LLC synchronous rectification control method, device and equipment and storage medium

Abstract

This invention discloses an LLC synchronous rectification control method, apparatus, device, and storage medium. The method includes acquiring resonance parameters and determining the resonance frequency and resonance period; determining the steady-state operating frequency based on the highest frequency of the MOSFET in the LLC resonant converter; determining the operating region of the LLC resonant converter based on the resonance frequency and the operating frequency; and controlling the on-time of the secondary-side synchronous rectifier diode of the LLC resonant converter based on the operating region. This invention determines the operating region by using the resonance frequency and the operating frequency, and then controls the on-time of the secondary-side synchronous rectifier diode, ensuring that the secondary-side synchronous rectifier diode turns off before the primary-side switch when operating in region II, thereby avoiding reverse current flow on the secondary side in region II and effectively improving the efficiency of the LLC resonant converter. Moreover, the control method of this invention is simple and clear, requiring only the implementation of the synchronous rectification timing described in the invention, without the need for additional detection circuitry.

Description

Technical Field

[0001] The present invention belongs to the technical field of switching power supplies, and particularly relates to an LLC synchronous rectification control method, device, equipment and storage medium. Background Art

[0002] With the maturity of switching power supply technology, the market application has an increasing demand for switching power supplies with high power, small size and high power density. Compared with the traditional analog control method, high-power switching power supply products tend to use digital control methods. The advantages of using digital control are flexible control strategies, convenient data exchange and communication with external devices, and also conducive to subsequent function upgrade and maintenance.

[0003] Since the way for LLC to achieve stable output regulation is PFM, for an LLC circuit with synchronous rectification at the output, when the conduction time T of the synchronous rectifier switch tube on-SR = T on-PR = T s / 2, that is, when alternating conduction at the traditional 50% duty cycle, the LLC main power stage in different working regions will present different working states. Then, when using digital control, when the LLC converter works at the resonant frequency point (fs = fr) and in region I (fs>fr), the converter works normally. As Figure 7 shown in the simulation results, where from top to bottom in the figure are the driving signals of the primary side switch tube, the driving signals of the secondary side synchronous rectifier tube, the current of the synchronous rectifier tube QSB, the resonant current and the magnetizing current. However, when the LLC converter works in region II (fs<fr), there will be a phenomenon that the energy of the secondary side output capacitor is inverted into the resonant cavity. As Figure 8 shown in the simulation results, where from top to bottom in the figure are the driving signals of the primary side switch tube, the driving signals of the secondary side synchronous rectifier tube, the current of the synchronous rectifier tube QSB, the resonant current and the magnetizing current, resulting in a decrease in the converter gain and efficiency, and a large current stress exists at the moment when the secondary side synchronous rectifier tube acts. It can be Figure 8 easily seen from the simulation results that when there is an inversion situation, the switching timing of the primary and secondary side switch tubes is: the secondary side synchronous rectifier tube and the primary side switch tube conduct and turn off simultaneously. Summary of the Invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide an LLC synchronous rectification control method, device, equipment and storage medium, so that there will be no situation of secondary side energy inversion when LLC works in region II.

[0005] The technical solutions provided by the present invention to solve the above technical problems are as follows:

[0006] In the first aspect, an embodiment of the present invention provides an LLC synchronous rectification control method, and the LLC synchronous rectification control method includes the following steps:

[0007] Obtain the resonance parameters to determine the resonant frequency and resonant period;

[0008] Determine the steady-state operating frequency based on the highest frequency of the MOSFET in the LLC resonant converter;

[0009] The operating region of the LLC resonant converter is determined based on the resonant frequency and the operating frequency.

[0010] The on-time of the secondary synchronous rectifier tube of the LLC resonant converter is controlled according to the operating region.

[0011] Furthermore, the resonance parameters include the resonant inductance value and the resonant capacitance value.

[0012] Furthermore, the determination of the steady-state operating frequency based on the highest frequency of the MOSFET in the LLC resonant converter specifically involves:

[0013] Based on the highest frequency of the MOSFET in the LLC resonant converter, the steady-state operating frequency is determined by scanning from the highest frequency.

