CN116155108A - Control method of bidirectional LLC resonant DC converter capable of stabilizing voltage in wide range - Google Patents
Control method of bidirectional LLC resonant DC converter capable of stabilizing voltage in wide range Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33584—Bidirectional converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/38—Means for preventing simultaneous conduction of switches
- H02M1/385—Means for preventing simultaneous conduction of switches with means for correcting output voltage deviations introduced by the dead time
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/01—Resonant DC/DC converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33571—Half-bridge at primary side of an isolation transformer
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33573—Full-bridge at primary side of an isolation transformer
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
The invention discloses a control method of a bidirectional LLC resonant DC converter capable of stabilizing voltage in a wide range, which comprises the following steps: in the first control mode: the switching tube in the primary bridge type conversion unit applies a fixed duty ratio of 50%, the driving dead time is included, the working frequency of the primary side is regulated according to the output voltage, the switching tube in the secondary bridge type conversion unit applies synchronous rectification driving, at the moment, the primary side is input, the secondary side is output or a load end, and the working state is forward rectification; in the second control mode: the working frequency applied to the secondary side switching tube is less than or equal to the resonant frequency, the effective conduction duty ratio is within the range of 40-60% of the resonant period, the driving duty ratio containing dead time is less than or equal to 50%, the secondary side is input, the primary side is output or a load end, the working state is reverse inversion voltage reduction, and the voltage reduction control of the input voltage or the control of the output gain is less than or equal to 1.
Description
Technical Field
The invention relates to the field of power electronic converters, in particular to a control method of a bidirectional LLC resonant direct current converter capable of stabilizing voltage in a wide range.
Background
With the development of dual-carbon economy, the current energy storage products and related fields of battery equipment are rapidly developed, the supply of energy sources is promoted, the requirements of battery energy storage products are further promoted, and the requirements of other portable inverter equipment and the like are increased, so that the power supply products capable of performing bidirectional conversion are also increased, the batteries are required to be charged or discharged by the equipment or the inverters, but due to the nature wide voltage range characteristics of the batteries, the corresponding voltage range required by the equipment is also increased and wider in consideration of the compatibility of different products, and therefore, the traditional two-set circuit (charging and discharging) is not provided with cost advantages, and the common single-stage conversion circuit is also insufficient in the aspects of efficiency and wide voltage range charging or discharging.
The topology of the currently popular and commonly available bidirectional direct current/direct current (DC/DC) converter is shown as a double active bridge DAB (dual active bridge) in the mode of fig. 1-1, a bidirectional LLC converter in the mode of fig. 1-2, a CLLC converter in the mode of fig. 1-3, a CLLLC converter in the mode of fig. 1-4 and the like, and as described by a plurality of students, DAB has the advantages that besides the circulation caused by current phase difference of primary side and secondary side cannot completely transfer energy, the soft switching range is small, the turn-off current is larger and the loss is higher as the load is lighter; many scholars try to improve with new control methods such as multiple phase shift control methods, but the control methods are very complex and have limited improvement effect. The bidirectional LLC converter has soft switching characteristics completely consistent with an LLC circuit in forward operation, but in reverse operation, the resonant tank is degenerated into an LC series resonant tank circuit with two elements by an LLC resonant tank circuit with three elements because the exciting inductance of a high-frequency transformer is clamped by the input alternating square wave voltage, and the maximum gain of the LC series resonant tank circuit is 1 by approximate analysis of a fundamental wave analysis method, namely, the circuit can only work in a voltage reduction mode without considering the transformer transformation ratio, which is an obvious defect for limiting the application of the bidirectional LLC circuit; aiming at the problem that the forward and reverse operation characteristics of the LLC resonant circuit with the traditional structure are inconsistent, a symmetrical CLLC topological structure is provided by the Je-Hoon J and the Ho-Sung K to realize the bidirectional symmetrical operation characteristic, which is also called as a (CLLLC) converter. The converter is a hot converter which is used in high-voltage high-power scenes at present in the industry, forward and reverse soft switching conversion and reverse boosting can be realized by utilizing forward and reverse symmetrical working characteristics, and the problem of reverse working of a bidirectional LLC converter is solved, but the converter is considered as an LLC converter only in terms of topology, so that the problem of narrower voltage stabilizing range of the LLC is still existed, and in addition, the converter is not suitable for the application scene requirement of outputting low-voltage high current due to a large number of circuit elements. In addition, the scholars also propose another CLLC converter, namely, a capacitor is added in a loop of the secondary side output of the isolation transformer on the basis of the bidirectional LLC converter, compared with the double LLC converter, the resonant inductor is reduced, and the related characteristics are deeply analyzed. However, due to the difference of the resonant networks in forward and reverse operation, the working characteristics in reverse operation are different from those of the traditional LLC resonant network, the gain curve in the inductive working area in reverse operation is not monotonous, the direct current gain characteristics of the converter in forward and reverse operation are greatly different, and the addition of the additional capacitor complicates the parameter design and control of the converter.
In summary, in the design of practical products, there may be many limitations to using the foregoing converters, and more in certain limited places, such as using a method of ac rectifying/inverting bus voltage following adjustment, the resonant frequency point of the operation of the bidirectional LLC converter connected at the back end to obtain soft switching. In addition, a two-stage conversion circuit scheme shown in fig. 2 is generally adopted, such as a conversion circuit of a household energy storage inverter or a low-voltage battery pack is generally implemented by first performing voltage stabilization through a first-stage boosting or voltage reduction scheme (buck-boost), and then performing isolation through first-stage LLC DC/DC conversion, and the scheme has the advantages that soft switching high efficiency can be implemented by utilizing LLC to work at a resonance frequency point, the voltage range of a high-voltage side needs to follow the battery voltage, which is equivalent to amplifying the battery voltage by N times, and then further performing voltage stabilization through buck-boost; the two-stage scheme has higher cost, but is a relatively mature compromise scheme. There are other ways of changing the turn ratio of the transformer by changing the turn ratio of the transformer or increasing or decreasing the transformer coil by using a similar circuit, but these methods introduce new problems, and the dc converter or the switching tube of the externally connected converter is subjected to high voltage due to the wide range of variable bus voltage, which results in increased cost and loss and even reduced reliability. Therefore, there is a need for a new solution that allows both a soft switching efficient conversion and a bi-directional conversion that is relatively simple and meets a wide range of voltages.
Disclosure of Invention
The invention mainly aims to overcome the defects of the prior art, and provides a control method of a bidirectional LLC resonant DC converter capable of stabilizing voltage in a wide range, which solves the technical problems that the prior bidirectional converter control technology is not suitable for wide-range voltage stabilizing conversion or is not suitable for low-voltage and high-current application scenes, and comprises the problems that a two-stage converter is required to be used for multiple conversion, flow guiding passage devices are more, soft switching of a full converter cannot be realized, so that the loss is large, and the method is not suitable for application in places with limited volume or relatively high cost requirements.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a control method of a bidirectional LLC resonant DC converter capable of stabilizing voltage in a wide range comprises a first power supply, a first filter capacitor, a primary bridge conversion unit, a first series resonance unit, an isolation transformer, a secondary bridge conversion unit, a second filter capacitor and a second power supply which are sequentially connected; the control method comprises a first control mode and a second control mode; the first control mode is a forward LLC variable frequency fixed duty cycle control mode in which: the switching tube in the primary bridge conversion unit applies a fixed duty ratio of 50%, including driving dead time; the first working frequency of a switching tube in the primary bridge conversion unit is changed according to the output voltage regulation requirement; a switching tube in the secondary bridge type conversion unit applies synchronous rectification driving; in the first control mode, the first power supply at the primary bridge conversion unit side is input, and the second power supply at the secondary bridge conversion unit side is a direct current output or a load end; at the moment, the working state of the bidirectional LLC resonant direct current converter is forward rectification; the second control mode is a reverse LLC variable frequency duty cycle adjustment control mode in which: the second operating frequency applied to the switching tube in the secondary bridge conversion unit is lower than or equal to the first resonant frequency of the first series resonant unit, the on time of the effective on duty is set to be in the range of 40-60% of the first resonant period of the first series resonant unit, and the driving duty including dead time is not more than 50%; in the second control mode, the second power supply on the secondary bridge conversion unit side is input, and the first power supply on the primary bridge conversion unit side is output or a load end; at the moment, the working state of the bidirectional LLC resonant direct current converter is reverse inversion voltage reduction, so that voltage reduction control of input voltage or control of output gain is less than or equal to 1 is realized.
