LLC resonant converter and control method thereof

Abstract

An LLC resonant converter includes a switching circuit, a resonant tank, a transformer, a synchronous rectification unit and a control unit. The switching circuit includes a first switch controlled by a first control signal and a second switch controlled by a second control signal, and the synchronous rectification unit includes a first synchronous rectification switch controlled by a first rectification control signal and a second synchronous rectification switch controlled by a second rectification control signal. The first control signal and the first rectification control signal include an operating frequency and a phase shift amount, and the second control signal and the second rectification control signal include an operating frequency and a phase shift amount. The control unit fixes one of the operating frequency and the phase shift amount when the operating frequency is lower than a certain value or the phase shift amount is higher than a certain value, so as to prolong the maintaining time of the LLC resonant converter. The present application also relates to a control method of an LLC resonant converter.

Description

Technical Field

[0001] This invention relates to an LLC resonant converter and its control method, and particularly to an LLC resonant converter with extended sustain time and its control method. Background Technology

[0002] LLC resonant converters offer advantages such as zero-voltage switching (ZVS turned-on) on the primary side, zero-current switching (ZCS turned-off) on the secondary side, and high efficiency. For example... Figure 2A Taking the full-bridge LLC resonant converter shown as an example, the current control method provides in-phase PWM signals to the first switch Q1 and the fourth switch Q4 on the primary side and the first synchronous rectifier switch SR1 on the secondary side, while the second switch Q2 and the third switch Q3 on the primary side and the second synchronous rectifier switch SR2 on the secondary side provide in-phase PWM control. However, this control method has the following disadvantages when the input voltage is insufficient:

[0003] 1. High-efficiency applications: In order to achieve high efficiency, the voltage gain value is usually designed to be relatively low, but this may result in insufficient voltage gain, which will reduce the hold-up time.

[0004] 2. High sustaining time application: In order to achieve a high sustaining time, the voltage gain value is usually designed to be relatively high. However, this can easily lead to lower efficiency and additional voltage stress on the resonant capacitor in the resonant slot 2.

[0005] Therefore, how to design an LLC resonant converter and its control method to maintain the LLC resonant converter at high efficiency without shortening the sustaining time and without causing additional voltage stress on the resonant capacitor is a major research topic that the inventors of this disclosure intend to conduct. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides an LLC resonant converter to overcome the limitations of existing technologies. Therefore, the LLC resonant converter of this invention includes a switching circuit, a resonant tank, a transformer, a synchronous rectification unit, and a control unit. The switching circuit includes a first switch and a second switch, and the resonant tank is coupled to the switching circuit. The transformer includes a primary side and a secondary side, and the primary side is coupled to the resonant tank. The synchronous rectification unit is coupled to the secondary side and includes a first synchronous rectification switch and a second synchronous rectification switch. The control unit provides a first control signal to control the first switch, a second control signal to control the second switch, a first rectification control signal to control the first synchronous rectification switch, and a second rectification control signal to control the second synchronous rectification switch based on the output voltage of the resonant converter. The first control signal and the first rectification control signal include an operating frequency and a phase shift, and the second control signal and the second rectification control signal also include an operating frequency and a phase shift. Specifically, the control unit controls the operating frequency to be frequency-converted and adjusts the phase shift when the operating frequency is lower than the phase shift frequency, and controls the operating frequency to be equal to the frequency threshold and adjusts the phase shift when the operating frequency is lower than the frequency threshold.

[0007] To address the aforementioned problems, this invention provides an LLC resonant converter to overcome the limitations of existing technologies. Therefore, the LLC resonant converter of this invention includes a switching circuit, a resonant tank, a transformer, a synchronous rectification unit, and a control unit. The switching circuit includes a first switch and a second switch, and the resonant tank is coupled to the switching circuit. The transformer includes a primary side and a secondary side, and the primary side is coupled to the resonant tank. The synchronous rectification unit is coupled to the secondary side and includes a first synchronous rectification switch and a second synchronous rectification switch. The control unit provides a first control signal to control the first switch, a second control signal to control the second switch, a first rectification control signal to control the first synchronous rectification switch, and a second rectification control signal to control the second synchronous rectification switch based on the output voltage of the resonant converter. The first control signal and the first rectification control signal include an operating frequency and a phase shift, and the second control signal and the second rectification control signal also include an operating frequency and a phase shift. Specifically, the control unit controls the operating frequency to be frequency-converted and adjusts the phase shift when the operating frequency is lower than the phase shift frequency, and controls the phase shift to be equal to the phase shift threshold and controls the operating frequency to be frequency-converted when the phase shift is higher than the phase shift threshold.

[0008] To address the aforementioned problems, this invention provides a control method for an LLC resonant converter to overcome the limitations of existing technologies. Therefore, the resonant converter of this invention includes a switching circuit, a transformer, and a synchronous rectification unit. The switching circuit includes a first switch controlled by a first control signal and a second switch controlled by a second control signal, and the synchronous rectification unit includes a first synchronous rectification switch controlled by a first rectification control signal and a second synchronous rectification switch controlled by a second rectification control signal. The control method includes: obtaining an operating frequency based on output voltage feedback; adjusting the phase shift of the first control signal and the first rectification control signal based on the operating frequency, and adjusting the phase shift of the second control signal and the second rectification control signal based on the operating frequency; determining whether the operating frequency is lower than the phase shift frequency; controlling the operating frequency to a variable frequency and adjusting the phase shift based on the operating frequency being lower than the phase shift frequency; and (a1) controlling the operating frequency to equal the frequency threshold and adjusting the phase shift based on the operating frequency being lower than the frequency threshold; or (a2) controlling the phase shift to equal the phase shift threshold and controlling the operating frequency to a variable frequency based on the phase shift being higher than the phase shift threshold.

