A slope-compensated LLC resonant converter soft-start method and system

Abstract

The application discloses a slope compensation LLC resonant converter soft-start method and system. The method comprises the following steps: S200, in the PWM mode, the duty cycle is adjusted to follow the reference voltage through the loop control quantity; S300, whether the loop control quantity is increased by a set change threshold compared with the comparison quantity; if yes, the current output voltage of the LLC resonant converter is read, and the ratio of the difference between the current output voltage and the output voltage during starting and the set change threshold is taken as a first change rate; otherwise, S500 is executed; S400, when the first change rate is greater than a set threshold, the direct current gain of the current LLC resonant converter returns to a set value; when the first change rate is not greater than the set threshold, the direct current gain is increased in a certain proportion; S500, whether the duty cycle is not less than a set duty cycle maximum value; if yes, the PWM mode is switched to the PFM mode; otherwise, S200 is returned. The application improves the stability and reliability of the starting process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resonant converter, and particularly relates to a slope compensation LLC resonant converter soft start method and system. BACKGROUND

[0002] LLC resonant converter has the advantages of zero-voltage switching of switching tubes and zero-current turn-off of rectifier diodes in a wide load range, soft switching, high efficiency and wide output voltage range, etc., and becomes a power converter with excellent performance and is widely used. Generally, a large-capacity output capacitor is configured at the output end of the LLC resonant converter to filter the switching current ripple and reduce the output voltage ripple. However, when the LLC resonant converter is powered on, the initial voltage of the output capacitor is zero, which is equivalent to the short circuit state of the transformer secondary side, resulting in the clamping of the transformer primary side voltage to zero, and at this time the impedance of the resonant cavity is extremely low. During the soft start process, the output capacitor needs to be charged, which will cause a large inrush current in the resonant cavity, so that the power device bears a high current stress and voltage stress, which may cause device damage, converter failure, and even trigger overcurrent protection, affecting the normal operation of the converter. To solve this problem, soft start technology is usually used to suppress the inrush current and ensure the safe and reliable start of the converter.

[0003] At present, the LLC resonant converter soft start methods mainly include:

[0004] Frequency reduction soft start: a higher working frequency is set in the initial stage of soft start to reduce the voltage and current stress in the resonant cavity, and then the working frequency is gradually reduced until the output voltage is established to complete the soft start. This method is relatively simple to implement, but it is limited by the maximum switching frequency of the resonant converter, and it is difficult to achieve a too high start frequency, resulting in limited suppression effect on the start inrush current.

[0005] Pulse width modulation soft start: the switching frequency is kept constant during the soft start process, and the output voltage is established by gradually increasing the duty cycle to 50%. This method is relatively easy to implement, and can effectively suppress the inrush current to a certain extent, but the soft start time is relatively long.

[0006] Composite control soft start: a soft start method combining PWM and pulse frequency modulation (PFM). The combination of PWM and PFM can reduce the peak value of the start inrush current to a certain extent, but there is a large gain change in the PWM to PFM mode switching, resulting in the problems of voltage plateau (voltage stays at a certain level and no longer rises) and voltage jump (voltage suddenly changes) in the soft start process.

[0007] Therefore, it is urgent to solve the technical problems existing in the above-mentioned LLC resonant converter soft start methods. SUMMARY

[0008] The application aims to provide a slope-compensated LLC resonant converter soft-start method and system to solve the problems of poor surge current suppression effect, large gain variation caused by the combination of PWM and PFM in the prior LLC resonant converter soft-start method.

[0009] To achieve the above-mentioned purpose, the application provides the following technical solutions.

[0010] The application provides a slope-compensated LLC resonant converter soft-start method, and the loop control quantity of the LLC resonant converter is controlled by a controller, including the following steps.

