Multi-mode resonant converter based on variable structure rectification unit

Abstract

The invention discloses a multi-mode resonant converter based on a variable structure rectification unit, and aims to meet the requirement for high-efficiency electric energy conversion in wide input voltage range application, a resonant converter represented by a traditional LLC needs to realize wide voltage gain adjustment by greatly adjusting the switching frequency. Over-wide frequency ranges often result in efficiency reduction and complex design of magnetic elements. Therefore, the CLLC resonant converter based on the full-bridge rectification mode, the double-voltage rectification mode and the quadruple-voltage rectification mode is provided, switching of the secondary rectification structure in the three working modes of the full-bridge rectification mode, the double-voltage rectification mode and the quadruple-voltage rectification mode is achieved by changing the switching sequence, and then it is guaranteed that the resonant converter widens the gain change range in the narrow frequency range. According to the rectification unit provided by the invention, a capacitor and diode network is dynamically configured by utilizing a controllable switch, the switching frequency regulation range is reduced in a wide input voltage range, and meanwhile, the soft switching characteristic of the CLLC resonant converter is ensured.

Description

Technical Field

[0001] The present invention relates to the field of direct current converters, and in particular to a multi-mode resonant converter based on a variable structure rectifier unit. Background Art

[0002] In recent years, LLC resonant converters have been widely used in server power supplies, renewable energy systems, and electric vehicle charging due to their excellent zero voltage switching (ZVS) and zero current shutdown (ZCS) characteristics. However, traditional LLC converters have significant limitations in applications with a wide input voltage range. To achieve voltage gain regulation, the switching frequency needs to be significantly adjusted away from the resonant frequency, resulting in an increase in magnetizing current, increased reactive circulating current losses, and reduced efficiency. In addition, the expansion of the frequency adjustment range complicates the design of magnetic components (such as transformers and resonant inductors). Especially when high voltage gain is required at the output end, the balance between the transformer ratio and the core volume further exacerbates the increase in system cost and volume.

[0003] To address the above issues, existing technologies have proposed a variety of improvement solutions. For example, the hybrid three-level configuration expands the gain range by switching between three-level and two-level modes, but the effect of widening the range is relatively limited. The dual-transformer structure expands the gain by changing the equivalent transformation ratio, but the core loss and conduction loss increase with the output voltage, limiting its efficiency performance under a wide input range.

[0004] Furthermore, traditional LLC converters generally use a passive rectification structure in a wide range of applications. The voltage stress of their diodes or synchronous rectifiers is directly related to the output voltage, resulting in high device selection costs and limited reliability in high-voltage output scenarios. Therefore, to achieve a wide gain range and high efficiency across the entire range, a wide-gain, multi-mode, switchable resonant converter is urgently needed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology. In order to address the problems of traditional LLC resonant converters in wide voltage range applications, such as excessive switching frequency adjustment range, complex magnetic component design, high device voltage stress, and reduced efficiency, a multi-mode resonant converter based on a variable structure rectifier unit is provided. By dynamically switching the secondary switch tube of the rectifier unit, bridge rectification, double voltage, and quadruple voltage rectification operating modes are achieved. In combination with the soft switching characteristics of the full-bridge resonant topology, the switching frequency adjustment range is significantly reduced. The voltage stress of the diode and switching device is effectively reduced by connecting capacitors and switch tubes in series, while ensuring zero voltage switching (ZVS) within the full gain range. This solution effectively resolves the contradiction between efficiency and frequency range in wide input voltage scenarios, simplifies magnetic component design, and improves system power density and reliability.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A multi-mode resonant converter based on a variable structure rectifier unit includes an input terminal, an input capacitor, an inverter unit, a resonant cavity, a transformer, a rectifier unit, an output capacitor, and an output terminal arranged in sequence;

[0008] The inverter unit is composed of two bridge arms connected in parallel, each bridge arm is composed of two main switching tubes connected in series, a node A is set between the two main switching tubes in one bridge arm, and a node B is set between the two main switching tubes in the other bridge arm;

[0009] The input capacitor is connected in parallel with the input power supply; the A node is connected to the same-name end of the resonant cavity and the primary winding of the transformer in sequence, and the B node is connected to the opposite-name end of the primary winding of the transformer;

[0010] The rectifier unit includes a first secondary switch tube, a second secondary switch tube, a third secondary switch tube, a fourth secondary switch tube, a first diode, a second diode and a third diode;

