Method for realizing full-bridge-half-bridge seamless switching of LLC resonant converter based on hybrid modulation

Abstract

The invention discloses a method for realizing full-bridge-half-bridge seamless switching of an LLC resonant converter based on hybrid modulation, and aims to solve the problems of resonant cavity energy abrupt change, output voltage fluctuation and resonant current impact caused by the difference of equivalent input voltage gain ratios of full-bridge (FB for short) and half-bridge (Half-bridge (HB for short) modes during topological switching of the LLC resonant converter. And meanwhile, the problems that the switching working frequency matching precision is low and the system is difficult to quickly enter a steady state due to lack of an FB and HB unified time domain model are solved, so that stable and efficient operation of the LLC resonant converter in a wide voltage gain range is realized. Meanwhile, according to the control method, the gain-frequency relation is solved in real time by constructing a time domain model with unified FB and HB modes, and continuous energy transition of the resonant cavity is guided in combination with hybrid modulation seamless switching control, so that the voltage gain adjustment range can be widened without introducing extra hardware, and the parameter adaptability and operation robustness of the control system are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronic conversion, and relates to a method for realizing full-bridge-half-bridge seamless switching of an LLC resonant converter based on hybrid modulation. BACKGROUND

[0002] In the fields of new energy storage, electric vehicle charging and discharging, industrial high-frequency power supply and the like with strict requirements on voltage regulation range, an LLC resonant converter has become a core power conversion unit due to its advantages of zero voltage switching (ZVS) characteristics, high conversion efficiency and low electromagnetic interference. However, the LLC resonant converter with a single topology structure has obvious limitations: a full-bridge (FB) topology is suitable for a high-voltage input and a low-gain output scene, but a high gain required for low-voltage input exceeds its inherent regulation range; an equivalent gain of a half-bridge (HB) topology is about half of that of the FB topology, and is suitable for a low-voltage input and a high-gain output requirement, but its inherent high-gain characteristic is excessive when the high-voltage input is used, and the switching loss and electromagnetic interference are greatly increased by frequency increasing and voltage reducing. Therefore, the FB-HB switching method for widening the voltage gain range has become a key technical direction for the LLC resonant converter to adapt to wide operating conditions.

[0003] The FB-HB switching method of the existing LLC resonant converter mainly includes four types: 1) threshold trigger hard switching technology, which directly switches the power tube driving signal to change the topology when the voltage reaches the threshold value by setting a fixed input voltage threshold, and the switching process does not interfere with the resonant cavity state; 2) frequency compensation switching technology, which pre-sets the frequency compensation values of the FB and HB modes based on experimental data, and adjusts the frequency by steps to offset part of the gain mutation when switching; 3) a multi-cycle gradual adjustment strategy using duty ratio, which constructs a multi-cycle transition process, fixes the switching frequency of the original topology and gradually adjusts the duty ratio of the power tube, and completes the switching after the resonant cavity equivalent voltage adapts to the new topology, and then restores the duty ratio to the rated value; and 4) hardware buffer auxiliary switching technology, which increases an auxiliary buffer capacitor, a clamping diode or an additional switch tube in the main circuit to suppress the current impact during switching.