Further, the control method of the bidirectional LLC resonant direct current converter capable of stabilizing voltage in a wide range further comprises the following steps: in the second control mode, when the output gain is more than or equal to 1, continuously increasing the second working frequency to be larger than the first resonant frequency, wherein the driving duty ratio of the secondary bridge conversion unit is fixed to be 50%, and the driving dead time is included; simultaneously applying synchronous driving to the switching tube in the primary bridge conversion unit, wherein the on time of the synchronous driving is the same as the driving of the secondary bridge conversion unit at the maximum, and the minimum or at least one half of the first resonance period is subtracted by one half of the switching period, and the dead time of the driving is included; the synchronous driving is delayed and delayed relative to the turn-on time of the corresponding inversion switching tube driving in the secondary bridge type conversion unit, and the sum of delay and turn-on time is within 45-55% of the first resonance period; at the moment, the working state of the bidirectional LLC resonant direct current converter is reverse inversion boosting, so that boosting control of input voltage or control of output gain is more than or equal to 1 is realized.
Further, in the first control mode, synchronous rectification driving consistent with the driving of the corresponding switching tube in the primary bridge conversion unit is applied to the switching tube in the secondary bridge conversion unit, and when the driving time of the primary bridge conversion unit is less than one half of the first resonance period, the synchronous rectification driving time is equal to or less than one half of the first resonance period; and in the second control mode, when the second working frequency is smaller than the first resonant frequency, synchronous rectification driving consistent with the driving of the corresponding switching tube in the secondary bridge conversion unit is applied to the switching tube in the primary bridge conversion unit, and meanwhile, the opening time is enlarged and advanced until the previous adjacent driving is closed and dead time is reserved.
Further, in the second control mode, synchronous driving and delay hysteresis are applied to the switching tubes in the primary bridge conversion unit, and when the primary bridge conversion unit is a full-bridge converter, only synchronous driving of the switching tubes of the upper half bridge or the lower half bridge is delayed, and other switching tubes of the lower half bridge or the upper half bridge are only delayed for synchronous driving on and off time is not delayed, or synchronous driving is not applied.
Further, the primary bridge type conversion unit is a full-bridge converter, a symmetrical half-bridge converter, an asymmetrical half-bridge converter, a three-level 'I' -shaped bridge arm, a 'T' -shaped converter bridge arm or a converter formed by combining a three-level bridge arm and a half-bridge arm; the symmetrical half-bridge converter is a half-bridge arm, or a single three-level I-shaped bridge arm, or a T-shaped converter bridge arm and voltage doubling capacitors are combined, or a first resonance capacitor in a first series resonance unit connected with the symmetrical half-bridge converter is removed, and two other resonance capacitors with the capacity being half of that of the first resonance capacitor are used for replacing two voltage doubling capacitors in the symmetrical half-bridge converter.
Further, the secondary bridge type conversion unit is a full-bridge converter, a symmetrical half-bridge converter, a push-pull converter, a three-level 'I' -shaped bridge arm, a 'T' -shaped converter bridge arm or a converter formed by combining a three-level bridge arm and a half-bridge arm; the symmetrical half-bridge converter is a half-bridge arm, or a single three-level I-shaped arm, or a T-shaped converter arm and a voltage doubling capacitor are combined; when the secondary bridge conversion unit is a push-pull converter, the corresponding secondary coil is a winding middle tap or two independent windings when the isolation transformer is connected with the push-pull converter; when the secondary bridge conversion unit is a full-bridge converter, a symmetrical half-bridge converter or a converter combining a three-level bridge arm and a half-bridge arm, the bidirectional LLC resonant direct current converter has the following characteristics A or B: A. the bidirectional LLC resonant direct current converter also comprises a second series resonance unit which is connected in series between the input port of the secondary bridge type conversion unit and the isolating transformer winding and consists of a second resonance capacitor and a second resonance inductor, and the bidirectional LLC resonant direct current converter is a CLLLC converter which equivalently contains 4 type LLC in a circuit; B. the bidirectional LLC resonant direct current converter also comprises a second resonant capacitor connected in series between the input port of the secondary bridge type conversion unit and the isolating transformer winding, and is a CLLC converter which equivalently contains 4 LLC in a circuit; the bidirectional LLC resonant dc converter further includes the following feature C: C. when the secondary bridge conversion unit is a symmetrical half-bridge converter and the bidirectional LLC resonant DC converter is a CLLLC converter or a CLLC converter, the second resonant capacitor is removed, and the other two resonant capacitors with the capacity of only half of the second resonant capacitor are used for replacing the two voltage doubling capacitors of the symmetrical half-bridge converter.
Further, the isolation transformer comprises an excitation inductance, or an independent isolation transformer is connected with the excitation inductance in parallel to form the isolation transformer; the first resonant inductor and the second resonant inductor are external inductors, or leakage inductance integrated by the isolation transformer, or combination of the external inductors and coupling leakage inductance inside the isolation transformer; when the primary side and the secondary side of the isolation transformer are multi-winding, one winding is connected in series or a plurality of windings are respectively connected in series with a resonance inductor and a resonance capacitor at the side and then connected with a bridge type conversion unit at the side; and can be equivalently an LLC converter, a CLLC converter or a CLLLC converter according to a conversion mode, wherein when no resonance device exists between an isolation transformer and a secondary bridge conversion unit of the bidirectional LLC resonant direct current converter, the bidirectional LLC resonant direct current converter is the LLC converter; when the same isolating transformer has a plurality of winding coils, if one end of a plurality of winding coils is connected together and the winding coils are connected to the same bridge conversion unit or the bridge conversion units which are equivalently connected in parallel, or a plurality of bridge conversion units are directly connected in parallel or can be equivalently connected with different isolating transformer windings in parallel, a first control mode or a second control mode is applied, and each bridge conversion unit connected with different isolating transformer windings can also apply a driving signal of phase interleaving control or an in-phase control driving signal.
Further, the forward rectifying conversion energy of the CLLLC converter is regarded as reverse inversion, while the reverse inversion energy is regarded as forward rectifying conversion; when the CLLLC converter performs forward rectification conversion, the second control mode can be applied in addition to the first control mode; when the CLLLC converter performs reverse inversion, the first control mode can be applied in addition to the second control mode; and determining the relative primary or secondary of the CLLLC converter in dependence on the control mode after selecting the applied control mode; when the second control mode is applied to perform reverse boost conversion and the primary bridge conversion unit is a full-bridge converter, synchronous rectification delay driving is applied to all switching tubes of the full-bridge converter.
Further, when the CLLC converter or the CLLLC converter performs forward rectification conversion and works in the first control mode, and when the input voltage is to be reduced or the gain is less than 1, the control mode can be switched in addition to the adjustment control of the first operating frequency greater than the first resonant frequency in the first control mode, and the reverse inversion voltage reduction mode smaller than the first resonant frequency in the second control mode is applied instead, and when it is determined that the voltage reduction conversion is not required, the second control mode is exited and the first control mode is entered.
