阅读说明：本技术 一种应用于双向cllc谐振变换器的同步整流电路及控制策略 (Synchronous rectification circuit and control strategy applied to bidirectional CLLC resonant converter ) 是由 陈宁 陈敏 李博栋 汪小青 孙欣楠 陈磊 张东博 于 2019-10-21 设计创作，主要内容包括：本发明涉及DC/DC变换器领域,旨在提供一种应用于双向CLLC谐振变换器的同步整流电路及控制策略。该电路包括原边桥、副边桥和CLLC谐振腔；在CLLC谐振腔的副边谐振电感Lrs磁芯上缠绕一个检测线圈,检测线圈的输出端、积分器和比较器依次相连；比较器的输出端与所述双向CLLC谐振变换器的控制器相连。本发明通过谐振电感电压间接地实现对谐振电流的检测,具有适用范围广、抗干扰性好的特点。无需添加额外的电流检测元件,不会带来额外的损耗,且具有更小的体积和更低的成本。本发明可较快速地检测谐振腔副边电流,进而在多种工况下均可实现较好的同步整流效果,提高变换器在多种工作状态下的变换效率。(The invention relates to the field of DC/DC converters, and aims to provide a synchronous rectification circuit and a control strategy applied to a bidirectional CLLC resonant converter. The circuit comprises a primary side bridge, a secondary side bridge and a CLLC resonant cavity; a detection coil is wound on a secondary side resonance inductor Lrs magnetic core of the CLLC resonant cavity, and the output end of the detection coil, the integrator and the comparator are sequentially connected; and the output end of the comparator is connected with the controller of the bidirectional CLLC resonant converter. The invention realizes the detection of the resonance current indirectly through the resonance inductance voltage, and has the characteristics of wide application range and good anti-interference performance. The method does not need to add an additional current detection element, does not bring additional loss, and has smaller volume and lower cost. The invention can detect the secondary side current of the resonant cavity more quickly, thereby realizing better synchronous rectification effect under various working conditions and improving the conversion efficiency of the converter under various working conditions.)

1. A synchronous rectification circuit applied to a bidirectional CLLC resonant converter comprises a primary side bridge, a secondary side bridge and a CLLC resonant cavity; the detection circuit is characterized in that a detection coil is wound on a secondary side resonant inductor Lrs magnetic core of the CLLC resonant cavity, and the output end of the detection coil, an integrator and a comparator are sequentially connected; and the output end of the comparator is connected with the controller of the bidirectional CLLC resonant converter.

2. A control strategy applied to synchronous rectification of a bidirectional CLLC resonant converter is characterized in that a detection coil Tsense is wound on a secondary side resonant inductor Lrs magnetic core of a CLLC resonant cavity and used for detecting the voltage at two ends of the resonant inductor Lrs; then, an integrator performs integral operation on the detected voltage to restore the information of the secondary side resonant current Is; the comparator compares the reduced secondary side current information with a zero level to obtain polarity information of high-frequency alternating current input by the secondary side bridge, and the polarity information is used for reflecting the conduction condition of a diode of the secondary side bridge; the controller captures the polarity information of the secondary resonant current Is and carries out synchronous rectification control on the secondary bridge in the next switching period according to the information.

3. The control strategy according to claim 2, characterized in that it comprises in particular the steps of:

(1) obtaining the resonance inductance voltage reduced by a ratio through a detection coil

Detecting the voltage at two ends of the resonance inductor by using a detection coil wound on the magnetic core of the secondary resonance inductor Lrs to obtain the voltage of the secondary resonance inductor; let the voltage across the resonant inductor be v_LrsThe number of turns of the coil of the resonant inductor is N, and the magnetic flux of the resonant inductor is phi_rObtaining a voltage across the resonant inductor of

(2) Integrating the detected resonant inductor voltage

Let the output voltage of the integrator be v_intThe voltage detected by the detection coil is used as the input of an integrator, and the output voltage of the integrator is expressed as

(3) comparing the output of the integrator with zero level to obtain the body diode conduction information

In the bidirectional CLLC resonant converter, the secondary side resonant inductance current is the input side current of the secondary side full bridge, and the polarity of the secondary side resonant inductance current determines the conduction condition of the secondary side full bridge body diode; comparing the output of the integrator with a zero level, outputting a comparison signal v_comp(ii) a For increased interference immunity, the zero level is set to a reference V slightly greater than zero_bias(ii) a When v is_int＞V_biasWhen, v_comp1, representing that the body diodes of the first non-adjacent transistors in the two bridge arms are in a current-flowing state; when v is_int＜V_biasWhen, v_comp0, the body diode representing the first set of transistors is in an off state;