[0011] The first secondary switch tube and the second diode are connected in series to form a first branch, and a C node is provided between the first secondary switch tube and the second diode;

[0012] The second secondary switch tube, the third secondary switch tube and the third diode are connected in series in sequence to form a second branch, a D node is provided between the second secondary switch tube and the third secondary switch tube, and an E node is provided between the third secondary switch tube and the third diode;

[0013] The first branch, the second branch and the output capacitor are connected in parallel with each other, the output capacitor is composed of the first output capacitor and the second output capacitor connected in series, and an F node is provided between the first output capacitor and the second output capacitor;

[0014] The like-name end of the secondary winding of the transformer is connected to the C node via the secondary resonant capacitor; the opposite-name end of the secondary winding of the transformer is connected to the E node;

[0015] A fourth secondary switch is connected between the D node and the F node, and the fourth secondary switch is connected in parallel with the first diode; the first diode is connected in parallel with the second secondary switch.

[0016] By dynamically switching the secondary switching tube in the rectifier unit, full-bridge rectification, double-voltage rectification and quadruple-voltage rectification operating modes can be achieved. The double-voltage rectification operating mode means that the output voltage is twice the output voltage of the full-bridge rectification operating mode, and the quadruple-voltage rectification operating mode means that the output voltage is four times the output voltage of the full-bridge rectification operating mode.

[0017] Furthermore, the transformer's magnetizing inductance is L m.

[0018] Furthermore, the resonant cavity is composed of a resonant capacitor and a resonant inductor connected in series, and the resonant inductor, the resonant capacitor, the excitation inductor and the secondary side resonant capacitor together constitute a full-bridge CLLC resonant conversion structure.

[0019] Furthermore, zero voltage switching (ZVS) can be achieved within the full load range.

[0020] The present invention also provides an application of a multi-mode resonant converter based on a variable structure rectifier unit, which is applied to photovoltaic power generation systems, electric vehicle charging devices and energy storage equipment.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] 1. By constructing a multi-mode rectification unit and dynamically switching rectification modes (bridge rectification, doubler rectification, and quadrupler rectification), the output voltage gain range is significantly widened, avoiding the problem of traditional LLCs requiring large frequency adjustments to cope with voltage changes. This structure achieves continuously adjustable output voltage through the preset and precise control of the mode switching threshold, combined with a narrow frequency adjustment range, which not only reduces the difficulty of magnetic device design but also improves conversion efficiency.

[0023] 2. The present invention adopts a control method of fixed duty cycle combined with variable frequency modulation, so that the main switch tube can achieve zero voltage turn-on (ZVS) under the entire operating range, significantly reducing switching losses and electromagnetic interference (EMI), and improving the overall energy efficiency level. It is particularly suitable for high-frequency and high-efficiency power conversion scenarios.

[0024] 3. The capacitors introduced in the rectifier unit, connected in series with the switching devices, significantly reduce the maximum voltage withstand by the switches and diodes. For example, in quadruple voltage mode, some diodes withstand only 1 / 4 of the output voltage, effectively supporting the use of low-voltage components, reducing component selection requirements and costs, and improving system reliability and integration.

[0025] 4. Since there is no need to increase the size of magnetic devices to cope with large frequency variations, and low voltage stress supports the selection of compact devices, this solution significantly reduces the volume of magnetic components and the overall size of the system, and improves power density. It is particularly suitable for application scenarios that are sensitive to size and weight, such as portable energy storage devices and high-density photovoltaic systems.

[0026] 5. The rectification mode automatically switches according to the input voltage, ensuring that the system operates in the optimal gain range under different input voltages, while avoiding output voltage disturbances caused by sudden changes, making the output characteristics more stable and reliable, and improving the power supply quality on the user side.

[0027] 6. The rectifier unit of the present invention can be seamlessly integrated into the existing LLC topology framework, adapts to the mainstream converter structure, has good system compatibility and scalability, and is conducive to standardization and industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the variable structure multi-mode rectifier switch device of the present invention.

[0029] Figure 2 It is a structural diagram of the CLLC resonant converter in full-bridge rectification mode.

[0030] Figure 3 It is a structural diagram of the CLLC resonant converter in double voltage rectification mode.

[0031] Figure 4 It is a structural diagram of the CLLC resonant converter in the quadruple voltage rectification working mode.

[0032] Figure 5 These are the gain curves of the CLLC resonant converter in three modes.

[0033] Figure 6 This is the simulation waveform of the four-fold voltage rectification.

