CN117477962B - Control method suitable for reverse discharge of LLC full-bridge direct-current converter - Google Patents
Control method suitable for reverse discharge of LLC full-bridge direct-current converter Download PDFInfo
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Abstract
The application relates to a control method suitable for reverse discharge of LLC full-bridge direct current converter, which is characterized in that the driving of an upper tube or a lower tube applied to each group of diagonal switching tubes in a primary full-bridge conversion unit and a secondary full-bridge conversion unit is the maximum duty ratio under a buck mode, the effective common on time is set to be within 45-55% of the resonance period, and the duty ratio is 50%; the driving of the upper tube or the lower tube applied to each group of diagonal switching tubes in the secondary full-bridge conversion unit is the maximum duty ratio in the boost mode, and the other switching tube is conducted together in advance by reference time td; the maximum duty ratio of the upper tube or the lower tube of the diagonal switching tube in the primary full-bridge conversion unit is applied to drive, the reference time td is delayed for the secondary full-bridge converter, and the other switching tube is advanced by 2 times, and is closed together by the reference time td; the operating frequency is adjusted according to the output voltage. The application can adapt to direct current conversion in a wide range and realize soft switching, reduce reactive circulation and realize high efficiency.
Description
Technical Field
The application relates to the field of power electronic converters, in particular to a control method suitable for reverse discharge of an LLC full-bridge direct current converter.
Background
With the rapid development of new energy storage products and related fields of battery equipment, the scenes of applying power batteries are more and more, such as power lithium batteries and hydrogen energy batteries, so that the demands for power products capable of performing bidirectional conversion on a wide range of battery voltages are more and more, and the power products are used for matching batteries to charge and discharge, but due to the characteristics of the lithium batteries and the like in a natural wide voltage range and the consideration of the compatibility of a plurality of batteries which cannot be connected in series, the voltage range required by the power products is also enlarged, so that the traditional LLC control mode, particularly the reverse discharge control method, is not suitable for the current technical requirements and needs to be improved in the technical method.
Patent document CN116155108B discloses a control method of bidirectional LLC resonant dc converter capable of voltage stabilization in a wide range, wherein the mentioned control method, compared with other traditional variable frequency control methods of adjusting duty ratio or phase shifting control fixed at resonant frequency or directly performing full duty ratio, can realize voltage adjustment in a wide range and soft switching in a larger extent in LLC full-bridge converter topology, but according to the control method, when the secondary full-bridge switching tube is turned off in a reverse buck mode, a larger current may be generated, and meanwhile, a larger reactive circulation recharge is generated in a boost mode, thereby causing cost increase and loss increase and even reliability decrease, and further affecting efficiency and switching tube type selection use.
Disclosure of Invention
The invention aims to provide a control method suitable for reverse discharge of an LLC full-bridge direct-current converter, which solves and optimizes the problems of inadaptation to reverse wide-range voltage stabilizing conversion application scenes, realization of soft switching only by a part of power section or voltage section and larger reactive circulation existing in the prior LLC full-bridge converter control technology.
The technical scheme adopted by the invention is as follows: a control method suitable for reverse discharge of an LLC full-bridge dc converter, said control method comprising the steps of:
s100: reading related setting conditions and sampling signals through an external controller, and judging whether the external working conditions meet normal working conditions or not and whether the LLC full-bridge direct current converter needs to work in a reverse discharge mode or not; if the external controller judges that the LLC full-bridge direct current converter needs to work in a forward working mode or other working modes, the related working modes are continuously executed, and if the external controller judges that the working conditions are met and the LLC full-bridge direct current converter needs to work in a reverse discharging mode, the step S200 is executed;
S200: entering an LLC full-bridge direct current converter reverse discharge control mode, wherein in the mode, a second direct current power supply at the secondary full-bridge conversion unit side is used as an input, and a first direct current power supply at the primary full-bridge conversion unit side is used as an output or load end; if the external controller judges that the LLC full-bridge direct-current converter needs to realize the voltage-reducing control of the input voltage or the control output gain is less than or equal to 1, the LLC full-bridge direct-current converter is marked as a voltage-reducing mode, and if the external controller judges that the LLC full-bridge direct-current converter needs to realize the voltage-increasing control of the input voltage or the control output gain is more than or equal to 1, the LLC full-bridge direct-current converter is marked as a voltage-increasing mode; taking 45-55% of the resonance period of the series resonance unit as reference time T 0, recording 2 times of time T 0 as reference time T 0, and recording the switching frequency under the corresponding time as f 0; the series resonance frequency of the LLC full-bridge direct-current converter is denoted as fr, and the corresponding series resonance period is denoted as Tr; the working frequency of the switching tube is recorded as fs, and the corresponding working period is recorded as Ts; adjusting the frequency to a corresponding boosting mode or a corresponding step-down mode according to voltage feedback of the input end and the output end, and working;
S300: when the LLC full-bridge direct-current converter works in a buck mode, the working frequency fs applied to the switching tubes in the secondary full-bridge conversion unit is lower than or equal to the series resonance frequency fr, and the total duty ratio of the driving of each switching tube in the LLC full-bridge direct-current converter including dead zones is less than or equal to 50%; the driving of one upper tube or lower tube of each group of diagonal switching tubes which are conducted in a rotating way is applied to the secondary full-bridge conversion unit, the effective common conduction time of each group of diagonal switching tubes which are conducted in the rotating way is set as the reference time t 0; meanwhile, switching conversion of the secondary full-bridge conversion unit is cooperated with driving of corresponding switching tubes connected with the same-name end of the isolation transformer in the primary full-bridge conversion unit, driving of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is the maximum duty ratio, and driving effective common conduction time of each group of diagonal switching tubes which are alternately conducted is consistent with effective common conduction time of the secondary full-bridge conversion unit; in the buck mode, the lower the working frequency of a switching tube in the secondary full-bridge conversion unit is, the more the buck is, the lowest working frequency is not lower than 50% of the series resonance frequency fr of the series resonance unit, the closer the working frequency is to fr, the closer the gain of the input voltage and the output voltage is to 1, and if the output voltage needs to be boosted, the working frequency fs needs to be boosted to enter a boost mode;
S400: when the LLC full-bridge direct-current converter works in a boost mode, the working frequency fs applied to a switching tube in the secondary full-bridge conversion unit is higher than or equal to the series resonance frequency fr; the total duty ratio of the driving of each switching tube in the LLC full-bridge direct current converter including dead zones is less than or equal to 50%; subtracting Ts/2 from T 0/2, and recording as reference time T d, wherein the drive of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the secondary full-bridge conversion unit is the maximum duty ratio, the other lower tube or upper tube is closed relative to advance reference time T d, and the effective common conduction time of each group of diagonal switching tubes which are alternately conducted in the secondary full-bridge conversion unit is Ts/2 minus dead time and reference time T d; meanwhile, the corresponding switching tube connected with the same-name end of the primary side of the isolation transformer in the primary full-bridge conversion unit is subjected to conversion of the secondary full-bridge conversion unit in cooperation with driving of which the lag time is reference time t d, the driving of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is the maximum duty ratio, meanwhile, the other switching tube in the diagonal switching tubes is relatively turned off by 2 times of reference time t d, and the driving effective common conduction time of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is Ts/2 minus dead time and2 times t d; in the boost mode, the higher the working frequency of a switching tube in the secondary full-bridge conversion unit is, the stronger the boost capability is, the closer the working frequency is to the series resonance frequency fr, the closer the gain of the input voltage and the output voltage is to 1, and if the output voltage needs to be reduced, the working frequency needs to be reduced to be converted into the buck mode.