[0011] S100, presetting a comparison quantity of the loop control quantity and reading the output voltage of the LLC resonant converter at startup;

[0012] S200, in the PWM soft-start mode, adjusting the duty cycle to follow the reference voltage through the loop control quantity;

[0013] S300, whether the loop control quantity is increased by a set change threshold compared with the comparison quantity; if yes, reading the current output voltage of the LLC resonant converter, taking the ratio of the difference between the current output voltage and the output voltage at startup and the set change threshold as a first change rate, updating the output voltage at startup to the current output voltage, and updating the comparison quantity to the current loop control quantity; otherwise, executing step S500;

[0014] S400, when the first change rate is greater than a set threshold, the DC gain of the LLC resonant converter returns to a set value; when the first change rate is not greater than the set threshold, increasing the DC gain by a certain proportion;

[0015] S500, whether the loop control quantity is large enough to make the duty cycle not less than a set duty cycle maximum value; if yes, updating the current duty cycle to the duty cycle maximum value, switching the PWM soft-start mode to a PFM soft-start mode, and completing the soft-start of the LLC resonant converter through the PFM soft-start mode; otherwise, returning to execute step S200; wherein in the PFM soft-start mode, the duty cycle is no longer directly adjusted by the loop control quantity, and the loop control quantity u is only used to reduce the switching frequency of the driving signal.

[0016] In one or more embodiments, the working frequency of the controller is fixed when the LLC resonant converter starts, and the fixed frequency is higher than the resonant frequency of the LLC resonant converter.

[0017] In one or more embodiments, the fixed frequency of the controller is not less than 1.5fr and not higher than 3fr.

[0018] In one or more embodiments, the initial duty cycle is between 0 and 0.2.

[0019] In one or more embodiments, when the LLC resonant converter is started, the controller outputs driving signals with a phase difference of 180° to drive the power switch of the LLC resonant converter to work.

[0020] In one or more embodiments, when the LLC resonant converter is started, soft start boost is achieved by adjusting the duty cycle.

[0021] In one or more embodiments, the soft start of the LLC resonant converter is completed by the PFM soft start mode, including the following steps:

[0022] S501, the controller outputs a loop control quantity according to the relationship between the reference voltage and the output voltage;

[0023] S502, whether the output loop control quantity is increased by a set change threshold compared with the comparison quantity; if yes, the current output voltage of the LLC resonant converter is read, the ratio of the difference between the current output voltage and the output voltage at startup to the set change threshold is taken as a second change rate, the output voltage at startup is updated to the current output voltage, and the comparison quantity is updated to the current loop control quantity; otherwise, step S504 is executed;

[0024] S503, when the second change rate is greater than a set threshold, the direct current gain of the current LLC resonant converter returns to a set value; when the second change rate is not greater than the set threshold, the direct current gain is increased by a certain proportion;

[0025] S504, whether the current output voltage reaches the rated output voltage: if yes, the soft start is ended; otherwise, step S501 is returned to be executed.

[0026] As another aspect of the application, a slope compensation LLC resonant converter soft start system is also provided, which comprises an LLC resonant converter, a voltage sampling module and a controller connected in sequence, the controller is connected with a plurality of switches on the control loop of the LLC resonant converter, and the controller is used to realize the above-mentioned slope compensation LLC resonant converter soft start method.

[0027] In one or more embodiments, the slope compensation LLC resonant converter soft start system further comprises an isolation driving module, one end of the isolation driving module is connected with the controller, and the other end is connected with a plurality of switches on the control loop of the LLC resonant converter.

[0028] In one or more embodiments, the controller comprises a DSP, a single-chip microcomputer, an ARM embedded processor or a FPGA programmable chip.

[0029] The application has the following advantages or beneficial effects by implementing one of the above technical solutions.

[0030] In the soft start stage, the controller detects the output voltage of the LLC resonant converter in real time, and dynamically compensates the DC gain of the controller according to the slope relationship between the output voltage and the loop control quantity, so as to enhance the regulation ability of the loop control quantity to the output voltage. In this process, it is ensured that the resonant current of the half-bridge LLC resonant converter or the full-bridge LLC resonant converter is always kept within an acceptable range when starting, the output voltage is quickly and stably established, and the soft start of the half-bridge LLC resonant converter or the full-bridge LLC resonant converter is completed. Further, the inrush current impact of the LLC resonant converter during startup can be effectively suppressed, and the output voltage can still be smoothly and quickly tracked to the reference voltage at the switching boundary of the PWM soft start mode and the PFM soft start mode, thereby improving the stability and reliability of the startup process, and having high engineering application value. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor. In the drawings:

[0032] Figure 1 is a slope compensation LLC resonant converter soft start method flow chart of the embodiment of the application;

[0033] Figure 2 is a flow chart of completing the soft start of the LLC resonant converter by the PFM soft start mode according to the embodiment of the application;

[0034] Figure 3 is a slope compensation LLC resonant converter soft start system block diagram according to the embodiment of the application;

