Wide-range input multi-mode LLC resonant converter and control method thereof

Abstract

The invention discloses a wide-range input multi-mode LLC resonant converter and a control method thereof, and belongs to the technical field of power electronics. The LLC resonant converter comprises a full-bridge inversion unit, a resonant cavity, a high-frequency transformer and a rectification unit. The full-bridge inversion unit is composed of switch tubes S1-S4, the high-frequency transformer is a transformer with a center tap and a transformation ratio of n: 1: 1, the rectification unit is composed of switch tubes S5-S6 and diodes D1-D2, and the variable turn ratio structure is composed of auxiliary switches Q1 and Q2. According to the control method, three operation modes are obtained through half-bridge and full-bridge switching of the inversion unit and combination of the turns ratio of the transformer, and different modes correspond to different input voltages. The wide voltage range input of the LLC resonant converter can be realized through the circuit reconstruction method, the converter can realize soft switching in different operation modes, the efficiency of the converter is improved, and the LLC resonant converter can be widely applied to charging occasions with a wide voltage input range.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically, to a wide voltage range input multimode LLC resonant converter based on topology reconstruction and its control method. Background Technology

[0002] With the increasing problems of energy shortages and environmental pollution, more and more experts and scholars are focusing on renewable energy sources such as wind, solar, and tidal power to achieve sustainable energy utilization. However, renewable energy power generation units are greatly affected by the environment, and changes in the environment can cause fluctuations in their output voltage. Therefore, renewable energy power generation has the characteristic of wide-range voltage output. In order to utilize renewable energy efficiently, safely, and stably, a high-efficiency DC-DC converter with electrical isolation and wide voltage range input capability is required.

[0003] LLC resonant converters are widely used in electric vehicles, battery chargers, photovoltaics, and fuel cells due to their advantages such as high efficiency, high power density, low switching losses, and small size. However, traditional LLC resonant converters suffer from problems such as excessively wide switching frequencies and high electromagnetic interference when achieving wide voltage range applications, leading to a decrease in converter efficiency. LLC resonant converters using phase-shift control have a fixed switching frequency and are easy to design with magnetic components, but excessively large phase shift angles can lead to increased losses and reduced efficiency. To achieve a wide voltage gain range while maintaining high efficiency, experts and scholars both domestically and internationally have conducted various research and improvements. In the research of wide voltage gain LLC resonant converters, the concept of topology reconstruction has received widespread attention. By adding or removing switching devices and combining different switching signals on traditional LLC resonant converters, various topologies with multiple operating modes have been constructed, achieving a wider voltage gain range.

[0004] Current improvements include constructing a dual-cavity resonator with three bridge arms in the rectifier unit, offering four operating modes and achieving a voltage gain of up to 6 times. However, in the single half-bridge mode, the non-operating resonator experiences significant current, reducing converter efficiency. Alternatively, a topology reconfiguration approach using dual cavities, with half-bridge and full-bridge inverter units and bridge and voltage doubler rectifier units, achieves ultra-wide voltage gain over a narrow frequency range. However, at low voltages, parasitic capacitance in the rectifier switches causes output voltage fluctuations, reducing converter efficiency. Other approaches aim to achieve wide gain by changing the control method. One scholar proposed a fixed-frequency voltage doubler LLC resonant converter, introducing an auxiliary switch on the secondary side to control the rectifier bridge's operation. The shared resonant element between the two cavities solves the current imbalance problem, but the converter's gain range is relatively low. Summary of the Invention

[0005] 1. The technical problem that the invention aims to solve To address the challenges of achieving a wide input voltage range and high efficiency in LLC resonant converters, this invention aims to overcome the aforementioned problems in conventional technologies by providing a wide-range input multi-mode LLC resonant converter and its control method. This converter is suitable for isolated DC-DC converters with a wide input voltage range, high power density, and high conversion efficiency. The invention features a simple topology and control mechanism, enables soft switching across the entire voltage range, and achieves high efficiency.

