CN114301301A

CN114301301A - Wide-range resonant soft-switching bidirectional direct-current converter and control method thereof

Info

Publication number: CN114301301A
Application number: CN202111442903.1A
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
Also published as: WO2023098218A1

Abstract

The invention relates to a wide-range resonant soft-switching bidirectional direct-current converter and a control method thereof, wherein the wide-range resonant soft-switching bidirectional direct-current converter comprises a first direct-current power supply, an input energy storage filter capacitor, a primary bridge type conversion unit, a series resonance unit, an isolation transformer, a secondary conversion unit, a resonance buffer unit, an output energy storage filter unit and a second direct-current power supply; the series resonance unit comprises a resonance capacitor and a resonance inductor which are connected in series; the resonance buffer unit comprises a buffer switch tube and a buffer capacitor which are connected in series. The invention can realize the wide-range soft switching conversion of the positive direction or the negative direction of the direct current voltage by applying driving signals with proper frequency and proper time sequence to the switching tubes in the primary bridge type conversion unit, the secondary conversion unit and the resonance buffer unit. Compared with a traditional one-way or two-way converter, the two-stage voltage stabilization conversion effect can be achieved, the converter is suitable for being connected with a load or a power supply device with a wider voltage range such as a storage battery, and high power density and high efficiency can be achieved.

Description

Wide-range resonant soft-switching bidirectional 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 resonant soft-switching bidirectional 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 resonant soft-switching bidirectional 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, two-stage converters are required to perform multiple conversion, more 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 resonant soft-switching bidirectional direct-current converter comprises a first direct-current power supply, an input energy storage filter capacitor, a primary bridge type conversion unit, a series resonance unit, an isolation transformer, a secondary conversion unit, a resonance buffer unit, an output energy storage filter unit 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 series resonance unit in series, and the secondary side of the isolation transformer is connected with the secondary conversion unit; the resonance buffer unit is connected with the secondary conversion unit in parallel, the output energy storage filtering unit is connected with the resonance buffer unit in parallel, and the second direct current power supply is connected with the output energy storage filtering unit;

the primary bridge conversion unit is a full bridge conversion unit or a half bridge conversion unit; the secondary conversion unit is a full-bridge conversion unit or a full-wave rectification converter; the series resonance unit comprises a resonance capacitor and a resonance inductor which are connected in series; the resonant capacitor is connected with the primary bridge type conversion unit, and the resonant inductor is connected with the primary side of the isolation transformer; the resonance buffer unit comprises a buffer switch tube and a buffer capacitor which are connected in series; the output energy storage filtering unit comprises an energy storage inductor and an output energy storage filtering capacitor which are connected in series; the second direct-current power supply is connected with the output energy storage filter capacitor;

when the primary bridge conversion unit is a full-bridge conversion unit, the primary bridge 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 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; when the primary 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 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;

when the secondary conversion unit is a full-bridge conversion unit, the secondary 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 secondary side of the isolation transformer is connected with the drain electrodes of the seventh switching tube and the eighth switching tube; when the secondary conversion unit is a full-wave rectification converter, the secondary conversion unit comprises a fifth switching tube and a sixth switching tube; the drain electrode of the fifth switching tube is connected with the drain electrode of the sixth switching tube and then connected with the source electrode of the buffer switching tube and one end of the energy storage inductor; the source electrodes of the fifth switching tube and the sixth switching tube are connected with the secondary side of the isolation transformer, and the secondary side of the isolation transformer is further connected with one end of the buffer capacitor.

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.

Further, when the primary bridge converting unit and the secondary converting unit perform only unidirectional rectification conversion, the first to eighth switching tubes may be diodes, or high-frequency switching tubes 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 resonance inductor is an external inductor, a coupling leakage inductor in the transformer or a coupling inductor of the external inductor and the internal leakage inductor of the transformer.

