阅读说明：本技术 Cllc谐振变换器的自适应同步整流控制方法及系统 (Self-adaptive synchronous rectification control method and system of CLLC resonant converter ) 是由 胡斯登 朱浩旗 于 2021-08-18 设计创作，主要内容包括：本发明公开了一种CLLC谐振变换器的自适应同步整流控制方法及系统,该方法包括：采样CLLC谐振变换器的输出电压和电流,并与各自的参考值进行比较后经PI控制得到原边开关器件的开关频率、导通时间及关断时间；构建CLLC谐振变换器的等效电路；根据CLLC谐振变换器的等效电路计算串联谐振频率；比较开关频率和串联谐振频率的大小,根据比较结果以及CLLC谐振变换器的原边开关器件的导通时间和关断时间,计算CLLC谐振变换器的副边开关器件的导通时间及关断时间。本发明不仅可轻松实现副边的同步整流,而且能使副边自适应原边的软启动,具有实用性高,成本低,简单可靠等优势。(The invention discloses a self-adaptive synchronous rectification control method and a system of a CLLC resonant converter, wherein the method comprises the following steps: sampling output voltage and current of the CLLC resonant converter, comparing the output voltage and current with respective reference values, and obtaining switching frequency, on-time and off-time of a primary side switching device through PI control; constructing an equivalent circuit of the CLLC resonant converter; calculating a series resonance frequency according to an equivalent circuit of the CLLC resonance converter; and comparing the switching frequency with the series resonance frequency, and calculating the on-time and the off-time of the secondary side switching device of the CLLC resonance converter according to the comparison result and the on-time and the off-time of the primary side switching device of the CLLC resonance converter. The invention not only can easily realize the synchronous rectification of the secondary side, but also can lead the secondary side to be self-adaptive to the soft start of the primary side, and has the advantages of high practicability, low cost, simplicity, reliability and the like.)

1. An adaptive synchronous rectification control method of a CLLC resonant converter is characterized by comprising the following steps:

sampling output voltage and current signals of the CLLC resonant converter, comparing the output voltage and current signals with respective reference signals, and obtaining the switching frequency, the on-time and the off-time of a primary side switching device of the CLLC resonant converter through PI control;

constructing an equivalent circuit of the CLLC resonant converter based on a primary side resonant capacitor, a secondary side resonant capacitor, a primary side resonant inductor and a transformer of the CLLC resonant converter;

calculating a series resonance frequency according to an equivalent circuit of the CLLC resonance converter;

comparing the switching frequency of the primary side switching device with the series resonance frequency, and calculating the on-time and the off-time of the secondary side switching device of the CLLC resonance converter according to the comparison result and the on-time and the off-time of the primary side switching device of the CLLC resonance converter;

and sequentially switching on the primary side switching device and the secondary side switching device of the CLLC resonant converter or sequentially switching off the primary side switching device and the secondary side switching device of the CLLC resonant converter according to the on-time or off-time of the primary side switching device and the secondary side switching device of the CLLC resonant converter.

2. The adaptive synchronous rectification control method of the CLLC resonant converter according to claim 1, wherein the equivalent circuit of the CLLC resonant converter comprises a primary side resonant capacitor C_r1Resonant inductor L_rAnd an inductance L_mAnd resonant capacitor C 'connected in series'_r2And an equivalent resistance R_eqResonant capacitance C 'in series'_r2And an equivalent resistance R_eqAre connected in parallel to the inductor L_mAt both ends of the same.

3. The adaptive synchronous rectification control method of the CLLC resonant converter according to claim 1, wherein the calculation method of the series resonance frequency is as follows:

wherein，C′_r2Is the equivalent capacitance of the secondary side, n is the turn ratio of the original secondary side, g is the ratio of the secondary side resonance capacitance to the primary side resonance capacitance, C_r1Is a primary side resonant capacitor, C_r2Is a secondary side resonant capacitor, L_rIs a primary side resonant inductor, f_r1Is the series resonant frequency.

4. The adaptive synchronous rectification control method of the CLLC resonant converter according to claim 1, wherein the method for calculating the on-time and the off-time of the primary side switching device of the CLLC resonant converter comprises the following steps:

wherein, t_{on_pri}Is the on-time of the primary side switching device, f_sFor the switching frequency, D is the duty cycle of the CLLC resonant converter, where Dmax is 0.5, t_{off_pri}The turn-off time of the primary side switching device.

5. The adaptive synchronous rectification control method of the CLLC resonant converter according to claim 1, wherein the method for calculating the on-time and the off-time of the secondary side switching device of the CLLC resonant converter comprises the following steps:

comparing the switching frequency of a primary side switching device of the CLLC resonant converter with the magnitude of the series resonant frequency;

when the switching frequency of a primary side switching device of the CLLC resonant converter is less than or equal to the series resonant frequency, adding the dead time and the delay time to the conduction time of the primary side switching device of the CLLC resonant converter to obtain the conduction time of a secondary side switching device of the CLLC resonant converter; subtracting dead zone time and delay time from turn-off time of a primary side switching device of the CLLC resonant converter to obtain turn-off time of a secondary side switching device of the CLLC resonant converter;

when the switching frequency of a primary side switching device of the CLLC resonant converter is greater than the series resonant frequency, adding the time delay time to the conduction time of the primary side switching device of the CLLC resonant converter to obtain the conduction time of a secondary side switching device of the CLLC resonant converter; and subtracting the delay time from the turn-off time of the primary side switching device of the CLLC resonant converter to obtain the turn-off time of the secondary side switching device of the CLLC resonant converter.