[0006] 2. Technical Solution To achieve the above objectives and technical effects, the technical solution provided by this invention is as follows: This invention provides a wide voltage range input multi-mode LLC resonant converter based on topology reconstruction, the structure of which includes a full-bridge inverter unit, a resonant cavity, a high-frequency transformer, a variable turns ratio structure, and a full-bridge rectifier unit; the full-bridge inverter unit includes a DC voltage source V in Switches S1-S4; the full-bridge inverter unit is connected to the resonant cavity, which includes a series resonant inductor L. r Magnetizing inductance L m Series resonant capacitor C r The resonant cavity is connected to a high-frequency transformer, which is a center-tapped transformer with a turns ratio of n:1:1. The high-frequency transformer is connected to a full-bridge rectifier circuit via a variable turns ratio structure. This structure includes auxiliary switches Q1 and Q2, each consisting of two common-source MOSFETs. The full-bridge rectifier unit includes switching transistors S5-S6, diodes D1-D2, and an output capacitor C. o With load R.

[0007] Furthermore, in the aforementioned wide voltage range input multi-mode LLC resonant converter, in the full-bridge inverter unit, switches S1 and S2 are connected in series to form the first bridge arm, and switches S3 and S4 are connected in series to form the second bridge arm, wherein the power supply V... in The positive terminals of transistors S1 and S3 are connected to their drains, respectively, while the sources of transistors S2 and S4 are connected to the DC voltage source V. in The negative terminal is connected.

[0008] Furthermore, in the aforementioned wide voltage range input multi-mode LLC resonant converter, the series resonant inductor L in the resonant cavity... r One end of the capacitor is connected to the midpoint of the first bridge arm, and the other end is connected to the same-name terminal of the high-frequency transformer. One end of the series resonant capacitor Cr is connected to the midpoint of the second bridge arm, and the other end is connected to the opposite-name terminal of the primary winding of the high-frequency transformer. The primary winding of the high-frequency transformer is connected to the magnetizing inductor L. m In parallel connection, the secondary side of the high-frequency transformer is connected to the auxiliary switch Q1, and the center tap is connected to the auxiliary switch Q2.

[0009] Furthermore, in the aforementioned wide-voltage-range input multi-mode LLC resonant converter, the full-bridge rectifier unit contains a third bridge arm formed by the series connection of switch S5 and diode D1, and a fourth bridge arm formed by the series connection of switch S6 and diode D2. The secondary side of the high-frequency transformer, with the same-name terminal and center tap connected to the midpoint of the third bridge arm via auxiliary switches Q1 and Q2, and the opposite-name terminal connected to the midpoint of the fourth bridge arm, connects the third bridge arm, the fourth bridge arm, and the output capacitor C. o It is connected in parallel with the load R.

[0010] Furthermore, the aforementioned wide voltage range input multi-mode LLC resonant converter, by controlling auxiliary switches Q1 and Q2, changes the transformer turns ratio and the structure of the inverter unit, enabling the converter to operate in half-bridge single-winding (HB-S) mode, full-bridge single-winding (FB-S) mode, and full-bridge dual-winding (FB-D) mode. When auxiliary switch Q2 is on and Q1 is off, the transformer ratio is n:1, switches S3 and S4 are off, and switches S1 and S2 alternately conduct to form a half-bridge inverter circuit, and the converter operates in half-bridge single-winding mode. When auxiliary switch Q2 is on and Q1 is off, the transformer ratio is n:1, and switches S1 and S4, along with switches S2 and S3, alternately conduct to form a full-bridge inverter circuit, and the converter operates in full-bridge single-winding mode. When auxiliary switch Q1 is on and Q2 is off, the transformer ratio is n:2, and switches S1 and S4, along with switches S2 and S3, alternately conduct to form a full-bridge inverter circuit, and the converter operates in full-bridge dual-winding mode.

[0011] This invention also provides a control method for a wide-voltage-range input multi-mode LLC resonant converter. Based on the aforementioned wide-voltage-range input multi-mode LLC resonant converter, in half-bridge single-winding mode and full-bridge single-winding mode, the converter employs frequency conversion control. Switch S6 has the same conduction state as switches S1 and S4, and switch S5 has the same conduction state as switches S2 and S3. The two sets of switches conduct alternately, and the output voltage is adjusted by changing the switching frequency. In full-bridge dual-winding mode, the converter employs phase-shift control. Switch S6 has a phase-shift duty cycle D relative to the conduction state of switches S1 and S4, and switch S5 also has a phase-shift duty cycle D relative to the conduction state of switches S2 and S3. In this mode, the converter's switching frequency is fixed, and the two sets of switches conduct alternately. The output voltage is adjusted by regulating the magnitude of the phase-shift duty cycle D. This allows the LLC resonant converter to achieve soft switching of the switches and diodes in all three operating modes.