[0009] The main objective and technical effect of this invention is that, by using a control unit to fix either the operating frequency or the phase shift when the operating frequency of the LLC resonant converter is as low as a certain value or as high as a certain value, the LLC resonant converter can be kept at high efficiency without shortening the holding time, and without causing an additional increase in voltage stress on the resonant capacitor.

[0010] To gain a deeper understanding of the techniques, means, and effects employed by this invention to achieve its intended purpose, please refer to the following detailed description and accompanying drawings. It is believed that the purpose, features, and characteristics of this invention can be understood in a thorough and specific manner from these drawings. However, the drawings are provided for reference and illustration only and are not intended to limit the scope of this invention. Attached Figure Description

[0011] Figure 1 This invention relates to an LLC resonant converter with an extended sustain time function;

[0012] Figure 2A The control method of the present invention can be used in conjunction with the first implementation circuit of an LLC resonant converter.

[0013] Figure 2B This is a second implementation circuit of an LLC resonant converter that can be used in conjunction with the control method of the present invention;

[0014] Figure 2C This is a third implementation circuit of an LLC resonant converter that can be used in conjunction with the control method of the present invention;

[0015] Figure 2D This is the fourth implementation circuit of the LLC resonant converter that can be used with the control method of the present invention;

[0016] Figure 3 This is a block diagram of the control unit of the present invention;

[0017] Figure 4A This is a schematic diagram of the frequency and phase of the LLC resonant converter of the present invention in the first control mode;

[0018] Figure 4B This is a schematic diagram of the frequency and phase of the LLC resonant converter of the present invention in the second control mode;

[0019] Figure 5A This is a schematic diagram of the control signals for the LLC resonant converter of the present invention operating in the first mode;

[0020] Figure 5B This is a schematic diagram of the control signals for the LLC resonant converter of the present invention operating in the second mode;

[0021] Figure 5C This is a schematic diagram of the control signals for the LLC resonant converter of the present invention operating in the third and fourth modes;

[0022] Figure 6 This is a flowchart of the control method for the LLC resonant converter of the present invention;

[0023] Figure 7A This is a detailed flowchart of the first control method for the LLC resonant converter of the present invention; and

[0024] Figure 7B This is a detailed flowchart of the second control method for the LLC resonant converter of the present invention.

[0025] Explanation of reference numerals in the attached figures:

[0026] 100…LLC resonant converter

[0027] 100-1… Primary side circuit

[0028] 100-2… Secondary side circuit

[0029] 1…Switching circuit

[0030] 12…First switch bridge arm

[0031] Q1…First Switch

[0032] Q2…Second switch

[0033] 14…Second switch bridge arm

[0034] Q3…Third switch

[0035] Q4…Fourth switch

[0036] 2…resonance slot

[0037] Lr…resonant inductor

[0038] Cr…resonant capacitor

[0039] 3…Transformer

[0040] 32… Primary Side

[0041] 34…Secondary side

[0042] 4…Synchronous Rectifier Unit

[0043] 42…First synchronous rectifier bridge arm

[0044] SR1…First synchronous rectifier switch

[0045] SR2…Second Synchronous Rectifier Switch

[0046] 44…Second synchronous rectifier bridge arm

[0047] SR3…Third Synchronous Rectifier Switch

[0048] SR4… Fourth Synchronous Rectifier Switch

[0049] 5…Control Unit

[0050] 52…Comparison Unit

[0051] 54…Voltage Controller

[0052] 56… Frequency limiter

[0053] 58…Signal Modulation Unit

[0054] 582… Frequency Controller

[0055] 584… Frequency and Phase Controller

[0056] 200…load

[0057] Vin…Input Voltage

[0058] Vo…output voltage

[0059] Vo_fb… Output voltage feedback value

[0060] Vo_ref… Output voltage reference value

[0061] Ver… Voltage error value

[0062] Sc… control signal

[0063] Sc1…First control signal

[0064] Sc2…Second control signal

[0065] Sc3…Third control signal

[0066] Sc4… Fourth control signal

[0067] Ssr1…First rectifier control signal

[0068] Ssr2…Second rectifier control signal

[0069] SSR3…Third rectifier control signal

[0070] SSR4… Fourth rectifier control signal

[0071] Cf… Frequency control command

[0072] Fsw…operation frequency

[0073] Fs…phase shift frequency

[0074] Fr…resonance frequency

[0075] Ft…frequency threshold

[0076] Fmax…highest frequency

[0077] Fmin…lowest frequency

[0078] Vs…phase shift

[0079] Vt…phase shift threshold

[0080] Vmax…Maximum phase shift

[0081] α…specific angle

[0082] M1…First Mode

[0083] M2…Second Mode

[0084] M3…Third Mode

[0085] M4, M4'... Fourth Mode

[0086] t1~t2”…time

[0087] S100~S340'…Steps Detailed Implementation

[0088] The technical content and detailed description of the present invention are explained below with reference to the accompanying drawings:

