Resonant converter with TPFC + LLC two-stage architecture and control method thereof

Abstract

The invention relates to a resonant converter with a TPFC + LLC two-stage architecture and a control method thereof. The resonant converter comprises an input filtering module, a totem pole PFC circuit, a full-bridge LLC resonant cavity, a full-bridge synchronous rectification circuit and a multi-mode digital control unit which are connected in sequence. During operation, the multi-mode digital control unit outputs a PWM signal to the totem pole PFC circuit so as to adjust the bus voltage Vbus output by the totem pole PFC circuit, outputs a PWM signal to the primary side full-bridge switching circuit of the full-bridge LLC resonant cavity so as to adjust the switching frequency fs of the full-bridge LLC resonant cavity, and controls the bus voltage Vbus and the switching frequency fs cooperatively so as to adjust the switching frequency fs of the full-bridge LLC resonant cavity. Enabling the full-bridge LLC resonant cavity to work in the optimized working configuration in any working interval; according to the scheme, the gain requirement of wide-range voltage output is reasonably decomposed and optimally distributed, so that the working frequency change range is remarkably reduced, and the efficiency, the dynamic performance and the reliability of the converter in an ultra-wide output voltage range are comprehensively improved.

Description

Technical Field

[0001] This invention relates to the field of resonant converter technology, and more specifically, to a resonant converter with a two-stage architecture of TPFC+LLC and its control method. Background Technology

[0002] LLC resonant converters are widely used in high-power DC-DC conversion applications such as data center server power supplies, communication power supplies, and new energy charging modules because their primary-side switching transistors can achieve zero-voltage turn-on and the secondary-side rectifier transistors can achieve zero-current turn-off.

[0003] However, in applications requiring ultra-wide output voltage ranges (e.g., continuously adjustable output voltage from 56V to 185V with a gain variation of approximately 3.3 times), such as battery formation testing, laboratory programmable power supplies, and laser power supplies, traditional single-mode LLC resonant converters face significant challenges: 1. Excessively wide switching frequency range: To achieve wide voltage output, the switching frequency of LLC needs to vary over an extremely wide range (e.g., from near the resonant frequency to several times the resonant frequency). Under light load or low voltage output, the switching frequency becomes extremely high, which leads to a sharp increase in switching losses and transformer core losses. This results in a severe "sunken" region on the overall efficiency curve of the converter over a wide voltage range, with low average efficiency.

[0004] 2. Limited gain capability under light load / low voltage: When the input voltage is fixed and the output voltage requirement is extremely low, the required voltage gain of the LLC converter is extremely high, often exceeding its reliable gain adjustment range. In this situation, it is difficult to maintain soft-switching conditions, the resonant cavity may become detuned, leading to waveform distortion, a sharp drop in efficiency, or even instability.

[0005] 3. Increased impact of parasitic parameters: At extreme high or low frequencies, the effects of parasitic parameters such as transformer leakage inductance, winding parasitic capacitance, and power device junction capacitance become non-negligible, causing voltage and current spikes and oscillations, exacerbating electromagnetic interference problems, and potentially endangering the safety of switching transistors.

[0006] To overcome the above-mentioned shortcomings, existing technologies have attempted to employ multi-stage conversion, multi-mode switching (such as hybrid full-bridge / half-bridge LLC), or the addition of additional active / passive auxiliary networks. However, these solutions either increase the complexity and cost of the system or can only improve performance to a limited extent. They are difficult to systematically solve the problem of ultra-wide range DC voltage output under the premise of high efficiency, low stress, and continuous adjustability. There is a need for a low-cost resonant converter with a two-stage architecture of TPFC+LLC and its control method that can solve the above problems. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a resonant converter with a two-stage TPFC+LLC architecture, and to provide a control method with a two-stage TPFC+LLC architecture, in order to address the above-mentioned deficiencies of the prior art.

[0008] The technical solution adopted by this invention to solve its technical problem is: A resonant converter with a two-stage architecture of TPFC+LLC is constructed, including an input filter module, a totem pole PFC circuit, a full-bridge LLC resonant cavity, a full-bridge synchronous rectifier circuit, and a multi-mode digital control unit connected in sequence.

