A resonant converter and a control method and control system thereof

Abstract

The application discloses a resonant converter and a control method and system thereof, and solves the problem of high output voltage of the resonant converter under light load or no load, and has the advantages of simple control and small ripple. The method comprises the following steps: judging whether the resonant converter works under light load or no load, if yes, adjusting the switching frequency of the resonant converter in the zero-voltage switching (ZVS) working area, and judging whether the resonant converter reaches a steady state; if the switching frequency reaches a preset limit value and the resonant converter still does not reach the steady state, switching to the zero-current switching (ZCS) working area, and continuing to adjust the switching frequency of the resonant converter until the resonant converter reaches the steady state.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a resonant converter and a control method and system thereof. BACKGROUND

[0002] Generally, a resonant converter (e.g. LLC resonant converter) adopts a variable frequency control mode. In an ideal case, the gain of the resonant converter decreases with the increase of the switching frequency. Therefore, when the resonant converter is in a light load or no load state, the switching frequency is generally increased to reduce the gain. However, due to the existence of the parasitic capacitance of the isolation transformer and the output rectifier tube, when the switching frequency exceeds a certain value of the resonant frequency, the gain abnormally increases, i.e. the output parameter drifts high.

[0003] To solve the problem of the output parameter drift high of the resonant converter in a light load or no load state, the prior art generally adopts a duty cycle-frequency hybrid regulation mode, an intermittent operation mode or a combination of the two. However, the duty cycle-frequency hybrid regulation mode is relatively complex in control, and the priority of the duty cycle and frequency regulation needs to be determined. The intermittent operation mode means that the resonant converter is regularly and intermittently operated at a relatively high frequency with an approximate 50% duty cycle to reduce the gain, but the ripple is large. The combination of the two has the problems of complex control and large ripple in a light load or no load state. SUMMARY

[0004] Therefore, the present application provides a resonant converter and a control method and system thereof to solve the problem of the output parameter drift high of the resonant converter in a light load or no load state, and has the advantages of simple control and small ripple.

[0005] A resonant converter control method, comprising:

[0006] determining whether the resonant converter is in a light load or no load state, and if so, adjusting the switching frequency of the resonant converter in a zero voltage switching (ZVS) operating region, and determining whether the resonant converter reaches a steady state;

[0007] if the resonant converter does not reach the steady state when the switching frequency reaches a preset limit value, switching to a zero current switching (ZCS) operating region, and continuing to adjust the switching frequency of the resonant converter until the resonant converter reaches the steady state.

[0008] Optionally, the switching to the zero current switching (ZCS) operating region comprises switching to a switching frequency corresponding to the same gain as the current switching frequency.

[0009] Optionally, the switching to a switching frequency corresponding to the same gain as the current switching frequency comprises:

[0010] The gain of the resonant converter is an equation with respect to the switching frequency. The gain value of the resonant converter corresponding to the switching frequency reaching the preset limit value is calculated according to the equation, and another switching frequency value corresponding to the gain value is solved according to the equation, and the resonant converter is controlled to switch to the other switching frequency value.

[0011] Optionally, the judging whether the resonant converter works in the light load or no load state comprises:

[0012] The running parameter of the resonant converter is judged whether it is less than a preset value, if yes, it is determined that the resonant converter works in the light load or no load state.

[0013] Optionally, when the resonant converter is used as a constant voltage source, the running parameter is any one or combination of the output current of the resonant converter, the resonant inductor current of the resonant converter, the resonant capacitor voltage of the resonant converter, the output power of the resonant converter and the input power of the resonant converter.

[0014] Optionally, when the resonant converter is used as a constant current source, the running parameter is any one or combination of the output voltage of the resonant converter, the resonant inductor current of the resonant converter, the resonant capacitor voltage of the resonant converter, the output power of the resonant converter and the input power of the resonant converter.

[0015] Optionally, when the resonant converter is used as a constant voltage source, the reaching of the steady state refers to that the output voltage of the resonant converter reaches stable;

[0016] When the resonant converter is used as a constant current source, the reaching of the steady state refers to that the output current of the resonant converter reaches stable.

[0017] Optionally, in the process of switching to the ZCS working area and continuously adjusting the switching frequency of the resonant converter until the resonant converter reaches the steady state, further comprising:

[0018] Once it is detected that the resonant converter recovers from the light load or no load state to the heavy load state, the control strategy under the heavy load is executed.