[0089] Please see Figure 1This invention relates to an LLC resonant converter with an extended hold time function. The LLC resonant converter 100 receives an input voltage Vin and converts it into an output voltage Vo to supply power to a load 200. The LLC resonant converter 100 includes a switching circuit 1, a resonant tank 2, a transformer 3, a synchronous rectification unit 4, and a control unit 5. The transformer 3 has a primary side 32 and a secondary side 34. The primary side 32 is coupled to the switching circuit 1 and the resonant tank 2, and the secondary side 34 is coupled to the synchronous rectification unit 4. The switching circuit 1 receives the input voltage Vin and includes a first switch Q1 and a second switch Q2. The resonant tank 2 is coupled to the switching circuit 1 and the primary side 32. By switching the first switch Q1 and the second switch Q2, the resonant circuit 2 resonates. The resonant tank 2 may include, for example, but not limited to, a resonant circuit composed of a capacitor or an inductor. The synchronous rectification unit 4 is coupled between the secondary side 34 and the load 200 and includes a first synchronous rectification switch SR1 and a second synchronous rectification switch SR2. When the LLC resonant converter is working normally, the first synchronous rectifier switch SR1 has the same turn-on timing as the first switch Q1 in the switching circuit 1, and the second synchronous rectifier switch SR2 has the same turn-on timing as the second switch Q2.

[0090] Control unit 5 is coupled to first switch Q1, second switch Q2, first synchronous rectifier switch SR1, and second synchronous rectifier switch SR2, and provides control signal Sc based on feedback (e.g., but not limited to, through a feedback circuit) of the output voltage Vo of resonant converter 100. Specifically, control signal Sc includes first control signal Sc1, second control signal Sc2, first rectification control signal Ssr1, and second rectification control signal Ssr2 to control first switch Q1, second switch Q2, first synchronous rectifier switch SR1, and second synchronous rectifier switch SR2, respectively.

[0091] Please see Figures 2A-2D The control method of this invention can be used in conjunction with the first to fourth implementation circuits of the LLC resonant converter, and further details can be found in the following references. Figure 1 .by Figure 2BBoth the primary-side circuit 100-1 and the secondary-side circuit 100-2 are described as full-bridge architectures. The primary-side circuit 100-1 includes a first switch arm 12 and a second switch arm 14 forming the switching circuit 1, and a resonant slot 2. The first switch arm 12 receives the input voltage Vin and includes a first switch Q1 and a second switch Q2 connected in series. The control unit 5 provides a first control signal Sc1 to control the first switch Q1 and a second control signal Sc2 to control the second switch Q2. The second switch arm 14 is connected in parallel with the first switch arm 12 and includes a third switch Q3 and a fourth switch Q4 connected in series. The control unit 5 provides a third control signal Sc3 to control the third switch Q3 and a fourth control signal Sc4 to control the fourth switch Q4. In the application of this invention, the first control signal Sc1 and the fourth control signal Sc4 are the same control signal, and the second control signal Sc2 and the third control signal Sc3 are the same control signal. Furthermore, the first control signal Sc1 and the second control signal Sc2 are interleaved control signals. Interleaved signals are preferably 180 degrees out of phase and can be complementary or non-complementary (e.g., but not limited to, signals that are not complementary due to a long switch-off time, or signals that have a dead time). The resonant slot 2 is coupled between the first switch arm 12 and the second switch arm 14, and is mainly composed of an LLC resonant slot consisting of a resonant inductor Lr, the magnetizing inductance of the transformer 3 (not shown), and a resonant capacitor Cr.

[0092] The secondary circuit 100-2 includes a first synchronous rectifier bridge arm 42 and a second synchronous rectifier bridge arm 44, which constitute the synchronous rectifier unit 4. The first synchronous rectifier bridge arm 42 is coupled to the secondary side 34 of the transformer 3 and includes a first synchronous rectifier switch SR1 and a second synchronous rectifier switch SR2 coupled in series. The second synchronous rectifier bridge arm 44 is connected in parallel to the first synchronous rectifier bridge arm 42 and includes a third synchronous rectifier switch SR3 and a fourth synchronous rectifier switch SR4 coupled in series. Specifically, the common connection point of the first synchronous rectifier switch SR1 and the second synchronous rectifier switch SR2 and the common connection point of the third synchronous rectifier switch SR3 and the fourth synchronous rectifier switch SR4 are respectively coupled to the two ends of the secondary side 34. Control unit 5 provides a first rectification control signal Ssr1 to control the first synchronous rectifier switch SR1, a second rectification control signal Ssr2 to control the second synchronous rectifier switch SR2, a third rectification control signal Ssr3 to control the third synchronous rectifier switch SR3, and a fourth rectification control signal Ssr4 to control the fourth synchronous rectifier switch SR4. The first rectification control signal Ssr1 and the fourth rectification control signal Ssr4 are the same control signal, and the second rectification control signal Ssr2 and the third rectification control signal Ssr3 are the same control signal. Furthermore, the first rectification control signal Ssr1 and the second rectification control signal Ssr2 are interleaved control signals.

