CN116388545B - LLC topology current limiting circuit - Google Patents
LLC topology current limiting circuit Download PDFInfo
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- CN116388545B CN116388545B CN202310651160.1A CN202310651160A CN116388545B CN 116388545 B CN116388545 B CN 116388545B CN 202310651160 A CN202310651160 A CN 202310651160A CN 116388545 B CN116388545 B CN 116388545B
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- 230000000670 limiting effect Effects 0.000 title claims abstract description 145
- 239000003990 capacitor Substances 0.000 claims abstract description 80
- 230000008859 change Effects 0.000 claims abstract description 12
- 230000004044 response Effects 0.000 claims abstract description 9
- 238000000034 method Methods 0.000 claims description 45
- 230000008569 process Effects 0.000 claims description 31
- 238000004458 analytical method Methods 0.000 claims description 29
- 230000007704 transition Effects 0.000 claims description 18
- 238000004364 calculation method Methods 0.000 claims description 12
- 238000004422 calculation algorithm Methods 0.000 claims description 5
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- 238000011217 control strategy Methods 0.000 description 3
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Classifications
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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
- H02M1/32—Means for protecting converters other than automatic disconnection
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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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- 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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Abstract
The invention discloses a current limiting circuit of LLC topology, comprising: the current limiting transformer T2, the diode D1, the diode D2, the resonant inductor, the resonant capacitor, the full-bridge LLC topological circuit and the transformer T1; two ends of the primary side of the current limiting transformer T2 are connected with two ends of the resonant capacitor, the secondary side of the current limiting transformer T2 is connected with the voltage input end through a diode D1 and a diode D2, and the cathodes of the diode D1 and the diode D2 are connected with the voltage input end; one end of the full-bridge LLC topology circuit is connected with a resonant inductor, the resonant inductor is connected with a resonant capacitor in series, the positive electrode of the resonant capacitor is connected with the resonant inductor, and the negative electrode of the resonant capacitor is connected with one end of the primary side of the transformer T1; the other end of the full-bridge LLC topological structure is connected with the other end of the primary side of the transformer T1. The scheme of the invention has simple and reliable circuit and low cost. Software participation is not needed, and the difficulty of the system is simplified. Voltage stress due to abrupt current change is not brought about. The dynamic response capability of the system with overload is enhanced.
Description
Technical Field
The invention relates to the technical field of current limiting circuits, in particular to a current limiting circuit of LLC topology.
Background
The current limiting schemes commonly used for full-bridge LLC topologies are as follows: 1. by accelerating the speed of the feedback circuit, the frequency is quickly turned up and the duty cycle is quickly turned down. 2. By sampling the main loop current, the drive is closed. Both of these industry-common approaches have common disadvantages: 1. systems that are not suitable for software control. 2. The LLC can have very large voltage stress in the process of driving the switching tube to change drastically, so that the stress of the switching tube exceeds the standard.
Disclosure of Invention
The present invention provides a current limiting circuit of LLC topology to solve the above-mentioned problems in the prior art.
The invention provides a current limiting circuit of LLC topology, comprising: the current limiting transformer T2, the diode D1, the diode D2, the resonant inductor, the resonant capacitor, the full-bridge LLC topological circuit and the transformer T1;
two ends of the primary side of the current limiting transformer T2 are connected with two ends of the resonant capacitor, the secondary side of the current limiting transformer T2 is connected with the voltage input end through a diode D1 and a diode D2, and the cathodes of the diode D1 and the diode D2 are connected with the voltage input end; one end of the full-bridge LLC topology circuit is connected with a resonant inductor, the resonant inductor is connected with a resonant capacitor in series, the positive electrode of the resonant capacitor is connected with the resonant inductor, and the negative electrode of the resonant capacitor is connected with one end of the primary side of the transformer T1;
the other end of the full-bridge LLC topological structure is connected with the other end of the primary side of the transformer T1.
Preferably, the current limiting transformer T2 is used to clamp the resonance voltage Vcr on the resonance capacitor Cr, and the diodes D1 and D2 are turned on when Vcr is greater than the input voltage Vin; the voltage Vcr across the resonant capacitor Cr is clamped to the same potential as n Vin, n being the turn ratio of the current limiting transformer T2.
Preferably, when loading a load, the equivalent structure of the current limiting circuit comprises:
the positive electrode of the battery is connected with a resonant inductor Lr, and the other end of the resonant inductor Lr is connected with one end of the primary side of the transformer T1;
the negative electrode of the battery is connected with the internal resistance of the battery, the internal resistance of the battery is connected with the positive electrode of the resonance capacitor Cr, and the negative electrode of the resonance capacitor Cr is connected with the other end of the primary side of the transformer T1;
the positive electrode of the resonant capacitor Cr is connected with the primary internal resistance of the current-limiting transformer T2, the other end of the primary internal resistance of the current-limiting transformer T2 is connected with the leakage inductance of the current-limiting transformer T2, the other end of the leakage inductance of the current-limiting transformer T2 is connected with one end of the primary of the current-limiting transformer T2, and the other end of the primary of the current-limiting transformer T2 is connected with the negative electrode of the resonant capacitor Cr;
the two ends of the primary side of the current limiting transformer T2 are connected with the secondary side equivalent resistor of the current limiting transformer T2 in parallel.
