CN114301300A

CN114301300A - Wide-range bidirectional resonant soft-switching direct-current converter and control method thereof

Info

Publication number: CN114301300A
Application number: CN202111440987.5A
Authority: CN
Inventors: 刘斌; 李玲
Original assignee: Liu Sanying
Current assignee: Liu Sanying
Priority date: 2021-11-30
Filing date: 2021-11-30
Publication date: 2022-04-08

Abstract

The application relates to a wide-range bidirectional resonant soft-switching direct-current converter and a control method thereof, and the converter comprises a first direct-current power supply, a second direct-current power supply, an input energy storage filter capacitor, a primary bridge type conversion unit, an isolation transformer, a secondary bridge type conversion unit and an output energy storage filter capacitor, wherein the input energy storage filter capacitor, the primary bridge type conversion unit, the isolation transformer, the secondary bridge type conversion unit and the output energy storage filter capacitor are sequentially arranged between the first direct-current power supply and the second direct-current power supply; the invention applies PWM driving signals with proper frequency and time sequence to the primary bridge conversion unit and the secondary bridge conversion unit, and can realize wide-range soft switching conversion of positive and negative directions of direct-current voltage. The two-stage type voltage stabilization conversion effect at present can be achieved, the voltage stabilization conversion circuit is suitable for connecting loads or power supply devices with wider voltage ranges such as storage batteries, and high power density and high efficiency can be achieved.

Description

Wide-range bidirectional resonant soft-switching direct-current converter and control method thereof

Technical Field

The application relates to the technical field of direct current converters, in particular to a wide-range bidirectional resonant soft-switching direct current converter and a control method thereof.

Background

With the rapid development of energy storage products and related fields of battery devices, there is an increasing demand for power supply products that can be bidirectionally switched. At present, a plurality of devices gradually apply batteries, and the batteries need to be charged or discharged, and due to the natural wide voltage range characteristic of the batteries and the consideration of the compatibility of different products, the corresponding voltage range is wider and wider, so that two sets of circuits are conventionally adopted for charging and discharging respectively. Today, the implementation of bidirectional conversion has not been cost effective, while the conventional single-stage circuit has been inadequate in terms of efficiency and satisfactory charging or discharging over a wide voltage range.

As shown in fig. 1, the current conversion circuit for low voltage battery pack is generally in two ways: one is to adopt two stages, usually through a one-stage boosting or voltage-reducing scheme, and then through a one-stage DC/DC voltage-stabilizing conversion. The two-stage scheme is more costly and the efficiency of the two-stage conversion is reduced. The other is to change the turns ratio of the transformer by adopting a change-over switch, increase or decrease the turns ratio of the transformer by changing the turns ratio of the transformer or adopting a similar circuit, and the implementation method mentioned in the patent with the patent number of CN107733236B, as shown in fig. 2, the essence is to increase or decrease the transformer coil by an additional transformer conversion circuit, thereby realizing different voltage ratios, the control principle is simple and direct, but higher switching tube stress can be caused by the change of high turns ratio, simultaneously the inductance and leakage inductance parameters of the original main transformer can be changed, new current loop interference can be introduced, the problem that the sudden change of voltage between two stages can bring another series of parameter changes in control, the adjustment of the duty ratio of the step property is easy to generate oscillation, and the realizability of the soft switching cooperation condition of the other two converters is relatively poor; therefore, additional conversion circuits and transformers are required, and the whole converter is complex in structure and difficult to popularize and apply.

Disclosure of Invention

The invention aims to provide a wide-range bidirectional resonant soft-switching direct-current converter and a control method thereof, which can realize the high-efficiency conversion of a soft switch, can be relatively simple and can meet the bidirectional conversion of wide-range voltage, and solve the technical problems that in the prior art, a two-stage converter is required to carry out multiple conversion, a plurality of current-guiding circuit-connecting devices are required, and the loss is large due to the adoption of a soft switch which cannot realize full conversion, so that the converter is not suitable for being applied in places with limited volume or relatively high cost requirements.

The technical scheme adopted by the invention is as follows: a wide-range bidirectional resonant soft-switching direct-current converter comprises a first direct-current power supply, an input energy storage filter capacitor, a primary bridge type conversion unit, a first series resonance unit, an isolation transformer, a second series resonance unit, a secondary bridge type conversion unit, an output energy storage filter capacitor and a second direct-current power supply; the input energy storage filter capacitor is connected with the primary bridge type conversion unit in parallel, and the primary bridge type conversion unit is also connected with the first direct current power supply; the primary side of the isolation transformer is connected with the primary bridge type conversion unit after being connected with the first series resonance unit in series, and the secondary side of the isolation transformer is connected with the secondary conversion unit after being connected with the second series resonance unit in series; the output energy storage filter capacitor is connected with the secondary conversion unit in parallel; the secondary bridge type conversion unit is also connected with the second direct current power supply;

the primary bridge conversion unit and the secondary bridge conversion unit are full bridge conversion units or half bridge conversion units; the first series resonant unit comprises a first resonant capacitor and a first resonant inductor which are connected in series, and the second series resonant unit comprises a second resonant capacitor and a second resonant inductor which are connected in series; the first resonant capacitor is connected with the primary bridge type conversion unit, and the first resonant inductor is connected with the primary side of the isolation transformer; the second resonant capacitor is connected with the secondary bridge type conversion unit, and the second resonant inductor is connected with the secondary side of the isolation transformer;