[0004] However, the above-mentioned FB-HB switching methods of the existing LLC resonant converter all have some defects that cannot be ignored: First, the existing frequency compensation switching technology lacks a unified mathematical model of the FB and HB modes, relies on fixed compensation parameters, cannot adapt to load changes and device parameter drift, has low frequency matching accuracy after switching, and needs to obtain the working frequency by table lookup method, which is very time-consuming; Second, the existing threshold-triggered hard switching technology does not provide over-control of the resonant cavity energy. The abrupt change in the equivalent input voltage gain ratio between FB and HB modes directly causes a severe surge in resonant current and a large fluctuation in output voltage. In extreme cases, this can lead to overcurrent damage to power devices. Third, the existing multi-cycle stepwise adjustment strategy using duty cycle also relies on the experimentally preset adjustment step size and number of cycles, which has poor adaptability and takes a long time for the complete transition process, which can easily destroy the ZVS soft switching condition and increase switching losses. Fourth, existing hardware buffer-assisted switching technology requires additional power devices and drive circuits, which not only increases system cost and size, but also increases circuit topology complexity, reduces the long-term reliability of the system, and significantly increases the failure rate of auxiliary circuits under harsh operating conditions. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a method for achieving seamless full-bridge to half-bridge switching of LLC resonant converters based on hybrid modulation. The aim is to solve the following problems: First, existing frequency compensation switching technologies lack a unified mathematical model for FB and HB modes, rely on fixed compensation parameters, cannot adapt to load changes and device parameter drift, have low frequency matching accuracy after switching, require table lookup to obtain the operating frequency, and involve time-consuming experimental data collection. Second, existing threshold-triggered hard switching technologies do not provide transitional control of resonant cavity energy, leading to abrupt changes in the equivalent input voltage gain ratio between FB and HB modes, directly causing severe resonant current surges and large output voltage fluctuations, potentially resulting in overcurrent damage to power devices in extreme cases. Third, existing multi-cycle gradual adjustment strategies using duty cycles also rely on experimentally preset adjustment step sizes and cycle numbers, resulting in poor adaptability, long transition times, and potential disruption of ZVS soft-switching conditions and increased switching losses. Fourth, existing hardware buffered auxiliary switching technologies require additional power devices and drive circuits, increasing system cost, size, and circuit topology complexity, reducing long-term system reliability, and significantly increasing auxiliary circuit failure rates under harsh operating conditions.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for achieving seamless full-bridge to half-bridge switching of an LLC resonant converter based on hybrid modulation is provided, comprising the following steps: (1) Obtain the device parameters of the LLC resonant converter, and obtain the unified time-domain model of the LLC resonant converter FB and HB based on the device parameters; (2) Obtain the corresponding frequency error based on the unified time-domain model of FB and HB obtained in step (1). And determine the frequency error. Is it greater than the preset reference frequency error value? If yes, return to step (1); otherwise proceed to step (3). (3) The frequency error obtained from step (2) Obtain the current operating frequency f of the LLC resonant converter. n The calculation flowchart is as follows Figure 3 As shown; (4) According to the output voltage V o The input voltage V of the LLC resonant converter is among the device parameters of the LLC resonant converter obtained in step (1). in and resonant capacitor voltage Perform per-unit scaling separately to obtain the per-unit normalized input voltage V of the LLC resonant converter. inN and normalized resonant voltage v CrN and in accordance with For the resonant inductor current of the LLC resonant converter and excitation inductor current Perform per-unit scaling separately to obtain the normalized resonant current i of the LLC resonant converter after per-unit scaling. LrN and normalized excitation current , where Z represents the characteristic impedance of the LLC resonant converter; (5) Based on the normalized input voltage V of the LLC resonant converter obtained in step (4) inN Normalized resonant voltage v CrN Normalized resonant current i LrN and normalized excitation current Establish the state plane trajectory of the LLC resonant converter in FB mode and HB mode; (6) Determine the input voltage V in the device parameters of the LLC resonant converter obtained in step (1). in Is it greater than the preset switching threshold voltage V of the LLC resonant converter? th If yes, proceed to step (7); otherwise, proceed to step (10). (7) Determine whether the LLC resonant converter is running to the end of the negative half-cycle of the three-element resonance or to the end of the positive half-cycle of the three-element resonance. If it is running to the end of the negative half-cycle of the three-element resonance, proceed to step (8). If it is running to the end of the positive half-cycle of the three-element resonance, proceed to step (9). (8) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB and HB modes, the switching time from the LLC resonant converter switching from FB mode to HB mode until the end of the negative half-cycle of the three-element resonant circuit is obtained. and duty cycle Then proceed to step (13); (9) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB mode and HB mode, the switching time from the LLC resonant converter switching from FB mode to HB mode until the end of the positive half-cycle of the three-element resonant circuit is obtained. and duty cycle Then proceed to step (13); (10) Determine whether the LLC resonant converter is running to the end of the negative half-cycle of the three-element resonance or to the end of the positive half-cycle of the three-element resonance. If it is running to the end of the negative half-cycle of the three-element resonance, proceed to step (11). If it is running to the end of the positive half-cycle of the three-element resonance, proceed to step (12). (11) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB and HB modes, the switching time from HB mode to the end of the negative half-cycle of the three-element resonant circuit when the LLC resonant converter switches from HB mode to FB mode is obtained. and duty cycle Then proceed to step (13); (12) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB and HB modes, the switching time from HB mode to FB mode of the LLC resonant converter until the end of the positive half-cycle of the three-element resonant circuit is obtained. and duty cycle Then proceed to step (13); (13) The switching time from FB mode to HB mode when the LLC resonant converter switches from FB mode to HB mode, as obtained in step (8), until the end of the negative half-cycle of the three-element resonant circuit. and duty cycle The switching time from FB mode to HB mode when the LLC resonant converter obtained in step (9) switches to the end of the positive half-cycle of the three-element resonant circuit. and duty cycle The switching time from HB mode to FB mode when the LLC resonant converter obtained in step (11) switches to the end of the negative half-cycle of the three-element resonant circuit. and duty cycle And when the LLC resonant converter obtained in step (12) switches from HB mode to FB mode, it runs until the end of the positive half-cycle of the three-element resonant circuit. and duty cycle The switching transistors of the LLC resonant converter are controlled to obtain the control result.