(4) the controller captures the on and off time of the body diode

By capturing a comparison signal v_compThe rising edge and the falling edge occur time, and the starting time and the ending time of the body diode through-current of the first group of transistors in one period are obtained; v. of_compThe rising edge of (d) indicates the beginning of the current flow through the body diode of the first group of transistors, and time is denoted t_on；v_compThe falling edge of (a) indicates that the body diode of the first group of transistors has finished flowing, and the occurrence time thereof is denoted by t_off(ii) a At t_on～t_offThe body diodes of the first group of transistors have current flowing in the time, and the synchronous rectification channels are kept on in the time period and are kept off at other moments in order to realize synchronous rectification;

(5) calculating the turn-on and turn-off time of the secondary side MOSFET and applying a driving signal in the next switching period

Because the on-off process of the MOSFET has a certain time delay, the controller needs to give a control signal in advance according to the on-off delay; of the enabling signalGiving time t_on′＝t_on-Δt_onThe given time of the turn-off signal is t_off′＝t_off-Δt_offWhere Δ t is_on、Δt_offRespectively turning on time delay and turning off time delay of the MOSFET; in the next switching cycle, the controller is at t_on' given the turn-on signal of the first group of transistors, at t_off' giving a turn-off signal for the first group of transistors to achieve synchronous rectification of the first group of transistors; due to the half-wave symmetry, the controller only needs to be at 0.5T in the last half period_s+t_on' give the turn-on signal of the second group of transistors and at 0.5T_s+t_off' given the turn-off signal of the second group of transistors, the synchronous rectification of the second group of transistors can be realized;

(6) in each switching period thereafter, the controller determines the turn-on time t of the next period according to the detected polarity information of the secondary side current_onAnd off time t_offAnd outputs corresponding on and off signals in the next period.

Technical Field

The invention relates to a synchronous rectification control strategy applied to a bidirectional CLLC resonant converter, relates to operation control of the bidirectional CLLC resonant converter, and belongs to the field of DC/DC converters.

Background

In recent years, new energy power generation, distributed power generation, frequency modulation service of power grids, and rapid development of micro-grid technology have put great demands on energy storage devices. By adding the energy storage equipment, the fluctuation of the power grid caused by the access of large-scale new energy power generation to the power grid can be effectively stabilized, so that the safety, economy and flexibility of the power system are improved. In the power system, the energy storage device has dual attributes of "source" and "charge", and needs to have the capability of absorbing and generating electric energy at the same time, so that the converter connecting the energy storage device and the power grid also needs to realize bidirectional flow of energy. The two-way isolation type DC/DC converter topology can be mainly divided into a Double Active Bridge (DAB) converter and a CLLC resonant converter at present. The CLLC converter has the characteristics of small turn-off current, small working circulation, easy realization of soft switching and the like, and can achieve high working efficiency while realizing high switching frequency, thereby having the advantages of high efficiency and high power density. In a traditional CLLC resonant converter, a primary side bridge is in a switching state to generate a high-frequency square wave voltage with a duty ratio of 50%, and a secondary side bridge is rectified by using a body diode without adding a driving signal. However, since the body diode of the MOSFET often has a relatively high conduction voltage drop, the converter will generate a relatively high conduction loss on the secondary side, which reduces the efficiency of the converter. By adopting a synchronous rectification strategy, the channel is opened when the diode is in through-flow, and the current passing through the body diode originally is transferred into the channel, so that the conduction voltage drop can be effectively reduced, the conduction loss of the rectification side is reduced, and higher efficiency is realized. However, unlike the conventional PWM DC/DC converter, the on-time of the secondary rectifier in the resonant converter and the primary side driving signal of the converter lack a clear correspondence, which makes the generation of the synchronous rectification driving signal difficult, and often requires an additional strategy to generate the synchronous rectification signal.