when the primary bridge type conversion unit and/or the secondary bridge type conversion unit is a full bridge type conversion unit, the primary bridge type conversion unit comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube; the first switching tube and the third switching tube are connected in series to form a first bridge arm, the second switching tube and the fourth switching tube are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are connected in parallel; the drain electrodes of the first switching tube and the second switching tube are connected with the anode of the first direct-current power supply and one end of the input energy storage filter capacitor, and the source electrodes of the third switching tube and the fourth switching tube are connected with the cathode of the first direct-current power supply and the other end of the input energy storage filter capacitor; the first resonant capacitor is connected with the drain electrode of the third switching tube, and the primary side of the isolation transformer is connected with the drain electrode of the fourth switching tube; the secondary bridge type conversion unit comprises a fifth switching tube, a sixth switching tube, a seventh switching tube and an eighth switching tube, the fifth switching tube and the seventh switching tube are connected in series to form a third bridge arm, the sixth switching tube and the eighth switching tube are connected in series to form a fourth bridge arm, and the third bridge arm and the fourth bridge arm are connected in parallel; the drain electrodes of the fifth switching tube and the sixth switching tube are connected with the anode of the second direct-current power supply and one end of the output energy-storage filter capacitor, and the source electrodes of the seventh switching tube and the eighth switching tube are connected with the cathode of the second direct-current power supply and the other end of the output energy-storage filter capacitor; the second resonant capacitor is connected with the drain electrode of the eighth switching tube, and the secondary side of the isolation transformer is connected with the drain electrode of the seventh switching tube;

when the primary bridge type conversion unit or the secondary bridge type conversion unit is a half-bridge type conversion unit, the primary bridge type conversion unit comprises a first switch tube and a second switch tube which are connected in series, the drain electrode of the first switch tube is connected with the positive electrode of the first direct current power supply and one end of the input energy storage filter capacitor, and the source electrode of the second switch tube is connected with the negative electrode of the first direct current power supply and the other end of the input energy storage filter capacitor; the first resonant capacitor is connected with the drain electrode of the second switching tube, and the primary side of the isolation transformer is connected with the source electrode of the second switching tube; the secondary bridge type conversion unit comprises a third switching tube and a fourth switching tube which are connected in series, the drain electrode of the third switching tube is connected with the anode of the second direct current power supply and one end of the output energy storage filter capacitor, and the source electrode of the fourth switching tube is connected with the cathode of the second direct current power supply and the other end of the output energy storage filter capacitor; the second resonant capacitor is connected with the drain electrode of the fourth switch tube, and the secondary side of the isolation transformer is connected with the source electrode of the fourth switch tube.

Further, the first direct current power supply and the second direct current power supply are direct current power supplies, rectified alternating current power supplies, step power supplies with switch control or loads capable of providing power supply voltage.

Furthermore, when the primary bridge type conversion unit and the secondary bridge type conversion unit only perform unidirectional rectification conversion, all the first to eighth switching tubes are switching tubes; when the primary bridge type conversion unit and the secondary bridge type conversion unit are in an H-shaped full bridge structure, two switching tubes of a common source electrode, a common drain electrode or a direct series connection bridge arm are switching tubes, and the other two switching tubes are diodes.

Further, the switch tube is a high-frequency switch tube provided with a reverse diode, and the reverse diode is an integrated diode, a parasitic diode or an additional diode.

Furthermore, the input energy storage filter capacitor and the output energy storage filter capacitor are nonpolar capacitors or polar capacitors; when the first direct-current power supply or the second direct-current power supply is a step-change power supply, the input energy storage filter capacitor and the output energy storage filter capacitor are equivalent capacitors with controllable switches connected in series with capacitors; the first resonant inductor and the second resonant inductor are external inductors, coupling leakage inductors in the transformer or coupling inductors of the external inductors and the leakage inductors in the transformer.

Further, the resonant frequency of the first resonant capacitor and the first resonant inductor

Wherein lr1 is the inductance of the first resonant inductor, cr1 is the capacitance of the first resonant capacitor; resonance frequency of the second resonance capacitor and the second resonance inductor

Wherein lr2 is an inductance value of the second resonant inductor, cr2 is a capacitance value of the second resonant capacitor, and f1₀＝f2₀。

The control method of the wide-range bidirectional resonant soft-switching direct-current converter comprises the following steps:

s100: judging whether the working state of the direct current converter is a forward working state or a reverse working state according to the voltage which needs to be output by the power state setting circuit sampling or external communication detection direct current converter; the positive working state means that the first direct current power supply is input and the second direct current power supply is output; the reverse working state means that the second direct current power supply is input and the first direct current power supply is output;

s200: judging whether the working states of the primary bridge type conversion unit and the secondary bridge type conversion unit are in an inversion state or a rectification state, and performing corresponding sequential logic configuration and PWM (pulse width modulation) driving configuration; the duty ratio of the switching tubes in the primary bridge conversion unit and the secondary bridge conversion unit is not more than 0.5 at most, and enough dead time is reserved;

s300: according to the working state judged in the steps S100 and S200, PWM driving control signals are applied to the switching tubes of the primary bridge type conversion unit and the secondary bridge type conversion unit; when the working state is judged to be the forward working state, the primary bridge type conversion unit carries out inversion conversion, converts the voltage of the first direct current power supply into high-frequency pulses, couples the high-frequency pulses to the secondary bridge type conversion unit through the first series resonance unit, the isolation transformer and the second series resonance unit, carries out high-frequency rectification through the secondary bridge type conversion unit and then transmits the high-frequency rectified high-frequency direct current to the output energy storage filter capacitor and the second direct current power supply; when the reverse working state is judged, the secondary bridge type conversion unit carries out inversion conversion, the voltage of the second direct current power supply is transmitted to the secondary bridge type conversion unit through the output energy storage filter capacitor to carry out high-frequency pulse conversion, is coupled with the isolation transformer through the second series resonance unit, is transmitted to the primary bridge type conversion unit through the first series resonance unit to carry out high-frequency rectification conversion, and then transmits the direct current voltage to the input energy storage filter capacitor and the first direct current power supply.

S400: when the direct current converter works in a forward working state, if the voltage value of the first direct current power supply is coupled by the isolation transformer and is higher than the set voltage value of the second direct current power supply, the PWM driving applied by the primary bridge type conversion unit is adjusted to reduce the duty ratio, otherwise, the adjustment duty ratio is increased;

when the direct current converter works in a reverse working state, if the voltage value of the second direct current power supply is higher than the set voltage value of the first direct current power supply after being coupled by the isolation transformer, the PWM driving applied by the secondary bridge type conversion unit is adjusted to reduce the duty ratio, otherwise, the adjustment duty ratio is increased;

s500: after the switching tubes of the primary bridge type conversion unit and the secondary bridge type conversion unit are conducted according to the setting, all driving signals of the primary bridge type conversion unit and the secondary bridge type conversion unit are turned off, and the input energy storage filter capacitor and the output energy storage filter capacitor are enabled to carry out follow current.

