Control method and control device of resonant converter, medium, processor and switching power supply

Abstract

The invention discloses a control method and a control device of a resonant converter, a medium, a processor and a switching power supply, the resonant converter comprises a primary side inverter bridge arm, a secondary side rectifier switching tube of the resonant converter is an active switching tube, the control method of the resonant converter comprises the following steps: a voltage obtained by superposing an output voltage of a primary inverter bridge arm of the resonant converter and voltages at the two ends of a primary winding of a transformer of the resonant converter acts on a resonant branch, so that the voltages at the two ends of the resonant branch are higher than the output voltage of the primary inverter bridge arm of the resonant converter; and the gain adjustment of the resonant converter is realized. On the premise of ensuring the soft switching characteristics of the primary and secondary side switching tubes, a wider output voltage gain adjusting range can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of switching converters, and in particular to a control method, a control device, a medium, a processor and a switching power supply of a resonant converter. Background Art

[0002] With the rapid development of power electronics technology, switching converters are increasingly widely used. People have put forward more requirements for switching converters: high power density, high reliability, high efficiency, wide gain range, etc. Resonant converters are favored by industry insiders for their advantages such as high efficiency, soft switching, and the ability to achieve higher power density.

[0003] For output voltage gain adjustment, the first conventional control method is to change the switching frequency of the resonant converter. When the gain adjustment range is wide, the switching frequency needs to vary within a wide range. When the frequency is too low, it is difficult to achieve zero voltage turn-on, and when the frequency is too high, it is difficult to achieve zero current turn-off. At the same time, the wider frequency conversion range brings great difficulties to the design and circuit control of magnetic devices such as transformers.

[0004] Another commonly used control method is fixed-frequency phase-shift control. Since the operating frequency is fixed, it is convenient for magnetic component design. However, in order to achieve wide gain range adjustment, the circuit needs to operate at a larger phase-shift angle, which will make it difficult for the lagging bridge arm in the phase-shift circuit to achieve soft switching. Therefore, under this control method, in order to meet the requirement that the lagging bridge arm can achieve soft switching at the maximum phase-shift angle, the phase-shift angle will be limited, which in turn leads to a limited gain range of the resonant converter of the traditional fixed-frequency phase-shift control.

[0005] In wide gain applications, in order to make the resonant converter operate efficiently within the soft switching range, the document "Hybrid Control Strategy of Full-Bridge LLC Resonant Converter" adopts a frequency conversion + phase shift hybrid control strategy. By reducing the gain reduction adjustment range under the phase shift control stage, the resonant converter can achieve soft switching performance under low voltage, and adopt frequency conversion phase shift hybrid control to achieve a 2-fold gain voltage range; however, under low gain operating conditions, the converter still works in the phase shift control mode. Assuming the output voltage of the resonant converter is V o , the primary-secondary turns ratio is n, and the switching period is T s , the magnetizing inductance is L m The maximum excitation current of the excitation inductor is the maximum turn-off current i of the primary switch tube. off , according to the resonant converter turn-off current expression It can be seen that at this time, the turn-off current of the primary switch tube is small, and it is difficult to complete the charging and discharging of the parasitic capacitance of the switch tube within the dead time. The primary switch tube loses its soft switching characteristics, which will reduce the efficiency of the resonant converter.

[0006] In short, when the resonant converter is used in a wide gain range, the circuit cannot take into account both high efficiency and wide gain characteristics due to the difficulty in achieving soft switching characteristics. Therefore, further research is needed on how to increase the gain adjustment range of the resonant converter while ensuring the soft switching characteristics of the converter. Summary of the invention

[0007] In view of this, the technical problem to be solved by the present invention is: to propose a control method, a control device, a medium, a processor and a switching power supply of a resonant converter, so as to achieve a wider output voltage gain adjustment range while ensuring the soft switching characteristics of the primary and secondary side switches.

[0008] As a first aspect of the present invention, an embodiment of a control method of a resonant converter is provided as follows:

[0009] A control method for a resonant converter, the resonant converter comprising a primary inverter bridge arm, the secondary rectifier switch tube of the resonant converter being an active switch tube, wherein the control method for the resonant converter comprises: applying a voltage obtained by superimposing an output voltage of the primary inverter bridge arm of the resonant converter and a voltage across a primary winding of a resonant converter transformer to a resonant branch, so that the voltage across the resonant branch is higher than the output voltage of the primary inverter bridge arm of the resonant converter, thereby achieving adjustment of the gain of the resonant converter.