[0035] Figure 4 is a slope compensation LLC resonant converter soft start system system structure diagram based on the half-bridge LLC resonant converter according to the embodiment of the application;

[0036] Figure 5 is a control effect diagram of the control scheme using the conventional PWM+PFM according to the embodiment of the application;

[0037] Figure 6 is a control effect diagram of the LLC resonant converter soft start scheme using the slope compensation according to the embodiment of the application. DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the present application clearer, the various exemplary embodiments to be described below will be described with reference to the corresponding drawings, which constitute a part of the exemplary embodiments and in which various exemplary embodiments that can be used to implement the present application are described. Unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present disclosure. It should be understood that they are only examples of processes, methods and apparatuses, etc. consistent with some aspects of the present disclosure as detailed in the appended claims, and other embodiments can be used or structural and functional modifications can be made to the embodiments listed herein without departing from the scope and spirit of the present application.

[0039] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse" and the like indicate the orientation or positional relationship based on the drawings shown, only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the elements referred to must have a specific orientation, structure and operation. The terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. The term "a plurality of" means two or more. The terms "connected", "connected" should be broadly understood, for example, it can be fixed connection, detachable connection, integral connection, mechanical connection, electrical connection, communication connection, direct connection, indirect connection through intermediate medium, internal communication of two elements or interaction relationship between two elements. The term "and / or" includes any and all combinations of one or more related listed items. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0040] In order to illustrate the technical solutions of the present application, the following specific embodiments are described, only showing the parts related to the embodiments of the present application.

[0041] Embodiment one:

[0042] As Figures 1-2 shown, the present application provides a slope compensation LLC resonant converter soft start method, the loop control quantity u of LLC resonant converter is controlled by controller, including the following steps:

[0043] S100, presetting the comparison quantity u1 of loop control quantity, reading the output voltage Uout1 of LLC resonant converter at start-up.

[0044] S200, in PWM soft start mode, the duty cycle D is adjusted by the loop control quantity u to follow the reference voltage, so that the output voltage can follow the reference voltage.

[0045] S300, whether the loop control quantity u increases the set change threshold du compared with the comparison quantity u1; if yes, reading the current output voltage Uout2 of the LLC resonant converter, taking the ratio of the difference between the current output voltage Uout2 and the output voltage Uout1 at the start and the set change threshold du as the first change rate k1 (k1= (Uout2-Uout1) / du), updating the output voltage Uout1 at the start to the current output voltage Uout2 (Uout1=Uout2), and updating the comparison quantity u1 to the current loop control quantity u (u1=u); otherwise, performing step S500.

[0046] S400, when the first change rate k1 is greater than the set threshold S1, the direct current gain of the LLC resonant converter returns to the set value; when the first change rate k1 is not greater than the set threshold S1, increasing the direct current gain in a certain proportion.

[0047] It can be understood that the direct current gain can be controlled by setting the digital controller.

[0048] S500, whether the loop control quantity u is large enough to make the duty cycle D not less than the set duty cycle maximum value Dmax; if yes, updating the current duty cycle D to the duty cycle maximum value Dmax (D=Dmax), switching the PWM soft start mode to the PFM soft start mode, and completing the soft start of the LLC resonant converter through the PFM soft start mode; otherwise, returning to perform step S200. In the PFM soft start mode, the duty cycle D is no longer directly adjusted by the loop control quantity u, and the loop control quantity u is only used to reduce the switching frequency of the driving signal.

[0049] It can be understood that the soft start process starts with a fixed frequency and increases the duty cycle; subsequently, the frequency is changed while the duty cycle is kept constant. The PFM participates in the frequency control process, and the greater the duty cycle, the greater the output voltage, and the smaller the frequency, the greater the output voltage. The soft start process changes, and in order to continue to increase the output voltage, the object of the control quantity u changes, and the frequency is affected.

[0050] In one or more embodiments, the soft start of the LLC resonant converter is completed through the PFM soft start mode, including the following steps:

[0051] S501, the controller outputs the loop control quantity u according to the relationship between the reference voltage and the output voltage. That is, the difference between the reference voltage and the output voltage is output as the loop control quantity u through the controller.