[0007] Preferably, the device parameters of the LLC resonant converter include the resonant inductance L of the LLC resonant converter. r The resonant capacitance C of the LLC resonant converter r The excitation inductance L of the LLC resonant converter m The input voltage V of the LLC resonant converter in The output voltage V of the LLC resonant converter o The equivalent resistance R of the output load of the LLC resonant converter, the transformer turns ratio n of the LLC resonant converter, and the operating frequency f of the LLC resonant converter. s .

[0008] Preferably, in step (1), the unified time-domain model of the LLC resonant converter FB and HB obtained based on the device parameters is obtained using the following formula: ; Where k is the control coefficient (1 for HB, 2 for FB). The resonant inductor L in the LLC resonant converter r and resonant capacitor C r The time of resonance, This refers to the three-element resonant angular frequency of the LLC resonant converter. Let A be the inductance ratio, and let B, C, and D be the key intermediate variables used to describe the state relationships in the FB and HB time-domain models.

[0009] Preferably, in step (2), the frequency error is calculated. The following formula is used: ; Step (3) is to obtain the current operating frequency f of the LLC resonant converter using the following formula. n : ; The characteristic impedance Z in step (4) is obtained using the following formula: .

[0010] Preferably, the state plane trajectory of the LLC resonant converter in FB mode and HB mode includes the state plane trajectory in binary resonance and the state plane trajectory in three-element resonance, and the ordinate of the state plane trajectory is the normalized resonant voltage i. LrN The horizontal axis represents the normalized resonant current v. CrN ; Step (5) Based on the normalized input voltage V of the LLC resonant converter inNNormalized resonant voltage i LrN With normalized resonant current v CrN The state plane trajectory in the FB mode of a two-element resonance is obtained using the following formula: ; ; Where, r FB1 Let r be the radius of the unit circle of the positive half-cycle of the binary resonance in FB mode. FB2 V is the radius of the unit circle of the negative half-cycle of the binary resonance in FB mode. in1N This is the normalized input voltage of the LLC resonant converter in FB mode; Secondly, the state plane trajectory in the HB mode of a binary resonance is obtained using the following formula: ; ; Where, r HB1 Let r be the radius of the unit circle of the positive half-cycle of the binary resonance in HB mode. HB2 V is the radius of the unit circle of the negative half-cycle of the binary resonance in HB mode. in2N The normalized input voltage of the LLC resonant converter in HB mode; Then, based on the normalized excitation inductance current The state plane trajectory in a three-element resonance is obtained using the following formula: ; Finally, by substituting the above formulas into the horizontal and vertical coordinate systems, the state plane trajectories in FB mode and HB mode can be obtained.

[0011] Preferably, step (8) specifically involves first obtaining the initial time, i.e., the resonant voltage at time t0, using the following formula. : ; Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from FB mode to HB mode. : ; Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage at times t1 and t2 when the LLC resonant converter switches from FB mode to HB mode. and : ; ; Next, based on the resonant voltage at times t1 and t2 when the LLC resonant converter switches from FB mode to HB mode... and Get the total switching time t all : ; in, For the excitation inductor current of the LLC resonant converter; Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from FB mode to HB mode of the LLC resonant converter, from the start of operation to the end of the negative half-cycle of the three-element resonant circuit. and duty cycle : ; .

[0012] Preferably, step (9) specifically involves first obtaining the resonant voltage at the initial time, i.e., time t3, using the following formula. : ; Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from FB mode to HB mode. : ; Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage at times t4 and t5 when the LLC resonant converter switches from FB mode to HB mode. and : ; ; Next, based on the resonant voltage at times t4 and t5 when the LLC resonant converter switches from FB mode to HB mode... and Get the total switching time t all : ; Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from FB mode to HB mode of the LLC resonant converter, from the start of operation to the end of the positive half-cycle of the three-element resonant circuit. and duty cycle : ; .

[0013] Preferably, step (11) specifically involves first obtaining the resonant voltage at the initial time, i.e., time t0, using the following formula. : ; Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from HB mode to FB mode. : ; Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage at times t1 and t2 when the LLC resonant converter switches from HB mode to FB mode. and : ; ; Next, based on the resonant voltage at times t1 and t2 when the LLC resonant converter switches from HB mode to FB mode... and Get the total switching time t all : ; Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from HB mode to FB mode of the LLC resonant converter, from the start of operation to the end of the negative half-cycle of the three-element resonant circuit. and duty cycle : ; .

[0014] Preferably, step (12) specifically involves first obtaining the resonant voltage at the initial time, i.e., time t3, using the following formula. : ; Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from HB mode to FB mode. : ; Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage at times t4 and t5 when the LLC resonant converter switches from HB mode to FB mode. and : ; ; Next, based on the resonant voltage at times t4 and t5 when the LLC resonant converter switches from HB mode to FB mode. and Get the total switching time t all : ; Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from HB mode to FB mode of the LLC resonant converter, from the start of operation to the end of the positive half-cycle of the three-element resonant circuit. and duty cycle : ; .