[0010] Preferably, the control method comprises the following steps in each working cycle of the resonant converter:

[0011] (1) obtaining a first gain of the resonant converter, where the first gain is a gain required by the resonant converter;

[0012] (2) Controlling the on-duty cycle of the secondary rectifier switch tube according to the first gain, thereby controlling the time during which the voltage obtained by superposing the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer acts on the resonant branch, so that the on-duty cycle of the secondary rectifier switch tube of the resonant converter increases with the increase of the first gain and decreases with the decrease of the first gain, thereby adjusting the actual gain of the resonant converter to the required gain.

[0013] Furthermore, the turn-on time of each pair of diagonal switch tubes in the primary inverter bridge arm is consistent with the turn-on time of the rectifier switch tube corresponding to the secondary winding connection branch of the resonant converter transformer.

[0014] Preferably, the operating frequency of the secondary rectifier switch tube of the resonant converter is the operating frequency of the primary switch tube of the resonant converter, or the operating frequency of the secondary rectifier switch tube of the resonant converter is equal to twice the operating frequency of the primary switch tube of the resonant converter.

[0015] Furthermore, when the operating frequency of the secondary rectifier switch tube is equal to the operating frequency of the primary switch tube of the resonant converter, the secondary rectifier switch tube is turned on once in one cycle to achieve gain adjustment of the resonant converter; when the operating frequency of the secondary rectifier switch tube is equal to twice the operating frequency of the primary switch tube of the resonant converter, the secondary rectifier switch tube is turned on twice in one cycle, the first turn-on is used to achieve gain adjustment of the resonant converter, and the second turn-on is used to achieve the synchronous rectification function of the secondary rectifier switch tube.

[0016] Furthermore, it is combined with frequency conversion control to form a hybrid control scheme, so that the secondary side active switch tube of the resonant converter is in a critical current continuous conduction mode.

[0017] Furthermore, under a determined load, a polynomial is used to fit the conduction duty cycle of the secondary rectifier switch tube and the first gain, and the conduction duty cycle of the secondary rectifier switch tube is controlled to change with the first gain.

[0018] As a second aspect of the present invention, the technical solution of the embodiment of the control device of the resonant converter provided is as follows:

[0019] A control device for a resonant converter, wherein the secondary rectifier switch tube of the resonant converter is an active switch tube, wherein the control device comprises the following modules:

[0020] A judging module, used to judge whether the resonant converter needs to adjust the gain;

[0021] The processing module is used to apply the voltage obtained by superimposing the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer to the resonant branch when the resonant converter needs to adjust the gain, so that the voltage across the resonant branch is higher than the output voltage of the primary inverter bridge arm of the resonant converter, thereby achieving the adjustment of the gain of the resonant converter.

[0022] As a third aspect of the present invention, an embodiment of a computer-readable storage medium is provided as follows:

[0023] A computer-readable storage medium, comprising a stored program, wherein the program executes the control method described in any one of the first aspects above.

[0024] As a fourth aspect of the present invention, an embodiment of a processor is provided as follows:

[0025] A processor is used to run a program, wherein the program executes any one of the control methods described in the first aspect when running.

[0026] As a fifth aspect of the present invention, an embodiment of a switching power supply is provided as follows:

[0027] A switching power supply comprises a resonant converter, wherein the secondary rectifier switch tube of the resonant converter is an active switch tube, and the resonant converter is controlled by the control device of the resonant converter described in the second aspect.

[0028] The present invention controls the on-duty cycle of the secondary-side rectifier switch tube according to the first gain, so that the voltage at both ends of the resonant branch composed of the resonant inductor and the resonant capacitor is higher than the output voltage of the primary inverter bridge arm, thereby controlling the time for the voltage after the superposition of the output voltage of the primary inverter bridge arm of the resonant converter and the voltage at both ends of the primary side of the transformer to act on the resonant branch. During this time period, the resonant inductor on the resonant branch is in an energy storage state, and acts as a boost inductor, having a boosting effect, so that the on-duty cycle of the secondary-side rectifier switch tube of the resonant converter increases with the increase of the first gain and decreases with the decrease of the first gain, so that the actual gain of the resonant converter can be adjusted to the required gain, which has the following beneficial effects compared with the prior art:

[0029] (1) The voltage across the resonant branch formed by the resonant inductor and the resonant capacitor is higher than the output voltage of the primary inverter bridge arm, so that the resonant inductor of the resonant branch acts as a boost inductor, so that the resonant converter has a wide gain adjustment capability;

[0030] (2) The voltage at both ends of the resonant branch can be made higher than the output voltage of the primary inverter bridge arm by simply controlling the conduction duty cycle of the secondary rectifier switch tube, thereby achieving gain adjustment. The control scheme is simple and easy to implement, and is suitable for wide voltage applications;

[0031] (3) Gain adjustment is achieved by controlling the on-duty cycle of the secondary rectifier switch tube. The resonant converter operates near the resonant frequency, which is convenient for optimizing the design of magnetic components such as inductors and transformers, and is conducive to the high power density design and application of switching power supplies.