Further, when the LLC full-bridge dc converter is in the boost mode and works with a heavy load, according to the magnitude of the output power or the ratio of the output power to the designed rated power, the time for driving each group of diagonal switching tubes in the secondary full-bridge conversion unit to be turned on in a rotating manner is gradually reduced from the reference time t d to zero, or the time for driving each group of diagonal switching tubes in the primary full-bridge conversion unit to be turned on in a rotating manner is gradually reduced from the reference time t d which is 2 times as long as the time for driving each group of diagonal switching tubes in the primary full-bridge conversion unit to be turned on in advance, and the time for driving each group of diagonal switching tubes in the primary full-bridge conversion unit to be turned off in a rotating manner is reduced to zero; the greater the output power, the less time the relative advance is turned off.
Further, when the LLC full-bridge dc converter is in the boost mode and works with a light load, according to the magnitude of the output power or the ratio of the output power to the designed rated power, which is received by the primary full-bridge conversion unit, the driving of the switching tube of each group of diagonal switching tubes that are turned on in a rotating manner in the primary full-bridge conversion unit is reduced to zero by 2 times of the reference time t d, and then the driving of the switching tube of each group of diagonal switching tubes that are turned on in a rotating manner in the secondary full-bridge conversion unit is adjusted to be gradually enlarged from the reference time t d, so that the smaller the output power is, the larger the time of the advanced shutdown is.
Further, in the step-down mode, when the working frequency fs of the switching tubes in the secondary full-bridge conversion unit is lower than the series resonance frequency fr and has fallen to the set frequency or the lower frequency limit, the effective conduction duty ratio of each group of diagonal switching tubes in the primary full-bridge conversion unit, which are turned on in a rotating way, is gradually enlarged, or the effective conduction duty ratio of each group of diagonal switching tubes in the secondary full-bridge conversion unit, which are turned on in a rotating way, is gradually reduced, or the effective conduction duty ratio of each group of diagonal switching tubes in the primary full-bridge conversion unit and the secondary full-bridge conversion unit, which are turned on in a rotating way, is simultaneously reduced, so that the output voltage is continuously reduced.
Further, in the boost mode, when the operating frequency fs of the switching tube in the secondary full-bridge conversion unit is higher than the series resonant frequency fr and has reached the set frequency or the upper frequency limit, the delay time applied by the driving of the switching tube connected with the same-name end of the isolation transformer in the primary full-bridge conversion unit converted by the secondary full-bridge conversion unit is continuously increased from the reference time t d, so that the continuous boost can be realized.
Further, the LLC full-bridge dc converter includes a first dc power supply V1, a first filter capacitor C1, a primary full-bridge conversion unit, a series resonance unit, an isolation transformer Tra, a secondary full-bridge conversion unit, a second filter capacitor C2, and a second dc power supply V2, which are sequentially connected;
The primary full-bridge conversion unit comprises a first full-bridge converter, the first full-bridge converter comprises a first switching tube Q1, a second switching tube Q2, a third switching tube Q3 and a fourth switching tube Q4, the first switching tube Q1 and the fourth switching tube Q4 form a group of diagonal switching tubes, and the second switching tube Q2 and the third switching tube Q3 form a group of diagonal switching tubes; the positive port DC1+ of the first direct current power supply V1 is connected with the drain electrode of the first switching tube Q1 and the drain electrode of the second switching tube Q2, and the negative port DC1 of the first direct current power supply V1 is connected with the source electrode of the third switching tube Q3 and the source electrode of the fourth switching tube Q4; one end of a resonance capacitor Cr in the series resonance unit is connected with the source electrode of the first switching tube Q1 and the drain electrode of the third switching tube Q3, the other end of the resonance capacitor Cr in the series resonance unit is connected with one end of a resonance inductor Lr in the series resonance unit, the other end of the resonance inductor Lr is connected with a primary side synonym end of an isolation transformer Tra, and the primary side synonym end of the isolation transformer Tra is connected with the source electrode of the second switching tube Q2 and the drain electrode of the fourth switching tube Q4;
the series resonance unit is formed by connecting a resonance capacitor Cr and a resonance inductor Lr in series, and the series resonance frequency of the series resonance unit is the resonance frequency of the series resonance unit Wherein Lr represents the resistance value of the resonant inductor Lr, cr represents the capacitance value of the resonant capacitor Cr; the isolation transformer Tra is an isolation transformer comprising an excitation inductance Lm, or an isolation transformer formed by connecting the isolation transformer and the excitation inductance Lm in parallel;
The secondary full-bridge conversion unit comprises a second full-bridge converter, the second full-bridge converter 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 eighth switching tube Q8 form a group of diagonal switching tubes, and the sixth switching tube Q6 and the seventh switching tube Q7 form a group of diagonal switching tubes; the secondary side synonym end of the isolation transformer Tra is connected with the source electrode of the sixth switching tube Q6 and the drain electrode of the eighth switching tube Q8 in the secondary full-bridge conversion unit, and the secondary side synonym end of the isolation transformer Tra is connected with the source electrode of the fifth switching tube Q5 and the drain electrode of the seventh switching tube Q7 in the secondary full-bridge conversion unit; the drain electrode of a sixth switching tube Q6 and the drain electrode of a fifth switching tube Q5 of the secondary full-bridge conversion unit are both connected with a positive port DC2+ of the second direct current power supply V2, and the source electrode of a seventh switching tube Q7 and the source electrode of an eighth switching tube Q8 are both connected with a negative port DC 2-of the second direct current power supply V2.
Further, when the LLC full-bridge dc converter is used in a reverse discharge mode, one switching tube of each group of diagonal switching tubes in the primary full-bridge conversion unit is switched to a rectifier diode, and if the LLC full-bridge dc converter is used in a buck mode, the rest switching tubes in the primary full-bridge conversion unit are driven to perform synchronous rectification or a maximum duty ratio, and if the LLC full-bridge dc converter is used in a boost mode, the rest switching tubes in the primary full-bridge conversion unit are driven to perform conversion of the cooperative secondary full-bridge conversion unit by the maximum duty ratio with a lag time of reference time t d, wherein the maximum duty ratio driving includes a dead time of not more than 50% of switching period.
Further, the secondary full-bridge conversion unit may be a full-wave rectification circuit or a voltage-multiplying rectification circuit capable of bidirectional conversion, when the working frequency fs of the switching tube in the secondary full-bridge conversion unit is less than or equal to fr, the effective on time of the driving of the switching tube applied to the full-wave rectification circuit or the voltage-multiplying rectification circuit is t 0, and when the working frequency fs of the switching tube in the secondary full-bridge conversion unit is more than or equal to fr, the driving of the switching tube applied to the full-wave conversion unit is the maximum duty ratio, including the dead time of 50%.