For a resonant converter, the traditional synchronous rectification strategies can be divided into a current detection type, a voltage detection type and a theoretical calculation type. The current detection type strategy is mainly to directly detect the secondary current through current sensors such as a mutual inductor, a Rogowski coil, a Hall element and the like, determine the conduction condition of a secondary rectifier tube according to the polarity of the secondary current, and generate a synchronous rectification driving signal according to the conduction condition. The current signal directly reflects the conduction condition of the secondary rectifier tube, and the detection of a tiny signal is not needed, so that the method has the advantages of wide application range and good anti-interference performance. However, in the scheme, an additional current sensor is required to be added to detect the high-frequency current in the resonant cavity, so that the size and the cost of the converter are increased. The voltage detection type strategy is mainly used for judging the current polarity by detecting the drain-source electrode voltage of the MOSFET, but the conduction voltage drop of the MOSFET is very small when the synchronous rectification is started, and the detection of the voltage is easily influenced by parasitic parameters, so that the error turn-off of the synchronous rectification tube is caused, and the synchronous rectification effect is influenced. The theoretical calculation type strategy directly calculates the on-off time of the synchronous rectifier tube by mainly using the working state of the converter in the resonance process, but needs to acquire accurate resonance parameters of the converter, and is difficult to accurately calculate the resonance process in the dynamic process.

Therefore, the traditional synchronous rectification strategies of the CLLC resonant converter have respective defects, and the application of the CLLC resonant converter in the bidirectional CLLC converter is limited. Therefore, there is a need for improvements to existing synchronous rectification techniques.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects in the prior art and provides a synchronous rectification strategy applied to a bidirectional CLLC resonant converter.

In order to solve the technical problem, the solution of the invention is as follows:

the synchronous rectification circuit applied to the bidirectional CLLC resonant converter comprises a primary side bridge, a secondary side bridge and a CLLC resonant cavity; a detection coil is wound on a secondary side resonance inductor Lrs magnetic core of the CLLC resonant cavity, and the output end of the detection coil, the integrator and the comparator are sequentially connected; and the output end of the comparator is connected with the controller of the bidirectional CLLC resonant converter.

The invention further provides a control strategy applied to synchronous rectification of the bidirectional CLLC resonant converter, which is characterized in that a detection coil Tsense is wound on a secondary side resonant inductor Lrs magnetic core of the CLLC resonant cavity and used for detecting the voltage at two ends of the resonant inductor Lrs; then, an integrator performs integral operation on the detected voltage to restore the information of the secondary side resonant current Is; the comparator compares the reduced secondary side current information with a zero level to obtain polarity information of high-frequency alternating current input by the secondary side bridge, and the polarity information is used for reflecting the conduction condition of a diode of the secondary side bridge; the controller captures the polarity information of the secondary resonant current Is and carries out synchronous rectification control on the secondary bridge in the next switching period according to the information.

In the present invention, the control strategy specifically includes the following steps:

step 1: and acquiring the secondary side resonance inductance voltage. Let the voltage across the resonant inductor be v_LrsThe number of turns of the coil of the resonant inductor is N, and the magnetic flux of the resonant inductor is phi_r. The voltage on the resonant inductor can be obtained as

If a detection coil is additionally added on the magnetic core, the voltage on the detection coil is

The specific relation between the voltage and the voltage at two ends of the resonance inductor is

The resonance inductance voltage reduced by a certain ratio can be obtained by adding the detection coil.

Step 2: the detected resonant inductor voltage is integrated. Let the output voltage of the integrator be v_intWith the voltage detected by the detection coil as the input of the integrator, the output voltage of the integrator can be expressed as

Wherein K_intThe integral coefficient is determined by the specific parameters of the integrator. According to inductance voltage equation

The output voltage of the integrator can be expressed as

This shows that the output voltage of the integrator is in direct proportion to the secondary side resonant current, and the detection of the resonant current can be realized by performing integration operation on the resonant inductor voltage.

And step 3: and comparing the output of the integrator with a zero level to acquire body diode conduction information. When i is_sWhen the current polarity is positive when the current polarity is greater than 0, the body diodes of Q5 and Q8 are conducted, and i_D5＝i_D8＝i_s(ii) a When i is_sWhen < 0, the current polarity is negative, the body diodes of Q6 and Q7 are turned on, and i_D6＝i_D7＝-i_s(ii) a When i is_sWhen the current is 0, the secondary side current is in an intermittent state, and Q5 to Q8 are all in an off state. Due to the half-wave symmetry of the current waveform, only the conduction states of the body diodes of the first group of transistors Q5 and Q8 which are not adjacent in the two bridge arms need to be detected. In order to increase the interference resistance in practical application, the output of the integrator is connected with a reference V slightly larger than zero_biasComparing to output a comparison signal v_comp. When v is_int＞V_biasWhen, v_compThe body diodes representing Q5, Q8 are in a current-passing state; when v is_int＜V_biasWhen, v_compAt 0, the body diodes representing Q5, Q8 are in the off state.

