TWI747535B - Llc resonance converter, control unit, and method of controlling the same - Google Patents

Abstract

An LLC resonance converter includes a square wave generator having a first switch and a second switch, a resonant tank, a transformer, a synchronous rectifying (SR) unit having a first SR switch and a second SR switch, and a control unit. The control unit provides a first control signal controls the first switch, a second control signal controls the second switch, a first rectifying control signal controls the first SR switch, a second rectifying control signal controls the second SR switch. When a frequency control command is less than a phase-shift frequency, the first control signal and the first rectifying control signal are frequency-variable and phase-shifted, and the second control signal and the second rectifying control signal are frequency-variable and phase-shifted.

Description

LLC resonant converter, control unit and control method thereof

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

LLC resonant converter (LLC resonant converter) is a DC-to-DC (DC) power converter. Compared with other DC converters, it has more advantages, but because its design and control methods are more complicated, it has received less attention in the past. And research. However, due to the advancement of circuit design and control technology in recent years, many control technologies related to LLC resonant converters have been developed, making the design of LLC resonant converters easier and making this technology gain more pay attention to. LLC resonant converter has the advantages of ZVS turned-on on the primary side, ZCS turned-off on the secondary side synchronous rectification (ZCS turned-off), and high efficiency.

Take a full-bridge LLC resonant converter as an example. Its primary side includes a first bridge arm composed of a first switch Q1 and a second switch Q2, and a third switch Q3 and a fourth switch Q4 composed of the first leg. Two bridge arms, where the first bridge arm and the second bridge arm are connected in parallel; the secondary side includes a synchronous rectification switch bridge arm composed of a first synchronous rectification switch SR1 and a second synchronous rectification switch SR2. The current control method provides PWM signals of the same phase for the first switch Q1 on the primary side, the fourth switch Q4, and the first synchronous rectifier switch SR1 on the secondary side, while the second switch Q2, the third switch Q3 and the secondary side The second synchronous rectifier switch SR2 on the stage side provides 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 and make the hold-up time lower.

2. High maintenance time application: In order to achieve a higher maintenance time, the voltage gain value is generally designed to be higher, but in this way, it is easy to cause the efficiency to become low.

In the prior art, in order to improve the above problems, the secondary-side synchronous rectification is used as a phase shift operation to obtain a higher voltage gain value to achieve a method of increasing the maintenance time. This method is to allow the first switch Q1 to the fourth switch Q4, the first synchronous rectifier switch SR1 and the second synchronous rectifier switch SR2 to operate at a required minimum fixed frequency, the first synchronous rectifier switch SR1 and the second synchronous rectifier switch SR2 starts to perform phase shifting to achieve a technology that increases the voltage gain value so that the maintenance time can be increased when the input voltage is insufficient. However, the disadvantage of this technology is that when operating at a lower switching frequency, the first synchronous rectifier switch SR1 and the second synchronous rectifier switch SR2 only begin to phase shift, and the voltage gain value changes greatly in the control, which will cause the output voltage to be difficult. controlled.

For this reason, how to design an LLC resonant converter, a control unit and a control method thereof to solve the problems existing in the prior art is an important subject studied by the inventor of this case.

The purpose of the present invention is to provide an LLC resonant converter to solve the problems existing in the prior art.

In order to achieve the aforementioned purpose, the LLC resonant converter proposed in the present invention includes a square wave generator, a resonant tank, a transformer, a synchronous rectification unit, and a control unit. The square wave generator has a first switch and a second switch connected in series with the first switch. The resonant tank is coupled to the square wave generator. The transformer has a primary side and a secondary side, The primary side is coupled to the resonance tank. The synchronous rectifier unit is coupled to the secondary side and has a first synchronous rectifier switch and a second synchronous rectifier switch. The control unit receives the output voltage of the resonant converter, obtains a frequency control command according to the output voltage, provides a first control signal to control the first switch, provides a second control signal to control the second switch, and provides a first rectification control signal to control the first synchronous rectification switch And providing a second rectification control signal to control the second synchronous rectification switch. When the frequency control command is higher than the phase shift frequency, the first control signal and the first rectification control signal are frequency conversion signals with the same phase, and the second control signal and the second rectification control signal are frequency conversion signals with the same phase. When the frequency control command is lower than the phase shift frequency, the first control signal and the first rectification control signal are frequency conversion signals with different phases, and the second control signal and the second rectification control signal are frequency conversion signals with different phases.