Preferably, when the resonance voltage Vcr of the resonance capacitor Cr is greater than n×vbat, the diodes D1 and D2 are turned on, the current-limiting transformer T2 is an ideal transformer, the leakage inductance lit2=0 of the current-limiting transformer T2, the primary internal resistance rt2=0 of the current-limiting transformer T2, the secondary equivalent resistance RL 1=0 of the current-limiting transformer T2, the resonance capacitor Cr is shorted by the internal resistance Rs of the battery, the voltage on the resonance capacitor Cr is n×vbat, vbat is the battery voltage, n is the turn ratio of the current-limiting transformer T2, and the current is limited by limiting the maximum value of the resonance capacitor voltage.
Preferably, the method further comprises a time domain analysis model of the full-bridge LLC topology circuit, which is used for analyzing the dynamic process of the full-bridge LLC topology circuit;
the time domain analysis model is a time domain analysis model based on modal iteration by analyzing the basic working modes of the full-bridge LLC topological circuit and the working modes thereof under different switching frequencies and load conditions, establishing transition criteria among the working modes based on a state plane track analysis method and solving modal duration and output voltage increment under different working modes.
Preferably, the transition criteria include: under different working modes, different mode transition processes exist, and the transition of different modes is needed to be analyzed by using instantaneous value criteria of state variables; setting the current mode of the full-bridge LLC topology circuit, and judging the next mode through judging conditions; the judging conditions include: and comparing the values of the time change rates of the resonant currents, and setting the subsequent mode with the largest time change rate of the resonant currents as a new mode.
Preferably, the output voltage increment includes: in the track operation of each mode, obtaining a track radius according to the position of the track circle center; the circle center of the track is determined by the output voltage, in the operation of a plurality of modes of each half switching period, the output voltage is assumed to be approximately unchanged, and after each half switching period is finished, the output voltage value is updated to drive the motion of the state track until the output voltage enters a steady state, and the state track is in a steady state; the expression of the output voltage increment per half switching cycle is calculated as follows:
selecting the time from the starting conduction time of the first rectifying tube of the secondary side to the starting conduction time of the commutation of the second rectifying tube as a half switching period, setting a track starting point and a track end point in the half switching period, wherein the track starting point is a negative peak value corresponding to the primary side exciting current at the starting time, the track end point is a positive peak value corresponding to the exciting current at the tail time, the exciting current waveforms are positive and negative symmetrically, and the integral of the exciting current in the half switching period is zero;
after the modal operation of half switching period is completed, the resonance capacitance voltage values of the track start point and the track end point are known values, and the increment value of the output voltage is calculated according to the increment of the output voltage in the half switching period and the relation between the resonance current and the resonance capacitance voltage.
Preferably, the time domain analysis model further includes: the frequency time constant optimizing unit is used for calculating the maximum value of the resonance current in the open-loop frequency modulation soft start process of the circuit based on the time domain analysis model;
the iterative calculation unit is used for combining an iterative algorithm to obtain the frequency time constant of the optimal open-loop frequency modulation starting method, so that the maximum value of the resonance current in the starting process just meets the constraint of a current limit value, and the response speed of the output voltage is ensured.
Preferably, the iterative calculation unit includes:
an initialization subunit, configured to initialize state quantities such as a resonant capacitor voltage, a resonant current, an output voltage, etc. in a circuit equation to zero, set a start switching frequency, and set an initial frequency time constant;
an operation subunit, configured to perform modal operation in a half switching period, obtain an output voltage increment and a resonance current peak value in the half period, and update a current calculation time and a corresponding output voltage and switching frequency;
a first judging subunit, configured to judge whether the output voltage enters a steady state: if the steady state is not entered, continuing to execute the operation of the operation subunit; if the starting state is in a steady state, calculating the maximum value of the resonant current in the whole starting process;
the second judging subunit is used for judging whether the maximum value of the resonance current is larger than or equal to the current limiting value, if not, correspondingly increasing or decreasing the frequency time constant according to the magnitude relation between the maximum value of the resonance current in the current starting process and the set current limiting value, and re-entering the initializing subunit for initializing operation, and restarting iterative operation; if yes, the iterative operation is ended, and the current frequency time constant is the optimal value.
Preferably, the full-bridge LLC topology circuit further includes: a closed loop current limiting model of the full-bridge LLC topology circuit;
the closed loop current limiting model comprises: on the state plane track, the circle center of the track reflects the magnitude of output voltage, the radius of the track reflects the magnitude of the amplitude of resonant current, and the radian of the track reflects the time of the switching period; establishing a relation among output voltage, resonant current and switching frequency based on the state track;
under the normal operation condition, the output voltage obtains the control quantity of the switching frequency through the regulator, and the output voltage is regulated and controlled in a closed loop; under the working conditions of soft start, output load and output overload operation, the output voltage obtains a switching frequency corresponding to a current limiting value through a voltage-frequency regulator, the switching frequency corresponding to the current limiting value is larger than a switching frequency control quantity, the current limiting ring starts to work, and the maximum value of the limiting resonant current is kept to be operated at the current limiting value;
under the working conditions of soft start and sudden load, the output voltage gradually rises to the instruction value, the switching frequency corresponding to the current limiting value is finally made to be smaller than the switching frequency control quantity, the current limiting ring is withdrawn from working, and normal closed loop voltage stabilizing adjustment is carried out; under the overload working condition, the output voltage is limited under the voltage value corresponding to the load resistance due to the effect of the current limiting ring, the switching frequency corresponding to the current limiting value is larger than the switching frequency control quantity, and the full-bridge LLC topology circuit always operates under the current limiting working condition.
