the two bridge arms of the full-bridge circuit are both provided with switch tubes. According to the LLC resonant converter, two low-side diodes are replaced by the switching tubes, a traditional control method can be compatible, the overlapping conduction time of the two switching tubes on the secondary side can be used as a control variable to adjust the gain of the converter, and the gain range of the LLC resonant converter is widened.

Description

Technical Field

[0001] The utility model mainly relates to the technical field of voltage converters, in particular to an LLC resonant converter with adjustable gain. Background Art

[0002] The LLC resonant converter is a switching power supply topology, usually composed of an input power supply, a resonant network, a switch tube, and an output rectifier. The LLC resonant converter controls the on and off of the switch tube to make the resonant network resonate to achieve energy transfer between the input and output. In the LLC resonant converter, the impedance of the resonant network determines the working state of the entire circuit. When the impedance of the resonant network is purely resistive, the LLC resonant converter has the highest working efficiency. Compared with traditional resonant converters, LLC resonant converters have higher efficiency, stronger adaptability, smaller space occupancy, better stability and lower EMI interference, meeting the needs of high-demand power supplies and high-quality power supplies in modern industry, information technology, communications, industrial automation, etc.

[0003] In a wide range of voltage input scenarios, in order to maintain the stability of the LLC resonant converter output voltage, the converter needs to obtain a wider voltage gain from the perspective of optimizing the control method and improving the topology. From the perspective of optimizing the control method, in order to enable the LLC resonant converter to adapt to a wide range of voltage inputs, a hybrid control method is proposed, that is, when the switching frequency is lower than the resonant frequency, the traditional variable frequency control is used. As the input voltage increases, the switching frequency gradually increases to the resonant frequency, the switching frequency is fixed to the resonant frequency, and the phase shift angle between the two bridge arms is adjusted to adjust the output power. Although the combination of variable frequency control and phase shift control broadens the input voltage range of the LLC resonant converter, in order to take into account efficiency, the phase shift angle of this hybrid control method still has certain limitations.

[0004] Based on the frequency conversion-phase shifting hybrid control, there is also a three-stage hybrid control method, which adds a combination of frequency conversion control and phase shifting control between the two adjustment areas, and further broadens the converter gain range through the segmented control method. However, the control method is more complex in the area where the two controls are combined, and has high requirements on the converter control logic. From the perspective of topology improvement, dual-bridge LLC resonant converters, staggered parallel Boost integrated LLC resonant converters, series bridge three-level LLC resonant converters, dual-transformer LLC resonant converters, etc. have been proposed one after another. Although these converters have achieved a wide range of voltage input to a certain extent, they have problems such as high design difficulty, high cost, large size, and low power density. Utility Model Content

[0005] The technical problem to be solved by the utility model is to provide a gain-adjustable LLC resonant converter, which replaces the two low-side diodes with a switch tube. It is compatible with traditional control methods and can also use the overlapping conduction time of the two secondary-side switch tubes as a control variable to adjust the converter gain, thereby broadening the gain range of the LLC resonant converter.

[0006] To solve the above technical problems, the utility model provides a gain-adjustable LLC resonant converter, including a primary side and a secondary side, wherein the secondary side includes a full-bridge circuit, and the high sides of the two bridge arms of the full-bridge circuit are both set as diodes, while the low sides of the two bridge arms of the full-bridge circuit are both set as switching tubes.

[0007] Furthermore, the LLC resonant converter with adjustable gain is a full-bridge LLC resonant converter.

[0008] Furthermore, the LLC resonant converter with adjustable gain is a half-bridge LLC resonant converter.

[0009] Furthermore, the switch tube is an insulated gate bipolar transistor, a metal oxide semiconductor field effect transistor or a bipolar transistor.