[0052] S502, whether the output loop control quantity u is increased by a set change threshold du compared with the comparison quantity u1 (the comparison quantity u1 is the updated comparison quantity u1); if yes, reading the current output voltage Uout2 of the LLC resonant converter, taking the ratio of the difference between the current output voltage Uout2 and the output voltage Uout1 at the start (the output voltage Uout1 at the start is the updated Uout1) and the set change threshold du as a second change rate k2, updating the output voltage Uout1 at the start to the current output voltage Uout2 (Uout1=Uout2), updating the comparison quantity u1 to the current loop control quantity u (u1=u); otherwise, performing step S504.

[0053] S503, when the second change rate k2 is greater than a set threshold S1, the direct current gain of the current LLC resonant converter returns to a set value; when the second change rate k2 is not greater than the set threshold S1, increasing the direct current gain by a certain proportion.

[0054] S504, whether the current output voltage Vout2 reaches the rated output voltage Vo: if yes, the soft start is ended; otherwise, returning to perform step S501.

[0055] Based on the above embodiment, during the start of the LLC resonant converter, the working frequency of the controller is fixed, and the fixed frequency is higher than the resonant frequency of the LLC resonant converter. In this way, the adjustment of the controller in the whole soft start process can be more fine and the resolution is higher.

[0056] Further, the fixed frequency of the controller is not less than 1.5fr and not higher than 3fr.

[0057] Based on the above embodiment, the initial duty ratio is valued between 0 and 0.2.

[0058] Based on the above embodiment, during the start of the LLC resonant converter, the controller outputs driving signals with a phase difference of 180° to drive the power switch tube of the LLC resonant converter to work.

[0059] Based on the above embodiment, during the start of the LLC resonant converter, the soft start boost is realized by adjusting the duty ratio.

[0060] The method of the embodiment controls the controller to detect the output voltage of the LLC resonant converter in real time in the soft start stage, and dynamically compensates the DC gain of the controller according to the slope relationship between the output voltage and the loop control quantity, so as to enhance the regulation ability of the loop control quantity to the output voltage. In this process, it is ensured that the resonant current of the half-bridge LLC resonant converter or the full-bridge LLC resonant converter is always kept within an acceptable range when the half-bridge LLC resonant converter or the full-bridge LLC resonant converter starts, the output voltage is quickly and stably established, and the soft start of the half-bridge LLC resonant converter or the full-bridge LLC resonant converter is completed. Further, the surge current impact of the LLC resonant converter during startup can be effectively inhibited, and it is ensured that the output voltage can still be smoothly and quickly tracked to the reference voltage at the switching boundary between the PWM soft start mode and the PFM soft start mode, so as to improve the stability and reliability of the startup process, and has high engineering application value.

[0061] Embodiment two:

[0062] As shown in Figures 3-4 The present application also provides a slope-compensated LLC resonant converter soft start system, which is suitable for LLC full-bridge resonant converters or LLC half-bridge resonant converters, and comprises an LLC resonant converter, a voltage sampling module and a controller connected in sequence. The controller is connected to the multiple switches in the control loop of the LLC resonant converter, and is used to implement the slope-compensated LLC resonant converter soft start method described in embodiment one. The method is consistent with that in embodiment one, and details are referred to embodiment one.

[0063] Based on the above embodiment, the slope-compensated LLC resonant converter soft start system further comprises an isolation driving module, one end of which is connected to the controller, and the other end of which is connected to the multiple switches in the control loop of the LLC resonant converter. The isolation driving module can well isolate the driving signals of the switches and avoid the influence between the signals.

[0064] Based on the above embodiment, the controller comprises a DSP, a single-chip microcomputer, an ARM embedded processor or an FPGA programmable chip.

[0065] As shown in Figures 5-6 The present embodiment also provides a slope-compensated LLC resonant converter soft start system composed of a half-bridge LLC resonant converter, and the slope-compensated LLC resonant converter soft start scheme of the present embodiment is compared with the conventional PWM+PFM control scheme through the system.

[0066] It can be seen from the comparison that, in the control effect diagram of the conventional PWM+PFM control scheme, the output voltage cannot monotonously rise near the switching point from the PWM soft start mode to the PFM soft start mode, and there is a voltage platform (as shown in Figure 5The LLC resonant converter soft-start scheme with the slope compensation of the present embodiment improves the voltage platform problem caused by insufficient gain near the switching point from the PWM soft-start mode to the PFM soft-start mode, effectively suppresses the surge current impact of the resonant cavity, and makes the soft-start process more stable and reliable.