[0009] The full-bridge LLC resonant cavity includes a primary-side full-bridge switching circuit, a resonant inductor Lr, a resonant capacitor Cr, and the primary winding of a transformer T1 connected in sequence. The magnetizing inductance Lm of the transformer T1 is equivalently connected in parallel across the primary winding.

[0010] The multi-mode digital control unit is configured to divide the entire target output voltage range into at least three working intervals based on the output voltage feedback value of the converter, and independently set the corresponding bus voltage Vbus control target and switching frequency fs working range for each working interval.

[0011] The control unit outputs a PWM signal to the totem pole PFC circuit to adjust its output bus voltage Vbus, and outputs a PWM signal to the primary side switch of the full-bridge LLC resonant cavity to adjust its switching frequency fs. By coordinating the control of Vbus and fs, the converter operates in an optimized operating mode under any output voltage.

[0012] Furthermore, the at least three operating ranges include a high-voltage range, a medium-voltage range, and a low-voltage range. In the high-voltage range, the bus voltage Vbus is controlled to remain within a first high-voltage range, and the switching frequency fs is controlled to operate within a first frequency range. In the medium-voltage range, the bus voltage Vbus is controlled to remain within a second medium-voltage range, which is lower than the first high-voltage range, and the switching frequency fs is controlled to operate within a second frequency range, which is higher than the first frequency range. In the low-voltage range, the bus voltage Vbus is controlled to vary within a third low-voltage range, and the switching frequency fs is controlled to operate within a third frequency range, which is higher than the second frequency range.

[0013] Furthermore, in the high-voltage range, the full-bridge LLC resonant cavity operates in under-resonance mode or quasi-resonance mode; in the medium-voltage range, it operates in over-resonance mode close to the resonance point; in the low-voltage range, it operates in over-resonance mode, and the bus voltage Vbus is controlled to allow it to drop to a level slightly higher than the rectified AC input voltage.

[0014] Furthermore, the multi-mode digital control unit switches between the high-voltage range, the medium-voltage range, and the low-voltage range according to the output voltage feedback value, and a hysteresis control logic is set at the switching point to prevent mode oscillation.

[0015] A control method for the above-mentioned TPFC + LLC resonant converter, which is executed by the multi-mode digital control unit, includes the following steps: S1 Sampling step: Real-time sample the output voltage Vo of the converter.

[0016] S2 Judgment step: Compare the output voltage Vo with a preset threshold value to judge the working range it belongs to, and the working range at least includes a high-voltage range, a medium-voltage range, and a low-voltage range.

[0017] S3 Target determination step: According to the determined working range, determine the corresponding bus voltage Vbus control target value and the switching frequency fs control target value.

[0018] S4 Control output step: a. Generate and output a PWM signal for controlling the totem-pole PFC circuit, so that the output bus voltage Vbus tracks the Vbus control target value.

[0019] b. Generate and output a PWM signal for controlling the primary-side switching tubes of the full-bridge LLC resonant cavity, so that its switching frequency fs tracks the fs control target value. [[ID=2||1]]

[0020] Furthermore, the judgment step is specifically: Preset the first voltage threshold V th1 and the second voltage threshold V th2 , and V th1 > V th2 ; When Vo ≥ V th1 , it is determined as the high-voltage range; When V th2 ≤ Vo < Vth1, it is determined as the medium-voltage range; When Vo < V th2 , it is determined as the low-voltage range.

[0021] Furthermore, a hysteresis comparison logic is adopted in the judgment step, including: When switching from the high-voltage range to the medium-voltage range, the switching threshold used is V th1 - Δ1; when switching from the medium-voltage range to the high-voltage range, the switching threshold used is V th1 ; when switching from the medium-voltage range to the low-voltage range, the switching threshold used is V th2 - Δ2; when switching from the low-voltage range to the medium-voltage range, the switching threshold used is V th2; where Δ1 and Δ2 are the hysteresis widths.