6. An adaptive synchronous rectification control system of a CLLC resonant converter is characterized by comprising:

the sampling adjusting module is used for sampling output voltage and current signals of the CLLC resonant converter, comparing the output voltage and current signals with respective reference signals, and obtaining the switching frequency, the on-time and the off-time of a primary side switching device of the CLLC resonant converter through PI control;

the equivalent circuit building module is used for building an equivalent circuit of the CLLC resonant converter based on a primary side resonant capacitor, a secondary side resonant capacitor, a primary side resonant inductor and a transformer of the CLLC resonant converter;

the series resonance frequency calculation module is used for calculating the series resonance frequency according to the equivalent circuit of the CLLC resonance converter;

the conduction time calculation module is used for comparing the switching frequency of the primary side switching device with the series resonance frequency and calculating the conduction time of the secondary side switching device of the CLLC resonance converter according to the comparison result and the conduction time of the primary side switching device of the CLLC resonance converter;

the turn-off time calculation module is used for comparing the switching frequency of the primary side switching device with the series resonance frequency and calculating the turn-off time of the secondary side switching device of the CLLC resonant converter according to the comparison result and the turn-off time of the primary side switching device of the CLLC resonant converter;

the driving module is used for sequentially conducting a primary side switching device and a secondary side switching device of the CLLC resonant converter according to the conducting time of the primary side switching device and the conducting time of the secondary side switching device of the CLLC resonant converter; and simultaneously, according to the turn-off time of the primary side switching device and the turn-off time of the secondary side switching device of the CLLC resonant converter, the primary side switching device and the secondary side switching device of the CLLC resonant converter are sequentially turned off.

7. The adaptive synchronous rectification control system of the CLLC resonant converter according to claim 6, wherein the method for calculating the series resonant frequency by the series resonant frequency calculation module is as follows:

wherein, C'_r2Is the equivalent capacitance of the secondary side, n is the turn ratio of the original secondary side, g is the ratio of the secondary side resonance capacitance to the primary side resonance capacitance, C_r1Is a primary side resonant capacitor, C_r2Is a secondary side resonant capacitor, L_rIs a primary side resonant inductor, f_r1Is the series resonant frequency.

8. The adaptive synchronous rectification control system of the CLLC resonant converter according to claim 6, wherein the method for obtaining the on-time and the off-time of the primary side switching device of the CLLC resonant converter by the sampling adjusting module comprises the following steps:

wherein, t_{on_pri}Is the on-time of the primary side switching device, f_sFor the switching frequency, D is the duty cycle of the CLLC resonant converter, where Dmax is 0.5, t_{off_pri}The turn-off time of the primary side switching device.

9. The adaptive synchronous rectification control system of the CLLC resonant converter according to claim 6, wherein the method for calculating the conduction time of the secondary side switching device of the CLLC resonant converter by the conduction time calculation module is as follows:

comparing the switching frequency of a primary side switching device of the CLLC resonant converter with the magnitude of the series resonant frequency;

when the switching frequency of a primary side switching device of the CLLC resonant converter is less than or equal to the series resonant frequency, adding the dead time and the delay time to the conduction time of the primary side switching device of the CLLC resonant converter to obtain the conduction time of a secondary side switching device of the CLLC resonant converter;

and when the switching frequency of the primary side switching device of the CLLC resonant converter is greater than the series resonant frequency, adding the time delay time to the conduction time of the primary side switching device of the CLLC resonant converter to obtain the conduction time of the secondary side switching device of the CLLC resonant converter.

10. The adaptive synchronous rectification control system of the CLLC resonant converter according to claim 6, wherein the method for calculating the turn-off time of the secondary side switching device of the CLLC resonant converter by the turn-off time calculation module is as follows:

comparing the switching frequency of a primary side switching device of the CLLC resonant converter with the magnitude of the series resonant frequency;

when the switching frequency of a primary side switching device of the CLLC resonant converter is less than or equal to the series resonant frequency, subtracting dead time and delay time from the turn-off time of the primary side switching device of the CLLC resonant converter to obtain the turn-off time of a secondary side switching device of the CLLC resonant converter;

and when the switching frequency of the primary side switching device of the CLLC resonant converter is greater than the series resonant frequency, subtracting the delay time from the turn-off time of the primary side switching device of the CLLC resonant converter to obtain the turn-off time of the secondary side switching device of the CLLC resonant converter.

Technical Field

The invention relates to the technical field of bidirectional DC-DC, in particular to a self-adaptive synchronous rectification control method and a self-adaptive synchronous rectification control system of a CLLC resonant converter.

