DC-DC conversion circuit and AC-DC conversion system

Abstract

The present application relates to a DC-DC conversion circuit and an AC-DC conversion system. The DC-DC conversion circuit includes an isolated DC-DC converter and a flyback converter, wherein the first DC terminal of the flyback converter is connected in parallel with the second DC terminal of the isolated DC-DC converter, the third DC terminal of the flyback converter is connected in series with the fourth DC terminal of the isolated DC-DC converter, the isolated DC-DC converter is used to convert the first voltage of the second DC terminal with the second voltage of the fourth DC terminal; the flyback converter is used to convert the first voltage with the third voltage of the third DC terminal; the second voltage is greater than the third voltage. The DC-DC conversion circuit of the present application has the characteristics of a wide input and output range. The AC-DC conversion system of the present application is designed based on the DC-DC conversion circuit, and has the characteristics of a wide input and output range and a low voltage ripple rate.

Description

Technical Field

[0001] The present application relates to the technical field of direct current converters, and in particular to a direct current-to-direct current conversion circuit and an alternating current-to-direct current conversion system. Background Art

[0002] Traditional DCDC converters are mostly two-stage topology structures connected in series, that is, the first stage uses a non-isolated converter, and the second stage uses an isolated converter with a fixed voltage gain, which has low transmission efficiency. In addition, in order to meet the requirements of photovoltaic systems, energy storage converters, etc. for DC side voltage ripple, it is usually necessary to configure an additional active decoupling circuit, which has a complex circuit structure. Summary of the invention

[0003] Based on this, it is necessary to provide a DC-DC conversion circuit and an AC-DC conversion system with high transmission efficiency.

[0004] In a first aspect, the present application provides a DC-DC conversion circuit, the DC-DC conversion circuit comprising an isolated DC-DC converter and a flyback converter, the first DC terminal of the flyback converter being connected in parallel with the second DC terminal of the isolated DC-DC converter, the third DC terminal of the flyback converter being connected in series with the fourth DC terminal of the isolated DC-DC converter,

[0005] The isolated DC-DC converter is used for converting the first voltage of the second DC terminal and the second voltage of the fourth DC terminal;

[0006] The flyback converter is used to convert the first voltage into a third voltage at the third DC terminal; the second voltage is greater than the third voltage.

[0007] In one embodiment, the flyback converter includes a transformer module, a first switch module, a first clamp module, a second switch module, and a second clamp module, wherein the primary side of the transformer module is connected to the first clamp module and the first switch module respectively, and the secondary side of the transformer module is connected to the second clamp module and the second switch module respectively;

[0008] The voltage transformation module is used to convert the first voltage and the third voltage;

[0009] The first clamping module is used to suppress the voltage spike on the primary side of the transformer module, recover leakage inductance energy, or realize zero voltage switching of the first switch module under specific conditions;

[0010] The second clamping module is used to suppress the voltage spike on the secondary side of the transformer module, recover leakage inductance energy, or realize zero voltage switching of the second switch module under specific conditions.

[0011] In one embodiment, the transformer module includes a first inductor, a second inductor, a third inductor and a transformer, wherein the first end of the primary winding of the transformer is respectively connected to the first end of the first inductor and the first end of the second inductor, the second end of the primary winding of the transformer is respectively connected to the second end of the second inductor, the first end of the first clamping module and the first end of the first switch module, the first end of the secondary winding of the transformer is connected to the first end of the third inductor, and the second end of the secondary winding of the transformer is respectively connected to the first end of the second clamping module and the first end of the second switch module;

[0012] The first clamping module includes a first capacitor and a first switch tube, wherein the first end of the first capacitor is connected to the second end of the first inductor, the second end of the first capacitor is connected to the first electrode of the first switch tube, and the second electrode of the first switch tube is connected to the first switch module;

[0013] The second clamping module includes a second capacitor and a second switch tube, wherein the first end of the second capacitor is connected to the second end of the third inductor, the second end of the second capacitor is connected to the first electrode of the second switch tube, and the second electrode of the second switch tube is connected to the second switch module.