[0022] Furthermore, the target determination step includes: In the high-voltage range, Vbus is controlled to stabilize near the first high-voltage target value, and fs is adjusted to vary within the first frequency range; in the medium-voltage range, Vbus is controlled to stabilize near the second medium-voltage target value, which is lower than the first high-voltage target value, and fs is adjusted to vary within the second frequency range; in the low-voltage range, the target value of Vbus is dynamically set according to the output voltage Vo, and the target value of Vbus decreases as Vo decreases, while fs is adjusted to vary within the third frequency range.

[0023] The beneficial effects of this invention are as follows: Through an innovative system-level collaborative control strategy, the gain requirements of a wide range of voltage outputs are rationally decomposed and optimized, thereby significantly reducing the operating frequency variation range and comprehensively improving the efficiency, dynamic performance, and reliability of the converter over an ultra-wide output voltage range, as detailed below: 1. Achieved efficient output with ultra-wide continuous voltage: Through the coordinated control strategy of "bus voltage following" and "three-segment gain mode division", the total voltage gain requirement of up to 3.3 times is decomposed into three optimized sub-operating modes; in each sub-mode, the required frequency regulation ratio and gain regulation ratio are significantly reduced, fundamentally avoiding the problem of excessively wide switching frequency variation in traditional solutions.

[0024] 2. Improved overall operating efficiency: Each operating range is configured to operate under the optimal (Vbus, fs) parameter combination; especially in the low-voltage output range where the traditional LLC efficiency is the lowest, this invention actively reduces the bus voltage Vbus, so that the LLC does not need to operate at extremely high switching frequencies, thereby significantly reducing switching losses and core losses, filling the "dip" in the efficiency curve, and greatly improving the average efficiency over the entire wide output voltage range.

[0025] 3. Improved dynamic performance and reliability: The digital control unit responds quickly, the two-stage converter works in concert, the mode switching process is smooth, and the output ripple is small; the hysteresis control logic effectively prevents mode boundary oscillations; at the same time, since the switching frequency is limited to a reasonable range (e.g., no more than 200kHz), the influence of circuit parasitic parameters is reduced, and the waveform quality and system reliability are improved.

[0026] 4. Solved the problem of insufficient gain under light load / low voltage: In the low voltage range, the required gain of the LLC stage is reduced by lowering Vbus, so that the LLC resonant cavity always works in the over-resonance region with sufficient gain capability, ensuring that good soft-switching characteristics can be maintained in the entire voltage range, and solving the problem that traditional LLC is difficult to work or even detuned under low voltage full load. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a block diagram of a resonant converter with a two-stage TPFC+LLC architecture according to a preferred embodiment of the present invention. Figure 2 This is a flowchart of a resonant converter control method with a two-stage architecture of TPFC+LLC according to a preferred embodiment of the present invention. Figure 3 This is a performance verification curve of the resonant converter with a two-stage architecture of TPFC+LLC according to a preferred embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, a clear and complete description will be provided below in conjunction with the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0029] A preferred embodiment of the present invention provides a resonant converter with a two-stage TPFC+LLC architecture, such as... Figure 1 As shown, its goal is to convert AC input (such as 90VAC-264VAC) into a continuously adjustable DC voltage output from 56V to 185V; The main circuit of the system consists of a cascaded totem-pole PFC in the front stage and a full-bridge LLC resonant cavity in the rear stage; the control core adopts a multi-mode digital control unit, such as the TMS320F28335 DSP from TI. The DSP acquires signals such as input voltage Vin, bus voltage Vbus, output voltage Vo, and output current Io, and generates PWM signals to drive the front-end PFC switch, the rear-end LLC primary-side full-bridge switch circuit, and the secondary-side full-bridge synchronous rectifier.

[0030] The resonant parameters of the full-bridge LLC resonant cavity are designed to make its resonant frequency fr 100kHz.

[0031] The implementation details of the control method in this embodiment are as follows: The output range of 56V-185V is divided into three operating zones, and the following control strategy is set: High voltage operating range (125V≤Vo≤185V): Vbus control: The PFC output bus voltage is stably controlled within a high voltage range of 405V (corresponding to the maximum output voltage of 185V) to 350V (corresponding to the lower limit of the range of 125V). Within this range, Vbus can be slightly and linearly reduced as Vo decreases, but the overall high voltage is maintained.