Further, the first dc power supply may be a three-level dc power supply, that is, a zero-voltage intermediate port may be added in addition to the positive port and the negative port, and at this time, two bridge arms in the primary full-bridge conversion unit are "I" type three-level bridge arms, "T" type three-level bridge arms, a combination of two three-level bridge arms, or a combination of two three-level bridge arms and two level bridge arms respectively.
Further, the isolation transformer Tra may be a multi-winding transformer, and each winding is connected to a rectifying or inverting unit to perform coupling transformation, so as to obtain other coupling voltages except the first direct current source and the second direct current source.
The invention has the beneficial effects that:
(1) From the voltage stabilizing range, special cooperative driving signals are applied to switching tubes of the primary full-bridge conversion unit and the secondary full-bridge conversion unit in a matched mode, and reverse discharge wide-range voltage boosting and voltage reducing regulation can be realized by adjusting the frequency;
(2) From the aspect of efficiency, the reactive circulation is reduced, the closing current of a secondary switching tube is reduced, and the efficiency is effectively improved besides the efficiency is improved due to single-stage conversion;
(3) Compared with the existing discharge control method of the bidirectional LLC converter, the soft switching implementation can better meet the soft switching implementation of different loads under a wide range of voltages;
(4) Because LLC full bridge is only one stage, can realize extremely simplifying control from the structure for the performance is more stable, and comprehensive price/performance ratio is high.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed 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 other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic circuit diagram of an LLC full-bridge converter in embodiment 1;
FIG. 2 is a schematic diagram of the primary-secondary cooperative driving of the LLC full-bridge converter under the control method of embodiment 1;
FIG. 3 is a schematic diagram of key waveforms of embodiment 1 in buck mode;
FIG. 4 is a schematic diagram of key waveforms of embodiment 1 in boost mode;
fig. 5 is a schematic circuit diagram of an LLC full-bridge converter in embodiment 2;
FIG. 6 is a schematic diagram of waveform references in buck mode for a prior art LLC full bridge converter control method;
fig. 7 is a schematic diagram of a bridge arm structure of a primary full-bridge conversion unit according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of other circuits of a secondary full-bridge inverter in an embodiment of the invention;
Fig. 9 is a schematic circuit diagram of the isolating transformer according to the embodiment of the present invention.
Detailed Description
In order that the above-recited objects, features and advantages of the present invention will be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than as described herein, and therefore the present invention is not limited to the specific embodiments disclosed below.
Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and the like in the description and in the claims, are not used for any order, quantity, or importance, but are used for distinguishing between different elements. Likewise, 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 "connected," and the like, are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", etc. are used merely to indicate a relative positional relationship, which changes accordingly when the absolute position of the object to be described changes.
The embodiment of the invention provides a control method suitable for reverse discharge of an LLC full-bridge direct-current converter, which comprises a first direct-current power supply, a first filter capacitor, a primary full-bridge conversion unit, a series resonance unit, an isolation transformer, a secondary full-bridge conversion unit, a second filter capacitor and a second direct-current power supply which are sequentially connected; if components/circuits continue to be added on the basis of this basic topology, different LLC converters can be morphed. If only one series resonant capacitor is added between the isolation transformer and the secondary full-bridge conversion unit, the bidirectional LLC resonant dc converter is specifically an equivalent LLC-containing CLLC converter in the circuit, and for convenience and simplicity in discussion, the control method of the embodiment of the invention is applicable to an LLC converter as shown in fig. 1 and an equivalent LLC-containing CLLC converter, but is not limited thereto.
Example 1
As shown in fig. 1, the full-bridge dc converter for LLC according to the embodiment includes a first dc power supply V1, a first filter capacitor C1, a primary full-bridge conversion unit, a series resonance unit, an isolation transformer Tra, a secondary full-bridge conversion unit, a second filter capacitor C2, and a second dc power supply V2, which are sequentially connected;
The primary full-bridge conversion unit comprises a first full-bridge converter, the first full-bridge converter comprises a first switching tube Q1, a second switching tube Q2, a third switching tube Q3 and a fourth switching tube Q4, the first switching tube Q1 and the fourth switching tube Q4 form a group of diagonal switching tubes, the first switching tube Q1 is an upper tube, the fourth switching tube Q4 is a lower tube, the second switching tube Q2 and the third switching tube Q3 form a group of diagonal switching tubes, the second switching tube Q2 is an upper tube, and the third switching tube Q3 is a lower tube; the positive port DC1+ of the first direct current power supply V1 is connected with the drain electrode of the first switching tube Q1 and the drain electrode of the second switching tube Q2, and the negative port DC1 of the first direct current power supply V1 is connected with the source electrode of the third switching tube Q3 and the source electrode of the fourth switching tube Q4; one end of a resonance capacitor Cr in the series resonance unit is connected with the source electrode of the first switching tube Q1 and the drain electrode of the third switching tube Q3, the other end of the resonance capacitor Cr in the series resonance unit is connected with one end of a resonance inductor Lr in the series resonance unit, the other end of the resonance inductor Lr is connected with a primary side synonym end of an isolation transformer Tra, and the primary side synonym end of the isolation transformer Tra is connected with the source electrode of the second switching tube Q2 and the drain electrode of the fourth switching tube Q4;
the series resonance unit is formed by connecting a resonance capacitor Cr and a resonance inductor Lr in series, and the series resonance frequency of the series resonance unit is the resonance frequency of the series resonance unit Wherein Lr represents the resistance value of the resonant inductor Lr, cr represents the capacitance value of the resonant capacitor Cr; the isolation transformer Tra is an isolation transformer comprising an excitation inductance Lm, or an isolation transformer formed by connecting the isolation transformer and the excitation inductance Lm in parallel;
the secondary full-bridge conversion unit comprises a second full-bridge converter, the second full-bridge converter 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 eighth switching tube Q8 form a group of diagonal switching tubes, the fifth switching tube Q5 is an upper tube, the eighth switching tube Q8 is a lower tube, the sixth switching tube Q6 and the seventh switching tube Q7 form a group of diagonal switching tubes, the sixth switching tube Q6 is an upper tube, and the seventh switching tube Q7 is a lower tube; the secondary side synonym end of the isolation transformer Tra is connected with the source electrode of the sixth switching tube Q6 and the drain electrode of the eighth switching tube Q8 in the secondary full-bridge conversion unit, and the secondary side synonym end of the isolation transformer Tra is connected with the source electrode of the fifth switching tube Q5 and the drain electrode of the seventh switching tube Q7 in the secondary full-bridge conversion unit; the drain electrode of a sixth switching tube Q6 and the drain electrode of a fifth switching tube Q5 of the secondary full-bridge conversion unit are both connected with a positive port DC2+ of the second direct current power supply V2, and the source electrode of a seventh switching tube Q7 and the source electrode of an eighth switching tube Q8 are both connected with a negative port DC 2-of the second direct current power supply V2.
