Control method and control device of resonant converter and switching power supply

Abstract

The invention discloses a control method and a control device of a resonant converter and a switching power supply, the resonant converter works in a non-frequency multiplication mode or a frequency multiplication mode to realize wide gain adjustment by controlling the switching frequency and / or duty ratio of all switching tubes in a primary side switching network, and the method specifically comprises the following steps: (1) when the gain demand is greater than or equal to 1, the resonant converter works in the non-frequency multiplication mode or the frequency multiplication mode; the frequency multiplier works in a non-frequency-doubling mode, and gain rising adjustment is achieved through two-level PFM control. (2) when the required gain G is less than 1, if the device works in a non-frequency-doubling mode, adopting three-level PWM (Pulse Width Modulation) control to realize gain reduction adjustment; (3) when the gain demand is less than 1, if the device works in a frequency doubling mode, frequency doubling PFM control is adopted to realize gain reduction adjustment; wherein mode switching is further involved between the non-frequency-doubling mode and the frequency-doubling mode, and smooth mode switching is achieved by inserting set transition driving pulses. According to the invention, high efficiency in a full gain range is ensured, and output voltage fluctuation can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of switching converters, and in particular to a control method, a control device and a switching power supply of a resonant converter. Background Art

[0002] With the rapid development of the field of power electronics, switching converters are increasingly widely used. Resonant converters are favored by industry insiders for their high efficiency, soft switching, and higher power density. However, the gain adjustment capability of traditional frequency conversion control is limited, and it is difficult to achieve soft switching characteristics when it is far away from the series resonant frequency of the resonant capacitor and the resonant inductor in the resonant cavity network, which inevitably affects the transmission efficiency and reliability of the converter. Various modulation strategies such as PWM control, phase shift control, and extended phase shift control have been extended from this, but many studies have shown that a single control strategy is difficult to take into account both wide gain application and high efficiency performance. Therefore, many scholars have also tried to study the combined control of different modulation methods, such as the invention patent "A Control Method for Resonant Converter" with publication number CN116207972A, which proposes a wide gain control method for resonant converters, and ensures the application advantages of a wide gain range through full half-bridge mode switching control. Since the full-bridge LLC resonant converter covers the topological structure of the half-bridge LLC, there is no need to add auxiliary circuits, and it is easier to broaden the gain range of the circuit system through mode switching control. However, for high-voltage applications such as photovoltaics, the voltage stress of the primary switch tube under the full-bridge structure is large, which is not conducive to device selection and will also increase hardware costs.

[0003] In high-voltage applications, a three-level topology is usually used to reduce the voltage stress of the switch tube; the series half-bridge three-level LLC resonant converter eliminates hardware voltage-equalizing devices such as flying capacitors and clamping diodes, and has the advantages of simple structure, low device cost, and easy PCB layout. It can perfectly replace the traditional full-bridge LLC topology in high-voltage applications.

[0004] Based on the trade-off between wide gain application and high efficiency performance, specific modulation strategies such as asymmetric PWM control, frequency doubling PWM control, and three-level alternating control, as well as hybrid control strategies of various mode combinations, have also been derived for the series half-bridge three-level LLC resonant converter. The document "Hybrid Control of Wide-Range Input Three-Level Half-Bridge LLC Converter" proposes a frequency conversion-phase shift hybrid control strategy, but it is difficult to achieve soft switching for phase-shift drive, and the primary side circulating current in the phase-shift mode will lead to low system efficiency. The document "Design of Wide-Input Stacked Half-Bridge LLC Converter Using GaN" uses frequency conversion-frequency doubling combination control to achieve a wider input and output voltage range, but the overall gain range of the circuit system is less than 3 times, and the efficiency of the circuit system is low. The U.S. patent "Isolated DC / DC converter with wide output voltage range and control method thereof" with publication number US11901826B2 introduces symmetrical frequency conversion modulation, three-level alternating modulation and asymmetrical frequency conversion modulation respectively. For the three-level alternating modulation scheme, although the current balance control of the primary switch tube can be achieved, due to the existence of half the level of the input voltage, the primary resonant cavity has a large circulating current loss, and the soft switching of the primary switch tube fails at low gain, which increases the switching loss of the circuit system and reduces the efficiency of the converter. In addition, the switching timing between the modes described in the patent is too complicated, and the PWM update implementation problem of the actual digital controller is not considered, which is not practical in engineering.

[0005] Therefore, it is necessary to propose an improved control strategy to overcome the shortcomings of the existing technology. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is: to propose a control method, a control device and a switching power supply of a resonant converter, without adding additional auxiliary circuits, by adjusting the switching frequency and / or duty cycle of the primary switch tube to make the resonant converter operate in a non-frequency doubling or frequency doubling mode, so as to broaden the gain adjustment capability of the resonant converter and ensure the optimal operating efficiency of the converter as much as possible; at the same time, smooth switching between modes is achieved to ensure the soft switching characteristics of the primary switch tube during the switching process.

[0007] As a first aspect of the present invention, an embodiment of a control method of a resonant converter is provided as follows: A control method for a resonant converter, wherein the primary circuit of the resonant converter comprises a primary switch network and an LLC resonant cavity network, wherein the primary switch network comprises two groups of switch tube bridge arm circuits connected in series or in parallel, wherein the first switch tube bridge arm circuit comprises a first switch tube and a second switch tube connected in series and a first capacitor connected in parallel with the first switch tube bridge arm circuit, and the second switch tube bridge arm circuit comprises a third switch tube and a fourth switch tube connected in series and a second capacitor connected in parallel with the second switch tube bridge arm circuit, wherein the first switch tube is at a higher potential than the second switch tube, and the third switch tube is at a higher potential than the fourth switch tube; the resonant converter maintains the same switching frequency of the four switch tubes in all working states, and one switch tube in each group of switch tube bridge arm circuits is a main control switch tube, the drive of the other switch tube is complementary to the drive of the main control switch tube, and the drive phase of the main control switch tubes in the two groups of switch tube bridge arm circuits is shifted by 180°; wherein the control method comprises: The wide gain adjustment is achieved by controlling the switching frequency and / or duty cycle of all the switch tubes in the primary switch network so that the resonant converter operates in a non-frequency doubling mode or a frequency doubling mode. Specifically: (1) When the gain requirement of the resonant converter is greater than or equal to 1, the resonant converter is operated in the non-frequency doubling mode, and two-level PFM control is used to achieve gain adjustment. At this time, the voltage injected into the LLC resonant cavity is in a conventional two-level state; (2) When the gain requirement of the resonant converter is less than 1, if the resonant converter is operated in the non-frequency doubling mode, a three-level PWM control is used to implement gain reduction regulation. At this time, the voltage injected into the LLC resonant cavity is in a three-level state; (3) When the gain requirement of the resonant converter is less than 1, if the resonant converter is operated in the frequency doubling mode, the frequency doubling PFM control is used to achieve gain reduction regulation. At this time, the voltage injected into the LLC resonant cavity is in a frequency doubling two-level state; There is also a mode switch between the non-frequency doubling mode and the frequency doubling mode, and a set transition driving pulse is inserted to achieve smooth mode switch.

[0008] Furthermore, the two-level PFM control includes: controlling the duty cycle of the main control switch tubes in each group of switch tube bridge arm circuits to be the same and fixed to a first set duty cycle, and achieving boost regulation only by adjusting the switching frequency of the main control switch tubes in each group of switch tube bridge arm circuits, wherein the switching frequency of the main control switch tubes in each group of switch tube bridge arm circuits is always less than or equal to the series resonant frequency of the resonant capacitor and the resonant inductor in the LLC resonant cavity network.

[0009] Preferably, the first set duty cycle is 0.5.