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

s100: according to the power state setting circuit sampling or external communication detection direct current circuit device voltage that needs to be output, judging whether the working state of the direct current converter is a forward working state or a reverse working state; 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 judging whether the resonance buffer unit is in a rectification buffer resonance state or an inversion resonance state; corresponding time sequence logic configuration and PWM driving configuration are carried out; the duty ratio of the switching tubes in the primary bridge conversion unit and the secondary conversion unit is not more than 0.5 at most, and enough dead time is reserved; the frequency of a driving signal applied to the buffer switch tube Q9 is 2 times of the frequency of a switch tube driving signal in a primary side bridge conversion unit or a secondary conversion unit, and the working frequency of the primary side bridge conversion unit is the same as that of the secondary conversion unit;

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, the secondary conversion unit and the resonance buffer 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 side through the series resonance unit and the isolation transformer, carries out high-frequency rectification through the secondary conversion unit, and then transmits the high-frequency pulses to the resonance buffer unit, the output energy storage filtering unit and the second direct current power supply; when the reverse working state is judged, the secondary conversion unit carries out inversion conversion, the voltage of the second direct current power supply is transmitted to the secondary conversion unit through the output energy storage filtering unit and the resonance buffer unit to carry out high-frequency pulse conversion, is transmitted to the primary side from the secondary side through the coupling of the isolation transformer, is transmitted to the primary bridge conversion unit through the series resonance unit to carry out high-frequency rectification conversion, and then is transmitted to the input 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 coupled by the transformer and is higher than the set voltage value of the first direct current power supply, the PWM driving applied by the secondary 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 conversion unit and the secondary conversion unit are switched on according to the setting, all driving signals of the primary bridge conversion unit and the secondary conversion unit are switched off, and the input energy storage filter capacitor and the output energy storage filter unit are enabled to carry out follow current.

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

Further, in steps S300 to S500, when the dc converter operates in the forward operating state, if the secondary 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 conversion unit is a full-wave rectification converter, PWM driving is only applied to the non-rectification-conducted switching tube in the next rectification conduction period before the next rectification conduction period starts; when the direct current converter works in a reverse working state, if the direct current converter is in a boosting 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 conversion unit, PWM driving is only applied to the non-rectification-conduction switching tube in the next rectification conduction period before the next rectification conduction period starts.

Further, in steps S300 to S500, the duty ratio of the snubber switching tube is adjusted to realize the adjustment of a certain range of output voltage in the corresponding conversion mode and the soft switching state of the secondary conversion unit; when the direct current converter works in a forward working state, the PWM driving applied to the buffer switch tube is delayed from the PWM driving of the primary bridge type conversion unit, namely a certain opening dead zone is reserved, and meanwhile the PWM driving applied to the buffer switch tube at the closing moment is consistent with the PWM driving of the primary bridge type conversion unit; when the direct current converter works in a reverse working state, the PWM driving applied to the buffer switch tube is delayed from the PWM driving of the secondary conversion unit, namely a certain opening dead zone is reserved, and the minimum dead zone time after the PWM driving applied to the buffer switch tube is closed is consistent with the minimum dead zone time of the PWM driving of the secondary conversion unit; if the direct current converter works in a boosting mode in a reverse working state, the buffer switch tube is not turned off earlier than the switch tube connected with the synonym end of the primary bridge type conversion unit.

Further, in steps S300 to S500, when the dc converter operates in the boost mode in the reverse operation state, the driving signal applied to the switching tube of the primary bridge converting unit for performing the boost operation is earlier than the driving signal of the secondary converting unit, and the driving signal applied to the switching tube of the primary bridge converting unit for performing the boost operation 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 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 switching implementation, the mutual matching of the series resonance converter and the resonance buffer unit is utilized, the soft switching of wide-range bidirectional conversion is realized, and the comprehensive performance of the series resonance soft switching 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) In addition, due to structural normalization control, the combined switching of a plurality of converters or transformer coils is overcome, the performance is more stable, and the comprehensive cost performance 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 schematic diagram of an embodiment of a primary bridge conversion unit according to the present invention;

FIG. 6 is a diagram illustrating an exemplary implementation of a secondary transform unit connection according to an embodiment of the present invention;

FIG. 7 is a circuit diagram of an embodiment of the present invention in a forward rectifying mode of operation;

FIG. 8 is a circuit diagram of an embodiment of the present invention in reverse rectification mode of operation;

FIG. 9 is a schematic waveform diagram illustrating a forward rectification operation of an embodiment of the present invention;

fig. 10 is a waveform diagram illustrating a reverse rectification operation state according to an embodiment of the present invention.