[0034] Figure 7 This is the double voltage rectifier simulation waveform.

[0035] Figure 8 It is the bridge rectifier simulation waveform. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] like Figure 1 As shown, this embodiment provides a multi-mode resonant converter based on a variable structure rectifier unit, including an input terminal, an input capacitor, an inverter unit, a resonant cavity, a transformer, a rectifier unit, an output capacitor and an output terminal arranged in sequence. In this embodiment, the input terminal voltage and the output terminal voltage are V in and V o , the output end is connected to a load R o .

[0038] The inverter unit consists of two bridge arms connected in parallel. One bridge arm consists of a main switch S1 and a main switch S3 connected in series. A node A is set between the main switches S1 and S3. The other bridge arm consists of a main switch S2 and a main switch S4 connected in series. A node B is set between the main switches S2 and S4.

[0039] Input capacitor C in The above-mentioned bridge arms are connected in parallel; Node A is connected to the same-name end of the resonant cavity and the primary winding of the transformer T in turn, and Node B is connected to the opposite-name end of the primary winding of the transformer T; the resonant capacitor C r and resonant inductor L r The transformers are composed in series, and the excitation inductances are L m , the transformer turns ratio is n:1.

[0040] The rectifier unit includes a secondary switch tube Q1, a secondary switch tube Q2, a secondary switch tube Q3, a secondary switch tube Q4, a diode D1, a diode D2 and a diode D3;

[0041] The secondary switch tube Q1 and the diode D2 are connected in series to form a first branch, and a node C is provided between the secondary switch tube Q1 and the diode D2;

[0042] The secondary switch tube Q2, the secondary switch tube Q3 and the diode D3 are sequentially connected in series to form a second branch. A node D is provided between the secondary switch tube Q2 and the secondary switch tube Q3, and a node E is provided between the secondary switch tube Q3 and the diode D3.

[0043] The first branch, the second branch and the output capacitor are connected in parallel. The output capacitor is composed of the output capacitor C o1 and output capacitor C o2 are connected in series, the output capacitor C o1 and output capacitor C o2 There is an F node between them;

[0044] The same-name end of the secondary winding of transformer T is connected to the secondary resonant capacitor C p Connected to node C; the opposite end of the secondary winding of transformer T is connected to node E; capacitor C p The capacitance across the two terminals is V Cp .

[0045] A secondary switch tube Q4 is connected between the D node and the F node. The secondary switch tube Q4 is connected in parallel with the diode D1. The diode D1 is connected in parallel with the secondary switch tube Q2.

[0046] By dynamically switching the secondary switching tube in the rectifier unit, full-bridge rectification, double-voltage rectification and quadruple-voltage rectification operating modes can be achieved. The double-voltage rectification operating mode means that the output voltage is twice the output voltage of the full-bridge rectification operating mode, and the quadruple-voltage rectification operating mode means that the output voltage is four times the output voltage of the full-bridge rectification operating mode.

[0047] In this embodiment, the resonant inductor is L r , the resonant capacitor is C r , excitation inductance L mand the secondary side resonant capacitor C p Form a full-bridge CLLC resonant conversion structure;

[0048] The inverter unit's four main switches, S1, S2, S3, and S4, operate at a fixed duty cycle, regulating the output voltage through variable frequency modulation to ensure zero voltage switching (ZVS) across the full gain range. This analysis demonstrates the wide-input voltage regulation effect under three operating conditions, using a voltage range of 25 to 100 V and an output voltage of 200 V as an example.

[0049] The LLC resonant converter is approximately analyzed using the Fundamental Harmonic Approximation (FHA) method. The equivalent AC resistance R ac The energy consumed is approximately equal to the energy consumed by the load, so

[0050]

[0051] Therefore, R ac It can be expressed as

[0052]

[0053] According to the definition of voltage gain of DC voltage converter nV o / V in , the expression of the DC voltage gain M of the CLLC resonant converter is approximately derived by using the equivalent fundamental wave analysis method:

[0054]

[0055] in, f s Expressed as the switching frequency, f r It is expressed as the resonant frequency, and h is the amplification factor of the output voltage.