[0014] The DC-DC conversion circuit includes an isolated DC-DC converter, a flyback converter and a control circuit. The first DC terminal of the flyback converter is connected in parallel with the second DC terminal of the isolated DC-DC converter, and the third DC terminal of the flyback converter is connected in series with the fourth DC terminal of the isolated DC-DC converter. The isolated DC-DC converter is used to convert the first voltage of the second DC terminal with the second voltage of the fourth DC terminal. The flyback converter is used to convert the first voltage with the third voltage of the third DC terminal. Since the fourth DC terminal of the isolated DC-DC converter and the third DC terminal of the flyback converter are connected in series, by setting the second voltage of the fourth DC terminal to be greater than the third voltage of the third DC terminal, the isolated DC-DC converter can process most of the power, and the flyback converter only processes a small part of the power, thereby improving the overall power transmission efficiency of the DC-DC conversion circuit. Since the flyback converter has the characteristics of a wide input and output range, when the input and output gain of the isolated DC-DC converter is fixed, by adjusting the third voltage of the flyback converter, the voltage after the third voltage and the second voltage are superimposed can meet the output requirements of the DC-DC conversion circuit.

[0015] In a second aspect, the present application further provides an AC-DC conversion system, comprising an AC-DC conversion circuit, a control circuit, and a DC-DC conversion circuit provided by any of the above embodiments, wherein:

[0016] The DC side of the AC-DC conversion circuit is respectively connected to the second DC end of the isolated DC-DC converter and the first DC end of the flyback converter, the AC side of the AC-DC conversion circuit is used to receive an AC signal, and the AC-DC conversion circuit is used to convert the AC signal and the first voltage;

[0017] The control circuit is connected to the AC-DC conversion circuit and the flyback converter respectively, and is used to control the working state of the AC-DC conversion circuit and / or the flyback converter according to the working mode of the AC-DC conversion system to change the first voltage and / or the fourth voltage; wherein the fourth voltage is the sum of the second voltage and the third voltage.

[0018] In one embodiment, the control circuit comprises:

[0019] a first control module, connected to the flyback converter, and configured to output a first control signal to the flyback converter according to a fourth voltage reference value and the fourth voltage when the working mode of the AC-DC conversion system is a forward working mode, so as to change a third voltage at a third DC terminal of the flyback converter; wherein, in the forward working mode, the electrical signal flows from the AC side of the AC-DC conversion circuit to the DC side;

[0020] a second control module connected to the AC-DC conversion circuit, configured to obtain a power proportion allocation table, and output a second control signal to the AC-DC conversion circuit according to the fourth voltage reference value, the power proportion allocation table and the AC signal, so as to change the first voltage when the working mode of the AC-DC conversion system is a forward working mode;

[0021] A third control module is connected to the flyback converter, and is used to obtain a power proportion allocation table, and when the working mode of the AC-DC conversion system is a reverse working mode, output the first control signal to the flyback converter according to the fourth voltage, the power proportion allocation table and the first voltage to change the third voltage; wherein, in the reverse working mode, the electrical signal flows from the DC side of the AC-DC conversion circuit to the AC side.

[0022] In one embodiment, the control circuit further includes:

[0023] The ripple compensation module is respectively connected to the first control module, the third control module and the flyback converter, and is used to obtain the feedback current of the third DC terminal, and adjust the duty cycle of the first control signal according to the feedback current so that the voltage ripple of the third voltage is inverse to the voltage ripple of the second voltage.

[0024] In one embodiment, the second control module includes:

[0025] a first power allocation unit, configured to obtain the power proportion allocation table, and determine a first voltage reference value according to the power proportion allocation table and the fourth voltage reference value;

[0026] The first voltage regulating unit is used to determine the duty cycle of the second control signal according to the first voltage reference value and the AC signal to change the first voltage.

[0027] In one embodiment, the first power distribution unit comprises:

[0028] a power coefficient regulator, configured to determine the second voltage reference value according to the power proportion allocation table and the fourth voltage reference value;

[0029] a limiter, used for limiting the amplitude of the second voltage reference value;

[0030] A multiplier is used to determine the first voltage reference value according to the second voltage reference value and the transformation ratio of the isolated DC-DC converter.