The reference signs explain: d1-a first diode, D2-a second diode, D3-a third diode, D4-a fourth diode, 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, Q9-a snubber switch tube, QA-switch tube A, QB-switch tube B, QC-switch tube C, QD-switch tube D, L1-energy storage inductor, Lr-resonant inductor, Lm-main excitation inductor, Tra-isolation transformer, Cr-resonant capacitor, Cr 1-a first resonant capacitor, Cr 2-a second capacitor, Cs-snubber capacitor, C1-an 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 to 4, a wide-range resonant soft-switching bidirectional DC converter includes a first DC power supply DC1, an input energy storage filter capacitor C1, a primary bridge conversion unit, a series resonance unit, an isolation transformer Tra, a secondary conversion unit, a resonance buffer unit, an output energy storage filter unit, 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 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 secondary conversion unit; the resonance buffer unit is connected with the secondary conversion unit in parallel, the output energy storage filtering unit is connected with the resonance buffer unit in parallel, and the second direct current power supply DC2 is connected with the output energy storage filtering unit;

the primary bridge conversion unit is a full bridge conversion unit or a half bridge conversion unit; the secondary conversion unit is a full-bridge conversion unit or a full-wave rectification converter; the series resonance unit comprises a resonance capacitor Cr and a resonance inductor Lr which are connected in series; the resonant capacitor Cr is connected with the primary bridge conversion unit, and the resonant inductor Lr is connected with the primary side of the isolation transformer Tra; the resonance buffer unit comprises a buffer switching tube Q9 and a buffer capacitor Cs which are connected in series; the output energy storage filtering unit comprises an energy storage inductor L1 and an output energy storage filtering capacitor C2 which are connected in series; the second direct current power supply DC2 is connected with the output energy storage filter capacitor C2;

when the primary 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 resonant capacitor Cr 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; when the primary bridge type conversion unit is a half-bridge type conversion unit, the primary bridge type conversion unit comprises a first switching tube Q1 and a second switching tube Q2 which are connected in series, the drain electrode 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 electrode of the second switching tube Q2 is connected with the negative electrode of the first direct-current power supply DC1 and the other end of the input energy storage filter capacitor C1; the resonant capacitor Cr is connected to the drain of the second switching tube Q2, and the primary side of the isolation transformer Tra is connected to the source of the second switching tube Q2;

when the secondary conversion unit is a full-bridge conversion unit, the secondary conversion unit comprises a fifth switch tube Q5, a sixth switch tube Q6, a seventh switch tube Q7 and an eighth switch 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; the secondary side of the isolation transformer Tra is connected to the drains of the seventh switching tube Q7 and the eighth switching tube Q8; when the secondary transformation unit is a full-wave rectification transformer, the secondary transformation unit comprises a fifth switch tube Q5 and a sixth switch tube Q6; the drain electrode of the fifth switching tube Q5 is connected with the drain electrode of the sixth switching tube Q6 and then connected with the source electrode of the buffer switching tube Q9 and one end of the energy storage inductor L1; the sources of the fifth switching tube Q5 and the sixth switching tube Q6 are connected to the secondary side of the isolation transformer Tra, and the secondary side of the isolation transformer Tra is further connected to one end of the snubber capacitor Cs.

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 resonance inductor Lr is an external inductor, a coupling leakage inductor inside the transformer or a coupling inductor of the external inductor and the internal leakage inductor inside the transformer.

When the primary bridge converting unit and the secondary converting unit perform only unidirectional rectification conversion, the first to eighth switching tubes Q8 may be diodes, or high-frequency switching tubes provided with a reverse diode, where the reverse diode is an integrated diode, a parasitic diode, or an additional diode.

As shown in fig. 5, the primary bridge converting unit may be a full bridge converting unit or a half bridge converting 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 first resonant capacitor Cr1 and a second resonant capacitor Cr2 are used to form another bridge arm in series, and Cr1 is Cr2 is 1/2 Cr, where Cr1 is a capacitance value of a first resonant capacitor Cr1, Cr2 is a capacitance value of a second resonant capacitor Cr2, Cr is a capacitance value of a resonant capacitor Cr in fig. 5(a), and the first resonant capacitor Cr1, the second resonant capacitor Cr2, and a 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, the secondary conversion unit may be a full-bridge conversion unit or a full-wave rectifier converter. Fig. 6(a) is a circuit diagram of a full-bridge converter unit, which adopts a switching tube a QA, a switching tube B QB, a switching tube C QC and a switching tube D QD to form a full-bridge converter; FIGS. 6(b) and 6(c) illustrate two different connection modes of a full-wave rectifier converter, which is also called a push-pull converter; in fig. 6(b), the switching tube C QC and the switching tube D QD are connected by a common drain, and when used for rectification, they are called full-wave rectifiers; in the diagram (c), the switch tube a QA and the switch tube B QB are connected by common source, and the circuit functions as the circuit shown in fig. 6 (B).