Further, when the LLC converter or the CLLC converter performs forward rectifying conversion, the LLC converter or the CLLC converter operates in a first control mode, and the first operating frequency is lower than the first resonant frequency and falls to a set frequency and is in a rising area, synchronous rectifying driving corresponding to the driving of the primary bridge conversion unit is applied to the switching tube in the secondary bridge conversion unit, and the switching tube relatively moves forward beyond the driving of the primary bridge conversion unit, so as to achieve continuous rising of the output voltage; when the output load approaches no load in the first control mode and the working frequency rises to the set frequency, the driving of the primary bridge type conversion unit is delayed and delayed relative to the synchronous rectification driving of the secondary bridge type conversion unit, so that the output voltage is continuously reduced, and the output voltage is ready to be switched to the second control mode for reverse inversion; and when the second working frequency is lower than the first resonant frequency and is reduced to a set frequency in a second control mode, synchronous rectification driving corresponding to the driving of the secondary bridge conversion unit is applied to a switching tube in the primary bridge conversion unit, the relative backward delay exceeds the driving of the switching tube corresponding to the secondary bridge conversion unit, or the synchronous driving of the primary bridge conversion unit is expanded and enlarged relative to the driving of the secondary bridge conversion unit, so that the output voltage is continuously reduced, and the primary bridge conversion unit is ready to be switched to the first control mode to continuously rectify forward.
Further, the bidirectional LLC resonant DC converter can be used for unidirectional DC conversion, works in a reverse inversion mode, and a switching tube in the primary bridge conversion unit can be used for synchronous rectification, or a switching tube which is used for rectification is used as a rectifying diode.
The beneficial technical effects of the invention are as follows:
(1) From the voltage stabilizing range, the reversible voltage stabilizing conversion of the traditional bidirectional LLC resonant direct current converter is improved under the advantage of ensuring the high-efficiency soft switching operation, so that the output voltage regulating range in the reverse operation is enlarged or more suitable. And the approximate forward conversion characteristic of the bidirectional LLC resonant DC converter during reverse conversion is realized.
(2) Structurally, the bidirectional LLC resonant DC converter overcomes the defect that the traditional bidirectional DC conversion with a wider range can be realized by two-stage voltage stabilizing conversion, and simplifies the complexity of multi-stage circuit conversion; and is simpler and more suitable for low voltage and high current scenarios than bi-directional CLLLC and CLLC converters.
(3) From the control aspect, the control mode and the control method are not only applicable to the bidirectional LLC converter, but also applicable to modified bidirectional LLC, such as a CLLC converter and a CLLLC converter; the CLLC converter and another wider-range buck control method and boost control method of the CLLLC converter during forward conversion are provided, and the voltage regulation range of the converter is effectively widened;
(4) In addition, the control is simplified from the normalization of structure, so that the performance is more stable, and the comprehensive cost performance is high.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, 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 that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIGS. 1-1 to 1-4 are prior art schematic diagrams of a common bi-directional LLC converter topology;
FIG. 2 is a schematic circuit diagram of a conventional bidirectional DC conversion implementation;
FIGS. 3-1 to 3-3 are block schematic diagrams of LLC/CLLC/CLLLC converters according to embodiments of the present invention;
FIG. 4 is a schematic diagram of the connection of a primary bridge conversion unit to a series resonant unit according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a specific connection implementation of a LLC converter secondary conversion unit according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of the connection of the secondary conversion units of the CLLLC/CLLC converter according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a three-level bridge arm implementation of an embodiment of the present invention;
8-1 through 8-4 are schematic diagrams of a multi-winding connection transformer assembly for an isolation transformer in accordance with an embodiment of the present invention;
FIG. 9 is a schematic diagram of waveforms for operation of an embodiment of the forward rectifying mode of an embodiment of the present invention;
FIG. 10 is a schematic diagram of waveforms for operation of an embodiment of the reverse buck mode of an embodiment of the present invention;
FIG. 11 is a schematic diagram of waveforms for operation in a reverse boost mode in accordance with an embodiment of the present invention;
FIG. 12 is a diagram illustrating waveforms for reverse boost mode operation according to an 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, however, the present invention may be practiced otherwise 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 belongs. 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 of a bidirectional LLC resonant DC converter capable of stabilizing voltage in a wide range, wherein the basic topological structure of the bidirectional LLC resonant DC converter comprises a first power supply, a first filter capacitor, a primary bridge conversion unit, a first series resonance unit, an isolation transformer, a secondary bridge conversion unit, a second filter capacitor and a second 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. For example, on the basis of the topology, a second series resonance unit is added between the isolation transformer and the secondary bridge conversion unit, and at this time, the bidirectional LLC resonant dc converter is specifically a CLLLC converter equivalently containing type 4 LLC in a circuit, and its structure is shown in fig. 3-2. For another example, based on the topology, only one series resonance capacitor is added between the isolation transformer and the secondary bridge conversion unit, and the bidirectional LLC resonant dc converter is specifically a CLLC converter with an equivalent circuit containing type 4 LLC, and the structure thereof is shown in fig. 3-3. If no additional components/circuits are added between the isolation transformer and the secondary bridge conversion unit, the bidirectional LLC resonant dc converter at this time is specifically an LLC converter, and its structure is shown in fig. 3-1. The control method according to the embodiment of the present invention is applicable to common bi-directional soft-switching dc converters such as the LLC converter shown in fig. 3-1, the CLLLC converter shown in fig. 3-2, and the CLLC converter shown in fig. 3-3, but is not limited thereto.
The LLC converter shown in FIG. 3-1, also called 4 LLC converter, has a structure shown in FIG. 3-1 and comprises a first power supply V1, a first filter capacitor C1, a primary bridge conversion unit 10, a first series resonance unit 21, an isolation transformer, a secondary bridge conversion unit 30, a second filter capacitor C2 and a second power supply V2 which are sequentially connected; wherein the first series resonant unit 21 is formed by connecting a first resonant capacitor Cr1 and a first resonant inductor Lr1 in series, and has a resonant frequency
The CLLLC converter shown in fig. 3-2, also called a double 4 type LLC converter, has a structure shown in fig. 3-2, and is modified based on the structure of the LLC converter shown in fig. 3-1 by adding a second series resonant unit 22 between the isolation transformer and the secondary bridge conversion unit 30, wherein the second series resonant unit 22 is formed by connecting a second resonant capacitor Cr2 and a second resonant inductor Lr2 in series. The CLLC converter shown in fig. 3-3, also known as a 4-11 type LLC converter, has a structure as shown in fig. 3-3, which is modified based on the structure of the LLC converter shown in fig. 3-1 by adding only one second resonant capacitor Cr2 between the isolation transformer and the secondary bridge converter unit 30. In the converters shown in fig. 3-1 to 3-3, the isolation transformer may be an isolation transformer comprising an excitation inductance Lm Alternatively, the isolation transformer is an isolation transformer formed by connecting an independent isolation transformer Tra and an excitation inductance Lm in parallel. Meanwhile, the parasitic capacitance of the switching tube of each bridge type conversion unit in the converter can be equivalently classified into a resonance capacitance or ignored according to the requirement;
as shown in fig. 4 (a), in some embodiments, the primary bridge converter unit may be a full bridge converter, where a positive port v+ of a dc source is connected to the drains of the first switching tube Q1 and the second switching tube Q2, and a negative port V-of the dc source is connected to the sources of the third switching tube Q3 and the fourth switching tube Q4; one end of a resonance capacitor Cr1 in the series resonance unit is connected with a source electrode of a first switching tube Q1 and a drain electrode of a third switching tube Q3 in the primary bridge conversion unit, the other end of the resonance capacitor Cr1 is connected with a resonance inductor Lr1, the other end of the resonance inductor Lr1 is connected with a primary side port 2 of an isolation transformer, and the primary side port 1 of the isolation transformer is connected with a source electrode of a second switching tube Q2 and a drain electrode of a fourth switching tube Q4 of the primary bridge conversion unit. In other embodiments, the primary bridge conversion unit may also be a half-bridge converter, for example, an asymmetric half-bridge converter shown in (b) of fig. 4, in which the Q2 and Q4 bridge legs are removed relative to the full-bridge converter, and the primary side port 1 of the isolation transformer is connected to the negative port of the dc source (or may be connected to the positive port of the dc source); or for example, the symmetrical half-bridge converter shown in fig. 4 (C) replaces the Q2 and Q4 bridge arms with the first capacitor C1 and the second capacitor C2 in series to form a new bridge arm relative to the full-bridge converter. In addition, the resonance capacitor Cr1 in the series resonance unit can be removed, and two resonance capacitors with the capacity of only half of the capacity of the resonance capacitor Cr1 can be used for replacing the C1 and C2 capacitors of the half-bridge converter.
