A control method for a resonant converter
By inserting drive pulse control for the transition process between the full and half-bridge modes, smooth switching of the LLC resonant converter is achieved, solving the problems of output voltage fluctuation and excessive device stress over a wide input voltage range, and improving the system's stability and EMI performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MORNSUN GUANGZHOU SCI & TECH
- Filing Date
- 2023-01-31
- Publication Date
- 2026-06-02
AI Technical Summary
Existing LLC resonant converters have difficulty achieving smooth switching over a wide input voltage range, resulting in output voltage fluctuations and excessive device stress, which affects system performance.
By inserting drive pulse control for the transition process between the full and half-bridge modes, zero-voltage switching (ZVS) of the switching transistors is ensured, and corresponding closed-loop control is performed after switching to achieve smooth switching.
It broadens the voltage gain range of the resonant converter, reduces output voltage fluctuations during switching, lowers the stress on the switching transistor, improves EMI performance, and enhances the stability and reliability of the system.
Smart Images
Figure CN116207972B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of switching converter technology, and more specifically to a control method for a resonant converter. Background Technology
[0002] With the rapid development of power electronics, switching converters are being used more and more widely. People are placing higher demands on switching converters: high power density, high reliability, high efficiency, small size, and wide input voltage range. LLC resonant converters are favored by industry professionals due to their high efficiency, soft switching, and ability to achieve higher power density. However, traditional LLC resonant converters generally require changing the switching frequency to regulate the output voltage. When the input voltage range is wide, the switching frequency needs to vary over a wide range. When the frequency is too low, it is difficult to achieve zero-voltage turn-on; when the frequency is too high, it is difficult to achieve zero-current turn-off. At the same time, the wide frequency range brings great difficulties to transformer design and circuit control. Therefore, many researchers have studied ways to improve the gain of LLC resonant converters and widen their input voltage range by changing the control method.
[0003] The Chinese invention patent CN108258910A, entitled "A Full-Bridge LLC Resonant Converter Circuit and Its Wide-Range Output Control Method," provides the following solution: when the output voltage Uo is greater than (Uomax + Uomin) / 2, the full-bridge LLC resonant converter circuit operates in full-bridge mode; when the output voltage Uo is less than (Uomax + Uomin) / 2, the full-bridge LLC resonant converter circuit operates in half-bridge mode; when the output voltage is equal to (Uomax + Uomin) / 2, the full-bridge and half-bridge operating modes are switched by giving an initial operating frequency to the complementary bridge arms; where Uomax is the rated maximum output voltage and Uomin is the rated minimum output voltage. However, this solution does not provide a method for determining the initial frequency. As a technician, it is not difficult to infer that the initial frequency should be the highest permissible operating frequency under the corresponding operating mode. Furthermore, this solution does not address the impact of the switching process on output voltage fluctuations and device stress. Under different operating load conditions, this control method will cause significant output voltage fluctuations, affecting system performance.
[0004] The solution provided by Chinese invention patent CN106411139B, entitled "A Control Method for a Wide Output Range LLC Converter," is as follows: During the switch from half-bridge LLC operating mode to full-bridge LLC operating mode, the operating frequencies of all power devices in the LLC resonant converter are increased to the highest permissible operating frequency of the full-bridge LLC operating mode, thereby achieving a smooth switch from half-bridge LLC operating mode to full-bridge LLC operating mode. While the patent does not specify the control scheme for switching from full-bridge LLC operating mode to half-bridge LLC operating mode, it is not difficult for someone skilled in the art to deduce that the possible control method is: During the switch from full-bridge LLC operating mode to half-bridge LLC operating mode, the operating frequencies of all power devices in the LLC resonant converter are increased to the highest permissible operating frequency of the half-bridge LLC operating mode, thereby achieving a smooth switch from full-bridge LLC operating mode to half-bridge LLC operating mode. However, this solution uses frequency conversion to increase the operating frequency during full-bridge and half-bridge switching. As is common technical knowledge, the voltage gain will decrease, which will affect the fluctuation of the output voltage. If the system is operating under heavy load, forcibly increasing the frequency will cause a large undershoot in the output voltage, affecting the system performance.