With the proposed LLC resonant converter, it is possible to achieve both high voltage gain value and improved (extended) maintenance time.

Another object of the present invention is to provide a control unit of LLC resonant converter to solve the problems existing in the prior art.

In order to achieve the foregoing purpose, the control unit of the LLC resonant converter proposed in the present invention provides a control signal to control the square wave generator on the primary side of the resonant converter, and provides a rectification control signal to control the synchronous rectification unit on the secondary side, and the control unit is based on The output voltage of the resonant converter gets the frequency control command. When the frequency control command is higher than the phase shift frequency, the control signal and the rectification control signal are frequency conversion signals with the same phase; when the frequency control command is lower than the phase shift frequency, the control signal and the rectification control signal are frequency conversion signals with different phases.

With the proposed control unit of the LLC resonant converter, it is possible to achieve both the high voltage gain value and the effect of improving (extending) the maintenance time.

Another object of the present invention is to provide a control method of LLC resonant converter to solve the problems existing in the prior art.

In order to achieve the foregoing purpose, the present invention provides a control method for an LLC resonant converter, wherein the LLC resonant converter includes a switching bridge arm arranged on the primary side of the transformer and a synchronous rectification unit arranged on the secondary side of the transformer, and the switch The bridge arm includes a first switch controlled by a first control signal and a second switch controlled by a second control signal. The synchronous rectification unit includes a first synchronous rectifier switch controlled by a first rectification control signal and a second rectifier control signal. The second synchronous rectification switch; the control method includes: obtaining the operating frequency according to the output voltage feedback value; judging whether the operating frequency is higher than the phase shift frequency; if the operating frequency is higher than the phase shift frequency, controlling the first control signal and the first rectification control The signal is a variable frequency signal with the same phase, and the second control signal and the second rectification control signal are controlled to be variable frequency signals with the same phase; and if the operating frequency is lower than the phase shift frequency, the first control signal and the first rectification control signal are controlled to be in phase The frequency conversion signals of different phases are controlled, and the second control signal and the second rectification control signal are controlled to be frequency conversion signals of different phases.

With the proposed control method of LLC resonant converter, it is possible to achieve both the high voltage gain value and the effect of improving (extending) the maintenance time.

In order to further understand the technology, means and effects of the present invention to achieve the intended purpose, please refer to the following detailed description and drawings of the present invention. I believe that the purpose, features and characteristics of the present invention can be obtained from this in depth and For specific understanding, however, the accompanying drawings are only provided for reference and illustration, and are not intended to limit the present invention.

10: LLC resonant converter

T: Transformer

12: Primary side circuit

14: Secondary side circuit

16: Controller

122: first switch bridge arm

124: second switch bridge arm

126: Resonance tank

142: The first synchronous rectifier bridge arm

144: Second synchronous rectifier bridge arm

Q1: The first switch

Q2: The second switch

Q3: The third switch

Q4: The fourth switch

SR1: The first synchronous rectifier switch

SR2: The second synchronous rectifier switch

SR3: The third synchronous rectifier switch

SR4: The fourth synchronous rectifier switch

Lr: Resonant inductance

Cr: Resonant capacitor

S _Q1 : the first control signal

S _Q2 : second control signal

S _Q3 : the third control signal

S _Q4 : Fourth control signal

S _SR1 : the first rectification control signal

S _SR2 : The second rectification control signal

S _SR3 : The third rectification control signal

S _SR4 : Fourth rectification control signal

161: comparison unit

162: Voltage Controller

163: frequency limiter

164: Frequency Controller

165: Frequency and Phase Controller

V _{OUT_FB} : Output voltage feedback value

V _{OUT_REF} : output voltage reference value

V _ERR : voltage error value

f _CMD : Frequency control command

α: Phase difference

f _R : resonance frequency

f _PS : Phase shift frequency

S11~S15: steps

Figure 1: is a circuit diagram of the first embodiment of the LLC resonant converter of the present invention.

Figure 2: is a circuit diagram of the second embodiment of the LLC resonant converter of the present invention.

Figure 3: is a circuit diagram of the third embodiment of the LLC resonant converter of the present invention.

Figure 4: is a circuit diagram of the fourth embodiment of the LLC resonant converter of the present invention.