Background

At present, the topology of a bidirectional electric vehicle-mounted charger is mainly an isolated bidirectional DC-DC converter, and commonly used are a double-active-bridge (DAB) converter, a bidirectional CLLC resonant converter and a bidirectional symmetrical CLLLC resonant converter. The bidirectional CLLC resonant converter is widely applied to a bidirectional electric vehicle charger by the advantages of high efficiency, simple control, small secondary side output EMI and the like.

The conventional CLLC resonant converter consists of a primary side full-bridge circuit, a resonant cavity circuit and a secondary side full-bridge circuit. The primary side full bridge circuit comprises four active power devices; the resonant cavity circuit comprises a primary resonant inductor L_rPrimary side resonance capacitor C_r1Transformer L_mAnd secondary side resonance capacitor C_r2(ii) a The secondary side full bridge circuit comprises four active power devices. The CLLC resonant converter can realize bidirectional flow of energy, and has the advantage of soft switching in a full load range. In the application of the traditional CLLC resonant converter, the active power device of the secondary side does not apply a driving signal, and the secondary side current flows through the body diode of the MOSFET, so that the secondary side generates high loss. Therefore, to further improve the efficiency of the CLLC resonant converter, some control methods of synchronous rectification are implemented. By giving a driving signal of the corresponding MOSFET when the secondary side body diode is conducted, current flows through a channel of the MOSFET, so that system loss can be reduced, and efficiency is improved.

The existing CLLC resonant converter synchronous rectification control method can be divided into a voltage detection type, a current detection type and a theoretical calculation type. The voltage detection type method judges the flowing direction of the secondary side current by detecting the drain-source voltage of the MOSFET, and is easily influenced by parasitic parameters, so that the synchronous rectifier tube is mistakenly conducted, and the reliability of a system is influenced. The current detection method is to add a current sensor in a circuit to detect the secondary side current, and has strong immunity and good applicability, but for high-frequency application, a current sensing device with higher precision is required, and the cost and the volume of the system are increased virtually. The theoretical calculation method is to deduce the on and off of the synchronous rectifier tube through accurate resonance parameter calculation, and the method needs to establish an accurate mathematical model, and is relatively complex to realize and relatively low in applicability.

Therefore, how to design a method for a CLLC resonant converter which can adapt to the load size and realize synchronous rectification and soft start on the secondary side still remains a technical problem to be solved.

Disclosure of Invention

In view of this, the invention provides a method and a system for controlling adaptive synchronous rectification of a CLLC resonant converter, which can adapt to various loads and can realize synchronous rectification and soft start on a secondary side.

The invention provides a self-adaptive synchronous rectification control method of a CLLC resonant converter in a first aspect, which comprises the following steps: sampling output voltage and current signals of the CLLC resonant converter, comparing the output voltage and current signals with respective reference signals, and obtaining the switching frequency, the on-time and the off-time of a primary side switching device of the CLLC resonant converter through PI control; constructing an equivalent circuit of the CLLC resonant converter based on a primary side resonant capacitor, a secondary side resonant capacitor, a primary side resonant inductor and a transformer of the CLLC resonant converter; calculating a series resonance frequency according to an equivalent circuit of the CLLC resonance converter; comparing the switching frequency of the primary side switching device with the series resonance frequency, and calculating the on-time and the off-time of the secondary side switching device of the CLLC resonance converter according to the comparison result and the on-time and the off-time of the primary side switching device of the CLLC resonance converter; and sequentially switching on or off the primary side switching device and the secondary side switching device of the CLLC resonant converter according to the on-time or off-time of the primary side switching device and the secondary side switching device of the CLLC resonant converter.

Furthermore, the equivalent circuit of the CLLC resonant converter comprises a primary side resonant capacitor C_r1Resonant inductor L_rAnd an inductance L_mAnd resonant capacitor C 'connected in series'_r2And an equivalent resistance R_eqResonant capacitance C 'in series'_r2And an equivalent resistance R_eqAre connected in parallel to the inductor L_mAt both ends of the same.

Further, the method for calculating the series resonance frequency comprises the following steps:

wherein, C'_r2Is the equivalent capacitance of the secondary side, n is the turn ratio of the original secondary side, g is the ratio of the secondary side resonance capacitance to the primary side resonance capacitance, C_r1Is a primary side resonant capacitor, C_r2Is a secondary side resonant capacitor, L_rIs a primary side resonant inductor, f_r1Is the series resonant frequency.

Further, the method for calculating the on-time and the off-time of the primary side switching device of the CLLC resonant converter comprises the following steps:

wherein, t_{on_pri}Is the on-time of the primary side switching device, f_sD is the duty ratio of the CLLC resonant converter, and the maximum D is 0.5, t_{off_pri}The turn-off time of the primary side switching device.