[0015] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: (1) Since the present invention adopts steps (1) to (3), it constructs a unified time-domain model for FB and HB modes, and solves the current operating frequency in real time based on the model. It does not rely on fixed compensation parameters and lookup table method, and can dynamically adapt to load changes and device parameter drift. Therefore, it can solve the technical problems of lack of unified mathematical model, low frequency matching accuracy and time-consuming experimental data collection in the existing frequency compensation switching technology. (2) Since the present invention adopts steps (5) to (12), it establishes the state plane trajectory in FB and HB modes, and accurately calculates the switching time and duty cycle in combination with the current operating frequency. It guides the continuous transition of resonant cavity energy with hybrid modulation to avoid sudden gain changes. Therefore, it can solve the technical problems of severe impact of resonant current, large fluctuation of output voltage and overcurrent damage of power devices in the existing threshold trigger hard switching technology. (3) Since the present invention adopts steps (5) to (12), it uses state plane trajectory analysis and precise switching parameter calculation, without the need for experimental preset adjustment step size and number of cycles. The switching transition process is fast and can maintain ZVS soft switching conditions. Therefore, it can solve the technical problems of poor adaptability, long transition time, easy destruction of ZVS characteristics and increased switching losses in the existing duty cycle multi-cycle gradual adjustment strategy. (4) Since the present invention adopts steps (1) to (13), it achieves seamless switching through a unified time-domain model, state plane trajectory analysis and hybrid modulation algorithm. It does not require additional hardware devices such as buffer capacitors and clamping diodes and supporting driving circuits. Therefore, it can solve the technical problems of high system cost, large size, high topology complexity and low long-term reliability of existing hardware buffer-assisted switching technology. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an LLC resonant converter operating in full-bridge mode; Figure 2 This is the schematic diagram of an LLC resonant converter operating in half-bridge mode; Figure 3 The present invention involves steps (2) and (3) to solve for the current operating frequency f of the LLC resonant converter. n The calculation flowchart; Figure 4 This is a diagram showing the switching trajectory from FB to HB in steps (7) to (9) of the present invention. Figure 5 This is a switching trajectory diagram from HB to FB in steps (10) to (12) of the present invention; Figure 6 This is a control flowchart of the method for achieving seamless switching between full-bridge and half-bridge in LLC converters based on hybrid modulation, as described in this invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0018] This invention discloses a method for achieving seamless switching between full-bridge and half-bridge modes in LLC resonant converters based on hybrid modulation. The aim is to solve the problems of sudden energy changes, output voltage fluctuations, and resonant current surges caused by the difference in equivalent input voltage gain ratio between full-bridge (FB) and half-bridge (HB) modes during topology switching in LLC resonant converters. It also addresses the issues of low switching frequency matching accuracy and difficulty in quickly reaching steady state caused by the lack of a unified time-domain model for FB and HB modes, thereby achieving stable and efficient operation of the LLC resonant converter over a wide voltage gain range. Furthermore, this control method solves the gain-frequency relationship in real time by constructing a unified time-domain model for FB and HB modes, and combines this with hybrid modulation seamless switching control to guide the continuous energy transition of the resonant cavity. This expands the voltage gain adjustment range without introducing additional hardware, improving the parameter adaptability and operational robustness of the control system. The topologies of full-bridge and half-bridge LLC resonant converters are as follows: Figure 1 and Figure 2 As shown.

[0019] like Figure 6 As shown, this invention provides a method for achieving seamless switching between full-bridge (FB) and half-bridge (HB) in an inductor-inductor-capacitor (LLC) resonant converter based on hybrid modulation, comprising the following steps: (1) Obtain the device parameters of the LLC resonant converter, and obtain the unified time-domain model of the LLC resonant converter FB and HB based on the device parameters.

[0020] Specifically, the device parameters of an LLC resonant converter include the resonant inductance L of the LLC resonant converter. r The resonant capacitance C of the LLC resonant converter r The excitation inductance L of the LLC resonant converter m The input voltage V of the LLC resonant converter in The output voltage V of the LLC resonant converter o The equivalent resistance R of the output load of the LLC resonant converter, the transformer turns ratio n of the LLC resonant converter, and the operating frequency f of the LLC resonant converter. s .

[0021] More specifically, this step obtains the unified time-domain model of the LLC resonant converter FB and HB based on the device parameters using the following formula: ; Where k is the control coefficient (1 for HB, 2 for FB). The resonant inductor L in the LLC resonant converterr and resonant capacitor C r The time of resonance, This refers to the three-element resonant angular frequency of the LLC resonant converter. Let A be the inductance ratio, and let B, C, and D be the key intermediate variables used to describe the state relationships in the FB and HB time-domain models.