Compared with the prior art, the invention has the following advantages:
the invention provides a current limiting circuit of LLC topology, comprising: the current limiting transformer T2, the diode D1, the diode D2, the resonant inductor, the resonant capacitor, the full-bridge LLC topological circuit and the transformer T1; two ends of the primary side of the current limiting transformer T2 are connected with two ends of the resonant capacitor, the secondary side of the current limiting transformer T2 is connected with the voltage input end through a diode D1 and a diode D2, and the cathodes of the diode D1 and the diode D2 are connected with the voltage input end; one end of the full-bridge LLC topology circuit is connected with a resonant inductor, the resonant inductor is connected with a resonant capacitor in series, the positive electrode of the resonant capacitor is connected with the resonant inductor, and the negative electrode of the resonant capacitor is connected with one end of the primary side of the transformer T1; the other end of the full-bridge LLC topological structure is connected with the other end of the primary side of the transformer T1. The scheme of the invention has simple and reliable circuit and low cost. Software participation is not needed, and the difficulty of the system is simplified. Voltage stress due to abrupt current change is not brought about. The dynamic response capability of the system with overload is enhanced.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate the invention and together with the embodiments of the invention, serve to explain the invention. In the drawings:
FIG. 1 is a circuit diagram of a current limiting circuit of an LLC topology in an embodiment of the present invention;
FIG. 2 is an equivalent circuit diagram of a current limiting circuit of an LLC topology according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of an iterative computation unit in an embodiment of the present invention.
Detailed Description
The preferred embodiments of the present invention will be described below with reference to the accompanying drawings, it being understood that the preferred embodiments described herein are for illustration and explanation of the present invention only, and are not intended to limit the present invention.
An embodiment of the present invention provides a current limiting circuit of an LLC topology, referring to fig. 1, the current limiting circuit includes: the current limiting transformer T2, the diode D1, the diode D2, the resonant inductor, the resonant capacitor, the full-bridge LLC topological circuit and the transformer T1;
two ends of the primary side of the current limiting transformer T2 are connected with two ends of the resonant capacitor, the secondary side of the current limiting transformer T2 is connected with the voltage input end through a diode D1 and a diode D2, and the cathodes of the diode D1 and the diode D2 are connected with the voltage input end; one end of the full-bridge LLC topology circuit is connected with a resonant inductor, the resonant inductor is connected with a resonant capacitor in series, the positive electrode of the resonant capacitor is connected with the resonant inductor, and the negative electrode of the resonant capacitor is connected with one end of the primary side of the transformer T1;
the other end of the full-bridge LLC topological structure is connected with the other end of the primary side of the transformer T1.
The working principle of the technical scheme is as follows: the scheme adopted by the embodiment comprises the following steps: the current limiting transformer T2, the diode D1, the diode D2, the resonant inductor, the resonant capacitor, the full-bridge LLC topological circuit and the transformer T1; two ends of the primary side of the current limiting transformer T2 are connected with two ends of the resonant capacitor, the secondary side of the current limiting transformer T2 is connected with the voltage input end through a diode D1 and a diode D2, and the cathodes of the diode D1 and the diode D2 are connected with the voltage input end; one end of the full-bridge LLC topology circuit is connected with a resonant inductor, the resonant inductor is connected with a resonant capacitor in series, the positive electrode of the resonant capacitor is connected with the resonant inductor, and the negative electrode of the resonant capacitor is connected with one end of the primary side of the transformer T1; the other end of the full-bridge LLC topological structure is connected with the other end of the primary side of the transformer T1.
In another embodiment, the current limiting transformer T2 is used to clamp the voltage on the resonant capacitor Vcr, and the diodes D1, D2 are turned on when the voltage on Vcr is greater than the input voltage Vin; the voltage on the capacitor Vcr is clamped to the same potential as n Vin, n being the turn ratio of the current limiting transformer T2.
The working principle of the technical scheme is as follows: the scheme adopted by the embodiment is that a current limiting transformer T2 is used for clamping the resonance voltage Vcr on a resonance capacitor Cr, and when the voltage on Vcr is greater than the input voltage Vin, diodes D1 and D2 are conducted; the resonant voltage Vcr on the resonant capacitor Cr is clamped to the same potential as n×vin, n being the turn ratio of the current limiting transformer T2.
In another embodiment, when loading a load, the equivalent structure of the current limiting circuit includes the following parts, referring to fig. 2 specifically, the positive electrode of the battery is connected to the resonant inductor Lr, and the other end of the resonant inductor Lr is connected to one end of the primary side of the transformer T1;
the negative electrode of the battery is connected with the internal resistance of the battery, the internal resistance of the battery is connected with the positive electrode of the resonance capacitor Cr, and the negative electrode of the resonance capacitor Cr is connected with the other end of the primary side of the transformer T1;
the positive electrode of the resonant capacitor Cr is connected with the primary internal resistance of the current-limiting transformer T2, the other end of the primary internal resistance of the current-limiting transformer T2 is connected with the leakage inductance of the current-limiting transformer T2, the other end of the leakage inductance of the current-limiting transformer T2 is connected with one end of the primary of the current-limiting transformer T2, and the other end of the primary of the current-limiting transformer T2 is connected with the negative electrode of the resonant capacitor Cr;
the two ends of the primary side of the current limiting transformer T2 are connected with the secondary side equivalent resistor of the current limiting transformer T2 in parallel.
