CN114583932B - Control circuit and control method for LLC resonant converter - Google Patents
Control circuit and control method for LLC resonant converter Download PDFInfo
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- CN114583932B CN114583932B CN202210461600.2A CN202210461600A CN114583932B CN 114583932 B CN114583932 B CN 114583932B CN 202210461600 A CN202210461600 A CN 202210461600A CN 114583932 B CN114583932 B CN 114583932B
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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
- H02M1/14—Arrangements for reducing ripples from dc input or output
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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
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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
Abstract
The application discloses a control circuit and a control method for an LLC resonant converter, firstly obtaining a resonant current signal of a resonant inductor Lr and a resonant voltage signal at two ends of a resonant capacitor Cr of a resonant circuit of the LLC resonant converter; and acquiring a switch driving signal according to the resonance current signal and the resonance voltage signal. The switch driving signal is used for realizing the switch control of a power switch tube of a switch inverter circuit of the LLC resonant converter. Because the current mode control of the LLC resonant converter is realized according to the resonant current signal and the resonant voltage signal, the stability and the reliability of a closed loop are greatly improved, the dynamic response speed of the converter is improved, the ripple voltage is reduced, and the control method is easy to realize.
Description
Technical Field
The invention relates to the technical field of direct current conversion, in particular to a control circuit and a control method for an LLC resonant converter.
Background
With the rapid development of power electronic technology, people have increasingly higher demands on various electronic products and also have increasingly higher demands on direct current power supplies. Referring to fig. 1, a circuit topology of a half-bridge LLC converter is shown, the basic circuit of the LLC resonant converter generally includes a controller with MOSFETs, a resonant network and a rectifier network. The controller alternately provides gate signals to the two MOSFETs at a 50% duty cycle, varying the operating frequency as the load varies, regulating the output voltage Vout, which is known as Pulse Frequency Modulation (PFM). The resonant network comprises two resonant inductances and a resonant capacitance (L-L-C). The resonant inductors lr, lm and the resonant capacitor Cr mainly serve as a voltage divider, and the impedance thereof changes with the operating frequency to obtain the required output voltage. The rectifier network converts the direct current input voltage into square waves through a half-bridge or full-bridge connected switch network and inputs the square waves into the resonant tank circuit, so that harmonic waves can be effectively filtered out, sinusoidal voltage and current waveforms are provided to be output to the transformer, and voltage scaling and primary/secondary isolation are achieved. Modulating the resonant square wave frequency of the resonant cavity controls the power flow of the converter. In LLC resonant converters, all semiconductor switches are soft-switching or zero-voltage switching (open for the primary MOSFET) and zero-current switching (open and closed for the secondary side rectifier), and thus have a lower electromagnetic emission level (EMI). However, the LLC resonant converter currently adopts a feedback quantity to directly control the switching frequency to realize the control method of the output power, and the method has the following disadvantages in practical application:
1) the loop response speed is low;
2) a bipolar point exists in a transfer function from control to output, and the stability is not easy to realize;
3) over-current protection and over-power protection are inaccurate.
Referring to fig. 2, a graph of a transfer function Bode from control to output in a direct frequency control method of an LLC converter is shown, where positions of two poles in the transfer function are not fixed at different output powers, and when designing the control method of the LLC converter, stability of closed loops needs to be considered in three different regions, respectively, which increases complexity of design.
Disclosure of Invention
The technical problem that this application mainly solved is how to realize the current mode control to LLC resonant converter.
According to a first aspect, there is provided in an embodiment a control circuit for an LLC resonant converter for converting a first direct current to a second direct current; the LLC resonant converter comprises a switch inverter circuit, a resonant circuit, a voltage transformation circuit, an output circuit and a switch drive control circuit;
the switch inverter circuit is connected with the resonant circuit and is used for converting the first direct current into high-frequency alternating current and outputting the high-frequency alternating current to the resonant circuit;
the resonance circuit is connected with the voltage transformation circuit and is used for performing resonance conversion on the high-frequency alternating current and outputting the high-frequency alternating current to the voltage transformation circuit;
the voltage transformation circuit is connected with the output circuit and is used for reducing the voltage of the high-frequency alternating current after resonance conversion and outputting the high-frequency alternating current to the output circuit;
the output circuit is used for outputting the second direct current;
the switch driving control circuit is connected with the switch inverter circuit and the resonance circuit and is used for monitoring a resonance current signal of a resonance inductor Lr of the resonance circuit and a resonance voltage signal at two ends of a resonance capacitor Cr and outputting a switch driving signal to a power switch tube of the switch inverter circuit according to the resonance current signal and the resonance voltage signal obtained by monitoring; the switch driving signal is used for realizing the switch control of a power switch tube of the switch inverter circuit.
According to a second aspect, an embodiment provides a control method for an LLC resonant converter for converting a first direct current to a second direct current, the control method comprising:
acquiring a resonant current signal of a resonant inductor Lr of a resonant circuit of the LLC resonant converter;
acquiring resonant voltage signals at two ends of a resonant capacitor Cr of a resonant circuit of the LLC resonant converter;
acquiring a switch driving signal according to the resonance current signal and the resonance voltage signal; the switch drive signal is used for realizing the LLC resonant converterSwitch with a switch bodyInversionCircuit arrangementThe power switch tube of (2).
In one embodiment, the switch driving signal is obtained according to the resonance current signal and the resonance voltage signal; the switch driving signal is used for realizing the switch control of a power switch tube of a switch inverter circuit of the LLC resonant converter, and the switch driving signal comprises the following components:
the switch driving signals comprise a high-end switch tube driving signal HG and a low-end switch tube driving signal LG; the high-side switching tube driving signal HG is used for driving a high-side power switching tube of a switching inverter circuit of the LLC resonant converter, and the low-side switching tube driving signal LG is used for driving a low-side power switching tube of the switching inverter circuit of the LLC resonant converter;
when the high-end switching tube driving signal HG is output and the resonant current signal crosses the zero point, sampling the resonant voltage signal to obtain a voltage sampling signal, and obtaining the voltage sampling signal and a voltage sum signal of a preset first preset voltage signal;
when the voltage sum signal is not larger than the resonance voltage signal, switching and outputting the low-side switching tube driving signal LG;
and the duration of the low-side switch tube driving signal LG is the same as that of the high-side switch tube driving signal HG.