[0022] (2) Obtain the corresponding frequency error based on the unified time-domain model of FB and HB obtained in step (1). And determine the frequency error. Is it greater than the preset reference frequency error value? If yes, return to step (1); otherwise, proceed to step (3).

[0023] Specifically, the preset reference frequency error value in this step The value is between 0 and 50K, preferably 25K.

[0024] More specifically, this step involves calculating the frequency error. The following formula is used: ; (3) The frequency error obtained from step (2) Obtain the current operating frequency f of the LLC resonant converter. n The calculation flowchart is as follows Figure 3 As shown; Specifically, this step involves using the following formula to obtain the current operating frequency f of the LLC resonant converter. n : ; The advantage of steps (1) to (3) above is that by establishing a unified time-domain model for FB and HB, the operating frequencies under FB and HB modes can be accurately solved, avoiding the gain error of the traditional fundamental wave analysis method, and providing a stable frequency basis for subsequent switching modulation.

[0025] (4) According to the output voltage V o The input voltage V of the LLC resonant converter is among the device parameters of the LLC resonant converter obtained in step (1). in and resonant capacitor voltage Perform per-unit scaling separately to obtain the per-unit normalized input voltage V of the LLC resonant converter. inN and normalized resonant voltage v CrN and in accordance with For the resonant inductor current of the LLC resonant converter and excitation inductor current Perform per-unit scaling separately to obtain the normalized resonant current i of the LLC resonant converter after per-unit scaling.LrN and normalized excitation current , where Z represents the characteristic impedance of the LLC resonant converter; Specifically, the characteristic impedance Z in this step is obtained using the following formula: ; The advantage of this step is that by normalizing the original variables into dimensionless parameters, the per-unit processing greatly simplifies the subsequent modeling and parameter switching calculations, reduces computational complexity, and improves the real-time performance of control.

[0026] (5) Based on the normalized input voltage V of the LLC resonant converter obtained in step (4) inN Normalized resonant voltage v CrN Normalized resonant current i LrN and normalized excitation current Establish the state plane trajectory of the LLC resonant converter in FB mode and HB mode; Specifically, the state plane trajectories of the LLC resonant converter in FB and HB modes include the state plane trajectories in binary resonance and three-element resonance, with the ordinate of the state plane trajectory being the normalized resonant voltage i. LrN The horizontal axis represents the normalized resonant current v. CrN .

[0027] More specifically, this step is based on the normalized input voltage V of the LLC resonant converter. inN Normalized resonant voltage i LrN With normalized resonant current v CrN The state plane trajectory in the FB mode of a two-element resonance is obtained using the following formula: ; ; Where, r FB1 Let r be the radius of the unit circle of the positive half-cycle of the binary resonance in FB mode. FB2 V is the radius of the unit circle of the negative half-cycle of the binary resonance in FB mode. in1N This is the normalized input voltage of the LLC resonant converter in FB mode; Secondly, the state plane trajectory in the HB mode of a binary resonance is obtained using the following formula: ; ; Where, r HB1 Let r be the radius of the unit circle of the positive half-cycle of the binary resonance in HB mode. HB2 V is the radius of the unit circle of the negative half-cycle of the binary resonance in HB mode.in2N The normalized input voltage of the LLC resonant converter in HB mode; Then, based on the normalized excitation inductance current The state plane trajectory in a three-element resonance is obtained using the following formula: ; Finally, by substituting the above formulas into the horizontal and vertical coordinate systems, the state plane trajectories in FB mode and HB mode can be obtained.

[0028] (6) Determine the input voltage V in the device parameters of the LLC resonant converter obtained in step (1). in Is it greater than the preset switching threshold voltage V of the LLC resonant converter? th If yes, proceed to step (7); otherwise, proceed to step (10).

[0029] Specifically, in this step, the threshold voltage V is switched. th The value range is between 280V and 320V, with 300V being preferred.

[0030] (7) Determine whether the LLC resonant converter is running to the end of the negative half-cycle of the three-element resonance or to the end of the positive half-cycle of the three-element resonance. If it is running to the end of the negative half-cycle of the three-element resonance, proceed to step (8). If it is running to the end of the positive half-cycle of the three-element resonance, proceed to step (9). (8) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB and HB modes, the switching time from the LLC resonant converter switching from FB mode to HB mode until the end of the negative half-cycle of the three-element resonant circuit is obtained. and duty cycle Then proceed to step (13); Specifically, this step involves first obtaining the initial (i.e., time t0) resonant voltage using the following formula. : ; Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from FB mode to HB mode. : ; Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage of the LLC resonant converter when it switches from FB mode to HB mode (i.e., at times t1 and t2). and : ; ; Next, based on the resonant voltage of the LLC resonant converter when it switches from FB mode to HB mode (i.e., at times t1 and t2) and Get the total switching time t all : ; in, This represents the excitation inductor current of the LLC resonant converter.