The working principle of the technical scheme is as follows: the scheme adopted by the embodiment is that when loading a load, the equivalent structure of the current limiting circuit comprises: the positive electrode of the battery is connected with a resonant inductor Lr, and the other end of the resonant inductor Lr is connected with one end of the primary side of the transformer T1; the negative electrode of the battery is connected with the internal resistance of the battery, the internal resistance of the battery is connected with the positive electrode of the resonance capacitor Cr, and the negative electrode of the resonance capacitor Cr is connected with the other end of the primary side of the transformer T1; the positive electrode of the resonant capacitor Cr is connected with the primary internal resistance of the current-limiting transformer T2, the other end of the primary internal resistance of the current-limiting transformer T2 is connected with the leakage inductance of the current-limiting transformer T2, the other end of the leakage inductance of the current-limiting transformer T2 is connected with one end of the primary of the current-limiting transformer T2, and the other end of the primary of the current-limiting transformer T2 is connected with the negative electrode of the resonant capacitor Cr; the two ends of the primary side of the current limiting transformer T2 are connected with the secondary side equivalent resistor of the current limiting transformer T2 in parallel.
In another embodiment, when the resonance voltage Vcr of the resonance capacitor Cr is greater than n×vbat, the diodes D1 and D2 are turned on, the current limiting transformer T2 is an ideal transformer, the leakage inductance lit2=0 of the current limiting transformer T2, the primary internal resistance rt2=0 of the current limiting transformer T2, the secondary equivalent resistance RL 1=0 of the current limiting transformer T2, the resonance capacitor Cr is shorted by the battery internal resistance Rs, the voltage on the resonance capacitor Cr is n×vbat, vbat is the battery voltage, n is the turn ratio of the current transformer T2, and the current limiting is performed by limiting the maximum value of the resonance capacitor voltage.
The working principle of the technical scheme is as follows: in the scheme adopted in this embodiment, when the resonance voltage Vcr of the resonance capacitor Cr is greater than n×vbat, the diodes D1 and D2 are turned on, the current-limiting transformer T2 is an ideal transformer, the leakage inductance lit2=0 of the current-limiting transformer T2, the primary internal resistance rt2=0 of the current-limiting transformer T2, the secondary equivalent resistance RL 1=0 of the current-limiting transformer T2, the resonance capacitor Cr is shorted by the battery internal resistance Rs, the voltage on the resonance capacitor Cr is n×vbat, vbat is the battery voltage, n is the turn ratio of the current-limiting transformer T2, and the current is limited by limiting the maximum value of the resonance capacitor voltage.
To sum up, the transformer T2 in fig. 1 is used to clamp the resonance voltage Vcr on the resonance capacitor Cr, and the diodes D1 and D2 are turned on when the voltage Vcr is greater than the input voltage Vin; the resonance voltage on Cr is clamped to the same potential as n x Vin. The circuit equivalent in loading is shown in fig. 2 (RS is the internal resistance of the battery, lr is the resonant inductance, cr is the resonant capacitance, T2 is the current limiting voltage device, lt 2 is the leakage inductance of the transformer, RT2 is the primary internal resistance of the transformer T2, RL1 is the secondary equivalent resistance of the transformer T2, and n is the turn ratio of T2).
When the voltage Vcr of the resonant capacitor is greater than n×vbat, D1 and D2 in fig. 1 are turned on, if the transformer T2 is an ideal transformer, lit2=0, rt2=0, rl1=0, i.e. Cr is shorted by Rs, the voltage on the capacitor is n times the battery voltage, i.e. n×vbat, vbat represents the battery voltage, and the current limiting effect is achieved by limiting the maximum value of the capacitor voltage.
In another embodiment, the method further comprises a time domain analysis model of the full-bridge LLC topology circuit, which is used for analyzing the dynamic process of the full-bridge LLC topology circuit;
the time domain analysis model is a time domain analysis model based on modal iteration by analyzing the basic working modes of the full-bridge LLC topological circuit and the working modes thereof under different switching frequencies and load conditions, establishing transition criteria among the working modes based on a state plane track analysis method and solving modal duration and output voltage increment under different working modes.
The working principle of the technical scheme is as follows: the scheme adopted by the embodiment is that the time domain analysis model also comprises a full-bridge LLC topological circuit and is used for analyzing the dynamic process of the full-bridge LLC topological circuit; the time domain analysis model is a time domain analysis model based on modal iteration by analyzing the basic working modes of the full-bridge LLC topological circuit and the working modes thereof under different switching frequencies and load conditions, establishing transition criteria among the working modes based on a state plane track analysis method and solving modal duration and output voltage increment under different working modes.
In another embodiment, the transition criteria include: under different working modes, different mode transition processes exist, and the transition of different modes is needed to be analyzed by using instantaneous value criteria of state variables; setting the current mode of the full-bridge LLC topology circuit, and judging the next mode through judging conditions; the judging conditions include: and comparing the values of the time change rates of the resonant currents, and setting the subsequent mode with the largest time change rate of the resonant currents as a new mode.