In steps S300 to S500, when the dc converter operates in the forward operating state, if the PWM drive applied to the primary bridge conversion unit increases the duty ratio to the maximum limit value and still cannot meet the requirement of the voltage value of the second dc power supply, fixing the duty ratio, adjusting the operating frequency to the optimal operating frequency point, entering the boost mode, increasing the PWM drive to one of the switching tubes of the rectifying and conducting bridge arm of the secondary bridge conversion unit in the non-current period immediately before the next rectifying and conducting period starts, and otherwise gradually decreasing the PWM drive duty ratio applied to the primary bridge conversion unit and exiting the boost mode; when the direct current converter works in a reverse working state, if the duty ratio of the PWM drive applied to the secondary bridge type conversion unit is increased to the maximum limit value and still cannot meet the requirement of a first direct current power supply voltage value, the PWM drive is added to a switching tube of a rectification conduction bridge arm in the primary bridge type conversion unit in a non-current period for boosting before the next rectification conduction period is about to start, otherwise, the duty ratio of the PWM drive applied to the primary bridge type conversion unit is gradually reduced according to control, and the boosting mode is quitted.

Further, in steps S300 to S500, the operating frequencies of the PWM driving signals of the switching tubes of the primary bridge converting unit and the secondary bridge converting unit are the same, and the frequency interval is 95% to 115% of the natural resonant frequency.

Further, in steps S300 to S500, when the dc converter operates in the boost mode in the forward operating state, if the secondary bridge conversion unit is a full-bridge conversion unit, the PWM driving is applied to only one of the switching tubes of the rectifying and conducting bridge arm in the non-current period immediately before the next rectifying and conducting period starts, or the PWM driving is applied to both of the switching tubes of the rectifying and conducting bridge arm in the non-current period; if the secondary bridge type conversion unit is a half-bridge rectifier type converter, PWM driving is added to the switching tube of the non-rectification conducting bridge arm in the next rectification conducting period before the next rectification conducting period is started; when the direct current converter works in a reverse working state, if the direct current converter is in a boost mode and the primary bridge type conversion unit is a full-bridge type conversion unit, PWM (pulse width modulation) drive is applied to only one switching tube of a rectification conduction bridge arm in a non-current period before the next rectification conduction period is about to start, or PWM drive is added to both switching tubes of the rectification conduction bridge arm in the non-current period; if the primary bridge conversion unit is a half-bridge converter, PWM driving is only added to the switching tubes of the non-rectification conducting bridge arms in the period just before the next rectification conducting period starts.

Further, in steps S300 to S500, when the dc converter operates in the boost mode in the reverse operating state, the driving signal applied to the switching tube for boosting in the primary bridge converting unit is earlier than the driving signal applied to the secondary bridge converting unit, and the driving signal applied to the switching tube for boosting in the primary bridge converting unit is a delay signal of the synchronous rectification signal in the upper period, that is, the period of the delay signal is the sum of the synchronous rectification duty cycle, the boost duty cycle and the dead time; if the direct current converter works in a non-boosting mode, the switching tubes in the primary bridge conversion unit and the secondary bridge conversion unit apply synchronous rectification driving signals.

The invention has the beneficial effects that:

(1) from the structure and performance, the problem that the bidirectional direct current conversion in a wider range can be realized only by a two-stage voltage stabilizing conversion circuit in the prior art is solved, and the complexity of the conversion of a multi-stage circuit is simplified;

(2) in terms of control, the voltage control mode that the traditional series resonance conversion needs wide-range frequency modulation is changed, the voltage regulation is realized mainly by regulating the duty ratio of the switching tube of each conversion unit, and the voltage regulation method is close to the voltage regulation control principle of the traditional bridge converter and is relatively simple;

(3) in terms of soft switch implementation, the series resonance unit is utilized to realize the soft switch of wide-range bidirectional conversion, and the comprehensive performance of the series resonance soft switch and the traditional bridge converter in a wide range is realized; high voltage spike stress and hard switching losses are avoided.

(4) From the aspect of applicability, the limitation that the traditional direct current power supply only can be a relatively stable direct current power supply is changed, and after the input energy storage filter capacitor is connected with the controllable switch in series, the input direct current power supply can be a step power supply with switch control.

(5) Due to structural normalization control, the combined switching of a plurality of converters or transformer coils is overcome, so that the performance is more stable, and the comprehensive performance-price ratio is high.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a block diagram of a conventional DC converter;

FIG. 2 is a schematic circuit diagram of a conventional bidirectional DC conversion implementation;

FIG. 3 is a block diagram of an embodiment of the present invention;

FIG. 4 is a circuit schematic of an embodiment of the present invention;

FIG. 5 is a circuit diagram of a primary bridge conversion unit or a secondary bridge conversion unit according to an embodiment of the present invention;

FIG. 6 is a circuit diagram of a full bridge conversion unit according to an embodiment of the present invention;

FIG. 7 is a circuit diagram of the forward rectifying mode of operation according to the present invention;

FIG. 8 is a circuit diagram of the reverse rectification operating mode according to the embodiment of the present invention;

FIG. 9 is a schematic waveform diagram illustrating a forward buck mode of operation according to an embodiment of the present invention;

FIG. 10 is a waveform diagram illustrating a forward boost operation according to an embodiment of the present invention;

FIG. 11 is a schematic waveform diagram illustrating a reverse buck mode of operation according to an embodiment of the present invention;

fig. 12 is a waveform diagram illustrating a reverse boosting operation according to an embodiment of the present invention.

The reference signs explain: d1-a first diode, D2-a second diode, DA-diode A, DB-diode B, Q1-a first switch tube, Q2-a second switch tube, Q3-a third switch tube, Q4-a fourth switch tube, Q5-a fifth switch tube, Q6-a sixth switch tube, Q7-a seventh switch tube, Q8-an eighth switch tube, QA-switch tube A, QB-switch tube B, QC-switch tube C, QD-switch tube D, Lr 1-a first resonant inductor, Lr 2-a second resonant inductor, Lm-a main excitation inductor, Tra-isolation transformer, CrA-resonant capacitor A, CrB-resonant capacitor B, Cr-resonant capacitor, Lr-resonant inductor, Cr 1-a first resonant capacitor, Cr 2-a second resonant capacitor, C1-input energy-storage filter capacitor, c2-output energy storage filter capacitor, DC 1-first direct current power supply, DC 2-second direct current power supply.