[0010] Furthermore, the three-level PWM control includes: achieving voltage reduction regulation by simultaneously adjusting the switching frequency and duty cycle of the main control switch tube in each group of switch tube bridge arm circuits, and at the same time minimizing the primary side circulating current loss of the resonant converter to improve efficiency, wherein the switching frequency of the main control switch tube in each group of switch tube bridge arm circuits is greater than the series resonant frequency of the resonant capacitor and the resonant inductor in the LLC resonant cavity network.

[0011] Furthermore, the frequency-doubled PFM control includes: controlling the duty cycle of the main control switch tubes in each group of switch tube bridge arm circuits to be the same and fixed to a second set duty cycle, and further voltage reduction regulation is achieved only by adjusting the switching frequency of the main control switch tubes in each group of switch tube bridge arm circuits, wherein the switching frequency of the main control switch tubes in each group of switch tube bridge arm circuits is less than the series resonant frequency of the resonant capacitor and the resonant inductor in the LLC resonant cavity network.

[0012] Preferably, the second set duty cycle is 0.25.

[0013] Furthermore, the mode switching between the non-frequency doubling mode and the frequency doubling mode includes: Detect input voltage, output voltage, ratio of input voltage to output voltage or switching frequency of switch tube; Whether to perform mode switching is determined by comparing with the set mode switching threshold. When the resonant converter meets the mode switching condition, the mode switching transition process is entered at the 0° or 180° phase moment of the main control switch tube, and the mode smooth switching is achieved according to the set transition drive pulse.

[0014] Furthermore, the mode switching threshold is set to 0.95-0.6 times the gain, and a hysteresis is set.

[0015] Furthermore, after the transition process is completed with the set transition driving pulse, the closed-loop control amount is suddenly increased or decreased to achieve dynamic compensation, so as to reduce the output voltage fluctuation.

[0016] Further, when the resonant converter switches from the non-frequency doubling mode to the frequency doubling mode, the inserted set transition drive pulse includes: if the first switch tube and the third switch tube are used as the main control switch tubes when working in the non-frequency doubling mode, then: Controlling the duty cycles of the first switch tube and the fourth switch tube to be the same and to be a third set duty cycle, wherein the driving of the first switch tube lags behind the driving of the fourth switch tube by 180°, and after a set transition period, the resonant converter enters a frequency doubling operation mode, and the first switch tube and the fourth switch tube are used as main control switch tubes; Alternatively, the duty cycles of the second switch tube and the third switch tube are controlled to be the same and to be a third set duty cycle, the driving of the second switch tube is 180° ahead of the driving of the third switch tube, and after a set transition period, the resonant converter enters a frequency doubling operation mode, and the second switch tube and the third switch tube are used as main control switch tubes.

[0017] Further, when the resonant converter switches from the non-frequency doubling mode to the frequency doubling mode, the inserted set transition drive pulse includes: if the second switch tube and the fourth switch tube are used as the main control switch tube when working in the non-frequency doubling mode, then: Controlling the duty cycles of the first switch tube and the fourth switch tube to be the same and to be a third set duty cycle, driving the first switch tube to be 180° ahead of driving the fourth switch tube, and after continuously setting a transition period, the resonant converter enters a frequency doubling operation mode, and the first switch tube and the fourth switch tube are used as main control switch tubes; Alternatively, the duty cycles of the second switch tube and the third switch tube are controlled to be the same and to be a third set duty cycle, the driving of the second switch tube lags behind the driving of the third switch tube by 180°, and after a set transition period, the resonant converter enters a frequency doubling operation mode, and the second switch tube and the third switch tube are used as main control switch tubes.

[0018] Preferably, the third set duty cycle is 0.25.

[0019] Further, when the resonant converter switches from the frequency doubling mode to the non-frequency doubling mode, the inserted set transition drive pulse includes: if the first switch tube and the fourth switch tube are used as the main control switch tubes when working in the frequency doubling mode, then: Controlling the duty cycle of the first switch tube to be a set minimum duty cycle, the duty cycle of the third switch tube to be a fourth set duty cycle, the driving of the first switch tube lags behind the driving of the third switch tube by 180°, and after continuing for a set transition period, the resonant converter enters a non-frequency doubling operation mode, and the first switch tube and the third switch tube are used as main control switch tubes; Or the duty cycle of the fourth switch tube is controlled to be a set minimum duty cycle, the duty cycle of the second switch tube is a fourth set duty cycle, the driving of the second switch tube is 180° ahead of the driving of the fourth switch tube, and after a set transition period, the resonant converter enters a non-frequency doubling operation mode, and the second switch tube and the fourth switch tube are used as the main control switch tubes.

[0020] Further, when the resonant converter switches from the frequency doubling mode to the non-frequency doubling mode, the inserted set transition drive pulse includes: if the second switch tube and the third switch tube are used as the main control switch tube when working in the frequency doubling mode, then: Controlling the duty cycle of the first switch tube to be a fourth set duty cycle, the duty cycle of the third switch tube to be a set minimum duty cycle, the driving of the first switch tube is 180° ahead of the driving of the third switch tube, and after a set transition period, the resonant converter enters a non-frequency doubling operation mode, and the first switch tube and the third switch tube are used as main control switch tubes; Or the duty cycle of the second switch tube is controlled to be a set minimum duty cycle, the duty cycle of the fourth switch tube is a fourth set duty cycle, the driving of the second switch tube lags behind the driving of the fourth switch tube by 180°, and after a set transition period, the resonant converter enters a non-frequency doubling working mode, and the second switch tube and the fourth switch tube are used as the main control switch tubes.

[0021] Preferably, the fourth set duty cycle is 0.5.

[0022] Furthermore, the number of cycles of the set transition period is N, where N is a positive integer, and within the set transition period, the switching frequency of the first to fourth switching tubes is greater than or equal to the series resonant frequency of the resonant capacitor and the resonant inductor in the LLC resonant cavity network.

[0023] As a second aspect of the present invention, an embodiment of a control device for a resonant converter is provided as follows: A control device for a resonant converter, wherein the primary circuit of the resonant converter comprises a primary switch network and an LLC resonant cavity network, wherein the primary switch network comprises two groups of switch tube bridge arm circuits connected in series or in parallel, wherein the first switch tube bridge arm circuit comprises a first switch tube and a second switch tube connected in series and a first capacitor connected in parallel with the first switch tube bridge arm circuit, and the second switch tube bridge arm circuit comprises a third switch tube and a fourth switch tube connected in series and a second capacitor connected in parallel with the second switch tube bridge arm circuit, wherein the first switch tube is at a higher potential than the second switch tube, and the third switch tube is at a higher potential than the fourth switch tube; the resonant converter maintains the same switching frequency of four switch tubes in all working states, and one switch tube in each group of switch tube bridge arm circuits is a main control switch tube, the drive of the other switch tube is complementary to the drive of the main control switch tube, and the drive phase of the main control switch tubes in the two groups of switch tube bridge arm circuits is shifted by 180°; wherein the control device is configured as follows: The wide gain adjustment is achieved by controlling the switching frequency and / or duty cycle of all the switch tubes in the primary switch network so that the resonant converter operates in a non-frequency doubling mode or a frequency doubling mode. Specifically: (1) When the gain requirement of the resonant converter is greater than or equal to 1, the resonant converter is operated in the non-frequency doubling mode, and two-level PFM control is used to achieve gain adjustment. At this time, the voltage injected into the LLC resonant cavity is in a conventional two-level state; (2) When the gain G requirement of the resonant converter is less than 1, if the resonant converter is operated in the non-frequency doubling mode, three-level PWM control is used to achieve gain reduction regulation. At this time, the voltage injected into the LLC resonant cavity is in a three-level state; (3) When the gain G requirement of the resonant converter is less than 1: if the resonant converter is operated in the frequency doubling mode, the frequency doubling PFM control is used to achieve gain reduction regulation. At this time, the voltage injected into the LLC resonant cavity is in a frequency doubling two-level state; There is also a mode switch between the non-frequency doubling mode and the frequency doubling mode, and a set transition driving pulse is inserted to achieve smooth mode switch.