And 4, step 4: the controller captures the on and off time of the body diode. By capturing a comparison signal v_compThe occurrence time of the rising edge and the falling edge can obtain the starting time and the ending time of the body diode current flowing of the Q5 and the Q8 in one period. v. of_compThe rising edge of (A) indicates the beginning of current flow through the body diodes of Q5, Q8, at time t_on；v_compThe falling edge of (D) indicates that the body diodes of Q5 and Q8 end the current flowing, and the occurrence time is marked as t_off. At t_on～t_offCurrent flows through Q5, Q8 during the time period, and the synchronous rectifying channel should be kept on during the time period and kept off at the rest of the time.

And 5: and calculating the turn-on and turn-off time of the secondary side MOSFET and applying a driving signal in the next switching period. Because the on and off processes of the MOSFET have certain time delay, the controller needs to give a control signal in advance according to the on and off delay. The on signal is given a time t_on′＝t_on-Δt_onThe given time of the turn-off signal is t_off′＝t_off-Δt_offWhere Δ t is_on、Δt_offRespectively the turn-on delay and the turn-off delay of the MOSFET. In the next switching cycle, the controller is at t_on' giving a turn-on signal for Q5, Q8, at t_off' turn-off signals of Q5 and Q8 are given to realize synchronous rectification of Q5 and Q8. Due to the half-wave symmetry, the controller only needs to be at 0.5T in the last half period_s+t_on' give Q6, Q7 on signal, and at 0.5T_s+t_off' given the turn-off signals of the second transistors Q6 and Q7 which are not adjacent in two bridge arms, the synchronous rectification of Q6 and Q7 can be realized.

Step 6: in each switching period thereafter, the controller determines the turn-on time t of the next period according to the detected polarity information of the secondary side current_onAnd off time t_offAnd outputs corresponding on and off signals in the next period.

Compared with the prior art, the invention has the beneficial effects that:

(1) the strategy provided by the invention indirectly realizes the detection of the resonance current through the resonance inductance voltage, and has the characteristics of wide application range and good anti-interference performance as the traditional current detection type strategy. But the amount directly detected in the strategy is the voltage amount, an additional current detection element is not needed, no additional loss is caused, and the strategy has smaller volume and lower cost.

(2) The control strategy provided by the invention can rapidly detect the secondary side current of the resonant cavity no matter under the condition of low resonant current under light load or under the working condition in the transient process, so that a good synchronous rectification effect can be realized under various working conditions, and the conversion efficiency of the converter under various working conditions is improved.

(3) The strategy provided by the invention does not need an additional controller, and the control strategy of synchronous rectification can be realized in the same digital controller with the closed-loop control of the converter, thereby reducing the cost of the converter.

Drawings

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

Fig. 1 is a circuit diagram of a conventional bidirectional CLLC resonant converter in a forward operation mode;

fig. 2 is a basic schematic diagram of the synchronous rectification strategy of the bidirectional CLLC resonant converter proposed in the present invention;

fig. 3 is a theoretical waveform diagram in the working process of the synchronous rectification strategy of the bidirectional CLLC resonant converter provided by the invention.

Detailed Description

The invention will be further described with reference to specific examples, but the scope of the invention is not limited thereto.

The power stage circuit of the traditional bidirectional CLLC resonant converter is composed of a primary side bridge, a secondary side bridge and a CLLC resonant cavity, and the topology of the power stage circuit is shown in fig. 1. In fig. 1: the converter operates in a forward mode, Vin being an input side voltage source and R1 being an output side load. MOSFETs Q1-Q4 form a primary side switch full bridge, Q5-Q8 form a secondary side switch full bridge, and the primary side switch full bridge and the secondary side switch full bridge are connected through a CLLC resonant cavity. The resonant cavity is composed of a primary side resonant inductor Lrp, a primary side resonant capacitor Crp, a secondary side resonant inductor Lrs, a secondary side resonant capacitor Crs and a transformer, wherein the excitation inductor of the transformer is Lm. And Co is an output side filter capacitor. The converter needs to control the primary and secondary side bridges according to the working states of input and output voltage \ current and the like and reference signals of working direction, transmission power and the like.