According to the control circuit and the control method for the LLC resonant converter of the embodiment, the current mode control of the LLC resonant converter is realized according to the resonant current signal and the resonant voltage signal, so that the stability and the reliability of a closed loop are greatly improved, the dynamic response speed of the converter is improved, the ripple voltage is reduced, and the control method is easy to realize.
Drawings
Fig. 1 is a circuit topology diagram of a half-bridge LLC resonant converter;
FIG. 2 is a graph of a transfer function Bode from control to output in a direct control frequency approach for an LLC resonant converter;
FIG. 3 is a schematic diagram of a circuit configuration of an LLC resonant converter in an embodiment;
FIG. 4 is a schematic diagram of a circuit configuration of an LLC resonant converter in another embodiment;
FIG. 5 is a schematic diagram of the circuit connections of the driving control circuit in one embodiment;
FIG. 6 is a schematic diagram of a circuit connection structure of a driving control circuit according to an embodiment;
fig. 7 is a schematic illustration of an electrical signal monitoring of the LLC resonant converter in an embodiment;
FIG. 8 is a timing diagram of the resonant current and the midpoint voltage of the half bridge in one embodiment;
FIG. 9 is a signal corresponding graph of a power switch tube driving control signal and a resonant circuit electrical signal in another embodiment;
FIG. 10 is a schematic diagram illustrating a comparison of waveforms of an electrical signal of the resonant converter at a system switching frequency higher than a resonant frequency in one embodiment;
FIG. 11 is a schematic diagram illustrating a comparison of waveforms of an electrical signal of the resonant converter at a system switching frequency lower than the resonant frequency in one embodiment;
FIG. 12 is a bode plot of transfer functions in one embodiment.
Detailed Description
The present invention will be described in further detail with reference to the following detailed description and accompanying drawings. Wherein like elements in different embodiments have been given like element numbers associated therewith. In the following description, numerous details are set forth in order to provide a better understanding of the present application. However, one skilled in the art will readily recognize that some of the features may be omitted or replaced with other elements, materials, methods in different instances. In some instances, certain operations related to the present application have not been shown or described in this specification in order not to obscure the core of the present application with unnecessary detail, and it is not necessary for those skilled in the art to describe these operations in detail, so that they may be fully understood from the description in the specification and the general knowledge in the art.
Furthermore, the described features, operations, or characteristics may be combined in any suitable manner to form various embodiments. Also, the various steps or actions in the method descriptions may be transposed or transposed in order, as will be apparent to one of ordinary skill in the art. Thus, the various sequences in the specification and drawings are for the purpose of describing certain embodiments only and are not intended to imply a required sequence unless otherwise indicated where such sequence must be followed.
The numbering of the components as such, e.g., "first", "second", etc., is used herein only to distinguish the objects as described, and does not have any sequential or technical meaning. The term "connected" and "coupled" when used in this application, unless otherwise indicated, includes both direct and indirect connections (couplings).
In the embodiment of the application, a control method for an LLC resonant converter is disclosed, first obtaining a resonant current signal of a resonant inductor Lr and a resonant voltage signal at two ends of a resonant capacitor Cr of a resonant circuit of the LLC resonant converter; and acquiring a switch driving signal according to the resonance current signal and the resonance voltage signal. The switch driving signal is used for realizing the switch control of a power switch tube of a switch inverter circuit of the LLC resonant converter. Because the current mode control of the LLC resonant converter is realized according to the resonant current signal and the resonant voltage signal, the stability and the reliability of a closed loop are greatly improved, the dynamic response speed of the converter is improved, the ripple voltage is reduced, and the control method is easy to realize.
Example one
Referring to fig. 3, a schematic diagram of a circuit structure of an LLC resonant converter in an embodiment is shown, where the LLC resonant converter is used to convert a first direct current V _ dc into a second direct current. The LLC resonant converter comprises a switch inverter circuit 1, a resonant circuit 2, a transformation circuit 3, an output circuit 4 and a switch drive control circuit 5. The switching inverter circuit 1 is connected to the resonant circuit 2, and is configured to convert the first direct current V _ dc into a high-frequency alternating current and output the high-frequency alternating current to the resonant circuit 2. The resonance circuit 2 is connected with the transformation circuit 3, and is used for performing resonance conversion on the high-frequency alternating current and outputting the high-frequency alternating current to the transformation circuit 3. The voltage transformation circuit 3 is connected with the output circuit 4, and is used for reducing the voltage of the high-frequency alternating current after the resonance conversion and outputting the high-frequency alternating current to the output circuit 4. The output circuit 4 is used for outputting the second direct current. The switch driving control circuit 5 is connected with the switch inverter circuit 1 and the resonant circuit 2, and is configured to monitor a resonant current signal of the resonant inductor Lr of the resonant circuit 2 and a resonant voltage signal at two ends of the resonant capacitor Cr, and output a switch driving signal to the power switch tube of the switch inverter circuit according to the resonant current signal and the resonant voltage signal obtained through monitoring. The switching drive signal is used for realizing the switching control of the power switching tube of the switching inverter circuit 1. The switching inverter circuit 1 includes a direct current positive input end, a direct current negative input end, a rectification positive output end and a rectification negative output end. The direct current positive input end and the direct current negative input end are used for inputting a first direct current V _ dc. The rectification positive output end and the rectification negative output end are connected with the resonance circuit 2. The resonant circuit 2 comprises a rectification positive connecting end, a rectification negative connecting end, a primary side positive connecting end and a primary side negative connecting end. The rectification positive connecting end and the rectification negative connecting end are respectively connected with the rectification positive output end and the rectification negative output end, and the primary side positive connecting end and the primary side negative connecting end are used for being connected with the voltage transformation circuit 3. The transformation circuit 3 comprises a first primary side connecting end, a second primary side connecting end, a first secondary side positive connecting end, a first secondary side negative connecting end, a second secondary side positive connecting end and a second secondary side negative connecting end. The first primary side connecting end and the second primary side connecting end are respectively connected with the primary side positive connecting end and the primary side negative connecting end. The first secondary positive connecting end, the first secondary negative connecting end, the second secondary positive connecting end and the second secondary negative connecting end are used for being connected with the output circuit 4. Output circuit 4 includes first input connection end, the second input connection end, the third input connection end, the fourth input connection end, output positive link and output negative link, first input connection end and second input connection end are connected with first secondary positive link and first secondary negative link respectively, third input connection end and fourth input connection end are connected with second secondary positive link and second secondary negative link respectively, output circuit 4's output positive link and output negative link are used for exporting the second direct current. The resonant circuit 2 comprises a resonant capacitor Cr and a resonant inductor Lr, one end of the resonant inductor Lr is