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: according to the power state setting circuit sampling or external communication detection direct current circuit device voltage that needs to be output, judging whether the working state of the direct current converter is a forward working state or a reverse working state; 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, the secondary conversion unit and the resonance buffer unit; when the working state is judged to be in the forward working state, the primary bridge type conversion unit carries out inversion conversion, converts the voltage of the first direct current power supply DC1 into high-frequency pulses, couples the high-frequency pulses to the secondary side through the series resonance unit and the isolation transformer Tra, carries out high-frequency rectification through the secondary conversion unit, and then transmits the high-frequency pulses to the resonance buffer unit, the output energy storage filtering unit and the second direct current power supply DC 2; when the reverse working state is judged, the secondary conversion unit carries out inversion conversion, the voltage of the second direct current power supply DC2 is transmitted to the secondary conversion unit through the output energy storage filtering unit and the resonance buffer unit to carry out high-frequency pulse conversion, is transmitted to the primary side from the secondary side through the isolation transformer Tra coupling, is transmitted to the primary bridge conversion unit through the series resonance unit to carry out high-frequency rectification conversion, and then is transmitted to the input filter capacitor 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 transformer and is higher than the set voltage value of the first direct current power supply DC1, the PWM drive applied by the secondary conversion unit is subjected to duty ratio reduction regulation, otherwise, the duty ratio is regulated to be 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 converter 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 105% 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 in a non-current period of the secondary conversion unit 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 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 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 conversion unit is gradually reduced according to the control and the boosting mode is quitted.

When the direct current converter works in a forward working state, if the secondary conversion unit is a full-bridge 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 immediately before the next rectification conduction period starts, or PWM drive is applied to both switching tubes of the rectification conduction bridge arm in the non-current period; if the secondary conversion unit is a full-wave rectification converter, PWM driving is only applied to the non-rectification-conducted switching tube in the next rectification conduction period before the next rectification conduction period starts; when the direct current converter works in a reverse working state, if the direct current converter is in a boosting 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 conversion unit, PWM driving is only applied to the non-rectification-conduction switching tube in the next rectification conduction period before the next rectification conduction period starts.

The regulation of a certain range of output voltage in a corresponding conversion mode and the soft switching state of the secondary conversion unit are realized by regulating the duty ratio of the buffer switching tube Q9; when the direct current converter works in a forward working state, the PWM driving applied to the buffer switch tube Q9 is delayed from the PWM driving of the primary bridge type conversion unit, namely a certain opening dead zone is reserved, and meanwhile the PWM driving applied to the buffer switch tube Q9 at the closing moment is consistent with the PWM driving of the primary bridge type conversion unit; when the direct current converter works in a reverse working state, the PWM driving applied to the buffer switch tube Q9 is delayed from the PWM driving of the secondary conversion unit, namely a certain opening dead zone is reserved, and the minimum dead zone time after the PWM driving applied to the buffer switch tube Q9 is closed is consistent with the minimum dead zone time of the PWM driving of the secondary conversion unit; if the dc converter operates in the boost mode in the reverse operation state, the snubber switch Q9 should not be turned off earlier than the switch connected to the different-name end of the primary bridge conversion unit.

When the direct current converter works in a boost mode in a reverse working state, a driving signal applied to a switching tube which does boost work in the primary bridge conversion unit is earlier than a driving signal of the secondary conversion unit, and the driving signal applied to the switching tube which plays a role in 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 conversion unit apply synchronous rectification driving signals.