As shown in fig. 5 (a), in some embodiments, the secondary bridge converter unit may be a full bridge converter, the port 3 on the secondary side of the isolation transformer is connected to the source of the second switching tube Q2 and the drain of the fourth switching tube Q4 of the secondary bridge converter unit, and the port 4 on the secondary side of the isolation transformer is connected to the source of the first switching tube Q1 and the drain of the third switching tube Q3 of the secondary bridge converter unit. The drains of the second switching tube Q2 and the first switching tube Q1 of the secondary bridge conversion unit are connected to the positive port of the output direct current source together, and the sources of the third switching tube Q3 and the fourth switching tube Q4 are connected to the negative port of the output direct current source together. In other embodiments, as shown in fig. 5 (b), the secondary bridge conversion unit may be a (symmetrical) half-bridge converter, where the Q2 and Q4 bridge arms are replaced by a first capacitor C1 and a second capacitor C2 connected in series to form a new bridge arm, compared to the full-bridge converter in fig. 5 (a). As shown in fig. 5 (c), the secondary bridge conversion unit may also be a common push-pull converter (or referred to as a push-pull rectifier, or may be referred to as a full-wave rectifier converter or a full-wave rectifier), where the port 3 on the secondary side of the isolation transformer is connected to the drain of the seventh switching tube Q7 of the secondary bridge conversion unit, the port 6 on the secondary side of the isolation transformer is connected to the drain of the eighth switching tube Q8 of the secondary bridge conversion unit, and the ports 4 and 5 on the secondary side of the isolation transformer are connected to the positive port v+ of the output dc source, and the sources of the seventh switching tube Q7 and the eighth switching tube Q8 are connected together to the negative port V of the output dc source. As shown in fig. 5 (d), another form of secondary bridge conversion unit is a variation of fig. 5 (c), and is also called a common drain connection method, in which the drains of Q7 and Q8 are connected to the positive port of the output dc source, the sources of Q7 and Q8 are respectively connected to the 3/6 port of the isolation transformer, and the secondary side ports 4 and 5 of the isolation transformer are connected to the negative port of the output dc source.
As shown in fig. 6, when the secondary bridge converter unit is a full-bridge converter or a half-bridge converter, a series resonant capacitor Cr2 and a series resonant inductor Lr2 are added between the port 4 on the secondary side of the isolation transformer and the input side of the secondary bridge converter unit, and in fig. 6, (a) and (b) are respectively a full-bridge CLLLC converter and a half-bridge CLLLC converter. If only the series resonant capacitance Cr2 is added, the full-bridge CLLC converter and the half-bridge CLLC converter are shown in fig. 6 (c) and (d), respectively. In addition, the resonance capacitor Cr2 in the series resonance unit can be removed, and two resonance capacitors having a capacity only half of the capacity of the resonance capacitor Cr2 can be used to replace the capacitors C1 and C2 of the half-bridge converter. In practical use, due to the circuit complexity of CLLLC converters and CLLC converters, the resonant frequency of the series resonant unit consisting of the resonant capacitor Cr2 and the resonant inductance Lr2 in CLLLC converters is better simplified and used
The optimal ratio of Cr2 to Cr1 is the square of the ratio of the primary side to the secondary side of the isolation transformer, and the optimal ratio of Lr1 to Lr2 is the square of the ratio of the primary side to the secondary side of the isolation transformer; this results in f1 0 And f2 0 Equal or similar, the characteristics are more consistent in the forward and reverse transformation. The inverse resonant frequency point of the CLLC converter is more complex to calculate, and various calculation formulas exist in the prior art. In the present invention, for better optimization and convenient use, cr2 and Cr1 units are made to be identical, lr1 is converted into a numerical value in microhenry (uh), cr2=cr1×lr1, then the reverse resonant frequency refers to the forward resonant frequency, fine tuning can be performed according to actual use needs, and the settable range is from minus 20% to plus 10%.
In addition, when the dc voltage is higher, the dc source V has an intermediate voltage V/2 port in addition to the positive/negative port, so that the bridge arm shown in (a) in fig. 7 in the primary bridge type conversion unit or the secondary bridge type conversion unit can be replaced by a three-level bridge arm or a combination thereof, that is, a common three-level "I" bridge arm shown in (b) in fig. 7, and a common three-level "T" bridge arm shown in (c) in fig. 7; if the switching tube is used for rectifying, the switching tube used for freewheeling in the middle of the three-level bridge arm can be replaced by a diode. The bridge arm shown in fig. 7 (a) is also called a two-level bridge arm, as opposed to a three-level bridge arm. The bridge converters shown in the primary bridge conversion unit and the secondary conversion unit are mainly bidirectional LLC resonant direct current converters with two output ports connected with isolation transformers, namely, the bidirectional LLC resonant direct current converters are provided with at least one bridge arm consisting of switching tubes, and various bridge arms shown in fig. 7 or respective combinations can be adopted. And simultaneously, a two-phase full bridge and a three-phase full bridge can be combined by the two-phase full bridge and the three-phase full bridge.
Lm is the excitation inductance of the isolation transformer Tra, or an independent external excitation inductance Lm is connected in parallel with the isolation transformer Tra, and the resonant inductances Lr1 and Lr2 are external inductances, or leakage inductances integrated by the isolation transformer Tra, or the integration of the external inductances and coupling leakage inductances inside the transformer. The primary and secondary sides of the isolation transformer Tra as shown in fig. 8-1 to 8-4 may be a multi-winding transformer combination, and when the isolation transformer Tra is multi-winding, one or more windings may be respectively connected in series with a resonance unit and then connected with a bridge type conversion unit, and may be equivalently a CLLC converter or a CLLLC converter according to a conversion mode. The winding ports of all the illustrated isolation transformers are only schematic, and the bridge type conversion units are not particularly limited to be connected with only two wires, such as the push-pull type converter connected with the aforementioned isolation transformer Tra, and the secondary winding is two windings or a winding with a middle tap, which are correspondingly connected according to the conversion units actually used. When the coils of the same transformer are connected with the same multiphase converter, the external parameters of each coil must be consistent, and the resonant devices are connected in series or not; if a three-phase full bridge is adopted, the primary side and the secondary side of the transformer are respectively provided with three coils, or the coils of three independent transformers. For example, the series resonance parameters of the three-phase full-bridge LLC/CLLC/CLLC converter, which are externally connected to the full-bridge converter, must be consistent, and the other ends of the three coils are connected to form a common point, which can be suspended or the midpoint of the voltage dividing capacitors connected with the voltage buses. The corresponding driving control of each converter needs to perform three-phase interleaving, phase staggering by 60 degrees or one sixth of a period, and the use of such a type of converter or the structure of the converter is a common technology, which is not described too much herein, and can be analyzed by a person skilled in the art or refer to the publication information related to the same line.