[0024] As a third aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows: A switching power supply, comprising a resonant converter, wherein the primary circuit of the resonant converter comprises a primary switch network and an LLC resonant cavity network, wherein the primary switch network is composed of two groups of switch tube bridge arm circuits connected in series or in parallel, wherein the first switch tube bridge arm circuit comprises a first switch tube and a second switch tube connected in series and a first capacitor connected in parallel with the first switch tube bridge arm circuit, and the second switch tube bridge arm circuit comprises a third switch tube and a fourth switch tube connected in series and a second capacitor connected in parallel with the second switch tube bridge arm circuit, wherein the first switch tube is at a higher potential than the second switch tube, and the third switch tube is at a higher potential than the fourth switch tube; the resonant converter maintains the same switching frequency of four switch tubes in all working states, and one switch tube in each group of switch tube bridge arm circuits is a main control switch tube, the drive of the other switch tube is complementary to the drive of the main control switch tube, and the drive phase of the main control switch tubes in the two groups of switch tube bridge arm circuits is shifted by 180°; wherein: the switching power supply further comprises the control device of the resonant converter described in any one of the second aspects above.

[0025] Terminology Note: Main control switch tube: refers to the switch tube in the same switch tube bridge arm circuit that actively adjusts the driving switch frequency and / or duty cycle according to closed-loop feedback control, while the driving switch frequency and duty cycle of another switch tube in the same switch tube bridge arm circuit change with the driving switch frequency and duty cycle of the main control switch tube, so that the driving switch frequencies of the two remain the same and the duty cycles maintain a complementary relationship.

[0026] Based on the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) By properly adjusting the operating frequency and / or duty cycle of the primary switch tube, the gain adjustment capability of the resonant converter can be effectively broadened without adding additional auxiliary circuits; (2) Under three-level PWM control, by simultaneously adjusting the switching frequency and duty cycle of the primary switch tube, the resonant converter operates in a critical current state, effectively reducing the primary side circulation loss and improving the efficiency of the resonant converter; (3) By judging the gain change of the circuit system and inserting appropriate transition process drive pulses, the control is relatively simple and can achieve smooth switching between modes, thereby improving the dynamic response performance and reliability of the switching process; (4) The soft switching characteristics of the primary switch tube under all working conditions are guaranteed, which reduces the stress of the switch tube and improves the EMI performance of the product, making it more reliable; (5) The proposed wide gain control method is convenient for the implementation of a digital controller and is compatible with the application scenarios of three-level LLC resonant converter and full-bridge LLC resonant converter, thus having higher practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1-a It is the topological structure diagram of the series half-bridge three-level LLC resonant converter; Figure 1-b It is the topological structure diagram of the full-bridge LLC resonant converter; Figure 2 A specific schematic diagram of a control method for a resonant converter according to the present invention; Figure 3 It is a key steady-state waveform diagram of the control method of the present invention under two-level PFM control; Figure 4-a The key steady-state waveform diagram of the control method of the present invention under three-level PWM control, wherein the first / third switch tube is the main control switch tube; Figure 4-b This is a key steady-state waveform diagram of the control method of the present invention under three-level PWM control, wherein the second / fourth switch tube is the main control switch tube; Figure 5-a This is a key steady-state waveform diagram of the control method of the present invention under the frequency-doubled PFM control, wherein the first / fourth switch tube is the main control switch tube; Figure 5-b This is a key steady-state waveform diagram of the control method of the present invention under the frequency-doubled PFM control, wherein the second / third switch tube is the main control switch tube; Figure 6 A flow chart showing mode switching implementation in a preferred embodiment of the present invention; Figure 7-aThis is a control timing diagram of the first switching process from non-frequency doubling mode to frequency doubling mode in a preferred embodiment of the present invention; Figure 7-b for Figure 7-a The equivalent timing diagram of , only the switching time is different; Figure 8-a This is a control timing diagram of the switching process from the second non-frequency doubling mode to the frequency doubling mode in a preferred embodiment of the present invention; Figure 8-b for Figure 8-a The equivalent timing diagram of , only the switching time is different; Figure 9-a This is a control timing diagram of the switching process from the third non-frequency doubling mode to the frequency doubling mode in a preferred embodiment of the present invention; Figure 9-b for Figure 9-a The equivalent timing diagram of , only the switching time is different; Figure 10-a This is a control timing diagram of the switching process from the fourth non-frequency doubling mode to the frequency doubling mode in a preferred embodiment of the present invention; Figure 10-b for Figure 10-a The equivalent timing diagram of , only the switching time is different; Figure 11-a This is a control timing diagram of the process of switching from the first frequency doubling mode to the non-frequency doubling mode in a preferred embodiment of the present invention; Figure 11-b for Figure 11-a The equivalent timing diagram of , only the switching time is different; Figure 12-a This is a control timing diagram of the process of switching from the second frequency doubling mode to the non-frequency doubling mode in a preferred embodiment of the present invention; Figure 12-b for Figure 12-a The equivalent timing diagram of , only the switching time is different; Figure 13-a This is a control timing diagram of the process of switching from the third frequency doubling mode to the non-frequency doubling mode in a preferred embodiment of the present invention; Figure 13-b for Figure 13-a The equivalent timing diagram of , only the switching time is different; Figure 14-a This is a control timing diagram of the process of switching from the fourth frequency doubling mode to the non-frequency doubling mode in a preferred embodiment of the present invention; Figure 14-b for Figure 14-a The equivalent timing diagram of , only the switching time is different; Fig.15 This is an experimental waveform diagram of the working condition where the input voltage jumps from low to high under the control timing of the preferred embodiment of the present invention (the input voltage jumps from 400V to 1000V); Fig.16This is an experimental waveform diagram of the working condition where the high input voltage jumps to the low input voltage under the control timing of the preferred embodiment of the present invention (the input voltage jumps from 1000V to 400V). DETAILED DESCRIPTION

[0028] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0029] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0030] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0031] It should be understood that, in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0032] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0033] like Figure 1-aAs shown, a typical topological structure diagram of the resonant converter used in the present invention is a series three-level LLC resonant converter, including a primary switch network I, an LLC resonant cavity network II, a transformer III and a secondary rectifier filter circuit IV; In specific implementation, its structure is as follows: The primary switch network I is composed of two groups of switch tube bridge arm circuits connected in series. The first group of switch tube bridge arms specifically includes a first switch tube S1 with a body diode or an external parallel diode, a second switch tube S2 and a first capacitor C1, wherein the source of the first switch tube S1 is connected to the drain of the second switch tube S2, which is marked as point A, one end of the first capacitor C1 is connected to the drain of the first switch tube S1 and the positive electrode of the power supply, and the other end of the first capacitor C1 is connected to the source of the second switch tube S2. The second group of switch tube bridge arms specifically includes a third switch tube S3 with a body diode or an external parallel diode, a fourth switch tube S4 and a second capacitor C2, wherein the source of the third switch tube S3 is connected to the drain of the fourth switch tube S4, which is marked as point B, one end of the second capacitor C2 is connected to the drain of the third switch tube S3 and the source of the second switch tube S2, and the other end of the second capacitor C2 is connected to the source of the fourth switch tube S4 and the negative electrode of the power supply; the LLC resonant cavity network II includes resonant capacitors connected in series in sequence. C r , resonant inductor L r and transformer equivalent magnetizing inductance L m , resonant capacitor C r The other end is connected to point A, and the transformer excitation inductance L m The other end of the transformer is connected to point B; the secondary side of the transformer III is connected to the input end of the rectifier filter circuit IV; the secondary side rectifier filter circuit IV includes a full-wave rectifier circuit composed of a secondary side first synchronous rectifier tube SR1 and a secondary side second synchronous rectifier tube SR2, and an output filter capacitor C o .