[0031] In one embodiment, the third control module includes:

[0032] a second power allocation unit, configured to obtain the power proportion allocation table, and determine the first voltage reference value according to the power proportion allocation table and the fourth voltage;

[0033] The second voltage regulating unit is used to adjust the duty cycle of the first control signal according to the first voltage reference value and the first voltage to change the third voltage.

[0034] In one embodiment, the AC-DC conversion system further includes:

[0035] The bus capacitor is connected in parallel to the second DC end of the isolated DC-DC converter, the first DC end of the flyback converter, and the DC side of the AC-DC conversion circuit.

[0036] The AC-DC conversion system includes an AC-DC conversion circuit, a control circuit and a DC-DC conversion circuit. The DC side of the AC-DC conversion circuit is respectively connected to the second DC end of the isolated DC-DC converter and the first DC end of the flyback converter, and the control circuit is respectively connected to the AC-DC conversion circuit and the flyback converter. The DC-DC conversion circuit includes an isolated DC-DC converter, a flyback converter and a control circuit, the first DC end of the flyback converter is connected in parallel with the second DC end of the isolated DC-DC converter, and the third DC end of the flyback converter is connected in series with the fourth DC end of the isolated DC-DC converter. When the AC-DC conversion system is in the forward working mode, the AC signal remains stable, and the working state of the AC-DC conversion circuit can be controlled by the control circuit to change the first voltage so that the second voltage changes accordingly, thereby ensuring that the isolated DC-DC conversion circuit transmits most of the power; further, the working state of the flyback converter is controlled by the control circuit to change the third voltage, thereby realizing dynamic adjustment of the fourth voltage formed by the superposition of the third voltage and the second voltage. When the AC-DC conversion system is in the reverse working mode, the fourth voltage remains stable. The working state of the flyback converter can be adjusted through the control circuit to change the third voltage so that the second voltage changes. The first voltage will change accordingly with the second voltage, thereby realizing dynamic adjustment of the first voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 is a structural block diagram of a DC-DC conversion circuit according to an embodiment;

[0039] Figure 2 A topological structure of a flyback converter according to an embodiment;

[0040] Figure 3 A structural block diagram of an AC-DC conversion system provided by an embodiment;

[0041] Figure 4 is a structural block diagram of a first control module in an embodiment;

[0042] Figure 5 A power distribution diagram of an isolated DC-DC converter and a flyback converter in one embodiment;

[0043] Figure 6is a structural block diagram of a second control module in an embodiment;

[0044] Figure 7 is a structural block diagram of a third control module in an embodiment;

[0045] Figure 8 It is a structural block diagram of a first control module and a ripple compensation module connected in one embodiment;

[0046] Fig. 9 is a structural block diagram of a third control module and a ripple compensation module connected in one embodiment;

[0047] Fig.10 is a structural block diagram of an AC-DC conversion system according to another embodiment;

[0048] Fig.11 is an equivalent circuit diagram of an AC-DC conversion system according to an embodiment;

[0049] Fig.12a In one embodiment, when the voltage compensation coefficient α=1, the current i dc Ripple peak-to-peak value and bus capacitance C dc , equivalent filter capacitor C in Relationship diagram;

[0050] Figure 12b for Fig.12a Grayscale image of

[0051] Fig.13a In one embodiment, when the voltage compensation coefficient α=0.9, the current i dc Ripple peak-to-peak value and bus capacitance C dc , equivalent filter capacitor C in Relationship diagram;

[0052] Fig.13b for Fig.13a Grayscale image of

[0053] Fig.14a In one embodiment, when the voltage compensation coefficient α=1, the peak-to-peak value of the bus voltage (i.e., the first voltage) ripple and the bus capacitance C dc , equivalent filter capacitor C in Relationship diagram;

[0054] Fig.14b for Fig.14a Grayscale image of

[0055] Fig.15a In one embodiment, when the voltage compensation coefficient α=0.9, the peak-to-peak value of the bus voltage ripple and the bus capacitance C dc , equivalent filter capacitor C in Relationship diagram;

[0056] Fig.15b for Fig.15a Grayscale image of

[0057] Fig.16 A comparison diagram of bus capacitance and ripple rate according to an embodiment.