[0010] Compared with the prior art, the utility model has the following beneficial effects: the secondary side includes a full-bridge circuit, and the high sides of the two bridge arms of the full-bridge circuit are set as diodes, and the low sides of the two bridge arms of the full-bridge circuit are set as switch tubes. Therefore, the improved LLC resonant converter can control the converter gain by adjusting the overlapping conduction time at a fixed frequency in the range of voltage gain M>1. Since the switching frequency is fixed, it is beneficial to the design of magnetic components; in the range of gain M<1, the converter can achieve a lower voltage gain than the traditional variable frequency control by combining phase shift control. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings are included to provide a further understanding of the present invention. They are included and constitute a part of the present invention. The accompanying drawings illustrate embodiments of the present invention and together with the specification serve to explain the principles of the present invention. In the accompanying drawings:

[0012] Figure 1 It is a schematic diagram of the topological structure of the LLC resonant converter with adjustable gain of the utility model;

[0013] Figure 2 It is a schematic diagram of switching conditions of a three-stage hybrid control mode when the LLC resonant converter with adjustable gain of the utility model is adopted;

[0014] Figure 3 It is a schematic diagram of a gain curve when a three-stage hybrid control mode of the LLC resonant converter with adjustable gain of the utility model is adopted. DETAILED DESCRIPTION

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present utility model, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of the present utility model. For ordinary technicians in this field, the present utility model can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0016] It should be understood that when a component is referred to as being "on another component," "connected to another component," "coupled to another component," or "contacting another component," it may be directly on, connected to, coupled to, or contacting the other component, or there may be intervening components. In contrast, when a component is referred to as being "directly on another component," "directly connected to," "directly coupled to," or "directly contacting" another component, there are no intervening components. Similarly, when a first component is referred to as being "electrically in contact with" or "electrically coupled to" a second component, there is an electrical path between the first component and the second component that allows current to flow. The electrical path may include capacitors, coupled inductors, and / or other components that allow current to flow, even without direct contact between conductive components.

[0017] Figure 1 This is a schematic diagram of the topological structure of the LLC resonant converter with adjustable gain of the utility model. Figure 1 As shown, it includes a primary side and a secondary side, wherein the secondary side includes a full-bridge circuit, and the high sides of the two bridge arms of the full-bridge circuit are both set as diodes, and the low sides of the two bridge arms of the full-bridge circuit are both set as switch tubes. It can be seen that the LLC resonant converter with adjustable gain in this embodiment replaces the two diodes on the low side of the traditional LLC resonant converter with switch tubes, which is compatible with traditional control methods and can also use the overlapping conduction time of the two switch tubes on the secondary side as a control variable to adjust the converter gain, thereby widening the gain range of the LLC resonant converter.

[0018] In some embodiments, the LLC resonant converter with adjustable gain is a full-bridge LLC resonant converter. The full-bridge LLC resonant converter uses four switch tubes on the primary side to form a complete bridge circuit. Therefore, the full-bridge LLC resonant converter can maintain high efficiency when the input voltage and output load change, and achieve a constant output voltage within a wide range. The advantages of the full-bridge LLC resonant converter are its high reliability, good voltage stabilization effect and fast dynamic response speed.

[0019] In some embodiments, the LLC resonant converter with adjustable gain is a half-bridge LLC resonant converter. The half-bridge LLC resonant converter uses two switching tubes on the primary side to form a half-bridge circuit. This structure is simpler than the full-bridge LLC resonant converter in terms of cost and complexity, but may be slightly inferior to the full-bridge LLC resonant converter in terms of efficiency. The advantages of the half-bridge LLC resonant converter are its simple structure, easy implementation and low cost.

[0020] In some embodiments, the switch tube is an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET) or a bipolar junction transistor (BJT). IGBT, MOSFET and BJT are suitable for different scenarios. IGBT is suitable for high-power conversion systems, MOSFET is suitable for small and medium power occasions, and BJT is often used for current amplification and switching.

[0021] In this embodiment, compared with the full-bridge rectifier structure of four diodes used in the traditional LLC resonant converter, the LLC resonant converter with adjustable gain in this embodiment replaces the original two low-side diodes with switch tubes, which is compatible with traditional control methods and can also use the overlapping conduction time of the two switches on the secondary side as a control variable to adjust the converter gain. Since the LLC resonant converter with adjustable gain in this embodiment can operate under fixed frequency conditions, it is beneficial to the design of magnetic components. The LLC resonant converter with adjustable gain in this embodiment can control the converter output voltage by adjusting the overlapping conduction time of the two switches on the secondary side. Therefore, the primary excitation inductance has little effect on the voltage gain, and its inductance can be appropriately increased to reduce losses.