Detailed Description

In order that the above objects, features and advantages of the present invention can be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those specifically described herein, and thus the present invention is not limited to the specific embodiments disclosed below.

Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this application belongs. The use of "first," "second," and similar terms in the description and claims of this patent application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. Also, the use of the terms "a" or "an" and the like do not denote a limitation of quantity, but rather denote the presence of at least one. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships are changed accordingly.

As shown in fig. 3 and 4, a wide-range bidirectional resonant soft-switching DC converter includes a first DC power supply DC1, an input energy storage filter capacitor C1, a primary bridge conversion unit, a first series resonance unit, an isolation transformer Tra, a second series resonance unit, a secondary bridge conversion unit, an output energy storage filter capacitor C2, and a second DC power supply DC 2; the input energy storage filter capacitor C1 is connected in parallel with the primary bridge conversion unit, and the primary bridge conversion unit is also connected with the first direct current power supply DC 1; the primary side of the isolation transformer Tra is connected with the first series resonance unit in series and then connected with the primary bridge type conversion unit, and the secondary side of the isolation transformer Tra is connected with the second series resonance unit in series and then connected with the secondary conversion unit; the output energy storage filter capacitor C2 is connected with the secondary conversion unit in parallel; the secondary bridge conversion unit is also connected with the second direct current power supply DC 2;

the primary bridge conversion unit and the secondary bridge conversion unit are full bridge conversion units or half bridge conversion units; the first series resonant unit comprises a first resonant capacitor Cr1 and a first resonant inductor Lr1 which are connected in series, and the second series resonant unit comprises a second resonant capacitor Cr2 and a second resonant inductor Lr2 which are connected in series; the first resonant capacitor Cr1 is connected to the primary bridge conversion unit, and the first resonant inductor Lr1 is connected to the primary side of the isolation transformer Tra; the second resonant capacitor Cr2 is connected to the secondary bridge conversion unit, and the second resonant inductor Lr2 is connected to the secondary side of the isolation transformer Tra;

when the primary bridge conversion unit and/or the secondary bridge conversion unit is a full bridge conversion unit, the primary bridge conversion unit comprises a first switch tube Q1, a second switch tube Q2, a third switch tube Q3 and a fourth switch tube Q4; the first switching tube Q1 and the third switching tube Q3 are connected in series to form a first bridge arm, the second switching tube Q2 and the fourth switching tube Q4 are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are connected in parallel; the drains of the first switching tube Q1 and the second switching tube Q2 are connected to the positive electrode of the first direct-current power supply DC1 and one end of the input energy-storage filter capacitor C1, and the sources of the third switching tube Q3 and the fourth switching tube Q4 are connected to the negative electrode of the first direct-current power supply DC1 and the other end of the input energy-storage filter capacitor C1; the first resonant capacitor Cr1 is connected to the drain of the third switching tube Q3, and the primary side of the isolation transformer Tra is connected to the drain of the fourth switching tube Q4; the secondary bridge type conversion unit comprises a fifth switching tube Q5, a sixth switching tube Q6, a seventh switching tube Q7 and an eighth switching tube Q8, the fifth switching tube Q5 and the seventh switching tube Q7 are connected in series to form a third bridge arm, the sixth switching tube Q6 and the eighth switching tube Q8 are connected in series to form a fourth bridge arm, and the third bridge arm and the fourth bridge arm are connected in parallel; drains of the fifth switching tube Q5 and the sixth switching tube Q6 are connected to an anode of the second DC power supply DC2 and one end of the output energy storage filter capacitor C2, and sources of the seventh switching tube Q7 and the eighth switching tube Q8 are connected to a cathode of the second DC power supply DC2 and the other end of the output energy storage filter capacitor C2; the second resonant capacitor Cr2 is connected to the drain of the eighth switching tube Q8, and the secondary side of the isolation transformer Tra is connected to the drain of the seventh switching tube Q7;

when the primary bridge conversion unit or the secondary bridge conversion unit is a half-bridge conversion unit, the primary bridge conversion unit comprises a first switching tube Q1 and a second switching tube Q2 which are connected in series, the drain of the first switching tube Q1 is connected with the positive electrode of the first direct-current power supply DC1 and one end of the input energy storage filter capacitor C1, and the source of the second switching tube Q2 is connected with the negative electrode of the first direct-current power supply DC2 and the other end of the input energy storage filter capacitor C1; the first resonant capacitor Cr1 is connected to the drain of the second switch Q2, and the primary side of the isolation transformer Tra is connected to the source of the second switch Q2; the secondary bridge type conversion unit comprises a third switching tube Q3 and a fourth switching tube Q4 which are connected in series, the drain electrode of the third switching tube Q3 is connected with the positive electrode of the second direct current power supply DC2 and one end of the output energy storage filter capacitor C2, and the source electrode of the fourth switching tube Q4 is connected with the negative electrode of the second direct current power supply DC2 and the other end of the output energy storage filter capacitor C2; the second resonant capacitor Cr2 is connected to the drain of the fourth switching tube Q4, and the secondary side of the isolation transformer Tra is connected to the source of the fourth switching tube Q4.

In the embodiment of the present invention, the first DC power supply DC1 and the second DC power supply DC2 are DC power supplies, rectified ac power supplies, step power supplies with switch control, or loads capable of providing power supply voltages. When the rectified three-phase alternating current is input as a direct current source, each phase voltage is different, and when the series switch is used for control switching, the rectified three-phase alternating current can be a step input power source. The input energy storage filter capacitor C1 and the output energy storage filter capacitor C2 are nonpolar capacitors or polar capacitors; when the first direct current power supply DC1 or the second direct current power supply DC2 is a step-change power supply, the input energy storage filter capacitor C1 and the output energy storage filter capacitor C2 are equivalent capacitors formed by connecting a controllable switch and a capacitor in series; the first resonant inductor Lr1 and the second resonant inductor Lr2 are external inductors, coupling leakage inductors inside the transformer or coupling inductors of the external inductors and the leakage inductors inside the transformer.