connected with the rectifying positive connection end, and the other end of the resonant inductor Lr is connected with the primary side positive connection end. One end of the resonant capacitor Cr is connected with the rectification negative connecting end, and the other end of the resonant capacitor Cr is connected with the primary side negative connecting end. The transformation circuit 3 comprises a transformer Tr, the transformer Tr comprises a primary winding and two secondary windings, one end of the primary winding is connected with a first primary connecting end, the other end of the primary winding is connected with a second primary connecting end, two ends of one secondary winding are respectively connected with a first secondary positive connecting end and a first secondary negative connecting end, and two ends of the other secondary winding are respectively connected with a second secondary positive connecting end and a second secondary negative connecting end. The output circuit 4 includes a diode D11, a diode D12, a capacitor C11, a resistor R11, and a resistor R12. The anode of the diode D11 is connected to the first input connection terminal of the output circuit 4, the cathode of the diode D11 is connected to the output positive connection terminal of the output circuit 4, the anode of the diode D12 is connected to the fourth input connection terminal of the output circuit 4, and the cathode of the diode D12 is connected to the output positive connection terminal of the output circuit 4. The capacitor C11 is connected in series with the resistor R11, one end of the series connection is connected with the output positive connection end of the output circuit, the other end of the series connection is connected with the output negative connection end of the output circuit 4, one end of the resistor R12 is connected with the output positive connection end of the output circuit 4, and the other end of the resistor R12 is connected with the output negative connection end of the output circuit 4. The second input connection end, the third input connection end and the output negative connection end of the output circuit 4 are electrically connected.
In an embodiment, the switching inverter circuit 1 is a full-bridge driving rectification circuit, and the switching inverter circuit 1 includes a first power switch tube S1, a second power switch tube S2, a third power switch tube S3, and a fourth power switch tube S4. A first pole of the first power switch S1 is connected to the dc positive input terminal, a second pole of the first power switch S1 is connected to the rectifying positive output terminal, and a control pole of the first power switch S1 is connected to the switch driving control circuit 5. A first pole of the second power switch tube S2 is connected to the rectification positive output end, a second pole of the second power switch tube S2 is connected to the dc negative input end, and a control pole of the second power switch tube S2 is connected to the switch driving control circuit 5. A first pole of the third power switch tube S3 is connected to the positive dc input terminal, a second pole of the third power switch tube S3 is connected to the negative rectification output terminal, and a control pole of the third power switch tube S3 is connected to the switch driving control circuit 5. A first pole of the fourth power switch tube S4 is connected to the rectification negative output end, a second pole of the fourth power switch tube S4 is connected to the dc negative input end, and a control pole of the fourth power switch tube S4 is connected to the switch driving control circuit 5.
Referring to fig. 4, a schematic circuit structure diagram of an LLC resonant converter in another embodiment is shown, in an embodiment, a switching inverter circuit 1 of the LLC resonant converter is a half-bridge driving rectifier circuit, the switching inverter circuit 1 includes a first power switch tube S5 and a second power switch tube S6, a first pole of the first power switch tube S5 is connected to a dc positive input terminal, a second pole of the first power switch tube S5 is connected to a rectifying positive output terminal, and a control pole of the first power switch tube S5 is connected to a switching driving control circuit 5. The first pole of the second power switch tube S6 is connected with the rectification positive output end, the second pole of the second power switch tube S6 is connected with the rectification negative output end, the control pole of the second power switch tube S6 is connected with the switch driving control circuit, and the direct current negative input end is electrically connected with the rectification negative output end.
In one embodiment, the switch driving control circuit 5 includes a switch driving circuit 40, a driving control circuit 30, a voltage sampling circuit 10, and a current conversion circuit 20. The voltage sampling circuit 10 is respectively connected to the resonant circuit 2 and the driving control circuit 30, and is configured to monitor a resonant voltage signal at two ends of a resonant capacitor Cr of the resonant circuit 2, and send the monitored resonant voltage signal to the driving control circuit 30. The voltage sampling circuit 10 includes a first connection end, a second connection end and a third connection end, the first connection end and the second connection end of the voltage sampling circuit 10 are respectively connected with two ends of the resonant capacitor Cr, and the third connection end of the voltage sampling circuit is connected with the driving control circuit 30. The current conversion circuit 20 is connected to the resonant circuit 2 and the driving control circuit 30, and is configured to monitor a resonant current signal flowing through the resonant inductor Lr of the resonant circuit 2, and output a resonant current monitoring signal obtained by monitoring the resonant current signal to the driving control circuit 30. The current conversion circuit includes a first connection terminal and a second connection terminal, the first connection terminal of the current conversion circuit 20 is connected to the resonance circuit 2, and the second connection terminal of the current conversion circuit 20 is connected to the driving control circuit 30.
Referring to fig. 5, which is a schematic circuit connection diagram of a driving control circuit in an embodiment, the driving control circuit 30 is connected to the switch driving circuit 40, and the driving control circuit 30 is configured to output a first PWM signal to the switch driving circuit 40. The switch driving circuit 40 is connected to the switch inverter circuit 1, and the switch driving circuit 40 is configured to output a switch driving signal according to the first PWM signal, where the switch driving signal includes a first power transistor driving signal DRV _ L and a second power transistor driving signal DRV _ H, where the first power transistor driving signal DRV _ L is used to drive a low-side power transistor of the switch inverter circuit 1, and the second power transistor driving signal DRV _ H is used to drive a high-side power transistor of the switch inverter circuit. The switch driving circuit 40 includes a first connection terminal, a second connection terminal, and a third connection terminal. The first connection terminal of the switch driving circuit 40 is connected to the driving control circuit 30 for inputting the first PWM signal. A second connection end of the switch driving circuit 40 is connected to the driving control circuit 30 and the switch inverter circuit 1, and is used for outputting the first power transistor driving signal DRV _ L. The third connection end of the switch driving circuit 40 is connected to the switch inverter circuit 1, and is used for outputting the second power transistor driving signal DRV _ H. The driving control circuit 30 includes a first connection terminal, a second connection terminal, a third connection terminal, and a fourth connection terminal. The first connection terminal of the driving control circuit 30 is connected to the first connection terminal of the switch driving circuit 40 for outputting the first PWM signal. A second connection terminal of the driving control circuit 30 is connected to the third connection terminal of the voltage sampling circuit 10, and is used for inputting the resonant voltage signal. The third connection terminal of the driving control circuit 30 is connected to the second connection terminal of the current converting circuit 20 for inputting the resonant current monitoring signal. A fourth connection terminal of the driving control circuit 30 is connected to the second connection terminal of the switch driving circuit 40, and is used for inputting the first power transistor driving signal DRV _ L. In one embodiment, the driving control circuit 30 is configured to output the first PWM signal according to the resonant voltage signal, the resonant current monitoring signal and the first power transistor driving signal DRV _ L.