If it is determined that the forward operation mode is the forward operation mode, i.e., the first DC power supply DC1 voltage is converted into the second DC power supply DC2 voltage, according to the control method, the operating frequency of the primary side bridge converter is set to the resonant frequency of the series resonant unit

Where Lr is an inductance value of the resonant inductor Lr, and Cr is a capacitance value of the resonant capacitor Cr. The switching frequency of the snubber switch Q9 of the resonant snubber unit is 2f0, and the secondary converter unit functions as a full-bridge rectifier, and a synchronous rectification signal may be applied to the secondary converter unit to achieve high efficiency. For the sake of 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 the circuit diagram 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 45%, and the operating frequency of the primary side bridge converter is adjusted to be higher than the resonant frequency, for example, 105% × f0, due to the presence of the series resonant unit in the primary side loop of the isolation transformer Tra. At the moment, the full-bridge converter is equal to an LLC full-bridge converter, soft switching is realized by the first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the fourth switch tube Q4, meanwhile, in order to realize soft switching of the buffer switch tube Q9, PWM driving applied to the buffer switch tube Q9 is slightly delayed, starting current charges a buffer capacitor Cs through an anti-parallel diode of the buffer switch tube Q9, and then the buffer switch tube Q9 is applied with driving switching on, so that zero-voltage switching is formed. Over time, the secondary rectified current gradually increases and takes a sine wave shape, and the current on the output side changes linearly due to the existence of the energy storage inductor L1. Therefore, the current for charging the buffer capacitor Cs at this time is the secondary rectified current I-rec-sec minus the current I-L1 of the energy storage inductor L1, and as time goes by, the secondary rectified current gradually decreases and the output current gradually increases, so that the buffer capacitor Cs starts to store energy and the energy storage inductor L1 discharges.

When the switch tube of the primary bridge conversion unit is turned off, it can be approximately considered that the voltage before the energy storage inductor L1 is about to disappear, and if the buffer switch tube Q9 is turned off immediately or slightly delayed, it means that the energy storage inductor L1 needs to continue current through the secondary conversion unit immediately. Before freewheeling, the energy storage inductor L1 will draw a current equivalent to the parasitic capacitance of the secondary conversion unit and gradually decrease to zero voltage. Therefore, the snubber switch Q9 may be regarded as a zero voltage turn-off. When the primary bridge conversion unit is switched on next time and the current of the energy storage inductor L1 is not cut off and flows forwards, the current of the energy storage inductor L1 can only flow afterward through the secondary rectifier conversion bridge, so that the isolation transformer Tra is always clamped to be zero, and preparation is provided for the next zero-voltage switching-on. Meanwhile, in the conversion process, the buffer switch tube Q9 and the buffer capacitor Cs assist the soft switching-on or soft switching-off of the secondary conversion unit, absorb and buffer redundant current of the primary bridge conversion unit, and enable the energy storage inductor L1 to work in a state of being applied with pulse voltage, similar to a voltage reduction state, so that the defects that the original series resonant converter can only adjust voltage by frequency conversion, the adjustment range is not large, and the duty ratio adjustment is nonlinear are well overcome. Through the matching of the resonant buffer units, the embodiment of the invention not only obtains the advantages of soft switching conversion, but also realizes the advantages of control simplicity of buck converter buck, and the relevant waveform schematic diagram is shown in fig. 9.

Therefore, when the embodiment of the invention is in a forward working state, if voltage regulation is required, the buffer switching tube Q9 is required to cooperate with the series resonance unit on the primary side to regulate the duty ratio, thereby realizing stable voltage regulation and soft switching. If the duty ratio of the PWM drive applied to the primary bridge type conversion unit is increased to the maximum limit value, and the voltage requirement of the second direct current power supply DC2 still cannot be met, the PWM drive applied to the primary bridge type conversion unit is fixed to be the maximum duty ratio, the working frequency of the primary bridge type conversion unit is adjusted to the optimal working frequency point to enter a boosting mode, the PWM drive is added to one switching tube of a rectification conduction bridge arm of the secondary conversion unit in the period which is not before the next rectification conduction period, the adjustment of the output voltage is realized by adjusting the duty ratio of the PWM drive, and the boosting mode is exited if the voltage requirement of the second direct current power supply DC2 can be met without boosting.