The working principle of the technical scheme is as follows: the scheme adopted by the embodiment is that the transition criteria include: under different working modes, different mode transition processes exist, and the transition of different modes is needed to be analyzed by using instantaneous value criteria of state variables; setting the current mode of the full-bridge LLC topology circuit, and judging the next mode through judging conditions; the judging conditions include: and comparing the values of the time change rates of the resonant currents, and setting the subsequent mode with the largest time change rate of the resonant currents as a new mode.
In another embodiment, the output voltage increment includes: in the track operation of each mode, obtaining a track radius according to the position of the track circle center; the circle center of the track is determined by the output voltage, in the operation of a plurality of modes of each half switching period, the output voltage is assumed to be approximately unchanged, and after each half switching period is finished, the output voltage value is updated to drive the motion of the state track until the output voltage enters a steady state, and the state track is in a steady state; the expression of the output voltage increment per half switching cycle is calculated as follows:
selecting the time from the starting conduction time of the first rectifying tube of the secondary side to the starting conduction time of the commutation of the second rectifying tube as a half switching period, setting a track starting point and a track end point in the half switching period, wherein the track starting point is a negative peak value corresponding to the primary side exciting current at the starting time, the track end point is a positive peak value corresponding to the exciting current at the tail time, the exciting current waveforms are positive and negative symmetrically, and the integral of the exciting current in the half switching period is zero;
after the modal operation of half switching period is completed, the resonance capacitance voltage values of the start point and the end point of the state track are known values, and the increment value of the output voltage is calculated according to the increment of the output voltage in the half switching period and the relation between the resonance current and the resonance capacitance voltage.
The working principle of the technical scheme is as follows: the scheme adopted by the embodiment is that the output voltage increment comprises: in the track operation of each mode, obtaining a track radius according to the position of the track circle center; the circle center of the track is determined by the output voltage, in the operation of a plurality of modes of each half switching period, the output voltage is assumed to be approximately unchanged, and after each half switching period is finished, the output voltage value is updated to drive the motion of the state track until the output voltage enters a steady state, and the state track is in a steady state; the expression of the output voltage increment per half switching cycle is calculated as follows: selecting the time from the starting conduction time of the first rectifying tube to the starting conduction time of the second rectifying tube as a half switching period, and setting a track starting point and a track end point as follows in the half switching period: the track starting point is a negative peak value corresponding to the primary exciting current at the starting moment, the track ending point is a positive peak value corresponding to the exciting current at the tail moment, the exciting current waveforms are positive and negative symmetrically, and the integral of the exciting current in a half switching period is zero; after the modal operation of half switching period is completed, the resonance capacitance voltage values of the start point and the end point of the state track are known values, and the increment value of the output voltage is calculated according to the increment of the output voltage in the half switching period and the relation between the resonance current and the resonance capacitance voltage.
Under the impact load working condition, output overload working condition and short circuit working condition of circuit starting and sudden load, the full-bridge LLC topological circuit has the problem of primary side resonant circuit current overshoot, and the damage of a switch device or false triggering of primary side overcurrent protection can be caused. The common open-loop frequency modulation or duty cycle modulation current limiting strategy has poor resonant current waveform control effect, large output voltage and resonant current fluctuation under overload working conditions, and lacks a simple current limiting parameter design method. The closed loop current limiting strategy can realize flexible current limiting characteristics, but resonant current or output current sampling needs to be increased, and the cost is high.
Setting is carried out aiming at modeling analysis, open-loop and closed-loop current limiting control technology of a dynamic process of a full-bridge LLC topological circuit. Firstly, the embodiment analyzes the basic working mode of the LLC circuit and the working modes under different switching frequencies and load conditions, and deduces the state equation descriptions of different working modes and the state plane track characteristics of different working modes. Based on a state plane analysis method, working mode transition criteria in a circuit dynamic process are solved, each mode duration in different working modes is solved, state quantity expressions such as output voltage increment, resonance current peak value and the like in a half switching period are deduced, and finally a time domain analysis model of the full-bridge LLC topology circuit is established by using iterative operation of modes. Compared with circuit simulation, the time domain model can save a large amount of time, can ensure enough calculation precision, and can be used for analyzing the dynamic change process of key circuit state quantity under the working conditions of soft start, sudden load and the like of a full-bridge LLC topology circuit.
In another embodiment, the time domain analysis model further comprises: the frequency time constant optimizing unit is used for calculating the maximum value of the resonance current in the open-loop frequency modulation soft start process of the circuit based on the time domain analysis model;
the iterative calculation unit is used for combining an iterative algorithm to obtain the frequency time constant of the optimal open-loop frequency modulation starting method, so that the maximum value of the resonance current in the starting process just meets the constraint of a current limit value, and meanwhile, the output voltage is ensured to have the response speed as high as possible.
The working principle of the technical scheme is as follows: the scheme adopted in this embodiment is that the time domain analysis model further includes: the frequency time constant optimizing unit is used for calculating the maximum value of the resonance current in the open-loop frequency modulation soft start process of the circuit based on the time domain analysis model; the iterative calculation unit is used for combining an iterative algorithm to obtain the frequency time constant of the optimal open-loop frequency modulation starting method, so that the maximum value of the resonance current in the starting process just meets the constraint of a current limit value, and meanwhile, the output voltage is ensured to have the response speed as high as possible.