[0032] (4) While controlling the voltage at both ends of the resonant branch composed of the resonant inductor and the resonant capacitor to be higher than the output voltage of the primary inverter bridge arm, the secondary rectifier switch tube is turned on for the second time to achieve synchronous rectification control of the secondary rectifier switch tube, thereby further improving the converter efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The schematic diagram of the resonant converter used in the control method of the present invention;

[0034] Figure 2 is a flow chart of a control method of a resonant converter according to a first embodiment of the present invention;

[0035] Figure 3 To adopt Figure 2 Output voltage gain curve achieved by the control method;

[0036] Figure 4 The first embodiment of the present invention adopts Figure 2 The first control timing diagram of the control method;

[0037] Figure 5 for Figure 4 Equivalent circuit diagram of the resonant converter in the [t0-t1] switching mode;

[0038] Figure 6 for Figure 4 Equivalent circuit diagram in the [t1-t2] switching mode;

[0039] Figure 7 for Figure 4 Equivalent circuit diagram in the [t2-t3] switching mode;

[0040] Figure 8 for Figure 4 Equivalent circuit diagram in the [t3-t4] switching mode;

[0041] Fig. 9 for Figure 4 Equivalent circuit diagram in the [t4-t5] switching mode;

[0042] Fig.10 The first embodiment of the present invention adopts Figure 2 The second control timing diagram of the control method;

[0043] Fig.11 FIG. 4 is a schematic diagram of a control device for a resonant converter according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0044] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0045] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0046] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0047] It should be understood that, in the specification, claims and drawings, when a step is described as being connected to another step, the step may be directly connected to the other step, or be connected to the other step through a third step; when an element / unit is described as being "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit, or be "connected" to the other element / unit through a third element / unit.

[0048] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0049] In order to ensure that the technical solution of the present invention is clearer, the technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0050] The schematic diagram of the resonant converter to which the control method proposed in the present invention is applicable is as follows: Figure 1 As shown, it includes an inverter circuit, LLC resonant cavity, transformer T and secondary side rectifier filter circuit. In the figure, Vin is the input power supply of the resonant converter, and Ro is the output load of the resonant converter.

[0051] The inverter circuit includes a full-bridge inverter circuit composed of switch tube S1, switch tube S2, switch tube S3, and switch tube S4; the LLC resonant cavity includes a resonant inductor Lr, an excitation inductor Lm, and a resonant capacitor Cr, wherein the resonant inductor Lr and the resonant capacitor Cr constitute a resonant branch; the transformer T includes a transformer T composed of a primary winding Np, and secondary windings Ns1 and Ns2; the secondary rectifier switch tubes in the rectifier and filter circuit are active switch tubes S5 and S6, and the active switch tubes S5 and S6 constitute a full-wave rectifier circuit, and the rectifier and filter circuit also includes an output filter capacitor Co.

[0052] It should be noted that Figure 1 This is only a typical example of a resonant converter to which the control method of the resonant converter of the present invention is applicable. The resonant converter to which the control method of the resonant converter of the present invention is applicable is not limited to Figure 1 The circuit also includes some other topological structures, such as a resonant converter in different forms, in which the primary side is a half-bridge inverter circuit and the secondary side is a full-bridge rectifier circuit or a current doubler rectifier circuit or a voltage doubler rectifier circuit.

[0053] In addition, the gain of the present invention refers to the normalized gain of the resonant converter. When the resonant converter is a half-bridge resonant converter, the normalized gain of the resonant converter is When the resonant converter is a full-bridge resonant converter, the normalized gain of the resonant converter is n is the turns ratio of the transformer, Vo is the nominal output voltage, and Vin is the nominal input voltage.

[0054] Figure 1 It is a full-bridge resonant converter. At the resonant frequency point, the switching frequency is equal to the resonant frequency. The resonant converter satisfies the relationship according to the turns ratio of the transformer:

[0055]

[0056] Users have different requirements for the gain of the resonant converter according to the application scenario. The present invention aims to achieve a wider output voltage gain adjustment range while ensuring the soft switching characteristics of the primary and secondary side switches.

[0057] First embodiment

[0058] The present embodiment provides a control method for a resonant converter, wherein the resonant converter includes a primary inverter bridge arm, and the secondary rectifier switch tube of the resonant converter is an active switch tube. The control method of the resonant converter of the present embodiment includes: applying a voltage obtained by superimposing the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer to the resonant branch, so that the voltage across the resonant branch is higher than the output voltage of the primary inverter bridge arm of the resonant converter, thereby achieving adjustment of the gain of the resonant converter.