[0014] Furthermore, determining the operating region of the LLC resonant converter based on the resonant frequency and the operating frequency includes:

[0015] The operating frequency is greater than or equal to the resonant frequency, and the operating region of the LLC resonant converter is determined to be ZVS operating region I.

[0016] Since the operating frequency is less than the resonant frequency, the operating region of the LLC resonant converter is determined to be the ZVS operating region II.

[0017] Furthermore, controlling the on-time of the secondary-side synchronous rectifier diode of the LLC resonant converter according to the operating region includes:

[0018] The working region is determined to be ZVS working region I, and the conduction time of the secondary-side synchronous rectifier of the LLC resonant converter is controlled as follows:

[0019] The working region is determined to be ZVS working region II, and the conduction time of the secondary synchronous rectifier of the LLC resonant converter is controlled as follows:

[0020] Among them, T on-SR T represents the on-time of the secondary-side synchronous rectifier diode. r This indicates the resonant period.

[0021] Secondly, embodiments of the present invention provide an LLC synchronous rectification control device, the LLC synchronous rectification control device comprising:

[0022] The resonance data determination unit is used to acquire resonance parameters and determine the resonance frequency and resonance period;

[0023] The operating frequency determination unit is used to determine the steady-state operating frequency based on the highest frequency of the MOS transistor in the LLC resonant converter.

[0024] The operating region determination unit is used to determine the operating region of the LLC resonant converter based on the resonant frequency and the operating frequency.

[0025] The conduction time control unit is used to control the conduction time of the secondary synchronous rectifier tube of the LLC resonant converter according to the operating region.

[0026] Furthermore, the work area determination unit includes:

[0027] The first determination unit is used to determine the working region of the LLC resonant converter as ZVS working region I when the working frequency is greater than or equal to the resonant frequency.

[0028] The second determination unit is used to determine that the operating region of the LLC resonant converter is ZVS operating region II when the operating frequency is less than the resonant frequency.

[0029] Furthermore, the conduction time control unit includes:

[0030] The first control unit is used to determine that the working region is ZVS working region I, and to control the on-time of the secondary-side synchronous rectifier of the LLC resonant converter as follows:

[0031] The second control unit is used to determine that the working region is ZVS working region II, and to control the on-time of the secondary-side synchronous rectifier tube of the LLC resonant converter as follows:

[0032] Among them, T on-SR T represents the on-time of the secondary-side synchronous rectifier diode. r This indicates the resonant period.

[0033] Thirdly, embodiments of the present invention provide an electronic device, the electronic device comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: when the computer program is executed by the processor, it implements the steps of the LLC synchronous rectification control method as described in the first aspect.

[0034] Fourthly, embodiments of the present invention provide a computer storage medium storing a computer program, which, when executed by a processor, implements the steps of the LLC synchronous rectification control method as described in the first aspect.

[0035] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0036] This invention determines the operating region by using the resonant frequency and the operating frequency, and then controls the conduction time of the secondary-side synchronous rectifier tube. This ensures that when operating in region II, the secondary-side synchronous rectifier tube turns off before the primary-side switch, thereby avoiding the situation of reverse current flow on the secondary side in region II and effectively improving the efficiency of the LLC resonant converter. Moreover, the control method of this invention is simple and clear. It can be implemented simply by following the synchronous rectification timing described in the invention, without the need to add additional detection circuits. Attached Figure Description

[0037] Figure 1 This is a circuit block diagram of the present invention;

[0038] Figure 2 A diagram showing the work area division for the LLC;

[0039] Figure 3 This is a flowchart illustrating the steps of the LLC synchronous rectification control method of the present invention.