When the LLC full-bridge direct current converter takes the side of the first direct current power supply V1 as input, the first direct current power supply V1 works as a power supply or an equivalent power supply to provide input energy for the whole converter, and the second direct current power supply V2 is an equivalent load or a load. When the LLC full-bridge direct current converter takes the side of the second direct current power supply V2 as input, the second direct current power supply V2 works as a power supply or an equivalent power supply to provide input energy for the whole converter, and the first direct current power supply V1 is a load or an equivalent load.
The converter-related circuit shown in fig. 1 constitutes a series connection in which the positions in the current loop are merely relative positions, and can be simply converted or shifted without changing the basic principle intended to be expressed in the present invention. The switching tube is a high-frequency switching tube provided with an anti-parallel diode or a high-frequency switching tube with an anti-parallel diode equivalent function; the anti-parallel diode is an integrated diode, a parasitic diode or an external diode; the relevant circuitry is also well known to those skilled in the art, and its specific principle of operation will be understood by those skilled in the art that it will not be further analyzed herein. The present invention is not limited to the above embodiments, and other combinations of the functions of the present invention are also within the scope of the present invention.
Aiming at the bidirectional LLC resonant direct current converter with various structures mentioned in the embodiment 1, the embodiment of the invention adopts the control method that:
S100: reading related setting conditions and sampling signals through an external controller, and judging whether the external working conditions meet normal working conditions or not and whether the LLC full-bridge direct current converter needs to work in a reverse discharge mode or not; and if the external controller judges that the LLC full-bridge direct current converter needs to work in a forward working mode or other working modes, continuing to execute the related working modes, and if the external controller judges that the working conditions are met and the LLC full-bridge direct current converter needs to work in a reverse discharging mode, executing step S200.
S200: entering an LLC full-bridge direct current converter reverse discharge control mode, wherein in the mode, a second direct current power supply at the secondary full-bridge conversion unit side is used as an input, and a first direct current power supply at the primary full-bridge conversion unit side is used as an output or load end; if the external controller judges that the LLC full-bridge direct-current converter needs to realize the voltage-reducing control of the input voltage or the control output gain is less than or equal to 1, the LLC full-bridge direct-current converter is marked as a voltage-reducing mode, and if the external controller judges that the LLC full-bridge direct-current converter needs to realize the voltage-increasing control of the input voltage or the control output gain is more than or equal to 1, the LLC full-bridge direct-current converter is marked as a voltage-increasing mode; taking 45-55% of the resonance period of the series resonance unit as reference time T 0, recording 2 times of time T 0 as reference time T 0, and recording the switching frequency under the corresponding time as f 0; the series resonance frequency of the LLC full-bridge direct-current converter is denoted as fr, and the corresponding series resonance period is denoted as Tr; the working frequency of the switching tube is recorded as fs, and the corresponding working period is recorded as Ts; and adjusting the frequency to a corresponding step-up mode or step-down mode according to the voltage feedback of the input end and the output end, and working.
S300: when the LLC full-bridge direct-current converter works in a buck mode, the working frequency fs applied to the switching tubes in the secondary full-bridge conversion unit is lower than or equal to the series resonance frequency fr, and the total duty ratio of the driving of each switching tube in the LLC full-bridge direct-current converter including dead zones is less than or equal to 50%; the driving of one upper tube or lower tube of each group of diagonal switching tubes which are conducted in a rotating way is applied to the secondary full-bridge conversion unit, the effective common conduction time of each group of diagonal switching tubes which are conducted in the rotating way is set as the reference time t 0; meanwhile, switching conversion of the secondary full-bridge conversion unit is cooperated with driving of corresponding switching tubes connected with the same-name end of the isolation transformer in the primary full-bridge conversion unit, driving of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is the maximum duty ratio, and driving effective common conduction time of each group of diagonal switching tubes which are alternately conducted is consistent with driving effective common conduction time of the secondary full-bridge conversion unit; in the buck mode, the lower the working frequency of a switching tube in the secondary full-bridge conversion unit is, the more the buck is, the lowest working frequency is not lower than 50% of the series resonance frequency fr of the series resonance unit, the closer the working frequency is to fr, the closer the gain of the input voltage and the output voltage is to 1, and if the output voltage needs to be boosted, the working frequency fs needs to be boosted to enter the boost mode.
In the step-down mode, when the working frequency fs of the switching tube in the secondary full-bridge conversion unit is lower than the series resonance frequency fr and has fallen to the set frequency or the lower frequency limit, the effective conduction duty ratio of each group of diagonal switching tubes in the primary full-bridge conversion unit in a rotating way is gradually enlarged, or the effective conduction duty ratio of each group of diagonal switching tubes in the secondary full-bridge conversion unit in the rotating way is gradually reduced, or the effective conduction duty ratio of each group of diagonal switching tubes in the primary full-bridge conversion unit and the secondary full-bridge conversion unit in the rotating way is simultaneously reduced, so that the output voltage is continuously reduced.
S400: when the LLC full-bridge direct-current converter works in a boost mode, the working frequency fs applied to a switching tube in the secondary full-bridge conversion unit is higher than or equal to the series resonance frequency fr; the total duty ratio of the driving of each switching tube in the LLC full-bridge direct current converter including dead zones is less than or equal to 50%; subtracting Ts/2 from T 0/2, and recording as reference time T d, wherein the drive of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the secondary full-bridge conversion unit is the maximum duty ratio, the other lower tube or upper tube is closed relative to advance reference time T d, and the effective common conduction time of each group of diagonal switching tubes which are alternately conducted in the secondary full-bridge conversion unit is Ts/2 minus dead time and reference time T d; meanwhile, the corresponding switching tube connected with the same-name end of the primary side of the isolation transformer in the primary full-bridge conversion unit is subjected to conversion of the secondary full-bridge conversion unit in cooperation with driving of which the lag time is reference time t d, the driving of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is the maximum duty ratio, meanwhile, the other switching tube in the diagonal switching tubes is relatively turned off by 2 times of reference time t d, and the driving effective common conduction time of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is Ts/2 minus dead time and2 times t d; in the boost mode, the higher the working frequency of a switching tube in the secondary full-bridge conversion unit is, the stronger the boost capability is, the closer the working frequency is to the series resonance frequency fr, the closer the gain of the input voltage and the output voltage is to 1, and if the output voltage needs to be reduced, the working frequency needs to be reduced to be converted into the buck mode.
In the boost mode, when the working frequency fs of the switching tube in the secondary full-bridge conversion unit is higher than the series resonance frequency fr and reaches the set frequency or the upper frequency limit, the hysteresis time applied by the driving of the switching tube connected with the same-name end of the isolation transformer in the primary full-bridge conversion unit which is converted by the cooperative secondary full-bridge conversion unit is continuously prolonged from the reference time t d, so that continuous boost can be realized.