The relation between the overshoot value and the convergence value of the resonant current at the starting time of the circuit and the initial switching frequency is matched with an initial driving pulse width optimization method, so that the resonant current at the starting time quickly enters the convergence state without overshooting, and the requirement of the initial switching frequency is reduced. And under the condition of lower resonant current limiting value, LLC circuit topology with split resonant capacitor structure is adopted, so that the design difficulty of the initial transition pulse number and pulse width is reduced. Based on a time domain analysis model of the full-bridge LLC topology circuit, the maximum value of the resonance current in the open loop current limiting soft start process is calculated, and an optimal frequency modulation time constant parameter is obtained by combining an iterative optimization algorithm, so that the requirement of the resonance current limiting value can be met, and meanwhile, the output voltage response is ensured to be as fast as possible.
In another embodiment, referring to fig. 3, the iterative calculation unit includes:
an initialization subunit, configured to initialize state quantities such as a resonant capacitor voltage, a resonant current, an output voltage, etc. in a circuit equation to zero, set a start switching frequency, and set an initial frequency time constant;
an operation subunit, configured to perform modal operation in a half switching period, obtain an output voltage increment and a resonance current peak value in the half period, and update a current calculation time and a corresponding output voltage and switching frequency;
a first judging subunit, configured to judge whether the output voltage enters a steady state: if the steady state is not entered, continuing to execute the operation of the operation subunit; if the starting state is in a steady state, calculating the maximum value of the resonant current in the whole starting process;
the second judging subunit is used for judging whether the maximum value of the resonance current is larger than or equal to the current limiting value, if not, correspondingly increasing or decreasing the frequency time constant according to the magnitude relation between the maximum value of the resonance current in the current starting process and the set current limiting value, and re-entering the initializing subunit for initializing operation, and restarting iterative operation; if yes, the iterative operation is ended, and the current frequency time constant is the optimal value.
The working principle of the technical scheme is as follows: the scheme adopted by the embodiment is that the iterative computation unit comprises: an initialization subunit, configured to initialize state quantities such as a resonant capacitor voltage, a resonant current, an output voltage, etc. in a circuit equation to zero, set a start switching frequency, and set an initial frequency time constant; an operation subunit, configured to perform modal operation in a half switching period, obtain an output voltage increment and a resonance current peak value in the half period, and update a current calculation time and a corresponding output voltage and switching frequency; a first judging subunit, configured to judge whether the output voltage enters a steady state: if the steady state is not entered, continuing to execute the operation of the operation subunit; if the starting state is in a steady state, calculating the maximum value of the resonant current in the whole starting process; the second judging subunit is used for judging whether the maximum value of the resonance current is larger than or equal to the current limiting value, if not, correspondingly increasing or decreasing the frequency time constant according to the magnitude relation between the maximum value of the resonance current in the current starting process and the set current limiting value, and re-entering the initializing subunit for initializing operation, and restarting iterative operation; if yes, the iterative operation is ended, and the current frequency time constant is the optimal value.
An excessively small tuning time constant will cause a large overshoot of the resonant current during start-up, while an excessively large tuning time constant will result in an excessively slow response of the output voltage, so that there is an optimal tuning time constant, so that the value of the overshoot of the resonant current at this constant is exactly equal to the desired current limit value, and the response of the output voltage reaches the fastest under this tuning mode and current limit constraint.
In another embodiment, the full-bridge LLC topology circuit further includes: a closed loop current limiting model of the full-bridge LLC topology circuit;
the closed loop current limiting model comprises: on the state plane track, the circle center of the track reflects the magnitude of output voltage, the radius of the track reflects the magnitude of the amplitude of resonant current, and the radian of the track reflects the time of the switching period; establishing a relation among output voltage, resonant current and switching frequency based on the state track;
under the normal operation condition, the output voltage obtains the control quantity of the switching frequency through the regulator, and the output voltage is regulated and controlled in a closed loop; under the working conditions of soft start, output load and output overload operation, the output voltage obtains a switching frequency corresponding to a current limiting value through a voltage-frequency regulator, the switching frequency corresponding to the current limiting value is larger than a switching frequency control quantity, the current limiting ring starts to work, and the maximum value of the limiting resonant current is kept to be operated at the current limiting value;
under the working conditions of soft start and sudden load, the output voltage gradually rises to the instruction value, the switching frequency corresponding to the current limiting value is finally made to be smaller than the switching frequency control quantity, the current limiting ring is withdrawn from working, and normal closed loop voltage stabilizing adjustment is carried out; under the overload working condition, the output voltage is limited under the voltage value corresponding to the load resistance due to the effect of the current limiting ring, the switching frequency corresponding to the current limiting value is larger than the switching frequency control quantity, and the full-bridge LLC topology circuit always operates under the current limiting working condition.
The working principle of the technical scheme is as follows: the scheme adopted by the embodiment is that the full-bridge LLC topology circuit further comprises: a closed loop current limiting model of the full-bridge LLC topology circuit; the closed loop current limiting model comprises: on the state plane track, the circle center of the track reflects the magnitude of output voltage, the radius of the track reflects the magnitude of the amplitude of resonant current, and the radian of the track reflects the time of the switching period; establishing a relation among output voltage, resonant current and switching frequency based on the state track; under the normal operation condition, the output voltage obtains the control quantity of the switching frequency through the regulator, and the output voltage is regulated and controlled in a closed loop; under the working conditions of soft start, output load and output overload operation, the output voltage obtains a switching frequency corresponding to a current limiting value through a voltage-frequency regulator, the switching frequency corresponding to the current limiting value is larger than a switching frequency control quantity, the current limiting ring starts to work, and the maximum value of the limiting resonant current is kept to be operated at the current limiting value; under the working conditions of soft start and sudden load, the output voltage gradually rises to the instruction value, the switching frequency corresponding to the current limiting value is finally made to be smaller than the switching frequency control quantity, the current limiting ring is withdrawn from working, and normal closed loop voltage stabilizing adjustment is carried out; under the overload working condition, the output voltage is limited under the voltage value corresponding to the load resistance due to the effect of the current limiting ring, the switching frequency corresponding to the current limiting value is larger than the switching frequency control quantity, and the full-bridge LLC topology circuit always operates under the current limiting working condition.