Figure 5: is a block diagram of the control circuit of the present invention.

Fig. 6 is a schematic diagram of the frequency and phase of the LLC resonant converter of the present invention operating in different modes.

7A to 7C are schematic diagrams of control signals of the LLC resonant converter of the present invention operating in different modes.

Fig. 8 is a flow chart of the 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.

The LLC resonant converter in this case includes a square wave generator, a resonant tank, a transformer, a synchronous rectification unit and a control unit. Wherein, the LLC resonant converter has a converter with a hold-up time extension function. The square wave generator is coupled to the resonance tank and the primary side of the transformer, and has a first switch and a second switch connected in series with the first switch. The synchronous rectifier unit is coupled to the secondary side of the transformer, and has a first synchronous rectifier switch and a second synchronous rectifier switch.

The control unit receives the output voltage signal output by the LLC resonant converter, where the output voltage signal can provide information about the output voltage of the LLC resonant converter. The control unit obtains the frequency control command according to the output voltage signal, 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 Control the second synchronous rectification switch. It is worth mentioning that the frequency control commands are the operating frequencies of the first control signal, the second control signal, the first rectification control signal, and the second rectification control signal.

In the following, the differences between different circuit topologies will be explained. Please refer to FIGS. 1 to 4, which are circuit diagrams of the first embodiment to the fourth embodiment of the LLC resonant converter of the present invention, respectively. The LLC resonant converter 10 includes a transformer T, a primary side circuit 12, a secondary side circuit 14 and a control unit 16.

The primary side circuit 12 shown in FIG. 1 and FIG. 2 is a full-bridge architecture. The primary side circuit 12 includes a first switching bridge arm 122, a second switching bridge arm 124, and a resonant tank 126 forming a square wave generator.

The first switch bridge arm 122 is coupled to the primary side of the transformer T, and has a first switch Q1 and a second switch Q2 connected in series with the first switch Q1. The control unit 16 provides the first control signal S _{Q1 to} control the first switch Q1, and provides the second control signal S _{Q2 to} control the second switch Q2. The second switch bridge arm 124 is connected in parallel with the first switch bridge arm 122, and has a third switch Q3 and a fourth switch Q4 connected in series with the third switch Q3. The control unit 16 provides the third control signal S _{Q3 to} control the third switch Q3, and provides the fourth control signal S _{Q4 to} control the fourth switch Q4. In the application of the present invention, the first control signal S _Q1 and the fourth control signal S _Q4 are the same control signal; the second control signal S _Q2 and the third control signal S _Q3 are the same control signal (see Figure 7A Show). In addition, the first control signal S _Q1 and the second control signal S _Q2 are complementary control signals.

The resonant tank 126 is coupled between the first switch bridge arm 122 and the second switch bridge arm 124, and is an LLC resonant tank mainly composed of a resonant inductor Lr, a magnetizing inductance of the transformer T (not shown), and a resonant capacitor Cr.

The primary side circuit 12 shown in FIGS. 3 and 4 is a half-bridge structure. The primary side circuit 12 includes a first switching bridge arm 122 and a resonant tank 126. The first switch bridge arm 122 is coupled to the primary side of the transformer T, and has a first switch Q1 and a second switch Q2 connected in series with the first switch Q1. The control unit 16 provides the first control signal S _{Q1 to} control the first switch Q1, and provides the second control signal S _{Q2 to} control the second switch Q2. In the application of the present invention, the first control signal S _Q1 and the second control signal S _Q2 are complementary control signals.

The resonant tank 126 is coupled to the first switch Q1 and the second switch Q2 of the first switch arm 122, and is mainly composed of a resonant inductor Lr, a magnetizing inductance of the transformer T (not shown), and a resonant capacitor Cr LLC resonance tank. The resonant tank in the present invention is not limited to the connection method shown in the figure, and the structure that can generate two resonant frequencies by using LC should be included in the scope of the present invention.