Taking a full bridge as an example, the primary bridge is composed of two sets of bridge arms connected in parallel, wherein Q1 and Q2 form a first bridge arm, and Q3 and Q4 form a second bridge arm. The middle points of the two bridge arms are connected with the primary side of the CLLC resonant cavity. The secondary side bridge also comprises two groups of bridge arms which are connected in parallel, Q5 and Q6 form a third bridge arm, Q7 and Q8 form a fourth bridge arm, and the midpoints of the third bridge arm and the fourth bridge arm are connected with the secondary side of the CLLC resonant cavity. The CLLC resonant cavity consists of a primary side resonant inductor Lrp, a primary side resonant capacitor Crp, a secondary side resonant inductor Lrs, a secondary side resonant capacitor Crs and a transformer, wherein the excitation inductor of the transformer is Lm. Lrp, Crp are located on the primary side of the transformer, and Lrs, Crs are located on the secondary side of the transformer.

Taking the forward operation mode as an example, the controller needs to control the primary bridge according to the output voltage or the output current and the given reference signal. The driving signals applied to the four MOSFETs on the primary side by the controller are all square wave signals with the duty ratio of 50%, wherein the driving signals of Q1 and Q2 are completely complementary, the driving signals of Q3 and Q4 are completely complementary, the driving signals of Q1 and Q4 are in the same phase, and the primary side bridge outputs a square wave voltage with the duty ratio of 50% and positive and negative symmetry to be applied to the resonant cavity. The controller changes the frequency of the output voltage of the primary bridge by changing the frequency of the driving signal of the primary bridge and realizes the adjustment of the output voltage or current by changing the impedance of the resonant cavity. Under the condition of not applying synchronous rectification, the secondary side bridge is always in an uncontrolled state in the process, and only the body diode of the secondary side bridge is utilized to play a role in rectification. With synchronous rectification applied, the secondary bridge is supplied with a suitable drive signal so that its channel is turned on at the moment the body diode begins to flow, current flows through the channel, and the channel is turned off at the zero crossing of the channel current. Synchronous rectification has a relatively strict requirement on the on and off time of a channel.

The control strategy provided by the invention can realize the detection of the secondary side current of the resonance cavity under the condition of not adding an additional detection element, thereby obtaining more accurate conduction and turn-off time of the body diode and further realizing better synchronous rectification effect.

Fig. 2 is a basic schematic diagram of the synchronous rectification strategy of the bidirectional CLLC resonant converter proposed in the present invention. In fig. 2: tsense is a detection coil which is an independent coil wound on the magnetic core of the secondary side resonance inductor Lrs and used for detecting the voltage at two ends of the resonance inductor Lrs. The integrator performs integration operation on the detected voltage to restore the information of the secondary resonant current Is. The comparator compares the restored secondary side current information with a reference slightly higher than zero to obtain polarity information of the high-frequency alternating current input by the secondary side bridge, so as to reflect the conduction condition of the body diode of the secondary side bridge. The controller captures the polarity information of the secondary resonant current Is and carries out synchronous rectification control on the secondary bridge in the next switching period according to the information.

The specific control method provided by the invention comprises the following steps:

step 1: when the synchronous rectification is not started (period 0-Ts in fig. 3), the controller applies a driving signal to the primary side bridge, and the secondary side bridge is in an uncontrolled state and is rectified by using the body diode of the secondary side bridge. The voltage across the resonant inductor is detected by a detection coil wound around the resonant inductor core, and the voltage across the detection coil can be expressed as

The voltage on the detection coil is proportional to the voltage across the resonant inductor, the amplitude of which is the voltage across the resonant inductor

And (4) doubling.

Step 2: the voltage signal detected by the detection coil is integrated by an integration circuit. The detected voltage signal is integrated by an integrator, and the result of the integration operation can be expressed as

Wherein K_intThe integration coefficient is determined by the specific circuit parameters of the integrator. According to inductance voltage equation

The output of the integrator beingThe output voltage of the integrator is proportional to the current flowing through the secondary resonant inductor, and it can be seen thatIs a reduced current signal. By adjusting the integral coefficient K of the integrator_intThe gain of the detection circuit can be adjusted to achieve matching between the resonant current amplitude and the integrator output voltage range.