Power supplies V1 and V2 connected to the primary bridge conversion unit and the secondary conversion unit; when the bidirectional LLC resonant DC converter takes the side V1 as the input, the input power V1 works as a power supply or an equivalent power supply to provide input energy for the whole converter, and the output power V2 is an equivalent power supply and is actually an equivalent load or a load. When the bidirectional LLC resonant direct current converter takes the side V2 as input, the original output power V2 works as a power supply or an equivalent power supply to provide input energy for the whole converter, and the original output power V1 is the equivalent power supply and is actually a load or an equivalent load.
The converter-related circuits shown in fig. 4 to 7, the positions of the related components connected in series 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; related circuits are also well known, and the specific principle of operation 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 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, which is mentioned in the previous embodiments, the embodiment of the invention provides a control method of the bidirectional LLC resonant direct current converter capable of stabilizing voltage in a wide range. The control method is implemented as follows.
Fig. 1-2 is a specific implementation of an LLC converter with the topology shown in fig. 3-1 (in case both the primary and the secondary bridge conversion units are full bridge converters), which may then be referred to as bi-directional full bridge LLC converters. Taking the bi-directional full-bridge LLC converter of FIGS. 1-2 as an example, the operating frequency may be greater than the first resonant frequency f1 assuming the converter is in an ideal state 0 The lowest does not approach or exceed the series-parallel resonant frequency fm,
it is guaranteed that there is sufficient frequency margin and that the circuit hardware parameters and load meet the gain of the input and output voltages over this frequency range is 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 primary bridge conversion unit side V1 is assumed to be a dc input, and the secondary bridge conversion unit side is assumed to be a dc output or load. The converter operating state in this control mode is a forward rectifying mode. The following control method, also called the first control mode, is adopted.
The first control mode is a forward LLC variable frequency fixed duty cycle control mode. At the control ofThe system mode is as follows: the switching tube in the primary bridge conversion unit applies a fixed duty ratio of 50%, including driving dead time; the working frequency fs1 of a switching tube in the primary bridge conversion unit is changed according to the output voltage regulation requirement; a switching tube in the secondary bridge type conversion unit applies synchronous rectification driving; in the control mode, the first power V1 on the primary bridge conversion unit side is input, and the second power V2 on the secondary bridge conversion unit side is dc output or load side; at this time, the working state of the bidirectional LLC resonant DC converter is forward rectification. Resonant frequency of resonant unit composed of Lr1 and Cr1
For boundary line, resonant frequency f1 0 Gain at 1, higher than resonant frequency f1 0 Gain is less than 1, lower than resonant frequency f1 0 The gain is larger than 1, and the working frequency fs1 is from high to low across the resonant frequency f1 0 The output voltage of the secondary bridge conversion unit will be higher and higher; whereas the output voltage will be lower and lower. In the first control mode, synchronous rectification driving consistent with the driving of the corresponding switching tube in the primary bridge conversion unit can be applied to the switching tube in the secondary bridge conversion unit, and when the driving time of the primary bridge conversion unit is less than 1/f1 of the resonance period 0 The synchronous rectification driving time is equal to or less than 1/f1 of the resonance period 0 One half of (a) of (b).
As shown in the waveform diagram of fig. 9, the bidirectional full-bridge LLC converter shown in fig. 1-2 performs forward rectification conversion, V1 is input, V2 is output, the load is 10 ohms, and the primary and secondary side turn ratio of the isolation transformer is 2:1, lm=50uh, lr=12uh, cr=88 nf, and applying a first control mode to control, operating at 100kHz, below the resonant frequency f1 0 In the full-bridge conversion unit of the primary side, the switching tubes Q1/Q4 and Q2/Q3 are respectively 50% duty ratio, the driving dead time between the tubes is included, the switching tubes Q6/Q7 and Q5/Q8 of the secondary side are subjected to synchronous rectification, the driving duty ratio is 28%, the conduction time is 2.8us, and the driving dead time is less than half of the resonance period 1/f1 0 A dead time is reserved between the half resonant period and the front and back of the resonant period. When the working frequency fs1 is greater than or equal toAt resonant frequency f1 0 The driving duty ratios of the switching tubes Q1/Q4 and Q2/Q3 are still respectively 50% duty ratio, and the driving dead time between the tubes is included; the switching tubes Q6/Q7 and Q5/Q8 on the secondary side can apply slightly smaller driving than the driving of the switching tubes Q1/Q4 and Q2/Q3 by synchronous rectification, and certain dead time is reserved before and after retraction.
The primary bridge converter unit side V1 is assumed to be a dc output connected load, and the secondary bridge converter unit side is assumed to be a dc input. The LLC converter operating state in this control mode is a reverse rectification mode. The following control method, also called a second control mode, is adopted. The second control mode is a reverse LLC variable frequency duty cycle adjustment control mode in which: the operating frequency fs2 applied to the switching tubes in the secondary bridge conversion unit is lower than or equal to the resonant frequency f1 0 The on time of the effective on duty is set to be 1/f1 of the resonance period 0 Within 40-60% (which may be any fixed value or may be a plurality of variable values, fixed as resonance period 1/f 1) 0 I.e., one half of the resonance period is optimal), and the drive duty ratio including the dead time is not more than 50%; when the operating frequency fs2 is lower than the resonant frequency f1 0 And when the switching tube in the primary bridge conversion unit is subjected to synchronous rectification driving consistent with the driving of the corresponding switching tube in the secondary bridge conversion unit, the on time can be prolonged until the previous adjacent driving is closed, and enough dead time is reserved. In the control mode, the second power V2 on the secondary bridge conversion unit side is input, and the first power V1 on the primary bridge conversion unit side is output or load side; at the moment, the working state of the bidirectional LLC resonant direct current converter is reverse inversion voltage reduction, so that voltage reduction control of input voltage or control of output gain is less than or equal to 1 is realized.
As shown in the waveform diagram of fig. 10, the bidirectional full-bridge LLC performs inverse inversion transformation, and continuously takes fig. 1-2 as an example, V2 is input, V1 is output, and has a load of 27 ohms, and the primary and secondary side turn ratios of the transformer are 2:1, lm=50uh, lr1=12uh, cr1=88nf, v2=148V and applying a second control mode related method, operating at 100kHz below the resonant frequency f1 0 The switching tubes Q6/Q7 and Q5/Q8 on the secondary side are respectively drivenThe dynamic duty ratio is 30%, the conduction time is about 3us, and the conduction time is close to and slightly smaller than 1/f1 of half of the resonance period 0 The method comprises the steps of carrying out a first treatment on the surface of the In the full-bridge conversion unit at the primary side, switching tubes Q1/Q4 and Q2/Q3 perform synchronous rectification, the driving duty ratio is 47%, the on time is about 4.7us and is close to 50%, and certain dead time is reserved in relation to half of the switching period and the front and back. The synchronous rectification drive is applied after the end of the adjacent previous drive, and the rectification of the diode is avoided to the greatest extent. The current waveforms of the primary side and the secondary side are more like bilateral symmetry overturning on the basis of forward rectification, and are just overturned with forward rectification to be reverse inversion depressurization. In addition, according to the input 148V, the output is 200V under the above conditions, and it is known that the gain g=200/148×2≡0.676 achieves a higher step-down ratio, whereas the conventional control method achieves a high output of 296V under the input condition, effectively reducing the voltage stress during switching, and achieving soft switching on the primary side and the secondary side. Applying the control method below the resonant frequency f1 0 The time-voltage gain is less than 1 and is close to the resonance frequency f1 0 The maximum voltage gain is infinitely close to 1, and the lower the operating frequency fs2 is, the farther the resonant frequency f1 is 0 The lower the depressurization. Since the gain of the output voltage relative to the input voltage is always smaller than 1, the mode is also called reverse inversion buck mode. When the input voltage V2 decreases, the operating frequency fs2 needs to be increased to the resonance frequency f1 0 The directions are close.