[0034] like Figure 1-bAs shown in FIG. 1 , another typical topological structure diagram of the resonant converter applied in the present invention is a full-bridge LLC resonant converter. Compared with the series three-level LLC resonant converter, the main difference is that the connection relationship of the switch tube bridge arm circuit of the primary switch network I is different. In the full-bridge LLC resonant converter, the primary switch network I is composed of two groups of parallel switch tube bridge arm circuits. The first group of switch tube bridge arms specifically includes a first switch tube S1 with a body diode or an external parallel diode, a second switch tube S2 and a first capacitor C1, wherein the source of the first switch tube S1 is connected to the drain of the second switch tube S2, which is marked as point A, and one end of the first capacitor C1 is connected to the first switch The drain of the third switch tube S1 is connected to the positive electrode of the power supply, the other end of the first capacitor C1 is connected to the source of the second switch tube S2 and the negative electrode of the power supply, the second group of switch tube bridge arms specifically includes a third switch tube S3 with a body diode or an external parallel diode, a fourth switch tube S4 and a second capacitor C2, wherein the source of the third switch tube S3 is connected to the drain of the fourth switch tube S4, which is marked as point B, one end of the second capacitor C2 is connected to the drain of the third switch tube S3 and the positive electrode of the power supply, and the other end of the second capacitor C2 is connected to the source of the fourth switch tube S4 and the negative electrode of the power supply; the remaining connection relationships are consistent with the series three-level LLC resonant converter and are not repeated here.

[0035] For those skilled in the art, the circuit shown in FIG1 also includes but is not limited to the following variations: (1) Replace the secondary side rectifier filter circuit V with a bridge rectifier structure consisting of four switching tubes or diodes; (2) Exchange resonant capacitor resonant capacitor C r and resonant inductor L r location.

[0036] like Figure 2 As shown, a specific schematic diagram of a control method for a resonant converter described in the present invention can be applied to a series three-level LLC resonant converter and a full-bridge LLC resonant converter, wherein G is the gain, and according to the gain requirement of the resonant converter, the switching frequency and / or duty cycle of all switching tubes in the primary switching network are reasonably controlled to make the resonant converter operate in a non-frequency doubling mode or a frequency doubling mode to achieve wide gain adjustment, wherein steady-state operation includes two-level PFM control and three-level PWM control in the non-frequency doubling mode, and includes frequency doubling PFM control in the frequency doubling mode.

[0037] It should be noted that Figure 2 This is just an example of the control method of the resonant converter of the present invention to control switching. Figure 2 The control method of the resonant converter of the present invention may also not include Figure 2 In the frequency multiplication mode, or does not include Figure 2The three-level PWM mode in the non-frequency doubling mode in the embodiment of the present invention can be specifically designed by technicians in this field according to their needs. Figure 2 Taking the application in series three-level LLC resonant converter as an example, a detailed introduction is given: The gain of the series three-level LLC resonant converter is G=2N ps *V o / V in , where N ps is the turns ratio of the transformer primary winding to the secondary winding, V o is the output voltage of the resonant converter, V in is the input voltage of the resonant converter.

[0038] When the gain requirement of the series three-level LLC resonant converter is G≥1, the series three-level LLC resonant converter is operated in the non-frequency doubling mode, and the two-level PFM control is used to achieve the gain control. At this time, the key steady-state waveform is as follows: Figure 3 As shown, V gs1 、V gs2 、V gs3 、V gs4 , respectively represent the driving pulse waveforms of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4, i Lr Represents the current flowing through the resonant inductor L r The resonant current, i Lm Indicates the current flowing through the magnetizing inductance L m The excitation current, i D1 , i D2 The driving pulse of the first switch tube S1 is controlled to be complementary to the driving pulse of the second switch tube S2, and the driving pulse of the third switch tube S3 is controlled to be complementary to the driving pulse of the fourth switch tube S4. The driving pulse of the first switch tube S1 and the driving pulse of the third switch tube S3 are phase-shifted by 180°. The duty cycle of all the switches is the same and is about 0.5, so that the voltage V injected into the LLC resonant cavity network is AB Keep 0, V in Two levels are converted, and the conversion frequency is consistent with the switching frequency of the switch tube. At this time, the switching frequency of all the switch tubes is the same. The gain adjustment is achieved by adjusting the switching frequency of the switch tube. Among them, the switching frequency of the switch tube is less than or equal to the series resonance frequency of the resonant capacitor and the resonant inductor in the LLC resonant cavity network. f r , specifically: .

[0039] When the gain requirement of the series three-level LLC resonant converter is G<1, the series three-level LLC resonant converter can work in non-frequency doubling mode or frequency doubling mode, depending on the actual application. According to the principle of optimal efficiency, when the gain requirement is 0.6<G<1, the non-frequency doubling mode is preferred and three-level PWM control is adopted. At this time, the key steady-state waveform is as follows: Figure 4-a and Figure 4-b As shown, Figure 4-a The working waveform when the first switch tube S1 and the third switch tube S3 are the main control switch tubes, the driving pulse of the first switch tube S1 and the driving pulse of the second switch tube S2 are controlled to be complementary to each other, the driving pulse of the third switch tube S3 and the driving pulse of the fourth switch tube S4 are controlled to be complementary to each other, the driving pulse of the first switch tube S1 and the driving pulse of the third switch tube S3 are phase-shifted by 180°, the switching frequencies of all the switch tubes are the same, and the gain reduction adjustment is mainly achieved by adjusting the duty cycle of the main control switch tube, and at the same time, the switching frequencies of all the switch tubes are adjusted so that the current flowing through the first synchronous rectifier tube SR1 on the secondary side and the second synchronous rectifier tube SR2 on the secondary side i D1 , i D2 Working in the critical conduction state, the primary side resonant current i Lr With excitation current i Lm The equal duration is just reduced to zero, and no additional circulating current loss will be generated on the primary side, which can improve the efficiency of the resonant converter. Under this control, the voltage V injected into the LLC resonant cavity network AB 0, 1 / 2V exists in 、V in The three levels are converted, but the conversion frequency is still consistent with the switching frequency of the switching tube.

[0040] and Figure 4-b This is the working waveform when the second switch tube S2 and the fourth switch tube S4 are the main control switch tubes. At this time, three-level PWM control can also be achieved, and the control effect is completely consistent with the first switch tube S1 and the third switch tube S3 being the main control switch tubes, and will not be repeated.

[0041] It should be noted that both the two-level PFM control and the three-level PWM control belong to the non-frequency doubling mode. The two controls can achieve a smooth transition without the need for additional switching control. Specifically, when the gain requirement G of the resonant converter gradually decreases from greater than 1 to 1, the switching frequency of the switch tube will gradually increase from less than the series resonant frequency to equal to the series resonant frequency. When the gain requirement G of the resonant converter is further reduced from 1, it will transition from the two-level PFM control to the three-level PWM control. At this time, the switching frequency of the switch tube is greater than the series resonant frequency, and the duty cycle of the main control switch tube is less than 0.5. There is only one set of one-to-one corresponding duty cycle and switching frequency that can make the current flowing through the first synchronous rectifier tube SR1 on the secondary side and the second synchronous rectifier tube SR2 on the secondary side i D1 , i D2 Working in the critical conduction state, the design is specifically based on the time domain modeling of the resonant converter. As the gain requirement G of the resonant converter further decreases, it is necessary to maintain i D1 , i D2 The switching frequency of the switch tube corresponding to the critical conduction state will gradually increase. At this time, the loss of the switch tube will increase. Therefore, in practical applications, a maximum switching frequency limit threshold will be set. Preferably, it is twice the series resonant frequency. When the switching frequency of the switch tube increases to the maximum switching frequency limit threshold, only the duty cycle is reduced to achieve further gain reduction adjustment. At this time i D1 , i D2 Work in discontinuous mode, or enter double frequency mode to achieve further gain reduction adjustment.