If it is determined that the embodiment of the present invention needs to operate in the reverse operation mode, that is, the voltage of the second DC power supply DC2 is converted into the voltage of the first DC power supply DC1, at this time, the primary bridge conversion unit mainly operates in the rectification mode. If it is not necessary to enter the boost mode after the voltage of the second DC power supply DC2 is reversely converted by the turns ratio of the isolation transformer Tra according to the calculation, fig. 4 can be simplified as shown in fig. 8, and the related principle is well known to those skilled in the art. For ease of discussion, assuming that embodiments of the present invention require entering boost mode, a converter with bridge-type switching transistors is necessary, even if only reverse rectification. Therefore, 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 conversion unit is applied to the maximum, and the PWM driving is added to one of the switching tubes of the non-rectifying and conducting bridge arm in the current period of the primary bridge conversion unit, that is, the PWM driving is added to only the third switching tube Q3 or the fourth switching tube Q4 which are non-rectifying and conducting in the current period in fig. 4, and meanwhile, the applied driving signal should be slightly earlier than the driving signal of the secondary conversion unit, and generally at least 2% -5% of the period is advanced. In an embodiment of the invention, the driving signal applied by the primary bridge transforming unit is 200ns earlier than the driving signal of the secondary transforming 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. When the next working cycle is started, because of the reversal of electromotive force, the voltage which should be applied to the input port of the primary bridge conversion unit forms a backflow path on the third switching tube Q3 and the fourth switching tube Q4, because the voltage of the resonant capacitor Cr of the series resonant unit cannot suddenly change and the port voltage of the isolation transformer Tra is directly coupled, the voltage is equivalent to applying energy storage to the resonant inductor Lr, and meanwhile, the energy storage inductor L1 on the secondary side is also in an energy storage state because the current flows through, the buffer switching tube Q9 is turned on because of applying a driving signal, and the buffer switching tube Q9 serves as a voltage source to supply power to the isolation transformer Tra, so as to make up the part of current which cannot be supplied by the energy storage inductor L1.

When the driving voltage applied to the third switching tube Q3 or the fourth switching tube Q4 is over, the short-circuit state disappears, the current of the resonant inductor Lr cannot be reversed immediately, and the induced electromotive force of the resonant inductor Lr can only carry out follow current in the reverse direction, so that the coupling voltage on the secondary side of the isolation transformer Tra is superposed with the voltage of the series resonant unit to turn on the primary bridge conversion unit, thereby completing the conversion process of supplying power from the second dc source to the first dc source. Meanwhile, the on/off of the snubber switch Q9 is directly related to the discharge supplementary energy of the snubber capacitor Cs, and therefore, the driving voltage of the snubber switch Q9 cannot be turned off before the rectification process of the primary bridge conversion unit is finished. After the buffer capacitor Cs starts to be charged reversely, the buffer switch tube Q9 must be turned off before the turned-on bridge arms of the fifth switch tube Q5, the sixth switch tube Q6, the seventh switch tube Q7 and the eighth switch tube Q8 are turned off, so as to obtain zero-voltage turn-off. At the same time when the opened arms of the fifth, sixth, seventh and eighth switching tubes Q5, Q6, Q7 and Q8 start to close, the current in the isolation transformer Tra cannot be immediately reversed, and only the current can be reversed through the parallel diode of the previously non-opened arm in the fifth, sixth, seventh and eighth switching tubes Q5, Q6, Q7 and Q8, that is, the current in the primary side coil of the isolation transformer Tra is reversely released to the side of the second DC power supply DC2, and the current direction of the energy storage inductor L1 cannot be reversed or suddenly changed, so that the voltage is continuously increased at the junction of the two currents, and finally the current is clamped and absorbed by the buffer capacitor Cs through the parallel diode of the buffer switching tube Q9. Therefore, when the fifth switching tube Q5 and the eighth switching tube Q8 are turned on previously, the diodes connected in reverse order to the sixth switching tube Q6 and the seventh switching tube Q7 freewheel. Therefore, when the next stage is turned on, the sixth switching tube Q6 and the seventh switching tube Q7 achieve zero voltage turn-on.

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 resonant soft-switching bidirectional 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 series resonance unit, an isolation transformer, a secondary conversion unit, a resonance buffer unit, an output energy storage filter unit 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 series resonance unit in series, and the secondary side of the isolation transformer is connected with the secondary conversion unit; the resonance buffer unit is connected with the secondary conversion unit in parallel, the output energy storage filtering unit is connected with the resonance buffer unit in parallel, and the second direct current power supply is connected with the output energy storage filtering unit;

2. The wide-range resonant soft-switching bidirectional dc converter according to 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 supplying power supply voltages.