[0012] Furthermore, in the control method for the wide-voltage-range input multi-mode LLC resonant converter, the operating mode is determined by comparing the input voltage magnitude with a set voltage threshold. The transformer turns ratio is controlled by turning auxiliary switches Q1 and Q2 on and off. The switching between half-bridge and full-bridge modes of the inverter unit is controlled by turning inverter unit switches S1-S4 on and off. The input voltage thresholds, from largest to smallest, correspond to half-bridge single-winding mode, full-bridge single-winding mode, and full-bridge dual-winding mode, respectively.

[0013] 3. Beneficial effects Compared with existing known technologies, the technical solution provided by this invention has the following significant advantages: (1) The present invention provides a wide-range input multi-mode LLC resonant converter with wide voltage input characteristics. By using a high-frequency transformer with a turns ratio of n:1:1 and a center tap, and by adding two auxiliary switches Q1 and Q2 on the secondary side of the transformer, and with the control of the switching transistors of the full-bridge inverter unit, the switching transistors of the rectifier unit can perform synchronous rectification or phase-shift control. Three operating modes can be generated by combining different switching modes. Different operating modes correspond to different input voltages, and three different voltage gains can be achieved. The circuit design and control are simple, the input voltage transformation range is wide, and it is suitable for applications with varying input voltages, such as photovoltaic applications.

[0014] (2) The wide-range input multi-mode LLC resonant converter of the present invention can realize a wide range of voltage input through frequency conversion-phase shift hybrid control. During phase shift control, the circulating current loss can be reduced. The converter can realize soft switching of the switching transistor and diode in the whole range and has high efficiency.

[0015] (3) The wide-range input multi-mode LLC resonant converter of the present invention can effectively compress the switching frequency range when using frequency conversion control compared with the traditional LLC resonant converter, and the static operating point is closer to the resonant frequency. The proposed topology reconfigurable LLC resonant converter can well meet the requirements of different wide input circuit levels. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the topology of the wide voltage range input multi-mode LLC resonant converter of the present invention; Figure 2 This is a schematic diagram of the main operating waveforms of the converter in full-bridge dual-winding mode of the present invention using phase-shift control; Figure 3 This is a schematic diagram of the equivalent circuit of the converter of the present invention in the half-bridge single-winding mode; Figure 4 This is a schematic diagram of the equivalent circuit of the converter of the present invention in the full-bridge single-winding mode; Figure 5 This is a schematic diagram of the equivalent circuit of the converter of the present invention in the full-bridge dual-winding mode; Figure 6 This is a schematic diagram of the voltage gain curves for the converter in three modes according to the present invention; Figure 7 This is a schematic diagram of the state plane trajectory of the converter of the present invention in the full-bridge dual-winding mode; Figure 8 This is a schematic diagram of the AC equivalent circuit of the converter of the present invention obtained by the fundamental wave analysis method; Figure 9 This is a closed-loop control block diagram of the converter of the present invention. Detailed Implementation

[0017] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0018] Example Figure 1 This is a schematic diagram of the wide voltage range input multi-mode LLC resonant converter in this embodiment, as shown below. Figure 1 As shown, the converter includes: a full-bridge inverter unit, a resonant cavity, a high-frequency transformer, a variable turns ratio structure, and a full-bridge rectifier unit; the full-bridge inverter unit includes a DC voltage source V. in Switches S1-S4; the full-bridge inverter unit is connected to the resonant cavity, which includes a series resonant inductor L. r Magnetizing inductance L m Series resonant capacitor C r The resonant cavity is connected to a high-frequency transformer, which is a center-tapped transformer with a turns ratio of n:1:1. The high-frequency transformer is connected to a full-bridge rectifier circuit via a variable turns ratio structure. This structure includes auxiliary switches Q1 and Q2, each consisting of two common-source MOSFETs. The full-bridge rectifier unit includes switching transistors S5-S6, diodes D1-D2, and an output capacitor C. o With load R.

[0019] In the full-bridge inverter unit, the source of switch S1 and the drain of switch S2 are connected in series to form the first bridge arm, and the source of switch S3 and the drain of switch S4 are connected in series to form the second bridge arm, wherein the power supply V in The positive terminals of transistors S1 and S3 are connected to their drains, respectively, while the sources of transistors S2 and S4 are connected to the DC voltage source V. in The negative terminal is connected.