[0005] US Patent No. 9263960B2, "Power converters for wide input or output voltage range and control methods thereof," proposes an alternative solution for switching the operating modes of a full-bridge and half-bridge LLC: using a gradual change in the duty cycle driven by the inverter circuit switching transistors to achieve switching between full-bridge and half-bridge modes, enabling the LLC to operate over a wide input voltage range of 4:1. However, the switching scheme proposed in this patent cannot achieve zero-voltage switching (ZVS) during the switching process of the inverter circuit switching transistors that are normally off in half-bridge mode. In practical use, this results in a large turn-on current, which resonates with the PCB trace inductance, causing an increase in voltage stress on the primary-side switching transistors. Simultaneously, the hard turn-on of the inverter circuit switching transistors also generates large current and voltage spikes in the power circuit, leading to a deterioration in the product's EMI performance. Furthermore, even if the proposed switching scheme can achieve full-bridge and half-bridge switching, the frequency variation range is large, with the lowest operating frequency being approximately one-quarter of the highest operating frequency, which is unfavorable for high power density transformer designs.
[0006] Based on the above research, the most effective way to broaden the voltage gain of the resonant converter is to control the converter to switch between full-bridge and half-bridge modes. However, how to achieve smooth switching between full-bridge and half-bridge modes and ensure that all inverter circuit switches can achieve ZVS during the switching process still needs further investigation. Summary of the Invention
[0007] In view of this, the technical problem to be solved by the present invention is to propose a wide gain control method for resonant converters, which can achieve smooth switching between full and half bridge modes while ensuring a wide range of output voltage gain of the resonant converter, and ensure the soft switching characteristics of power semiconductor devices during the switching process without affecting output stability.
[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:
[0009] According to one aspect of the present invention, a control method for a resonant converter is provided. The resonant converter includes switching transistors Q1, Q2, Q3, and Q4, a resonant capacitor, and a resonant inductor. Switches Q1 and Q2 are connected in series to form a first bridge arm, and switches Q3 and Q4 are connected in series to form a second bridge arm. The first bridge arm and the second bridge arm are connected in parallel. The control method for the resonant converter includes:
[0010] When the input voltage of the resonant converter is greater than the switching threshold and the resonant converter is operating in full-bridge mode, the resonant converter is controlled to perform a full-bridge to half-bridge transition process, so that the resonant converter switches from full-bridge mode to half-bridge mode. During the full-bridge to half-bridge transition process, the driving pulse width of switch Q1 is 0.75 to 1.75 times half of the resonant converter's resonant period; the driving pulse width of switch Q2 is 1.25 to 2.5 times half of the resonant converter's resonant period; switch Q3 remains off; and switch Q4 remains on.
[0011] When the input voltage is less than the switching threshold and the resonant converter is operating in half-bridge mode, the resonant converter is controlled to perform a half-bridge to full-bridge transition process, so that the resonant converter switches from half-bridge mode to full-bridge mode. During the half-bridge to full-bridge transition process: the driving pulse width of switch Q1 is 0.75 to 1.75 times the driving pulse width of switch Q1 when the resonant converter is operating in half-bridge mode; the driving pulse width of switch Q2 is 1.25 to 2.5 times the driving pulse width of switch Q2 when the resonant converter is operating in half-bridge mode; switch Q3 is turned off; switch Q4 is turned off simultaneously with switch Q1.
[0012] Optionally, during the transition from a full-bridge to a half-bridge, the driving pulses of switching transistors Q1 to Q6 have one or more cycles; during the transition from a half-bridge to a full-bridge, the driving pulses of switching transistors Q1 to Q6 have one or more cycles.
[0013] Optionally, the resonant converter also includes a clamping branch composed of switch Q5 and switch Q6. During the transition from a full-bridge to a half-bridge, the driving pulse of switch Q5 is complementary to the driving pulse of switch Q1, and the driving pulse of switch Q6 is complementary to the driving pulse of switch Q2. During the transition from a half-bridge to a full-bridge, the driving pulse of switch Q5 is complementary to the driving pulse of switch Q1, and the driving pulse of switch Q6 is complementary to the driving pulse of switch Q2.
[0014] Optionally, the switching threshold is between NVo and 2NVo, with hysteresis allowed, where N is the turns ratio of the primary winding to the secondary winding of the transformer in the resonant converter, and Vo is the output voltage of the resonant converter. Preferably, the switching threshold is 1.5*NVo.
[0015] According to another aspect of the present invention, a control method for a resonant converter is also provided. The resonant converter includes switching transistors Q1, Q2, Q3, and Q4, a resonant capacitor, and a resonant inductor. Switches Q1 and Q2 are connected in series to form a first bridge arm, and switches Q3 and Q4 are connected in series to form a second bridge arm. The first bridge arm and the second bridge arm are connected in parallel. The control method for the resonant converter includes:
[0016] When the input voltage of the resonant converter is greater than the switching threshold and the resonant converter is operating in full-bridge mode, the resonant converter is controlled to perform a full-bridge to half-bridge transition process, so that the resonant converter switches from full-bridge mode to half-bridge mode. During the full-bridge to half-bridge transition process, the driving pulse width of switch Q1 is 0.75 to 1.75 times half of the resonant converter's resonant period; the driving pulse width of switch Q2 is 1.25 to 2.5 times half of the resonant converter's resonant period; switch Q3 remains off; and switch Q4 remains on.