[0040] Figure 4 This is a block diagram of the LLC synchronous rectification control device of the present invention;

[0041] Figure 5 This is a phase plane diagram of the analytical method of the present invention;

[0042] Figure 6 Timing waveform diagram for LLC operating in region II;

[0043] Figure 7 This is a schematic diagram of the simulation waveforms of the LLC operating at the resonant point and in region I without employing the strategy of this invention;

[0044] Figure 8 This is a schematic diagram of the simulation waveform when the LLC is operating in region II without employing the strategy of this invention;

[0045] Figure 9 A schematic diagram of the simulation waveform when LLC is operating in region II when the strategy of this invention is implemented;

[0046] Figure 10 This is a schematic diagram of the simulation waveform when LLC is operating in region II according to an embodiment of the present invention.

[0047] The attached figures are labeled as follows:

[0048] Cr, resonant capacitor;

[0049] Lr, resonant inductance;

[0050] Lm, magnetizing inductance;

[0051] QPA, LLC top tube;

[0052] QPB, LLC lower tube;

[0053] Primary-side drive signal A, LLC upper-side control signal;

[0054] Primary-side drive signal B, LLC lower-side control signal;

[0055] QSA, QSB, secondary-side synchronous rectifier tubes;

[0056] Secondary-side drive signal A, secondary-side drive signal B, secondary-side synchronous rectifier drive signal. Detailed Implementation

[0057] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0058] refer to Figure 1 The LLC resonant converter used in this scheme is composed of an input bus capacitor, an input square wave generating network, a resonant capacitor, a resonant inductor, a transformer, and an output rectifier network connected in sequence. Its control system includes a digital control system, a primary-side drive isolation unit, a primary-side switch, a secondary-side synchronous rectifier, a primary-side drive signal amplification unit, and a secondary-side drive signal amplification unit. The digital control system, as the core of the control, outputs control signals to the primary-side switch and the secondary-side synchronous rectifier. Its primary-side switch control signal output is connected to one end of the primary-side drive isolation unit, and its secondary-side switch control signal output is connected to one end of the secondary-side drive signal amplification unit. The other end of the primary-side drive isolation unit is connected to one end of the primary-side drive signal amplification unit. The other end of the secondary-side drive signal amplification unit outputs a drive signal to the gate of the secondary-side synchronous rectifier, and the other end of the primary-side drive signal amplification unit outputs a drive signal to the gate of the primary-side switch.

[0059] like Figure 8The diagram shows the simulated waveforms of the LLC resonant converter operating in region II without intervention. It can be seen that the switching sequence of the primary and secondary switches is as follows: the secondary synchronous rectifier and the primary switch are simultaneously turned on and off, resulting in reverse current flow into the secondary capacitor. Solving this problem requires analysis of this phenomenon.

[0060] It should be noted that the operating region of the LLC resonant converter can be divided into ZVS operating region I and ZVS operating region II, such as... Figure 2 As shown, with the resonant frequency f r As the dividing point, f r The right side is ZVS workspace area I, f r The left side is ZVS workspace area II.

[0061] refer to Figure 3 This invention provides an LLC synchronous rectification control method, which includes the following steps:

[0062] S100. Obtain the resonance parameters and determine the resonance frequency and resonance period.

[0063] The resonant parameters include the resonant inductance and resonant capacitance values.

[0064] The resonant frequency is calculated as follows: L r C is the resonant inductance value. r This is the resonant capacitance value. The resonant period is T. r With resonant frequency f r Inversely proportional.

[0065] S200. Determine the steady-state operating frequency based on the highest frequency of the MOSFET in the LLC resonant converter.

[0066] S300. Determine the operating region of the LLC resonant converter based on the resonant frequency and the operating frequency.

[0067] S400. Control the conduction time of the secondary synchronous rectifier tube of the LLC resonant converter according to the working area.

[0068] This invention determines the operating region by using the resonant frequency and the operating frequency, and then controls the conduction time of the secondary-side synchronous rectifier tube. This ensures that when operating in region II, the secondary-side synchronous rectifier tube turns off before the primary-side switch, thereby avoiding the situation of reverse current flow on the secondary side in region II and effectively improving the efficiency of the LLC resonant converter. Moreover, the control method of this invention is simple and clear. It can be implemented simply by following the synchronous rectification timing described in the invention, without the need to add additional detection circuits.