[0032] fs control: controls the LLC to operate in underresonant or quasi-resonant mode, with the switching frequency adjustable in the range of 55kHz to 100kHz; high voltage output is achieved using a lower switching frequency, resulting in optimal efficiency.

[0033] Medium voltage operating range (80V≤Vo<125V): Vbus control: Stabilizes the bus voltage within a medium range of 370V (corresponding to 125V) to 320V (corresponding to 80V).

[0034] fs control: Controls the LLC to operate in over-resonance mode close to the resonant point (fr=100kHz), with the switching frequency finely adjusted within the range of 100kHz to 150kHz. This range represents the peak plateau of system efficiency.

[0035] Low-voltage operating range (56V≤Vo<80V): Vbus control: The "bus voltage follow" strategy is activated; the control target value of Vbus starts from 320V (when Vo=80V) and actively decreases as Vo decreases; for example, when the input is 220VAC and Vo=56V, Vbus can be reduced to 330V (this value is slightly higher than the peak value after input rectification to ensure normal operation of PFC), and the gain requirement of the subsequent stage is compensated by reducing the gain of the preceding stage.

[0036] fs control: LLC operates in deep overresonant mode, with the switching frequency adjustable in the range of 150kHz to 200kHz; since Vbus has been significantly reduced, fs is prevented from further soaring to above 250kHz, thereby controlling high-frequency losses.

[0037] Mode switching and hysteresis control implementation: In the DSP program, set: V th1 =125V,V th2 =80V, Δ1=5V, Δ2=3V.

[0038] When Vo remains below 120V (V th1 When -Δ1), the system switches from the high-pressure range to the medium-pressure range.

[0039] When Vo rises back to 125V (V th1 When the system switches from the medium-pressure zone back to the high-pressure zone, the system switches back to the high-pressure zone.

[0040] When Vo remains below 77V (V th2 When -Δ2), the system switches from the medium-pressure range to the low-pressure range.

[0041] When Vo rises back to 80V (Vth2), the system switches from the low-voltage range back to the medium-voltage range.

[0042] This invention reduces the bus voltage Vbus, allowing the LLC resonant converter to operate at a very high switching frequency when the output voltage is low, thereby avoiding the surge in core loss and the influence of parasitic parameters at high frequencies. Technical effectiveness verification: Reference Figure 3 As can be seen from the efficiency curve diagram, after adopting the three-stage collaborative control method of the present invention, refer to... Figure 2 The efficiency curve becomes very flat throughout the 56V-185V range, especially in the low-voltage range of 56V-80V, where the efficiency improvement is particularly significant, fully demonstrating the excellent effect of this invention in solving the problem of ultra-wide range output efficiency.

[0043] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A resonant converter with a two-stage architecture of TPFC+LLC, characterized in that, It includes an input filter module, a totem-pole PFC circuit, a full-bridge LLC resonant cavity, a full-bridge synchronous rectifier circuit, and a multi-mode digital control unit connected in sequence; the full-bridge LLC resonant cavity includes a primary-side full-bridge switching circuit, a resonant inductor Lr, a resonant capacitor Cr, and the magnetizing inductance Lm of transformer T1; the primary side of transformer T1 is connected in series in the full-bridge LLC resonant cavity, and the secondary side is connected to the full-bridge synchronous rectifier circuit; The multi-mode digital control unit is configured to: divide the output voltage range into at least three working intervals based on the output voltage feedback value of the full-bridge LLC resonant cavity, and set different bus voltage Vbus control targets and switching frequency fs working ranges for each working interval; During operation, the multi-mode digital control unit outputs a PWM signal to the totem pole PFC circuit to adjust its output bus voltage Vbus, and outputs a PWM signal to the primary side full-bridge switching circuit of the full-bridge LLC resonant cavity to adjust its switching frequency fs. By coordinating the control of the bus voltage Vbus and the switching frequency fs, the full-bridge LLC resonant cavity can operate in an optimized working configuration in any working range.

