TWI752891B - Llc resonance converter, control unit, and method of controlling the same - Google Patents

Abstract

An LLC resonance converter includes a switching circuit, a resonant tank, 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 the operating frequency and the phase shift amount. When the operating frequency is low to a specific value or the phase shift amount is high to a specific value, the control unit fixes one of them to extend a hold-up time of the LLC resonant converter.

Description

LLC resonant converter and control method thereof

The present invention relates to an LLC resonant converter and a control method thereof, in particular to an LLC resonant converter with extended maintenance time and a control method thereof.

The LLC resonant converter has the advantages of primary side switch zero voltage turn-on (ZVS turned-on), secondary side synchronous rectification zero current turn-off (ZCS turned-off) and high efficiency. Take the full-bridge LLC converter as shown in FIG. 2A as an example, the current control method is the first switch Q1, the fourth switch Q4 on the primary side and the first synchronous rectification switch on the secondary side SR1 provides the same-phase PWM signal, and the second switch Q2, the third switch Q3 on the primary side, and the second synchronous rectification switch SR2 on the secondary side provide the same-phase PWM control. However, this control method has the following disadvantages when the input voltage is insufficient:

1. High-efficiency application: In order to achieve high efficiency, the gain value of the voltage is generally designed to be relatively low, but it may cause insufficient voltage gain, making the hold-up time lower.

2. High maintenance time application: In order to achieve a high maintenance time, the gain value of the voltage is generally designed to be relatively high, but this will easily lead to lower efficiency and additionally increase the voltage stress of the resonant capacitor in the resonant tank 2 .

Therefore, how to design an LLC resonant converter and a control method thereof so as to maintain the LLC resonant converter 100 at high efficiency without shortening the holding time and without additionally increasing the voltage stress of the resonant capacitor, is the It is a major subject for the author of this case to study.

In order to solve the above problems, the present invention provides an LLC resonant converter to overcome the problems of the prior art. Therefore, the LLC resonant converter of the present 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 resonance 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 resonance 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, provides a second control signal to control the second switch, provides a first rectification control signal to control the first synchronous rectification switch, and provides a second rectification control signal to control the first switch according to the output voltage of the resonant converter. Two synchronous rectification switches, the first control signal and the first rectification control signal include the operating frequency and the phase shift amount, and the second control signal and the second rectification control signal include the operating frequency and the phase shift amount. The control unit controls the operating frequency to be frequency-converted and adjusts the phase shift amount according to the operating frequency lower than the phase shift frequency, and controls the operating frequency to be equal to the frequency threshold and adjusts the phase shift amount when the operating frequency is lower than the frequency threshold.

In order to solve the above problems, the present invention provides an LLC resonant converter to overcome the problems of the prior art. Therefore, the LLC resonant converter of the present invention includes a switching circuit, a resonant tank, a voltage transformer controller, synchronous rectifier unit and control unit. The switching circuit includes a first switch and a second switch, and the resonance 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 resonance 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, provides a second control signal to control the second switch, provides a first rectification control signal to control the first synchronous rectification switch, and provides a second rectification control signal to control the first switch according to the output voltage of the resonant converter. Two synchronous rectification switches, the first control signal and the first rectification control signal include the operating frequency and the phase shift amount, and the second control signal and the second rectification control signal include the operating frequency and the phase shift amount. The control unit controls the operating frequency to frequency conversion and adjusts the phase shift amount when the operating frequency is lower than the phase shift frequency, and controls the phase shift amount to be equal to the phase shift threshold and controls the operating frequency to frequency conversion when the phase shift amount is higher than the phase shift threshold.

In order to solve the above problems, the present invention provides a control method of an LLC resonant converter to overcome the problems of the prior art. Therefore, the resonant converter of the present 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 switch controlled by the first control signal. The first synchronous rectification switch controlled by the rectification control signal and the second synchronous rectification switch controlled by the second rectification control signal. The control method includes: obtaining the operating frequency according to the output voltage feedback. The phase shift amount of the first control signal and the first rectification control signal is adjusted according to the operating frequency, and the phase shift amount of the second control signal and the second rectification control signal is adjusted according to the operating frequency. Determine if the operating frequency is lower than the phase shift frequency. According to the operating frequency being lower than the phase-shifting frequency, the operating frequency is controlled to be variable frequency and the phase-shifting amount is adjusted. and (a1) control the operating frequency to be equal to the frequency threshold and adjust the phase shift amount according to the operating frequency as low as the frequency threshold value; or (a2) control the phase shift amount to be equal to the phase shift threshold value and control the operating frequency according to the phase shift amount up to the phase shift threshold value for frequency conversion.