[0093] in, Figures 2C-2D The primary-side circuit 100-1 of the LLC resonant converter 100 shown is a half-bridge architecture. Figure 2A , 2C The secondary circuit 100-2 of the LLC resonant converter 100 shown is a center-taped architecture. It should be noted that... Figures 2A-2D The components, control signals, and control descriptions in the following paragraphs all use the same numbering to represent the same control method, and will not be repeated here.

[0094] Please see Figure 3 This is a block diagram of the control unit of the present invention, which can be further referenced. Figures 1-2D To facilitate the explanation of the operation and control principle of the LLC resonant converter 100, therefore, it is used as... Figure 2A The circuit topology shown is illustrated below. Control unit 5 receives the output voltage signal corresponding to the output voltage Vo of LLC resonant converter 100, and obtains a frequency control command Cf based on the feedback of the output voltage Vo, thereby controlling the operating frequency Fsw of each control signal Sc in LLC resonant converter 100 according to the frequency control command Cf. Specifically, control unit 5 receives the output voltage feedback value Vo_fb and the output voltage reference value Vo_ref of LLC resonant converter 100 through comparison unit 52. After comparing the output voltage reference value Vo_ref with the output voltage feedback value Vo_fb, comparison unit 52 obtains the voltage error value Ver.

[0095] The voltage controller 54 of control unit 5 receives the voltage error value Ver and calculates the voltage error value Ver to obtain the frequency control command Cf corresponding to the operating frequency Fsw of each control signal Sc in LLC resonant converter 100. Taking the voltage controller 54 as a proportional-integral (PI) controller as an example, this is not intended to limit the invention. The voltage controller 54 performs a linear combination operation of proportional and integral values ​​on the voltage error value Ver to obtain the control quantity, i.e., the frequency control command Cf. Furthermore, to ensure that the frequency control command Cf does not exceed the maximum value of the control command quantity (i.e., the corresponding...), Figures 4A-4B The highest frequency (Fmax) or lower than the minimum value of the control command (i.e., the corresponding Figures 4A-4B The lowest frequency Fmin), therefore, the upper and lower limits of the frequency control command Cf are limited by the frequency limiter 56, so as to limit the highest frequency Fmax and the lowest frequency Fmin of the operating frequency Fsw.

[0096] The signal modulation unit 58 of the control unit 5 includes a frequency controller 582 and a frequency and phase controller 584. The frequency controller 582 adjusts the operating frequencies Fsw of the first control signal Sc1 and the second control signal Sc2 according to the frequency control command Cf, and the frequency and phase controller 584 adjusts the operating frequencies Fsw of the first rectification control signal Ssr1 and the second rectification control signal Ssr2, as well as the phase shift Vs. The waveforms generated by the frequency controller 582 and the frequency and phase controller 584, after comparison by a comparator and control by logic circuits, produce pulse width modulation signals, which are the first control signal Sc1, the second control signal Sc2, the first rectification control signal Ssr1, and the second rectification control signal Ssr2 corresponding to the frequency control command Cf. The frequency controller 582 and the frequency and phase controller 584 may, for example but not limited to, adjust the duty cycles of the first control signal Sc1, the second control signal Sc2, the first rectification control signal Ssr1, and the second rectification control signal Ssr2.

[0097] Please see Figures 4A-4B These are schematic diagrams showing the frequency and phase of the LLC resonant converter of the present invention under the first and second control modes, respectively. See also the related diagrams. Figures 1-3 .exist Figure 4A In this mode, when the operating frequency Fsw (associated with the frequency control command Cf) is higher than the phase shift frequency Fs set by the control unit 5 and higher than the resonant frequency Fr of the LLC resonant converter 10, the LLC resonant converter 10 operates in the first mode M1. In this mode, the control unit 5 controls the operating frequency Fsw of the first control signal Sc1 and the first rectification control signal Ssr1 to be frequency-converted, and the phase shift Vs is 0 degrees. The frequency conversion refers to the adjustment of the operating frequency Fsw with the change of the input voltage Vin, and the change of the input voltage Vin can be known through the feedback of the output voltage Vo. The phase shift Vs refers to the phase difference between the rectification control signals Ssr1 and Ssr2 and the control signals Sc1 and Sc2, and its range can be from 0 degrees to 180 degrees. A phase shift Vs of 0 degrees means that the two signals are turned on simultaneously. Since the second control signal Sc and the second rectification control signal Ssr2 are interleaved with the first control signal Sc1 and the first rectification control signal Ssr1, respectively, their operating frequency Fsw and phase shift Vs are the same as those of the first control signal Sc1 and the first rectification control signal Ssr1. Specifically, the lower the input voltage Vin, the more the operating mode of the LLC resonant converter 10 will gradually shift from the first mode M1 to the fourth mode M4. This means that the operating frequency Fsw will be lower, and the phase shift Vs will gradually increase from 0 degrees at appropriate times.

[0098] When the operating frequency Fsw is higher than the phase shift frequency Fs but lower than the resonant frequency Fr, the LLC resonant converter 10 operates in the second mode M2. In this mode, the control unit 5 controls the operating frequency Fsw of the first control signal Sc1 and the first rectification control signal Ssr1 to be frequency-converted, and the phase shift Vs is 0 degrees (the same applies to the second control signal Sc and the second rectification control signal Ssr2). At the same time, the control unit 5 limits the duty cycle of the first rectification control signal Ssr1 and the second rectification control signal Ssr2 to not exceed the resonant period to prevent energy from flowing back from the secondary side circuit 100-2 to the primary side circuit 100-1 during switching.