[0067] The above description is merely preferred embodiments of the present application, and variations and / or equivalents of these features and embodiments can be practiced in various applications without departing from the spirit and scope of the present application. In addition, those skilled in the art will appreciate that modifications to the described embodiments can be made without departing from the spirit and scope of the present application. Accordingly, the present application is not limited to the described embodiments, but rather encompasses all such variations and equivalents that fall within the scope of the claims.

Claims

1. A slope-compensated soft-start method for an LLC resonant converter, characterized in that, The loop control parameters of the LLC resonant converter are controlled by a controller, including the following steps: S100, a comparison value of the preset loop control quantity, reads the output voltage of the LLC resonant converter when it starts up; S200: In PWM soft-start mode, the duty cycle is adjusted by the loop control quantity to follow the reference voltage; S300: Has the loop control quantity increased by a set change threshold compared to the comparison quantity? If so, read the current output voltage of the LLC resonant converter, and use the ratio of the difference between the current output voltage and the output voltage at startup to the set change threshold as the first change rate. Update the output voltage at startup to the current output voltage, and update the comparison quantity to the current loop control quantity. Otherwise, execute step S500. S400: When the first rate of change is greater than the set threshold, the DC gain of the LLC resonant converter returns to the set value; when the first rate of change is not greater than the set threshold, the DC gain is increased by a certain proportion. S500: Is the loop control quantity large enough to make the duty cycle not less than the set maximum duty cycle value? If so, the current duty cycle is updated to the maximum duty cycle value, and the PWM soft start mode is switched to the PFM soft start mode. The soft start of the LLC resonant converter is completed through the PFM soft start mode. Otherwise, return to step S200; In PFM soft-start mode, the duty cycle is no longer directly adjusted by the loop control quantity; the loop control quantity is only used to reduce the switching frequency of the drive signal.

2. The slope-compensated soft-start method for an LLC resonant converter according to claim 1, characterized in that, When the LLC resonant converter starts up, the controller operates at a fixed frequency, which is higher than the resonant frequency of the LLC resonant converter.

3. The slope-compensated soft-start method for an LLC resonant converter according to claim 2, characterized in that, The controller's fixed frequency is no less than 1.5fr and no more than 3fr.

4. The slope-compensated soft-start method for an LLC resonant converter according to claim 1, characterized in that, The initial duty cycle is between 0 and 0.

2.

5. The slope-compensated soft-start method for an LLC resonant converter according to claim 1, characterized in that, When the LLC resonant converter starts up, the controller outputs a drive signal with a phase difference of 180° to drive the power switch of the LLC resonant converter.

6. The slope-compensated soft-start method for an LLC resonant converter according to claim 1, characterized in that, When the LLC resonant converter starts up, a soft-start boost is achieved by adjusting the duty cycle.

7. The slope-compensated soft-start method for an LLC resonant converter according to claim 1, characterized in that, The soft start of an LLC resonant converter using PFM soft start mode includes the following steps: S501: The controller outputs a loop control quantity based on the relationship between the reference voltage and the output voltage. S502. Does the output loop control quantity increase the set change threshold compared to the comparison quantity? If so, read the current output voltage of the LLC resonant converter, and use the ratio of the difference between the current output voltage and the output voltage at startup to the set change threshold as the second change rate. Update the output voltage at startup to the current output voltage, and update the comparison quantity to the current loop control quantity. Otherwise, execute step S504. S503. When the second rate of change is greater than the set threshold, the DC gain of the current LLC resonant converter returns to the set value; when the second rate of change is not greater than the set threshold, the DC gain is increased by a certain proportion. S504. Has the current output voltage reached the rated output voltage? If yes, the soft start ends; otherwise, return to step S501.

8. A slope-compensated soft-start system for an LLC resonant converter, characterized in that, The device includes an LLC resonant converter, a voltage sampling module, and a controller connected in sequence. The controller is connected to multiple switches on the control loop of the LLC resonant converter. The controller is used to implement the slope-compensated soft-start method for an LLC resonant converter as described in any one of claims 1-7.

9. A slope-compensated LLC resonant converter soft-start system according to claim 8, characterized in that, It also includes an isolation drive module, one end of which is connected to the controller, and the other end is connected to multiple switches in the control loop of the LLC resonant converter.

10. A slope-compensated LLC resonant converter soft-start system according to claim 8, characterized in that, The controller includes a DSP, a microcontroller, an ARM embedded processor, or an FPGA programmable chip.

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