[0017] According to another aspect of the present invention, a control method for a resonant converter is also provided. The resonant converter includes switching transistors Q1, Q2, Q3, and Q4, a resonant capacitor, and a resonant inductor. Switches Q1 and Q2 are connected in series to form a first bridge arm, and switches Q3 and Q4 are connected in series to form a second bridge arm. The first bridge arm and the second bridge arm are connected in parallel. The control method for the resonant converter includes:
[0018] When the input voltage of the resonant converter is less than the switching threshold and the resonant converter is operating in half-bridge mode, the resonant converter is controlled to perform a half-bridge to full-bridge transition process, so that the resonant converter switches from half-bridge mode to full-bridge mode. During the half-bridge to full-bridge transition process, the driving pulse width of switch Q1 is 0.75 to 1.75 times the pulse width of switch Q1 when the resonant converter is operating in half-bridge mode; the driving pulse width of switch Q2 is 1.25 to 2.5 times the pulse width of switch Q2 when the resonant converter is operating in half-bridge mode; switch Q3 is turned off; switch Q4 is turned off at the same time as switch Q1.
[0019] According to another aspect of the present invention, a control method for a resonant converter is also provided. The resonant converter includes switching transistors Q1, Q2, Q3, and Q4, a clamping branch composed of switching transistors Q5 and Q6, a resonant capacitor, and a resonant inductor. Switches Q1 and Q2 are connected in series to form a first bridge arm, and switching transistors Q3 and Q4 are connected in series to form a second bridge arm. The first bridge arm and the second bridge arm are connected in parallel. The control method for the resonant converter includes:
[0020] When the input voltage of the resonant converter is greater than the switching threshold and the resonant converter is operating in full-bridge mode, the resonant converter is controlled to switch directly from full-bridge mode to half-bridge mode. Specifically, when the resonant converter is operating in full-bridge mode, the pulse widths of switches Q1, Q2, Q3, and Q4 are all controlled by a closed loop. Switch Q5 in the clamping branch is complementary to switch Q1, and switch Q6 in the clamping branch is complementary to switch Q2. When the resonant converter is operating in half-bridge mode, switches Q1 and Q2 are complementary to each other. Switch Q4 remains on, while switches Q3, Q5, and Q6 remain off.
[0021] According to another aspect of the present invention, a control method for a resonant converter is also provided. The resonant converter includes switching transistors Q1, Q2, Q3, and Q4, a clamping branch composed of switching transistors Q5 and Q6, a resonant capacitor, and a resonant inductor. Switches Q1 and Q2 are connected in series to form a first bridge arm, and switches Q3 and Q4 are connected in series to form a second bridge arm. The first bridge arm and the second bridge arm are connected in parallel. The control method for the resonant converter includes:
[0022] When the input voltage of the resonant converter is less than the switching threshold and the resonant converter is operating in half-bridge mode, the resonant converter is controlled to perform a half-bridge to full-bridge transition process, so that the resonant converter switches from half-bridge mode to full-bridge mode; wherein,
[0023] During the transition from half-bridge to full-bridge, the driving pulse width of switch Q1 is greater than the preset minimum pulse width of switch Q1 and less than half the resonant period of the resonant converter; the driving pulse width of switch Q2 is 0.75 to 1.25 times half the resonant period of the resonant converter; switch Q3 remains off; the driving pulse of switch Q4 is consistent with the driving pulse of switch Q1; the driving pulse of switch Q5 is complementary to the driving pulse of switch Q1; and the driving pulse of switch Q6 is consistent with the driving pulse of switch Q2.
[0024] According to another aspect of the present invention, a control method for a resonant converter is also provided. The resonant converter includes switching transistors Q1, Q2, Q3, and Q4, a clamping branch composed of switching transistors Q5 and Q6, a resonant capacitor, and a resonant inductor. Switches Q1 and Q2 are connected in series to form a first bridge arm, and switching transistors Q3 and Q4 are connected in series to form a second bridge arm. The first bridge arm and the second bridge arm are connected in parallel. The control method for the resonant converter includes:
[0025] When the input voltage of the resonant converter is greater than the switching threshold and the resonant converter is operating in full-bridge mode, the resonant converter is controlled to perform a full-bridge to half-bridge transition process, so that the resonant converter switches from full-bridge mode to half-bridge mode.