[0022] Figure 2 This is a schematic diagram of the switching conditions of the three-stage hybrid control mode when the LLC resonant converter with adjustable gain of the utility model is used. Figure 2 As shown in the figure, in order to explain the mode switching conditions, the resonant frequency f r , switching frequency f c , reference voltage at the resonance point V r Take this as an example to illustrate, f s is the switching frequency. V in < V r and f s < f c When the converter switches at a fixed frequency f s The switching frequency f c, the converter gain can be adjusted by adjusting the overlapping conduction time of S5 and S6; when V in < V r and f s > f c When , the converter is adjusted by time-shift control; when V in > V r When the switching frequency is fixed f s is the resonant frequency f r , adjust the phase shift angle between the leading bridge arm and the trailing bridge arm to adjust the converter gain.

[0023] Figure 3 This is a schematic diagram of the gain curve when the three-stage hybrid control method of the LLC resonant converter with adjustable gain is adopted in the utility model. Figure 3 As shown, the resonant frequency point is used as the switching point between phase shift control and time shift control, which is denoted as mode switching point 1. In the range where the switching frequency is greater than the resonant frequency, the converter gain is less than 1, and the slope of the gain curve is small. A wider frequency modulation range is required to adjust the gain, and the secondary diode cannot achieve ZCS (zero current switching); in the range where the switching frequency is less than the resonant frequency, the converter gain is greater than 1, and the slope of the gain curve is large, which is suitable for variable frequency control. The switching point between time shift control and improved topology overlapping conduction control is set at a position below the resonance point, which is denoted as mode switching point 2. f n = 0.7, for example, f n > 0.7, the converter uses time-shift control to adjust the gain. At this time, the overlapping conduction time of S5 and S6 is 0, and the phase shift angle between the leading bridge arm and the lagging bridge arm is 0. f n < 0.7, the control mode switches from time-shift control to improved topology control, and the overlapping conduction time of switches S5 and S6 is adjusted. At this time, the switching frequency is fixed at 0.75 times the resonant frequency, and the phase shift angle between the leading bridge arm and the lagging bridge arm is 0.

[0024] The LLC resonant converter with adjustable gain provided in this embodiment can control the converter gain by adjusting the overlapping conduction time at a fixed frequency in the range of voltage gain M>1. Since the switching frequency is fixed, it is beneficial to the design of magnetic components. In the range of gain M<1, the converter can achieve a lower voltage gain than the traditional variable frequency control by combining phase shift control. The LLC resonant converter in this embodiment switches the control mode of different frequency bands, gives full play to the advantages of each control method, combines the improved structure, time shift control and phase shift control, and broadens the gain range of the traditional LLC resonant converter.

[0025] For those skilled in the art, the above utility model disclosure is only used as an example and does not constitute a limitation of the utility model. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and amendments to the utility model. Such modifications, improvements and amendments are suggested in the utility model, so such modifications, improvements and amendments still belong to the spirit and scope of the exemplary embodiments of the utility model.

[0026] Although the present invention has been described with reference to the current specific embodiments, ordinary technicians in this technical field should recognize that the above embodiments are only used to illustrate the present invention, and various equivalent changes or substitutions may be made without departing from the spirit of the present invention. Therefore, as long as the changes and modifications to the above embodiments are within the scope of the essential spirit of the present invention, they will fall within the scope of the claims of the present invention.

Claims

1. A gain-adjustable LLC resonant converter, comprising a primary side and a secondary side, characterized in that: The secondary side includes a full-bridge circuit, and the high sides of the two bridge arms of the full-bridge circuit are both set as diodes, and the low sides of the two bridge arms of the full-bridge circuit are both set as switch tubes.

2. The LLC resonant converter with adjustable gain according to claim 1, characterized in that: The LLC resonant converter with adjustable gain is a full-bridge LLC resonant converter.

3. The LLC resonant converter with adjustable gain according to claim 1, characterized in that: The LLC resonant converter with adjustable gain is a half-bridge LLC resonant converter.

4. The LLC resonant converter with adjustable gain according to any one of claims 1 to 3, characterized in that: The switch tube is an insulated gate bipolar transistor, a metal oxide semiconductor field effect transistor or a bipolar transistor.

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