CN114421780B - Resonant converter and control method - Google Patents

Resonant converter and control method Download PDF

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Publication number
CN114421780B
CN114421780B CN202210238980.3A CN202210238980A CN114421780B CN 114421780 B CN114421780 B CN 114421780B CN 202210238980 A CN202210238980 A CN 202210238980A CN 114421780 B CN114421780 B CN 114421780B
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switching tube
node
switching
conversion circuit
voltage conversion
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CN114421780A (en
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肖荣
易德刚
佘畅
陈齐
其他发明人请求不公开姓名
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Shenzhen Sofarsolar Co Ltd
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Shenzhen Sofarsolar Co Ltd
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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
    • H02M3/3353—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 at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter
    • 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
    • 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 embodiment of the invention provides a resonant converter and a control method, which are characterized in that the method is used for the resonant converter, and the resonant converter comprises a first voltage conversion circuit, a second voltage conversion circuit and a resonant cavity circuit. The second voltage conversion circuit comprises a first bridge arm and a second bridge arm which are connected in parallel, and each bridge arm comprises two switching tubes which are connected in series. And a first end and a second end of the resonant cavity circuit are respectively connected with the first voltage conversion circuit, and a third end and a fourth end are respectively connected with the midpoint of the first bridge arm and the midpoint of the second bridge arm. The method comprises the following steps: when the second voltage conversion circuit is used for an inverter circuit and the first voltage conversion circuit is used for a rectifier circuit, acquiring a free oscillation period when the voltage between the midpoint of the first bridge arm and the midpoint of the second bridge arm is in a free oscillation state; and combining equivalent circuits of the converter under each switching mode to obtain the conduction time, thereby realizing approximate soft switching. The method can enable the resonant converter to operate more stably and more efficiently under the condition of light load.

Description

Resonant converter and control method
Technical Field
The embodiment of the invention relates to the technical field of power electronics, in particular to a resonant converter and a control method.
Background
The resonant converter has the characteristics of electric isolation, strong soft switching capability, high efficiency and the like, and becomes an application and research hotspot in various application fields. In the prior art, a resonant converter generally adopts a frequency conversion control mode to complete function realization, and under a light load condition, the gain of the resonant converter changes very slowly along with the switching frequency, so that under the traditional frequency conversion control mode, the resonant converter is difficult to realize stable operation under the light load condition by changing the switching frequency, and therefore a new control method needs to be provided to ensure that the resonant converter can still stably and efficiently operate under the light load condition.
Disclosure of Invention
The embodiment of the invention aims to provide a resonant converter and a control method, so that the resonant converter can run more stably and more efficiently under the condition of light load.
In a first aspect, a resonant converter control method is provided for a resonant converter including a first voltage conversion circuit, a second voltage conversion circuit, and a resonant cavity circuit.
The second voltage conversion circuit comprises two parallel bridge arms, wherein one bridge arm comprises a fifth switching tube and a sixth switching tube which are connected in series, the other bridge arm comprises a seventh switching tube and an eighth switching tube which are connected in series, the fifth switching tube and the sixth switching tube are connected to the first node, the seventh switching tube and the eighth switching tube are connected to the second node, and each switching tube comprises a diode which is connected in reverse parallel.
The first end and the second end of the resonant cavity circuit are respectively connected with the first voltage conversion circuit, and the third end and the fourth end are respectively connected with the first node and the second node.
The method comprises the following steps:
when the second voltage conversion circuit is used for an inverter circuit and the first voltage conversion circuit is used for a rectifier circuit, acquiring the free oscillation period of the voltages of the first node and the second node in a high-frequency free oscillation state;
obtaining the conduction time according to the free oscillation period;
and controlling the on-off of the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube according to the on-off time.
In some embodiments, the first voltage conversion circuit comprises two parallel legs, wherein one leg comprises a first diode and a second diode connected in series, the other leg comprises a third diode and a fourth diode connected in series, the first diode and the second diode are connected to a third node, and the third diode and the fourth diode are connected to a fourth node.
The resonant cavity circuit comprises a first capacitor, a first inductor, a second inductor and a transformer, wherein the first capacitor is connected between a third node and the first end of the primary side of the transformer in series, the first inductor is connected between a fourth node and the second end of the primary side of the transformer in series, and the second inductor is connected between the first end and the second end of the primary side of the transformer in parallel.
The first voltage conversion circuit includes a first junction capacitor, and the second voltage conversion circuit includes a second junction capacitor.
The free oscillation period described above is obtained by the following relationship:
Figure 313695DEST_PATH_IMAGE001
and the frequency converter is characterized in that Cjp is a parameter of the first junction capacitor, Cjs is a parameter of the second junction capacitor, N is an original secondary side turn ratio of the transformer, Cr is a parameter of the first capacitor, Lr is a parameter of the first inductor, Lm is a parameter of the second inductor, and s is a complex frequency.
In some embodiments, the free-running period and the on-time satisfy the following relationship:
Figure 421460DEST_PATH_IMAGE002
wherein ton is the on-time, fsw is the switching frequency, Tosc is the free oscillation period, n is a non-negative integer, and f is a first function.