[0026] During the transition from a full-bridge to a half-bridge, the driving pulse width of switch Q1 is 0.75 to 1.25 times half the resonant period of the resonant converter; the driving pulse width of switch Q3 is greater than the minimum pulse width set for switch Q3 and less than half the resonant period of the resonant converter; switches Q2 and Q4 are controlled by the full-bridge modal closed-loop control; the driving pulse of switch Q5 in the clamping branch is complementary to the driving pulse of switch Q1, and the driving pulse of switch Q6 in the clamping branch is complementary to the driving pulse of switch Q2.
[0027] The wide-gain control method for resonant converters proposed in this invention inserts a transition process drive pulse during the full-half-bridge switching process, causing the resonant cavity to generate the negative current required to achieve ZVS, thus avoiding the excessive stress problem caused by hard switching of the switching transistors during the switching process. Simultaneously, after the full-half-bridge transition process is completed, corresponding full-bridge or half-bridge closed-loop control is performed, enabling smooth switching without affecting output stability.
[0028] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:
[0029] (1) By dividing the input voltage of the resonant converter into two intervals, the resonant converter can be controlled to work in full-bridge or half-bridge mode, which can effectively broaden the voltage gain range of the resonant converter. Moreover, within the same gain range, this control method can ensure a narrower frequency conversion range, which is beneficial for the high power density design and application of high power power supplies.
[0030] (2) By setting the driving pulse width during the transition process, smooth switching between full and half bridge modes can be achieved, and the output voltage overshoot and undershoot during the switching process is small, and the switching cycle is controllable;
[0031] (3) The resonant converter can achieve ZVS in the switching process of the full and half bridge, which reduces the stress of the switching transistors and improves the EMI performance of the product, making it more reliable. Attached Figure Description
[0032] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.
[0033] Figure 1 A schematic diagram of a resonant converter is shown for the preferred embodiment;
[0034] Figure 2 The output voltage gain curve of the resonant converter;
[0035] Figure 3 The control logic diagram for the proposed resonant converter control method is implemented.
[0036] Figure 4 Timing diagram of the driving pulses for the transition process of a full-bridge to half-bridge switch in the preferred embodiment 1;
[0037] Figure 5 Timing diagram of the driving pulses for the half-bridge to full-bridge transition process in the preferred embodiment 1;
[0038] Figure 6 Timing diagram of the driving pulses for the transition process of the full-bridge to half-bridge switch in the second optimal embodiment;
[0039] Figure 7 Timing diagram of the driving pulses for the half-bridge to full-bridge transition process in the second optimal embodiment;
[0040] Figure 8 The timing diagram of the driving pulses for the transition process of the full-bridge to half-bridge switch in the best embodiment three;
[0041] Figure 9 The waveform diagram of the full-bridge to half-bridge switching experiment under the control timing of the best embodiment 1 is shown.
[0042] Figure 10The waveform diagram shows the experimental process of switching from a half-bridge to a full-bridge under the control timing of the best embodiment. Detailed Implementation
[0043] To ensure that the technical solution of the present invention is clearer, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.
[0044] The control method for the wide-gain resonant converter involved in this invention is applied to the schematic diagram of a clamp resonant converter, as shown in the figure. Figure 1 As shown, the clamped resonant converter (hereinafter referred to as the converter) includes an inverter circuit, an LLC resonant cavity, a clamping branch, a transformer, and a secondary-side rectifier and filter circuit. Figure 1 In this context, Vin represents the input power supply of the converter, and Ro represents the output load of the converter.
[0045] The inverter circuit includes a full-bridge inverter circuit composed of switching transistors Q1, Q2, Q3, and Q4; the LLC resonant cavity includes a resonant inductor Lr, a magnetizing inductor Lm, and a resonant capacitor Cr; a clamping branch composed of switching transistors Q5 and Q6; a transformer T composed of a primary winding Np and secondary windings Ns1 and Ns2; and a secondary rectifier and filter circuit including a full-wave rectifier circuit composed of rectifier transistors D1 and D2 and an output filter capacitor Co. Switches Q1 and Q2 are connected in series to form the first bridge arm, and switches Q3 and Q4 are connected in series to form the second bridge arm. The first and second bridge arms are connected in parallel. One end of the resonant capacitor Cr is connected to the first bridge arm, and the resonant inductor Lr is connected to the second bridge arm.