When the primary bridge type conversion unit and the secondary bridge type conversion unit only carry out unidirectional rectification conversion, all the first to eighth switch tubes Q1-Q8 are switch tubes; when the primary bridge type conversion unit and the secondary bridge type conversion unit are in an H-shaped full bridge structure, two switching tubes of a common source electrode, a common drain electrode or a direct series connection bridge arm are switching tubes, and the other two switching tubes are diodes. The switch tube is a high-frequency switch tube provided with a reverse diode, and the reverse diode is an integrated diode, a parasitic diode or an additional diode.

The resonant frequency of the first resonant capacitor Cr1 and the first resonant inductor Lr1

Wherein Lr1 is the inductance of the first resonant inductor Lr1, and cr1 is the first resonant inductorCapacitance of the capacitor Cr 1; the resonant frequency of the second resonant capacitor Cr2 and the second resonant inductor Lr2

Where Lr2 is the inductance of the second resonant inductor Lr2, Cr2 is the capacitance of the second resonant capacitor Cr2, and f1₀＝f2₀。

As shown in fig. 5, when the primary bridge conversion unit and the secondary bridge conversion unit perform bridge inversion or synchronous rectification, the primary bridge conversion unit may be a full-bridge conversion unit or a half-bridge conversion unit. Fig. 5(a) is a circuit diagram of a full-bridge converter, which is a full-bridge converter composed of a switching tube a QA, a switching tube B QB, a switching tube C QC and a switching tube D QD, and a series resonant unit composed of a resonant capacitor Cr and a resonant inductor Lr; fig. 5(b) is a connection manner of a half-bridge conversion unit, a switching tube a QA and a switching tube C QC are used to form a bridge arm, and a resonant capacitor Cr and a resonant inductor Lr together form a series resonant unit; fig. 5(C) shows another connection mode of the half-bridge conversion unit, where a switching tube a QA and a switching tube C QC are used to form a first bridge arm, a resonant capacitor a CrA and a resonant capacitor B CrB are connected in series to form another bridge arm, and crA ═ CrB ═ 1/2 × Cr, where crA is the capacitance value of the resonant capacitor a CrA, CrB is the capacitance value of the resonant capacitor B CrB, Cr is the capacitance value of the resonant capacitor Cr in fig. 5(a), and the resonant capacitor ACrA, the resonant capacitor B CrB and the resonant inductor Lr together form a series resonant unit. The series relation between the series resonance unit and the transformer coil, and the connection sequence of the resonance capacitor Cr and the resonance inductor Lr in the series loop can be adjusted.

As shown in fig. 6, when the primary bridge conversion unit and the secondary bridge conversion unit perform rectification conversion, the primary bridge conversion unit and the secondary bridge conversion unit may adopt full-bridge conversion units shown in fig. 6(a) -6 (C), fig. 6(a) adopts a full-bridge converter composed of a switching tube AQA, a switching tube B QB, a switching tube C QC and a switching tube D QD, and a series resonance unit is formed by a resonance capacitor Cr and a resonance inductor Lr; fig. 6(B) adopts a bridge arm formed by connecting a switching tube B QB and a switching tube D QD in series, and a diode ADA and a diode B DB in series, and similarly, a bridge arm formed by connecting a switching tube a QA and a switching tube C QC in series, and a diode a DA and a diode B DB in series; fig. 6(c) adopts a common drain connection mode of a switching tube a QA and a switching tube B QB, and a bridge arm is formed by connecting the switching tube B QB and a diode a DA in series, and another bridge arm is formed by connecting the switching tube a QA and a diode B DB in series; similarly, a common source connection mode of a switching tube C QC and a switching tube D QD can also be adopted, the switching tube C QC and a diode A DA are connected in series to form one bridge arm, and the switching tube D QD and a diode B DB are connected in series to form the other bridge arm.

The related rectifying or inverting circuits shown in fig. 5 and 6 are well known circuits, and the specific operation principle thereof will be understood by those skilled in the art and will not be further analyzed herein. The present invention is not limited to the above embodiments, and other combinations that can achieve the functions of the present invention are also within the scope of the present invention.

The control method adopted by the embodiment of the invention comprises the following steps:

s100: judging whether the working state of the direct current converter is a forward working state or a reverse working state according to the voltage which needs to be output by the power state setting circuit sampling or external communication detection direct current converter; the positive working state means that the first direct current power supply DC1 is input, and the second direct current power supply DC2 is output; the reverse working state means that the second direct current power supply DC2 is input, and the first direct current power supply DC1 is output;

s300: according to the working state judged in the steps S100 and S200, PWM driving control signals are applied to the switching tubes of the primary bridge type conversion unit and the secondary bridge type conversion unit; when the working state is judged to be the forward working state, the primary bridge type conversion unit carries out inversion conversion, the voltage of the first direct current power supply DC1 is converted into high-frequency pulses, the high-frequency pulses are transmitted to the secondary bridge type conversion unit through the coupling of the first series resonance unit, the isolation transformer Tra and the second series resonance unit, and the high-frequency pulses are transmitted to the output energy storage filter capacitor C2 and the second direct current power supply DC2 after being subjected to high-frequency rectification by the secondary bridge type conversion unit; when the reverse working state is judged, the secondary bridge type conversion unit carries out inversion conversion, the voltage of the second direct current power supply DC2 is transmitted to the secondary bridge type conversion unit through the output energy storage filter capacitor C2 to carry out high-frequency pulse conversion, is coupled with the isolation transformer Tra through the second series resonance unit, is transmitted to the primary bridge type conversion unit through the first series resonance unit to carry out high-frequency rectification conversion, and then is transmitted to the input energy storage filter capacitor C1 and the first direct current power supply DC 1.