As shown in fig. 4, in one embodiment, the voltage sampling circuit 10 includes a first sampling capacitor C31 and a second sampling capacitor C32. One end of the first sampling capacitor C31 is connected to the first connection end of the voltage sampling circuit 10, and the other end is connected to the second connection end of the voltage sampling circuit 10. One end of the second sampling capacitor C32 is connected to the second connection end of the voltage sampling circuit 10, and the other end is connected to the third connection end of the voltage sampling circuit 10. In one embodiment, the current converting circuit 20 includes a first converting capacitor C21, a first converting resistor R21, and a first comparator 21. One end of the first conversion capacitor C21 is connected to the first connection end of the current conversion circuit 20, and the other end is connected to the positive input end of the first comparator 21. Two ends of the first converting resistor R21 are connected to the positive input end and the negative input end of the first comparator 21, respectively. The output terminal of the first comparator 21 is connected to the drive control circuit 30, and the negative input terminal of the first comparator 21 is grounded.
Referring to fig. 6, which is a schematic diagram of a circuit connection structure of the driving control circuit in an embodiment, the driving control circuit 30 further includes a fifth connection end, and the fifth connection end of the driving control circuit 30 is used for inputting a preset first preset voltage signal Vloop. The drive control circuit 30 further includes a zero-crossing detection circuit 60, a sampling control circuit 70, a drive signal feedback circuit 80, and an SR flip-flop 90. The zero-crossing point detection circuit 60 is respectively connected to the third connection terminal of the driving control circuit 30 and the sampling control circuit 70, and the zero-crossing point detection circuit 60 is configured to output a sampling activation signal to the sampling control circuit 70 when the resonant current monitoring signal iLr crosses the zero point. In one embodiment, the zero-crossing point detecting circuit 60 includes a first determining circuit 61 and a first rising edge flip-flop 62, and the first determining circuit 61 is respectively connected to the third connection terminal of the driving control circuit 30 and the first rising edge flip-flop 62, and is configured to compare the resonant current monitoring signal iLr input to the third connection terminal of the driving control circuit 30 with a value of 0, and output a first trigger signal to the first rising edge flip-flop 62 when the resonant current monitoring signal iLr is 0. The first rising edge flip-flop 62 is connected to the sampling control circuit 70, and the first rising edge flip-flop 62 outputs a sampling activation signal to the sampling control circuit 70 in response to a first trigger signal.
The sampling control circuit 70 is connected to the second connection terminal, the fifth connection terminal, and the SR flip-flop 90 of the drive control circuit 30, respectively. The sampling control circuit 70 is configured to sample the resonant voltage signal Vcr in response to the sampling activation signal, sum the sampled voltage sampling signal with the first preset voltage signal Vloop, and output an R trigger signal to an R signal input end of the SR flip-flop 90 when the sum of the voltage sampling signal and the first preset voltage signal Vloop is not greater than the resonant voltage signal Vcr. In one embodiment, the sampling control circuit 70 includes a sampling activation circuit 72, an adder 73, a gain circuit 71, a comparator 74, and a second rising edge flip-flop 75. The sampling activation circuit 72 includes a first connection end, a second connection end, and a third connection end, the first connection end of the sampling activation circuit 72 is connected to the zero-crossing point detection circuit 60 for inputting a sampling activation signal, the second connection end of the sampling activation circuit 72 is connected to the second connection end of the driving control circuit 30 for inputting a resonant voltage signal Vcr, and the third connection end of the sampling activation circuit 72 is connected to one input end of the adder 73. The gain circuit 71 includes a first connection end and a second connection end, the first connection end of the gain circuit 71 is connected to the fifth connection end of the driving control circuit 30 for inputting the first preset voltage signal Vloop, and the second connection end of the gain circuit 71 is connected to the other input end of the adder 73. The output terminal of the adder 73 is connected to the negative input terminal of the comparator 74, and is configured to send the sum of the sampled voltage sample signal obtained by sampling and the first preset voltage signal Vloop to the comparator. The positive input end of the comparator 74 is connected to the second connection end of the driving control circuit 30, the output end of the comparator 74 is connected to the second rising edge flip-flop 75, and the comparator 74 is configured to compare the sum of the resonant voltage signal Vcr and the sampled voltage sampling signal with the first preset voltage signal Vloop, and output the second trigger signal to the second rising edge flip-flop 75 when the resonant voltage signal Vcr is large. The second rising edge flip-flop 75 includes a first connection terminal and a second connection terminal, and the first connection terminal of the second rising edge flip-flop 75 is connected to the output terminal of the comparator 74 for inputting the second trigger signal. A second connection terminal of the second rising edge flip-flop 75 is connected to the R signal input terminal of the SR flip-flop 90, and the second rising edge flip-flop 75 is configured to output the R trigger signal to the R signal input terminal of the SR flip-flop 90 in response to the second trigger signal.
In an embodiment, the first preset voltage signal Vloop is an output of a closed-loop control of an output voltage or an output current of the LLC resonant converter. In an embodiment, the first preset voltage signal Vloop is output by a voltage stabilizing loop formed by a TL431 and an optocoupler. In the digital control, the first preset voltage signal Vloop is output by proportional integral or calculation and processing of other controllers according to an error value between an output voltage sample and an output voltage set value. The output of the first preset voltage signal Vloop of the voltage loop is used for realizing voltage stabilization control on the output of the LLC resonant converter, and generally, the larger the output of the first preset voltage signal Vloop is, the larger the transmission power of the LLC resonant converter is. Since the first preset voltage signal Vloop does not affect the invention of the present application, the circuit related to the generation of the first preset voltage signal Vloop is not described in detail. In one embodiment, the first predetermined voltage signal Vloop may be set to a predetermined constant value.