[0046] The converter has four steady-state operating states: When the input voltage is low, the converter operates in full-bridge PFM mode; when the input voltage is medium-low, the converter operates in full-bridge PWM mode; when the input voltage is medium-high, the converter operates in half-bridge PFM mode; and when the input voltage is high, the converter operates in half-bridge PWM mode. The timing sequence for each mode is as follows:
[0047] Full-bridge PFM mode: In the inverter circuit, the duty cycle of switches Q1 and Q2 in the first bridge arm is 50%, and the drive pulses of switches Q1 and Q2 are complementary with a phase difference of 180°; the drive of switch Q3 is the same as that of switch Q2, and the drive of switch Q4 in the second bridge arm is the same as that of switch Q1; switches Q5 and Q6 in the clamping branch are always off; the gain of the converter is adjusted by the closed-loop control of the switching frequency.
[0048] Full-bridge PWM mode: The driving phases of switches Q1 and Q2 are 180° apart, and their duty cycles are the same, both less than 50%; the driving of switch Q3 is the same as that of switch Q2, and the driving of switch Q4 is the same as that of switch Q1; switch Q5 in the clamping branch is complementary to switches Q1 / Q4, and switch Q6 in the clamping branch is complementary to switches Q2 / Q3; the operating frequencies of switches Q1 to Q6 are fixed at the resonant frequency, and the gain of the converter is controlled by adjusting the duty cycles of switches Q1 to Q4 in the inverter circuit through closed-loop adjustment;
[0049] Half-bridge PFM mode: The duty cycles of switches Q1 and Q2 are both 50%, and the drive pulses of switches Q1 and Q2 are complementary with a phase difference of 180°; switch Q3 is always off, and switch Q4 is always on; switches Q5 and Q6 in the clamping branch are always off; the gain of the converter is adjusted by controlling the switching frequency through closed loop.
[0050] Half-bridge PWM mode: The driving phases of switches Q1 and Q2 are 180° apart, and their duty cycles are the same, both less than 50%; switch Q3 is always off, and switch Q4 is always on; switch Q5 in the clamping branch is complementary to switch Q1, and switch Q6 in the clamping branch is complementary to switch Q2; the operating frequencies of switches Q1 to Q4 are fixed at the resonant frequency, and the gain of the converter is controlled by adjusting the duty cycles of switches Q1 to Q4 in the inverter circuit through closed-loop adjustment.
[0051] The gain curves corresponding to each operating mode are as follows: Figure 2 As shown, the vertical axis represents the gain G, and the horizontal axis represents the switching frequency f or the duty cycle D1 of the switching transistor Q1. Figure 2 The curve shown above represents the gain curve in full-bridge mode. When the switching frequency f is less than the resonant frequency fr of the resonant inductor Lr and capacitor Cr, the converter operates in full-bridge PFM mode, and the gain is adjusted by adjusting the operating frequency. When the switching frequency f is equal to the resonant frequency fr, the converter operates in full-bridge PWM mode, and the gain is adjusted by adjusting the duty cycle D1 of the switching transistor Q1. The gain in half-bridge mode is half that of full-bridge mode, so the gain curve in half-bridge mode can be obtained by shifting the gain curve of full-bridge mode downward.
[0052] Since the gain is continuous and there is no mode transition between the full-bridge PFM mode and the full-bridge PWM mode, conventional control can be used to switch between these two control modes. Similarly, there is no mode transition between the half-bridge PFM mode and the half-bridge PWM mode, so no special switching control method is required.
[0053] Based on the steady-state operating modes of the converter, the switching between full-bridge and half-bridge modes is also the switching process between full-bridge PWM mode and half-bridge PFM mode. Figure 2As shown in the gain curve, the gain is discontinuous between the full-bridge PWM mode in region B and the half-bridge PFM mode in region C. Therefore, it is necessary to add a transition process drive pulse.
[0054] The control logic diagram for the converter control method proposed in this invention is as follows: Figure 3 As shown. By setting a switching threshold, the input voltage is divided into two operating ranges. To avoid the converter switching back and forth between full-bridge and half-bridge modes, the switching threshold is set with hysteresis.
[0055] When the input voltage is greater than the switching threshold, if the converter is operating in full-bridge mode, the control converter performs a full-bridge to half-bridge transition process, causing the resonant converter to switch from full-bridge mode to half-bridge mode. After entering half-bridge mode, the corresponding drive pulse timing is adjusted by the half-bridge working closed-loop control. If the converter is operating in half-bridge mode, the control converter operates normally in half-bridge control mode.
[0056] When the input voltage is less than the switching threshold, if the converter is operating in half-bridge mode, the control converter performs a half-bridge to full-bridge transition process, causing the resonant converter to switch from half-bridge mode to full-bridge mode. After entering full-bridge mode, the corresponding drive pulse timing is adjusted by the full-bridge working closed-loop control. If the converter is operating in full-bridge mode, the converter operates normally in full-bridge control mode.