[0099] When the operating frequency Fsw is lower than the phase shift frequency Fs but higher than the preset frequency threshold Ft of the control unit 5, the LLC resonant converter 10 operates in the third mode M3. In this mode, the control unit 5 controls the operating frequency Fsw of the first control signal Sc1 and the first rectification control signal Ssr1 to be frequency-converted, and adjusts the phase shift Vs according to the change of the input voltage Vin (the same applies to the second control signal Sc and the second rectification control signal Ssr2). Therefore, as the operating frequency Fsw decreases, the phase shift Vs gradually increases from 0 degrees. The phase shift Vs can be leading or lagging. That is, the control unit 5 can control the phase of the first rectification control signal Ssr1 to lead the first control signal Sc1, or control the phase of the first control signal Sc1 to lag the first rectification control signal Ssr1, depending on whether the operating frequency Fsw is lower than the frequency threshold Ft (the same applies to the second control signal Sc and the second rectification control signal Ssr2).

[0100] When the operating frequency Fsw continuously decreases to equal the preset frequency threshold Ft of the control unit 5, the LLC resonant converter 10 operates in the fourth mode M4. In this mode, the control unit 5 controls the operating frequency Fsw of the first control signal Sc1 and the first rectification control signal Ssr1 to be equal to the frequency threshold Ft, and still adjusts the phase shift Vs according to the change of the input voltage Vin (the same applies to the second control signal Sc and the second rectification control signal Ssr2). Therefore, although the voltage error value Ver calculated internally by the control unit 5 may continuously increase, the operating frequency Fsw can be limited by setting the corresponding frequency threshold Ft in the voltage controller 54 or the signal modulation unit 58. The phase shift Vs is gradually increased according to the decrease of the input voltage Vin until the maximum phase shift Vmax before the LLC resonant converter 100 fails. The maximum phase shift Vmax can also be set separately by the control unit 5.

[0101] exist Figure 4B In the middle, the curves of the LLC resonant converter 10 operating in the first mode M1 to the third mode M3 are all consistent with... Figure 4AThe same applies here, and will not be repeated. The LLC resonant converter 10 operates in the fourth mode, M4', until the phase shift Vs gradually increases from 0 degrees in the third mode M3 to the phase shift threshold Vt preset by the control unit 5. In this mode, the control unit 5 controls the operating frequency Fsw of the first control signal Sc1 and the first rectification control signal Ssr1 to be frequency-converted, and controls the phase shift Vs to be fixed and equal to the phase shift threshold Vt (the same applies to the second control signal Sc and the second rectification control signal Ssr2). The frequency threshold Ft' corresponding to the phase shift threshold Vt is determined by the control unit 5, but it is only the operating frequency Fsw at the current point.

[0102] Therefore, although the voltage error value Ver calculated internally by the control unit 5 may continuously increase, causing the operating frequency Fsw to continuously decrease, the phase shift Vs can be limited by setting the corresponding phase shift threshold Vt in the frequency and phase controller 584. The operating frequency Fsw is gradually reduced according to the decrease of the input voltage Vin, until it reaches the lowest frequency Fmin before the LLC resonant converter 100 fails. The lowest frequency Fmin can also be set separately by the control unit 5.

[0103] Please see Figures 5A-5C These are schematic diagrams of the control signals for the LLC resonant converter of the present invention operating in the first to fourth modes, respectively. See also the attached diagrams. Figures 1-4B .exist Figure 5A In the first mode M1, the first control signal Sc1 and the first rectification control signal Ssr1 provided by the control unit 5 are frequency conversion signals with the same phase. Simultaneously, the second control signal Sc2 and the second rectification control signal Ssr2 are also frequency conversion signals with the same phase. Therefore, the phase shift Vs of the rising edge of the conduction signals of the first control signal Sc1 and the first rectification control signal Ssr1 is 0 degrees, and the phase shift Vs of the rising edge of the conduction signals of the second control signal Sc2 and the second rectification control signal Ssr2 is also 0 degrees.

[0104] exist Figure 5B In the second mode M2, the first control signal Sc1 and the first rectification control signal Ssr1 provided by the control unit 5 are frequency conversion signals with the same phase. Simultaneously, the second control signal Sc2 and the second rectification control signal Ssr2 are also frequency conversion signals with the same phase. That is, the phase shift Vs of the rising edge of the conduction signals of the first control signal Sc1 and the first rectification control signal Ssr1 is 0 degrees, and the phase shift Vs of the rising edge of the conduction signals of the second control signal Sc2 and the second rectification control signal Ssr2 is also 0 degrees. In this mode, the control unit 5 limits the duty cycle (responsibility cycle) of the first rectification control signal Ssr1 and the second rectification control signal Ssr2 to not exceed the resonant period. The resonant period is the reciprocal of the resonant frequency Fr, which is 1 / Fr.