[0042] In order to balance the efficiency and gain adjustment capability of the resonant converter, the optimal gain range of the frequency doubling mode is 0.4<G<0.9. When the resonant converter works in the frequency doubling mode, the frequency doubling PFM control is adopted. At this time, the key steady-state waveform is as follows: Figure 5-a and Figure 5-b As shown, Figure 5-a The working waveform when the first switch tube S1 and the fourth switch tube S4 are the main control switch tubes. The driving pulse of the first switch tube S1 is controlled to be complementary to the driving pulse of the second switch tube S2, the driving pulse of the third switch tube S3 is controlled to be complementary to the driving pulse of the fourth switch tube S4, the driving pulses of the main control switch tubes S1 and S4 are phase-shifted by 180°, and the duty ratios of the main control switch tubes S1 and S4 are the same and are about 0.25, so that the voltage V injected into the LLC resonant cavity network AB Keep 0, 1 / 2V in Two-level conversion, but the conversion frequency is twice the switching frequency of the switch tube. Compared with the two-level PFM control, due to the voltage V injected into the LLC resonant cavity network ABThe conversion amplitude is halved, at the same V AB At the conversion frequency, the gain adjustment capability of the frequency-doubled PFM control is halved, so at this time, it is only necessary to adjust the switching frequency of the switch tube to around 0.5 times the series resonant frequency to achieve further gain reduction adjustment.

[0043] and Figure 5-b is the working waveform when the second switch tube S2 and the third switch tube S3 are the main control switch tubes. At this time, the frequency doubling PFM control can also be achieved. The main difference between the control effect and the control effect when the first switch tube S1 and the fourth switch tube S4 are the main control switch tubes is the voltage V injected into the LLC resonant cavity network at this time. AB is maintained at 1 / 2V in 、V in The two levels are converted, and the rest remain unchanged and will not be elaborated on.

[0044] It should be noted that although the gain adjustment of the resonant converter is continuously changed when operating in the non-frequency doubling mode and the frequency doubling mode (such as Figure 2 shown), but from Figure 3 From the steady-state key working waveforms of different controls in FIG5 , it can be seen that in the steady-state operation of the two different modes, the main control switch tubes in the first switch tube S1 to the fourth switch tube S4 are different, and the driving control timing between the two modes cannot be directly connected. In order to achieve smooth switching between the non-frequency doubling mode and the frequency doubling mode, a control method of a resonant converter proposed in the present application also involves mode switching control, which is as follows: like Figure 6 The figure shows a flow chart of mode switching implementation in a preferred embodiment of the present invention. Specifically, the mode switching threshold is determined by the resonant converter gain. For wide input voltage and constant output voltage applications, the input voltage can be compared with the set mode switching threshold to determine whether mode switching is required. Specifically: When the input voltage is greater than the set mode switching threshold, if the resonant converter is operating in the non-frequency doubling mode at this time, the non-frequency doubling mode to frequency doubling mode transition process control driving pulse is called at the 0° or 180° phase moment of the corresponding main control switch tube in the non-frequency doubling mode. After the transition process control driving pulse continues for a set period, the closed-loop control amount is controlled to perform a sudden increase operation, so that it is closer to the steady-state control amount required to operate in the frequency doubling mode under the input voltage, so as to reduce the output voltage fluctuation caused by the mode switching, and then enter the normal frequency doubling mode closed-loop control; on the contrary, if the input voltage is greater than the set mode switching threshold, the resonant converter is already operating in the frequency doubling mode, and the frequency doubling mode operation is maintained; When the input voltage is less than the set mode switching threshold, if the resonant converter is operating in the frequency doubling mode at this time, the corresponding main control switch tube in the frequency doubling mode will call the frequency doubling mode to switch to the non-frequency doubling mode transition process control drive pulse at the 0° or 180° phase moment, and the transition process control drive pulse will continue for a set period of time, and then the closed-loop control amount will be controlled to perform a sudden reduction operation, so that it is closer to the steady-state control amount required to operate in the non-frequency doubling mode under the input voltage, and then enter the normal non-frequency doubling mode closed-loop control; on the contrary, if the input voltage is less than the set mode switching threshold, the resonant converter is already operating in the non-frequency doubling mode, and the non-frequency doubling mode is maintained.

[0045] It should be noted that, since the input voltage, output voltage and even the switching frequency of the switch tube of the resonant converter can reflect the change of the resonant converter gain, in addition to judging the mode switching based on the input voltage, the mode switching can also be judged based on the output voltage or the ratio of the input voltage to the output voltage or the switching frequency of the switch tube. Different mode switching thresholds can be set according to different application requirements. In practical applications, the mode switching threshold can usually be set around 0.8 times the gain according to the principle of optimal efficiency. Furthermore, in order to avoid switching back and forth between modes, the set mode switching threshold is usually set with hysteresis to improve the robustness of the resonant converter.

[0046] It should also be noted that the present invention can control the closed-loop control quantity to perform a sudden increase / decrease operation after the driving pulse is controlled to continue for a set period during the mode switching transition process by directly switching the closed-loop control quantity to the set threshold, or it can gradually increase / decrease to the set threshold at a certain rate of change, specifically to ensure that the output voltage fluctuation caused by the mode switching is within an acceptable range.

[0047] Depending on the main control switch tube in non-frequency doubling mode and frequency doubling mode, the driving pulse control timing in the mode switching transition process will be different, as follows: When the first switch tube S1 and the third switch tube S3 are the main control switches in the non-frequency doubling mode, the driving pulse can be controlled in the transition process from the non-frequency doubling mode to the frequency doubling mode according to Figure 7-a and Figure 7-b The transition process is carried out in the manner shown, the driving pulse of the first switch tube S1 and the driving pulse of the second switch tube S2 are maintained to be complementary to each other, the driving pulse of the third switch tube S3 and the driving pulse of the fourth switch tube S4 are complementary to each other, the driving duty ratios of the first switch tube S1 and the fourth switch tube S4 are controlled to be the same and the third set duty ratio (for example, 0.25), the driving of the first switch tube S1 lags behind the driving of the fourth switch tube S4 by 180°, the switching frequency of the first switch tube S1 to the fourth switch tube S4 is greater than the series resonant frequency, so that the resonant converter works in the frequency doubling mode during the transition process to realize the resonant capacitor C rThe voltage transition is smooth, ensuring zero voltage turn-on of the first switch tube S1 to the fourth switch tube S4 during the transition process, thereby improving reliability. After the mode switching transition process is completed, the resonant converter uses the first switch tube S1 and the fourth switch tube S4 as the main control switch tubes to perform steady-state operation in the frequency doubling mode, and maintains that the driving of the first switch tube S1 lags behind the driving of the fourth switch tube S4 by 180°. Or you can follow Figure 8-a and Figure 8-b The transition process is carried out in the manner shown, the driving pulse of the first switch tube S1 is maintained to be complementary to the driving pulse of the second switch tube S2, the driving pulse of the third switch tube S3 is maintained to be complementary to the driving pulse of the fourth switch tube S4, the driving duty ratio of the second switch tube S2 and the third switch tube S3 is controlled to be the same and a third set duty ratio (for example, 0.25), the driving of the second switch tube S2 is 180° ahead of the driving of the third switch tube S3, the switching frequency of the first switch tube S1 to the fourth switch tube S4 is greater than the series resonant frequency, so that the resonant converter works in a frequency doubling mode during the transition process to realize the resonant capacitor C r The voltage transitions smoothly, ensuring zero voltage turn-on of the first switch tube S1 to the fourth switch tube S4 during the transition process, thereby improving reliability. After the mode switching transition process is completed, the resonant converter uses the second switch tube S2 and the third switch tube S3 as the main control switch tubes to perform steady-state operation in the double frequency mode, and maintains the drive of the second switch tube S2 ahead of the drive of the third switch tube S3 by 180°.