When the LLC full-bridge direct-current converter works in the boost mode with heavy load, if the load connected with the V1 end of the first direct-current source or the equivalent load is larger and exceeds 60% or more of the rated load, according to the output power connected with the primary full-bridge conversion unit or the ratio of the output power to the designed rated power, the time for driving each group of diagonal switching tubes which are turned on in a rotating way in the secondary full-bridge conversion unit to be turned off in advance is gradually reduced from the reference time t d to zero, or the time for driving each group of diagonal switching tubes which are turned on in a rotating way in the primary full-bridge conversion unit to be turned on in advance is gradually reduced from the reference time t d which is 2 times, and the time for driving each group of diagonal switching tubes which are turned on in a rotating way in the primary full-bridge conversion unit to be turned off in advance is gradually reduced to zero; the greater the output power, the less time the relative advance is turned off.
When the LLC full-bridge direct current converter works in the boost mode with light load, if the load connected to the first direct current source end or the equivalent load is smaller and is lower than 10% of the rated load or lower, driving of a switching tube with the relative early closing time of 2 times of the reference time t d in each group of diagonal switching tubes which are in turn-on in the primary full-bridge conversion unit is reduced to zero according to the output power connected to the primary full-bridge conversion unit or the ratio of the output power to the designed rated power, and then driving of the switching tube with the relative early closing time of 2 times of the reference time t d in each group of diagonal switching tubes which are in turn-on in the secondary full-bridge conversion unit is regulated to be gradually enlarged from the reference time t d, and the smaller the output power is, the larger the early closing time is.
For the LLC full-bridge dc converter shown in fig. 1, when the converter is in an ideal state, the operating frequency may be greater than the series resonant frequency fr, with the lowest not approaching or exceeding the series-parallel resonant frequency fm, thereby ensuring a sufficient frequency margin, where,Lm represents the inductance value of the excitation inductance; and the circuit hardware parameters and load meet the gain of the input and output voltages over that frequency range are unidirectional. The switching tubes in the circuit are all provided with high-frequency switching tubes with inverse diode, or can be equivalently used as high-frequency switching tubes with inverse diode function.
The first dc power source V1 is assumed to be a dc input, the second dc power source V2 is a dc output or a load, and the working state of the converter in the control mode is a forward rectification mode, which is a common LLC forward conversion, or a so-called forward charging conversion, which belongs to a conversion known to those skilled in the art, and will not be described here. The second direct current power supply V2 is used as direct current input, the first direct current power supply V1 is used as direct current output or load, and the working state of the converter in the control mode is a reverse rectification mode, namely the reverse discharge conversion in the embodiment of the invention.
Assuming that the voltage reduction control of the input voltage is required to be realized or the control output gain is less than or equal to 1 through an external controller, the voltage reduction mode is recorded, 45-55% of the resonance period of the series resonance unit is taken as reference time T 0, 2 times of time T 0 is recorded as reference time T 0, and the switching frequency under the corresponding time is recorded as f 0; for simplicity of discussion, the series resonant frequency fr is directly used as the switching operating frequency f 0, and the frequency is adjusted to the corresponding buck-boost mode according to the voltage feedback of the input and output terminals to operate.
The working frequency applied to a switching tube in the secondary full-bridge conversion unit is lower than or equal to fr; the total duty ratio of the driving of each switching tube in the converter including dead zone is not more than 50%, the driving of one upper tube or lower tube of each group of diagonal switching tubes which are conducted in a rotating way is the maximum duty ratio, and the driving effective common conduction time of each group of diagonal switching tubes which are conducted in a rotating way after being conducted is set to be within 45-55% of the series resonance period of the series resonance unit, and the time is equal to t 0＝T0/2; meanwhile, synchronous driving is applied to switching tubes connected with the same-name ends of the isolation transformer Tra in the primary full-bridge conversion unit to cooperate with switching conversion of the secondary full-bridge conversion unit, and driving of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is the maximum duty ratio, and driving effective common conduction time of the upper tube or the lower tube is consistent with driving effective common conduction time of the secondary after each turn-on; the switching tube can be two upper tubes or lower tubes, or a left bridge arm or a right bridge arm works at the maximum duty ratio, then the other two switching tubes work at the duty ratio of the set effective common conduction time, or the driving of the maximum duty ratio is applied to the full bridge, and the required effective common conduction time is modulated through phase shifting. As shown in the driving waveforms of fig. 2, fig. 2 (a) and fig. 2 (b) each show a driving in this mode, the operating frequency in fig. 2 (a) is far from the series resonance frequency, and the operating frequency in fig. 2 (b) is near the resonance frequency. In the step-down mode, when the working frequency of a switching tube in the secondary full-bridge conversion unit is lower than the series resonance frequency fr and has fallen to the set frequency or the lower frequency limit, the effective conduction duty ratio of each group of diagonal switching tubes in the primary full-bridge conversion unit in a rotating way is gradually enlarged, or the effective conduction duty ratio of each group of diagonal switching tubes in the secondary full-bridge conversion unit in the rotating way is gradually reduced, or the effective conduction duty ratio of each group of diagonal switching tubes in the primary full-bridge conversion unit and the secondary full-bridge conversion unit in the rotating way is simultaneously reduced, so that the output voltage is continuously reduced. Meanwhile, in the mode, the lower the working frequency is, the more the voltage is reduced, and the lowest frequency is not lower than 50% of the series resonance frequency and higher than the series-parallel resonance frequency; the working frequency is close to f 0, the gain of the input voltage and the output voltage is infinitely close to 1, the output voltage needs to be boosted, and the working frequency needs to be increased to enter a boosting mode.
Fig. 3 is a key waveform of reverse discharge conversion performed by the LLC full-bridge dc converter, taking a parameter in a bidirectional LLC resonant dc converter control method capable of wide-range voltage stabilization (hereinafter referred to as a reference patent) in patent document CN116155108B as an example, the second dc power V2 is input, the first dc power V1 is output and has a load of 27 ohms, and the primary-secondary turn ratio of the isolation transformer Tra is 2:1, lm=50uh, lr=12uh, cr=88 nf, the voltage value v2=68v of the second dc power supply and applying the buck control mode related control method, when the operating frequency fs is about 100kHz, lower than the resonance frequency fr, the driving duty ratio of the sixth switching tube Q6 or the seventh switching tube Q7 on the secondary side and the driving duty ratio of the fifth switching tube Q5 or the eighth switching tube Q8 are 30%, the on time is about 3us, and is close to and slightly smaller than 50% of the series resonance period Tr, that is, within the range of 45-55% of the series resonance period; in the primary full-bridge conversion unit, the third switching tube Q3 or the fourth switching tube Q4 applies a driving duty ratio of 47%, the on time is about 4.7us, the duty ratio is close to 50%, and the dead time is 0.3us. The driving duty ratio applied by the first switching tube Q1 or the second switching tube Q2 is 29%, the on time is about 2.9us, the duty ratio is slightly less than 30%, a margin is left with respect to 50% of the series resonance period, the voltage V1 output by the end of the first direct current power supply V1 also reaches 200V, and compared with the waveform of the conventional LLC full bridge converter shown in fig. 6, the current of the embodiment 1 at the secondary side is closer to the chord type resonance current, so that the switch at the secondary side more accords with the soft switching characteristic when being turned off. By applying the control method of the embodiment of the application, the voltage gain is smaller than 1 when the voltage gain is lower than the series resonance frequency fr, the maximum voltage gain is infinitely close to 1 when the voltage gain is close to the series resonance frequency fr, and the lower the switching tube working frequency fs is, the lower the voltage drop is when the switching tube working frequency fs is far from the series resonance frequency fr. When the input voltage V2 decreases or the load increases, the switching tube operating frequency fs needs to be increased and approaches the series resonance frequency fr.