The main purpose and effect of the present invention is to use the control unit to fix the operating frequency or the phase shift when the operating frequency of the LLC resonant converter is low to a specific value or the phase shift is high to a specific value. On the one hand, the LLC resonant converter can be maintained at high efficiency without shortening the maintenance time, and the voltage stress of the resonant capacitor will not be increased additionally.

In order to further understand the technology, means and effect adopted by the present invention to achieve the predetermined purpose, please refer to the following detailed description and accompanying drawings of the present invention. For specific understanding, however, the accompanying drawings are only provided for reference and description, and are not intended to limit the present invention.

100:LLC Resonant Converter

100-1: Primary side circuit

100-2: Secondary side circuit

1: switch circuit

12: The first switch bridge arm

Q1: The first switch

Q2: Second switch

14: Second switch bridge arm

Q3: The third switch

Q4: Fourth switch

2: Resonant tank

Lr: resonant inductance

Cr: resonant capacitor

3: Transformer

32: Primary side

34: Secondary side

4: Synchronous rectifier unit

42: The first synchronous rectifier bridge arm

SR1: The first synchronous rectifier switch

SR2: Second Synchronous Rectifier Switch

44: Second synchronous rectifier bridge arm

SR3: The third synchronous rectifier switch

SR4: Fourth synchronous rectifier switch

5: Control unit

52: Comparison unit

54: Voltage Controller

56: Frequency Limiter

58: Signal modulation unit

582: Frequency Controller

584: Frequency and Phase Controllers

200: load

Vin: input voltage

Vo: output voltage

Vo_fb: output voltage feedback value

Vo_ref: output voltage reference value

Ver: voltage error value

Sc: control signal

Sc1: The first control signal

Sc2: The second control signal

Sc3: the third control signal

Sc4: Fourth control signal

Ssr1: The first rectifier control signal

Ssr2: The second rectifier control signal

Ssr3: The third rectifier control signal

Ssr4: Fourth rectifier control signal

Cf: frequency control command

Fsw: operating frequency

Fs: Phase shift frequency

Fr: resonance frequency

Ft: frequency threshold

Fmax: the highest frequency

Fmin: minimum frequency

Vs: Phase shift amount

Vt: phase shift threshold

Vmax: maximum phase shift amount

α: specific angle

M1: first mode

M2: Second Mode

M3: third mode

M4, M4': Fourth mode

t1~t2'': time

S100~S340’: Steps

FIG. 1 is the LLC resonant converter with the function of prolonging the holding time of the present invention; FIG. 2A is the first implementation circuit of the LLC resonant converter that can be used with the control method of the present invention; FIG. 2B is the control method of the present invention. The second implementation circuit of the LLC resonant converter; FIG. 2C is the third implementation circuit of the LLC resonant converter to which the control method of the present invention can be used; FIG. 2D is the first circuit of the LLC resonant converter to which the control method of the present invention can be used. Four implementation circuits; FIG. 3 is a block schematic diagram of the control unit of the present invention; 4A is a schematic diagram of the frequency and phase of the LLC resonant converter of the present invention in a first control mode; 4B is a schematic diagram of the frequency and phase of the LLC resonant converter of the present invention in the second control mode; 5A is a schematic diagram of a control signal of the LLC resonant converter of the present invention operating in a first mode; 5B is a schematic diagram of the control signal of the LLC resonant converter of the present invention operating in the second mode; 5C is a schematic diagram of the control signals of the LLC resonant converter of the present invention operating in the third mode and the fourth mode; FIG. 6 is a flowchart of the control method of the LLC resonant converter of the present invention; FIG. 7A is the LLC resonant converter of the present invention. A detailed flow chart of the first control method; and FIG. 7B is a detailed flow chart of the second control method of the LLC resonant converter of the present invention.