The open loop current limiting method has simple control logic, only needs the resonant current to flow through the current trigger signal, but has poor waveform control quality, and particularly under the overload working condition, the output voltage and the resonant current in the wave-by-wave current limiting method have large fluctuation, so that the closed loop current limiting method is needed under the condition of requiring better current waveform control. The conventional closed-loop current limiting method forms closed-loop feedback by sampling the resonant current or the resonant capacitor voltage, but the application of the method is limited due to the high requirement of the sampling rate of the high-frequency signal.
It can be seen from the full-bridge LLC topology that the operating characteristics of the resonant current are affected by both the clamping voltages on the input excitation source and the excitation inductance, i.e. by the switching frequency and the output voltage. According to the existing output voltage sampling amount, the desired closed loop current limiting characteristic can be realized by combining the regulation and control of the switching frequency, the resonant current sampling can be saved, and the hysteresis regulation characteristic of a current sampling method can be avoided. The embodiment analyzes the relation among the resonant current, the switching frequency and the output voltage, proposes a corresponding closed-loop current limiting control strategy, and verifies the feasibility of the control strategy and the accuracy of an analysis result through experiments.
The beneficial effects of the technical scheme are as follows: the scheme provided by the embodiment analyzes the relation among the resonance current peak value, the output voltage and the switching frequency under the influence of exciting current, and further provides a closed-loop current-limiting control strategy for limiting the current sampling of the switching frequency in real time based on the output voltage, so that the resonance current peak value under the soft start, sudden load process and overload working condition is controlled at a constant current-limiting value, and optimal resonance current stress control is realized. The article gives out the design principle of the current limiting parameter, and analyzes the upper limit value of the output voltage under the overload current limiting working condition and the establishment time of the output voltage in the current limiting starting process.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (8)
1. A current limiting circuit of an LLC topology, comprising: the current limiting transformer T2, the diode D1, the diode D2, the resonant inductor, the resonant capacitor, the full-bridge LLC topological circuit and the transformer T1;
two ends of the primary side of the current limiting transformer T2 are connected with two ends of the resonant capacitor, the secondary side of the current limiting transformer T2 is connected with the voltage input end through a diode D1 and a diode D2, and the cathodes of the diode D1 and the diode D2 are connected with the voltage input end; one end of the full-bridge LLC topology circuit is connected with a resonant inductor, the resonant inductor is connected with a resonant capacitor in series, the positive electrode of the resonant capacitor is connected with the resonant inductor, and the negative electrode of the resonant capacitor is connected with one end of the primary side of the transformer T1;
the other end of the full-bridge LLC topological structure is connected with the other end of the primary side of the transformer T1;
when loading a load, the equivalent structure of the current limiting circuit comprises:
the positive electrode of the battery is connected with a resonant inductor Lr, and the other end of the resonant inductor Lr is connected with one end of the primary side of the transformer T1;
the negative electrode of the battery is connected with the internal resistance of the battery, the internal resistance of the battery is connected with the positive electrode of the resonance capacitor Cr, and the negative electrode of the resonance capacitor Cr is connected with the other end of the primary side of the transformer T1;
the positive electrode of the resonant capacitor Cr is connected with the primary internal resistance of the current-limiting transformer T2, the other end of the primary internal resistance of the current-limiting transformer T2 is connected with the leakage inductance of the current-limiting transformer T2, the other end of the leakage inductance of the current-limiting transformer T2 is connected with one end of the primary of the current-limiting transformer T2, and the other end of the primary of the current-limiting transformer T2 is connected with the negative electrode of the resonant capacitor Cr;
the two ends of the primary side of the current limiting transformer T2 are connected in parallel with the secondary side equivalent resistor of the current limiting transformer T2;
when the resonance voltage Vcr of the resonance capacitor Cr is greater than n×vbat, the diodes D1 and D2 are turned on, the current-limiting transformer T2 is an ideal transformer, the leakage inductance lit2=0 of the current-limiting transformer T2, the primary internal resistance rt2=0 of the current-limiting transformer T2, the secondary equivalent resistance RL 1=0 of the current-limiting transformer T2, the resonance capacitor Cr is shorted by the battery internal resistance Rs, the voltage on the resonance capacitor Cr is n×vbat, vbat is the battery voltage, n is the turn ratio of the current-limiting transformer T2, and the current is limited by limiting the maximum value of the resonance capacitor voltage.
2. A current limiting circuit of LLC topology as defined in claim 1, wherein,
the current limiting transformer T2 is used for clamping the resonance voltage Vcr on the resonance capacitor Cr, and the diodes D1 and D2 are conducted when Vcr is larger than the input voltage Vin; the resonant voltage Vcr on the resonant capacitor Cr is clamped to the same potential as n×vin, n being the turn ratio of the current limiting transformer T2.