[0031] Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from FB mode to HB mode of the LLC resonant converter, from the start of operation to the end of the negative half-cycle of the three-element resonant circuit. and duty cycle : ; ; (9) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB mode and HB mode, the switching time from the LLC resonant converter switching from FB mode to HB mode until the end of the positive half-cycle of the three-element resonant circuit is obtained. and duty cycle Then proceed to step (13); Specifically, this step involves first obtaining the initial (i.e., time t3) resonant voltage using the following formula. : ; Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from FB mode to HB mode. : ; Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage of the LLC resonant converter when it switches from FB mode to HB mode (i.e., at times t4 and t5). and : ; ; Next, based on the resonant voltage of the LLC resonant converter when it switches from FB mode to HB mode (i.e., at times t4 and t5). and Get the total switching time t all : ; Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from FB mode to HB mode of the LLC resonant converter, from the start of operation to the end of the positive half-cycle of the three-element resonant circuit. and duty cycle : ; ; (10) Determine whether the LLC resonant converter is running to the end of the negative half-cycle of the three-element resonance or to the end of the positive half-cycle of the three-element resonance. If it is running to the end of the negative half-cycle of the three-element resonance, proceed to step (11). If it is running to the end of the positive half-cycle of the three-element resonance, proceed to step (12). (11) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB and HB modes, the switching time from HB mode to the end of the negative half-cycle of the three-element resonant circuit when the LLC resonant converter switches from HB mode to FB mode is obtained. and duty cycle Then proceed to step (13); Specifically, this step involves first obtaining the initial (i.e., time t0) resonant voltage using the following formula. : ; Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from HB mode to FB mode. : ; Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage of the LLC resonant converter when it switches from HB mode to FB mode (i.e., at times t1 and t2). and : ; ; Next, based on the resonant voltage of the LLC resonant converter when it switches from HB mode to FB mode (i.e., at times t1 and t2)... and Get the total switching time t all : ; Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from HB mode to FB mode of the LLC resonant converter, from the start of operation to the end of the negative half-cycle of the three-element resonant circuit. and duty cycle : ; ; (12) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB and HB modes, the switching time from HB mode to FB mode of the LLC resonant converter until the end of the positive half-cycle of the three-element resonant circuit is obtained. and duty cycle Then proceed to step (13); Specifically, this step involves first obtaining the initial (i.e., time t3) resonant voltage using the following formula. : ; Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from HB mode to FB mode. : ; Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage of the LLC resonant converter when it switches from HB mode to FB mode (i.e., at times t4 and t5). and : ; ; Next, based on the resonant voltage of the LLC resonant converter when it switches from HB mode to FB mode (i.e., at times t4 and t5). and Get the total switching time t all : ; Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from HB mode to FB mode of the LLC resonant converter, from the start of operation to the end of the positive half-cycle of the three-element resonant circuit. and duty cycle : ; ; The advantages of steps (7) to (12) above are that by accurately utilizing the two switching opportunities at the end of the positive and negative half-cycles of the three-element resonance, the switching time and duty cycle of FB-HB switching can be accurately calculated without the need for an additional transition period, making the switching faster. At the same time, the energy of the resonant cavity is continuously transitioned, avoiding sudden changes in gain and current and voltage impacts, maintaining ZVS characteristics, and improving switching stability and response efficiency.

[0032] (13) The switching time from FB mode to HB mode when the LLC resonant converter switches from FB mode to HB mode, as obtained in step (8), until the end of the negative half-cycle of the three-element resonant circuit. and duty cycle The switching time from FB mode to HB mode when the LLC resonant converter obtained in step (9) switches to the end of the positive half-cycle of the three-element resonant circuit. and duty cycle The switching time from HB mode to FB mode when the LLC resonant converter obtained in step (11) switches to the end of the negative half-cycle of the three-element resonant circuit. and duty cycle And when the LLC resonant converter obtained in step (12) switches from HB mode to FB mode, it runs until the end of the positive half-cycle of the three-element resonant circuit. and duty cycle The switching transistors of the LLC resonant converter are controlled to obtain the control results. The FB-HB switching trajectory is as follows: Figure 4 and Figure 5 As shown.