[0105] exist Figure 5C In the third mode M3 and the fourth mode M4, the control unit 16 adjusts the phase shift Vs of the first control signal Sc1 and the first rectification control signal Ssr1 according to the change of the input voltage Vin. Simultaneously, it adjusts the phase shift Vs of the second control signal Sc2 and the second rectification control signal Ssr2. That is, the phase shift Vs of the rising edge of the conduction signals of the first control signal Sc1 and the first rectification control signal Ssr1 increases with lower frequencies, for example... Figure 5C The phase shift Vs is represented by a specific angle α (corresponding to the magnitude of the phase shift Vs), where α is any number from 0 to 180 degrees and greater than 0. It is worth noting that the control unit 5 controls the phase of the first rectifier control signal Ssr1 to lead the phase of the first control signal Sc1. Specifically, this is achieved by increasing the conduction period of the first synchronous rectifier switch SR1, so that the rising edge of the first rectifier control signal Ssr1 leads (from time 0 to time t1), i.e., leading by a specific angle α. The control methods for the second control signal Sc2 and the second rectifier control signal Ssr2 are similar and will not be elaborated further here.

[0106] Therefore, when the operating frequency Fsw is lower than the phase shift frequency Fs, the control unit 5 limits the duty cycle to be higher than the resonant period so that the phase can lead. Through this control method, when the input voltage Vin is insufficient and the output voltage Vo begins to drop, the LLC resonant converter 10 can still maintain its output voltage above a certain level for a certain period, giving the downstream coupled electronic products (load 200) sufficient time to react and to completely store or back up the data before power failure.

[0107] Please see Figure 6 This is a flowchart of the control method for the LLC resonant converter of the present invention, which can be further referenced. Figures 1-5C The circuit architecture of the LLC resonant converter 100 is as follows: Figures 2A-2D As shown, the control method includes obtaining the operating frequency based on output voltage feedback (S100). In a preferred embodiment, the control unit 5 receives feedback from the output voltage and determines the operating frequency Fsw of the first switch Q1, the second switch Q2, the first synchronous rectifier switch SR1, and the second synchronous rectifier switch SR2. Then, the phase shift of the first control signal and the first rectifier control signal is adjusted according to the operating frequency, and the phase shift of the second control signal and the second rectifier control signal is adjusted according to the operating frequency (S120). In a preferred embodiment, the control unit 5 adjusts the phase shift Vs of the first control signal Sc1 and the first rectifier control signal Ssr1 according to the change in the operating frequency Fsw, and the same applies to the phase shift Vs of the second control signal Sc2 and the second rectifier control signal Ssr2.

[0108] Then, it is determined whether the operating frequency is lower than the phase shift frequency, and the operating frequency is controlled to be variable frequency and the phase shift amount is adjusted according to the operating frequency being lower than the phase shift frequency (S140). In a preferred embodiment, the control unit 5 determines whether the operating frequency Fsw is lower than the phase shift frequency Fs. When the operating frequency Fsw is higher than the phase shift frequency Fs, the control unit 5 controls the operating frequency Fsw of the first control signal Sc1 and the first rectification control signal Ssr1 to be variable frequency, and the phase shift amount Vs is 0 degrees (the same applies to the second control signal Sc and the second rectification control signal Ssr2). When the operating frequency Fsw is lower than the phase shift frequency Fs, the control unit 5 controls the operating frequency Fsw of the first control signal Sc1 and the first rectification control signal Ssr1 to be variable frequency, and adjusts the phase shift amount Vs according to the change in the input voltage Vin (the same applies to the second control signal Sc and the second rectification control signal Ssr2).

[0109] Specifically, when the operating frequency Fsw is higher than the phase shift frequency Fs but lower than the resonant frequency Fr, the control unit 5 limits the duty cycle of the first rectifier control signal Ssr1 and the second rectifier control signal Ssr2 to not exceed the resonant period, in order to prevent energy from the secondary side circuit 100-2 from flowing back to the primary side circuit 100-1 during switching. However, when the operating frequency Fsw is lower than the phase shift frequency Fs, the control unit 5 limits the duty cycle to be higher than the resonant period, so that its phase can lead.

[0110] Finally, the operating frequency is controlled to be equal to the frequency threshold and the phase shift is adjusted according to the operating frequency being lower than the frequency threshold (S160), or the phase shift is controlled to be equal to the phase shift threshold and the operating frequency is controlled to be frequency-converted according to the phase shift being higher than the phase shift threshold (S180).

[0111] In step (S160), the fixed operating frequency Fsw is preferably implemented such that the control unit 5 controls the operating frequency Fsw of the first control signal Sc1 and the first rectification control signal Ssr1 to be equal to the frequency threshold Ft, and still adjusts the phase shift Vs according to the change of the input voltage Vin (the same applies to the second control signal Sc and the second rectification control signal Ssr2). The control unit 5 increases the conduction period of the first synchronous rectification switch SR1 to achieve a leading phase of the rising edge of the conduction signal of the first rectification control signal Ssr1, and similarly increases the conduction period of the second synchronous rectification switch SR2 to achieve a leading phase of the rising edge of the conduction signal of the second rectification control signal Ssr2. In step (S180), the fixed phase shift Vs is preferably implemented such that the control unit 5 controls the operating frequency Fsw of the first control signal Sc1 and the first rectification control signal Ssr1 to be frequency-converted, and controls the phase shift Vs to be equal to the phase shift threshold Vt (the same applies to the second control signal Sc and the second rectification control signal Ssr2).