[0069] In one embodiment, the steady-state operating frequency is determined based on the highest frequency of the MOSFET in the LLC resonant converter, specifically as follows:

[0070] Based on the highest frequency of the MOSFET in the LLC resonant converter, the steady-state operating frequency is determined by scanning from the highest frequency.

[0071] In one embodiment, step 300 includes:

[0072] S301. The operating frequency is greater than or equal to the resonant frequency, and the operating region of the LLC resonant converter is determined to be ZVS operating region I.

[0073] S302. The operating frequency is less than the resonant frequency, so the operating region of the LLC resonant converter is determined to be the ZVS operating region II.

[0074] In one embodiment, step 400 includes:

[0075] S401. Determine the working region as ZVS working region I, and control the on-time of the secondary-side synchronous rectifier tube of the LLC resonant converter as follows:

[0076] Specifically, if it is determined that in the ZVS operating region I of the LLC resonant converter, the secondary-side synchronous rectifier uses the same gate drive signal as the corresponding primary-side switch, then the conduction time of the secondary-side synchronous rectifier of the LLC resonant converter is controlled as follows:

[0077] S402. Determine the working region as ZVS working region II, and control the on-time of the secondary-side synchronous rectifier tube of the LLC resonant converter as follows:

[0078] Among these, determining the ZVS operating region II of the LLC resonant converter is achieved by calculating the resonant frequency point f. r The corresponding resonant period T r To limit the conduction time T of the secondary synchronizing tube on-SR for: This ensures that the frequency of the secondary-side synchronous rectifier is equal to the frequency of the primary-side switch, and that the secondary-side synchronous rectifier turns off before the primary-side switch, thus preventing reverse current flow from the secondary side.

[0079] The specific analysis process of the embodiments of the present invention is as follows:

[0080] When the LLC operates at the resonant point, by f s =f r It can be known When LLC operates in region I, by f s >f r It can be known When LLC operates in region II, by f s <fr It can be known In practical applications, the dead time t usually needs to be considered. d To ensure the primary-side switch ZVS. Based on the above working process analysis, when LLC operates in region II, T... on-SR >T r / 2, so after the energy transfer from the primary side to the secondary side is completed, the secondary side switch, which should have been turned off, remains on, causing the voltage across the magnetizing inductor Lm to remain clamped. r C r The resonance continues, causing some of the energy in the output capacitor to flow back into the resonant cavity via the transformer coupling. When the conduction time ends and the primary and secondary switches are turned off simultaneously, the secondary side of the transformer is disconnected, and the LLC operation enters the dead time. During the dead time, the resonant current freewheels through the body diode of the complementary switch in the rectifier circuit, and some energy is re-injected into the output capacitor. The energy in the resonant cavity decreases, and the current decreases. This is the backflow phenomenon and its hazards when the LLC operates in region II.

[0081] like Figure 6 The figure shows the timing sequence of the LLC resonant converter operating in region II. Figure 6 The time-domain process is further analyzed using the planar trajectory method, as follows:

[0082] Working state one (t0~t1):

[0083] The excitation current changes linearly, as follows:

[0084]

[0085] Where -I Lm0 V is the excitation current value at time t0. O This represents the average value of the output voltage.

[0086] The resonant current approximately varies sinusoidally, as follows:

[0087]

[0088] Where -V Cr0 The voltage across the resonant capacitor is at time t0. The resonant angular frequency, Characteristic impedance,

[0089] The resonant current at time t1 is:

[0090]

[0091] Operating state two (t1~t2), three-element resonance, combined with state one, yields the phase plane diagram as follows: Figure 5 As shown.