The driving signal feedback circuit 80 is connected to the fourth connection terminal of the driving control circuit 30 and the SR flip-flop 90. The driving signal feedback circuit 80 is used to output an S-trigger signal to an S-signal input terminal of the SR flip-flop 90. The S trigger signal is synchronized with the falling edge of the first power tube driving signal DRV _ L. In one embodiment, the driving signal feedback circuit 80 includes a first falling edge flip-flop 82, an OR circuit 83, and a start signal generating circuit 81. The start signal generating circuit 81 is configured to generate a predetermined start square wave signal, and output the predetermined start square wave signal to an input terminal of the OR circuit 83. The first falling edge flip-flop 82 includes a first connection end and a second connection end, and the first connection end of the first falling edge flip-flop 82 is connected to the fourth connection end of the driving control circuit 30, and is used for inputting the first power transistor driving signal DRV _ L. A second connection of the first falling edge flip-flop 82 is connected to a further input of the OR circuit 83. An output terminal of the OR circuit 83 is connected to an S signal input terminal of the SR flip-flop 90. The Q output terminal of the SR flip-flop 90 is connected to the switch driving circuit 40, and is used for generating the first PWM signal and outputting the first PWM signal to the switch driving circuit 40.
The control circuit of the LLC resonant converter disclosed in the embodiment of the application comprises a switch drive control circuit. The switch driving control circuit comprises a switch driving circuit, a driving control circuit, a voltage sampling circuit and a current conversion circuit. Firstly, a switch driving control circuit acquires a resonant current signal of a resonant inductor Lr of a resonant circuit of the LLC resonant converter and a resonant voltage signal at two ends of a resonant capacitor Cr; and acquiring a switch driving signal according to the resonance current signal and the resonance voltage signal. The switch driving signal is used for realizing the switch control of a power switch tube of a switch inverter circuit of the LLC resonant converter. Because the current mode control of the LLC resonant converter is realized according to the resonant current signal and the resonant voltage signal, the stability and the reliability of a closed loop are greatly improved, the dynamic response speed of the converter is improved, the ripple voltage is reduced, and the control method is easy to realize.
Example two
The present application also discloses a control method for an LLC resonant converter, wherein the LLC resonant converter is configured to convert a first direct current to a second direct current, the control method comprising:
acquiring a resonant current signal of a resonant inductor Lr of a resonant circuit of the LLC resonant converter and acquiring resonant voltage signals at two ends of a resonant capacitor Cr of the resonant circuit of the LLC resonant converter; and acquiring a switch driving signal according to the resonance current signal and the resonance voltage signal. The switch driving signal is used for realizing the switch control of a power switch tube of a switch inverter circuit of the LLC resonant converter.
In one embodiment, obtaining the switch driving signal according to the resonant current signal and the resonant voltage signal includes:
the switch driving signals include a high-side switch tube driving signal HG and a low-side switch tube driving signal LG. And the high-end switch tube driving signal HG is used for driving a high-side power switch tube of a switch inverter circuit of the LLC resonant converter, and the low-end switch tube driving signal LG is used for driving a low-side power switch tube of the switch inverter circuit of the LLC resonant converter. When a high-end switching tube driving signal HG is output and a resonant current signal crosses zero, sampling is carried out on the resonant voltage signal to obtain a voltage sampling signal, and the voltage sampling signal and a voltage sum signal of a preset first preset voltage signal are obtained; and when the voltage sum signal is not greater than the resonance voltage signal, switching to output a low-side switch tube driving signal LG. The duration of the low-side switch tube driving signal LG is the same as that of the high-side switch tube driving signal HG. In one embodiment, the duration of the low-side switch-transistor driving signal LG is timed by a timer or an integrator, so that the duration of the low-side switch-transistor driving signal LG is the same as that of the high-side switch-transistor driving signal HG.
The following is a description of the principle of implementing current mode control on an LLC resonant converter according to a resonant current signal and a resonant voltage signal, which specifically includes:
as shown in fig. 3 and 4, the LLC resonant converters driven by the full bridge and the half bridge, respectively, when the LLC resonant converter works, the current flowing from the power supply to the LC resonant cavity through the switching tube may be represented as a voltage change of the resonant capacitor, specifically, the magnetic field energy of the inductor is transferred to the electric field energy of the capacitor, and the LLC converter realizes high-efficiency power conversion efficiency by relying on the principle of resonance. In fig. 3, the voltage sampling circuit 10 samples voltage signals at two ends of the resonant capacitor by using a high-resistance differential principle, and the current conversion circuit 20 samples a resonant current by using a current mutual inductance or a hall principle.
Referring to fig. 7, an electrical signal monitoring diagram of the LLC resonant converter in an embodiment is shown, where a first line is a signal timing diagram of a first power transistor driving signal DRV _ L (hereinafter, referred to as DRV _ L) and a second power transistor driving signal DRV _ H (hereinafter, referred to as DRV _ H), a second line is a current waveform diagram of a resonant current, and a third line is a voltage waveform diagram of a resonant capacitor. When the resonant current crosses zero, it means that the resonant current flows into the resonant capacitor completely, and the voltage corresponding to the resonant capacitor reaches the peak value. As shown in the second row of fig. 7, the upper and lower sine waves are the wave form of the resonant current, and the straight line and the jump are zero crossing points of the resonant current from negative direction to positive direction. As shown in the third row of fig. 7, the voltage signal of the resonant capacitor corresponds to the negative voltage peak of the resonant capacitor when the negative direction of the resonant current crosses to the positive direction.
The application proposes to sample the voltage of the resonant capacitor, since the resonant current leads the capacitor by 90 ° in phase, and a capacitor in series can be used to extract the resonant current signal from the voltage of the resonant capacitor in a differential manner. As shown in fig. 4, the voltage of the resonant capacitor can be obtained by directly using a method of connecting two capacitors in series, where Vcr is a sample of the voltage of the resonant capacitor, and iLr is a sample of the resonant current.