[0019] Optionally, the control strategy under the heavy load comprises: adjusting the switching frequency of the resonant converter in the ZVS working area until the resonant converter reaches the steady state.

[0020] Optionally, the once detecting that the resonant converter recovers from the light load or no load state to the heavy load state and executing the control strategy under the heavy load comprises:

[0021] Once it is detected that the resonant converter recovers from the light load or no load state to the heavy load state, a switching frequency corresponding to the same gain as the current switching frequency is calculated, it is judged whether the calculated switching frequency is greater than the preset limit value, if not, the switching frequency is switched to the calculated switching frequency first, and then the control strategy under the heavy load is started to be executed; if yes, the switching frequency is switched to the preset limit value first, and then the control strategy under the heavy load is started to be executed.

[0022] A resonant converter control system, comprising: a control circuit, a sampling circuit and a driving circuit;

[0023] The control circuit stores a program, and the control circuit is used to realize the resonant converter control method as described above by running the program;

[0024] The sampling circuit is used to collect the operating parameters of the resonant converter required when the method is implemented under the control of the control circuit;

[0025] The driving circuit is used to adjust the switching frequency of the resonant converter under the control of the control circuit.

[0026] A resonant converter, comprising: a power main circuit and any one of the above resonant converter control systems.

[0027] Optionally, the resonant converter is an LLC resonant converter or an LC resonant converter.

[0028] As can be seen from the above technical solutions, the present application defaults that the resonant converter performs frequency conversion control in the ZVS working area, and the loss is low; if the resonant converter is about to enter the interval with abnormally increased gain and the resonant converter has not reached the steady state, the resonant converter is switched to continue working in the ZCS working area to ensure that it can reach the steady state, and since it is in the light load or no load state at this time, even if it works in the ZCS working area, there will not be too much loss. Compared with the prior art, the present application solves the problem of high output parameter drift of the resonant converter under light load or no load, and the loss is low, and it is realized only by frequency conversion control, the control is simple, and the output ripple is small. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious work.

[0030] Figure 1 A resonant converter control method flow chart disclosed in the embodiments of the present application;

[0031] Figure 2 Fig. 1 is a schematic diagram of a non-interleaved half-bridge LLC resonant converter topology disclosed by the prior art;

[0032] Figure 3 Fig. 2 is a schematic diagram of a gain curve of a certain model of resonant converter working in a heavy load range disclosed by the prior art;

[0033] Figure 4 Fig. 3 is a schematic diagram of a gain curve of a certain model of resonant converter working in a light load or no load range disclosed by the embodiment of the present application;

[0034] Figure 5 Fig. 4 is a flow chart of another resonant converter control method disclosed by the embodiment of the present application;

[0035] Figure 6 Fig. 5 is a schematic diagram of a resonant converter control system structure disclosed by the embodiment of the present application. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of the present application.

[0037] Referring to Figure 1 The embodiment of the present application discloses a resonant converter control method, which comprises:

[0038] Step S01: judging whether the resonant converter works in a light load or no load state, if yes, entering step S02, if not, it is indicated that the resonant converter works in a heavy load state, and entering step S04.

[0039] Specifically, the main power circuit of the resonant converter comprises: a switching network, a resonant circuit, an isolation transformer, a rectifier circuit and a filter circuit connected in sequence between a power supply Vin and a load. According to different switching network topologies, the resonant converter can be divided into a half-bridge resonant converter and a full-bridge resonant converter. According to whether the switching network is multi-phase interleaved, the resonant converter can be divided into a non-interleaved resonant converter and a multi-phase interleaved resonant converter, which can be 2-phase interleaved or 3-phase interleaved, etc. According to different resonant circuit topologies, the resonant converter can be divided into an LLC resonant converter, an LC resonant converter, etc., wherein the LLC resonant converter becomes the first choice of switching power supply due to its high frequency and high efficiency. Figure 2 Fig. 1 shows a typical topology of a non-interleaved half-bridge LLC resonant converter (its resonant circuit comprises a resonant inductor Lr, a resonant capacitor Cr and an excitation inductor Lm),Figure 2 As an example, the embodiments of the present application are applicable to any type of resonant converter, and are not limited to Figure 2 .