The secondary side circuit 14 shown in FIG. 1 and FIG. 3 is a center-taped structure. The secondary side circuit 14 includes a first synchronous rectification bridge arm 142 coupled to the secondary side of the transformer T, and has a first synchronous rectification switch SR1 and a second synchronous rectification switch SR2 connected in series with the first synchronous rectification switch SR1. The output side of the LLC resonant converter 10 is formed through the common contact point of the center tap of the transformer T and the first synchronous rectification switch SR1 and the second synchronous rectification switch SR2. The control unit 16 provides the first rectification control signal S _{SR1 to} control the first synchronous rectification switch SR1, and provides the second rectification control signal S _{SR2 to} control the second synchronous rectification switch SR2. In the application of the present invention, the first rectification control signal S _SR1 and the second rectification control signal S _SR2 are complementary control signals (see FIG. 7A ).

The secondary side circuit 14 shown in FIGS. 2 and 4 has a full-bridge architecture. The secondary side circuit 14 includes a first synchronous rectification bridge arm 142 and a second synchronous rectification bridge arm 144. The first synchronous rectification bridge arm 142 is coupled to the secondary side of the transformer T, and has a first synchronous rectification switch SR1 and a second synchronous rectification switch SR2 connected in series with the first synchronous rectification switch SR1. The second synchronous rectification bridge arm 144 is connected in parallel with the first synchronous rectification bridge arm 142, and has a third synchronous rectification switch SR3 and a fourth synchronous rectification switch SR4 connected in series with the third synchronous rectification switch SR3. The control unit 16 provides the first rectification control signal S _{SR1 to} control the first synchronous rectification switch SR1, provides the second rectification control signal S _{SR2 to} control the second synchronous rectification switch SR2, and provides the third rectification control signal S _{SR3 to} control the third synchronous rectification. The switch SR3 provides a fourth rectification control signal S _{SR4 to} control the fourth synchronous rectification switch SR4. The first rectification control signal S _SR1 and the fourth rectification control signal S _SR4 are the same control signal; the second rectification control signal S _SR2 and the third rectification control signal S _SR3 are the same control signal. In addition, the first rectification control signal S _SR1 and the second rectification control signal S _SR2 are complementary control signals.

Hereinafter, in order to facilitate the description of the operation and control principle of the LLC resonant converter, the circuit topology shown in FIG. 1 is taken as an example for description. Please refer to FIG. 5 and FIG. 6, which are respectively the controller of the present invention The block diagram of the control circuit and the frequency and phase diagram of the LLC resonant converter of the present invention operating in different modes.

The control unit 16 receives the output voltage signal output by the LLC resonant converter 10, and obtains the frequency control command f _CMD according to the output voltage signal. Specifically, the control unit 16 receives the output voltage feedback value V _{OUT_FB} and the output voltage reference value V _{OUT_REF of the} LLC resonant converter 10 through the comparison unit 161. _{Wherein, the comparison unit 161 subtracts} and compares the output voltage reference value V OUT_REF and the output voltage feedback value V _{OUT_FB} to obtain the voltage error value V _ERR .

The voltage controller 162 of the control unit 16 receives the voltage error value V _ERR and calculates the voltage error value V _ERR to obtain the frequency control command f _CMD . Taking the voltage controller 162 as a proportional-integral controller (PI controller) as an example, the present invention is not limited by this. The voltage controller 162 performs a proportional and integral linear combination operation on the voltage error value V _ERR to obtain the control quantity, that is, the frequency control command f _CMD . Furthermore, in order to ensure that the frequency control command f _{CMD is} not higher than the maximum value of the control command amount f _MAX or lower than the minimum value of the control command amount f _MIN , therefore, the upper limit of the frequency control command f _{CMD is limited by the frequency limiter 163} Value and lower limit.

Please refer to FIG. 7A to FIG. 7C, which are schematic diagrams of the control signals of the LLC resonant converter of the present invention operating in different modes. Refer to FIG. 6 for cooperation. When the frequency control command f _{CMD is} higher than the phase shift frequency f _PS set by the control unit 16 and higher than the resonant frequency f _R of the LLC resonant converter 10, the LLC resonant converter 10 operates in the first mode M1 (see FIG. 7A for cooperation) In this mode, the first control signal S _Q1 (the same signal as the fourth control signal S _Q4 ) provided by the control unit 16 and the first rectification control signal S _SR1 are variable frequency signals with the same phase, and at the same time, the second control signal S _Q2 (the same signal as the third control signal S _Q3 ) and the second rectification control signal (S _SR2 ) are variable frequency signals with the same phase. Therefore, the phase difference α between the rising edge of the turn-on signal of the first control signal S _Q1 and the first rectification control signal S _SR1 is 0 degrees, and the rising edge of the turn-on signal of the second control signal S _Q2 and the second rectification control signal S _SR2 The phase difference α is also 0 degrees. In this mode, the first switch Q1 on the primary side, the second switch Q2, the third switch Q3, and the fourth switch Q4, and the first synchronous rectifier switch SR1 and the second synchronous rectifier switch SR2 on the secondary side all work in variable frequency mode. . The frequency conversion control in this mode is implemented through the frequency controller 164 shown in FIG. 5.