If the external controller judges that the boost control of the input voltage needs to be realized or the control output gain is more than or equal to 1, the boost mode is recorded. The working frequency fs applied to the switching tube in the secondary full-bridge conversion unit is higher than or equal to the series resonance frequency fr; at this time, the total duty ratio of the driving of each switching tube in the converter including the dead zone is not more than 50%, T 0/2 minus Ts/2 is recorded as a reference time T d, the driving of one upper tube or lower tube of each group of diagonal switching tubes which are turned on in a rotating way in the secondary full-bridge conversion unit is the maximum duty ratio, the other lower tube or upper tube is turned off relative to the advance reference time T d, and the driving effective common on time after the turning on of each group of diagonal switching tubes which are turned on in the secondary full-bridge conversion unit is Ts/2 minus the dead zone time and the reference time T d; meanwhile, a switching tube connected with the same-name end of the primary side of the isolation transformer in the primary full-bridge conversion unit is subjected to conversion by a driving cooperation secondary full-bridge conversion unit, wherein the delay time is the reference time t d, the driving of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is the maximum duty ratio, meanwhile, the other diagonal switching tube is relatively turned off by 2 times of the reference time t d, and the driving effective common conduction time after the switching tube of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is turned on is one half of the switching period minus the dead time and 2 times of t d; ; that is, the two upper or lower tubes or the left or right bridge arm operate at the maximum duty ratio, the other two switch tubes operate at the duty ratio of the set effective common on time, or the driving of applying the maximum duty ratio to the full bridge, the required driving effective common on time is modulated through phase shifting, the relevant driving is shown as the waveforms shown in (c) in fig. 2 and (d) in fig. 2, the operating frequency in (c) in fig. 2 is close to the resonant frequency, and the operating frequency in (d) in fig. 2 is far away from the series resonant frequency. The driving waveforms shown in fig. 2 are only an example of the control method according to the embodiment of the present invention, and other driving methods for achieving the control method according to the embodiment of the present invention are also included in the scope of the present invention.
When the LLC full-bridge direct-current converter works with heavy load in the boost mode, according to the magnitude of output power connected by a primary full-bridge conversion unit or the ratio of the output power to the designed rated power, gradually reducing the time for relatively closing the diagonal switching tube drive in the secondary full-bridge conversion unit in advance from the reference time t d to zero, or gradually reducing the time for relatively closing the other diagonal switching tube drive of the primary full-bridge conversion unit in advance from 2 times of the reference time t d to zero; the greater the output power, the less time the relative advance is turned off.
When the LLC full-bridge direct-current converter works with light load in the boost mode, in order to reduce reactive circulation and reduce the closing current amplitude of the secondary side full-bridge switching tube, according to the output power of the primary full-bridge conversion unit or the ratio of the output power to the designed rated power, the driving of the switching tube with the relative early closing time of 2 times of the reference time t d in the driving of the diagonal switching tube in the primary full-bridge conversion unit is directly reduced to zero, namely is directly closed, and then the relative early closing time of the driving of the diagonal switching tube in the secondary full-bridge conversion unit is adjusted to be gradually enlarged from the reference time t d, and the smaller the output power is, the larger the early closing time is. In this mode, the higher the switching frequency, the stronger the boosting capability, the closer the operating frequency is to f 0, the closer the input voltage and the output voltage gain are to 1, and if the output voltage needs to be reduced, the operating frequency needs to be reduced to be shifted to the reduced mode.
Still further, as discussed under the parameters of the above-mentioned reference patent, when the input voltage is gradually reduced to 89V, the output voltage needs to be boosted or the gain is made to be greater than 1 to be stabilized to 200V or more, the operating frequency is increased to be greater than the frequency f 0 according to the boost mode control method, the driving duty ratio of the seventh switching tube Q7 or the eighth switching tube Q8 of the secondary full-bridge conversion unit is adjusted to be about 180kHz, wherein the driving duty ratio comprises the dead time of the driving, the third switching tube Q3 or the fourth switching tube Q4 of the primary full-bridge conversion unit is driven by applying the duty ratio of 50% of the delay t d =600ns, the dead time of the driving is included, and the on time is about 2.59us; meanwhile, according to the load condition, the driving time t d and 2 times t d of the fifth switching tube Q5, the sixth switching tube Q6 and the first switching tube Q1 and the second switching tube Q2 in the secondary full-bridge conversion unit are reduced to t d in advance, so that soft switching under different loads is realized, the output voltage is 204V under the condition, and a higher step-up ratio is achieved; as shown in fig. 4, the currents of the switching tubes of the primary full-bridge converter and the secondary full-bridge converter can meet the requirement of better soft switching.
Example 2
When the direct current low voltage is required to be converted into direct current high voltage, the LLC full-bridge direct current converter can be used only for one-way reverse discharge and works in a reverse inversion mode, at the moment, one switching tube in each diagonal corner of the primary full-bridge conversion unit is required to be changed into a rectifier diode, namely, the circuit structure shown in fig. 5 is adjusted, at the moment, if the LLC full-bridge direct current converter works in a buck mode, the rest switching tubes in the primary full-bridge conversion unit are driven to carry out synchronous rectification or the maximum duty ratio, and if the LLC full-bridge direct current converter works in a boost mode, the rest switching tubes in the primary full-bridge conversion unit are driven to carry out conversion of the secondary full-bridge conversion unit by the maximum duty ratio with the lag time of reference time t d, and the maximum duty ratio driving comprises dead zones which are not more than 50%.
In addition, on the basis of embodiment 1, when the first dc power V1 is three-level, that is, except for the positive port and the negative port, a zero-voltage intermediate port is further added, and at this time, two bridge arms in the primary full-bridge conversion unit are "I" -type three-level bridge arms, "T" -type three-level bridge arms, a combination of two three-level bridge arms, or a combination of two three-level bridge arms and two level bridge arms respectively. Fig. 7 is a schematic diagram of a bridge arm structure of a primary full-bridge conversion unit in the embodiment of the present invention, where (a) in fig. 7 is a two-level bridge arm, (b) in fig. 7 is an "I" type three-level bridge arm, and (c) in fig. 7 is a "T" type three-level bridge arm.