[0033] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for achieving seamless switching between full-bridge and half-bridge modes in an LLC resonant converter based on hybrid modulation, characterized in that, Includes the following steps: (1) Obtain the device parameters of the LLC resonant converter, and obtain the unified time-domain model of the LLC resonant converter FB and HB based on the device parameters; (2) Obtain the corresponding frequency error based on the unified time-domain model of FB and HB obtained in step (1). And determine the frequency error. Is it greater than the preset reference frequency error value? If yes, return to step (1); otherwise proceed to step (3). (3) The frequency error obtained from step (2) Obtain the current operating frequency f of the LLC resonant converter. n The calculation flowchart is shown in Figure 3; (4) According to the output voltage V o The input voltage V of the LLC resonant converter is among the device parameters of the LLC resonant converter obtained in step (1). in and resonant capacitor voltage Perform per-unit scaling separately to obtain the per-unit normalized input voltage V of the LLC resonant converter. inN and normalized resonant voltage v CrN and in accordance with For the resonant inductor current of the LLC resonant converter and excitation inductor current Perform per-unit scaling separately to obtain the normalized resonant current i of the LLC resonant converter after per-unit scaling. LrN and normalized excitation current , where Z represents the characteristic impedance of the LLC resonant converter; (5) Based on the normalized input voltage V of the LLC resonant converter obtained in step (4) inN Normalized resonant voltage v CrN Normalized resonant current i LrN and normalized excitation current Establish the state plane trajectory of the LLC resonant converter in FB mode and HB mode; (6) Determine the input voltage V in the device parameters of the LLC resonant converter obtained in step (1). in Is it greater than the preset switching threshold voltage V of the LLC resonant converter? th If yes, proceed to step (7); otherwise, proceed to step (10). (7) Determine whether the LLC resonant converter is running to the end of the negative half-cycle of the three-element resonance or to the end of the positive half-cycle of the three-element resonance. If it is running to the end of the negative half-cycle of the three-element resonance, proceed to step (8). If it is running to the end of the positive half-cycle of the three-element resonance, proceed to step (9). (8) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB and HB modes, the switching time from the LLC resonant converter switching from FB mode to HB mode until the end of the negative half-cycle of the three-element resonant circuit is obtained. and duty cycle Then proceed to step (13); (9) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB mode and HB mode, the switching time from the LLC resonant converter switching from FB mode to HB mode until the end of the positive half-cycle of the three-element resonant circuit is obtained. and duty cycle Then proceed to step (13); (10) Determine whether the LLC resonant converter is running to the end of the negative half-cycle of the three-element resonance or to the end of the positive half-cycle of the three-element resonance. If it is running to the end of the negative half-cycle of the three-element resonance, proceed to step (11). If it is running to the end of the positive half-cycle of the three-element resonance, proceed to step (12). (11) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB and HB modes, the switching time from HB mode to the end of the negative half-cycle of the three-element resonant circuit when the LLC resonant converter switches from HB mode to FB mode is obtained. and duty cycle Then proceed to step (13); (12) The current operating frequency f of the LLC resonant converter obtained in step (3) n Based on the state plane trajectories of the LLC resonant converter obtained in step (5) in FB and HB modes, the switching time from HB mode to FB mode of the LLC resonant converter until the end of the positive half-cycle of the three-element resonant circuit is obtained. and duty cycle Then proceed to step (13); (13) The switching time from FB mode to HB mode when the LLC resonant converter switches from FB mode to HB mode, as obtained in step (8), until the end of the negative half-cycle of the three-element resonant circuit. and duty cycle The switching time from FB mode to HB mode when the LLC resonant converter obtained in step (9) switches to the end of the positive half-cycle of the three-element resonant circuit. and duty cycle The switching time from HB mode to the end of the negative half-cycle of the three-element resonant converter when the LLC resonant converter obtained in step (11) switches from HB mode to FB mode. and duty cycle And when the LLC resonant converter obtained in step (12) switches from HB mode to FB mode, it runs until the end of the positive half-cycle of the three-element resonant circuit. and duty cycle The switching transistors of the LLC resonant converter are controlled to obtain the control result.

2. The method for achieving seamless full-bridge to half-bridge switching of an LLC resonant converter based on hybrid modulation according to claim 1, characterized in that, The device parameters of the LLC resonant converter include the resonant inductance L of the LLC resonant converter. r The resonant capacitance C of the LLC resonant converter r The excitation inductance L of the LLC resonant converter m The input voltage V of the LLC resonant converter in The output voltage V of the LLC resonant converter o The equivalent resistance R of the output load of the LLC resonant converter, the transformer turns ratio n of the LLC resonant converter, and the operating frequency f of the LLC resonant converter. s .

3. The method for achieving seamless full-bridge to half-bridge switching of an LLC resonant converter based on hybrid modulation according to claim 1 or 2, characterized in that, In step (1), the unified time-domain model of the LLC resonant converter FB and HB obtained based on the device parameters is obtained using the following formula: ； Where k is the control coefficient (1 for HB, 2 for FB). For the resonant inductor L in the LLC resonant converter r and resonant capacitor C r The time of resonance, This refers to the three-element resonant angular frequency of the LLC resonant converter. Let A be the inductance ratio, and let B, C, and D be the key intermediate variables used to describe the state relationships in the FB and HB time-domain models.