The technical content and detailed description of the present invention are described as follows in conjunction with the drawings: Please refer to FIG. 1 for the LLC resonant converter with the function of prolonging the holding time of the present invention. The LLC resonant converter 100 receives the input voltage Vin, and converts the input voltage Vin to the output voltage Vo, so as to provide the output voltage Vo to power the 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 , and 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 , and the resonant circuit 2 is resonated by the switching of the first switch Q1 and the second switch Q2 . Wherein, the resonant tank 2 may include, for example, but not limited to, a resonant circuit composed of capacitors or inductors. The synchronous rectification unit 4 is coupled between the secondary side 34 and the load 200, and includes a first Step rectification switch SR1 and second synchronous rectification switch SR2. When the LLC resonant converter works normally, the first synchronous rectification switch SR1 and the first switch Q1 in the switching circuit 1 have the same turn-on sequence, and the second synchronous rectifier switch SR2 and the second switch Q2 have the same turn-on sequence.

The control unit 5 is coupled to the first switch Q1, the second switch Q2, the first synchronous rectification switch SR1 and the second synchronous rectification switch SR2, and feedback according to the output voltage Vo of the resonant converter 100 (for example, but not limited to, through feedback circuit) to provide the control signal Sc. Specifically, the control signal Sc includes a first control signal Sc1, a second control signal Sc2, a first rectification control signal Ssr1 and a second rectification control signal Ssr2 to control the first switch Q1, the second switch Q2 and the first synchronous rectification switch respectively SR1 and the second synchronous rectification switch SR2.

Please refer to FIGS. 2A to 2D for the first to fourth implementation circuits of the LLC resonant converter to which the control method of the present invention can be used in combination, and refer to FIG. 1 in combination. The primary side circuit 100 - 1 and the secondary side circuit 100 - 2 in FIG. 2B are both shown as full-bridge structures. The primary side circuit 100 - 1 includes the first switch bridge arm 12 and The second switch bridge arm 14 and the resonant tank 2 . The first switch bridge arm 12 receives the input voltage Vin, and includes a first switch Q1 and a second switch Q2 coupled in series. The control unit 5 provides a first control signal Sc1 to control the first switch Q1, and provides a second control signal Sc2 to control the second switch Q2. The second switch bridge arm 14 is connected in parallel with the first switch bridge arm 12 , and includes a third switch Q3 and a fourth switch Q4 coupled in series. The control unit 5 provides a third control signal Sc3 to control the third switch Q3, and provides a fourth control signal Sc4 to control the fourth switch Q4. In the application of the present 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. In addition, the first control signal Sc1 and the second control signal Sc2 are interleaved control signals. Interleaved means that the phases are preferably 180 degrees out of phase, and can be complementary or non-complementary (for example, but not limited to, the switch is turned off for a long time, causing the signals to be non-complementary, or there is a difference between the two signals. dead time, etc.). The resonant tank 2 is coupled between the first switch bridge arm 12 and the second switch bridge arm 14 , and is mainly an LLC resonant tank composed of the resonant inductance Lr, the magnetizing inductance of the transformer 3 (not shown) and the resonant capacitor Cr.

The secondary side circuit 100 - 2 includes a first synchronous rectification bridge arm 42 and a second synchronous rectification bridge arm 44 that constitute the synchronous rectification unit 4 . The first synchronous rectification bridge arm 42 is coupled to the secondary side 34 of the transformer 3 and includes a first synchronous rectification switch SR1 and a second synchronous rectification switch SR2 coupled in series. The second synchronous rectification bridge arm 44 is connected in parallel with the first synchronous rectification bridge arm 42 , and includes a third synchronous rectification switch SR3 and a fourth synchronous rectification switch SR4 coupled in series, specifically, the first synchronous rectification switch SR1 and the second synchronous rectification switch SR1 The common contact of the switch SR2 and the common contact of the third synchronous rectification switch SR3 and the fourth synchronous rectification switch SR4 are respectively coupled to two ends of the secondary side 34 . The control unit 5 provides a first rectification control signal Ssr1 to control the first synchronous rectification switch SR1, provides a second rectification control signal Ssr2 to control the second synchronous rectification switch SR2, provides a third rectification control signal Ssr3 to control the third synchronous rectification switch SR3, and provides a third rectification control signal Ssr3 to control the third synchronous rectification switch SR3. The four rectification control signals Ssr4 control the fourth synchronous rectification 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. In addition, the first rectification control signal Ssr1 and the second rectification control signal Ssr2 are interleaved control signals.

The primary side circuit 100 - 1 of the LLC resonant converter 100 shown in FIGS. 2C to 2D is a half-bridge structure. The secondary side circuit 100 - 2 of the LLC resonant converter 100 shown in FIGS. 2A and 2C is a center-taped structure. It should be noted that the elements, control signals, and control descriptions in the following paragraphs in FIGS. 2A to 2D are represented by the same numbers to represent the same control methods, and will not be repeated here.