[0040] Whether the resonant converter works in a light load or no load state can be determined by judging whether the operating parameter of the resonant converter is less than a preset value. If the operating parameter of the resonant converter is less than the preset value, it is determined that the resonant converter works in a light load or no load state.

[0041] The resonant converter can be used as a constant voltage source or a constant current source. When the resonant converter is used as a constant voltage source, the operating parameter for judging whether the resonant converter works in a light load or no load state can be any one or a combination of the output current of the resonant converter, the resonant inductor current of the resonant converter, the resonant capacitor voltage of the resonant converter, the output power of the resonant converter, and the input power of the resonant converter. When the resonant converter is used as a constant current source, the operating parameter for judging whether the resonant converter works in a light load or no load state can be any one or a combination of the output voltage of the resonant converter, the resonant inductor current of the resonant converter, the resonant capacitor voltage of the resonant converter, the output power of the resonant converter, and the input power of the resonant converter.

[0042] The resonant converter uses resonant elements to make the switching voltage or current periodically pass through zero points, thereby realizing ZVS (Zero Voltage Switch) or ZCS (Zero Current Switch) and reducing switching loss. When the resonant converter is inductive, ZVS can be realized; when the resonant converter is capacitive, ZCS can be realized. That is, the entire operating region of the resonant converter is divided into two operating regions of ZVS and ZCS, and the dividing line between ZVS and ZCS is a pure resistive gain curve.

[0043] In order to reduce switching loss, the resonant converter is initially defaulted to work in the ZVS operating region. When the resonant converter is in a light load or no load state, as the load gradually decreases (i.e., the gain required by the resonant converter gradually decreases), the required gain is achieved by increasing the switching frequency. However, due to the existence of the parasitic capacitance of the isolation transformer and the output rectifier tube, when the switching frequency exceeds a certain value of the resonant frequency, the gain abnormally increases, i.e., the output parameter drifts high (when the resonant converter is used as a constant voltage source, the output parameter drift high refers to the output voltage of the resonant converter drifting high; when the resonant converter is used as a constant current source, the output parameter drift high refers to the output current of the resonant converter drifting high).

[0044] Taking a certain type of resonant converter as an example, the gain curve of this type of resonant converter operating in the heavy load range is as follows: Figure 3 As shown, Figure 3 The vertical axis M represents the gain of the resonant converter, and the horizontal axis f represents the gain of the resonant converter. N The ratio of the switching frequency to the resonant frequency of the resonant converter. Figure 3 Only the switching frequency range of 0 to 3 times the resonant frequency before entering the abnormal gain increase range is shown. Figure 3 The dashed curve in the figure represents the gain curve of this type of resonant converter under heavy load. The solid curve is the boundary between the ZVS and ZCS operating regions. The dashed curve to the left of point P represents the ZCS operating region, and the dashed curve to the right of point P represents the ZVS operating region. The existing control method for this type of resonant converter is as follows: when the required gain of this type of resonant converter gradually decreases, the switching frequency needs to be increased to make the resonant converter reach the required gain. Assuming that this type of resonant converter requires the gain to vary within the range of 0.68 to 1.2, from... Figure 3 It can be seen that the gain range of 0.68 to 1.2 corresponds to a switching frequency between 0.7 and 3 times the resonant frequency within the ZVS interval (i.e., Figure 3 The operating range 1) shown in the figure meets the full gain range requirement since it does not exceed three times the resonant frequency. Therefore, the control strategy under heavy load given in step S04 below can be directly applied. However, if this type of resonant converter operates in no-load or light-load mode, its gain curve will change compared to the heavy-load mode, for example, it will change as follows: Figure 4 As shown ( Figure 4 Similarly, only the switching frequency range of 0 to 3 times the resonant frequency is shown; it is assumed that the abnormal increase in gain only begins to occur when the frequency exceeds 3 times the resonant frequency. Figure 4 (The range of abnormally increased gain is not shown in the diagram). Assuming that this type of resonant converter requires the gain to vary within the range of 0.2 to 1.2, from... Figure 4 It can be seen that the switching frequency corresponding to the gain range of 0.2 to 1.2 in the ZVS interval exceeds 3 times the resonant frequency, which cannot meet the requirements of the full gain range. A corresponding solution needs to be given. See steps S02 to S03 below for details.