Further, the method for calculating the on-time and the off-time of the secondary side switching device of the CLLC resonant converter comprises the following steps: comparing the switching frequency of a primary side switching device of the CLLC resonant converter with the magnitude of the series resonant frequency; when the switching frequency of a primary side switching device of the CLLC resonant converter is less than or equal to the series resonant frequency, adding the dead time and the delay time to the conduction time of the primary side switching device of the CLLC resonant converter to obtain the conduction time of a secondary side switching device of the CLLC resonant converter; subtracting dead zone time and delay time from turn-off time of a primary side switching device of the CLLC resonant converter to obtain turn-off time of a secondary side switching device of the CLLC resonant converter; when the switching frequency of a primary side switching device of the CLLC resonant converter is greater than the series resonant frequency, adding the time delay time to the conduction time of the primary side switching device of the CLLC resonant converter to obtain the conduction time of a secondary side switching device of the CLLC resonant converter; and subtracting the delay time from the turn-off time of the primary side switching device of the CLLC resonant converter to obtain the turn-off time of the secondary side switching device of the CLLC resonant converter.

The invention provides an adaptive synchronous rectification control system of a CLLC resonant converter, which comprises: the sampling adjusting module is used for sampling output voltage and current signals of the CLLC resonant converter, comparing the output voltage and current signals with respective reference signals, and obtaining the switching frequency, the on-time and the off-time of a primary side switching device of the CLLC resonant converter through PI control; the equivalent circuit building module is used for building an equivalent circuit of the CLLC resonant converter based on a primary side resonant capacitor, a secondary side resonant capacitor, a primary side resonant inductor and a transformer of the CLLC resonant converter; the series resonance frequency calculation module is used for calculating the series resonance frequency according to the equivalent circuit of the CLLC resonance converter; the conduction time calculation module is used for comparing the switching frequency of the primary side switching device with the series resonance frequency and calculating the conduction time of the secondary side switching device of the CLLC resonance converter according to the comparison result and the conduction time of the primary side switching device of the CLLC resonance converter; the turn-off time calculation module is used for comparing the switching frequency of the primary side switching device with the series resonance frequency and calculating the turn-off time of the secondary side switching device of the CLLC resonance converter according to the comparison result and the turn-off time of the primary side switching device of the CLLC resonance converter; the driving module is used for sequentially conducting a primary side switching device and a secondary side switching device of the CLLC resonant converter according to the conducting time of the primary side switching device and the conducting time of the secondary side switching device of the CLLC resonant converter; and simultaneously, according to the turn-off time of the primary side switching device and the turn-off time of the secondary side switching device of the CLLC resonant converter, the primary side switching device and the secondary side switching device of the CLLC resonant converter are sequentially turned off.

According to the self-adaptive synchronous rectification control system and method of the CLLC resonant converter, the series resonance frequency is calculated, the on-time and the off-time of the secondary side switching device are calculated by comparing the switching frequency with the series resonance frequency and the on-time and the off-time of the primary side switching device, and the switching time and the switching frequency of the secondary side switching device can be self-adaptive to the switching time and the switching frequency of the primary side switching device. Finally, the secondary side switching device can realize the synchronous rectification function, and can be self-adaptive to the soft start process of the primary side switching device to realize the soft start of the secondary side.

Drawings

For purposes of illustration and not limitation, the present invention will now be described in accordance with its preferred embodiments, particularly with reference to the accompanying drawings, in which:

fig. 1 is a topology diagram of a CLLC resonant converter;

fig. 2 is a schematic structural diagram of an adaptive synchronous rectification control system of a CLLC resonant converter according to an embodiment of the present invention;

fig. 3 is an equivalent circuit diagram of a CLLC resonant converter;

FIG. 4 is a diagram of a driving waveform when a switching frequency is equal to or lower than a series resonance frequency;

fig. 5 is a flowchart of an adaptive synchronous rectification control method of a CLLC resonant converter according to a second embodiment of the present invention;

fig. 6 is an experimental result of an adaptive synchronous rectification control method using a CLLC resonant converter;

fig. 7 is a driving waveform diagram corresponding to the primary side and the secondary side.

Detailed Description

In order that the above objects, features and advantages of the present invention can be more clearly understood, a detailed description of the present invention will be given below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and features of the embodiments may be combined with each other without conflict.

In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention, and the described embodiments are merely a subset of the embodiments of the present invention, rather than a complete embodiment. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Fig. 1 is a topological diagram of a CLLC resonant converter, which is composed of a primary side full bridge circuit 11, a resonant cavity circuit 12 and a secondary side full bridge circuit 13. The primary side full bridge circuit 11 comprises four switching power devices (Q)₁，Q₂，Q₃And Q₄) (ii) a Resonant cavity circuit 12 includes a primary resonant inductor L_rPrimary side resonance capacitor C_r1Transformer L_mAnd secondary side resonance capacitor C_r2(ii) a The secondary side full bridge circuit 13 includes four switching power devices (Q)₅，Q₆，Q₇And Q₈). The CLLC resonant converter can realize bidirectional flow of energy, and has the advantage of soft switching in a full load range. In the application of the traditional CLLC resonant converter, the active power device of the secondary side does not apply a driving signal, and the secondary side current flows through the body diode of the MOSFET, so that the secondary side generates high loss.