S400: when the direct current converter works in a forward working state, if the voltage value of the first direct current power supply DC1 is coupled by the isolation transformer Tra and is higher than the set voltage value of the second direct current power supply DC2, the PWM drive applied by the primary bridge type conversion unit is subjected to duty ratio reduction regulation, otherwise, the regulation duty ratio is increased;

when the direct current converter works in a reverse working state, if the voltage value of the second direct current power supply DC2 is coupled by the isolation transformer Tra and is higher than the set voltage value of the first direct current power supply DC1, the PWM drive applied by the secondary bridge type conversion unit is subjected to duty ratio reduction regulation, otherwise, the regulation duty ratio is increased;

In steps S300 to S500, the operating frequencies of the PWM driving signals of the switching tubes of the primary bridge conversion unit and the secondary bridge conversion unit are the same, and the frequency interval is 95% to 115% of the natural resonant frequency. In the embodiment of the invention, the working frequency of the PWM driving signals of the switching tubes of the primary bridge conversion unit and the secondary bridge conversion unit is 102.5% of the natural resonant frequency.

When the direct current converter works in a forward working state, if the duty ratio of the PWM drive applied to the primary bridge type conversion unit is increased to the maximum limit value and still cannot meet the requirement of the voltage value of the second direct current power supply DC2, fixing the duty ratio, adjusting the working frequency to the optimal working frequency point, entering a boosting mode, increasing the PWM drive to one switching tube of a rectification conduction bridge arm of the secondary bridge type conversion unit in a non-current period before the next rectification conduction period is about to start, and otherwise, gradually reducing the duty ratio of the PWM drive applied to the primary bridge type conversion unit and exiting the boosting mode; when the direct current converter works in a reverse working state, if the duty ratio of the PWM drive applied to the secondary bridge type conversion unit is increased to the maximum limit value and still cannot meet the requirement of the voltage value of the first direct current power supply DC1, the PWM drive is added to the switching tube of the rectification conduction bridge arm in the primary bridge type conversion unit in the period which is not the period for boosting before the next rectification conduction period is started, and otherwise, the duty ratio of the PWM drive applied to the primary bridge type conversion unit is gradually reduced according to the control and the boosting mode is quitted.

When the direct current converter works in a boost mode in a forward working state, if the secondary bridge type conversion unit is a full-bridge type conversion unit, PWM (pulse width modulation) drive is applied to only one switching tube of a rectification conduction bridge arm in a non-current period before the next rectification conduction period is about to start, or PWM drive is added to two switching tubes of the rectification conduction bridge arm in the non-current period; if the secondary bridge type conversion unit is a half-bridge rectifier type converter, PWM driving is added to the switching tube of the non-rectification conducting bridge arm in the next rectification conducting period before the next rectification conducting period is started; when the direct current converter works in a reverse working state, if the direct current converter is in a boost mode and the primary bridge type conversion unit is a full-bridge type conversion unit, PWM (pulse width modulation) drive is applied to only one switching tube of a rectification conduction bridge arm in a non-current period before the next rectification conduction period is about to start, or PWM drive is added to both switching tubes of the rectification conduction bridge arm in the non-current period; if the primary bridge conversion unit is a half-bridge converter, PWM driving is only added to the switching tubes of the non-rectification conducting bridge arms in the period just before the next rectification conducting period starts.

When the direct current converter works in a boost mode in a reverse working state, a driving signal applied to a switching tube for boosting in the primary bridge conversion unit is earlier than a driving signal applied to the secondary bridge conversion unit, and the driving signal applied to the switching tube for boosting in the primary bridge conversion unit is a delay signal of an upper-period synchronous rectification signal, namely the period of the delay signal is the sum of a synchronous rectification duty ratio, a boost duty ratio and dead time; if the direct current converter works in a non-boosting mode, the switching tubes in the primary bridge conversion unit and the secondary bridge conversion unit apply synchronous rectification driving signals.

If it is determined that the embodiment of the present invention is in the forward operation mode, i.e., the first dc power voltage is converted into the second dc power voltage, according to the above-mentioned control method, the operating frequency of the primary bridge converting unit is set to the resonant frequency of the first series resonant unit

In this case, the secondary bridge converting unit functions as a full bridge rectifier, and a synchronous rectification signal may be applied to the secondary bridge converting unit in order to obtain high efficiency. For convenience of discussion, the fifth switching tube Q5 and the sixth switching tube Q6 may be regarded as diode rectification without any driving signal, and fig. 4 may be simplified into a circuit diagram as shown in fig. 7; according to the calculation, if the output voltage is the highest voltage point of the second direct current power supply DC2, the output voltage is converted to the input side through the turn ratio of the isolation transformer Tra, and the converted output voltage is slightly lower than the input voltage. Therefore, according to the control method, the duty ratio of the bridge conversion driving applied to the first switching tube Q1, the second switching tube Q2, the third switching tube Q3 and the fourth switching tube Q4 is about 50%, preferably 47.5%, and due to the existence of the first series resonant unit in the primary side loop of the isolation transformer Tra, the operating frequency of the primary side bridge converter needs to be adjusted so that the operating frequency of the primary side bridge converter is higher than the resonant frequency, for example, 102.5% f 1. At this time, the primary bridge conversion unit is equal to a series LLC full-bridge converter, and the first switching tube Q1, the second switching tube Q2, the third switching tube Q3 and the fourth switching tube Q4 all realize soft switching; the relevant specific operation mode is not essentially different from the conventional LLC conversion,it will be understood by those skilled in the art that no further description is provided herein.