[0112] Please see Figures 7A-7B These are detailed flowcharts of the first and second control methods for the LLC resonant converter of the present invention, respectively. See also the related flowcharts. Figures 1-6 .like Figure 7A As shown, the control method of the LLC resonant converter 100 at a fixed operating frequency Fsw includes: first, receiving an output voltage feedback value and an output voltage reference value corresponding to the output voltage, and comparing the output voltage feedback value and the output voltage reference value to generate a voltage error value (S200). Then, calculating the voltage error value to obtain a frequency control command corresponding to the operating frequency (S220). The control unit 5 can modulate interleaved first control signals Sc1 and second control signals Sc2 according to the frequency control command Cf, and modulate a first rectifier control signal Ssr1 corresponding to the first control signal Sc1 according to the frequency control command Cf, and a second rectifier control signal Ssr2 corresponding to the second control signal Sc2 according to the frequency control command Cf. The operating frequency Fsw is generated by the frequency control command Cf, thus allowing for the corresponding determination of the control mode.

[0113] Then, it is determined whether the operating frequency is higher than the phase shift frequency (S240). If yes (i.e., the operating frequency Fsw is higher than the phase shift frequency Fs), the operating frequencies of the first control signal and the second control signal are controlled to be frequency-converted, and the operating frequencies of the first rectification control signal and the second rectification control signal are also controlled to be frequency-converted (S300). If no (i.e., the operating frequency Fsw is lower than the phase shift frequency Fs), it is determined whether the operating frequency is higher than the frequency threshold (S260). If yes (i.e., the operating frequency Fsw is higher than the frequency threshold Ft), the operating frequencies of the first control signal and the second control signal are controlled to be frequency-converted, and the operating frequencies of the first rectification control signal and the second rectification control signal are also controlled to be frequency-converted and the phase shift is adjusted (S320). If no (i.e., the operating frequency Fsw is lower than the frequency threshold Ft), the operating frequencies of the first control signal and the second control signal are fixed at the frequency threshold, and the operating frequencies of the first rectification control signal and the second rectification control signal are also fixed at the frequency threshold and the phase shift is adjusted (S340).

[0114] like Figure 7B As shown, in the control method of the LLC resonant converter 100 with a fixed phase shift Vs, steps (S200) to (S240) and (S300) to (S320) are the same as... Figure 7AThe difference lies in the determination in step (S240). If the determination is negative (i.e., the operating frequency Fsw is lower than the phase shift frequency Fs), then it is determined whether the phase shift is higher than the phase shift threshold (S260'). Otherwise, proceed to step (S320). If the determination is positive (i.e., the phase shift Vs equals the phase shift threshold Vt), then the operating frequencies of the first control signal and the second control signal are controlled to be frequency-converted, and the operating frequencies of the first rectifier control signal and the second rectifier control signal are controlled to be frequency-converted while fixing the phase shift at the phase shift threshold (S340').

[0115] Therefore, utilizing Figure 7A and Figure 7B The control method allows the LLC resonant converter 100 to maintain a voltage above a certain level for a period of time even when the input voltage Vin is insufficient, giving the downstream coupled electronic products (load 200) enough time to react and to fully store or back up the data before the power failure.

[0116] The above description is merely a detailed explanation and accompanying drawings of preferred embodiments of the present invention, and the features of the present invention are not limited thereto, nor are they intended to limit the present invention. The scope of the present invention should be determined by the claims. All embodiments that conform to the concept of the claims of the present invention and similar variations thereof should be included in the scope of the present invention. Any variations or modifications that can be easily conceived by those skilled in the art within the field of the present invention can be covered by the claims disclosed herein.

Claims

1. An LLC resonant converter, comprising: A switching circuit includes a first switch and a second switch; A resonant slot is coupled to the switching circuit; A transformer includes a primary side and a secondary side, the primary side being coupled to the resonant slot; A synchronous rectification unit, coupled to the secondary side, includes a first synchronous rectification switch and a second synchronous rectification switch; and A control unit provides a first control signal to control the first switch, a second control signal to control the second switch, a first rectification control signal to control the first synchronous rectification switch, and a second rectification control signal to control the second synchronous rectification switch according to an output voltage of the resonant converter. The first control signal and the first rectification control signal have an operating frequency and a phase shift, and the second control signal and the second rectification control signal have the operating frequency and the phase shift. Specifically, the control unit controls the operating frequency to be frequency-converted and adjusts the phase shift amount when the operating frequency is lower than a phase shift frequency, and controls the operating frequency to be equal to a frequency threshold and adjusts the phase shift amount when the operating frequency is lower than a frequency threshold. The control unit controls the phase of the first rectifier control signal to lead the phase of the first control signal based on the operating frequency being lower than the frequency threshold, and controls the phase of the second rectifier control signal to lead the phase of the second control signal.

2. The LLC resonant converter as claimed in claim 1, wherein the control unit limits the duty cycle of the first rectification control signal and the second rectification control signal to not exceed one resonant period based on the operating frequency being higher than the phase shift frequency but lower than a resonant frequency.

3. The LLC resonant converter of claim 2, wherein the control unit limits the duty cycle to be higher than the resonant period based on the fact that the operating frequency is lower than the phase shift frequency.