The following is a system and method for adaptive synchronous rectification control for a CLLC resonant converter. The details are as follows.

Example one

Fig. 2 is a schematic structural diagram of an adaptive synchronous rectification control system of a CLLC resonant converter according to an embodiment of the present invention. The CLLC resonant converter comprises a primary side full-bridge circuit 11, a resonant cavity circuit 12 and a secondary side full-bridge circuit 13; the primary side full bridge circuit 11 includes four switching devices (Q)₁，Q₂，Q₃And Q₄) (ii) a Resonant cavity circuit 12 includes a primary resonant inductor L_rPrimary side resonance capacitor C_r1Transformer L_mAnd secondary side resonance capacitor C_r2(ii) a The secondary side full bridge circuit 13 includes four switching devices (Q)₅，Q₆，Q₇And Q₈)。

As shown in fig. 2, the adaptive synchronous rectification control system of the CLLC resonant converter includes:

and the sampling adjusting module 201 is used for sampling the output voltage and current signals of the CLLC resonant converter, comparing the output voltage and current signals with respective reference signals, and obtaining the switching frequency, the on-time and the off-time of a primary side switching device of the CLLC resonant converter through PI control.

The equivalent circuit constructing module 202 is used for constructing an equivalent circuit of the CLLC resonant converter based on the primary side resonant capacitor, the secondary side resonant capacitor, the primary side resonant inductor and the transformer of the CLLC resonant converter.

And the series resonance frequency calculation module 203 is used for calculating the series resonance frequency according to the equivalent circuit of the CLLC resonance converter.

And the conduction time calculation module 204 is configured to compare the switching frequency of the primary side switching device with the series resonance frequency, and calculate the conduction time of the secondary side switching device of the CLLC resonant converter according to the comparison result and the conduction time of the primary side switching device of the CLLC resonant converter.

And the turn-off time calculation module 205 is configured to compare the switching frequency of the primary side switching device with the series resonance frequency, and calculate the turn-off time of the secondary side switching device of the CLLC resonant converter according to the comparison result and the turn-off time of the primary side switching device of the CLLC resonant converter.

The driving module 206 is configured to sequentially turn on the primary side switching device and the secondary side switching device of the CLLC resonant converter according to the turn-on time of the primary side switching device and the turn-on time of the secondary side switching device of the CLLC resonant converter; and simultaneously, according to the turn-off time of the primary side switching device and the turn-off time of the secondary side switching device of the CLLC resonant converter, the primary side switching device and the secondary side switching device of the CLLC resonant converter are sequentially turned off.

In this embodiment, the method for calculating the on-time and the off-time of the primary side switching device of the CLLC resonant converter by the sampling adjustment module 201 includes:

wherein, t_{on_pri}Is the on-time of the primary side switching device, f_sFor the switching frequency, D is the duty cycle of the CLLC resonant converter, where Dmax is 0.5, t_{off_pri}The turn-off time of the primary side switching device.

In this embodiment, the specific method for constructing the equivalent circuit of the CLLC resonant converter by the equivalent circuit constructing module 202 is as follows:

the equivalent circuit of the CLLC resonant converter can be obtained by Fundamental analysis (FHA).

Fig. 3 is a circuit diagram of an equivalent circuit of the CLLC resonant converter. As shown in fig. 3, the equivalent circuit of the CLLC resonant converter includes a primary resonant capacitor C_r1Resonant inductor L_rAnd an inductance L_mAnd resonant capacitor C 'connected in series'_r2And an equivalent resistance R_eqResonant capacitance C 'in series'_r2And an equivalent resistance R_eqAre connected in parallel to the inductor L_mAt both ends of the same.

In this embodiment, the specific method for calculating the series resonant frequency by the series resonant frequency calculating module 203 is as follows:

wherein, C'_r2Is the equivalent capacitance of the secondary side, n is the turn ratio of the original secondary side, and g is the ratio of the secondary side resonance capacitance to the primary side resonance capacitance，C_r1Is primary side resonance capacitance value, C_r2Is a secondary resonance capacitance value, L_rIs primary side resonance inductance value, f_r1Is the series resonant frequency.

In this embodiment, the specific method for calculating the on-time of the secondary side switching device of the CLLC resonant converter by the on-time calculating module 204 is as follows:

(1) according to the switching frequency f_sCalculating the switching device (Q) of the CLLC resonant converter₁And Q₄) The on-time of (c).

Firstly according to the switching frequency f of the primary side switching device_sCalculating the primary switching device Q₁On-time of the switching device Q₁And Q₃Are complementary to each other, a switching device Q₁And Q₄Are the same, and a switching device Q₂And Q₃The drive signals of (a) are the same.

Primary side switching device Q₁The method for calculating the on-time of (c) is as follows:

wherein, t_{on_pri}Is the on-time of the primary side switching device, f_sFor the switching frequency, D is the duty cycle of the CLLC resonant converter, where D is 0.5 max.