[0059] The output voltage of the primary inverter bridge arm of the resonant converter refers to the voltage between the midpoints of the primary inverter bridge arm of the resonant converter, for example Figure 1 The resonant converter in the figure refers to the voltage between point A and point B. The voltage after the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer are superimposed on the resonant branch. The output voltage of the primary inverter bridge arm of the resonant converter is recorded as VAB, the voltage across the primary winding of the resonant converter transformer is recorded as VNp, and the voltage across the resonant branch is recorded as V1. When the switch tube S1 in the first bridge arm and the switch tube S4 in the second bridge arm are turned on at the same time, the primary inverter bridge arm output voltage VAB of the resonant converter, the resonant branch voltage V1 and the primary winding VNp of the resonant converter transformer form a voltage loop. According to Kirchhoff's loop voltage law, V1 = VAB-VNp.

[0060] The control method of this embodiment makes the voltage at both ends of the resonant branch composed of the resonant inductor and the resonant capacitor higher than the output voltage of the primary inverter bridge arm, so that the voltage at both ends of the resonant inductor in the resonant branch is higher, so that the resonant inductor is in an energy storage charging state, and the resonant inductor acts as a boost inductor, so that the resonant converter has a boost function, thereby achieving wide gain adjustment. Under this control method, the frequency adjustment range of the traditional frequency control method is effectively reduced, which is conducive to the optimized design of magnetic devices such as transformers and inductors, and improves power density.

[0061] The control method of this embodiment applies the voltage obtained by superimposing the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer to the resonant branch, so that the voltage across the resonant branch composed of the resonant inductor and the resonant capacitor is higher than the output voltage of the primary inverter bridge arm, including but not limited to the following methods: secondary side phase shift control, primary-secondary side phase shift control, controlling the conduction duty cycle of the secondary side rectifier switch tube, etc.

[0062] Figure 2 This is a flow chart of a control method for a resonant converter according to the first embodiment of the present invention. The on-duty ratio of the secondary rectifier switch tube is controlled to realize that the voltage obtained by superimposing the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer is applied to the resonant branch. Figure 2 , the control method comprises the following steps in each working cycle of the resonant converter:

[0063] Obtaining a first gain of the resonant converter, where the first gain is a gain required by the resonant converter;

[0064] The actual gain of the resonant converter is adjusted, and the on-duty cycle of the secondary rectifier switch tube is controlled according to the first gain, thereby controlling the time for the voltage obtained by superimposing the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer on the resonant branch, so that the on-duty cycle of the secondary rectifier switch tube of the resonant converter increases with the increase of the first gain and decreases with the decrease of the first gain, so that the actual gain of the resonant converter can be adjusted to the required gain.

[0065] In the control method of this embodiment, during the conduction time of the secondary rectifier switch tube, the positive and negative directions of the voltage across the primary winding of the resonant converter transformer are opposite to the positive and negative directions of the output voltage of the primary inverter bridge arm of the resonant converter. Figure 2 The control method must be able to achieve that the voltage across the resonant branch is higher than the output voltage of the primary inverter bridge arm of the resonant converter.

[0066] The actual gain of the resonant converter is measured with a prototype, and the curve of the change of the conduction duty cycle of the secondary rectifier switch tube is as follows: Figure 3 As shown, the horizontal axis represents the duty cycle D of the secondary rectifier switch tube, and the vertical axis represents the gain G. Figure 2 It can be seen from the gain curve that the control method of this embodiment can effectively improve the gain of the resonant converter.

[0067] The specific parameters of the resonant converter during the above gain curve test are: input voltage Vin is 400V, transformer primary-secondary turns ratio is 17:1:1, nominal output voltage Vo is 24V, resonant capacitor Cr is 94nF, resonant inductor Lr is 26uH, excitation inductor Lm is 156uH, switching frequency is 100kHz, and the specific control logic of the resonant converter is: control the resonant converter operating frequency to remain fixed; the primary switch tubes S1~S4 keep the duty cycle at 0.5 and fixed, the switch tubes S1 and S2 are complementary, the switch tubes S1 and S4 are turned on and off at the same time, and the switch tubes S2 and S3 are turned on and off at the same time; keep the working state of the primary switch tube unchanged, and only realize the output voltage gain adjustment by controlling the conduction duty cycle of the secondary rectifier switch tube. It should be noted that the specific circuit parameters are only for the convenience of engineers and technicians in this field to better understand the technical solution of this embodiment, and the parameters of the resonant converter during the specific implementation of the control method of this embodiment are not limited to this.