[0056] (1) Full-bridge rectification mode: When the secondary switches Q1, Q2, Q3 and Q4 are all turned off, the structure of the CLLC resonant converter is as follows: Figure 2 As shown, the secondary side rectifier unit is a bridge rectifier, and the capacitor C p Plays the role of isolating DC, V Cp The voltage is 0, h is 1, and the equivalent AC resistance expression in this mode is:

[0057]

[0058] The corresponding quality factor Q n1 The expression is

[0059]

[0060] The DC voltage gain M1 of the CLLC resonant converter is expressed as

[0061]

[0062] (2) Double voltage rectification mode: When the secondary switches Q2, Q3 and Q4 are all turned off, and the drive signal of the secondary switch Q1 is consistent with that of the main switch S2, the structure of the CLLC resonant converter is as follows: Figure 3 As shown, the secondary side rectifier unit is a double voltage rectifier, and the output voltage is twice the output voltage of the full bridge rectifier mode, V Cp The voltage is V o / 2, h is 2, the equivalent AC resistance expression in this mode is

[0063]

[0064] The corresponding quality factor Q n2 The expression is

[0065]

[0066] The DC voltage gain M2 of the CLLC resonant converter in this mode is expressed as

[0067]

[0068] (3) Quadruple voltage rectification mode: When the switching frequency of the secondary switches Q2 and Q3 is 1 / 2 times that of the main switches (S1-S4), the drive signal of the secondary switch Q4 is consistent with that of the main switch S1, and the drive signal of the secondary switch Q1 is consistent with that of the main switch S2, the structure of the LLC resonant converter is as follows: Figure 4 As shown, the secondary side rectifier unit is a quadruple voltage rectifier, and the output voltage is four times the output voltage of the full-bridge rectifier mode, V Cp The voltage is V o / 4, h is 4, the equivalent AC resistance expression in this mode is

[0069]

[0070] The corresponding quality factor Q n3 The expression is

[0071]

[0072] The DC voltage gain M3 of the CLLC resonant converter in this mode is expressed as

[0073]

[0074] The gain curves corresponding to full-bridge rectification, double voltage rectification and quadruple voltage rectification modes are as follows: Figure 5As shown, two switching voltage thresholds V e1 and V e2 (V e1 <V e2 ), when the input voltage is higher than V e2 The CLLC resonant converter is in full-bridge rectification mode. When the input voltage is lower than V e2 and higher than V e1 The CLLC resonant converter is in double voltage rectification mode. When the input voltage is lower than V e1 When , the CLLC resonant converter is in the quadruple voltage rectification mode. The bold part of the gain curve in the figure is the frequency modulation range and working range of the CLLC resonant converter.

[0075] The following simulation is taken as an example. The input voltage range is 25~100V and the resonant capacitor C r is 170n, the resonant inductor L r The output power is 250W and the output voltage is 200V. ds Represents the drain-source voltage of the main switch tube S1, V gs It represents the driving signal of the main switch tube S1. In the simulation software, the conduction is represented by a high level 1, and the shutdown is represented by a low level 0. m Expressed as the excitation current, i r Expressed as resonant current, V o Expressed as output voltage, i rec Expressed as rectified output current.

[0076] When the input voltage is ≤49V and ≥25V, the DC converter is in quadruple voltage rectification. Taking the input voltage of 25V as an example, the simulation waveform is as follows Figure 6 As shown, the main switch tube S1 achieves zero voltage turn-on, the secondary side achieves zero current turn-off, and realizes four-fold voltage rectification, and the output voltage is approximately 200V.

[0077] When the input voltage is ≤69V and ≥50V, the DC converter is in double voltage rectification. Taking the input voltage of 50V as an example, the simulation waveform is as follows Figure 7 As shown, the main switch tube S1 achieves zero voltage turn-on, the secondary side achieves zero current turn-off, and double voltage rectification is achieved, and the output voltage is approximately 200V.

[0078] When the input voltage is ≤100V and ≥70V, the DC converter is in full-bridge rectification. Taking the input voltage of 100V as an example, the simulation waveform is as follows: Figure 8 As shown, the main switch tube S1 achieves zero voltage turn-on, the secondary side achieves zero current turn-off, and full-bridge rectification is achieved, and the output voltage is approximately 200V.

[0079] In summary:

[0080] 1. The CLLC resonant converter provided in this embodiment has a wide voltage gain range and a narrow frequency range: the gain curves of the DC converter in three modes are as follows: Figure 5 As shown, controllable switches Q1, Q2, Q3, and Q4 are introduced into the secondary rectifier unit. Adjusting the switching frequency and drive signal of these controllable switches changes the rectifier unit and switches between different gain modes. Different mode switching thresholds are set based on the actual gain range and frequency range of the converter. When the input voltage changes, the rectifier unit mode is switched according to the corresponding operating conditions. By adjusting the switching frequency (PFM) and duty cycle, a smooth transition is achieved, avoiding voltage fluctuations, and thus realizing a DC converter with a wide gain and narrow frequency range.