[0058] Description of reference numerals:

[0059] 10-DC-DC conversion circuit, 100-isolated DC-DC converter, 110-second DC terminal, 120-fourth DC terminal, 200-flyback converter, 210-first DC terminal, 220-third DC terminal, 201-transformer module, 202-first switch module, 203-second switch module, 204-first clamp module, 205-second clamp module, 300-control circuit, 310-first control module, 320-second control module, 321-first power distribution unit, 322-first voltage regulation unit, 330-third control module, 331-second power distribution unit, 332-second voltage regulation unit, 340-ripple compensation unit, 20-AC-DC conversion circuit, 30-control circuit, 40-bus capacitor. DETAILED DESCRIPTION

[0060] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0062] It is understood that the terms "first", "second", etc. used in this application may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element. For example, a first inductor may be referred to as a second inductor, and similarly, a second inductor may be referred to as a first inductor without departing from the scope of this application. Both the first inductor and the second inductor are inductors, but they are not the same inductor.

[0063] It can be understood that the “connection” in the following embodiments should be understood as “electrical connection”, “communication connection”, etc. if the connected circuits, modules, units, etc. have electrical signals or data transmission between each other.

[0064] It can be understood that “at least one” means one or more, “plurality” means two or more, and “at least a portion of an element” means a part or all of an element.

[0065] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" and the like specify the presence of stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the relevant listed items.

[0066] In one embodiment, Figure 1 As shown, the present application provides a DC-DC conversion circuit, including an isolated DC-DC converter 100 and a flyback converter 200, wherein a first DC terminal 210 of the flyback converter 200 is connected in parallel with a second DC terminal 110 of the isolated DC-DC converter 100, and a third DC terminal 220 of the flyback converter 200 is connected in series with a fourth DC terminal 120 of the isolated DC-DC converter 100.

[0067] The DC-DC conversion circuit of the present application has a bidirectional working mode. In the embodiment of the present application, the forward working mode of the DC-DC conversion circuit is defined as a working mode in which the electrical signal flows from the second DC terminal 110 of the isolated DC-DC converter 100 to the fourth DC terminal 120, and the reverse working mode is defined as a working mode in which the electrical signal flows from the fourth DC terminal 120 of the isolated DC-DC converter 100 to the second DC terminal 110. When the DC-DC conversion circuit is in the forward working mode, the first DC terminal 210 of the flyback converter 200 is used as the input terminal, the third DC terminal 220 is used as the output terminal, the second DC terminal 110 of the isolated DC-DC converter 100 is used as the input terminal, and the fourth DC terminal 120 is used as the output terminal; when the DC-DC conversion circuit is in the reverse working mode, the third DC terminal 220 of the flyback converter 200 is used as the input terminal, the first DC terminal 210 is used as the output terminal, the fourth DC terminal 120 of the isolated DC-DC converter 100 is used as the input terminal, and the second DC terminal 110 is used as the output terminal.

[0068] The isolated DC-DC converter 100 is used to convert the first voltage of the second DC terminal 110 with the second voltage of the fourth DC terminal 120. It can be understood that the isolated DC-DC converter 100 can convert the first voltage into the second voltage when the DC-DC conversion circuit is in the forward working mode; when the DC-DC conversion circuit is in the reverse working mode, the second voltage can be converted into the first voltage. The isolated DC-DC converter 100 can be any one of an LLC resonant circuit, a CLLC resonant circuit or a CLLLC resonant circuit. In an embodiment of the present application, the isolated DC-DC converter 100 operates in a fixed frequency mode, and the first voltage is proportional to the second voltage. The first voltage, the second voltage, the third voltage and the fourth voltage in the embodiment of the present application are all DC signals. In some application scenarios, such as power supplies, energy routers, and energy storage converters, the first voltage can be a bus voltage.

[0069] The flyback converter 200 is used to convert the first voltage into a third voltage of the third DC terminal 220. It can be understood that the isolated DC-DC converter 100 can convert the first voltage into the third voltage when the DC-DC conversion circuit is in the forward working mode; and can convert the third voltage into the first voltage when the DC-DC conversion circuit is in the reverse working mode.