Referring to fig. 8, a timing diagram of the resonant current and the half-bridge midpoint voltage in an embodiment is shown, where iR is the resonant current and vHB is the half-bridge midpoint voltage. The zero crossing point iLr _ ZCD of the signal representing the resonant current is monitored and at this point in time the voltage of the resonant capacitor is sampled by a triggered sample/hold (sample/hold). According to the principle described above, when the resonant current crosses zero, the voltage peak of the resonant capacitor is corresponded. When the resonant converter works in the inductive region, when the switch HG (high-side power switch tube) is turned on, the current does not flow into the resonant cavity from the power supply immediately, but waits for the direction of the resonant current to be reversed, and starts to flow into the resonant cavity from the voltage source after the polarity conversion occurs.
Therefore, the time when the resonant current reverses is the time when the zero-crossing point iLr _ ZCD of the resonant current changes from low to high, so that the current actually flowing into the resonant cavity after the HG switch is turned on or the integral of the charge flowing into the resonant capacitor is represented by the difference Δ Vcr between the positive voltages of the resonant capacitor from the negative peak to the positive peak. The current flowing into the resonant cavity is controlled by controlling the negative peak voltage of the resonant capacitor to the increment delta Vcr voltage of the resonant capacitor voltage set by the feedback loop, and the power flowing into the resonant cavity when HG is switched on is also controlled equivalently. The power transmitted when the HG is switched on can be calculated from the voltage of the primary side bus and the current flowing into the resonant cavity:
Pout=Vin*Iin=ΔVcr*Cr*fsw*Vin；
therefore, by controlling the voltage increment delta Vcr from the voltage of the resonant capacitor to the closing point of the HG switch when the resonant current crosses zero, the power control of the LLC resonant converter can be realized, and the control method of the current mode is realized.
Referring to fig. 9, it is a signal corresponding diagram of a power switch tube driving control signal and a resonant circuit electrical signal in another embodiment, and the current mode control of the LLC resonant converter is implemented according to the monitored and obtained resonant circuit electrical signal, and the specific control flow includes:
iLr is a resonant current sampling signal, vCr is a voltage sampling signal of the resonant capacitor, and Vloop is an output value of the voltage outer loop. When the resonance current iLr is monitored to be larger than 0, sampling/holding of the resonance capacitor Vcr is triggered, the S/H output is added with a set value of a voltage outer loop vloop and then is compared with a voltage sampling value vCr of the resonance capacitor, when the voltage of the resonance capacitor is higher than the resonance set value, a signal for closing HG is triggered, an LG signal is started after dead zone time is inserted, the length of the HG opening time is copied to the low end opening, the consistency of the HG/LG opening time is realized, and the problem of current imbalance of the LLC resonance converter is solved.
Referring to fig. 6, after LG is turned off, a falling edge signal is taken, an SR trigger is reset, an HG signal in a new period is turned on again, zero-crossing signal iLr _ ZCD of resonant current is waited for, then (S/H) resonant capacitor voltage is sampled and held, after Vloop is added, capacitor voltage is waited to rise to a resonant capacitor set point, HG is turned off, and the operation is repeated, so that the steady-state operation of the system is realized.
Referring to fig. 10 and fig. 11, a schematic diagram of comparing waveforms of an electrical signal of the resonant converter when the system switching frequency is higher than the resonant frequency and a schematic diagram of comparing waveforms of the electrical signal of the resonant converter when the system switching frequency is lower than the resonant frequency are shown, respectively. In fig. 10 and 11, the sine wave electric signals in the waveform diagram of the first row are the voltage sum signals of the voltage sampling signal (the sampling electric signal Vcr _ ZCD of the resonance capacitor Vcr) and the first preset voltage signal (Vloop) at the upper end line of the first row, and the sampling electric signal Vcr _ ZCD obtained by sampling the resonance capacitor voltage at the resonance current ZCD point with S/H is shown at the lower end line of the first row. The waveform diagram in the second row represents the transition electric signal of the resonance current iLr and the switching control timing waveform diagram of HG. The waveform diagram in the third row shows the waveform of the resonant current sampling signal iLr. The waveform diagram in the fourth row shows a voltage sampling signal waveform diagram of the resonance capacitor vCr. The waveform diagram in the fifth row represents the waveform diagrams of the first power tube driving signal DRV _ L and the second power tube driving signal DRV _ H.
Referring to fig. 12, a bode plot of the transfer function of an embodiment is a plot of the transfer function of the control quantity to the output voltage, with the ordinate units of the Magni tude plot and the Phase plot being "dB" and "°", respectively. When an alternating current signal is analyzed, and a transfer function from a capacitor voltage increment set value delta Vcr to an output voltage is scanned, the problems of pole displacement, phase displacement and the like caused by second-order double poles are not seen in the gain and the phase of a bode diagram of the transfer function even if the alternating current signal works in a region lower than a resonance frequency, and the alternating current signal is a waveform of a typical first-order system. Therefore, the voltage of the resonant capacitor at the zero crossing point of the resonant current is controlled to be increased to the difference value delta Vcr between the resonant capacitors set by the feedback loop, so that the current mode control of the LLC converter is realized, and the stability and reliability of the closed loop are greatly improved. Because the increment of current flowing into the resonant cavity is directly controlled, the output power is also directly controlled, and therefore, the method has more advantages and better reliability than a method for directly controlling the frequency in the aspects of overcurrent, short circuit and the like.
The application discloses a control method for LLC resonant converter, through control at the voltage of resonant capacitor of resonant current zero passage point to feedback the Δ Vcr between the resonant capacitor who sets for, realized the current mode control to the LLC converter, by a wide margin promotion closed loop stability and reliability, promoted the dynamic behavior of system, also because low frequency department DC gain is high, better than the power frequency ripple suppression effect of the LLC converter of direct control frequency, the low frequency ripple also can be better. And because the increment of the resonant current is directly controlled, the output power is also directly controlled, so that the method has more advantages and better reliability than a method for directly controlling the frequency in the problems of overcurrent, short circuit and the like.
The control method and the circuit for the LLC resonant converter disclosed in the embodiment of the application realize the control of the current mode LLC in a simple mode, improve the dynamic response speed of the converter, reduce the ripple voltage and are easy to realize.