[0081] 2. The voltage stress of the secondary switch tube of the rectifier unit is small: when the rectifier unit is a full-bridge rectifier, the secondary switch tubes Q1, Q4 and diode D3 only bear V o / 2 voltage stress, the secondary switches Q2, Q3 and diode D2 only withstand V o / 3 voltage stress; when the rectifier unit is double voltage rectifier, the switch tubes Q2, Q3 and diode D3 only bear V o / 2 voltage stress, diode D2 withstands V o When the rectifier unit is a quadruple voltage rectifier, the diode D3 only bears the voltage stress of V o / 4 voltage stress, diode D2 and secondary switches Q2, Q3 only withstand V o / 2 voltage stress.

[0082] The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention. The above specific embodiments are merely illustrative and not restrictive. Without departing from the scope of the present invention and the scope of protection of the claims, those skilled in the art may make various specific modifications based on the teachings of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A multi-mode resonant converter based on a variable structure rectifier unit, characterized in that: It includes an input side power supply, an input capacitor, an inverter unit, a resonant cavity, a transformer, a rectifier unit, an output capacitor and an output terminal which are arranged in sequence; The inverter unit is composed of two bridge arms connected in parallel, each bridge arm is composed of two main switching tubes connected in series, a node A is set between the two main switching tubes in one bridge arm, and a node B is set between the two main switching tubes in the other bridge arm; The input capacitance (C in ) is connected in parallel with the input power supply; Node A is connected to the same-name end of the resonant cavity and the primary winding of the transformer (T) in sequence, and Node B is connected to the opposite-name end of the primary winding of the transformer (T); The rectifier unit comprises a first secondary switch tube (Q1), a second secondary switch tube (Q2), a third secondary switch tube (Q3), a fourth secondary switch tube (Q4), a first diode (D1), a second diode (D2) and a third diode (D3); The first secondary switch tube (Q1) and the second diode (D2) are connected in series to form a first branch, and a C node is provided between the first secondary switch tube (Q1) and the second diode (D2); A second secondary switch tube (Q2), a third secondary switch tube (Q3) and a third diode (D3) are sequentially connected in series to form a second branch; a D node is provided between the second secondary switch tube (Q2) and the third secondary switch tube (Q3); and an E node is provided between the third secondary switch tube (Q3) and the third diode (D3); The first branch, the second branch and the output capacitor are connected in parallel. The output capacitor consists of the first output capacitor (C o1 ) and the second output capacitor (C o2 ) are connected in series, the first output capacitor (C o1 ) and the second output capacitor (C o2 ) are provided with an F node between them; The same-name end of the secondary winding of the transformer (T) is connected to the secondary resonant capacitor (C p ) is connected to the C node; the opposite end of the secondary winding of the transformer (T) is connected to the E node; A fourth secondary switch tube (Q4) is connected between the D node and the F node, and the fourth secondary switch tube (Q4) is connected in parallel with the first diode (D1); the first diode (D1) is connected in parallel with the second secondary switch tube (Q2); by dynamically switching the secondary switch tubes in the rectifier unit, full-bridge rectification, double-voltage rectification and quadruple-voltage rectification operating modes can be realized, the double-voltage rectification operating mode means that the output voltage is twice the output voltage of the full-bridge rectification operating mode, and the quadruple-voltage rectification operating mode means that the output voltage is four times the output voltage of the full-bridge rectification operating mode.

2. The multi-mode resonant converter based on a variable structure rectifier unit according to claim 1, characterized in that: The transformer's magnetizing inductance is L m . According to a multi-mode resonant converter based on a variable structure rectifier unit according to claim 1, it is characterized in that the resonant cavity is composed of a resonant capacitor and a resonant inductor connected in series, and the resonant inductor, the resonant capacitor, the excitation inductor and the secondary side resonant capacitor together constitute a full-bridge CLLC resonant conversion structure.

3. The multi-mode resonant converter based on a variable structure rectifier unit according to claim 1, characterized in that: It can achieve zero voltage switching (ZVS) within the full load range.

4. An application of a multi-mode resonant converter based on a variable structure rectifier unit, characterized in that: Applied to photovoltaic power generation systems, electric vehicle charging devices and energy storage equipment.

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