(2) Comparing the switching frequency f of the switching devices on the primary side_sWith series resonance frequency f_r1The size of (a) is (b),

(3) when switching frequency f of the primary switching device_sLess than or equal to series resonance frequency f_r1In time, the primary side switching device Q of the CLLC resonant converter₁Plus dead time t_deadAnd a delay time t_delayObtaining a secondary side switching device Q of the CLLC resonant converter₅The on-time of (c). Switching device Q₅Drive signal of and Q₇Complementary, switching device Q₅Drive signal of and Q₈Same, switching device Q₆And Q₇The drive signals of (a) are the same. When the switching frequency of the primary switching device is onRate f_sLess than or equal to series resonance frequency f_r1Time, switch device Q₁And Q₄Switching device Q₂And Q₃Switching device Q₅And Q₈Switching device Q₆And Q₇The drive waveform of (2) is shown in fig. 4.

Wherein, the secondary side switching device Q of the CLLC resonant converter₅The on-time of (d) is:

t_{on_sec}＝t_{on_pri}+t_dead+t_delay

wherein, t_{on_pri}Is the conduction time, t, of the primary side switching device_deadAs dead time, t_delayFor a delay time, t_{on_sec}The on-time of the secondary side switching device.

(4) When switching frequency f of the primary switching device_s> series resonance frequency f_r1In time, the primary side switching device Q of the CLLC resonant converter₁On-time plus delay time t_delayObtaining a secondary side switching device Q of the CLLC resonant converter₅The on-time of (c). Switching device Q₅Drive signal of and Q₇Complementary, switching device Q₅Drive signal of and Q₈Same, switching device Q₆And Q₇The drive signals of (a) are the same.

Wherein, the secondary side switching device Q of the CLLC resonant converter₅The on-time of (d) is:

t_{on_sec}＝t_{on_pri}+t_delay

wherein, t_{on_pri}Is the conduction time, t, of the primary side switching device_delayFor a delay time, t_{on_sec}The on-time of the secondary side switching device.

In this embodiment, the specific method for calculating the turn-off time of the secondary side switching device of the CLLC resonant converter by the turn-off time calculation module 205 is as follows:

(1) according to the switching frequency f of the primary switching device_sCalculating the primary side switching device (Q) of the CLLC resonant converter₁And Q₄) The off-time of.

According to the switching frequencyRate f_sCalculating the primary switching device Q₁The off-time of. Switching device Q₁And Q₃Are complementary to each other, a switching device Q₁And Q₄Are the same, and a switching device Q₂And Q₃The drive signals of (a) are the same.

Primary side switching device Q₁The off-time calculation method comprises the following steps:

wherein, t_{off_pri}Is the turn-off time of the primary side switching device, f_sFor the switching frequency, D is the duty cycle of the CLLC resonant converter, where D is 0.5 max.

(2) Comparing the switching frequency f of the switching devices on the primary side_sWith series resonance frequency f_r1The size of (2).

(3) When switching frequency f of the primary switching device_sLess than or equal to series resonance frequency f_r1In time, the primary side switching device Q of the CLLC resonant converter₁Off-time minus dead time t_deadAnd a delay time t_delayObtaining a secondary side switching device Q of the CLLC resonant converter₅The off-time of. Switching device Q₅Drive signal of and Q₇Complementary, switching device Q₅Drive signal of and Q₈Same, switching device Q₆And Q₇The drive signals of (a) are the same. When switching frequency f_sLess than or equal to series resonance frequency f_r1Time, switch device Q₁And Q₄Switching device Q₂And Q₃Switching device Q₅And Q₈Switching device Q₆And Q₇The drive waveform of (2) is shown in fig. 4.

Wherein, the secondary side switching device Q of the CLLC resonant converter₅The off-time of (d) is:

t_{off_sec}＝t_{off_pri}-t_dead-t_delay

wherein, t_{off_pri}Is the turn-off time, t, of the primary side switching device_deadAs dead time, t_delayFor a delay time, t_{off_sec}The turn-off time of the secondary side switching device.

(4) When switching frequency f of the primary switching device_s> series resonance frequency f_r1In time, the primary side switching device Q of the CLLC resonant converter₁Off time minus delay time t_delayObtaining a secondary side switching device Q of the CLLC resonant converter₅The off-time of. Switching device Q₅Drive signal of and Q₇Complementary, switching device Q₅Drive signal of and Q₈Same, switching device Q₆And Q₇The drive signals of (a) are the same.

Wherein, the secondary side switching device Q of the CLLC resonant converter₅The off-time of (d) is:

t_{off_sec}＝t_{off_pri}-t_delay

wherein, t_{off_pri}Is the turn-off time, t, of the primary side switching device_delayFor a delay time, t_{off_sec}The turn-off time of the secondary side switching device.

The self-adaptive synchronous rectification control system of the CLLC resonant converter calculates the series resonance frequency at first, and calculates the conduction time of the secondary side switching device by comparing the switching frequency with the series resonance frequency and the conduction time of the primary side switching device; and then calculating the turn-off time of the secondary side switching device according to the turn-off time of the primary side switching device, so that the switching time and frequency of the secondary side switching device can be adaptive to the switching time and frequency of the primary side switching device.