When the frequency control command f _{CMD is} higher than the phase shift frequency f _PS set by the control unit 16 but lower than the resonant frequency f _R of the LLC resonant converter 10, the LLC resonant converter 10 operates in the second mode M2 (see FIG. 7B for cooperation) In this mode, the first control signal S _Q1 (the same signal as the fourth control signal S _Q4 ) provided by the control unit 16 and the first rectification control signal S _SR1 are variable frequency signals with the same phase, and at the same time, the second control signal S _Q2 (the same signal as the third control signal S _Q3 ) and the second rectification control signal (S _SR2 ) are variable frequency signals with the same phase. That is, the _{phase difference α between the rising edges of the turn-on signals of the first control signal S Q1} and the first rectification control signal S _SR1 is 0 degrees, and the turn-on signals of the second control signal S _Q2 and the second rectification control signal S _SR2 rise The phase difference α is also 0 degrees. In this mode, the duty cycle (duty cycle, duty cycle) of the first rectification control signal S _SR1 and the second rectification control signal S _{SR2 is the resonant period, where the resonant period is the reciprocal of the resonant frequency f R} , namely 1 /f _R. In this mode, the first switch Q1 on the primary side, the second switch Q2, the third switch Q3, and the fourth switch Q4, and the first synchronous rectifier switch SR1 and the second synchronous rectifier switch SR2 on the secondary side all work in variable frequency mode. And the duty cycle of the first synchronous rectification switch SR1 and the second synchronous rectification switch SR2 on the secondary side will be limited to the resonant period. That is, the conduction time of the first synchronous rectification switch SR1 is limited from the original time 0 to time t1 to time 0 to time t1'; the conduction time of the second synchronous rectification switch SR2 is limited to the original time t1 to time t2 Time t1 to time t2'. The frequency conversion control in this mode is realized through the frequency controller 164 shown in FIG. 5.

When the frequency control command f _{CMD is} lower than the phase shift frequency f _PS set by the control unit 16, the LLC resonant converter 10 operates in the third mode M3 (for cooperation, see FIG. 7C). In this mode, the control unit 16 provides the first The control signal S _Q1 (the same signal as the fourth control signal S _Q4 ) and the first rectification control signal S _SR1 are variable-frequency signals with different phases. At the same time, the second control signal S _Q2 (the same signal as the third control signal S _Q3) Signal) and the second rectification control signal S _SR2 are variable frequency signals with different phases. That is, the _{phase difference α between the rising edge of the turn-on signal of the first control signal S Q1} and the first rectification control signal S _SR1 increases with the lower the frequency. For example, the illustrated Φ _L is 0 to 180 and greater than 0. Any number. It is worth mentioning that the control unit 16 controls _{the phase of the first rectification control signal S SR1} to lead the phase of the first control signal S _Q1 by Φ _L degrees. The specific control method is to increase the conduction period of the first synchronous rectification switch SR1 to achieve _{the leading edge phase of the conduction signal of the first rectification control signal S SR1} (from the original time 0 leading to time t1", that is, leading Φ _L degrees). Similarly, the _{phase difference α between the rising edge of the turn-on signal of the second control signal S Q2} and the second rectification control signal S _SR2 increases with the lower the frequency. It is also controlled by the second synchronous rectification The conduction period of the switch SR2 is increased to achieve _{the leading edge phase of the conduction signal of the second rectification control signal S SR2} (advance from the original time t1 to time t2", that is, advance Φ _L degrees). With this control method, when the output voltage of the LLC resonant converter 10 starts to drop due to insufficient input voltage, the output voltage of the LLC resonant converter 10 can still be maintained within a voltage range for a maintenance time, so that the back-end coupled electronic products There is enough time to respond, and complete storage or backup of the data before the power failure.