[0048] When the second switch tube S2 and the fourth switch tube S4 are the main control switches in the non-frequency doubling mode, the driving pulse can be controlled in the transition process from the non-frequency doubling mode to the frequency doubling mode according to Figure 9-a and Figure 9-b The transition process is carried out in the manner shown, the driving pulse of the first switch tube S1 and the driving pulse of the second switch tube S2 are maintained to be complementary to each other, the driving pulse of the third switch tube S3 and the driving pulse of the fourth switch tube S4 are complementary to each other, the driving duty ratios of the first switch tube S1 and the fourth switch tube S4 are controlled to be the same and the third set duty ratio (for example, 0.25), the driving of the first switch tube S1 is 180° ahead of the driving of the fourth switch tube S4, the switching frequency of the first switch tube S1 to the fourth switch tube S4 is greater than the series resonant frequency, so that the resonant converter works in the frequency doubling mode during the transition process to realize the resonant capacitor C r The voltage transition is smooth, ensuring zero voltage turn-on of the first switch tube S1 to the fourth switch tube S4 during the transition process, thereby improving reliability. After the mode switching transition process is completed, the resonant converter uses the first switch tube S1 and the fourth switch tube S4 as the main control switch tubes to perform steady-state operation in the frequency doubling mode, and maintains that the drive of the first switch tube S1 is 180° ahead of the drive of the fourth switch tube S4. Or you can follow Figure 10-a and Figure 10-b The transition process is carried out in the manner shown, the driving pulse of the first switch tube S1 is maintained to be complementary to the driving pulse of the second switch tube S2, the driving pulse of the third switch tube S3 is maintained to be complementary to the driving pulse of the fourth switch tube S4, the driving duty ratio of the second switch tube S2 and the third switch tube S3 is controlled to be the same and a third set duty ratio (for example, 0.25), the driving of the second switch tube S2 lags behind the driving of the third switch tube S3 by 180°, the switching frequency of the first switch tube S1 to the fourth switch tube S4 is greater than the series resonant frequency, so that the resonant converter works in a frequency doubling mode during the transition process to realize the resonant capacitor C r The voltage transitions smoothly, ensuring zero voltage turn-on of the first switch tube S1 to the fourth switch tube S4 during the transition process, thereby improving reliability. After the mode switching transition process is completed, the resonant converter uses the second switch tube S2 and the third switch tube S3 as the main control switch tubes to perform steady-state operation in the double frequency mode, and maintains that the drive of the second switch tube S2 lags behind the drive of the third switch tube S3 by 180°.

[0049] When the first switch tube S1 and the fourth switch tube S4 are the main control switches in the frequency doubling mode, the driving pulse can be controlled in the transition process from the frequency doubling mode to the non-frequency doubling mode according to Figure 11-a and Figure 11-b The method shown in the figure is as follows. During the transition process, the driving pulse of the first switch tube S1 and the driving pulse of the second switch tube S2 are maintained to be complementary to each other, and the driving pulse of the third switch tube S3 and the driving pulse of the fourth switch tube S4 are complementary to each other. The driving duty cycle of the first switch tube S1 is controlled to be the minimum duty cycle, and the driving duty cycle of the third switch tube S3 is the fourth set duty cycle (for example, 0.5). The driving of the first switch tube S1 lags behind the driving of the third switch tube S3 by 180°. The switching frequency of the first switch tube S1 to the fourth switch tube S4 is greater than the series resonant frequency, so that the resonant converter works in a non-frequency doubling mode during the transition process to realize the resonant capacitor. C r The voltage transition is smooth, ensuring zero voltage turn-on of the first switch tube S1 to the fourth switch tube S4 during the transition process, thereby improving reliability. After the mode switching transition process is completed, the resonant converter uses the first switch tube S1 and the third switch tube S3 as the main control switch tubes to perform steady-state operation in the non-frequency doubling mode, and maintains that the driving of the first switch tube S1 lags behind the driving of the third switch tube S3 by 180°. Or you can follow Figure 12-a and Figure 12-bThe transition process is carried out in the manner shown, the driving pulse of the first switch tube S1 and the driving pulse of the second switch tube S2 are maintained to be complementary to each other, the driving pulse of the third switch tube S3 and the driving pulse of the fourth switch tube S4 are complementary to each other, the driving duty cycle of the fourth switch tube S4 is controlled to be the minimum duty cycle, the driving duty cycle of the second switch tube S2 is the fourth set duty cycle (for example, 0.5), the driving of the second switch tube S2 is 180° ahead of the driving of the fourth switch tube S4, the switching frequency of the first switch tube S1 to the fourth switch tube S4 is greater than the series resonant frequency, so that the resonant converter works in a non-frequency doubling mode during the transition process to realize the resonant capacitor C r The voltage transitions smoothly, ensuring zero voltage turn-on of the first switch tube S1 to the fourth switch tube S4 during the transition process, thereby improving reliability. After the mode switching transition process is completed, the resonant converter uses the second switch tube S2 and the fourth switch tube S4 as the main control switch tubes to perform steady-state operation in the non-frequency doubling mode, and maintains the drive of the second switch tube S2 ahead of the drive of the fourth switch tube S4 by 180°.

[0050] When the second switch tube S2 and the third switch tube S3 are the main control switches in the frequency doubling mode, the driving pulse can be controlled in the transition process from the frequency doubling mode to the non-frequency doubling mode according to Figure 13-a and Figure 13-b The method shown in the figure is as follows. During the transition process, the driving pulse of the first switch tube S1 and the driving pulse of the second switch tube S2 are maintained to be complementary to each other, and the driving pulse of the third switch tube S3 and the driving pulse of the fourth switch tube S4 are complementary to each other. The driving duty cycle of the third switch tube S3 is controlled to be the minimum duty cycle, and the driving duty cycle of the first switch tube S1 is the fourth set duty cycle (for example, 0.5). The driving of the first switch tube S1 is 180° ahead of the driving of the third switch tube S3. The switching frequency of the first switch tube S1 to the fourth switch tube S4 is greater than the series resonant frequency, so that the resonant converter works in a non-frequency doubling mode during the transition process to realize the resonant capacitor. C r The voltage transition is smooth, ensuring the zero voltage turn-on of the first switch tube S1 to the fourth switch tube S4 during the transition process, thereby improving reliability. After the mode switching transition process is completed, the resonant converter uses the first switch tube S1 and the third switch tube S3 as the main control switch tubes to perform steady-state operation in the non-frequency doubling mode, and maintains the driving of the first switch tube S1 ahead of the driving of the third switch tube S3 by 180°. Or you can follow Figure 14-a and Figure 14-bThe method shown in the figure is as follows. During the transition process, the driving pulse of the first switch tube S1 and the driving pulse of the second switch tube S2 are maintained to be complementary to each other, the driving pulse of the third switch tube S3 and the driving pulse of the fourth switch tube S4 are complementary to each other, the driving duty cycle of the second switch tube S2 is controlled to be the minimum duty cycle, the driving duty cycle of the fourth switch tube S4 is the fourth set duty cycle (for example, 0.5), the driving of the second switch tube S2 lags behind the driving of the fourth switch tube S4 by 180°, the switching frequency of the first switch tube S1 to the fourth switch tube S4 is greater than the series resonant frequency, so that the resonant converter works in a non-frequency doubling mode during the transition process to realize the resonant capacitor C r The voltage transitions smoothly, ensuring zero voltage turn-on of the first switch tube S1 to the fourth switch tube S4 during the transition process, thereby improving reliability. After the mode switching transition process is completed, the resonant converter uses the second switch tube S2 and the fourth switch tube S4 as the main control switch tubes to perform steady-state operation in the non-frequency doubling mode, and maintains that the drive of the second switch tube S2 lags behind the drive of the fourth switch tube S4 by 180°.