The present invention has been described in terms of specific examples, which are provided to aid understanding of the invention and are not intended to be limiting. Numerous simple deductions, modifications or substitutions may also be made by those skilled in the art in light of the present teachings.
Claims (7)
1. A control circuit for an LLC resonant converter, characterized in that the LLC resonant converter is adapted to convert a first direct current into a second direct current; the LLC resonant converter comprises a switch inverter circuit, a resonant circuit, a voltage transformation circuit, an output circuit and a switch drive control circuit;
the switch inverter circuit is connected with the resonant circuit and is used for converting the first direct current into high-frequency alternating current and outputting the high-frequency alternating current to the resonant circuit;
the resonance circuit is connected with the transformation circuit and is used for carrying out resonance conversion on the high-frequency alternating current and outputting the high-frequency alternating current to the transformation circuit;
the voltage transformation circuit is connected with the output circuit and is used for reducing the voltage of the high-frequency alternating current after resonance conversion and outputting the high-frequency alternating current to the output circuit;
the output circuit is used for outputting the second direct current;
the switch driving control circuit is connected with the switch inverter circuit and the resonance circuit and is used for monitoring a resonance current signal of a resonance inductor Lr of the resonance circuit and a resonance voltage signal at two ends of a resonance capacitor Cr, and outputting a switch driving signal to a power switch tube of the switch inverter circuit according to the resonance current signal and the resonance voltage signal obtained through monitoring; the switch driving signal is used for realizing the switch control of a power switch tube of the switch inverter circuit;
the switch driving control circuit comprises a switch driving circuit, a driving control circuit, a voltage sampling circuit and a current conversion circuit;
the voltage sampling circuit is respectively connected with the resonant circuit and the drive control circuit and is used for monitoring resonant voltage signals at two ends of a resonant capacitor Cr of the resonant circuit and sending the resonant voltage signals obtained by monitoring to the drive control circuit; the voltage sampling circuit comprises a first connecting end, a second connecting end and a third connecting end, the first connecting end and the second connecting end of the voltage sampling circuit are respectively connected with two ends of the resonant capacitor Cr, and the third connecting end of the voltage sampling circuit is connected with the driving control circuit;
the current conversion circuit is respectively connected with the resonance circuit and the drive control circuit and is used for monitoring a resonance current signal flowing through a resonance inductor Lr of the resonance circuit and outputting a resonance current monitoring signal obtained by monitoring the resonance current signal to the drive control circuit; the current conversion circuit comprises a first connecting end and a second connecting end, the first connecting end of the current conversion circuit is connected with the resonance circuit, and the second connecting end of the current conversion circuit is connected with the drive control circuit;
the drive control circuit is connected with the switch drive circuit and is used for outputting a first PWM signal to the switch drive circuit;
the switch driving circuit is connected with the switch inverter circuit and is used for outputting the switch driving signal according to the first PWM signal, and the switch driving signal comprises a first power tube driving signal and a second power tube driving signal; the switch driving circuit comprises a first connecting end, a second connecting end and a third connecting end; the first connecting end of the switch driving circuit is connected with the driving control circuit and is used for inputting the first PWM signal; a second connecting end of the switch driving circuit is connected with the driving control circuit and the switch inverter circuit and is used for outputting a driving signal of the first power tube; a third connecting end of the switch driving circuit is connected with the switch inverter circuit and used for outputting a driving signal of the second power tube;
the drive control circuit comprises a first connecting end, a second connecting end, a third connecting end and a fourth connecting end; the first connection end of the drive control circuit is connected with the first connection end of the switch drive circuit and is used for outputting the first PWM signal; the second connecting end of the driving control circuit is connected with the third connecting end of the voltage sampling circuit and used for inputting the resonance voltage signal; the third connecting end of the driving control circuit is connected with the second connecting end of the current conversion circuit and is used for inputting the resonant current monitoring signal; the fourth connecting end of the drive control circuit is connected with the second connecting end of the switch drive circuit and is used for inputting the drive signal of the first power tube;
the driving control circuit further comprises a fifth connecting end, and the fifth connecting end of the driving control circuit is used for inputting a preset first preset voltage signal;
the drive control circuit also comprises a zero-crossing detection circuit, a sampling control circuit, a drive signal feedback circuit and an SR trigger;
the zero crossing point detection circuit is respectively connected with the third connecting end of the drive control circuit and the sampling control circuit; the zero crossing point detection circuit is used for outputting a sampling activation signal to the sampling control circuit when the resonant current monitoring signal crosses a zero point;
the sampling control circuit is respectively connected with the second connecting end and the fifth connecting end of the driving control circuit and the SR trigger; the sampling control circuit is used for responding to the sampling activation signal to sample the resonance voltage signal, summing a voltage sampling signal obtained by sampling with the first preset voltage signal, and outputting an R trigger signal to an R signal input end of the SR trigger when the sum of the voltage sampling signal and the first preset voltage signal is not larger than the resonance voltage signal;
the driving signal feedback circuit is connected with a fourth connecting end of the driving control circuit and the SR trigger; the driving signal feedback circuit is used for outputting an S trigger signal to an S signal input end of the SR trigger; the S trigger signal is synchronous with the falling edge of the first power tube driving signal;
and the Q output end of the SR trigger is connected with the switch driving circuit and used for outputting the first PWM signal.