[0068] Figure 4This is the first control timing diagram of the first embodiment of the present invention, wherein Vgs1 is the driving pulse of the primary side switch tubes S1 and S4; Vgs2 is the driving pulse of the primary side switch tubes S2 and S3; Vgs5 and Vgs6 are the driving pulses of the secondary side active switch tubes S5 and S6 respectively; VAB is the input voltage of the resonant cavity, that is, the voltage across the source of the switch tube S1 and the drain of the switch tube S4; iLr and iLm are the currents flowing through the resonant inductor Lr and the excitation inductor Lm respectively; is5 and is6 are the currents flowing through the secondary side rectifier switch tubes S5 and S6 respectively.

[0069] from Figure 4 It can be seen that the duty cycle of the driving pulse Vgs1 of the primary switch tubes S1 and S4 and the driving pulse Vgs2 of the switch tubes S2 and S3 are equal to 0.5, and the driving pulses Vgs1 and Vgs2 are complementary (ignoring the dead time); the driving pulse Vgs6 of the secondary rectifier switch tube S6 is consistent with the turn-on time of the driving pulse Vgs1 of the primary switch tubes S1 and S4; the driving pulse Vgs5 of the secondary rectifier switch tube S5 is consistent with the turn-on time of the driving pulse Vgs2 of the primary switch tubes S2 and S3; the turn-on duty cycle of the driving pulses Vgs5 and Vgs6 of the secondary rectifier switch tubes S5 and S6 is the same; the output voltage gain is adjusted by controlling the duty cycle of the driving pulses Vgs5 and Vgs6 of the secondary rectifier switch tubes S5 and S6.

[0070] It should be noted that Figure 4 When the control sequence is implemented, a reasonable dead time must be set between the driving pulses of the switch tubes S1 and S2, and between the driving pulses of the switch tubes S4 and S3 to achieve soft switching of the switch tubes S1 to S4. Coss1 to Coss6 represent the output capacitance of the six switch tubes S1 to S6 respectively.

[0071] Figure 5 for Figure 4 Equivalent circuit diagram of the resonant converter in the [t0-t1] switching mode; Figure 6 for Figure 4 Equivalent circuit diagram in the [t1-t2] switching mode; Figure 7 for Figure 4 Equivalent circuit diagram in the [t2-t3] switching mode; Figure 8 for Figure 4 Equivalent circuit diagram in the [t3-t4] switching mode; Fig. 9 for Figure 4 The equivalent circuit diagram in the [t4-t5] switching mode. Figures 4 to 9 The specific working process of the resonant converter control method proposed in this embodiment in the positive half cycle is described in detail. Due to the symmetry between the positive half cycle and the negative half cycle of the resonant converter, generally only half a cycle is described.

[0072] Switching mode 1 [t0, t1]: as shown in the attached Figure 5 As shown, at time t0, the driving pulses of the switches S1 and S4 arrive, and the switches S1 and S4 realize ZVS conduction; during this period, the switches S1 and S4 are in the on state, and the input voltage VAB of the resonant cavity is Vin; at time t0, the secondary rectifier switch S6 is also turned on at the same time, and the output filter capacitor Co forms a discharge loop through the switch S6. At this time, the current is6 flowing through the switch S6 is a negative current and increases linearly; under the action of the secondary discharge loop, the resonant current rises linearly, and at this time the resonant current iLr is greater than the excitation current iLm, and the primary side transmits energy to the secondary side. This energy does not provide energy to the load as power reflux, and the load energy is provided by the output filter capacitor Co.

[0073] Switching mode 1 [t1, t2]: as shown in the attached Figure 6 As shown, the switch tubes S1 and S4 continue to be turned on, and the input voltage VAB of the resonant cavity is always Vin; at time t1, the secondary rectifier switch tube S6 is turned off, and the output filter capacitor Co continues to discharge through the parasitic capacitor Coss6 of the switch tube S6, and the current flowing through the secondary winding NS2 continues to increase linearly in a negative direction; under the action of the secondary discharge loop, the resonant current continues to rise linearly, the resonant current iLr is greater than the excitation current iLm, and the primary side still transmits power back to the secondary side; the output filter capacitor Co provides energy for load follow-up.

[0074] Switching mode 1 [t2, t3]: as shown in the attached Figure 7 As shown, at time t2, the discharge of the parasitic capacitor Coss6 of the secondary rectifier switch tube S6 is completed, the secondary rectifier switch tube S6 is completely turned off, the negative current flowing through the secondary winding NS2 increases linearly to the maximum, and the primary resonant current also rises linearly to the maximum; the inductor current cannot change suddenly, and during this period, the primary resonant current iLr is still greater than the excitation current iLm, and the primary side transmits energy to the secondary side through the body diode of the switch tube S5 to charge the filter capacitor Co and provide energy to the load at the same time; in addition, under the clamping effect of the output voltage Vo, the excitation current of the excitation inductor Lm rises linearly, but is less than the resonant current iLr; the resonant current iLr gradually decreases under the resonance of the resonant inductor Lr and the resonant capacitor Cr.