[0057] The switching threshold voltage can be designed between NVo and 2NVo, preferably between 1.5*NVo, where N is the turns ratio of the primary winding to the secondary winding of transformer T, and Vo is the output voltage of the converter.
[0058] In addition, the number of cycles of the drive pulses for the transition process of full-half-bridge switching insertion can be set as needed, preferably 1 to 5 switching cycles.
[0059] The transition process drive pulses for full-half-bridge switching include, but are not limited to, the following embodiments:
[0060] First Embodiment
[0061] The timing diagram of the driving pulses during the transition process from a full-bridge to a half-bridge is as follows: Figure 4 As shown, the drive pulse width of switch Q1 is wider than when it operates in full-bridge mode, and is set to 0.75 to 1.75 times half the resonant period of the resonant converter; the drive pulse width of switch Q2 is wider than when it operates in full-bridge mode, and is set to 1.25 to 2.5 times half the resonant period of the resonant converter; switch Q3 remains off; switch Q4 remains on; in the clamping branch, switch Q5 is complementary to switch Q1, and switch Q6 is complementary to switch Q2.
[0062] The timing diagram of the driving pulse for the half-bridge to full-bridge transition process is as follows: Figure 5As shown, the driving pulse of switch Q is 0.75 to 1.75 times the driving pulse width of switch Q1 when the resonant converter is operating in half-bridge mode; the driving pulse width of switch Q2 is wider than when operating in half-bridge mode, and is set to 1.25 to 2.5 times the driving pulse width of switch Q2 in half-bridge mode; switch Q3 is kept off; switch Q4 is turned off at the same time as switch Q1; switch Q5 in the clamping branch is directly complementary to switch Q1, and switch Q6 in the clamping branch is directly complementary to switch Q2.
[0063] The switching process can be set to one or more cycles to achieve the switching.
[0064] Second Embodiment
[0065] The timing diagram of the drive pulses for switching from a full-bridge to a half-bridge is as follows: Figure 6 As shown, when the resonant converter operates in full-bridge mode, the pulse widths of switches Q1, Q2, Q3, and Q4 are all controlled by a closed loop. Switch Q5 in the clamping branch is directly complementary to switch Q1, and switch Q6 in the clamping branch is directly complementary to switch Q2. When the resonant converter operates in half-bridge mode, the complementary switches Q1 and Q2 are turned on; switch Q4 remains on, while switches Q3, Q5, and Q6 remain off.
[0066] In this embodiment, due to the clamping branch composed of switch Q5 and switch Q6, when the resonant converter is operating in full-bridge mode, switch Q5 and switch Q1 are complementary in conduction, and switch Q6 and switch Q2 are complementary in conduction. This allows the switch from full-bridge mode to half-bridge mode to be switched without a transition process. That is, when the input voltage of the resonant converter is greater than the switching threshold, if the resonant converter is operating in full-bridge mode, the resonant converter can be directly switched from full-bridge mode to half-bridge mode.
[0067] The timing diagram of the driving pulse for the half-bridge to full-bridge transition process is as follows: Figure 7 As shown, the driving pulse of switch Q1 is a series of specific pulses, and the pulse width is set to be greater than the minimum pulse width set for switch Q1 and less than half of the resonant period, preferably set to 0.25 times half of the resonant period; the driving pulse of switch Q2 is a series of specific pulses, set to 0.75 to 1.25 times half of the resonant period; switch Q3 remains in the off state; the pulse width of switch Q4 is the same as that of Q1; switch Q5 in the clamping branch is complementary to switch Q1, and switch Q6 in the clamping branch is complementary to switch Q2.
[0068] The switching process can be set to one or more cycles to achieve the switching.
[0069] Third Embodiment
[0070] The timing diagram of the control pulse drive pulse for the transition process between a full-bridge and a half-bridge bridge can also be shown as follows: Figure 8 As shown, the driving pulse of switch Q1 is a series of specific pulses. The width of this pulse can be set to be around half the half-cycle resonant pulse width of the resonant converter's resonant period, preferably 0.75 to 1.25 times the half-cycle resonant pulse width of half the resonant period. Switch Q2 is controlled by a full-bridge mode closed-loop control. The driving pulse of switch Q3 is a series of specific pulses. The width of this pulse can be set to be greater than the minimum pulse width set for switch Q3 and less than half the half-cycle resonant pulse width of the resonant period, preferably 0.25 times the half-cycle resonant pulse width of half the resonant period. The pulse width of switch Q4 is controlled by a full-bridge mode closed-loop control. Switch Q5 in the clamping branch is directly complementary to switch Q1, and switch Q6 in the clamping branch is directly complementary to switch Q2.