In some embodiments, the controlling the on/off of the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube according to the on-time includes:
in the on-time of the positive half switching period, controlling the fifth switching tube and the eighth switching tube to be on and controlling the sixth switching tube and the seventh switching tube to be off;
controlling a fifth switching tube, a sixth switching tube, a seventh switching tube and an eighth switching tube to be cut off in the rest time of the positive half switching period;
in the conducting time of the negative half switching period, controlling the sixth switching tube and the seventh switching tube to be conducted and controlling the fifth switching tube and the eighth switching tube to be cut off;
and controlling the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube to be cut off in the rest time of the negative half switching period.
In a second aspect, a resonant converter is provided that includes a first voltage translation circuit, a second voltage translation circuit, a resonant cavity circuit, at least one processor, and a memory coupled to the processor.
The second voltage conversion circuit comprises two parallel bridge arms, wherein one bridge arm comprises a fifth switching tube and a sixth switching tube which are connected in series, the other bridge arm comprises a seventh switching tube and an eighth switching tube which are connected in series, the fifth switching tube and the sixth switching tube are connected to a first node, and the seventh switching tube and the eighth switching tube are connected to a second node.
The first end and the second end of the resonant cavity circuit are respectively connected with the first voltage conversion circuit, and the third end and the fourth end are respectively connected with the first node and the second node.
The memory stores instructions executable by the at least one processor to cause the at least one processor to perform the method.
In some embodiments, in a single switching cycle, the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube are in a turn-off period, and when the primary side resonant current of the transformer drops to zero, the voltage between the first node and the second node is in a free oscillation state.
In a third aspect, a power supply system is provided, which comprises a resonant converter as described above.
Compared with the prior art, the embodiment of the invention at least has the following beneficial effects: the embodiment of the invention provides a control method of a resonant converter, which is applied to the resonant converter. The method obtains a conduction time according to the free oscillation period of the resonant converter, and controls the on-off of a fifth switching tube, a sixth switching tube, a seventh switching tube and an eighth switching tube in the resonant converter according to the conduction time. Due to the fact that the control method of PWM (pulse width modulation) is used (namely the on-time of the switching tube is set by adjusting the duty ratio of the control signal), the output voltage ripple of the resonant converter is small, the resonant converter can run more stably under the light load condition, all the switching tubes work in a mode similar to soft switching, switching loss is reduced, and therefore the efficiency of the resonant converter is improved.
Drawings
One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the figures in which like reference numerals refer to similar elements and which are not to scale unless otherwise specified.
Fig. 1 is a schematic diagram of a topology of a resonant converter according to an embodiment of the present invention;
FIGS. 2a to 2e are schematic equivalent circuit diagrams of resonant converters in modes 1 to 5 according to an embodiment of the present invention;
fig. 3 is a schematic flowchart of a resonant converter control method according to an embodiment of the present invention;
fig. 4 is a waveform diagram illustrating operation of a resonant converter according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a process for solving for turn-on time according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of a resonant converter according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that, if not conflicted, the various features of the embodiments of the invention may be combined with each other within the scope of protection of the present application. In addition, although the functional blocks are divided in the device diagram, in some cases, the blocks may be divided differently from those in the device. Further, the terms "first," "second," and the like, as used herein, do not limit the data and the execution order, but merely distinguish the same items or similar items having substantially the same functions and actions.
Referring to fig. 1, fig. 1 shows a topology of a resonant converter. The resonant converter 10 includes a first voltage conversion circuit 100, a second voltage conversion circuit 200, and a resonant cavity circuit 300.
The second voltage conversion circuit 200 includes two parallel-connected bridge arms, one of the two bridge arms includes a fifth switching tube Q5 and a sixth switching tube Q6 connected in series, the other bridge arm includes a seventh switching tube Q7 and an eighth switching tube Q8 connected in series, the fifth switching tube Q5 and the sixth switching tube Q6 are connected to the first node c, the seventh switching tube Q7 and the eighth switching tube Q8 are connected to the second node d, and a connection point of the two parallel-connected bridge arms is used for connecting the second power supply.
In this embodiment, the first voltage converting circuit 100 also includes two parallel-connected bridge arms, one of the two bridge arms includes a first switch tube Q1 and a second switch tube Q2 connected in series, the other bridge arm includes a third switch tube Q3 and a fourth switch tube Q4 connected in series, the first switch tube Q1 and the second switch tube Q2 are connected to the third node a, the third switch tube Q3 and the fourth switch tube Q4 are connected to the fourth node b, and a parallel connection point of the two parallel-connected bridge arms is used for connecting a parallel connection point of a first power supply and a filter capacitor connected in parallel.
The resonant tank circuit 300 includes a first inductance Lr (i.e., resonant inductance), a first capacitance Cr (i.e., resonant capacitance), a second inductance Lm (i.e., excitation inductance), and a transformer T. A first end (i.e., the first end of the resonant cavity circuit 300) of the resonant capacitor Cr is connected to the third node a, a second end of the resonant capacitor Cr is connected to the first end of the primary winding of the transformer T and the first end of the excitation inductor Lm, a first end (i.e., the second end of the resonant circuit 300) of the resonant inductor Lr is connected to the fourth node b, a second end of the resonant inductor Lr is connected to the second end of the primary winding of the transformer T and the second end of the excitation inductor Lm, and a first end and a second end (i.e., the third end and the fourth end of the resonant cavity circuit 300) of the secondary winding of the transformer T are connected to the first node c and the second node d of the second voltage conversion circuit 200, respectively.