As shown in fig. 11, assuming that the input voltage is gradually reduced to 89V without changing the hardware condition shown in fig. 10, the output voltage needs to be boosted or gain is greater than 1 to be stabilized to 200V, and according to the boost mode control method of the second control mode, the operating frequency fs2 is increased to be greater than the resonance frequency f1 0 The switching tubes Q6/Q7 and Q5/Q8 of the secondary bridge conversion unit are respectively drive duty ratio 50% with 180kHz, wherein dead time of drive is included, and real on time is about 2.6us; simultaneously, synchronous driving is applied to switching tubes Q3 and Q4 (or Q1 and Q2) in the primary bridge conversion unit, the on time of the synchronous driving can be the same as that of the secondary driving at maximum, and the duty ratio is 47% and is about 2.6us; dead time duty cycle including drive 50%; at least or at least two One-half resonance period 1/f1 0 Subtracting one half of the switching period, including dead time of the drive; the synchronous drive delays by about 0.6us relative to the turn-on time of the corresponding inverter switching tube drive in the secondary bridge conversion unit, and the sum of the delay time and the turn-on time is 2.6us+0.6us=3.2 us, which is equal to one half of the resonance period 1/f1 0 And within plus or minus 10% of one-half of the resonance period (i.e., resonance period 1/f 1) 0 In the range of 45 to 55 percent); the sum of the times is also the optimal time.
In the second control mode, synchronous driving and delay hysteresis are applied to the switching tubes in the primary bridge conversion unit, when the primary bridge conversion unit is a full-bridge converter, only the synchronous driving of the switching tubes of the upper half bridge or the lower half bridge is delayed, and the switching tubes of the other lower half bridge or the upper half bridge are only switched on for delay of synchronous rectification driving and the switching-off time is not delayed, or synchronous rectification driving is not applied. Since the bridge conversion units in the bidirectional LLC full-bridge converter of this example are full-bridge converters, only the switching transistors Q3, Q4 (or the switching transistors Q1, Q2) of the lower half bridge are synchronous-drive delayed in the illustration, only synchronous rectification (drive time 1.925us, approximately 2 us) is performed on the upper half bridge Q1, Q2 (or the switching transistors Q3, Q4) and no drive delay (or no synchronous rectification drive is applied) is performed on the off time. The control method can avoid the current recovery peak when the secondary side switching tubes Q5-Q8 are turned off, ensures the soft switching to the greatest extent, and is the optimal mode of applying the synchronous drive by the bidirectional LLC/CLLC full bridge. At the same time the synchronous rectification drive in the example of the figure reaches the maximum applicable range, avoiding diode rectification as much as possible. The current waveforms of the primary side Q3/Q4 and the secondary sides Q5-Q8 are more like bilateral symmetry overturning on the basis of forward rectification, and just overturning with forward rectification to reduce the voltage to reversely invert the voltage to boost. Furthermore, from the input 89V, the output is 202V under the above conditions, and the gain g=202/89×2≡1.135 is known; when the input is 79V and the switching frequency reaches 200K, the output is 202V under the above conditions, and it is known that the gain g=202/80×2≡1.263 reaches a higher step-up ratio. The higher the operating frequency in this mode, the greater the gain. Because the reverse inversion mode gain is greater than 1, the reverse inversion boosting mode is also called as reverse inversion boosting mode.
In addition, when the gain of the output voltage in the second control mode is equal to or greater than 1, the operating frequency fs2 can be fixed at the resonant frequency f1 0 Or in the range of negative 5% to positive 10% (i.e. resonant frequency f 1) 0 In the range of 95% to 110%) of the voltage in the secondary bridge conversion unit, and applying synchronous drive to the switching tubes in the primary bridge conversion unit, wherein the synchronous drive delays with respect to the drive on time of the corresponding inverter switching tubes in the secondary bridge conversion unit, the synchronous drive on time can be the same as the drive time of the secondary and ensures that the switching tubes have enough dead time, at least it is necessary to ensure that the drive of the corresponding inverter switching tubes in the secondary bridge conversion unit can be conducted enough to enable the boost gain of the output voltage to reach the preset requirement after the drive of the corresponding inverter switching tubes is turned off, the longer the synchronous drive delay exceeds the on time of the corresponding secondary drive, the larger the gain is, but the reverse circulation is formed after the synchronous drive is excessive, and the resonance period is generally not more than 1/f1 0 Twenty-five percent of (f). As shown in fig. 12, the operating frequency fs2 was fixed at 160kHz, the synchronous drive lag exceeded 0.6us, and when the V2 voltage was input 89V, the V1 load 27 ohms was still regulated at 198V.
According to the waveform and the data of the embodiment, the reverse conversion gain can reach the range of 0.676-1.263 times in the second control mode, while the gain can only be 1 or the constant frequency operation can only be carried out under the resonance frequency under the input condition in the traditional hard switch full-bridge conversion control mode, and the output voltage is unstable; however, the control method applied to the embodiment of the invention effectively realizes the voltage boosting and realizes the soft switching of the primary side and the secondary side. Therefore, the second control mode well solves the control difficult problem of the current bidirectional LLC, realizes wide input in reverse conversion, not only can stabilize voltage output, but also can realize soft switching.
When LLC converter or CLLC converter performs forward rectification conversion, i.e. the operating frequency fs1 is lower than the resonant frequency f1 in the first control mode 0 And falls to the set frequency and is in the rising area, and the switching tube in the secondary bridge conversion unit can be applied to the primary bridge conversion unit for drivingThe corresponding synchronous rectification driving and relative forward movement exceeding the driving of the primary bridge conversion unit are moved, the more the forward movement advances, the higher the boost is, and the maximum forward movement does not exceed the resonance period 1/f1 0 10% of (C). When the output load approaches no load in the first control mode, the working frequency rises to a set frequency point, the driving of the primary bridge type conversion unit can be delayed and delayed relative to the synchronous rectification driving of the secondary bridge type conversion unit, the output voltage can be continuously reduced, and particularly in a critical state requiring the switching of the bidirectional conversion state at any time, the mode is similar to the boosting mode driving in the second control mode, so that the switching or the transition to the second control mode can be smoothly performed for reverse inversion. The operating frequency fs2 in the second control mode is lower than the resonant frequency f1 0 When the frequency is lowered to the set frequency, the synchronous rectification driving corresponding to the driving of the secondary bridge conversion unit is applied to the switching tube in the primary bridge conversion unit, the relative backward delay exceeds the driving of the switching tube corresponding to the secondary bridge conversion unit, the more the backward delay is, the lower the voltage is, and the maximum backward delay is not more than one half of the switching period minus one half of the resonance period 1/f1 0 The method comprises the steps of carrying out a first treatment on the surface of the Or the synchronous driving of the primary bridge conversion unit is expanded and enlarged relative to the driving of the secondary bridge conversion unit, the output voltage can be reduced continuously, and particularly in a critical state requiring the switching of the bidirectional conversion state at any time, the mode is similar to the boost mode driving in the first control mode, so that the switching or transition to the first control mode can be carried out smoothly for forward rectification.