[0092] It can be seen that in state two, the resonant current is equal to the excitation current with a slight increase, and the resonant current value at time t2 is i. Lr (t2), as can be seen from the phase plane diagram:

[0093] i Lr (t2)=I Lm0 ;

[0094]

[0095] If you think Then we have:

[0096]

[0097] We can obtain:

[0098]

[0099] In fact, there are:

[0100]

[0101] Because the excitation current changes linearly, the actual duration of t0 to t1 is... That is, the duration of energy transfer (the required conduction time of the secondary switch) is:

[0102] The above analysis shows that for a synchronous rectifier LLC circuit operating at the resonant frequency and in region I, the primary and secondary sides can use the same gate drive signal. For an LLC circuit operating in region II, the conduction time of the secondary-side synchronous rectifier is:

[0103]

[0104] The above is the analysis and derivation of the conduction time of the secondary-side synchronous rectification. Therefore, for the execution process of the digital control system, as follows... Figure 3 As shown, the resonant parameters of the LLC resonant converter are first given: resonant inductance value L r The resonant capacitance value C r The resonant frequency f is calculated by the digital control system. r and the resonant period T r When the LLC resonant converter starts working, during the output voltage build-up process, the digital control system starts from the highest frequency f of the given MOSFET. max Start by scanning the LLC resonant converter's operating frequency from high to low, and read the operating frequency f when the output is built up to the rated output. s , and the resonant frequency f r Compare; when f s >f rWhen the converter is determined to be operating in Zone I, the secondary-side synchronous rectification turn-on signal is made the same as the turn-on signal of the corresponding primary-side switch; when f s <f r When the converter is determined to be operating in region II, the given secondary-side synchronous rectification conduction time is: T. on-SR <T r / 2.

[0105] as follows Figure 9 and Figure 10 The figure shows the simulation results of an embodiment of the present invention. From top to bottom, the figures represent the primary-side switch drive signal, the secondary-side synchronous rectifier drive signal, the current of the synchronous rectifier QSB, the resonant current, and the magnetizing current. The parameters selected in this embodiment are as follows: L r =47.5uH, C r =66nC, from Figure 10 It can be seen that at this time, the secondary-side synchronous rectifier diode and the corresponding primary-side switch diode are turned on simultaneously, and the secondary-side switch diode is turned off before the primary-side switch diode, and T on-SR =5.19μs < 5.56μs = T r / 2

[0106] Therefore, by adopting a partitioned control strategy, this invention can control the conduction time of the secondary-side synchronous rectifier when the LLC resonant converter is operating in the ZVS operating region II, thereby avoiding the situation of backflow caused by the primary and secondary-side switching transistors being turned on and off simultaneously in region II.

[0107] refer to Figure 4 This invention provides an LLC synchronous rectification control device, which includes:

[0108] The resonance data determination unit is used to acquire resonance parameters and determine the resonance frequency and resonance period;

[0109] The operating frequency determination unit is used to determine the steady-state operating frequency based on the highest frequency of the MOS transistor in the LLC resonant converter.

[0110] The operating region determination unit is used to determine the operating region of the LLC resonant converter based on the resonant frequency and the operating frequency.

[0111] The conduction time control unit is used to control the conduction time of the secondary synchronous rectifier tube of the LLC resonant converter according to the operating region.

[0112] In one embodiment, the working area determination unit includes:

[0113] The first determination unit is used to determine the working region of the LLC resonant converter as ZVS working region I when the working frequency is greater than or equal to the resonant frequency.

[0114] The second determination unit is used to determine that the operating region of the LLC resonant converter is ZVS operating region II when the operating frequency is less than the resonant frequency.

[0115] In one embodiment, the on-time control unit includes:

[0116] The first control unit is used to determine that the working region is ZVS working region I, and to control the on-time of the secondary-side synchronous rectifier of the LLC resonant converter as follows:

[0117] The second control unit is used to determine that the working region is ZVS working region II, and to control the on-time of the secondary-side synchronous rectifier tube of the LLC resonant converter as follows:

[0118] Among them, T on-SR T represents the on-time of the secondary-side synchronous rectifier diode. r This indicates the resonant period.

[0119] It should be noted that for details not disclosed in the start-up control device of this embodiment, please refer to the details disclosed in the start-up control method of this embodiment, which will not be repeated here.

[0120] This invention provides an electronic device, which includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: when the computer program is executed by the processor, it implements the steps of the LLC synchronous rectification control method as described above.