In addition, in the embodiment, each of the switch transistors is connected in anti-parallel with a freewheeling diode, and each of the switch transistors has a junction capacitor.
In the prior art, in order to achieve a good operation condition of the resonant converter under a light load condition, the following solutions are generally adopted:
and (I) increasing dead load. But this approach actually sacrifices some light load efficiency due to the additional load increase.
And (II) adopting the modes of phase shifting, width modulation and the like. The method reduces the transmission power and realizes light-load operation by reducing the action time of the square wave excitation voltage of the resonant cavity, but the soft switching characteristic is lost under the condition of light load when the phase shift angle is too large or the duty ratio is too small, and the operation efficiency of the converter is reduced.
And (III) adopting a burst mode. According to the method, the switching loss of the resonant converter under the light load condition is reduced by realizing the intermittent control of the converter, but the intermittent control causes the problem of large output voltage ripple.
Specifically, in the embodiment shown in fig. 1, Vdc1 is a high-voltage dc side voltage (dc bus voltage), Vdc2 is a low-voltage dc side voltage (battery module voltage), switching tubes Q1 to Q4 on the high-voltage side (i.e., the side where the first voltage conversion circuit 100 is located) are IGBT tubes, and switching tubes Q5 to Q8 on the low-voltage side (i.e., the side where the second voltage conversion circuit 200 is located) are MOSFET tubes.
When the resonant converter 10 is operated in step-down and reverse power transmission (i.e., the second voltage converting circuit 200 is used for inversion, and the first voltage converting circuit 100 is used for rectification) and under a light load condition, the switching tube control signal of the first voltage converting circuit 100 is always at a low level and is in an uncontrolled rectification mode, while the conduction states of the switching tubes on the diagonal of the second voltage converting circuit 200 are the same, and the switching frequency remains unchanged.
Generally, the resonant converter 10 operates as follows:
first, the fifth switching tube Q5 and the eighth switching tube Q8 in the second voltage conversion circuit 200 are turned on for a period of time, where the on-time is ton; after the time ton, the fifth switching tube Q5 and the eighth switching tube Q8 are turned off, at this time, all the switching tubes in the second voltage conversion circuit 200 are turned off, and the turn-off time is set as toff; after the time toff, the sixth switching tube Q6 and the seventh switching tube Q7 are turned on for a ton time period, and then the sixth switching tube Q6 and the seventh switching tube Q7 are turned off for the toff time period, and the process is repeated.
Through a combined analysis of the operation process and the operation principle of the resonant converter 10, in a positive half cycle of the operation of the resonant converter 10, that is, the fifth switching tube Q5 and the eighth switching tube Q8 are turned on, and the process of switching the sixth switching tube Q6 and the seventh switching tube Q7 to be turned on mainly experiences 5 modes (mode of repeatedly conducting the diode during oscillation is ignored), a reference point (i.e., t0) of t =0 is set as a rising edge of the control signal of the fifth switching tube Q5 and the eighth switching tube Q8 (i.e., a starting point of mode 1), and then conduction conditions of each switching device (controllable device and non-controllable device) of each mode are shown in table 1.
Figure DEST_PATH_IMAGE003
Where "1" indicates that the corresponding device is in an on state, and "0" indicates that the corresponding device is in an off state.
Referring to fig. 2a to 2e, fig. 2a to 2e respectively show equivalent circuit diagrams of modes 1 to 5. The working principle of each mode is as follows:
mode 1 (i.e., t)0~t1In the time period), as shown in fig. 2a, the driving signals of the fifth switch Q5 and the eighth switch Q8 are at a high level, the fifth switch Q5 and the eighth switch Q8 are turned on, the on time is ton, the first diode D1 and the fourth diode D4 are turned on, the power source Vdc2 across the magnetizing inductor Lm is clamped in the forward direction, and the resonant inductor Lr, the resonant capacitor Cr, the high-voltage side power source Vdc1, the low-voltage side power source Vdc2 and the turned-on switching devices form a series resonant circuit.
Mode 2 (i.e., t)1~t2Period of time): as shown in FIG. 2b, the fifth switch tubeThe driving signals of the Q5 and the eighth switching tube Q8 are low level, the fifth switching tube Q5 and the eighth switching tube Q8 are turned on and off, at this time, the current at the midpoint of the bridge arm of the second voltage conversion circuit 200 flows through the sixth diode D6 and the seventh diode D7, the first diode D1 and the fourth diode D4 continue to be turned on, and the voltage across the excitation inductor Lm is reversely clamped by the low-voltage side power supply Vdc 2.
Modality 3 (i.e., t)2~t3Time period), as shown in fig. 2c, the fifth switching tube Q5 and the eighth switching tube Q8 continue to turn off, the bridge midpoint current of the second voltage conversion circuit 200 freewheels through the sixth diode D6 and the seventh diode D7, the second diode D2 and the third diode D3 are turned on, and the voltage across the magnetizing inductor Lm continues to be reverse-clamped by the low-voltage side power supply Vdc2 until the bridge midpoint current of the second voltage conversion circuit 200 drops to zero.