[0075] Switching mode 1 [t3, t4]: as shown in the attached Figure 8 As shown, at time t3, the resonant current iLr is equal to the excitation current iLm, and the body diode current flowing through the secondary rectifier switch tube S5 naturally passes through 0, and the secondary rectifier switch tube S5 is turned off at zero current to avoid the diode reverse recovery problem; during this period, the excitation current and the resonant current iLr are equal and remain unchanged, and the filter capacitor Co provides energy for the load to continue current.

[0076] Switching mode 1 [t4, t5]: as shown in the attached Fig. 9 As shown, at time t4, the switch tube S1 is turned off, the resonant current iLr is equal to the excitation current iLm, and the body diode of the secondary side rectifier switch tube S5 is still in the reverse cut-off state; the resonant current iLr charges the output capacitors Coss1 and Coss4 of the switch tubes S1 and S4, and discharges the output capacitors Coss2 and Coss3 of the switch tubes S2 and S3; when the voltage across the capacitors Coss2 and Coss3 drops to 0, the body diodes of the switch tubes S2 and S3 are turned on, providing conditions for the switch tubes S2 and S3 to achieve zero voltage turn-on; at time t5, the switch tubes S2 and S3 achieve ZVS turn-on, and the circuit enters the negative half cycle.

[0077] According to the description of the working process of the above resonant converter, the primary side switch tubes can all achieve zero voltage turn-on, the secondary side rectifier switch tubes can also achieve zero current turn-off, there is no problem of diode reverse recovery, and all switching devices can maintain soft switching characteristics.

[0078] Furthermore, the conduction time of each pair of diagonal switch tubes in the primary inverter bridge arm is consistent with the conduction time of the rectifier switch tube corresponding to the secondary winding connection branch of the resonant converter transformer. Specifically, Figure 1 For example:

[0079] The driving pulse of the rectifier switch tube S5 corresponding to the branch connected to the same-name end of the secondary side of the resonant converter transformer is consistent with the driving pulse of the primary switch lower tube S4 corresponding to the branch connected to the opposite-name end of the primary side of the transformer; the driving pulse of the rectifier switch tube S6 corresponding to the branch connected to the opposite-name end of the secondary side of the resonant converter transformer is consistent with the driving pulse of the primary switch upper tube S1 corresponding to the branch connected to the same-name end of the primary side of the transformer;

[0080] Alternatively, the driving pulse of the rectifier switch tube S6 corresponding to the branch connecting the opposite-name ends of the secondary side of the resonant converter transformer is consistent with the turn-on moment of the driving pulse of the primary switch upper tube S1 corresponding to the branch connecting the same-name ends of the primary side of the transformer; the driving pulse of the rectifier switch tube S5 corresponding to the branch connecting the same-name ends of the secondary side of the resonant converter transformer is consistent with the turn-on moment of the driving pulse of the primary switch lower tube S4 corresponding to the branch connecting the opposite-name ends of the primary side of the transformer.

[0081] Further, Figure 2 In the control method, the operating frequency of the secondary rectifier switch tube can be the operating frequency of the primary switch tube of the resonant converter. At this time, the secondary rectifier switch tube is turned on once in one cycle to achieve the gain adjustment of the resonant converter, corresponding to Figure 4 Timing diagram of . Figure 2 The operating frequency of the secondary rectifier switch tube in the control method can also be equal to twice the operating frequency of the primary switch tube of the resonant converter, corresponding to Fig.10 The operating frequency of the secondary rectifier switch tube is equal to twice the operating frequency of the primary switch tube of the resonant converter. The secondary rectifier switch tube is turned on twice in one cycle. The first turn-on is used to adjust the gain of the resonant converter, and the second turn-on is used to realize the synchronous rectification function of the secondary rectifier switch tube. The purpose is to reduce the rectification loss of the secondary rectifier circuit and improve the conversion efficiency.