In the forward operation mode, if the bridge conversion driving duty ratio applied to the first switching tube Q1, the second switching tube Q2, the third switching tube Q3 and the fourth switching tube Q4 is too large to make the output voltage higher than the voltage to be regulated, the driving duty ratio of the first switching tube Q1, the second switching tube Q2, the third switching tube Q3 and the fourth switching tube Q4 of the primary bridge conversion unit is adjusted to be small, which is called a step-down mode; at this time, after the duty ratio of the primary bridge conversion unit is turned off, since the current of the resonant circuit cannot suddenly change, the electromotive forces of the first resonant inductor Lr1 and the exciting inductor Lm change, and the current on the primary side of the isolation transformer Tra freewheels through the anti-parallel diode of the switching tube that was not turned on before. If the duty ratios of the switching tubes are all turned off at this time, the follow current reversely charges the input energy storage filter capacitor C1 or the first direct current power supply DC1, and meanwhile, the secondary side of the isolation transformer Tra releases part of energy originally stored in the second resonant inductor Lr2 and the excitation inductor Lm due to the transformer coupling voltage to enable follow current to be conducted; however, if the duty ratio of the common-source switching tube, the common-drain switching tube, or the two switching tubes of one of the direct series arms applied to the primary full-bridge conversion unit is fixed to 47.5%, and the driving waveform is as shown in fig. 9, the freewheeling current circulates through the turned-on common-source switching tube or the common-drain switching tube, for example, the third switching tube Q3 and the fourth switching tube Q4, the series voltage of the first resonant inductor Lr1 and the first resonant capacitor Cr1 is applied to the isolation transformer Tra, and the energy is coupled and transferred to the secondary side, that is, the energy is rectified and output through the secondary side. The difference between the two methods is that the follow current characteristic of the traditional buck converter is more approached by the latter method. Meanwhile, under the conversion characteristic, the output voltage is lower, mainly because of the loss of effective duty ratio caused by the volt-second balance characteristic of a transformer and an inductor during the follow current; in contrast, the magnetic reset process of the primary side freewheeling energy returning to the input energy storage filter capacitor C1 is faster, so that after the next turn-on, the effective transfer time of the current is longer, and the energy transferred to the secondary side by the backward flow is more, and the loss is also larger.

Therefore, in the embodiment of the present invention, when the full-bridge converter is in the inverter operating mode, if the full-bridge converter needs the buck mode, differential driving is preferentially applied to two switching tubes that are turned on each time, one of the two switching tubes is duty ratio driving obtained according to control calculation, and the other switching tube is fixed maximum duty ratio driving or driving with a duty ratio of 47.5%, that is, the duty ratio applied to the full-bridge common-source switching tube, the common-drain switching tube, or two switching tubes of one of the direct series-connected bridge arms at this time is fixed to 47.5% or close to the maximum duty ratio, so that the state of the full-bridge conversion unit in the freewheel operating mode is changed, and the embodiment of the present invention is closer to the freewheel characteristic of the conventional buck converter in the freewheel operating mode.

Under the forward working mode, according to the control method, if the duty ratio of the PWM drive applied to the primary conversion unit is increased to the maximum limit value and still the voltage requirement of the second DC power supply DC2 cannot be met, the PWM drive applied to the primary conversion unit is fixed to the maximum duty ratio, the working frequency is adjusted to the optimal working frequency point, and the boost mode is entered, the PWM drive can be added to one of the switching tubes of the rectifying and conducting bridge arm in the secondary bridge conversion unit in the non-current period immediately before the next rectifying and conducting period starts, the adjustment of the output voltage is realized by adjusting the duty ratio of the drive, and the boost mode is exited if the voltage requirement of the second DC power supply DC2 can be met without boosting. Meanwhile, when the duty ratio of the drive corresponds to the invalid duty ratio interval of the primary side of the isolation transformer Tra, after a switching tube of the primary side of the isolation transformer Tra is switched on and before the current is not corrected, the drive of the secondary bridge type conversion unit is only used for synchronous rectification, namely, the boost drive corresponds to the drive starting point of the primary side of the isolation transformer Tra, the invalid boost duty ratio in a short time exists, and the specific drive waveform time sequence can refer to fig. 10. Meanwhile, according to the principle of symmetry consistency of the topological structure, the first switching tube Q1 can be regarded as the sixth switching tube Q6, the second switching tube Q2 can be regarded as the fifth switching tube Q5, the third switching tube Q3 can be regarded as the eighth switching tube Q8, and the fourth switching tube Q4 can be regarded as the seventh switching tube Q7.

If it is determined that the embodiment of the present invention needs to operate in the reverse operation mode, i.e., converting the second dc voltage into the first dc voltage, the primary bridge converting unit is mainly in the rectification mode, and for the convenience of discussion, the circuit diagram shown in fig. 8 can be simplified in fig. 4. According to the principle of symmetry consistency of a topological structure, the first switching tube Q1 can be regarded as a sixth switching tube Q6, the second switching tube Q2 can be regarded as a fifth switching tube Q5, the third switching tube Q3 can be regarded as an eighth switching tube Q8, and the fourth switching tube Q4 can be regarded as a seventh switching tube Q7; the related principle in the reverse mode is the same as the forward operation mode discussed above, and details are not repeated herein, and the driving waveform in the reverse mode can refer to fig. 11, where only the driving application principle and the operation principle after entering the boost mode are analyzed.