By the self-adaptive synchronous rectification control system of the CLLC resonant converter, when the CLLC resonant converter is started, the primary side switching device is in soft start, and the secondary side switching device can self-adapt to the soft start process of the primary side switching device, so that the soft start of the secondary side is realized.

The self-adaptive synchronous rectification control system of the CLLC resonant converter can self-adapt to various loads, can realize synchronous rectification during forward working and reverse working, avoids an additional sensing device and a complex algorithm, reduces the system cost and the volume, enables a synchronous rectification control scheme to be easier to realize, and has higher practicability. Meanwhile, the secondary switch device is adaptive to the soft start process of the switch in the primary full-bridge circuit, and the current impact in the start process of the secondary switch device can be reduced.

Example two

Fig. 5 is a flowchart of an adaptive synchronous rectification control method of a CLLC resonant converter according to a second embodiment of the present invention. Referring to fig. 5, the adaptive synchronous rectification control method of the CLLC resonant converter includes:

s301, sampling output voltage and current signals of the CLLC resonant converter, comparing the output voltage and current signals with respective reference signals, and obtaining the switching frequency, the on-time and the off-time of a primary side switching device of the CLLC resonant converter through PI control.

S302, constructing an equivalent circuit of the CLLC resonant converter based on the primary side resonant capacitor, the secondary side resonant capacitor, the primary side resonant inductor and the transformer of the CLLC resonant converter.

And S303, calculating the series resonance frequency according to the equivalent circuit of the CLLC resonance converter.

And S304, comparing the switching frequency of the primary side switching device with the series resonance frequency, and calculating the on-time and the off-time of the secondary side switching device of the CLLC resonant converter according to the comparison result and the on-time and the off-time of the primary side switching device of the CLLC resonant converter.

S305, sequentially conducting a primary side switching device and a secondary side switching device of the CLLC resonant converter according to the conducting time of the primary side switching device and the conducting time of the secondary side switching device of the CLLC resonant converter; and simultaneously, according to the turn-off time of the primary side switching device and the turn-off time of the secondary side switching device of the CLLC resonant converter, the primary side switching device and the secondary side switching device of the CLLC resonant converter are sequentially turned off.

Specifically, the method for constructing the equivalent circuit of the CLLC resonant converter specifically includes:

the equivalent circuit of the CLLC resonant converter can be obtained by Fundamental analysis (FHA). The equivalent circuit of the CLLC resonant converter comprises a primary side resonant capacitorC_r1Resonant inductor L_rAnd an inductance L_mAnd resonant capacitor C 'connected in series'_r2And an equivalent resistance R_eqResonant capacitance C 'in series'_r2And an equivalent resistance R_eqAre connected in parallel to the inductor L_mAt both ends of the same.

The specific method of the series resonance frequency is as follows:

wherein, C'_r2Is the equivalent capacitance of the secondary side, n is the turn ratio of the original secondary side, g is the ratio of the secondary side resonance capacitance to the primary side resonance capacitance, C_r1Is primary side resonance capacitance value, C_r2Is a secondary resonance capacitance value, L_rIs primary side resonance inductance value, f_r1Is the series resonant frequency.

The specific method for the conducting time of the secondary side switching device of the CLLC resonant converter comprises the following steps:

(4-1-1) according to the switching frequency f_sCalculating the switching device (Q) of the CLLC resonant converter₁And Q₄) The on-time of (c).

According to the switching frequency f_sCalculating the primary switching device Q₁On-time of the switching device Q₁And Q₃Are complementary to each other, a switching device Q₁And Q₄Are the same, and a switching device Q₂And Q₃The drive signals of (a) are the same.

Primary side switching device Q₁The method for calculating the on-time of (c) is as follows:

wherein, t_{on_pri}Is the on-time of the primary side switching device, f_sFor the switching frequency, D is the duty cycle of the CLLC resonant converter, where D is 0.5 max.

(4-1-2) comparison of switching frequency f of Primary side switching device_sWith series resonance frequency f_r1The size of (a) is (b),

(4-1-3) switching frequency f of primary side switching device_sLess than or equal to series resonance frequency f_r1In time, the primary side switching device Q of the CLLC resonant converter₁Plus dead time t_deadAnd a delay time t_delayObtaining a secondary side switching device Q of the CLLC resonant converter₅The on-time of (c). Switching device Q₅Drive signal of and Q₇Complementary, switching device Q₅Drive signal of and Q₈Same, switching device Q₆And Q₇The drive signals of (a) are the same.

Wherein, the secondary side switching device Q of the CLLC resonant converter₅The on-time of (d) is:

t_{on_sec}＝t_{on_pri}+t_dead+t_delay

wherein, t_{on_pri}Is the conduction time, t, of the primary side switching device_deadAs dead time, t_delayFor a delay time, t_{off_sec}The on-time of the secondary side switching device.