On the other hand, the secondary full-bridge conversion unit may also be a full-wave rectification circuit or a voltage-doubler rectification circuit capable of bidirectional conversion, as shown in fig. 8, wherein (a) in fig. 8 is a conventional full-bridge converter, (b) in fig. 8 is a voltage-doubler rectification circuit, and (c) and (d) in fig. 8 are full-wave rectification circuits of common source and common drain, respectively. When the working frequency fs of the switching tube in the secondary full-bridge conversion unit is smaller than or equal to fr, the effective on time of the driving of the switching tube applied to the full-wave rectification circuit or the voltage doubling rectification circuit is t 0, and when the working frequency fs of the switching tube in the secondary full-bridge conversion unit is larger than or equal to fr, the driving of the switching tube applied to the full-wave conversion unit is the maximum duty ratio, and the dead time is 50%.
The winding ports of the isolation transformer Tra shown in all the figures are only schematic, and it is not specific to the bridge type conversion unit connecting only two wires of the ports, and a converter comprising the figures shown in the figures is used. The isolation transformer Tra may also be a multi-winding transformer, and each winding is connected to a rectifying or inverting unit, for example, as shown in fig. 9, where a multi-winding is disposed on the secondary side of the isolation transformer Tra, and the rectifying or inverting unit performs voltage coupling input or output conversion to obtain voltages other than the first and second dc sources, or a multi-winding is disposed on the primary side, which also falls within the scope of the present invention.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The control method suitable for reverse discharge of the LLC full-bridge direct current converter is characterized by comprising the following steps of:
s100: reading related setting conditions and sampling signals through an external controller, and judging whether the external working conditions meet normal working conditions or not and whether the LLC full-bridge direct current converter needs to work in a reverse discharge mode or not; if the external controller judges that the LLC full-bridge direct current converter needs to work in a forward working mode or other working modes, the related working modes are continuously executed, and if the external controller judges that the working conditions are met and the LLC full-bridge direct current converter needs to work in a reverse discharging mode, the step S200 is executed;
S200: entering an LLC full-bridge direct current converter reverse discharge control mode, wherein in the mode, a second direct current power supply at the secondary full-bridge conversion unit side is used as an input, and a first direct current power supply at the primary full-bridge conversion unit side is used as an output or load end; if the external controller judges that the LLC full-bridge direct-current converter needs to realize the voltage-reducing control of the input voltage or the control output gain is less than or equal to 1, the LLC full-bridge direct-current converter is marked as a voltage-reducing mode, and if the external controller judges that the LLC full-bridge direct-current converter needs to realize the voltage-increasing control of the input voltage or the control output gain is more than or equal to 1, the LLC full-bridge direct-current converter is marked as a voltage-increasing mode; taking 45-55% of the resonance period of the series resonance unit as reference time T 0, recording 2 times of time T 0 as reference time T 0, and recording the switching frequency corresponding to the reference time T 0 as f 0; the series resonance frequency of the LLC full-bridge direct-current converter is denoted as fr, and the corresponding series resonance period is denoted as Tr; the working frequency of the switching tube is recorded as fs, and the corresponding working period is recorded as Ts; adjusting the frequency to a corresponding boosting mode or a corresponding step-down mode according to voltage feedback of the input end and the output end, and working;
S300: when the LLC full-bridge direct-current converter works in a buck mode, the working frequency fs applied to the switching tubes in the secondary full-bridge conversion unit is lower than or equal to the series resonance frequency fr, and the total duty ratio of the driving of each switching tube in the LLC full-bridge direct-current converter including dead zones is less than or equal to 50%; the driving of one upper tube or lower tube of each group of diagonal switching tubes which are conducted in a rotating way is applied to the secondary full-bridge conversion unit, the effective common conduction time of each group of diagonal switching tubes which are conducted in the rotating way is set as the reference time t 0; meanwhile, switching conversion of the secondary full-bridge conversion unit is cooperated with driving of corresponding switching tubes connected with the same-name end of the isolation transformer in the primary full-bridge conversion unit, driving of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is the maximum duty ratio, and driving effective common conduction time of each group of diagonal switching tubes which are alternately conducted is consistent with effective common conduction time of the secondary full-bridge conversion unit; in the buck mode, the lower the working frequency of a switching tube in the secondary full-bridge conversion unit is, the more the buck is, the lowest working frequency is not lower than 50% of the series resonance frequency fr of the series resonance unit, the closer the working frequency is to fr, the closer the gain of the input voltage and the output voltage is to 1, and if the output voltage needs to be boosted, the working frequency fs needs to be boosted to enter a boost mode;
S400: when the LLC full-bridge direct-current converter works in a boost mode, the working frequency fs applied to a switching tube in the secondary full-bridge conversion unit is higher than or equal to the series resonance frequency fr; the total duty ratio of the driving of each switching tube in the LLC full-bridge direct current converter including dead zones is less than or equal to 50%; the T 0/2 minus the Ts/2 is recorded as reference time td, the driving of one upper tube or lower tube of each group of diagonal switching tubes which are turned on in a rotating way in the secondary full-bridge conversion unit is the maximum duty ratio, the other lower tube or upper tube is turned off relatively in advance of the reference time td, and the effective common on time of each group of diagonal switching tubes which are turned on in the rotating way in the secondary full-bridge conversion unit is the Ts/2 minus the dead time and the reference time td; meanwhile, the corresponding switching tube connected with the same-name end of the primary side of the isolation transformer in the primary full-bridge conversion unit is subjected to conversion by the driving cooperation secondary full-bridge conversion unit, the driving of one upper tube or lower tube of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is the maximum duty ratio, meanwhile, the other switching tube in the diagonal switching tubes is relatively turned off by 2 times of the reference time td, and the driving effective common conduction time of each group of diagonal switching tubes which are alternately conducted in the primary full-bridge conversion unit is Ts/2 minus the dead time and 2 times of td; in the boost mode, the higher the working frequency of a switching tube in the secondary full-bridge conversion unit is, the stronger the boost capability is, the closer the working frequency is to the series resonance frequency fr, the closer the gain of the input voltage and the output voltage is to 1, and if the output voltage needs to be reduced, the working frequency needs to be reduced to be converted into the buck mode.
2. The control method for reverse discharge of LLC full-bridge direct current converter according to claim 1, wherein when the LLC full-bridge direct current converter is operated in the boost mode with heavy load, according to the output power or the ratio of the output power to the designed rated power, the time of relatively early closing of each group of diagonal switching tube driving in turn-on in the secondary full-bridge conversion unit is gradually reduced from the reference time td to zero, or the time of relatively early closing of each group of diagonal switching tubes driving in turn-on in the primary full-bridge conversion unit is gradually reduced from 2 times of the reference time td, and the minimum is reduced to zero; the greater the output power, the less time the relative advance is turned off.
3. The control method for reverse discharge of LLC full-bridge direct current converter according to claim 1, wherein when said LLC full-bridge direct current converter is operated in said boost mode with light load, according to the output power of primary full-bridge conversion unit or the ratio of output power to designed rated power, the driving of the switching tube whose relative early turn-off time is 2 times of reference time td in each group of diagonal switching tubes which are turned on in turn in primary full-bridge conversion unit is reduced to zero, then the driving relative early turn-off time in each group of diagonal switching tubes which are turned on in turn in secondary full-bridge conversion unit is regulated to be gradually enlarged from reference time td, the smaller the output power is, the larger the time of early turn-off is.