[0121] It should be noted that for details not disclosed in the electronic device of this embodiment, please refer to the details disclosed in the start-up control method of this embodiment, which will not be repeated here.

[0122] This invention also provides a computer storage medium storing a computer program, which, when executed by a processor, implements the steps of the LLC synchronous rectification control method described above.

[0123] It should be noted that for details not disclosed in the computer storage medium of this embodiment of the invention, please refer to the details disclosed in the startup control method of this embodiment of the invention, which will not be repeated here.

[0124] The above description of the embodiments is only as an example of the present invention and is not intended to limit the scope of the present invention. Therefore, any modifications or equivalent substitutions made without departing from the principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of LLC synchronous rectification control, characterized by, The LLC synchronous rectification control method includes the following steps: Obtain the resonance parameters to determine the resonant frequency and resonant period; Determine the steady-state operating frequency based on the highest frequency of the MOSFET in the LLC resonant converter; The operating region of the LLC resonant converter is determined based on the resonant frequency and the operating frequency, including: when the operating frequency is greater than or equal to the resonant frequency, the operating region of the LLC resonant converter is determined to be ZVS operating region I; when the operating frequency is less than the resonant frequency, the operating region of the LLC resonant converter is determined to be ZVS operating region II. According to the operating region, the conduction time of the secondary synchronous rectifier of the LLC resonant converter is controlled, including: when the operating region is determined to be ZVS operating region II, the conduction time of the secondary synchronous rectifier of the LLC resonant converter is controlled to be less than half a resonant cycle to prevent the secondary current from flowing back.

2. The LLC synchronous rectification control method of claim 1, wherein: The resonance parameters include the resonant inductance value and the resonant capacitance value.

3. The LLC synchronous rectification control method of claim 1, wherein: The determination of the steady-state operating frequency based on the highest frequency of the MOSFET in the LLC resonant converter is specifically as follows: Based on the highest frequency of the MOSFET in the LLC resonant converter, the steady-state operating frequency is determined by scanning from the highest frequency.

4. The LLC synchronous rectification control method of claim 1, wherein: The method of controlling the conduction time of the secondary synchronous rectifier of the LLC resonant converter according to the working region further includes: when the working region is determined to be ZVS working region I, controlling the conduction time of the secondary synchronous rectifier of the LLC resonant converter to be equal to half a resonant cycle.

5. An LLC synchronous rectification control device, characterized in that, The LLC synchronous rectification control device includes: The resonance data determination unit is used to acquire resonance parameters and determine the resonance frequency and resonance period; The operating frequency determination unit is used to determine the steady-state operating frequency based on the highest frequency of the MOS transistor in the LLC resonant converter. The working area determination unit is used to determine the working area of ​​the LLC resonant converter based on the resonant frequency and the working frequency, including: a first determination unit, used to determine the working area of ​​the LLC resonant converter as ZVS working area I when the working frequency is greater than or equal to the resonant frequency; and a second determination unit, used to determine the working area of ​​the LLC resonant converter as ZVS working area II when the working frequency is less than the resonant frequency. The conduction time control unit is used to control the conduction time of the secondary synchronous rectifier of the LLC resonant converter according to the working region, including: a second control unit, used to control the conduction time of the secondary synchronous rectifier of the LLC resonant converter to be less than half a resonant cycle when the working region is determined to be ZVS working region II, so as to prevent the secondary current from flowing back.

6. The LLC synchronous rectification control device according to claim 5, characterized in that: The conduction time control unit further includes: a first control unit, used to control the conduction time of the secondary synchronous rectifier tube of the LLC resonant converter to be equal to half a resonant cycle when the working region is determined to be ZVS working region I.

7. An electronic device, characterized in that, The electronic device includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: when the computer program is executed by the processor, it implements the steps of the LLC synchronous rectification control method as described in any one of claims 1 to 4.

8. A computer storage medium, characterized in that, The computer storage medium stores a computer program, which, when executed by a processor, implements the steps of the LLC synchronous rectification control method as described in any one of claims 1 to 4.

Images