Mode 4 (i.e., t)3~t4Period of time): as shown in fig. 2D, when the bridge midpoint current of the second voltage conversion circuit 200 drops to zero, the sixth diode D6 and the seventh diode D7 are turned off, the resonant inductor Lr, the resonant capacitor Cr, the excitation inductor Lm, and the junction capacitors (Cj 5, Cj6, Cj7, and Cj 8) together form a resonant circuit, and the bridge midpoint voltage Vcd of the second voltage conversion circuit 200 is in a free resonance state. The bridge arm midpoint current i2 of the second voltage conversion circuit 200 is in a high-frequency oscillation stage, when the current i2 oscillates to a negative half cycle, the fifth junction capacitor Cj5 and the eighth junction capacitor Cj8 discharge, and the sixth junction capacitor Cj6 and the seventh junction capacitor Cj7 charge; and when the current i2 oscillates to the positive half cycle, the fifth junction capacitor Cj5 and the eighth junction capacitor Cj8 are charged, and the sixth junction capacitor Cj6 and the seventh junction capacitor Cj7 are discharged. When the current i2 oscillates to the positive half cycle and approaches the zero crossing, the sixth diode D6 and the seventh diode D7 conduct. In mode 3, since the second diode D2 and the third diode D3 are kept conductive, the bridge arm midpoint output voltage Vab of the first voltage conversion circuit 100 is-Vdc 1, which causes the primary side excitation current im1 to continuously decrease until it is 0.
Mode 5 (i.e., t)4~t5Period of time): as shown in FIG. 2e, at time T4, the primary resonant current i1 of the transformer T drops to zero, and the second diode D2 and the third diode D3 are turned offThe junction capacitances Cj1 to Cj8, the resonant inductor Lr, the resonant capacitor Cr, and the excitation inductor Lm together constitute a resonant circuit, and the bridge arm midpoint voltage Vcd of the second voltage conversion circuit 200 is in a high-frequency free resonance state.
Referring to fig. 3, when the second voltage converting circuit 200 of the resonant converter 10 is used as an inverter circuit and the first voltage converting circuit 100 is used as a rectifier circuit, the resonant converter control method includes the following steps:
s301: and acquiring the free oscillation period when the voltage between the first node and the second node is in a high-frequency free oscillation state.
Specifically, under a light load condition, the resonant converter 10 enters the fixed-frequency PWM control mode, and when all the switching tubes in the second voltage conversion circuit 200 are in an off state, a high-frequency free oscillation state exists between the first node and the second node in the second voltage conversion circuit 200.
S302: and obtaining the conduction time according to the free oscillation period.
Specifically, a conduction time can be obtained according to the free oscillation period and each circuit mode equivalent circuit.
S303: and controlling the on-off of the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube according to the on-time.
By the control method of the resonant converter, the conduction time can be adjusted so that the conduction time point of the switching tube in the resonant converter just falls at the minimum point of the voltage at two ends of the drain electrode and the source electrode of the switching tube in the free oscillation period, thereby realizing approximate soft switching and improving the light-load operation efficiency.
It should be noted that the above-mentioned "high frequency" does not refer to a specific frequency, but refers to a switching frequency of the resonant converter in the present embodiment.
Specifically, as is clear from the operation characteristic analysis of the resonant converter 10, at the time point corresponding to the high-frequency free oscillation period and the peak value of Vcd, the drain-source voltages Vds _ Q5 and Vds _ Q8 of the fifth switching tube Q5 and the eighth switching tube Q8 are minimum; at the time corresponding to the high-frequency free oscillation period and the valley value of Vcd, the drain-source voltage Vds _ Q6 and Vds _ Q7 of the sixth switching tube Q6 and the seventh switching tube Q7 are minimum. That is, when the fifth switching transistor Q5 and the eighth switching transistor Q8 are turned on at a time point corresponding to the peak value of the high-frequency free oscillation period Vcd, and the sixth switching transistor Q6 and the seventh switching transistor Q7 are turned on at a time point corresponding to the valley value of the high-frequency free oscillation period Vcd, the switching loss of the switching transistors is the lowest, and the obtained effect is similar to the zero-voltage turn-on of the switching transistors.
Referring to fig. 4, fig. 4 shows the operating waveforms of the positive half cycle of the resonant converter 10. As can be seen from fig. 4, in the positive half cycle, if the resonant converter 10 enters the high-frequency oscillation state at time t4 (accordingly, the midpoint voltage Vcd of the arm of the second voltage conversion circuit 200 also enters the high-frequency oscillation state), and the switching loss of the switching tube is to be minimized (that is, if the sixth switching tube Q6 and the seventh switching tube Q7 are turned on at the time point corresponding to the valley value of Vcd during the high-frequency free oscillation period), the switching-on time t5 must satisfy the following relationship:
Figure 396369DEST_PATH_IMAGE004
wherein ton is the on-time of the switching tube, i.e. the duty ratio of the switching tube control signal, toff is the duration of the switching tubes in the second voltage conversion circuit 200 being all in the off-state, fsw is the switching frequency, n is a non-negative integer, and Tosc is the oscillation period.