2. The resonant converter with a two-stage TPFC+LLC architecture according to claim 1, characterized in that, The three operating ranges are high-pressure range, medium-pressure range, and low-pressure range; In the high-voltage range, the bus voltage Vbus is controlled to be maintained within the first high-voltage range, and the switching frequency fs is controlled to operate within the first frequency range. In the medium-voltage range, the bus voltage Vbus is controlled to be maintained in a second medium-voltage range that is lower than the first high-voltage range, and the switching frequency fs is controlled to operate in a second frequency range that is higher than the first frequency range. In the low-voltage range, the bus voltage Vbus is controlled to vary within a third low-voltage range, and the switching frequency fs is controlled to operate within a third frequency range that is higher than the second frequency range.

3. The resonant converter with a two-stage TPFC+LLC architecture according to claim 2, characterized in that, In the high-voltage range, the full-bridge LLC resonant cavity operates in underresonant mode or quasi-resonant mode; In the medium voltage range, the full-bridge LLC resonant cavity operates in an over-resonance mode close to the resonance point; In the low-voltage range, the full-bridge LLC resonant cavity operates in over-resonance mode, and the bus voltage Vbus is controlled to allow it to drop to a level slightly higher than the rectified AC input voltage.

4. The resonant converter with a two-stage TPFC+LLC architecture according to claim 2, characterized in that, The multi-mode digital control unit switches between the high-voltage range, medium-voltage range, and low-voltage range based on the output voltage feedback value, and hysteresis control logic is set at the switching point.

5. A control method for a resonant converter with a two-stage TPFC+LLC architecture as described in any one of claims 1 to 4, executed by a multi-mode digital control unit, characterized in that, Includes the following steps: Sample the output voltage Vo of the full-bridge LLC resonant cavity; The output voltage Vo is compared with a threshold to determine its operating range, which includes at least the high voltage range, medium voltage range, and low voltage range. Based on the determined operating range, determine the corresponding target values ​​for bus voltage Vbus and switching frequency fs. Generate and output the PWM signal to control the totem pole PFC circuit, so that its output bus voltage Vbus tracks the Vbus control target value; Generate and output a PWM signal to control the primary side full-bridge switching circuit of the full-bridge LLC resonant cavity, so that its switching frequency fs tracks the target value of fs control.

6. The control method according to claim 5, characterized in that, The specific steps for determining the working range are as follows: a first voltage threshold V th1 a second voltage threshold V th2 , and V th1 >V th2 ; When Vo≥V th1 At that time, it was determined to be a high-voltage area; When V th2 ≤Vo <V th1 At that time, it was determined to be a medium-pressure zone; When Vo <V th2 At that time, it was determined to be a low-pressure area.

7. The control method according to claim 6, characterized in that, When determining the operating range based on the output voltage Vo, hysteresis comparison logic is used to prevent mode oscillation, including: When switching from the high-voltage zone to the medium-voltage zone, the switching threshold used is V. th1 -Δ1, where Δ1 is the width of the first hysteresis loop; When switching from the medium-voltage range to the high-voltage range, the switching threshold used is V. th1 ; When switching from the medium-voltage range to the low-voltage range, the switching threshold used is V. th2 -Δ2, where Δ2 is the width of the second hysteresis loop; When switching from the low-voltage range to the medium-voltage range, the switching threshold used is V. th2 .

8. The control method according to claim 5, characterized in that, Based on the determined operating range, the corresponding target values ​​for bus voltage Vbus and switching frequency fs are determined, including: In the high-voltage range, Vbus is controlled to remain stable near the first high-voltage target value, and fs is adjusted to vary within the first frequency range. In the medium-voltage range, Vbus is controlled to be stable near the second medium-voltage target value, which is lower than the first high-voltage target value, and fs is adjusted to vary in the second frequency range, which is higher than the first frequency range. In the low-voltage range, the target value of Vbus is dynamically set according to the output voltage Vo, and the target value of Vbus decreases as Vo decreases. At the same time, fs is adjusted to vary in a third frequency range that is higher than the second frequency range.

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