4. The LLC resonant converter of claim 1, wherein the control unit comprises: A comparison unit receives an output voltage feedback value and an output voltage reference value corresponding to the output voltage, and compares the output voltage feedback value and the output voltage reference value to generate a voltage error value; A voltage controller receives the voltage error value, performs calculations on the voltage error value to obtain a frequency control command corresponding to the operating frequency; and A signal modulation unit modulates the interleaved first control signal and the second control signal according to the frequency control command, modulates the first rectification control signal corresponding to the first control signal according to the frequency control command, and modulates the second rectification control signal corresponding to the second control signal according to the frequency control command.

5. The LLC resonant converter of claim 1, wherein the switching circuit includes a first switch bridge arm composed of the first switch and the second switch to form a half-bridge circuit architecture.

6. The LLC resonant converter as claimed in claim 1, wherein the switching circuit includes a first switch bridge arm composed of the first switch and the second switch, and a second switch bridge arm composed of a third switch and a fourth switch, to form a full-bridge circuit architecture.

7. The LLC resonant converter as claimed in claim 1, wherein the transformer is a center-tapped structure, and the first synchronous rectifier switch and the second synchronous rectifier switch are respectively coupled to the two ends of the transformer.

8. The LLC resonant converter as claimed in claim 1, wherein the transformer is coupled to a first synchronous rectifier bridge arm composed of the first synchronous rectifier switch and the second synchronous rectifier switch, and a second synchronous rectifier bridge arm composed of a third synchronous rectifier switch and a fourth synchronous rectifier switch, to form a full-bridge rectifier circuit architecture.

9. An LLC resonant converter, comprising: A switching circuit includes a first switch and a second switch; A resonant slot is coupled to the switching circuit; A transformer includes a primary side and a secondary side, the primary side being coupled to the resonant slot; A synchronous rectification unit, coupled to the secondary side, includes a first synchronous rectification switch and a second synchronous rectification switch; and A control unit provides a first control signal to control the first switch, a second control signal to control the second switch, a first rectification control signal to control the first synchronous rectification switch, and a second rectification control signal to control the second synchronous rectification switch according to an output voltage of the resonant converter. The first control signal and the first rectification control signal have an operating frequency and a phase shift, and the second control signal and the second rectification control signal have the operating frequency and the phase shift. Specifically, the control unit controls the operating frequency to be variable frequency and adjusts the phase shift amount when the operating frequency is lower than a phase shift frequency, and controls the phase shift amount to be equal to the phase shift threshold and controls the operating frequency to be variable frequency when the phase shift amount is higher than a phase shift threshold. The control unit controls the phase of the first rectifier control signal to lead the phase of the first control signal based on the operating frequency being as low as a frequency threshold, and controls the phase of the second rectifier control signal to lead the phase of the second control signal.

10. The LLC resonant converter of claim 9, wherein the control unit limits the duty cycle of the first rectification control signal and the second rectification control signal to not exceed one resonant period based on the operating frequency being higher than the phase shift frequency but lower than a resonant frequency.

11. The LLC resonant converter of claim 10, wherein the control unit limits the duty cycle to be higher than the resonant period based on the operating frequency being lower than the phase shift frequency.

12. A control method for an LLC resonant converter, wherein the resonant converter includes a switching circuit, a transformer, and a synchronous rectification unit; the switching circuit includes a first switch controlled by a first control signal and a second switch controlled by a second control signal; and the synchronous rectification unit includes a first synchronous rectification switch controlled by a first rectification control signal and a second synchronous rectification switch controlled by a second rectification control signal; the first control signal, the second control signal, the first rectification control signal, and the second rectification control signal have an operating frequency; the control method includes: The operating frequency is obtained based on an output voltage feedback. The phase shift of the first control signal and the first rectification control signal, as well as the phase shift of the second control signal and the second rectification control signal, are adjusted according to the operating frequency. Determine whether the operating frequency is lower than a phase shift frequency; Based on the fact that the operating frequency is lower than the phase shift frequency, the operating frequency is controlled to be a variable frequency and the phase shift amount is adjusted; and (a1) Based on the fact that the operating frequency is as low as a frequency threshold, control the operating frequency to be equal to the frequency threshold and adjust the phase shift; or (a2) Based on the phase shift amount being higher than a phase shift threshold, the phase shift amount is controlled to be equal to the phase shift threshold, and the operating frequency is controlled to be variable frequency. Step (a1) includes: Based on the operating frequency being as low as the frequency threshold, the phase of the first rectifier control signal is controlled to lead the phase of the first control signal, and the phase of the second rectifier control signal is controlled to lead the phase of the second control signal.

13. The control method for the LLC resonant converter as described in claim 12, further comprising: The duty cycle of the first rectifier control signal and the second rectifier control signal is limited to no more than one resonant period based on the fact that the operating frequency is higher than the phase shift frequency but lower than a resonant frequency.

14. The control method for an LLC resonant converter as described in claim 13, further comprising: The duty cycle is limited to be higher than the resonant period because the operating frequency is lower than the phase shift frequency.

15. The control method for an LLC resonant converter as described in claim 12, further comprising: Receive an output voltage feedback value and an output voltage reference value corresponding to the output voltage, and compare the output voltage feedback value and the output voltage reference value to generate a voltage error value; The voltage error value is used to calculate a frequency control command corresponding to the operating frequency; The first control signal and the second control signal are modulated according to the frequency control command; and The first rectifier control signal corresponding to the first control signal is modulated according to the frequency control command, and the second rectifier control signal corresponding to the second control signal is modulated according to the frequency control command.

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