Since in this operating mode the switching frequency fsw in the resonant converter 10 is determined and maintained constant and the high-frequency oscillation entry time t4 is determined by the switching-tube on-time ton (i.e. ton has a predetermined functional relationship with t 4), since the switching frequency fsw is known, it is easy to know from the above-mentioned relationship that when the free-oscillation period Tosc is determined, the corresponding switching-tube on-time ton is obtained; if the on/off of the switching tube is controlled based on this switching tube on time ton so that the above relationship is satisfied, the switching loss of the switching tube can be minimized, and the efficiency of the resonant converter 10 can be improved.
It should be noted that, due to the symmetry of the positive and negative half-cycle operating waveforms of the system (i.e., the resonant converter), when the conduction time points corresponding to the switching tubes Q6 and Q7 exactly fall at the valley point of the free oscillation period, the conduction time points corresponding to the switching tubes Q5 and Q8 corresponding to the negative half-cycle also exactly fall at the peak point of the free oscillation period, so the above analysis process is performed only in the mode corresponding to the positive half-cycle within one switching cycle of the resonant converter, and the way of analyzing the negative half-cycle is consistent with the positive half-cycle, and thus no further description is given here.
The embodiment of the invention provides a control method of a resonant converter, which is applied to the resonant converter. The method obtains the conduction time according to the free oscillation period of the resonant converter, and controls the on-off of a fifth switching tube, a sixth switching tube, a seventh switching tube and an eighth switching tube in the resonant converter according to the conduction time. Due to the fact that the control method of PWM (pulse width modulation) is used (namely the on-time of the switching tube is set by adjusting the duty ratio of the control signal), the output voltage ripple of the resonant converter is small, the resonant converter can run more stably under the light load condition, the switching tube works in a mode similar to soft switching, switching loss is reduced, and the efficiency of the resonant converter is improved.
In some embodiments (such as the resonant converter 10 described above), the time domain and complex frequency domain analysis of each mode in the positive half period of the resonant converter 10 may obtain the following characteristic expression (obtained by performing a pull transform on the time domain expression):
Figure 206062DEST_PATH_IMAGE005
wherein, Cjs is a junction capacitance of the second voltage conversion circuit 200, N is an original secondary winding ratio of the transformer in the resonant cavity circuit, Cr is a resonant capacitance in the resonant cavity circuit, Lr is a resonant inductance in the resonant cavity circuit, Lm is an excitation inductance of the transformer T, and s is a complex frequency.
The free oscillation period Tosc of the midpoint voltage Vcd of the bridge arm of the second voltage conversion circuit 200 in the high-frequency free oscillation state can be obtained by solving the characteristic expression, specifically, the characteristic frequency obtained by solving the characteristic expression is the free oscillation frequency in the high-frequency free oscillation state, and the period corresponding to the characteristic frequency is Tosc. In other embodiments, the free oscillation period Tosc may also be obtained according to experimental measurement, that is, an actual circuit structure is built according to an actual schematic diagram of the resonant converter, and the free oscillation period Tosc may be obtained by adding a test signal and detecting an output working waveform diagram of the test signal.
In some embodiments, the free-running period Tosc and the on-time ton satisfy the following relationship:
Figure 822988DEST_PATH_IMAGE006
wherein ton is the on-time, fsw is the switching frequency, Tosc is the free oscillation period, n is a non-negative integer, and f is the first function.
Specifically, referring to fig. 2a to 2e again, the differential equation of the equivalent circuit shown in fig. 2a is:
Figure 909893DEST_PATH_IMAGE007
(1)
the complex frequency domain (s-domain) equation is:
Figure 586862DEST_PATH_IMAGE008
(2)
wherein i10,1 is the initial time value of i1 in the modality, im0,1 is the initial time value of im in the modality, ucr0,1 is the initial time value of ucr in the modality.
Neglecting the resistance, solving the time domain expression of each variable as:
Figure 622865DEST_PATH_IMAGE009
(3)
the end time of modality 1 is:
Figure 777902DEST_PATH_IMAGE010
(4)
wherein ton is the pulse width of the switching tube control signal.
The differential equation for the equivalent circuit shown in fig. 2b is:
Figure 984893DEST_PATH_IMAGE011
(5)
the complex frequency domain (s-domain) equation is:
Figure 832763DEST_PATH_IMAGE012
(6)
wherein i10,2 is the initial time value of i1 in the modality, im0,2 is the initial time value of im in the modality, ucr0,2 is the initial time value of ucr in the modality.
Solving to obtain time domain expressions of all variables as follows:
Figure 351469DEST_PATH_IMAGE013
(7)
if the end condition of modality 2 is i1=0, the corresponding time is:
Figure 310198DEST_PATH_IMAGE014
(8)
the differential equation for the equivalent circuit shown in fig. 2c is:
Figure 106116DEST_PATH_IMAGE015
(9)
the complex frequency domain (s-domain) equation is:
Figure 253DEST_PATH_IMAGE016
(10)
wherein i10,3 is the initial time value of i1 in the modality, im0,3 is the initial time value of im in the modality, ucr0,3 is the initial time value of ucr in the modality.