And step 3: and comparing the output signal of the integrator with a zero level to obtain body diode conduction information. The output signal of the integrator is a secondary side resonance inductance current signal obtained after reduction, and the amplitude is in direct proportion to the secondary side current. In a bidirectional CLLC resonant converter, the secondary side resonant inductor current, i.e., the secondary side full bridge input side current, has a polarity that determines the conduction of the secondary side full bridge body diode. When secondary side resonates the inductive current i_sWhen the current is larger than 0, the body diodes of Q5 and Q8 are in a conducting state, and the conducting current is i_D5＝i_D8＝i_sAnd the body diodes of Q6, Q7 are in the off state. When i is_sWhen < 0, the body diodes of Q6 and Q7 are in conduction state, and the conduction current is i_D6＝i_D7＝-i_sAnd the body diodes of Q5, Q8 are in the off state. When i is_sWhen the value is 0, no current flows through the secondary side of the resonant cavity, and the body diodes of all devices on the secondary side are in a cut-off state. Due to the integrator output signal v_intResonant current i with secondary side_sProportional ratio of i_sCan be given by v_intIs indirectly known. In practice, only i needs to be in one period due to the half-wave symmetry of the circuit waveform_s> 0, i.e. v_intA time > 0 is sufficient. Meanwhile, to avoid misjudgment caused by reverse recovery and parasitic parameters, v is used_intSame reference V slightly higher than zero_biasComparing, outputting the comparison result and recording as v_comp. When v is_int＞V_biasWhen the result v is compared_comp1, indicating that the body diodes of Q5, Q8 are in a current-passing state; when v is_int＜V_biasWhen the result v is compared_compAt 0, the body diodes of Q5 and Q8 are in the off state.

And 4, step 4: the controller captures the through-flow timing of the body diode. The controller outputs a signal v to the comparator_compThe rising edge and the falling edge of the switch are captured, so that the internal body of one switching period can be obtainedThe moment when the diode starts to flow and ends to flow. When v is captured_compIndicates the secondary side resonant current i at the rising edge of_sWhen the voltage starts to be positive, the body diodes of Q5 and Q8 start to flow, and the time is recorded as t_on(ii) a When v is captured_compAt the falling edge of (d), a secondary side resonant current i is indicated_sAfter the voltage has dropped to zero, the body diodes of Q5 and Q8 end to flow, and enter the cut-off state, and the time is recorded as t_off. For synchronous rectification, the driving signal makes the channels of Q5 and Q8 at t_on～t_offThe interval remains on and the rest of the time remains off.

And 5: the controller calculates the time for applying the on and off signals according to the detected through-current moment and the on and off delay of the driving circuit, and starts synchronous rectification in the next switching period. Because a certain delay exists in the switching process of the driving circuit and the MOSFET, in order to realize good synchronous rectification, the controller needs to compensate the detected through-current moment according to the driving delay and send a switching-on signal and a switching-off signal to the driving circuit in advance. The turn-on delay of Δ t in consideration of the driving circuit and the MOSFET switching process_onWith turn-off delay of Δ t_offThen the controller should be at t for the next switching cycle_on′＝t_on-Δt_onThe on signals of Q5 and Q8 are sent to the drive circuit at the moment_off′＝t_off-Δt_offAnd (3) sending out turn-off signals of Q5 and Q8 to realize synchronous rectification of Q5 and Q8. Due to the half-wave symmetry, the synchronous rectification of the Q6 and the Q7 can be realized only by delaying the driving signals of the Q5 and the Q8 by half a switching period, namely at 0.5T_s+t_on' applying Q6, Q7 turn-on signal at 0.5T_s+t_off' apply Q6, Q7 off signal.

Step 6: in each switching period thereafter, the controller determines the turn-on time t of the next period according to the detected polarity information of the secondary side current_onAnd off time t_offAnd outputs corresponding on and off signals in the next period.

FIG. 3 shows the synchronous rectification strategy of the bidirectional CLLC resonant converter proposed in the present invention during operationThe theoretical waveform diagram of (1). In FIG. 3, the switching frequency is lower than the resonance frequency (f)_s＜f_r) For example, the figure shows a theoretical waveform diagram of the synchronous rectification strategy of the bidirectional CLLC resonant converter in the working process. Is the secondary side current of the resonant cavity, i.e. the input current of the secondary side full bridge. Vsense is the voltage detected by the detection coil, which is proportional to the voltage across the resonant inductor. Vint is the signal resulting from the integration of Vsense, compared to a reference Vbias slightly above zero. Vcomp is a signal obtained after comparison between Vint and Vbias, and reflects the conduction condition of the secondary full-bridge body diode. The Drive is a secondary side bridge driving signal output by the controller and is used for realizing synchronous rectification of the secondary side bridge. And the controller performs synchronous rectification control on the secondary side bridge in the period of Ts-2 Ts according to the signals detected in the period of 0-Ts.

Finally, it is also noted that the above-mentioned lists merely illustrate a few specific embodiments of the invention. It is obvious that the invention is not limited to the above embodiments, but that many variations are possible. For example, the inductor current information obtained according to the strategy provided by the invention can also be applied to other purposes such as converter protection, closed-loop control and the like. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.