Please refer to FIG. 3 for a block diagram of the control unit according to the present invention, and refer to FIGS. 1 to 2D in combination. To facilitate the description of the operation and control principle of the LLC resonant converter 100 , the circuit topology shown in FIG. 2A is used as an example for description. The control unit 5 receives an output voltage signal corresponding to the output voltage Vo of the LLC resonant converter 100, and obtains a frequency control command Cf according to the feedback of the output voltage Vo, so as to control each control signal Sc in the LLC resonant converter 100 according to the frequency control command Cf The operating frequency Fsw. Specifically, the control unit 5 receives the output voltage feedback value Vo_fb and the output voltage reference value Vo_ref of the LLC resonant converter 100 through the comparison unit 52 . The comparison unit 52 obtains the voltage error value Ver by comparing the output voltage reference value Vo_ref with the output voltage feedback value Vo_fb.

The voltage controller 54 of the control unit 5 receives the voltage error value Ver, and operates on the voltage error value Ver to obtain a frequency control command Cf corresponding to the operating frequency Fsw of each control signal Sc in the LLC resonant converter 100 . Take the voltage controller 54 as a proportional-integral controller (PI controller) as an example, but this does not limit the present invention. The voltage controller 54 performs a proportional and integral linear combination operation on the voltage error value Ver to obtain a control amount, that is, a frequency control command Cf. Furthermore, in order to ensure that the frequency control command Cf will not be higher than the maximum value of the control command amount (that is, corresponding to the highest frequency Fmax in Figs. 4A-4B) or lower than the minimum value of the control command amount (that is, corresponding to the lowest frequency Fmin in Figs. Therefore, the upper limit value and the lower limit value of the frequency control command Cf are limited by the frequency limiter 56 to limit the maximum frequency Fmax and the minimum frequency Fmin of the operating frequency Fsw.

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 is used for adjusting the operating frequency 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 is used to adjust the operating frequency Fsw and the phase shift amount Vs of the first rectification control signal Ssr1 and the second rectification control signal Ssr2 . The waveforms produced by the frequency controller 582 and the frequency and phase controller 584 are compared by comparators and logic After the circuit is controlled, the generated PWM signals 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 can also adjust the duty ratio of the first control signal Sc1 , the second control signal Sc2 , the first rectification control signal Ssr1 and the second rectification control signal Ssr2 , for example, but not limited to, the frequency controller 582 and the frequency and phase controller 584 .

Please refer to FIGS. 4A to 4B for schematic diagrams of the frequency and phase of the LLC resonant converter of the present invention in the first control mode and the second control mode, respectively, and refer to FIGS. 1 to 3 in combination. In FIG. 4A, when the operating frequency Fsw (related to the frequency control command Cf) is higher than the phase shift frequency Fs set by the control unit 5 and higher than the resonance frequency Fr of the LLC resonant converter 10, the LLC resonant converter 10 operates at the first A 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 variable, and the phase shift Vs is 0 degrees. The frequency conversion refers to that the operating frequency Fsw is adjusted 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 amount Vs refers to the phase difference that the rectification control signals Ssr1 and Ssr2 are turned on earlier than the control signals Sc1 and Sc2, and the variation range can be between 0 degrees and 180 degrees. The signal is turned on at the same time. 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, the operating frequency Fsw and the phase shift amount Vs are the same as the first control signal Sc1 and the first rectification control signal Ssr1. The first rectification control signal Ssr1. Wherein, the lower the input voltage Vin is, the operating mode of the LLC resonant converter 10 will gradually move from the first mode M1 to the fourth mode M4. That is, the lower the operating frequency Fsw will be, and the phase shift amount Vs will be gradually increased from 0 degrees at an appropriate time.

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 first control signal The operating frequency Fsw of Sc1 and the first rectification control signal Ssr1 is frequency conversion, and the phase shift Vs is 0 degrees (the same is true for 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 not to exceed the resonance period, so as to prevent the energy of the secondary side circuit 100 - 2 from being recharged to the primary side circuit 100 during the switching operation. -1.

The LLC resonant converter 10 operates in the third mode M3 when the operating frequency Fsw is lower than the phase shift frequency Fs and higher than the frequency threshold Ft 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 adjusts the phase shift amount Vs according to the change of the input voltage Vin (the second control signal Sc and the second The same is true for the rectification control signal Ssr2). Therefore, as the operating frequency Fsw becomes lower and lower, the phase shift amount Vs will gradually increase from 0 degrees. Wherein, the phase shift amount Vs may 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 ( The same is true for the second control signal Sc and the second rectification control signal Ssr2).