[0051] It should be noted that, for the control method of the resonant converter provided by the present invention, in actual applications, a dead time will be added between the driving pulses of two complementary conductive switches in the same switch tube bridge arm circuit to avoid the two complementary conductive switches in the switch tube bridge arm circuit being common, and at the same time, the necessary preparation time can be provided for the corresponding switch tube to achieve zero voltage switching. The specific dead time size can be set according to the actual zero voltage switching situation of the switch tube.

[0052] In a specific embodiment, the rated output power of the series three-level LLC resonant converter in FIG1 is 960W, the input voltage Vin varies in the range of 250-1000V, the nominal output voltage is 24V, and the series resonant frequency is 100kHz. Under full power operation conditions, the input voltage is set to jump between high and low voltage conditions, and the following is obtained: Fig.15 , Fig.16 The experimental waveform shown, where V gs1 is the driving waveform of the first switch tube S1, V o is the output voltage waveform, i Lr is the resonant current waveform. Fig.15 , Fig.16 The experimental waveform shows that during the mode switching process, the output voltage overshoot and undershoot amplitude is small, less than 3%Vo, and the resonant current in the switching process i Lr The transition is smooth and there is no obvious current stress, which verifies the effectiveness of the mode switching control strategy.

[0053] The embodiment of the present invention further provides a control device of a resonant converter, which is configured to execute the control method of the resonant converter of the present invention; and provides a switching power supply, comprising Figure 1-a and Figure 1-b This type of resonant converter and a control device for the resonant converter provided by an embodiment of the present invention.

[0054] In the description of the above embodiments, the control method of the resonant converter of the present invention adopts a multi-mode combination method, and by reasonably adjusting the operating frequency and / or duty cycle and other driving timings of the primary switch tube, the gain adjustment capability of the resonant converter is effectively broadened while maintaining high efficiency; in addition, by judging the gain change of the resonant converter, the transition process control drive pulse is inserted to achieve smooth switching between modes and ensure the dynamic response performance of the switching process; the entire control method is simple and effective, and is conducive to the implementation of a digital controller, providing a simple and feasible preferred control scheme for the current resonant DC-DC power supply with high efficiency, high power density and wide voltage range requirements.

[0055] It should be noted that the embodiments described above are merely examples of the technical solutions and contents of the present invention, and it should be noted that the above embodiments should not be regarded as limiting the present invention. For those skilled in the art, several improvements and modifications may be made without departing from the spirit and scope of the present invention, but they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims, and should also be regarded as the protection scope of the present invention.

Claims

1. A control method for a resonant converter, wherein the primary circuit of the resonant converter comprises a primary switch network and an LLC resonant cavity network, wherein the primary switch network comprises two groups of switch tube bridge arm circuits connected in series or in parallel, wherein the first switch tube bridge arm circuit comprises a first switch tube and a second switch tube connected in series and a first capacitor connected in parallel with the first switch tube bridge arm circuit, and the second switch tube bridge arm circuit comprises a third switch tube and a fourth switch tube connected in series and a second capacitor connected in parallel with the second switch tube bridge arm circuit, wherein the first switch tube is at a higher potential than the second switch tube, and the third switch tube is at a higher potential than the fourth switch tube; the resonant converter maintains the same switching frequency of the four switch tubes in all working states, and one switch tube in each group of switch tube bridge arm circuits is a main control switch tube, the drive of the other switch tube is complementary to the drive of the main control switch tube, and the drive phase of the main control switch tubes in the two groups of switch tube bridge arm circuits is shifted by 180°; characterized in that The control method comprises: The wide gain adjustment is achieved by controlling the switching frequency and / or duty cycle of all the switch tubes in the primary switch network so that the resonant converter operates in a non-frequency doubling mode or a frequency doubling mode. Specifically: (1) When the gain requirement of the resonant converter is greater than or equal to 1, the resonant converter is operated in the non-frequency doubling mode, and two-level PFM control is used to achieve gain adjustment. At this time, the voltage injected into the LLC resonant cavity is in a conventional two-level state; (2) When the gain requirement of the resonant converter is less than 1, if the resonant converter is operated in the non-frequency doubling mode, a three-level PWM control is used to implement gain reduction regulation. At this time, the voltage injected into the LLC resonant cavity is in a three-level state; (3) When the gain requirement of the resonant converter is less than 1, if the resonant converter is operated in the frequency doubling mode, the frequency doubling PFM control is used to achieve gain reduction regulation. At this time, the voltage injected into the LLC resonant cavity is in a frequency doubling two-level state; There is also a mode switch between the non-frequency doubling mode and the frequency doubling mode, and a set transition driving pulse is inserted to achieve smooth mode switch.

2. The control method of the resonant converter according to claim 1, characterized in that: The two-level PFM control includes: controlling the duty cycle of the main control switch tubes in each group of switch tube bridge arm circuits to be the same and fixed to a first set duty cycle, and achieving boost regulation only by adjusting the switching frequency of the main control switch tubes in each group of switch tube bridge arm circuits, wherein the switching frequency of the main control switch tubes in each group of switch tube bridge arm circuits is always less than or equal to the series resonant frequency of the resonant capacitor and the resonant inductor in the LLC resonant cavity network.

3. The control method of the resonant converter according to claim 2, characterized in that: The first set duty cycle is 0.

5.

4. The control method of the resonant converter according to claim 1, characterized in that: The three-level PWM control includes: achieving step-down regulation by simultaneously adjusting the switching frequency and duty cycle of the main control switch tube in each group of switch tube bridge arm circuits, and at the same time minimizing the primary side circulating current loss of the resonant converter to improve efficiency, wherein the switching frequency of the main control switch tube in each group of switch tube bridge arm circuits is greater than the series resonant frequency of the resonant capacitor and the resonant inductor in the LLC resonant cavity network.

5. The control method of the resonant converter according to claim 1, characterized in that: The frequency-doubled PFM control includes: controlling the duty cycles of the main control switches in each group of switch tube bridge arm circuits to be the same and fixed to a second set duty cycle, and further voltage reduction regulation is achieved only by adjusting the switching frequency of the main control switches in each group of switch tube bridge arm circuits, wherein the switching frequency of the main control switches in each group of switch tube bridge arm circuits is less than the series resonant frequency of the resonant capacitor and the resonant inductor in the LLC resonant cavity network.

6. The control method of the resonant converter according to claim 5, characterized in that: The second set duty cycle is 0.

25.

7. The control method of the resonant converter according to claim 1, characterized in that: The mode switching between the non-frequency doubling mode and the frequency doubling mode includes: Detect input voltage, output voltage, ratio of input voltage to output voltage or switching frequency of switch tube; Whether to perform mode switching is determined by comparing with the set mode switching threshold. When the resonant converter meets the mode switching condition, the mode switching transition process is entered at the 0° or 180° phase moment of the main control switch tube, and the mode smooth switching is achieved according to the set transition drive pulse.

8. The control method of the resonant converter according to claim 7, characterized in that: The setting mode switching threshold is 0.95~0.6 times the gain, and the hysteresis is set.

9. The control method of the resonant converter according to claim 7, characterized in that: After the transition process is completed with the set transition drive pulse, the closed-loop control amount is suddenly increased or decreased to achieve dynamic compensation to reduce output voltage fluctuations.