[0045] Step S02: Adjust the switching frequency of the resonant converter within the ZVS operating region, and simultaneously determine whether the resonant converter has reached a steady state; if the resonant converter has reached a steady state before the switching frequency reaches the preset limit value, the current round of control ends; if the resonant converter has not reached a steady state before the switching frequency reaches the preset limit value, proceed to step S03.

[0046] Step S03: Switch to the ZCS working region and continue to adjust the switching frequency of the resonant converter until the resonant converter reaches a steady state. This round of control ends.

[0047] Step S04: Adopt the control strategy under heavy load (the control strategy under heavy load is briefly described as follows: under heavy load, it is a typical ZVS operating region control strategy, that is, as the output power increases, the required gain of the resonant circuit increases, and the switching frequency needs to be reduced accordingly; conversely, if the output power decreases, the required gain of the resonant circuit decreases, and the switching frequency needs to be increased accordingly; in short, the control strategy under heavy load is to adjust the switching frequency of the resonant converter within the ZVS operating region until the resonant converter reaches a steady state), thus ending this round of control.

[0048] Specifically, during frequency conversion control within the ZVS operating range, it is determined in real time whether the resonant converter has reached the required gain (i.e., whether it has reached steady state). If the switching frequency of the resonant converter reaches the preset limit value (within... Figure 4 In the given example, if the preset limit value is set to ≤3 times the resonant frequency and the resonant converter still has not reached a steady state, then switch to the ZCS operating region to continue adjusting the switching frequency of the resonant converter. Frequency conversion control in the ZCS operating region will not cause output parameter instability, only a slight increase in switching losses (since it is a light load or no load, even if it is operating in the ZCS operating region, the switching losses will not be too large). If the resonant converter has reached a steady state before the switching frequency reaches the preset limit value, then there is no need to switch.

[0049] Still in use Figure 4 For example, if the required gain of this type of resonant converter is to vary within the range of 0.2 to 1.2, and the converter has not yet reached steady state when the switching frequency is increased to three times the resonant frequency, then it will switch to the ZCS operating region to continue operating. Within the corresponding frequency band of the ZCS operating region (see...),... Figure 4 The working range 2) shown in the figure can also satisfy the gain variation in the range of 0.2 to 1.2.

[0050] In summary, this invention requires the resonant converter to operate within the ZVS (Zero-Voltage-Side) region by default when under light load or no load, resulting in low losses. If the resonant converter has not reached steady state when it is about to enter a region of abnormally increased gain, it switches to the ZCS (Zero-Side-Cut) region to continue operating and ensure it reaches steady state. Since this is under light load or no load, there will be minimal losses even when operating within the ZCS region. This invention executes in real-time and cyclically during the operation of the resonant converter, solving the problem of high output parameter drift under light load or no load conditions. Furthermore, it achieves low losses and is implemented solely through frequency conversion control, resulting in simple control and low output ripple.

[0051] Optionally, to avoid the large fluctuation of the output parameter at the switching moment in step S03, the embodiment of the present application requires that the switching process is seamless switching, that is, switching to the switching frequency corresponding to the same gain as the current switching frequency, so that the gain corresponding to the switching frequency of the resonant converter before and after switching is consistent. Still using Figure 4 In the example given, when the switching frequency is increased to 3 times the resonant frequency, the resonant converter of this type has not yet reached steady state, so the switching frequency F0 in the ZCS operating region is switched to, and the frequency is continued to be varied from F0. Since the gain corresponding to 3 times the resonant frequency and F0 is basically the same, both being 0.85, the fluctuation of the output parameter is very small.

[0052] The specific method for the resonant converter to achieve the above seamless switching is as follows: the gain of the resonant converter is an equation with respect to the switching frequency, the gain value corresponding to the switching frequency reaching the preset limit value is calculated according to the equation, and another switching frequency value corresponding to the gain value is solved according to the equation, and the resonant converter is controlled to switch to the another switching frequency value.