The LLC resonant converter 10 operates in the fourth mode M4 when the operating frequency Fsw continues to decrease to be equal to the frequency threshold Ft 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 equal to the frequency threshold Ft, and still adjusts the phase shift amount Vs according to the change of the input voltage Vin (the second control signal Sc The same is true for the second rectification control signal Ssr2). Therefore, although the voltage error value Ver calculated inside the control unit 5 may increase continuously, the operating frequency Fsw can be limited by setting the corresponding frequency threshold value Ft in the voltage controller 54 or the signal modulation unit 58 . The phase shift amount Vs is gradually increased according to the decrease of the input voltage Vin until the maximum phase shift amount Vmax before the LLC resonant converter 100 fails. The maximum phase shift amount Vmax may also be set separately by the control unit 5 .

In FIG. 4B , the curves of the LLC resonant converter 10 operating in the first mode M1 to the third mode M3 are the same as those in FIG. 4A , and details are not repeated here. Until the phase shift amount Vs gradually increases from 0 degrees in the third mode M3 to the phase shift threshold Vt preset by 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 variable, and controls the phase shift amount Vs to be fixed and equal to the phase shift threshold Vt (the second control signal Sc and the second The same is true for the rectification control signal Ssr2). The frequency threshold Ft' corresponding to the phase shift threshold Vt point is determined according to the control unit 5, but it is only the operating frequency Fsw of the current point.

Therefore, although the voltage error value Ver calculated inside the control unit 5 may be continuously increased and the operating frequency Fsw may be continuously decreased, the phase shift threshold Vt can be set by the frequency and phase controller 584 to limit the phase shift. Shift Vs. The operating frequency Fsw is gradually lowered according to the decrease of the input voltage Vin until the minimum frequency Fmin before the LLC resonant converter 100 fails. The minimum frequency Fmin can also be set separately by the control unit 5 .

Please refer to FIGS. 5A to 5C, which are schematic diagrams of the control signals of the LLC resonant converter of the present invention operating in the first mode to the fourth mode, respectively, and refer to FIGS. 1 to 4B in combination. In the first mode M1 in FIG. 5A , the first control signal Sc1 and the first rectification control signal Ssr1 provided by the control unit 5 are frequency-converted signals with the same phase. Meanwhile, the second control signal Sc2 and the second rectification control signal Ssr2 are frequency-converted signals with the same phase. Therefore, the phase shift amount Vs between the first control signal Sc1 and the rising edge of the conduction signal of the first rectification control signal Ssr1 is 0 degrees, and the phase shift between the second control signal Sc2 and the rising edge of the conduction signal of the second rectification control signal Ssr2 The shift amount Vs is also 0 degrees.

In the second mode M2 in FIG. 5B , the first control signal Sc1 and the first rectification control signal Ssr1 provided by the control unit 5 are frequency-converted signals with the same phase. At the same time, the second control signal Sc2 and the The second rectification control signal Ssr2 is a frequency conversion signal with the same phase. That is, the phase shift amount Vs of the rising edge of the conduction signal between the first control signal Sc1 and the first rectification control signal Ssr1 is 0 degrees, and the difference between the rising edge of the conduction signal of the second control signal Sc2 and the second rectification control signal Ssr2 is 0 degrees. The phase shift amount Vs is also 0 degrees. In this mode, the control unit 5 limits the duty cycle (duty cycle) of the first rectification control signal Ssr1 and the second rectification control signal Ssr2 to not exceed the resonance period. The resonant period is the reciprocal of the resonant frequency Fr, which is 1/Fr.

In the third mode M3 and the fourth mode M4 in FIG. 5C , the control unit 16 adjusts the phase shift amount Vs of the first control signal Sc1 and the first rectification control signal Ssr1 according to the change of the input voltage Vin. At the same time, the phase shift amount Vs of the second control signal Sc2 and the second rectification control signal Ssr2 is adjusted. That is, the phase shift amount Vs of the rising edge of the turn-on signal of the first control signal Sc1 and the first rectification control signal Ssr1 increases as the frequency decreases. For example, the phase shift amount Vs in FIG. 5C is a certain The angle α (corresponding to the magnitude of the phase shift amount Vs) is represented, and α is an arbitrary number from 0 to 180 and greater than 0. It is worth mentioning that the control unit 5 controls the phase of the first rectification control signal Ssr1 to lead the phase of the first control signal Sc1. The specific control method is to control the turn-on period of the first synchronous rectification switch SR1 to increase, so that the phase of the rising edge of the turn-on signal of the first rectification control signal Ssr1 is advanced (from the original time 0 to the time t1'', that is, the advance specific angle α). The control methods of the second control signal Sc2 and the second rectification control signal Ssr2 are also the same, which will not be repeated here.