[0082] Fig.10 The specific control logic is as follows:

[0083] For the primary side, the operating frequency of the primary side switch tube of the resonant converter is controlled to remain fixed; the duty cycle of the primary side switch tubes S1 to S4 is kept fixed at 0.5, the switch tube S1 and the switch tube S2 are complementary turned on, the switch tube S1 and the switch tube S4 are turned on and turned off at the same time, and the switch tube S2 and the switch tube S3 are turned on and turned off at the same time;

[0084] For the secondary side, the secondary side rectifier switch tube is turned on twice in one cycle, so the operating frequency of the secondary side rectifier switch tube is twice that of the primary side switch tube; in each working cycle, the turn-on time of the secondary side rectifier switch tube S6 is controlled to be consistent with the primary side switch tube S1, and the turn-on time of the secondary side rectifier switch tube S5 is consistent with the primary side switch tube S2, and the conduction duty cycle of the secondary side rectifier switch tube S5 is the same as that of the secondary side rectifier switch tube S6; due to the symmetry of the positive half cycle and the negative half cycle of the resonant converter, taking the timing of the positive half cycle as an example, it includes: in the time period [t0, t1], the secondary side rectifier switch tube S6 is turned on, and the conduction duty cycle The ratio is marked as the first conduction duty cycle D, and the first conduction is used to achieve output voltage gain adjustment; the period [t1, t2] is the dead time; the period [t2, t3] is to control the secondary rectifier switch tube S5 to conduct, which is used to achieve the synchronous rectification function; the period [t3, t4] is the resonant current equal to the excitation current, and no current flows through the secondary rectifier switch tube; the period [t4, t5] is the dead time; then enter the timing of the negative half cycle; the reasonable dead time is set between the two conduction duty cycles of the secondary rectifier switch tubes S5 and S6 to ensure the soft switching of the secondary rectifier switch tube. During the entire control process, the working state of the primary switch tube remains unchanged.

[0085] Fig.10 Under the control timing, the resonant converter also has five switching modes in a half cycle. The detailed working process is similar to Figure 4 The above are basically the same, and technicians in this field can analyze them by themselves, so I will not go into details here.

[0086] Further, Figure 2 The control method and its improvement can also be combined with frequency conversion control to form a hybrid control scheme, so that the secondary side active switch tube of the resonant converter is in a critical current continuous conduction mode.

[0087] Further, Figure 2 The control method uses a polynomial to fit the conduction duty cycle D of the secondary rectifier switch tube and the first gain G under a certain load, and controls the conduction duty cycle of the secondary rectifier switch tube to change with the first gain.

[0088] Among them, polynomial fitting is a mathematical tool. The present invention can obtain the equations that these data points need to satisfy by fitting the data points under the open loop. The equation is used for closed-loop control. This embodiment is based on the prototype parameters of the above-mentioned resonant converter and uses polynomial fitting to obtain the conduction duty cycle D and the first gain G of the secondary side rectifier switch tube that satisfy the following relationship:

[0089] G=188000·D 4 -23752·D 3 +1195·D 2 -18·D+1.

[0090] It should be noted that the above relationship is only an example. Those skilled in the art can also fit it into a quadratic equation, a cubic equation or a quintic equation as needed. Also, since there may be errors in the measurement of the above data points, there will be certain errors in the above relationship.

[0091] Furthermore, the operating frequency of the primary switch tube of the resonant converter is the resonant frequency, the purpose of which is to optimize the design of the magnetic device, reduce the volume of the magnetic device, and improve the power density. It should be noted that due to the design errors of the resonant inductor and the resonant capacitor, the operating frequency of the switch tube is not completely consistent with the resonant frequency, but is near the resonant frequency. The present invention regards the operating frequency as the resonant frequency within the error range acceptable to technicians in this field.

[0092] Second embodiment

[0093] This embodiment provides a control device for a resonant converter, wherein the secondary rectifier tube of the resonant converter is an active switch tube. Fig.11 The schematic diagram of the control device of the resonant converter according to the second embodiment of the present invention is shown in FIG. Fig.10 , the control device of this embodiment includes the following modules:

[0094] An acquisition module, used to acquire a first gain of the resonant converter, where the first gain is a gain required by the resonant converter;

[0095] A processing module is used to adjust the actual gain of the resonant converter, and control the on-duty cycle of the secondary rectifier switch tube according to the first gain, so that the on-duty cycle of the secondary rectifier switch tube of the resonant converter increases with the increase of the first gain and decreases with the decrease of the first gain, so that the actual gain of the resonant converter will be adjusted to the required gain.

[0096] The control device of the resonant converter proposed in this embodiment can achieve wide gain range adjustment by controlling the conduction duty cycle of the secondary rectifier switch tube, and the control method is simple and feasible; thus, wide gain range control can be achieved without frequency modulation. Furthermore, when the primary switch tube operates near the resonant frequency, it is convenient to optimize the design of magnetic components such as inductors and transformers, which is beneficial to the high power density design and application of switching power supplies; in addition, the control device of this embodiment maintains the soft switching performance of the resonant converter, and can achieve ZVS of the primary switch tube and ZCS of the secondary rectifier switch tube; at the same time, the synchronous rectification function of the secondary rectifier switch tube can be achieved by turning on the secondary rectifier switch tube for the second time, which is beneficial to improving the conversion efficiency of the converter.