In this mode, the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 on the primary side keep working in the variable frequency mode, while the first synchronous rectifier switch SR1 and the second synchronous rectifier switch on the secondary side SR2 works in variable frequency mode and phase shift (phase lead) mode. The frequency conversion control and phase advance control in this mode are implemented through the frequency and phase controller 165 shown in FIG. 5.

Please refer to FIG. 8, which is a flowchart of the control method of the LLC resonant converter of the present invention. The LLC resonant converter includes a square wave generator arranged on the primary side of the transformer and a synchronous rectification unit arranged on the secondary side of the transformer. The square wave generator includes at least a first switch controlled by a first control signal and a second switch controlled by a second control signal. The synchronous rectification unit at least 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. First, the output voltage feedback value and the output voltage reference value are received, and the output voltage feedback value and the output voltage reference value are compared to generate a voltage error value (S11). Then, the voltage error value is calculated to obtain the frequency control command (S12). Then, it is judged whether the frequency control command is higher than the phase shift frequency (S13). If yes (that is, the frequency control command is higher than the phase shift frequency), control the first control signal and the first The rectification control signal is a variable frequency signal with the same phase, and the second control signal and the second rectification control signal are controlled to be a variable frequency signal with the same phase (S14). If not (that is, the frequency control command is lower than the phase shift frequency), control the first control signal and the first rectification control signal to be variable-frequency signals with different phases, and control the second control signal and the second rectification control signal to be phase-different Frequency conversion signal (S15).

Step (S14) further includes: when the frequency control command is higher than the phase shift frequency but lower than the resonance frequency, controlling the duty cycle of the first rectification control signal and the second rectification control signal to be the resonance period.

Step (S15) further includes: when the frequency control command is lower than the phase shift frequency, controlling the phase of the first rectification control signal to lead the phase of the first control signal, and controlling the phase of the second rectification control signal to lead the phase of the second control signal .

Therefore, when the input voltage is insufficient, the LLC resonant converter can still maintain the output voltage within a voltage range for a period of time, so that the electronic products coupled to the back end have enough time to react and perform complete data storage before the power failure. Or backup.

The above are only detailed descriptions and drawings of the preferred embodiments of the present invention. However, the features of the present invention are not limited to these, and are not intended to limit the present invention. The full scope of the present invention should be covered by the following patent application scope As the standard, all embodiments that conform to the spirit of the patent application of the present invention and similar changes should be included in the scope of the present invention. Anyone familiar with the art in the field of the present invention can easily think of changes or Modifications can be covered in the following patent scope of this case.

16: control unit

S _Q1 : the first control signal

S _Q2 : second control signal

S _Q3 : the third control signal

S _Q4 : Fourth control signal

S _SR1 : the first rectification control signal

S _SR2 : The second rectification control signal

161: comparison unit

162: Voltage Controller

163: frequency limiter

164: Frequency Controller

165: Frequency and Phase Controller

V _{OUT_FB} : Output voltage feedback value

V _{OUT_REF} : output voltage reference value

V _ERR : voltage error value

f _CMD : Frequency control command

Claims (17)