Therefore, when the operating frequency Fsw is lower than the phase shift frequency Fs, the control unit 5 restricts the duty cycle to be higher than the resonant period, so that the phase can be advanced. With this control method, when the output voltage Vo of the LLC resonant converter 10 starts to drop due to insufficient input voltage Vin, the output voltage Vo of the LLC resonant converter 10 can still be maintained above a specific voltage for a period of time, so that the back-end coupled The electronic product (the load 200 ) has enough time to respond and perform complete storage or backup of the data before the power failure.

Please refer to FIG. 6 for a flowchart of the control method of the LLC resonant converter of the present invention, and refer to FIGS. 1 to 5C in combination. The circuit structure of the LLC resonant converter 100 is shown in FIGS. 2A to 2D , and the control method includes: obtaining the operating frequency according to the output voltage feedback ( S100 ). In a preferred embodiment, the control unit 5 determines the operating frequency Fsw of the first switch Q1 , the second switch Q2 , the first synchronous rectification switch SR1 and the second synchronous rectification switch SR2 by receiving the feedback of the output voltage. Then, the phase shift amount of the first control signal and the first rectification control signal is adjusted according to the operating frequency, and the phase shift amount of the second control signal and the second rectification control signal is adjusted according to the operating frequency ( S120 ). In a preferred embodiment, the control unit 5 adjusts the phase shift amount Vs of the first control signal Sc1 and the first rectification control signal Ssr1 according to the change of the operating frequency Fsw, and the difference between the second control signal Sc2 and the second rectification control signal Ssr2 is The same is true for the phase shift amount Vs.

Then, it is determined whether the operation frequency is lower than the phase shift frequency, so as to control the operation frequency to be frequency conversion and adjust the phase shift amount according to the operation frequency 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, and the phase shift amount Vs is 0 degrees (the second control signal Sc and the The same is true for 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 of the input voltage Vin (th The same is true for the two control signals Sc and the second rectification control signal Ssr2).

Wherein, 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 rectification control signal Ssr1 and the second rectification control signal Ssr2 not to exceed the resonant period to avoid the switching action , the energy of the secondary side circuit 100-2 is fed back to the primary side circuit 100-1. 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 the phase can lead to the phenomenon.

Finally, control the operating frequency to be equal to the frequency threshold and adjust the phase shift amount according to the operating frequency being lower than a frequency threshold (S160), or control the phase shift amount to be equal to the phase shift amount according to the phase shift amount being higher than a phase shift threshold Phase shift the threshold and control the operating frequency to be frequency conversion (S180).

In the fixed operating frequency Fsw of step ( S160 ), a preferred embodiment is 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 is still based on the input voltage Vin to adjust the phase shift amount Vs (the same is true for the second control signal Sc and the second rectification control signal Ssr2). The control unit 5 controls the turn-on period of the first synchronous rectification switch SR1 to increase, so that the rising edge of the turn-on signal of the first rectification control signal Ssr1 is advanced in phase, and also controls the turn-on period of the second synchronous rectifier switch SR2 to increase. large, so as to achieve the phase advance of the rising edge of the turn-on signal of the second rectification control signal Ssr2. In the fixed phase shift amount Vs in step ( S180 ), a preferred embodiment is 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 variable frequency, and the control phase shift amount Vs is equal to Phase shift threshold Vt (the same is true for the second control signal Sc and the second rectification control signal Ssr2).

Please refer to FIGS. 7A to 7B for the detailed flow charts of the first control method and the second control method of the LLC resonant converter of the present invention, respectively, and refer to FIGS. 1 to 6 in combination. As shown in FIG. 7A , the control method of the LLC resonant converter 100 at a fixed operating frequency Fsw includes: first, receiving an output voltage feedback value corresponding to the output voltage and an output voltage reference value, and comparing the output voltage feedback value and the output voltage reference value value to generate a voltage error value (S200). Then, the voltage error value is operated to obtain a frequency control command corresponding to the operating frequency (S220). The control unit 5 can modulate the interleaved first control signal Sc1 and the second control signal Sc2 according to the frequency control command Cf, and modulate the first rectification control signal Ssr1 corresponding to the first control signal Sc1 according to the frequency control command Cf, and According to the frequency control command Cf modulation corresponding The second rectification control signal Ssr2 in the second control signal Sc2. Among them, the operating frequency Fsw is generated by the frequency control command Cf, so the control method can be judged accordingly.