Furthermore, since the CLLC converter and the CLLLC converter are both variants based on the LLC converter of fig. 3-1, and the relevant performance is similar to that of the LLC converter, the control method of the above-described embodiment can also be applied to the CLLC converter and the CLLLC converter, as will be appreciated by those skilled in the art or alternatively implemented according to the control method of the LLC converter described above. However, it should be noted that, since the CLLLC converter is a symmetrical bidirectional LLC converter, the CLLLC converter can be regarded as reverse inversion from the other side when performing forward rectifying conversion, and the other side can be regarded as forward rectifying conversion when performing reverse inverting conversion, so that the CLLLC converter is forward rectifying conversionThe stream transformation may apply a second control mode related method in addition to the first control mode related method. The reverse inversion transformation may apply the first control pattern-related method in addition to the second control pattern-related method. After the control mode is selected, the relative primary or secondary designation of the transducer is determined based on the control mode. When the second control mode is applied to perform reverse boost conversion and the primary bridge conversion unit is a full-bridge converter, synchronous rectification delay driving is applied to all switching tubes of the full-bridge converter. Due to the aforementioned characteristics and control methods, when the CLLC converter or CLLLC converter performs forward rectification conversion and operates in the first control mode, when the input voltage is required to perform voltage reduction or conversion with gain smaller than 1, the operating frequency fs1 operable in the conventional LLC frequency conversion first control mode is greater than the resonance frequency f1 0 Besides the regulation control, the intelligent switching can also be realized by adopting a compound control method, and the second control mode is applied to be smaller than the resonant frequency f1 0 And (3) exiting the second control mode and entering the first control mode when the step-down conversion is judged not to be needed.
In practical use, the LLC converter can be used for unidirectional direct current conversion, the converter is operated in a reverse inversion mode, and the switching tube in the primary bridge conversion unit can be used for synchronous rectification, or the switching tube only used for rectification can be used for rectification diode. Such as an on-board inverter, converts the battery voltage to a higher dc voltage for conversion by the inverter without the need for forward rectifying charging.
Sometimes, the power of the use scene is larger, a plurality of bidirectional LLC resonant DC converters can be directly connected in parallel, or the situation that a plurality of bidirectional LLC resonant DC converters are connected in parallel can be equivalently used for expanding the power; or the number of voltage paths needing to be supplied is large, more than two windings of the isolation transformer Tra can be used for connecting a plurality of bridge type conversion units, and a first control mode or a second control mode can be applied. When the same isolating transformer is provided with a plurality of winding coils, if one end of the winding coils is connected together and the winding coils are connected to the same bridge conversion unit or the equivalent parallel bridge conversion units, or a plurality of bridge conversion units are directly connected in parallel or can be connected with different isolating transformer windings in parallel, a first control mode or a second control mode is applied, and each bridge conversion unit connected with different isolating transformer windings can also apply a phase interleaving control driving signal or an in-phase control driving signal.
In summary, the invention essentially overcomes and solves the problem that the bidirectional LLC/CLLC/CLLLC converter cannot regulate voltage/voltage in a wide range when performing reverse conversion, or can meet the requirement of regulating voltage/voltage in a wide range when performing reverse conversion under the condition of better realizing soft switching, and provides good choice for low-voltage and high-current places, such as adopting the bidirectional LLC converter, and avoiding the complexity and current discomfort of adopting the CLLC/CLLLC converter.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several equivalent substitutions and obvious modifications can be made without departing from the spirit of the invention, and the same should be considered to be within the scope of the invention.
Claims (12)
1. A control method of a bidirectional LLC resonant DC converter capable of stabilizing voltage in a wide range is characterized by comprising the following steps:
the bidirectional LLC resonant direct current converter comprises a first power supply, a first filter capacitor, a primary bridge type conversion unit, a first series resonance unit, an isolation transformer, a secondary bridge type conversion unit, a second filter capacitor and a second power supply which are sequentially connected;
The control method comprises a first control mode and a second control mode;
the first control mode is a forward LLC variable frequency fixed duty cycle control mode in which: the switching tube in the primary bridge conversion unit applies a fixed duty ratio of 50%, including driving dead time; the first working frequency of a switching tube in the primary bridge conversion unit is changed according to the output voltage regulation requirement; a switching tube in the secondary bridge type conversion unit applies synchronous rectification driving; in the first control mode, the first power supply at the primary bridge conversion unit side is input, and the second power supply at the secondary bridge conversion unit side is a direct current output or a load end; at the moment, the working state of the bidirectional LLC resonant direct current converter is forward rectification;
the second control mode is a reverse LLC variable frequency duty cycle adjustment control mode in which: the second operating frequency applied to the switching tube in the secondary bridge conversion unit is lower than or equal to the first resonant frequency of the first series resonant unit, the on time of the effective on duty is set to be in the range of 40-60% of the first resonant period of the first series resonant unit, and the driving duty including dead time is not more than 50%; in the second control mode, the second power supply on the secondary bridge conversion unit side is input, and the first power supply on the primary bridge conversion unit side is output or a load end; at the moment, the working state of the bidirectional LLC resonant direct current converter is reverse inversion voltage reduction, so that voltage reduction control of input voltage or control of output gain is less than or equal to 1 is realized.
2. The method for controlling a bidirectional LLC resonant dc converter capable of wide range voltage regulation as set forth in claim 1, further comprising:
in the second control mode, when the output gain is more than or equal to 1, continuously increasing the second working frequency to be larger than the first resonant frequency, wherein the driving duty ratio of the secondary bridge conversion unit is fixed to be 50%, and the driving dead time is included; simultaneously applying synchronous driving to the switching tube in the primary bridge conversion unit, wherein the on time of the synchronous driving is the same as the driving of the secondary bridge conversion unit at the maximum, and the minimum or at least one half of the first resonance period is subtracted by one half of the switching period, and the dead time of the driving is included; the synchronous driving is delayed and delayed relative to the turn-on time of the corresponding inversion switching tube driving in the secondary bridge type conversion unit, and the sum of delay and turn-on time is within 45-55% of the first resonance period; at the moment, the working state of the bidirectional LLC resonant direct current converter is reverse inversion boosting, so that boosting control of input voltage or control of output gain is more than or equal to 1 is realized.
3. The method for controlling a bidirectional LLC resonant dc converter capable of wide range voltage regulation as set forth in claim 1, further comprising:
In the second control mode, when the output gain is more than or equal to 1, setting the second working frequency to be in the range of 95-110% of the first resonant frequency, simultaneously applying synchronous driving to the switching tube in the primary bridge type conversion unit, and delaying the synchronous driving relative to the driving on time of the corresponding inversion switching tube in the secondary bridge type conversion unit, wherein the synchronous driving on time is the same as the driving time of the secondary bridge type conversion unit at the maximum and ensures that driving dead time is reserved, and the minimum is that the on time capable of enabling the boost gain of the output voltage to reach the preset requirement is reserved after the driving of the corresponding inversion switching tube in the secondary bridge type conversion unit is closed.
4. The method for controlling a bidirectional LLC resonant dc converter capable of wide range voltage regulation as set forth in claim 1, wherein:
in the first control mode, synchronous rectification driving consistent with the driving of a corresponding switching tube in the primary bridge conversion unit is applied to the switching tube in the secondary bridge conversion unit, and when the driving time of the primary bridge conversion unit is less than one half of the first resonance period, the synchronous rectification driving time is equal to or less than one half of the first resonance period;
And in the second control mode, when the second working frequency is smaller than the first resonant frequency, synchronous rectification driving consistent with the driving of the corresponding switching tube in the secondary bridge conversion unit is applied to the switching tube in the primary bridge conversion unit, and meanwhile, the opening time is enlarged and advanced until the previous adjacent driving is closed and dead time is reserved.