[0071] The switching process can be set to one or more cycles to achieve the switching.
[0072] A clamped resonant converter with 24V output and 600W power was used to build an experimental prototype to verify the switching process between full-bridge and half-bridge modes. The switching control timing of the optimal embodiment was adopted, and the experimental waveforms of the switching process from full-bridge to half-bridge mode were obtained as follows: Figure 9 As shown, the waveforms include the stress waveform A1 of switch Q2, the output voltage waveform A2, and the stress waveform A3 of switch Q6. Figure 9 It can be seen that the maximum output voltage undershoot during the full-bridge to half-bridge switching process is 370mV, only 1.6% Vo. Furthermore, the experimental waveforms for the half-bridge to full-bridge mode switching process are as follows: Figure 10 As shown, the waveforms include the stress waveform A1 of switch Q2, the output voltage waveform A2, and the stress waveform A3 of switch Q6. Figure 10 It can be seen that the maximum output voltage undershoot during the half-bridge to full-bridge switching process is 306mV, only 1.3% Vo. Furthermore, the primary-side switches of the converter achieve ZVS throughout the entire switching process, and the voltage stress on the switches is relatively low.
[0073] The wide-gain control method for resonant converters proposed in this invention achieves smooth switching between full- and half-bridge modes by inserting transition process drive pulses, and the output voltage overshoot and undershoot during the switching process are small. In addition, the power switches can achieve ZVS during the full- and half-bridge switching process, which reduces the stress on the switches and improves the EMI performance of the product. The introduced full- and half-bridge switching control strategy can better guarantee the output voltage gain range of the converter, which is beneficial to the high power density design and application of high power supplies.
[0074] The above description of the embodiments is only for the purpose of helping to understand the inventive concept of this application and is not intended to limit the present invention. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made without departing from the principle of the present invention should be included within the protection scope of the present invention.
Claims
1. A control method for a resonant converter, the resonant converter comprising switching transistors Q1, Q2, Q3, and Q4, a resonant capacitor, and a resonant inductor, wherein switching transistors Q1 and Q2 are connected in series to form a first bridge arm, switching transistors Q3 and Q4 are connected in series to form a second bridge arm, and the first and second bridge arms are connected in parallel; characterized in that, The control method for the resonant converter includes: When the input voltage of the resonant converter is greater than the switching threshold and the resonant converter is operating in full-bridge mode, the resonant converter is controlled to perform a full-bridge to half-bridge transition process, so that the resonant converter switches from full-bridge mode to half-bridge mode. During the full-bridge to half-bridge transition process, the driving pulse width of switch Q1 is 0.75 to 1.75 times half of the resonant converter's resonant period; the driving pulse width of switch Q2 is 1.25 to 2.5 times half of the resonant converter's resonant period; switch Q3 remains off; and switch Q4 remains on. When the input voltage is less than the switching threshold and the resonant converter is operating in half-bridge mode, the resonant converter is controlled to perform a half-bridge to full-bridge transition process, so that the resonant converter switches from half-bridge mode to full-bridge mode. During the half-bridge to full-bridge transition process: the driving pulse width of switch Q1 is 0.75 to 1.75 times the driving pulse width of switch Q1 when the resonant converter is operating in half-bridge mode; the driving pulse width of switch Q2 is 1.25 to 2.5 times the driving pulse width of switch Q2 when the resonant converter is operating in half-bridge mode; switch Q3 is turned off; switch Q4 is turned off simultaneously with switch Q1.
2. The control method for the resonant converter according to claim 1, in the transition process from full-bridge to half-bridge, the driving pulses of switching transistors Q1 to Q6 have one or more cycles; in the transition process from half-bridge to full-bridge, the driving pulses of switching transistors Q1 to Q6 have one or more cycles.
3. The control method for the resonant converter according to claim 1, wherein the resonant converter further comprises a clamping branch composed of switching transistors Q5 and Q6, wherein during the transition from a full-bridge to a half-bridge, the driving pulse of switching transistor Q5 is complementary to the driving pulse of switching transistor Q1, and the driving pulse of switching transistor Q6 is complementary to the driving pulse of switching transistor Q2; during the transition from a half-bridge to a full-bridge, the driving pulse of switching transistor Q5 is complementary to the driving pulse of switching transistor Q1, and the driving pulse of switching transistor Q6 is complementary to the driving pulse of switching transistor Q2.
4. The control method for the resonant converter according to claim 1, characterized in that, The switching threshold is between NVo and 2NVo, with hysteresis allowed. N is the turns ratio of the primary winding to the secondary winding of the transformer in the resonant converter, and Vo is the output voltage of the resonant converter.