Then, it is judged whether the operation frequency is higher than the phase shift frequency (S240). If (that is, 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 conversion, and the operating frequencies of the first rectification control signal and the second rectification control signal are controlled to be frequency conversion ( S300). If no (ie 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 (that is, 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 variable frequency, and the operating frequencies of the first rectification control signal and the second rectification control signal are controlled to be variable frequency and adjusted. Phase shift amount (S320). If no (that is, 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 controlled to be fixed at the frequency threshold, and the operating frequencies of the first rectification control signal and the second rectification control signal are controlled to be fixed. At the frequency threshold and adjust the phase shift amount (S340).

As shown in FIG. 7B , in the control method for the fixed phase shift Vs of the LLC resonant converter 100 , the steps ( S200 ) to ( S240 ) and ( S300 ) to ( S320 ) are the same as those of FIG. 7A , and the difference lies in the step ( S240 ). If it is determined that it is not (that is, the operating frequency Fsw is lower than the phase shift frequency Fs), it is determined whether the phase shift amount is higher than the phase shift threshold (S260'). Otherwise, go to step (S320). If (that is, the phase shift amount Vs is equal to the phase shift threshold Vt), the operating frequencies of the first control signal and the second control signal are controlled to be variable frequency, and the operating frequencies of the first rectification control signal and the second rectification control signal are controlled to be variable frequency and The fixed phase shift amount is the phase shift threshold (S340').

Therefore, using the control methods of FIGS. 7A and 7B , the LLC resonant converter 100 can still maintain a voltage above a certain voltage for a period of time when the input voltage Vin is insufficient, so that the electronic products ( The load 200) has enough time to respond and perform complete storage or backup of the data before the power failure.

However, the above descriptions are only the detailed descriptions and drawings of the preferred embodiments of the present invention, but the features of the present invention are not limited thereto, and are not intended to limit the present invention. The scope of the patent shall prevail, and all embodiments that are consistent with the spirit of the scope of the patent application of the present invention and similar variations thereof shall be included in the scope of the present invention. Anyone who is familiar with the art in the field of the present invention can easily think Changes or modifications can be covered by the following patent scope of the present case.

S100~S180: Steps

Claims (17)