2. The control circuit of claim 1, wherein the switching inverter circuit comprises a dc positive input terminal, a dc negative input terminal, a rectified positive output terminal, and a rectified negative output terminal; the direct current positive input end and the direct current negative input end are used for inputting the first direct current; the rectification positive output end and the rectification negative output end are connected with the resonant circuit;
the resonant circuit comprises a rectification positive connecting end, a rectification negative connecting end, a primary side positive connecting end and a primary side negative connecting end; the rectification positive connecting end and the rectification negative connecting end are respectively connected with the rectification positive output end and the rectification negative output end, and the primary side positive connecting end and the primary side negative connecting end are used for being connected with the transformation circuit;
the transformation circuit comprises a first primary side connecting end, a second primary side connecting end, a first secondary side positive connecting end, a first secondary side negative connecting end, a second secondary side positive connecting end and a second secondary side negative connecting end; the first primary side connecting end and the second primary side connecting end are respectively connected with the primary side positive connecting end and the primary side negative connecting end; the first secondary side positive connecting end, the first secondary side negative connecting end, the second secondary side positive connecting end and the second secondary side negative connecting end are used for being connected with the output circuit;
the output circuit comprises a first input connecting end, a second input connecting end, a third input connecting end, a fourth input connecting end, an output positive connecting end and an output negative connecting end; the first input connection end and the second input connection end are respectively connected with the first secondary positive connection end and the first secondary negative connection end, and the third input connection end and the fourth input connection end are respectively connected with the second secondary positive connection end and the second secondary negative connection end; the output positive connecting end and the output negative connecting end of the output circuit are used for outputting the second direct current;
the resonance circuit comprises a resonance capacitor Cr and a resonance inductor Lr; one end of the resonant inductor Lr is connected with the rectifying positive connecting end, and the other end of the resonant inductor Lr is connected with the primary side positive connecting end; one end of the resonant capacitor Cr is connected with the rectification negative connection end, and the other end of the resonant capacitor Cr is connected with the primary side negative connection end;
the transformer circuit comprises a transformer Tr, wherein the transformer Tr comprises a primary winding and two secondary windings; one end of the primary winding is connected with the first primary connecting end, the other end of the primary winding is connected with the second primary connecting end, two ends of one secondary winding are respectively connected with the first secondary positive connecting end and the first secondary negative connecting end, and two ends of the other secondary winding are respectively connected with the second secondary positive connecting end and the second secondary negative connecting end;
the output circuit comprises a diode D11, a diode D12, a capacitor C11, a resistor R11 and a resistor R12; the anode of the diode D11 is connected with the first input connection end of the output circuit, and the cathode of the diode D11 is connected with the output positive connection end of the output circuit; the anode of the diode D12 is connected with the fourth input connecting end of the output circuit, and the cathode of the diode D12 is connected with the output positive connecting end of the output circuit; the capacitor C11 is connected with the resistor R11 in series, one end of the series connection is connected with the output positive connecting end of the output circuit, and the other end of the series connection is connected with the output negative connecting end of the output circuit; one end of the resistor R12 is connected with the output positive connecting end of the output circuit, and the other end of the resistor R12 is connected with the output negative connecting end of the output circuit; and the second input connecting end, the third input connecting end and the output negative connecting end of the output circuit are electrically connected.
3. The control circuit of claim 2, wherein the switching inverter circuit comprises a first power switch transistor S1, a second power switch transistor S2, a third power switch transistor S3 and a fourth power switch transistor S4; a first pole of the first power switch tube S1 is connected to the dc positive input end, a second pole of the first power switch tube S1 is connected to the rectifying positive output end, and a control pole of the first power switch tube S1 is connected to the switch driving control circuit; a first pole of the second power switch tube S2 is connected with the rectification positive output end, a second pole of the second power switch tube S2 is connected with the direct current negative input end, and a control pole of the second power switch tube S2 is connected with the switch driving control circuit; a first pole of the third power switch tube S3 is connected to the dc positive input terminal, a second pole of the third power switch tube S3 is connected to the rectification negative output terminal, and a control pole of the third power switch tube S3 is connected to the switch driving control circuit; a first pole of the fourth power switch tube S4 is connected to the rectification negative output end, a second pole of the fourth power switch tube S4 is connected to the dc negative input end, and a control pole of the fourth power switch tube S4 is connected to the switch driving control circuit.
4. The control circuit of claim 2, wherein the switching inverter circuit comprises a first power switch S5 and a second power switch S6; a first pole of the first power switch tube S5 is connected to the dc positive input terminal, a second pole of the first power switch tube S5 is connected to the rectifying positive output terminal, and a control pole of the first power switch tube S5 is connected to the switch driving control circuit; a first pole of a second power switch tube S6 is connected with the rectification positive output end, a second pole of a second power switch tube S6 is connected with the rectification negative output end, and a control pole of the second power switch tube S6 is connected with the switch driving control circuit; the direct current negative input end is electrically connected with the rectification negative output end.
5. The control circuit of claim 1, wherein the voltage sampling circuit comprises a first sampling capacitor and a second sampling capacitor; one end of the first sampling capacitor is connected with the first connecting end of the voltage sampling circuit, and the other end of the first sampling capacitor is connected with the second connecting end of the voltage sampling circuit; one end of the second sampling capacitor is connected with the second connecting end of the voltage sampling circuit, and the other end of the second sampling capacitor is connected with the third connecting end of the voltage sampling circuit.
6. The control circuit of claim 1, wherein the current conversion circuit comprises a first conversion capacitor, a first conversion resistor, and a first comparator; one end of the first conversion capacitor is connected with the first connection end of the current conversion circuit, and the other end of the first conversion capacitor is connected with the positive input end of the first comparator; two ends of the first conversion resistor are respectively connected with the positive input end and the negative input end of the first comparator; the output end of the first comparator is connected with the driving control circuit, and the negative input end of the first comparator is grounded.
7. A control method for an LLC resonant converter, the LLC resonant converter being configured to convert a first direct current to a second direct current, the control method comprising:
acquiring a resonant current signal of a resonant inductor Lr of a resonant circuit of the LLC resonant converter;
acquiring resonant voltage signals at two ends of a resonant capacitor Cr of a resonant circuit of the LLC resonant converter;
acquiring a switch driving signal according to the resonance current signal and the resonance voltage signal; the switch driving signal is used for realizing the switch control of a power switch tube of a switch inverter circuit of the LLC resonant converter, and the switch driving signal comprises the following components:
the switch driving signals comprise a high-end switch tube driving signal HG and a low-end switch tube driving signal LG; the high-side switch tube driving signal HG is used for driving a high-side power switch tube of a switch inverter circuit of the LLC resonant converter, and the low-side switch tube driving signal LG is used for driving a low-side power switch tube of the switch inverter circuit of the LLC resonant converter;
when the high-end switching tube driving signal HG is output and the resonant current signal crosses zero, sampling the resonant voltage signal to obtain a voltage sampling signal, and obtaining the voltage sampling signal and a voltage sum signal of a preset first preset voltage signal;
when the voltage sum signal is not greater than the resonance voltage signal, switching and outputting a driving signal LG of the low-side switch tube;
the duration of the low-side switch tube driving signal LG is the same as that of the high-side switch tube driving signal HG.
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