An LLC resonant converter includes: a square wave generator with a first switch and a second switch connected in series with the first switch; a resonant tank coupled to the square wave generator; a transformer with a primary side and On the secondary side, the primary side is coupled to the resonant tank and the first switch and the second switch of the square wave generator; a synchronous rectifier unit, coupled to the secondary side, has a first synchronous rectifier switch and a A second synchronous rectifier switch; and a control unit that receives an output voltage of the resonant converter, obtains a frequency control command according to the output voltage, provides a first control signal to control the first switch, and 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 second synchronous rectification switch; wherein, when the frequency control command is higher than a phase shift frequency, The first control signal and the first rectification control signal are variable frequency signals with the same phase, and the second control signal and the second rectification control signal are variable frequency signals with the same phase; when the frequency control command is lower than the phase shift frequency At this time, the first control signal and the first rectification control signal are frequency conversion signals with different phases, and the second control signal and the second rectification control signal are frequency conversion signals with different phases. The LLC resonant converter according to claim 1, wherein when the frequency control command is higher than the phase shift frequency but lower than a resonant frequency, the duty ratio of the first rectification control signal and the second rectification control signal It is a resonant period. The LLC resonant converter according to claim 1, wherein when the frequency control command is lower than the phase shift frequency, the phase of the first rectification control signal leads the phase of the first control signal, and the second rectification control The phase of the signal leads the phase of the second control signal. The LLC resonant converter according to claim 1, wherein the control unit includes: a comparison unit that receives an output voltage feedback value and an output voltage reference value corresponding to the output voltage, and compares the output voltage feedback value with The output voltage reference value generates a voltage error value; and a voltage controller receives the voltage error value and performs operations on the voltage error value to obtain the frequency control command. The LLC resonant converter according to claim 1, wherein the square wave generator 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 according to claim 1, wherein the square wave generator includes a first switch bridge arm composed of the first switch and the second switch, and a third switch and a fourth switch. A second switch bridge arm is composed of switches to form a full-bridge circuit structure. The LLC resonant converter according to claim 1, wherein the transformer has a center-tap structure, and the first synchronous rectifier switch and the second synchronous rectifier switch are respectively coupled to two ends of the transformer. The LLC resonant converter according to 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 third synchronous rectification switch A second synchronous rectifier bridge arm composed of a fourth synchronous rectifier switch forms a full-bridge rectifier circuit structure. The LLC resonant converter according to claim 3, wherein the on-period of the first synchronous rectification switch is controlled to increase, so that the phase of the first rectification control signal leads the first control The phase of the signal; by controlling the on-period of the second synchronous rectification switch to increase, so that the phase of the second rectification control signal leads the phase of the second control signal. A control unit of an LLC resonant converter. The control unit provides a control signal to control a square wave generator on a primary side of the resonant converter. The square wave generator has a first switch and a second switch connected in series with the first switch, A rectification control signal is provided to control a synchronous rectification unit on the secondary side, and the control unit obtains a frequency control command according to an output voltage of the resonant converter; wherein, when the frequency control command is higher than a phase shift frequency, the The control signal and the rectification control signal are variable frequency signals with the same phase; when the frequency control command is lower than the phase shift frequency, the control signal and the rectification control signal are variable frequency signals with different phases. The control unit of the LLC resonant converter according to claim 10, wherein when the frequency control command is higher than the phase shift frequency but lower than a resonant frequency, the duty cycle of the rectification control signal is a resonant period. For the control unit of the LLC resonant converter described in claim 10, when the frequency control command is lower than the phase shift frequency, the phase of the rectification control signal leads the phase of the control signal. The control unit of the LLC resonant converter according to claim 12, wherein the on-period of a synchronous rectification switch corresponding to the rectification control signal is controlled to increase, so that the phase of the rectification control signal leads the phase of the control signal . A control method of an LLC resonant converter, wherein the resonant converter includes a switching bridge arm coupled to a primary side of a transformer and a synchronous rectification unit coupled to the primary side of the transformer, and the switching bridge arm It includes a first switch controlled by a first control signal and a second switch controlled by a second control signal. The synchronous rectification unit includes a first rectifier control signal. A first synchronous rectification switch controlled by a second rectification control signal and a second synchronous rectification switch controlled by a second rectification control signal; the control method includes: obtaining an operating frequency according to an output voltage feedback value; judging whether the operating frequency is higher than a Phase shift frequency; if the operating frequency is higher than the phase shift frequency, control the first control signal and the first rectification control signal to be variable frequency signals with the same phase, and control the second control signal and the second rectification control signal to be Frequency conversion signals with the same phase; if the operating frequency is lower than the phase shift frequency, the first control signal and the first rectification control signal are controlled to be frequency conversion signals with different phases, and the second control signal and the second rectification control signal are controlled The control signal is a variable frequency signal with different phases. The control method of the LLC resonant converter according to claim 14, further comprising: when the operating frequency is higher than the phase shift frequency but lower than a resonant frequency, controlling the first rectification control signal and the second rectification control signal The duty cycle of is a resonant period. The control method of the LLC resonant converter according to claim 14, further comprising: when the operating frequency is lower than the phase shift frequency, controlling the phase of the first rectification control signal to lead the phase of the first control signal, and controlling The phase of the second rectification control signal leads the phase of the second control signal. The control method of the LLC resonant converter according to claim 16, wherein the on-period of the first synchronous rectification switch is controlled to increase, so that the phase of the first rectification control signal leads the phase of the first control signal; The conduction period of the second synchronous rectification switch is increased, so that the phase of the second rectification control signal leads the phase of the second control signal.

Images