5. The control method for the resonant converter according to claim 4, characterized in that, The switching threshold is 1.
5. NVo.
6. A control method for a resonant converter, the resonant converter comprising switching transistors Q1, Q2, Q3, and Q4, a resonant capacitor, and a resonant inductor, wherein switching transistors Q1 and Q2 are connected in series to form a first bridge arm, switching transistors Q3 and Q4 are connected in series to form a second bridge arm, and the first and second bridge arms are connected in parallel; characterized in that, The control method for the resonant converter includes: When the input voltage of the resonant converter is greater than the switching threshold and the resonant converter is operating in full-bridge mode, the resonant converter is controlled to perform a full-bridge to half-bridge transition process, so that the resonant converter switches from full-bridge mode to half-bridge mode. During the full-bridge to half-bridge transition process, the driving pulse width of switch Q1 is 0.75 to 1.75 times half of the resonant converter's resonant period; the driving pulse width of switch Q2 is 1.25 to 2.5 times half of the resonant converter's resonant period; switch Q3 remains off; and switch Q4 remains on.
7. A control method for a resonant converter, the resonant converter comprising switching transistors Q1, Q2, Q3, and Q4, a resonant capacitor, and a resonant inductor, wherein switching transistors Q1 and Q2 are connected in series to form a first bridge arm, switching transistors Q3 and Q4 are connected in series to form a second bridge arm, and the first and second bridge arms are connected in parallel; characterized in that, The control method for the resonant converter includes: When the input voltage of the resonant converter is less than the switching threshold and the resonant converter is operating in half-bridge mode, the resonant converter is controlled to perform a half-bridge to full-bridge transition process, so that the resonant converter switches from half-bridge mode to full-bridge mode. During the half-bridge to full-bridge transition process, the driving pulse width of switch Q1 is 0.75 to 1.75 times the pulse width of switch Q1 when the resonant converter is operating in half-bridge mode; the driving pulse width of switch Q2 is 1.25 to 2.5 times the pulse width of switch Q2 when the resonant converter is operating in half-bridge mode; switch Q3 is turned off; switch Q4 is turned off at the same time as switch Q1.
8. A control method for a resonant converter, the resonant converter comprising switching transistors Q1, Q2, Q3, and Q4, a clamping branch composed of switching transistors Q5 and Q6, a resonant capacitor, and a resonant inductor, wherein switching transistors Q1 and Q2 are connected in series to form a first bridge arm, and switching transistors Q3 and Q4 are connected in series to form a second bridge arm, and the first and second bridge arms are connected in parallel; characterized in that, The control method for the resonant converter includes: When the input voltage of the resonant converter is less than the switching threshold and the resonant converter is operating in half-bridge mode, the resonant converter is controlled to perform a half-bridge to full-bridge transition process, so that the resonant converter switches from half-bridge mode to full-bridge mode; wherein, During the transition from half-bridge to full-bridge, the driving pulse width of switch Q1 is greater than the preset minimum pulse width of switch Q1 and less than half the resonant period of the resonant converter; the driving pulse width of switch Q2 is 0.75 to 1.25 times half the resonant period of the resonant converter; switch Q3 remains off; the driving pulse of switch Q4 is consistent with the driving pulse of switch Q1; the driving pulse of switch Q5 is complementary to the driving pulse of switch Q1; and the driving pulse of switch Q6 is consistent with the driving pulse of switch Q2.
9. A control method for a resonant converter, the resonant converter comprising switching transistors Q1, Q2, Q3, and Q4, a clamping branch composed of switching transistors Q5 and Q6, a resonant capacitor, and a resonant inductor, wherein switching transistors Q1 and Q2 are connected in series to form a first bridge arm, and switching transistors Q3 and Q4 are connected in series to form a second bridge arm, and the first and second bridge arms are connected in parallel; characterized in that, The control method for the resonant converter includes: When the input voltage of the resonant converter is greater than the switching threshold and the resonant converter is operating in full-bridge mode, the resonant converter is controlled to perform a full-bridge to half-bridge transition process, so that the resonant converter switches from full-bridge mode to half-bridge mode. During the transition from a full-bridge to a half-bridge, the driving pulse width of switch Q1 is 0.75 to 1.25 times half the resonant period of the resonant converter; the driving pulse width of switch Q3 is greater than the minimum pulse width set for switch Q3 and less than half the resonant period of the resonant converter; switches Q2 and Q4 are controlled by the full-bridge modal closed-loop control; the driving pulse of switch Q5 in the clamping branch is complementary to the driving pulse of switch Q1, and the driving pulse of switch Q6 in the clamping branch is complementary to the driving pulse of switch Q2.