4. The method for achieving seamless full-bridge to half-bridge switching of an LLC resonant converter based on hybrid modulation according to any one of claims 1 to 3, characterized in that, In step (2), the frequency error is calculated. The following formula is used: ； Step (3) is to obtain the current operating frequency f of the LLC resonant converter using the following formula. n : ； The characteristic impedance Z in step (4) is obtained using the following formula: 。 5. The method for achieving seamless full-bridge to half-bridge switching of an LLC resonant converter based on hybrid modulation according to claim 4, characterized in that, The state plane trajectories of the LLC resonant converter in FB and HB modes include the state plane trajectories in binary resonance and ternary resonance. The ordinate of the state plane trajectory is the normalized resonant voltage i. LrN The horizontal axis represents the normalized resonant current v. CrN ; Step (5) Based on the normalized input voltage V of the LLC resonant converter inN Normalized resonant voltage i LrN With normalized resonant current v CrN The state plane trajectory in the FB mode of a two-element resonance is obtained using the following formula: ； ； Where, r FB1 Let r be the radius of the unit circle of the positive half-cycle of the binary resonance in FB mode. FB2 V is the radius of the unit circle of the negative half-cycle of the binary resonance in FB mode. in1N This is the normalized input voltage of the LLC resonant converter in FB mode; Secondly, the state plane trajectory in the HB mode of a binary resonance is obtained using the following formula: ； ； Where, r HB1 Let r be the radius of the unit circle of the positive half-cycle of the binary resonance in HB mode. HB2 V is the radius of the unit circle of the negative half-cycle of the binary resonance in HB mode. in2N This is the normalized input voltage of the LLC resonant converter in HB mode; Then, based on the normalized excitation inductance current The state plane trajectory in a three-element resonance is obtained using the following formula: ； Finally, by substituting the above formulas into the horizontal and vertical coordinate systems, the state plane trajectories in FB mode and HB mode can be obtained.

6. The method for achieving seamless full-bridge to half-bridge switching of an LLC resonant converter based on hybrid modulation according to claim 5, characterized in that, Step (8) specifically involves first obtaining the initial time, i.e., the resonant voltage at time t0, using the following formula. : ； Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from FB mode to HB mode. : ； Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage at times t1 and t2 when the LLC resonant converter switches from FB mode to HB mode. and : ； ； Next, based on the resonant voltage at times t1 and t2 when the LLC resonant converter switches from FB mode to HB mode... and Get the total switching time t all : ； in, This is the excitation inductor current of the LLC resonant converter; Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from FB mode to HB mode of the LLC resonant converter, from the start of operation to the end of the negative half-cycle of the three-element resonant circuit. and duty cycle : ； 。 7. The method for achieving seamless full-bridge to half-bridge switching of an LLC resonant converter based on hybrid modulation according to claim 6, characterized in that, Step (9) specifically involves first obtaining the resonant voltage at the initial time, i.e., time t3, using the following formula. : ； Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from FB mode to HB mode. : ； Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage at times t4 and t5 when the LLC resonant converter switches from FB mode to HB mode. and : ； ； Next, based on the resonant voltage at times t4 and t5 when the LLC resonant converter switches from FB mode to HB mode... and Get the total switching time t all : ； Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from FB mode to HB mode of the LLC resonant converter, from the end of the positive half-cycle of the three-element resonant circuit. and duty cycle : ； 。 8. The method for achieving seamless full-bridge to half-bridge switching of an LLC resonant converter based on hybrid modulation according to claim 7, characterized in that, Step (11) specifically involves first obtaining the resonant voltage at the initial time, i.e., time t0, using the following formula. : ； Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from HB mode to FB mode. : ； Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage at times t1 and t2 when the LLC resonant converter switches from HB mode to FB mode. and : ； ； Next, based on the resonant voltage at times t1 and t2 when the LLC resonant converter switches from HB mode to FB mode... and Get the total switching time t all : ； Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from HB mode to FB mode of the LLC resonant converter, from the start of operation to the end of the negative half-cycle of the three-element resonant circuit. and duty cycle : ； 。 9. The method for achieving seamless full-bridge to half-bridge switching of an LLC resonant converter based on hybrid modulation according to claim 8, characterized in that, Step (12) specifically involves first obtaining the resonant voltage at the initial time, i.e., time t3, using the following formula. : ； Then, based on the obtained initial resonant voltage Obtain the radius of the state circle when the LLC resonant converter switches from HB mode to FB mode. : ； Then, with the radius of the state circle Given the hypotenuse of a right triangle, obtain the resonant voltage at times t4 and t5 when the LLC resonant converter switches from HB mode to FB mode. and : ； ； Next, based on the resonant voltage at times t4 and t5 when the LLC resonant converter switches from HB mode to FB mode. and Get the total switching time t all : ； Finally, based on the current operating frequency f of the LLC resonant converter obtained in step (3), n and total switching time t all Obtain the switching time from HB mode to FB mode of the LLC resonant converter, from the start of operation to the end of the positive half-cycle of the three-element resonant circuit. and duty cycle : ； 。

Images