Solving to obtain time domain expressions of all variables as follows:
Figure 881622DEST_PATH_IMAGE017
(11)
the ending condition of the mode 3 is i2=0, the change amplitude of the slope of the expression i1(t) in the corresponding time period is small, i1(t) can be considered to be linearly changed in the corresponding time period, and the slope at t = t2 is taken as the slope of the linear change, then
Figure 909621DEST_PATH_IMAGE018
(12)
The expression i1(t) can thus be approximated as:
Figure 684678DEST_PATH_IMAGE019
(13)
therefore, the approximate time at which i2=0 (i.e., the time at which modality 3 switches to modality 4) can be solved as:
Figure 608772DEST_PATH_IMAGE020
(14)
the differential equation for the equivalent circuit shown in fig. 2d is:
Figure 243016DEST_PATH_IMAGE021
(15)
the complex frequency domain (s-domain) equation is:
Figure 543547DEST_PATH_IMAGE022
(16)
wherein i10,4-1 is the initial time value of i1 in the modality, im0,4-1 is the initial time value of im in the modality, ucr0,4-1 is the initial time value of ucr in the modality, ucj60,4-1 is the initial time value of ucj6 in the modality, ucj80,4-1 is the initial time value of ucj8 in the modality, ucj50,4-1 is the initial time value of ucj5 in the modality.
By approximation, the resulting time domain solution is:
Figure 455002DEST_PATH_IMAGE023
(17)
considering the implementation of the soft switching (i.e. zero voltage switching) of the switching tubes Q6 and Q7, the high-frequency oscillation component needs to be analyzed, and if the voltage on the resonant capacitor Cr is approximately constant, the time domain expression of i2 can be obtained as follows:
Figure 549997DEST_PATH_IMAGE024
(18)
thus, the resonant frequency, period, and half-cycle are:
Figure 671537DEST_PATH_IMAGE025
(19)
the end condition of modality 4 is im =0, and the corresponding time is:
Figure 775759DEST_PATH_IMAGE026
(20)
the differential equation for the equivalent circuit shown in fig. 2e is:
Figure 525410DEST_PATH_IMAGE027
(21)
the complex frequency domain (s-domain) equation is:
Figure 56885DEST_PATH_IMAGE028
(22)
wherein i10,5-1 is the initial time value of i1 in the modality, im0,5-1 is the initial time value of im in the modality, ucr0,5-1 is the initial time value of ucr in the modality, ucj60,5-1 is the initial time value of ucj6 in the modality, ucj80,5-1 is the initial time value of ucj8 in the modality, ucj20,5-1 is the initial time value of ucj2 in the modality, ucj40,5-1 is the initial time value of ucj4 in the modality.
To obtain the analytical expression, the time domain solution obtained by approximation is:
Figure 134563DEST_PATH_IMAGE029
(23)
considering the implementation of the soft switching (i.e. zero voltage switching) of the sixth switching tube Q6 and the seventh switching tube Q7, the high frequency oscillation component needs to be analyzed, and the s-domain result obtained by laplace transform can obtain a characteristic polynomial:
Figure 917842DEST_PATH_IMAGE030
(24)
the characteristic frequency of the characteristic polynomial is obtained by solving, the characteristic frequency is the high-frequency free oscillation frequency, and the reciprocal of the characteristic frequency is the corresponding free oscillation period Tosc.
As can be seen from fig. 4, in order to realize the soft switching operation mode of the switching tube in the high-frequency free oscillation section, the switching tubes Q6 and Q7 need to be turned on under the condition that the following formula (25) is satisfied, that is, the switching tubes Q6 and Q7 are turned on at the voltage valley point of the high-frequency free oscillation section, and the on-time ton satisfies the formula (25), where the formula (25) is as follows:
Figure 662944DEST_PATH_IMAGE031
(25)
at this time, the switching tube of the second voltage conversion circuit 200 can approximately realize zero voltage switching on, thereby reducing switching loss and improving the efficiency of the resonant converter under the light load condition.
The analysis process is a theoretical analysis process, and ton and t4 influence each other, that is, ton change influences t4, and t4 can determine ton, so that it is difficult to obtain an analytical expression of the correlation between the ton and t4, and for practical application, an exhaustive method and a fitting method can be adopted by means of a mathematical tool, an analytical expression of ton about t4 is fitted by using a real data result, and finally, the numerical value of ton is solved by using the fitted analytical expression according to actual working conditions. Referring to fig. 5, fig. 5 shows a schematic diagram of a process for solving the on-time ton, specifically, the method includes the following steps:
s501: in a reasonable value range, a group of ton values are exhausted to form an array, each value in the array is sequentially substituted into a time domain expression (particularly the expression 4, the expression 8, the expression 14 and the expression 20) obtained by mode analysis under a specific working condition corresponding to Vdc1 and Vdc2, and the value of t4 is obtained according to the time domain expression under each mode.
S502: whether t4 satisfies the relationship ton + toff > t4 is determined, and if so, the set of t4, Vdc1 and Vdc2 is recorded as valid data.
S503: after all the working conditions are exhausted, an analytical expression (i.e. a first function) of ton (t4, Vdc1, Vdc2) is obtained by fitting according to all the obtained valid data.