3. The current limiting circuit of an LLC topology according to claim 1, further comprising a time domain analysis model of the full-bridge LLC topology circuit for analyzing dynamic processes of the full-bridge LLC topology circuit;
the time domain analysis model is a time domain analysis model based on modal iteration by analyzing the basic working modes of the full-bridge LLC topological circuit and the working modes thereof under different switching frequencies and load conditions, establishing transition criteria among the working modes based on a state plane track analysis method and solving modal duration and output voltage increment under different working modes.
4. A current limiting circuit of LLC topology as claimed in claim 3, wherein,
the transition criteria include: under different working modes, different mode transition processes exist, and the transition of different modes is needed to be analyzed by using instantaneous value criteria of state variables; setting the current mode of the full-bridge LLC topology circuit, and judging the next mode through judging conditions; the judging conditions include: and comparing the values of the time change rates of the resonant currents, and setting the subsequent mode with the largest time change rate of the resonant currents as a new mode.
5. A current limiting circuit of LLC topology as claimed in claim 3, wherein,
the output voltage increment includes: in the track operation of each mode, obtaining a track radius according to the position of the track circle center; the circle center of the track is determined by the output voltage, in the operation of a plurality of modes of each half switching period, the output voltage is assumed to be approximately unchanged, and after each half switching period is finished, the output voltage value is updated to drive the motion of the state track until the output voltage enters a steady state, and the state track is in a steady state; the expression of the output voltage increment per half switching cycle is calculated as follows:
selecting the time from the starting conduction time of the first rectifying tube of the secondary side to the starting conduction time of the commutation of the second rectifying tube as a half switching period, setting a track starting point and a track end point in the half switching period, wherein the track starting point is a negative peak value corresponding to the primary side exciting current at the starting time, the track end point is a positive peak value corresponding to the exciting current at the tail time, the exciting current waveforms are positive and negative symmetrically, and the integral of the exciting current in the half switching period is zero;
after the modal operation of half switching period is completed, the resonance capacitance voltage values of the track start point and the track end point are known values, and the increment value of the output voltage is calculated according to the increment of the output voltage in the half switching period and the relation between the resonance current and the resonance capacitance voltage.
6. A current limiting circuit of LLC topology as claimed in claim 3, wherein,
the time domain analysis model further includes: the frequency time constant optimizing unit is used for calculating the maximum value of the resonance current in the open-loop frequency modulation soft start process of the circuit based on the time domain analysis model;
the iterative calculation unit is used for combining an iterative algorithm to obtain the frequency time constant of the optimal open-loop frequency modulation starting method, so that the maximum value of the resonance current in the starting process just meets the constraint of a current limit value, and the response speed of the output voltage is ensured.
7. A current limiting circuit of an LLC topology as claimed in claim 6, wherein said iterative calculation unit comprises:
an initialization subunit, configured to initialize the state quantity of the resonant capacitor voltage, the resonant current and the output voltage in the circuit equation to zero, set the starting switching frequency, and set an initial frequency time constant;
an operation subunit, configured to perform modal operation in a half switching period, obtain an output voltage increment and a resonance current peak value in the half period, and update a current calculation time and a corresponding output voltage and switching frequency;
a first judging subunit, configured to judge whether the output voltage enters a steady state: if the steady state is not entered, continuing to execute the operation of the operation subunit; if the starting state is in a steady state, calculating the maximum value of the resonant current in the whole starting process;
the second judging subunit is used for judging whether the maximum value of the resonance current is larger than or equal to the current limiting value, if not, correspondingly increasing or decreasing the frequency time constant according to the magnitude relation between the maximum value of the resonance current in the current starting process and the set current limiting value, and re-entering the initializing subunit for initializing operation, and restarting iterative operation; if yes, the iterative operation is ended, and the current frequency time constant is the optimal value.
8. A current limiting circuit of an LLC topology according to claim 1, wherein said full bridge LLC topology circuit further comprises: a closed loop current limiting model of the full-bridge LLC topology circuit;
the closed loop current limiting model comprises: on the state plane track, the circle center of the track reflects the magnitude of output voltage, the radius of the track reflects the magnitude of the amplitude of resonant current, and the radian of the track reflects the time of the switching period; establishing a relation among output voltage, resonant current and switching frequency based on the state track;
under the normal operation condition, the output voltage obtains the control quantity of the switching frequency through the regulator, and the output voltage is regulated and controlled in a closed loop; under the working conditions of soft start, output load and output overload operation, the output voltage obtains a switching frequency corresponding to a current limiting value through a voltage-frequency regulator, the switching frequency corresponding to the current limiting value is larger than a switching frequency control quantity, the current limiting ring starts to work, and the maximum value of the limiting resonant current is kept to be operated at the current limiting value;
under the working conditions of soft start and sudden load, the output voltage gradually rises to the instruction value, the switching frequency corresponding to the current limiting value is finally made to be smaller than the switching frequency control quantity, the current limiting ring is withdrawn from working, and normal closed loop voltage stabilizing adjustment is carried out; under the overload working condition, the output voltage is limited under the voltage value corresponding to the load resistance due to the effect of the current limiting ring, the switching frequency corresponding to the current limiting value is larger than the switching frequency control quantity, and the full-bridge LLC topology circuit always operates under the current limiting working condition.
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