5. A method of controlling a bi-directional LLC resonant dc converter capable of wide range voltage regulation in accordance with any of claims 1-4, characterized by: in the second control mode, synchronous driving and delay hysteresis are applied to the switching tubes in the primary bridge conversion unit, when the primary bridge conversion unit is a full-bridge converter, only the synchronous driving of the switching tubes of the upper half bridge or the lower half bridge is delayed, and the switching tubes of the other lower half bridge or the upper half bridge are only opened and delayed by synchronous driving and the turn-off time is not delayed, or synchronous driving is not applied.
6. A method of controlling a bi-directional LLC resonant dc converter capable of wide range voltage regulation in accordance with any of claims 1-4, characterized by: the primary bridge type conversion unit is a full-bridge converter, a symmetrical half-bridge converter, an asymmetrical half-bridge converter, a three-level 'I' -shaped bridge arm, a 'T' -shaped converter bridge arm or a converter formed by combining a three-level bridge arm and a half-bridge arm;
The symmetrical half-bridge converter is a half-bridge arm, or a single three-level I-shaped bridge arm, or a T-shaped converter bridge arm and voltage doubling capacitors are combined, or a first resonance capacitor in a first series resonance unit connected with the symmetrical half-bridge converter is removed, and two other resonance capacitors with the capacity being half of that of the first resonance capacitor are used for replacing two voltage doubling capacitors in the symmetrical half-bridge converter.
7. A method of controlling a bi-directional LLC resonant dc converter capable of wide range voltage regulation in accordance with any of claims 1-4, characterized by: the secondary bridge type conversion unit is a full-bridge converter, a symmetrical half-bridge converter, a push-pull converter, a three-level 'I' -shaped bridge arm, a 'T' -shaped converter bridge arm or a converter formed by combining a three-level bridge arm and a half-bridge arm; the symmetrical half-bridge converter is a half-bridge arm, or a single three-level I-shaped arm, or a T-shaped converter arm and a voltage doubling capacitor are combined;
when the secondary bridge conversion unit is a push-pull converter, the corresponding secondary coil is a winding middle tap or two independent windings when the isolation transformer is connected with the push-pull converter;
When the secondary bridge conversion unit is a full-bridge converter, a symmetrical half-bridge converter or a converter combining a three-level bridge arm and a half-bridge arm, the bidirectional LLC resonant direct current converter has the following characteristics A or B:
A. the bidirectional LLC resonant direct current converter also comprises a second series resonance unit which is connected in series between the input port of the secondary bridge type conversion unit and the isolating transformer winding and consists of a second resonance capacitor and a second resonance inductor, and the bidirectional LLC resonant direct current converter is a CLLLC converter which equivalently contains 4 type LLC in a circuit;
B. the bidirectional LLC resonant direct current converter also comprises a second resonant capacitor connected in series between the input port of the secondary bridge type conversion unit and the isolating transformer winding, and is a CLLC converter which equivalently contains 4 LLC in a circuit;
the bidirectional LLC resonant dc converter further includes the following feature C:
C. when the secondary bridge conversion unit is a symmetrical half-bridge converter and the bidirectional LLC resonant DC converter is a CLLLC converter or a CLLC converter, the second resonant capacitor is removed, and the other two resonant capacitors with the capacity of only half of the second resonant capacitor are used for replacing the two voltage doubling capacitors of the symmetrical half-bridge converter.
8. The method for controlling a bidirectional LLC resonant dc converter capable of wide range voltage regulation as set forth in claim 7, wherein: the isolation transformer comprises an excitation inductor, or an independent isolation transformer is connected with the excitation inductor in parallel to form the isolation transformer; the first resonant inductor and the second resonant inductor are external inductors, or leakage inductance integrated by the isolation transformer, or combination of the external inductors and coupling leakage inductance inside the isolation transformer; when the primary side and the secondary side of the isolation transformer are multi-winding, one winding is connected in series or a plurality of windings are respectively connected in series with a resonance inductor and a resonance capacitor at the side and then connected with a bridge type conversion unit at the side; and can be equivalently an LLC converter, a CLLC converter or a CLLLC converter according to a conversion mode, wherein when no resonance device exists between an isolation transformer and a secondary bridge conversion unit of the bidirectional LLC resonant direct current converter, the bidirectional LLC resonant direct current converter is the LLC converter; when the same isolating transformer has a plurality of winding coils, if one end of a plurality of winding coils is connected together and the winding coils are connected to the same bridge conversion unit or equivalent parallel bridge conversion units, or a plurality of bridge conversion units are directly connected in parallel or can be connected with different isolating transformer windings in an equivalent parallel manner, a first control mode or a second control mode is applied, and each bridge conversion unit connected with different isolating transformer windings can also apply a driving signal of phase interleaving control or an in-phase control driving signal.
9. The method for controlling a bidirectional LLC resonant dc converter capable of wide range voltage regulation as set forth in claim 7, wherein: the forward rectifying conversion energy of the CLLLC converter is regarded as reverse inversion, and the reverse inversion energy is regarded as forward rectifying conversion; when the CLLLC converter performs forward rectification conversion, the second control mode can be applied in addition to the first control mode; when the CLLLC converter performs reverse inversion, the first control mode can be applied in addition to the second control mode; and determining the relative primary or secondary of the CLLLC converter in dependence on the control mode after selecting the applied control mode; when the second control mode is applied to perform reverse boost conversion and the primary bridge conversion unit is a full-bridge converter, synchronous rectification delay driving is applied to all switching tubes of the full-bridge converter.
10. The method for controlling a bidirectional LLC resonant dc converter capable of wide range voltage regulation as set forth in claim 7, wherein: when the CLLC converter or the CLLLC converter performs forward rectification conversion and works in a first control mode, and when input voltage is to be reduced or the gain is less than 1, besides the first working frequency in the first control mode is greater than the first resonant frequency to perform adjustment control, the control mode can be switched, a reverse inversion voltage reduction mode which is smaller than the first resonant frequency in a second control mode is applied, and when the condition that the voltage reduction conversion is not needed is judged, the second control mode is exited and the first control mode is entered.
11. The method for controlling a bidirectional LLC resonant dc converter capable of wide range voltage regulation as set forth in claim 8, wherein: when the LLC converter or the CLLC converter performs forward rectifying conversion, the LLC converter or the CLLC converter works in a first control mode, the first working frequency is lower than the first resonant frequency and falls to a set frequency and is in a rising ascending region, synchronous rectifying driving corresponding to the driving of the primary bridge conversion unit is applied to a switching tube in the secondary bridge conversion unit, and the switching tube relatively moves forward beyond the driving of the primary bridge conversion unit so as to realize continuous rising of output voltage; when the output load approaches no load in the first control mode and the working frequency rises to the set frequency, the driving of the primary bridge type conversion unit is delayed and delayed relative to the synchronous rectification driving of the secondary bridge type conversion unit, so that the output voltage is continuously reduced, and the output voltage is ready to be switched to the second control mode for reverse inversion; and when the second working frequency is lower than the first resonant frequency and is reduced to a set frequency in a second control mode, synchronous rectification driving corresponding to the driving of the secondary bridge conversion unit is applied to a switching tube in the primary bridge conversion unit, the relative backward delay exceeds the driving of the switching tube corresponding to the secondary bridge conversion unit, or the synchronous driving of the primary bridge conversion unit is expanded and enlarged relative to the driving of the secondary bridge conversion unit, so that the output voltage is continuously reduced, and the primary bridge conversion unit is ready to be switched to the first control mode to continuously rectify forward.
12. The method for controlling a bidirectional LLC resonant dc converter capable of wide range voltage regulation as set forth in claim 8, wherein: the bidirectional LLC resonant DC converter can be used for unidirectional DC conversion, works in a reverse inversion mode, and a switching tube in the primary bridge conversion unit can be used for synchronous rectification, or a switching tube only used for rectification is used as a rectifying diode.
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