[0053] The following takes the non-interleaved half-bridge LLC resonant converter shown in Figure 2 and Figure 4 as an example to give the process of implementing the above seamless switching:

[0054] Figure 2 The gain of the non-interleaved half-bridge LLC resonant converter shown in

[0055]

[0056] In the formula:

[0057] M(f N ) represents the gain of the circuit;

[0058] f N represents the ratio of the switching frequency to the resonant frequency;

[0059] Q represents the quality factor, Lr is the resonant inductance, Cr is the resonant capacitance, n is the turns ratio of the primary and secondary of the isolation transformer, and Ro is the equivalent resistance of the output;

[0060] λ represents the ratio of the magnetizing inductance Lm to the resonant inductance Lr,

[0061] When the circuit design is completed, it can be known that under a certain load, the parameters Q and λ in the above equation are constant values, and based on the parameters shown in Figure 4 , the seamless switching includes the following three steps:

[0062] 1) Figure 4In the middle, lambda = 5, Q = 0.01, then calculate the gain value M(3) = 0.85 at the 3 times resonance frequency;

[0063] 2) inverse equation Two solutions of the equation can be obtained, f N1 = 3 and f N2 = 0.29;

[0064] 3) Switch to the 0.29 times resonance frequency of the ZCS region, so that the gain before and after switching is basically the same, and the switching process will not cause the fluctuation of the output parameters; after switching is completed, the switching frequency of the resonant converter is adjusted on the basis of f N2 Until the resonant converter reaches a steady state.

[0065] And, as Figure 4 Known, the segmented frequency control method of the application also makes the resonant converter avoid the interval near the gain peak value where the gain increases sharply, and the control effect is better.

[0066] Optionally, considering that the resonant converter works in the ZCS working area, and in order to reduce switching loss, the embodiment of the application requires that the resonant converter switches back to work in the ZVS working area when it returns to the heavy load state. The corresponding control flow chart is shown in Figure 5 , including:

[0067] Step S11: Determine whether the resonant converter works in a light load or an empty load state, if yes, go to step S12, if no, go to step S16.

[0068] Step S12: Adjust the switching frequency of the resonant converter in the ZVS working area, and determine whether the resonant converter reaches a steady state; if the switching frequency of the resonant converter reaches a preset limit value, the resonant converter has reached a steady state, and the current control ends; if the switching frequency of the resonant converter reaches the preset limit value, the resonant converter has not reached a steady state, go to step S13.

[0069] Step S13: Switch to the ZCS working area, and continue to adjust the switching frequency of the resonant converter;

[0070] Step S14: Determine whether the resonant converter works in a heavy load state, if yes, go to step S16, if no, it indicates that the resonant converter is still in a light load or an empty load state, go to step S15.

[0071] Step S15: Determine whether the resonant converter reaches a steady state, if yes, the current control ends, if no, return to step S13.

[0072] Step S16: using the control strategy under heavy load (the control strategy under heavy load is prior art, which is not discussed herein), and the current round of control ends.

[0073] Optionally, once it is detected that the resonant converter recovers from the light load or no load state to the heavy load state, a switching frequency corresponding to the same gain as the current switching frequency is calculated (the calculation method of the switching frequency corresponding to the same gain as the current switching frequency is the same as above, which is not described herein again), and it is judged whether the calculated switching frequency is greater than the preset limit value. If not, the switching frequency is switched to the calculated switching frequency first, and then the control strategy under heavy load is executed, thereby avoiding the problem of abnormal increase of gain, i.e., high output parameter drift. If yes, the switching frequency is switched to the preset limit value first, and then the control strategy under heavy load is executed, thereby realizing seamless switching.

[0074] In addition, corresponding to the above method embodiments, the embodiments of the present application also disclose a resonant converter control system, as shown in Figure 6 which comprises a control circuit 200, a sampling circuit 100 and a driving circuit 300.

[0075] The control circuit stores a program, and the control circuit is used to realize any one of the control methods disclosed above by running the program.

[0076] The sampling circuit is used to collect the operating parameters of the resonant converter required when the control method is implemented under the control of the control circuit.

[0077] The driving circuit is used to drive the switch tube in the switching network of the resonant converter under the control of the control circuit, thereby adjusting the switching frequency of the resonant converter.

[0078] In addition, the embodiments of the present application also disclose a resonant converter, which comprises a power main circuit and any one of the resonant converter control systems disclosed above. Optionally, the resonant converter is an LLC resonant converter or an LC resonant converter.

[0079] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts of each embodiment can be referred to each other. For the resonant converter control system and the resonant converter disclosed by the embodiments, since they correspond to the method disclosed by the embodiments, the description is relatively simple, and the relevant parts can be referred to the method part.