(4-1-4) switching frequency f of primary side switching device_s> series resonance frequency f_r1In time, the primary side switching device Q of the CLLC resonant converter₁On-time plus delay time t_delayObtaining a secondary side switching device Q of the CLLC resonant converter₅The on-time of (c). Switching device Q₅Drive signal of and Q₇Complementary, switching device Q₅Drive signal of and Q₈Same, switching device Q₆And Q₇The drive signals of (a) are the same.

Wherein, the secondary side switching device Q of the CLLC resonant converter₅The on-time of (d) is:

t_{on_sec}＝t_{on_pri}+t_delay

wherein, t_{on_pri}Is the conduction time, t, of the primary side switching device_delayFor a delay time, t_{off_sec}The on-time of the secondary side switching device.

The specific method for the turn-off time of the secondary side switching device of the CLLC resonant converter comprises the following steps:

(4-2-1) switching frequency f according to primary side switching device_sCalculating the switching device (Q) of the CLLC resonant converter₁And Q₄) The off-time of.

Firstly according to the switching frequency f of the primary side switching device_sCalculating the primary switching device Q₁The off-time of. Switching device Q₁And Q₃Are complementary to each other, a switching device Q₁And Q₄Are the same, and a switching device Q₂And Q₃The drive signals of (a) are the same.

Primary side switching device Q₁The off-time calculation method comprises the following steps:

wherein, t_{off_pri}Is the turn-off time of the primary side switching device, f_sFor the switching frequency, D is the duty cycle of the CLLC resonant converter, where D is 0.5 max.

(4-2-2) comparison of switching frequency f of Primary side switching device_sWith series resonance frequency f_r1The size of (a) is (b),

(4-2-3) switching frequency f of primary side switching device_sLess than or equal to series resonance frequency f_r1In time, the primary side switching device Q of the CLLC resonant converter₁Off-time minus dead time t_deadAnd a delay time t_delayObtaining a secondary side switching device Q of the CLLC resonant converter₅The off-time of. Switching device Q₅Drive signal of and Q₇Complementary, switching device Q₅Drive signal of and Q₈Same, a switching deviceQ₆And Q₇The drive signals of (a) are the same.

Wherein, the secondary side switching device Q of the CLLC resonant converter₅The off-time of (d) is:

t_{off_sec}＝t_{off_pri}-t_dead-t_delay

wherein, t_{off_pri}Is the turn-off time, t, of the primary side switching device_deadAs dead time, t_delayFor a delay time, t_{off_sec}The turn-off time of the secondary side switching device.

(4-2-4) switching frequency f of primary side switching device_s> series resonance frequency f_r1In time, the primary side switching device Q of the CLLC resonant converter₁On-time minus delay time t_deadObtaining a secondary side switching device Q of the CLLC resonant converter₅The on-time of (c). Switching device Q₅Drive signal of and Q₇Complementary, switching device Q₅Drive signal of and Q₈Same, switching device Q₆And Q₇The drive signals of (a) are the same.

Wherein, the secondary side switching device Q of the CLLC resonant converter₅The off-time of (d) is:

t_{off_sec}＝t_{off_pri}-t_delay

wherein, t_{off_pri}Is the conduction time, t, of the primary side switching device_delayFor a delay time, t_{off_sec}The on-time of the secondary side switching device.

The self-adaptive synchronous rectification control system of the CLLC resonant converter calculates the series resonance frequency at first, and calculates the conduction time of the secondary side switching device by comparing the switching frequency with the series resonance frequency and the conduction time of the primary side switching device; and then calculating the turn-off time of the secondary side switching device according to the turn-off time of the primary side switching device, so that the switching time and frequency of the secondary side switching device can be adaptive to the switching time and frequency of the primary side switching device.

In the present embodiment, the above-described adaptive synchronous rectification control method will be used at a 6.6kW CLLC resonant converter. The tested switching frequency ranges from 200kHz to 400kHz, the input voltage ranges from 380Vdc to 700Vdc, and the output voltage ranges from 240Vdc to 420 Vdc. The circuit topology is identical to that of fig. 1. Fig. 6 is an experimental result of an adaptive synchronous rectification control method using a CLLC resonant converter. Fig. 7 is a driving waveform diagram corresponding to the primary side and the secondary side.

By the self-adaptive synchronous rectification control method of the CLLC resonant converter, the secondary side can not only realize the synchronous rectification function, but also self-adapt to the soft start process of the primary side switching device when the CLLC resonant converter is in the primary side soft start, so that the soft start of the secondary side is realized.

According to the self-adaptive synchronous rectification control method of the CLLC resonant converter, the secondary side can self-adapt to the size of the load to realize synchronous rectification, an additional sensing device and a complex algorithm are avoided, the system cost and the volume are reduced, the synchronous rectification control scheme is easier to realize simply, and the practicability is higher. Meanwhile, the secondary side switching device is adaptive to the soft starting process of the primary side switching device, and the current impact of the secondary side circuit in the starting process can be reduced.

The above-described embodiments should not be construed as limiting the scope of the invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions can occur, depending on design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.