[0020] The series resonant inductor L in the resonant cavity r One end of the capacitor is connected to the midpoint of the first bridge arm, and the other end is connected to the same-name terminal of the primary winding of the high-frequency transformer. One end of the series resonant capacitor Cr is connected to the midpoint of the second bridge arm, and the other end is connected to the opposite-name terminal of the primary winding of the high-frequency transformer. The primary winding of the high-frequency transformer is connected to the magnetizing inductor L. m In parallel connection, the secondary side of the high-frequency transformer is connected to the auxiliary switch Q1, and the center tap is connected to the auxiliary switch Q2.

[0021] In the full-bridge rectifier unit, the drain of switch S5 and the anode of diode D1 are connected in series to form the third bridge arm, and the drain of switch S6 and the anode of diode D2 are connected in series to form the fourth bridge arm. The same-name terminal of the secondary side of the high-frequency transformer is connected to the center tap via auxiliary switches Q1 and Q2 to the midpoint of the third bridge arm, and the opposite-name terminal of the secondary side of the high-frequency transformer is connected to the midpoint of the fourth bridge arm. The third bridge arm, the fourth bridge arm, and the output capacitor C are connected together. o It is connected in parallel with the load R.

[0022] like Figure 2 The figure shows the key waveforms of the converter operating in full-bridge dual-winding mode. At this time, the converter operates at the series resonant frequency, and its resonant inductor current... i Lr With resonant capacitor voltage v Cr All waveforms are sinusoidal, with 10 key time points within one switching cycle. In this mode, switches S1 and S4 are complementary to switches S2 and S3 with a 50% duty cycle, and switch S6 is activated when switch S1 is turned on. t delay After conduction. In this mode, the switching frequency remains unchanged. f s It is always equal to the series resonant frequency f r By controlling the delayed conduction time t delay The output voltage of the converter is controlled to achieve phase shift control.

[0023] To simplify the analysis, the switching transistors and diodes in the converter are considered ideal components, and all components in the resonant cavity are also considered ideal components. The influence of parasitic parameters of the switching transistors on the resonance process is ignored during the analysis. The voltage gain of the converter is analyzed using the First Harmonic Approximation (FHA) method. Higher harmonics are ignored, and only the fundamental component is considered to simplify the circuit, reducing the nonlinear circuit to a linear circuit. In other words, the resonant converter is equivalent to a simple steady-state AC model. The AC equivalent impedance is defined as... R eq Quality factor Q for:

[0024] The transformer turns ratio is n:1; V o I o For output voltage and output current; R is the load resistance; L r For resonant inductance, C r It is a resonant capacitor.

[0025] The equivalent circuit diagram of the half-bridge single-winding (HB-S) mode is as follows: Figure 3 As shown, inverter unit switch S3 is always off, and S4 is always on, so the inverter unit operates in half-bridge mode. Auxiliary switch Q1 is off, and Q2 is on. The turns ratio of the high-frequency transformer is... n 1. In the inverter unit, switches S1 and S2 are complementary, operating with a 50% duty cycle. In the rectifier unit, switches S6 and S1 are in the same conduction state, and S5 and S2 are in the same conduction state. This mode operates using frequency conversion control, and its working principle is similar to that of a half-bridge LLC resonant converter. Based on the basic equivalent model and performing a Fourier series expansion on the resonant cavity input voltage, the voltage gain formula for the half-bridge single-winding mode can be obtained from the converter's transfer function and by taking the modulus:

[0026] Among them, V AB_1 V is the effective value of the fundamental voltage of the resonant cavity input voltage. sec_1 This is the effective value of the secondary fundamental voltage referred to the primary side.

[0027] definition k For resonant inductance L r With excitation inductance L m inductance ratio, f n The normalized switching frequency has the following value:

[0028] in, f s For switching frequency, f r The resonant frequency of the resonant cavity in series. f m This is the resonant frequency of the parallel resonant cavity. k , Q , f n Substituting the values, we can obtain the voltage gain formula for the half-bridge single-winding mode:

[0029] The equivalent circuit diagram of the full-bridge single-winding (FB-S) mode is as follows: Figure 4 As shown, the inverter bridge is in full-bridge mode, auxiliary switch Q1 is off, Q2 is on, and the high-frequency transformer turns ratio is...n 1. In the inverter unit, switches S1 and S4 are in the same conduction state, and S2 and S3 are in the same conduction state. Switches S1 and S4 are complementary to S2 and S3. In the rectifier unit, switch S6 is in the same conduction state as S1, and S5 is in the same conduction state as S2. This mode operates using frequency conversion control, and its working principle is similar to that of a full-bridge LLC resonant converter. Similarly, the voltage gain formula for the full-bridge single-winding mode can be obtained:

[0030] The equivalent circuit diagram of the full-bridge dual-winding (FB-D) mode is as follows: Figure 5 As shown, the inverter bridge is in full-bridge mode, with auxiliary switch Q1 on and Q2 off, and the high-frequency transformer turns ratio is... n 2. Using time-domain analysis in full-bridge dual-winding mode, neglecting converter power losses, based on energy conservation, we have:

[0031] in , i Lr For inductor current, T s Define the phase shift angle as the period time. for:

[0032] In the linear charging section of the capacitor, the capacitor voltage is approximated as a constant value, let... Q =4 Q Duty cycle According to the inductor current at each stage i Lr (t) and capacitor voltage v Cr The expression (t) yields the gain of the converter in FB-D mode. M FB-D for:

[0033] in N = n / 2, combined with voltage gain M with normalized frequency f n The relationship between duty cycle D and the overall gain curve of the converter can be obtained, such as... Figure 6 As shown, the converter's three modes can achieve a smooth transition in voltage gain.

[0034] Figure 7 This is a schematic diagram of the state plane trajectory of the converter in full-bridge dual-winding mode, where the arc segment A0B0 represents the time interval from t0 to t1. vCr and i Lr The trajectory of the running state, the center of the arc is ( V in ,0) radius is r 1. The state trajectory of the resonant cavity of the converter during the process t1~t2 is as follows: Figure 7 The arc segment B0C0 has the same center and radius as A0B0. At times t2~t3... v Cr and i Lr The state trajectory is Figure 7 The arc segment C0D0 in the middle, the center of the arc is ( V in - NV o ,0), the radius of the arc is r 2. Figure 7 The circular arc segment D0E0 represents the converter at time t3~t4. v Cr and i Lr The state trajectory, where the center of the arc is ( V in - NV o ,0), the radius of the arc is r 2. In this process, the characteristic impedance is represented by Z0, where r 1. r 2 is:

[0035] t4~t5 v Cr and i Lr The state trajectory is Figure 7 The elliptical arc E0A1 in the diagram has its center point at ( ). V in ,0), characterized by Z1, major semi-axis a and short half shaft b They are respectively:

[0036] Figure 8 The diagram shows the AC equivalent circuit of the proposed LLC resonant converter obtained using the fundamental frequency analysis method. Figure 9The block diagram for the closed-loop control of the proposed LLC resonant converter is shown. The operating mode is determined by comparing the input voltage magnitude with the set voltage threshold. Frequency conversion control is used in half-bridge single-winding mode and full-bridge single-winding mode, while phase-shift control is used in full-bridge dual-winding mode. The transformer turns ratio is controlled by turning auxiliary switches Q1 and Q2 on and off, and the switching between half-bridge and full-bridge modes is controlled by turning inverter unit switches S1-S4 on and off. The input voltage thresholds, from largest to smallest, correspond to half-bridge single-winding mode, full-bridge single-winding mode, and full-bridge dual-winding mode. This control method achieves a stable voltage output.

[0037] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A wide-range input multi-mode LLC resonant converter, characterized in that: It includes a full-bridge inverter unit, a resonant cavity, a high-frequency transformer, a variable turns ratio structure, and a full-bridge rectifier unit; the full-bridge inverter unit includes a DC voltage source V. in Switches S1-S4; the full-bridge inverter unit is connected to the resonant cavity, which includes a series resonant inductor L. r Magnetizing inductance L m Series resonant capacitor C r The resonant cavity is connected to a high-frequency transformer, which is a center-tapped transformer with a turns ratio of n:1:

1. The high-frequency transformer is connected to a full-bridge rectifier circuit via a variable turns ratio structure, which includes auxiliary switches Q1 and Q2. The full-bridge rectifier unit includes switching transistors S5-S6, diodes D1-D2, and output capacitor C. o With load R.

2. The wide-range input multi-mode LLC resonant converter according to claim 1, characterized in that: The auxiliary switch consists of two common-source MOSFETs.