Specifically, the analytical expression is ton = a × t4+ B × Vdc1+ C × Vdc2, where A, B, C is the coefficients of t4, Vdc1, and Vdc2, respectively.
S504: the allowable number n of oscillation cycles is determined, the value of t4 is calculated according to the relation of t4=1/2fsw-nTosc, and the calculated value is substituted into the fitted analytical expression of ton (t4, Vdc1 and Vdc2), so that the numerical solution of ton can be obtained according to the analytical expression.
In some embodiments, to facilitate and speed control, the Tosc is calculated in advance and stored in a controller (e.g., a DSP), and the controller substitutes specific values of t4, Vdc1 and Vdc2 according to an expression of ton (t4, Vdc1 and Vdc2), so as to find a specific value of ton, and sets a control signal of the switching tube according to the value, so that the switching tube realizes a soft switching operation mode.
It should be noted that, for convenience of explaining the resonant converter control method provided in the present application, the circuit structures of the first voltage conversion circuit, the second voltage conversion circuit and the resonant cavity circuit are merely shown by way of example, the resonant converter 10 is actually selected as an LLC resonant type bidirectional DC-DC converter, which follows the general working principle of LLC resonant converters, in other embodiments, the resonant converter 10 may also be a resonant converter of other structure (e.g. a unidirectional DC-DC converter) and type (e.g. a CLLC resonant converter, an LC resonant converter, etc.), the structures of the first voltage conversion circuit, the second voltage conversion circuit and the resonant cavity circuit are also changed adaptively, the working mode process of the converter is also changed correspondingly, however, the analysis mechanism is similar, and the basic principle of the light-load efficiency optimization method is the same, and the method belongs to the protection scope of the invention.
Referring to fig. 6, fig. 6 is a structure of a resonant converter according to an embodiment of the present invention, in which the resonant converter 10 includes a first voltage converting circuit 100, a second voltage converting circuit 200, a resonant cavity circuit 300, at least one processor 400, and a memory 500 communicatively connected to the at least one processor.
The second voltage conversion circuit 200 includes two parallel-connected bridge arms, one of the bridge arms includes a fifth switching tube Q5 and a sixth switching tube Q6 connected in series, the other bridge arm includes a seventh switching tube Q7 and an eighth switching tube Q8 connected in series, the fifth switching tube Q5 and the sixth switching tube Q6 are connected to the first node c, and the seventh switching tube Q7 and the eighth switching tube Q8 are connected to the second node d.
The first terminal and the second terminal of the resonant cavity circuit 300 are respectively connected to the first voltage converting circuit 100, and the third terminal and the fourth terminal are respectively connected to the first node c and the sixth node d.
The memory 500 stores instructions executable by at least one processor to enable the at least one processor to perform a resonant converter control method according to any one of the embodiments of the present invention.
In some embodiments, referring to fig. 6 again, the first voltage conversion circuit 100 also includes two parallel-connected legs, one of the legs includes a first switching tube Q1 and a second switching tube Q2 connected in series, the other leg includes a third switching tube Q3 and a fourth switching tube Q4 connected in series, the first switching tube Q1 and the second switching tube Q2 are connected to the third node a, and the third switching tube Q3 and the fourth switching tube Q4 are connected to the fourth node b.
In some embodiments, referring again to fig. 6, the resonant cavity circuit 300 includes a first inductor (i.e., resonant inductor Lr), a first capacitor (i.e., resonant capacitor Cr), and a transformer T including an exciting inductor Lm. A first end (i.e., the first end of the resonant cavity circuit 300) of the resonant capacitor Cr is connected to the third node a, a second end of the resonant capacitor Cr is connected to the first end of the primary winding of the transformer T and the first end of the excitation inductor Lm, a first end (i.e., the second end of the resonant circuit 300) of the resonant inductor Lr is connected to the fourth node b, a second end of the resonant inductor Lr is connected to the second end of the primary winding of the transformer T and the second end of the excitation inductor Lm, and a first end and a second end (i.e., the third end and the fourth end of the resonant cavity circuit 300) of the secondary winding of the transformer T are connected to the first node c and the second node d of the second voltage conversion circuit 200, respectively.
In some embodiments, during a single switching period, when the fifth switching tube Q5, the sixth switching tube Q6, the seventh switching tube Q7 and the eighth switching tube Q8 are in the off period, the voltage Vcd between the first node c and the second node d is in a free oscillation state when the primary side resonant current of the transformer T is reduced to zero.
The embodiment of the invention also provides a power supply system which comprises the resonant converter provided by any one of the embodiments.
It should be clear to a person skilled in the art that the method provided by the embodiments of the present invention can be implemented by using different hardware circuits, and is not limited to the hardware circuits exemplified in the present application. The above illustrated topology of the resonant converter is intended to explain and illustrate the basic inventive content of the present invention and is not intended to limit the scope of the invention as claimed. Further variations and modifications in those embodiments may occur to persons skilled in the art from the disclosure of this specification, which is intended to convey the substance of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the embodiments of the present application without departing from the spirit and scope of the claims of the application. Thus, if such modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present application and their equivalents, the present application is also intended to encompass such modifications and variations.