Since the driving duty ratio of the fifth switching tube Q5, the sixth switching tube Q6, the seventh switching tube Q7 and the eighth switching tube Q8 in the secondary bridge conversion unit is applied to the maximum, the PWM driving needs to be added to one of the switching tubes of the bridge arm of the primary bridge conversion unit that is not in rectifying conduction in the present period, that is, the boost PWM driving needs to be added to the third switching tube Q3 or the fourth switching tube Q4 that is not in rectifying conduction in the present period, the first switching tube Q1 and the second switching tube Q2 can be synchronously rectified or regarded as diodes, the driving waveforms are as shown in fig. 12, and the driving signal applied to the primary bridge conversion unit should be slightly earlier than the driving signal of the secondary bridge conversion unit, generally at least 2% -5% of the period ahead. In the embodiment of the invention, the driving signal applied by the primary bridge converting unit is 200ns earlier than the driving signal of the secondary bridge converting unit. Because two of the switching tubes of the primary bridge conversion unit are in non-rectification conduction in the present period, namely in rectification conduction in the previous period or in a forward path of electromotive force of a rectification loop of the transformer, the mode of turning on the switching tubes in advance is zero-voltage turning on. Meanwhile, according to the conduction mode, in combination with synchronous rectification, the boost PWM drive can also be understood as the continuation of the PWM drive with the synchronous rectification function, and the value is equal to the sum of the synchronous rectification duty ratio plus the boost duty ratio and the dead time; after entering the next working period, because the port voltage enters a similar output side short-circuit state along with the reversal of the inductive electromotive force and the transformer induced voltage, the rectified voltage which is supposed to be applied to the primary side port of the primary bridge type conversion unit forms a path backflow on the third switching tube Q3 and the fourth switching tube Q4, and because the voltage of the first resonant capacitor Cr1 of the first series resonant unit and the voltage of the second resonant capacitor Cr2 of the second series resonant unit cannot change suddenly, and the transformer port voltage is directly coupled, the first series resonant capacitor Cr and the first series resonant inductor Lr are in an energy storage state; when the driving voltage applied to the third switching tube Q3 or the fourth switching tube Q4 is over, the short-circuit state disappears, and the first resonant inductor Lr1, the first resonant capacitor Cr1, the second resonant inductor Lr2 and the second resonant capacitor Cr2 continue to resonate and freewheel; the voltage of the second series resonant unit is superimposed by the coupling voltage on the secondary side of the isolation transformer Tra, so that the primary bridge conversion unit is turned on, thereby completing the step-up conversion process of the second DC power supply DC2 to supply power to the first DC power supply DC 1. Therefore, in the process, the third switching tube Q3 and the fourth switching tube Q4 realize zero-voltage zero-current turn-on and zero-voltage turn-off, and the first switching tube Q1 and the second switching tube Q2 realize zero-voltage turn-on and zero-voltage zero-current turn-off.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A wide-range bidirectional resonant soft-switching direct-current converter is characterized by comprising a first direct-current power supply, an input energy storage filter capacitor, a primary bridge type conversion unit, a first series resonance unit, an isolation transformer, a second series resonance unit, a secondary bridge type conversion unit, an output energy storage filter capacitor and a second direct-current power supply; the input energy storage filter capacitor is connected with the primary bridge type conversion unit in parallel, and the primary bridge type conversion unit is also connected with the first direct current power supply; the primary side of the isolation transformer is connected with the primary bridge type conversion unit after being connected with the first series resonance unit in series, and the secondary side of the isolation transformer is connected with the secondary conversion unit after being connected with the second series resonance unit in series; the output energy storage filter capacitor is connected with the secondary conversion unit in parallel; the secondary bridge type conversion unit is also connected with the second direct current power supply;

2. The wide range bidirectional resonant soft-switching dc converter of claim 1, wherein the first dc power supply and the second dc power supply are dc power supplies, rectified ac power supplies, step-by-step power supplies with switching control, or loads capable of providing power supply voltages.

3. The wide-range bidirectional resonant soft-switching dc converter according to claim 1, wherein the first to eighth switching transistors are all switching transistors when the primary bridge converting unit and the secondary bridge converting unit perform only one-way rectification conversion; when the primary bridge type conversion unit and the secondary bridge type conversion unit are in an H-shaped full bridge structure, two switching tubes of a common source electrode, a common drain electrode or a direct series connection bridge arm are switching tubes, and the other two switching tubes are diodes.

4. The wide-range bidirectional resonant soft-switching direct-current converter according to claim 3, wherein the switching tube is a high-frequency switching tube provided with a merged-inversion diode, and the merged-inversion diode is an integrated diode, a parasitic diode or an extra diode.

5. The wide-range bidirectional resonant soft-switching dc converter according to claim 1, wherein the input and output storage capacitors are non-polar capacitors or polar capacitors; when the first direct-current power supply or the second direct-current power supply is a step-change power supply, the input energy storage filter capacitor and the output energy storage filter capacitor are equivalent capacitors with controllable switches connected in series with capacitors; the first resonant inductor and the second resonant inductor are external inductors, coupling leakage inductors in the transformer or coupling inductors of the external inductors and the leakage inductors in the transformer.

6. The wide range bidirectional resonant soft-switching dc converter according to claim 1, wherein the resonant frequency of the first resonant capacitor and the first resonant inductor

7. A control method for a wide-range resonant bidirectional soft-switching DC converter, which is used for controlling the wide-range bidirectional resonant bidirectional soft-switching DC converter as claimed in any one of claims 1 to 6, comprises the following steps:

8. The method as claimed in claim 7, wherein in steps S300-S500, the operating frequencies of the PWM driving signals of the switching tubes of the primary bridge converting unit and the secondary bridge converting unit are the same, and the frequency range is 95% -115% of the natural resonant frequency.

9. The method as claimed in claim 7, wherein in steps S300 to S500, when the dc converter operates in the boost mode in the forward operating state, if the secondary bridge converting unit is a full-bridge converting unit, the PWM driving is applied to only one of the switching tubes of the rectifying and conducting bridge arm in the non-current period immediately before the next rectifying and conducting period starts, or the PWM driving is applied to both of the switching tubes of the rectifying and conducting bridge arm in the non-current period; if the secondary bridge type conversion unit is a half-bridge rectifier type converter, PWM driving is added to the switching tube of the non-rectification conducting bridge arm in the next rectification conducting period before the next rectification conducting period is started; when the direct current converter works in a reverse working state, if the direct current converter is in a boost mode and the primary bridge type conversion unit is a full-bridge type conversion unit, PWM (pulse width modulation) drive is applied to only one switching tube of a rectification conduction bridge arm in a non-current period before the next rectification conduction period is about to start, or PWM drive is added to both switching tubes of the rectification conduction bridge arm in the non-current period; if the primary bridge conversion unit is a half-bridge converter, PWM driving is only added to the switching tubes of the non-rectification conducting bridge arms in the period just before the next rectification conducting period starts.

10. The method as claimed in claim 7, wherein in steps S300 to S500, when the dc converter operates in the boost mode in the reverse operating state, the driving signal applied to the switching transistor for boosting in the primary bridge converting unit is earlier than the driving signal applied to the secondary bridge converting unit, and the driving signal applied to the switching transistor for boosting in the primary bridge converting unit is a delay signal of the synchronous rectification signal in the upper cycle, that is, the period of the delay signal is the sum of the synchronous rectification duty cycle, the boost duty cycle and the dead time; if the direct current converter works in a non-boosting mode, the switching tubes in the primary bridge conversion unit and the secondary bridge conversion unit apply synchronous rectification driving signals.