3. The wide-range input multi-mode LLC resonant converter according to claim 1, characterized in that: In the full-bridge inverter unit, the source of switch S1 and the drain of switch S2 are connected in series to form the first bridge arm, and the source of switch S3 and the drain of switch S4 are connected in series to form the second bridge arm, wherein the power supply V in The positive terminals of transistors S1 and S3 are connected to their drains, respectively, while the sources of transistors S2 and S4 are connected to the DC voltage source V. in The negative terminal is connected.

4. A wide-range input multi-mode LLC resonant converter according to claim 1, characterized in that: The series resonant inductor L in the resonant cavity r One end of the series resonant capacitor Cr is connected to the midpoint of the first bridge arm, and the other end is connected to the same-name terminal of the primary winding of the high-frequency transformer. One end of the series resonant capacitor Cr is connected to the midpoint of the second bridge arm, and the other end is connected to the opposite-name terminal of the primary winding of the high-frequency transformer. The primary winding of the high-frequency transformer is connected to the magnetizing inductor L. m in parallel.

5. A wide-range input multi-mode LLC resonant converter according to claim 1, characterized in that: The secondary side of the high-frequency transformer is connected to the auxiliary switch Q1 with a variable turns ratio structure, and the center tap of the high-frequency transformer is connected to the auxiliary switch Q2.

6. A wide-range input multi-mode LLC resonant converter according to claim 1, characterized in that: In the full-bridge rectifier unit, the drain of switch S5 and the anode of diode D1 are connected in series to form the third bridge arm, and the drain of switch S6 and the anode of diode D2 are connected in series to form the fourth bridge arm. The same-name terminal of the secondary side of the high-frequency transformer is connected to the center tap via auxiliary switches Q1 and Q2 to the midpoint of the third bridge arm, and the opposite-name terminal of the secondary side of the high-frequency transformer is connected to the midpoint of the fourth bridge arm. The third bridge arm, the fourth bridge arm, and the output capacitor C are connected together. o It is connected in parallel with the load R.

7. A wide-range input multi-mode LLC resonant converter according to any one of claims 1-6, characterized in that: By controlling auxiliary switches Q1 and Q2, the transformer turns ratio and the structure of the inverter unit are changed, enabling the converter to operate in half-bridge single-winding mode, full-bridge single-winding mode, and full-bridge dual-winding mode. When auxiliary switch Q2 is on and Q1 is off, the transformer turns ratio is n:1, switches S3 and S4 are off, and switches S1 and S2 alternately conduct to form a half-bridge inverter circuit, and the converter operates in half-bridge single-winding mode. When auxiliary switch Q2 is on and Q1 is off, the transformer turns ratio is n:1, and switches S1 and S4, along with switches S2 and S3, alternately conduct to form a full-bridge inverter circuit, and the converter operates in full-bridge single-winding mode. When auxiliary switch Q1 is on and Q2 is off, the transformer turns ratio is n:2, and switches S1 and S4, along with switches S2 and S3, alternately conduct to form a full-bridge inverter circuit, and the converter operates in full-bridge dual-winding mode.

8. A control method for a wide-range input multi-mode LLC resonant converter according to any one of claims 1-7, characterized in that: In half-bridge single-winding mode and full-bridge single-winding mode, the converter uses frequency conversion control. Switch S6 is in the same conduction state as switches S1 and S4, and switch S5 is in the same conduction state as switches S2 and S3. The two sets of switches conduct alternately, and the output voltage is adjusted by changing the switching frequency. In full-bridge dual-winding mode, the converter uses phase-shift control. Switch S6 has a phase-shift duty cycle D relative to the conduction state of switches S1 and S4. Switch S5 has a phase-shift duty cycle D relative to the conduction state of switches S2 and S3. In this mode, the converter switching frequency is fixed, and the two sets of switches conduct alternately. The output voltage is adjusted by adjusting the magnitude of the phase-shift duty cycle D. This allows the LLC resonant converter to achieve soft switching of the switches and diodes in the three operating modes.

9. The control method for a wide-range input multi-mode LLC resonant converter according to claim 8, characterized in that: The operating mode is determined by comparing the input voltage with the set voltage threshold. The transformer turns ratio is controlled by turning auxiliary switches Q1 and Q2 on and off. The switching between half-bridge and full-bridge mode of the inverter unit is controlled by turning inverter unit switches S1-S4 on and off. The input voltage thresholds, from largest to smallest, correspond to half-bridge single-winding mode, full-bridge single-winding mode, and full-bridge dual-winding mode, respectively.

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