3. The wide-range resonant soft-switching bidirectional dc converter according to claim 1, wherein when the primary bridge converting unit and the secondary converting unit perform only one-directional rectifying conversion, the first to eighth switching transistors may be diodes, or high-frequency switching transistors provided with a nand diode, and the nand diode is an integrated diode, a parasitic diode or an extra diode.

4. The wide-range resonant soft-switching bidirectional 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 resonance inductor is an external inductor, a coupling leakage inductor in the transformer or a coupling inductor of the external inductor and the internal leakage inductor of the transformer.

5. A control method for a wide-range resonant soft-switching bidirectional DC converter, which is used for controlling the wide-range resonant soft-switching bidirectional DC converter as claimed in any one of claims 1 to 4, comprises the following steps:

6. The method as claimed in claim 5, wherein in steps S300-S500, the PWM driving signals of the switching tubes of the primary bridge converting unit and the secondary bridge converting unit have the same operating frequency, and the frequency range is 95% -115% of the natural resonant frequency.

7. The method for controlling the wide-range resonant soft-switching bidirectional direct-current converter according to claim 5, wherein in steps S300 to S500, when the direct-current converter is in a forward operating state, if the PWM driving applied to the primary bridge conversion unit increases the duty ratio to the maximum limit value and still cannot meet the requirement of the second direct-current power supply voltage value, the duty ratio is fixed, the operating frequency is adjusted to the optimal operating frequency point, the boost mode is entered, the PWM driving is increased for one of the switching tubes of the rectifying and conducting bridge arm of the secondary conversion unit in the period other than the current period immediately before the next rectifying and conducting period starts, and otherwise, the PWM driving duty ratio applied to the primary bridge conversion unit is gradually decreased and the boost mode is exited; when the direct current converter works in a reverse working state, if the duty ratio of the PWM drive applied to the secondary conversion unit is increased to the maximum limit value and still cannot meet the requirement of the first direct current power supply voltage value, the PWM drive is added to the switching tube of the rectification conduction bridge arm in the primary bridge conversion unit in the period which is not the period for boosting before the next rectification conduction period is about to start, and otherwise, the duty ratio of the PWM drive applied to the primary bridge conversion unit is gradually reduced according to control and the boosting mode is quitted.

8. The method for controlling a wide-range resonant soft-switching bidirectional DC converter according to claim 5, wherein in steps S300-S500, when the DC converter is operating in a forward operating state, if the secondary 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, or both 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; if the secondary conversion unit is a full-wave rectification converter, PWM driving is only applied to the non-rectification-conducted switching tube in the next rectification conduction period before the next rectification conduction period starts; when the direct current converter works in a reverse working state, if the direct current converter is in a boosting 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 conversion unit, PWM driving is only applied to the non-rectification-conduction switching tube in the next rectification conduction period before the next rectification conduction period starts.

9. The control method of the wide-range resonant soft-switching bidirectional direct-current converter according to claim 5, wherein in steps S300 to S500, the regulation of the output voltage within a certain range in the corresponding conversion mode and the soft-switching state of the secondary conversion unit are realized by regulating the duty ratio of the buffer switching tube; when the direct current converter works in a forward working state, the PWM driving applied to the buffer switch tube is delayed from the PWM driving of the primary bridge type conversion unit, namely a certain opening dead zone is reserved, and meanwhile the PWM driving applied to the buffer switch tube at the closing moment is consistent with the PWM driving of the primary bridge type conversion unit; when the direct current converter works in a reverse working state, the PWM driving applied to the buffer switch tube is delayed from the PWM driving of the secondary conversion unit, namely a certain opening dead zone is reserved, and the minimum dead zone time after the PWM driving applied to the buffer switch tube is closed is consistent with the minimum dead zone time of the PWM driving of the secondary conversion unit; if the direct current converter works in a boosting mode in a reverse working state, the buffer switch tube is not turned off earlier than the switch tube connected with the synonym end of the primary bridge type conversion unit.

10. The method for controlling a wide-range resonant soft-switching bidirectional DC converter according to claim 5, wherein in steps S300-S500, when the DC converter operates in a boost mode in a reverse operation state, the driving signal applied to the switching tube of the primary bridge converting unit for performing the boost operation is earlier than the driving signal applied to the secondary converting unit, and the driving signal applied to the switching tube of the primary bridge converting unit for performing the boost operation 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 conversion unit apply synchronous rectification driving signals.