4. The control method for reverse discharge of an LLC full-bridge dc converter according to claim 1, wherein in the step-down mode, when the operating frequency fs of the switching tubes in the secondary full-bridge conversion unit is lower than the series resonant frequency fr and has fallen to a set frequency or a lower frequency limit, the effective on-duty ratio of each set of diagonal switching tubes in the primary full-bridge conversion unit, which are turned on alternately, is gradually increased, or the effective on-duty ratio of each set of diagonal switching tubes in the secondary full-bridge conversion unit, which are turned on alternately, is gradually decreased, or the effective on-duty ratios of each set of diagonal switching tubes in the primary and secondary full-bridge conversion units, which are turned on alternately, are simultaneously decreased, so that the output voltage continues to be reduced.
5. The control method for reverse discharge of LLC full-bridge direct current converter according to claim 1, wherein in said boost mode, when the operating frequency fs of the switching tube in the secondary full-bridge conversion unit is higher than said series resonance frequency fr and has reached a set frequency or upper limit of frequency, the delay time applied by the switching tube driving connected to the same-name end of the isolation transformer in the primary full-bridge conversion unit converted in cooperation with the secondary full-bridge conversion unit is further extended from the reference time td, and further boost can be realized.
6. The method for controlling reverse discharge of an LLC full-bridge dc converter according to any one of claims 1 to 5, wherein the LLC full-bridge dc converter includes a first dc power supply V1, a first filter capacitor C1, a primary full-bridge conversion unit, a series resonant unit, an isolation transformer Tra, a secondary full-bridge conversion unit, a second filter capacitor C2, and a second dc power supply V2, which are sequentially connected;
The primary full-bridge conversion unit comprises a first full-bridge converter, the first full-bridge converter comprises a first switching tube Q1, a second switching tube Q2, a third switching tube Q3 and a fourth switching tube Q4, the first switching tube Q1 and the fourth switching tube Q4 form a group of diagonal switching tubes, and the second switching tube Q2 and the third switching tube Q3 form a group of diagonal switching tubes; the positive port DC1+ of the first direct current power supply V1 is connected with the drain electrode of the first switching tube Q1 and the drain electrode of the second switching tube Q2, and the negative port DC1 of the first direct current power supply V1 is connected with the source electrode of the third switching tube Q3 and the source electrode of the fourth switching tube Q4; one end of a resonance capacitor Cr in the series resonance unit is connected with the source electrode of the first switching tube Q1 and the drain electrode of the third switching tube Q3, the other end of the resonance capacitor Cr in the series resonance unit is connected with one end of a resonance inductor Lr in the series resonance unit, the other end of the resonance inductor Lr is connected with a primary side synonym end of an isolation transformer Tra, and the primary side synonym end of the isolation transformer Tra is connected with the source electrode of the second switching tube Q2 and the drain electrode of the fourth switching tube Q4;
the isolation transformer Tra is an isolation transformer comprising an excitation inductance Lm, or an isolation transformer formed by connecting the isolation transformer and the excitation inductance Lm in parallel;
The secondary full-bridge conversion unit comprises a second full-bridge converter, the second full-bridge converter 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 eighth switching tube Q8 form a group of diagonal switching tubes, and the sixth switching tube Q6 and the seventh switching tube Q7 form a group of diagonal switching tubes; the secondary side synonym end of the isolation transformer Tra is connected with the source electrode of the sixth switching tube Q6 and the drain electrode of the eighth switching tube Q8 in the secondary full-bridge conversion unit, and the secondary side synonym end of the isolation transformer Tra is connected with the source electrode of the fifth switching tube Q5 and the drain electrode of the seventh switching tube Q7 in the secondary full-bridge conversion unit; the drain electrode of a sixth switching tube Q6 and the drain electrode of a fifth switching tube Q5 of the secondary full-bridge conversion unit are both connected with a positive port DC2+ of the second direct current power supply V2, and the source electrode of a seventh switching tube Q7 and the source electrode of an eighth switching tube Q8 are both connected with a negative port DC 2-of the second direct current power supply V2.
7. The method according to claim 6, wherein when the LLC full-bridge dc converter is used in reverse discharge in only one direction, one switching tube of each group of diagonal switching tubes in the primary full-bridge conversion unit is switched to a rectifier diode when the LLC full-bridge dc converter is operated in reverse inversion mode, and when the LLC full-bridge dc converter is operated in buck mode, the remaining switching tubes in the primary full-bridge conversion unit are driven to perform synchronous rectification or a maximum duty ratio, and when the LLC full-bridge dc converter is operated in boost mode, the remaining switching tubes in the primary full-bridge conversion unit are driven to perform conversion in cooperation with the secondary full-bridge conversion unit by the maximum duty ratio with a delay time of the reference time td, and the maximum duty ratio drive includes a dead time of not more than 50% of the switching period.
8. The control method for reverse discharge of LLC full-bridge dc converter as claimed in claim 6, wherein said secondary full-bridge conversion unit is a full-wave rectifier circuit capable of performing bidirectional conversion, and when the operating frequency fs of the switching tubes in the secondary full-bridge conversion unit is equal to or less than fr, the driving effective conduction time of the switching tubes applied to said full-wave rectifier circuit is t 0, and when the operating frequency fs of the switching tubes in the secondary full-bridge conversion unit is equal to or more than fr, the driving of the switching tubes applied to said full-wave rectifier circuit is a maximum duty ratio, including a dead time of 50%.
9. The method of claim 6, wherein the first dc power source V1 is a three-level dc power source, that is, a zero-voltage intermediate port is added in addition to the positive port and the negative port, and two bridge arms in the primary full-bridge conversion unit are two "I" -shaped three-level bridge arms, two "T" -shaped three-level bridge arms, a combination of "I" -shaped three-level bridge arms and two-level bridge arms, or a combination of "T" -shaped three-level bridge arms and two-level bridge arms.
10. The method according to claim 6, wherein the isolation transformer Tra is a multi-winding transformer, and each winding is connected to a rectifying or inverting unit for coupling conversion to obtain other coupling voltages except the first dc power supply V1 and the second dc power supply V2.
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| CN112202336A (en) * | 2020-09-17 | 2021-01-08 | 华南理工大学 | Control method of bidirectional CLLLC type converter capable of automatically switching power directions |
| CN116155108A (en) * | 2023-01-04 | 2023-05-23 | 深圳市迪威电气有限公司 | Control method of bidirectional LLC resonant DC converter capable of stabilizing voltage in wide range |
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| CN109560711B (en) * | 2019-01-22 | 2020-02-11 | 山东大学 | Isolated bidirectional DC-DC converter and modulation method thereof |
| CN114301301A (en) * | 2021-11-30 | 2022-04-08 | 刘三英 | Wide-range resonant soft-switching bidirectional direct-current converter and control method thereof |
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| CN116155108A (en) * | 2023-01-04 | 2023-05-23 | 深圳市迪威电气有限公司 | Control method of bidirectional LLC resonant DC converter capable of stabilizing voltage in wide range |
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