[0097] Third embodiment

[0098] If the unit integrated in the control device in the above-mentioned second embodiment is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server or a network device, etc.) to perform all or part of the steps of the above-mentioned methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program codes.

[0099] Therefore, the third embodiment of the present invention provides a computer-readable storage medium, which includes a stored program, and the program executes the control method of any specific implementation method of the first embodiment.

[0100] Fourth embodiment

[0101] A fourth embodiment of the present invention provides a processor for running a program, wherein the program executes the control method of any specific implementation method of the first embodiment when running.

[0102] Fifth embodiment

[0103] A fifth embodiment of the present invention provides a switching power supply, including a resonant converter, wherein the secondary rectifier tube of the resonant converter is an active switch tube, and the resonant converter is controlled by the control device of the resonant converter in the second embodiment.

[0104] The description of the above embodiments is only used to help understand the inventive concept of the present application and is not intended to limit the present invention. For ordinary technicians in this technical field, any modifications, equivalent substitutions, improvements, etc. made without departing from the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A control method for a resonant converter, wherein the resonant converter comprises a primary inverter bridge arm, and the secondary rectifier switch tube of the resonant converter is an active switch tube, characterized in that: The control method of the resonant converter includes: applying a voltage obtained by superimposing the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer to the resonant branch, so that the voltage across the resonant branch is higher than the output voltage of the primary inverter bridge arm of the resonant converter, thereby achieving adjustment of the gain of the resonant converter.

2. The control method of the resonant converter according to claim 1, characterized in that: The control method comprises the following steps in each working cycle of the resonant converter: (1) obtaining a first gain of the resonant converter, where the first gain is a gain required by the resonant converter; (2) Controlling the on-duty cycle of the secondary rectifier switch tube according to the first gain, thereby controlling the time during which the voltage obtained by superposing the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer acts on the resonant branch, so that the on-duty cycle of the secondary rectifier switch tube of the resonant converter increases with the increase of the first gain and decreases with the decrease of the first gain, thereby adjusting the actual gain of the resonant converter to the required gain.

3. The control method according to claim 2, characterized in that: The turn-on time of each pair of diagonal switch tubes in the primary inverter bridge arm is consistent with the turn-on time of the rectifier switch tube corresponding to the secondary winding connection branch of the resonant converter transformer.

4. The control method of the resonant converter according to claim 2, characterized in that: The operating frequency of the secondary rectifier switch tube of the resonant converter is the operating frequency of the primary switch tube of the resonant converter, or the operating frequency of the secondary rectifier switch tube of the resonant converter is equal to twice the operating frequency of the primary switch tube of the resonant converter.

5. The control method of the resonant converter according to claim 4, characterized in that: When the operating frequency of the secondary rectifier switch tube is equal to the operating frequency of the primary switch tube of the resonant converter, the secondary rectifier switch tube is turned on once in one cycle to achieve gain adjustment of the resonant converter; when the operating frequency of the secondary rectifier switch tube is equal to twice the operating frequency of the primary switch tube of the resonant converter, the secondary rectifier switch tube is turned on twice in one cycle, the first turn-on is used to achieve gain adjustment of the resonant converter, and the second turn-on is used to achieve the synchronous rectification function of the secondary rectifier switch tube.

6. The control method of the resonant converter according to claim 2, 3, 4 or 5, characterized in that: Combined with the frequency conversion control, a hybrid control scheme is formed, so that the secondary side active switch tube of the resonant converter is in a critical current continuous conduction mode.

7. The control method according to claim 2, characterized in that: Under a certain load, a polynomial is used to fit the conduction duty cycle of the secondary rectifier switch tube and the first gain, and the conduction duty cycle of the secondary rectifier switch tube is controlled to change with the first gain.

8. A control device for a resonant converter, wherein the secondary rectifier switch tube of the resonant converter is an active switch tube, characterized in that: The control device comprises the following modules: A judging module, used to judge whether the resonant converter needs to adjust the gain; The processing module is used to apply the voltage obtained by superimposing the output voltage of the primary inverter bridge arm of the resonant converter and the voltage across the primary winding of the resonant converter transformer to the resonant branch when the resonant converter needs to adjust the gain, so that the voltage across the resonant branch is higher than the output voltage of the primary inverter bridge arm of the resonant converter, thereby achieving the adjustment of the gain of the resonant converter.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a stored program, wherein the program executes the control method according to any one of claims 1 to 7.

10. A processor, characterized in that: The processor is used to run a program, wherein the program executes the control method described in any one of claims 1 to 7 when running.

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