[0080] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and, while certain embodiments according to the principles set forth herein are shown and described, it is to be understood that the same are not limiting of the scope of the application as it is set forth in the appended claims, and that various modifications are made within the scope of the appended claims. Therefore, it is contemplated to cover the claims falling within the scope of the claims.

Claims

1. A resonant converter control method, characterized by, The method comprises the following steps: determining whether the resonant converter is working in a light load or no load state, if yes, adjusting the switching frequency of the resonant converter in a zero voltage switching (ZVS) working area, and determining whether the resonant converter reaches a steady state; if the resonant converter does not reach the steady state when the switching frequency reaches a preset limit value, switching to a zero current switching (ZCS) working area, and continuing to adjust the switching frequency of the resonant converter until the resonant converter reaches the steady state; wherein the switching to the ZCS working area comprises: switching to a switching frequency corresponding to the same gain as the current switching frequency.

2. The resonant converter control method of claim 1, wherein, The switching to the switching frequency corresponding to the same gain as the current switching frequency comprises: the gain of the resonant converter is an equation about the switching frequency, the gain value of the resonant converter corresponding to the switching frequency reaching the preset limit value is calculated according to the equation, and another switching frequency value corresponding to the gain value is solved according to the equation, and the resonant converter is switched to the other switching frequency value.

3. The resonant converter control method according to claim 1 or 2, characterized by, The determination of whether the resonant converter is working in a light load or no load state comprises: determining whether the operating parameter of the resonant converter is less than a preset value, if yes, determining that the resonant converter is working in a light load or no load state.

4. The resonant converter control method of claim 3, wherein, When the resonant converter is used as a constant voltage source, the operating parameter is any one or combination of the output current of the resonant converter, the resonant inductor current of the resonant converter, the resonant capacitor voltage of the resonant converter, the output power of the resonant converter and the input power of the resonant converter.

5. The resonant converter control method of claim 3, wherein, When the resonant converter is used as a constant current source, the operating parameter is any one or combination of the output voltage of the resonant converter, the resonant inductor current of the resonant converter, the resonant capacitor voltage of the resonant converter, the output power of the resonant converter and the input power of the resonant converter.

6. The resonant converter control method according to claim 1 or 2, characterized by, When the resonant converter is used as a constant voltage source, the reaching of the steady state means that the output voltage of the resonant converter reaches stability. When the resonant converter is used as a constant current source, the reaching of the steady state means that the output current of the resonant converter reaches stability.

7. The resonant converter control method according to claim 1 or 2, characterized by, In the process of switching to the ZCS working area, continuing to adjust the switching frequency of the resonant converter until the resonant converter reaches the steady state, the method further comprises: once it is detected that the resonant converter recovers from the light load or no load state to a heavy load state, executing a control strategy under the heavy load.

8. The resonant converter control method of claim 7, wherein, The control strategy under the heavy load comprises: adjusting the switching frequency of the resonant converter in the ZVS working area until the resonant converter reaches the steady state.

9. The resonant converter control method of claim 7, wherein, The execution of the control strategy under the heavy load once it is detected that the resonant converter recovers from the light load or no load state to a heavy load state comprises: once it is detected that the resonant converter recovers from the light load or no load state to a heavy load state, calculating a switching frequency corresponding to the same gain as the current switching frequency, determining whether the calculated switching frequency is greater than the preset limit value, if no, switching to the calculated switching frequency first, and then starting to execute the control strategy under the heavy load; if yes, switching the switching frequency to the preset limit value first, and then starting to execute the control strategy under the heavy load.

10. A resonant converter control system characterized by, The method comprises the following steps: a control circuit, a sampling circuit and a driving circuit; The control circuit stores a program, and the control circuit is used to realize the resonant converter control method according to any one of claims 1-9 by running the program. The sampling circuit is used to collect operating parameters of the resonant converter required when the method is realized under the control of the control circuit. The drive circuit is used to adjust the switching frequency of the resonant converter under the control of the control circuit.

11. A resonant converter characterized by, Comprise: The power main circuit and the resonant converter control system according to claim 10.

12. The resonant converter of claim 11, wherein, The resonant converter is an LLC resonant converter or an LC resonant converter.

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