An LLC resonant converter, comprising: a switching circuit, including a first switch and a second switch; a resonant tank, coupled to the switching circuit; a transformer, including a primary side and a secondary side, the primary side is coupled the resonant tank; a synchronous rectification unit, coupled to the secondary side, including a first synchronous rectification switch and a second synchronous rectification switch; and a control unit, respectively providing a first synchronous rectification switch according to an output voltage of the resonant converter A control signal controls the first switch, a second control signal controls the second switch, a first rectification control signal controls the first synchronous rectification switch, and a second rectification control signal controls the second synchronous rectification switch; the first rectification control signal controls the second synchronous rectification switch; The 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; wherein the control unit is based on the operation When the frequency is lower than a phase shift frequency, the operating frequency is controlled to be frequency-converted and the phase shift amount is adjusted, and the operating frequency is controlled to be equal to the frequency threshold and the phase shift amount is adjusted according to the operating frequency being lower than a frequency threshold. The LLC resonant converter of claim 1, wherein the control unit limits a proportion of the first rectification control signal and the second rectification control signal according to the operating frequency higher than the phase shift frequency but lower than a resonance frequency The empty ratio does not exceed one resonance period. The LLC resonant converter of claim 2, wherein the control unit limits the duty cycle above the resonant period according to the operating frequency being lower than the phase shift frequency. The LLC resonant converter of claim 1, wherein the control unit controls the phase of the first rectification control signal to lead the phase of the first control signal according to the operating frequency falling below the frequency threshold, and controls the first rectification control signal to lead the phase of the first control signal. The phase of the second rectified control signal leads the phase of the second control signal. The LLC resonant converter of claim 1, wherein the control unit comprises: a comparison unit, receiving an output voltage feedback value corresponding to the output voltage and an output voltage reference value, and comparing the output voltage feedback value with the output voltage feedback value The output voltage reference value generates a voltage error value; a voltage controller receives the voltage error value, performs operation on the voltage error value to obtain a frequency control command corresponding to the operating frequency; and a signal modulation unit controls the frequency according to the frequency command to modulate the interleaved first control signal and the second control signal, modulate the first rectification control signal corresponding to the first control signal according to the frequency control command, and modulate the first rectification control signal corresponding to the first control signal according to the frequency control command The second rectification control signal of the two control signals. 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 structure. The LLC resonant converter of claim 1, wherein the switching circuit comprises a first switch bridge arm composed of the first switch and the second switch, and a third switch and a fourth switch The second switch bridge arm forms a full bridge circuit structure. The LLC resonant converter of claim 1, wherein the transformer is a center-tapped structure, and the first synchronous rectification switch and the second synchronous rectification switch are respectively coupled to two ends of the transformer. The LLC resonant converter of claim 1, wherein the transformer is coupled to a first synchronous rectification bridge arm composed of the first synchronous rectification switch and the second synchronous rectification switch, and a A second synchronous rectification bridge arm composed of the third synchronous rectification switch and a fourth synchronous rectification switch forms a full-bridge rectification circuit structure. An LLC resonant converter, comprising: a switching circuit, including a first switch and a second switch; a resonant tank, coupled to the switching circuit; a transformer, including a primary side and a secondary side, the primary side is coupled the resonant tank; a synchronous rectification unit, coupled to the secondary side, including a first synchronous rectification switch and a second synchronous rectification switch; and a control unit, respectively providing a first synchronous rectification switch according to an output voltage of the resonant converter A control signal controls the first switch, a second control signal controls the second switch, a first rectification control signal controls the first synchronous rectification switch, and a second rectification control signal controls the second synchronous rectification switch. The 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; wherein the control unit is based on the operation When the frequency is lower than a phase shift frequency, the operating frequency is controlled to be variable frequency and the phase shift amount is adjusted, and according to the phase shift amount being higher than a phase shift threshold value, the phase shift amount is controlled to be equal to the phase shift threshold value and the operating frequency is controlled to be frequency conversion. The LLC resonant converter of claim 10, wherein the control unit limits a proportion of the first rectification control signal and the second rectification control signal according to the operating frequency higher than the phase shift frequency but lower than a resonance frequency The empty ratio does not exceed one resonance period. The LLC resonant converter of claim 11, wherein the control unit limits the duty cycle above the resonant period according to the operating frequency being lower than the phase shift frequency. A control method of an LLC resonant converter, wherein the resonant converter comprises a switching circuit, a transformer and a synchronous rectification unit, the switching circuit comprises a first switch controlled by a first control signal and a second control signal A second switch controlled by 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: obtaining the operating frequency according to an output voltage feedback; adjusting the first control according to the operating frequency a phase shift amount between the signal and the first rectification control signal and the phase shift amount between the second control signal and the second rectification control signal; determine whether the operating frequency is lower than a phase shift frequency; and (a1) control the operating frequency to be equal to the frequency threshold and adjust the phase shift amount according to the operating frequency falling below a frequency threshold; or (a2) ) controls the phase shift amount to be equal to the phase shift threshold value and controls the operating frequency to be frequency conversion according to the phase shift amount as high as a phase shift threshold value. The control method for an LLC resonant converter as claimed in claim 13, further comprising: limiting the difference between the first rectification control signal and the second rectification control signal according to the operating frequency higher than the phase shift frequency but lower than a resonance frequency A duty cycle does not exceed a resonant period. The control method for an LLC resonant converter as claimed in claim 14, further comprising: limiting the duty cycle to be higher than the resonant period according to the operating frequency being lower than the phase shift frequency. The control method for an LLC resonant converter as claimed in claim 13, wherein step (a1) comprises: controlling the phase of the first rectification control signal to lead the phase of the first control signal according to the operating frequency being as low as the frequency threshold , and the phase of the second rectification control signal is controlled to lead the phase of the second control signal. The control method for an LLC resonant converter as claimed in claim 13, further comprising: 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 generate a voltage error value; perform operation on the voltage error value to obtain a frequency control command corresponding to the operating frequency; modulate the interleaved first control signal and the second control signal according to the frequency control command; and The frequency control command modulates the first rectification control signal corresponding to the first control signal, and modulates the second rectification control signal corresponding to the second control signal according to the frequency control command.

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