10. The control method of the resonant converter according to claim 1, characterized in that: When the resonant converter switches from the non-frequency doubling mode to the frequency doubling mode, the inserted set transition drive pulse includes: if the first switch tube and the third switch tube are used as the main control switch tubes when working in the non-frequency doubling mode, then: Controlling the duty cycles of the first switch tube and the fourth switch tube to be the same and to be a third set duty cycle, wherein the driving of the first switch tube lags behind the driving of the fourth switch tube by 180°, and after a set transition period, the resonant converter enters a frequency doubling operation mode, and the first switch tube and the fourth switch tube are used as main control switch tubes; Alternatively, the duty cycles of the second switch tube and the third switch tube are controlled to be the same and to be a third set duty cycle, the driving of the second switch tube is 180° ahead of the driving of the third switch tube, and after a set transition period, the resonant converter enters a frequency doubling operation mode, and the second switch tube and the third switch tube are used as main control switch tubes.

11. The control method of the resonant converter according to claim 1, characterized in that: When the resonant converter switches from the non-frequency doubling mode to the frequency doubling mode, the inserted set transition drive pulse includes: if the second switch tube and the fourth switch tube are used as the main control switch tubes when working in the non-frequency doubling mode, then: Controlling the duty cycles of the first switch tube and the fourth switch tube to be the same and to be a third set duty cycle, driving the first switch tube to be 180° ahead of driving the fourth switch tube, and after continuously setting a transition period, the resonant converter enters a frequency doubling operation mode, and the first switch tube and the fourth switch tube are used as main control switch tubes; Alternatively, the duty cycles of the second switch tube and the third switch tube are controlled to be the same and to be a third set duty cycle, the driving of the second switch tube lags behind the driving of the third switch tube by 180°, and after a set transition period, the resonant converter enters a frequency doubling operation mode, and the second switch tube and the third switch tube are used as main control switch tubes.

12. The control method of the resonant converter according to any one of claims 10 to 11, characterized in that: The third set duty cycle is 0.

25.

13. The control method of the resonant converter according to claim 1, characterized in that: When the resonant converter switches from the frequency doubling mode to the non-frequency doubling mode, the inserted set transition drive pulse includes: if the first switch tube and the fourth switch tube are used as the main control switch tubes when working in the frequency doubling mode, then: Controlling the duty cycle of the first switch tube to be a set minimum duty cycle, the duty cycle of the third switch tube to be a fourth set duty cycle, the driving of the first switch tube lags behind the driving of the third switch tube by 180°, and after continuing for a set transition period, the resonant converter enters a non-frequency doubling operation mode, and the first switch tube and the third switch tube are used as main control switch tubes; Or the duty cycle of the fourth switch tube is controlled to be a set minimum duty cycle, the duty cycle of the second switch tube is a fourth set duty cycle, the driving of the second switch tube is 180° ahead of the driving of the fourth switch tube, and after a set transition period, the resonant converter enters a non-frequency doubling operation mode, and the second switch tube and the fourth switch tube are used as the main control switch tubes.

14. The control method of the resonant converter according to claim 1, characterized in that: When the resonant converter switches from the frequency doubling mode to the non-frequency doubling mode, the inserted set transition drive pulse includes: if the second switch tube and the third switch tube are used as the main control switch tubes when working in the frequency doubling mode, then: Controlling the duty cycle of the first switch tube to be a fourth set duty cycle, the duty cycle of the third switch tube to be a set minimum duty cycle, the driving of the first switch tube is 180° ahead of the driving of the third switch tube, and after a set transition period, the resonant converter enters a non-frequency doubling operation mode, and the first switch tube and the third switch tube are used as main control switch tubes; Or the duty cycle of the second switch tube is controlled to be a set minimum duty cycle, the duty cycle of the fourth switch tube is a fourth set duty cycle, the driving of the second switch tube lags behind the driving of the fourth switch tube by 180°, and after a set transition period, the resonant converter enters a non-frequency doubling working mode, and the second switch tube and the fourth switch tube are used as the main control switch tubes.

15. The control method of the resonant converter according to any one of claims 13 to 14, characterized in that: The fourth set duty cycle is 0.

5.

16. The control method of the resonant converter according to any one of claims 10, 11, 13 and 14, characterized in that: The number of cycles of the set transition period is N, where N is a positive integer, and within the set transition period, the switching frequency of the first to fourth switching tubes is greater than or equal to the series resonant frequency of the resonant capacitor and the resonant inductor in the LLC resonant cavity network.

17. A control device for a resonant converter, wherein the primary circuit of the resonant converter comprises a primary switch network and an LLC resonant cavity network, wherein the primary switch network comprises two groups of switch tube bridge arm circuits connected in series or in parallel, wherein the first switch tube bridge arm circuit comprises a first switch tube and a second switch tube connected in series and a first capacitor connected in parallel with the first switch tube bridge arm circuit, and the second switch tube bridge arm circuit comprises a third switch tube and a fourth switch tube connected in series and a second capacitor connected in parallel with the second switch tube bridge arm circuit, wherein the first switch tube is at a higher potential than the second switch tube, and the third switch tube is at a higher potential than the fourth switch tube; the resonant converter maintains the same switching frequency of the four switch tubes in all working states, and one switch tube in each group of switch tube bridge arm circuits is a main control switch tube, the drive of the other switch tube is complementary to the drive of the main control switch tube, and the drive phase of the main control switch tubes in the two groups of switch tube bridge arm circuits is shifted by 180°; characterized in that The control device is configured to: The wide gain adjustment is achieved by controlling the switching frequency and / or duty cycle of all the switch tubes in the primary switch network so that the resonant converter operates in a non-frequency doubling mode or a frequency doubling mode. Specifically: (1) When the gain requirement of the resonant converter is greater than or equal to 1, the resonant converter is operated in the non-frequency doubling mode, and two-level PFM control is used to achieve gain adjustment. At this time, the voltage injected into the LLC resonant cavity is in a conventional two-level state; (2) When the gain G requirement of the resonant converter is less than 1, if the resonant converter is operated in the non-frequency doubling mode, three-level PWM control is used to achieve gain reduction regulation. At this time, the voltage injected into the LLC resonant cavity is in a three-level state; (3) When the gain G requirement of the resonant converter is less than 1: if the resonant converter is operated in the frequency doubling mode, the frequency doubling PFM control is used to achieve gain reduction regulation. At this time, the voltage injected into the LLC resonant cavity is in a frequency doubling two-level state; There is also a mode switch between the non-frequency doubling mode and the frequency doubling mode, and a set transition driving pulse is inserted to achieve smooth mode switch.

18. A switching power supply, comprising a resonant converter, wherein the primary circuit of the resonant converter comprises a primary switch network and an LLC resonant cavity network, wherein the primary switch network is composed of two groups of switch tube bridge arm circuits connected in series or in parallel, wherein the first switch tube bridge arm circuit comprises a first switch tube and a second switch tube connected in series and a first capacitor connected in parallel with the first switch tube bridge arm circuit, and the second switch tube bridge arm circuit comprises a third switch tube and a fourth switch tube connected in series and a second capacitor connected in parallel with the second switch tube bridge arm circuit, wherein the first switch tube is at a higher potential than the second switch tube, and the third switch tube is at a higher potential than the fourth switch tube; the resonant converter maintains the same switching frequency of the four switch tubes in all working states, and one switch tube in each group of switch tube bridge arm circuits is a main control switch tube, the drive of the other switch tube is complementary to the drive of the main control switch tube, and the drive phase of the main control switch tubes in the two groups of switch tube bridge arm circuits is shifted by 180°; characterized in that: The switching power supply further comprises a control device for the resonant converter according to any one of claims 17.

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