Claims (9)

1. A control method of a resonant converter is characterized in that the method is used for the resonant converter, and the resonant converter comprises a first voltage conversion circuit, a second voltage conversion circuit and a resonant cavity circuit;
the second voltage conversion circuit comprises two parallel bridge arms, wherein one bridge arm comprises a fifth switching tube and a sixth switching tube which are connected in series, the other bridge arm comprises a seventh switching tube and an eighth switching tube which are connected in series, the fifth switching tube and the sixth switching tube are connected to a first node, the seventh switching tube and the eighth switching tube are connected to a second node, and each switching tube comprises a diode which is connected in reverse parallel;
a first end and a second end of the resonant cavity circuit are respectively connected with the first voltage conversion circuit, and a third end and a fourth end of the resonant cavity circuit are respectively connected with the first node and the second node;
the method comprises the following steps:
when a second voltage conversion circuit is used for an inverter circuit and a first voltage conversion circuit is used for a rectifier circuit, acquiring a free oscillation period of a voltage between a first node and a second node in a high-frequency free oscillation state;
obtaining the conduction time according to the free oscillation period;
controlling the on-off of the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube according to the conducting time;
the free-running period and the on-time satisfy the following relationship:
ton=A*(1/2fsw-nTosc)+B*Vdc1+C*Vdc2；
wherein ton is the on-time, fsw is a switching frequency, Tosc is the free oscillation period, n is a non-negative integer, Vdc1 is a high voltage dc side voltage, Vdc2 is a low voltage dc side voltage, a is a coefficient of a high frequency oscillation entering time, B is a coefficient of the high voltage dc side voltage, and C is a coefficient of the low voltage dc side voltage.
2. The method of claim 1, wherein the first voltage conversion circuit comprises two parallel legs, wherein one leg comprises a first diode and a second diode connected in series, the other leg comprises a third diode and a fourth diode connected in series, the first diode and the second diode are connected to a third node, and the third diode and the fourth diode are connected to a fourth node;
the resonant cavity circuit comprises a first capacitor, a first inductor, a second inductor and a transformer, wherein the first capacitor is connected in series between the third node and the first end of the primary side of the transformer, the first inductor is connected in series between the fourth node and the second end of the primary side of the transformer, and the second inductor is connected in parallel to the first end and the second end of the primary side of the transformer;
the first voltage conversion circuit comprises a first junction capacitor, and the second voltage conversion circuit comprises a second junction capacitor;
the free oscillation period is obtained by the following relation:
Figure 8770DEST_PATH_IMAGE001
the capacitance of the first junction capacitor is a capacitance of the second junction capacitor, and the capacitance of the second junction capacitor is a capacitance of the first junction capacitor.
3. The method according to claim 1, wherein the controlling the on/off of the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube according to the on-time comprises:
in the on-time of a positive half switching period, controlling the fifth switching tube and the eighth switching tube to be on, and controlling the sixth switching tube and the seventh switching tube to be off;
in the remaining time of the positive half switching period, the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube are controlled to be cut off;
in the on time of a negative half switching cycle, controlling the sixth switching tube and the seventh switching tube to be on, and controlling the fifth switching tube and the eighth switching tube to be off;
and controlling the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube to be cut off in the remaining time of the negative half switching period.
4. A resonant converter, comprising:
a first voltage conversion circuit;
the second voltage conversion circuit comprises two parallel bridge arms, one bridge arm comprises a fifth switching tube and a sixth switching tube which are connected in series, the other bridge arm comprises a seventh switching tube and an eighth switching tube which are connected in series, the fifth switching tube and the sixth switching tube are connected to a first node, and the seventh switching tube and the eighth switching tube are connected to a second node;
a first end and a second end of the resonant cavity circuit are respectively connected with the first voltage conversion circuit, and a third end and a fourth end of the resonant cavity circuit are respectively connected with the first node and the second node;
at least one processor, and
a memory communicatively coupled to the at least one processor, wherein the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the method of any of claims 1-3.
5. The resonant converter according to claim 4, wherein the first voltage conversion circuit comprises two parallel-connected bridge legs, one of the two bridge legs comprises a first switching tube and a second switching tube connected in series, the other bridge leg comprises a third switching tube and a fourth switching tube connected in series, the first switching tube and the second switching tube are connected to a third node, and the third switching tube and the fourth switching tube are connected to a fourth node.
6. The resonant converter according to claim 5, wherein the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are all connected in parallel with a diode.
7. The resonant converter of claim 6, wherein the resonant tank circuit comprises a first capacitor, a first inductor, a second inductor, and a transformer, wherein the first capacitor is connected in series between the third node and the first end of the primary side of the transformer, the first inductor is connected in series between the fourth node and the second end of the primary side of the transformer, and the second inductor is connected in parallel to the first end and the second end of the primary side of the transformer;
and the first end and the second end of the secondary side of the transformer are respectively connected with the first node and the second node.
8. The resonant converter of claim 7,
in a single switching period, the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube are in a cut-off period, and when a primary side resonant current of the transformer is reduced to zero, a voltage between the first node and the second node is in a high-frequency free oscillation state.
9. A power supply system comprising a resonant converter according to any of claims 4 to 8.
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