[0070] The second voltage is greater than the third voltage. The DC-DC conversion circuit of the present application is a partial power structure, that is, the isolated DC-DC converter 100 processes most of the power, and the flyback converter 200 processes only a small part of the power. Since the fourth DC terminal of the isolated DC-DC converter 100 and the third DC terminal of the flyback converter 200 are connected in series, their power distribution is related to the second voltage and the third voltage, and therefore, the second voltage can be set to be greater than the third voltage.

[0071] In the embodiment of the present application, the DC-DC conversion circuit includes an isolated DC-DC converter 100, a flyback converter 200 and a control circuit 300. The first DC terminal 210 of the flyback converter 200 is connected in parallel with the second DC terminal 110 of the isolated DC-DC converter 100, and the third DC terminal 220 of the flyback converter 200 is connected in series with the fourth DC terminal 120 of the isolated DC-DC converter 100. The isolated DC-DC converter 100 is used to convert a first voltage of the second DC terminal 110 with a second voltage of the fourth DC terminal 120. The flyback converter 200 is used to convert the first voltage with the third voltage of the third DC terminal 220. Since the fourth DC terminal of the isolated DC-DC converter 100 and the third DC terminal of the flyback converter 200 are connected in series, by setting the second voltage of the fourth DC terminal 120 to be greater than the third voltage of the third DC terminal 220, the isolated DC-DC converter 100 can process most of the power, and the flyback converter 200 can only process a small part of the power, thereby improving the overall power transmission efficiency of the DC-DC conversion circuit. Since the flyback converter 200 has the characteristics of a wide input and output range, when the input and output gain of the isolated DC-DC converter 100 is fixed, by adjusting the third voltage of the flyback converter 200, the voltage after the third voltage and the second voltage are superimposed can meet the output requirements of the DC-DC conversion circuit.

[0072] In one embodiment, Figure 2 As shown, the flyback converter 200 includes a transformer module 201, a first switch module 202, a first clamp module 204, a second switch module 203, and a second clamp module 205. The primary side of the transformer module 201 is connected to the first clamp module 204 and the first switch module 202, respectively, and the secondary side of the transformer module 201 is connected to the second clamp module 205 and the second switch module 203, respectively.

[0073] Among them, the transformer module 201 is used to convert the first voltage and the third voltage. The first clamping module 204 is used to suppress the voltage spike on the primary side of the transformer module 201, recover the leakage inductance energy, or realize the zero voltage opening of the first switch module under specific conditions. The second clamping module 205 is used to suppress the voltage spike on the secondary side of the transformer module 201, recover the leakage inductance energy, or realize the zero voltage opening of the second switch module under specific conditions. During the operation of the flyback converter 200, due to the existence of the leakage inductance of the transformer module 201, a voltage spike will appear in the loop. Therefore, it is necessary to set a clamping module on the primary side and the secondary side of the transformer module 201 to suppress the voltage spike in the loop and recover the leakage inductance energy.

[0074] Exemplarily, the first switch module 202 and the second switch module 203 can be power devices such as MOS tubes or IGBT tubes, respectively. For the first clamp module 204, the specific condition refers to the resonance of the distributed capacitance Coss1 in the first clamp module 204 and the first switch module 202 with the primary side of the transformer module 201. Under this condition, the source-drain voltage of the first switch module 202 is zero, and the zero-voltage switching of the first switch module can be achieved. For the second clamp module 205, the specific condition refers to the resonance of the distributed capacitance Coss2 in the second clamp module 205 and the second switch module 203 with the secondary side of the transformer module 201. Under this condition, the source-drain voltage of the second switch module is zero, and the zero-voltage switching of the second switch module 203 can be achieved.

[0075] For further information, please refer to Figure 2 The transformer module 201 includes a first inductor L1, a second inductor L2, a third inductor L3 and a transformer T, wherein the first end of the primary winding of the transformer T is respectively connected to the first end of the first inductor L1 and the first end of the second inductor L2, the second end of the primary winding of the transformer T is respectively connected to the second end of the second inductor L2, the first end of the first clamping module 204, and the first end of the first switch module 202, the first end of the secondary winding of the transformer T is connected to the first end of the third inductor L3, and the second end of the secondary winding of the transformer T is respectively connected to the first end of the second clamping module 205 and the first end of the second switch module 203.

[0076] The first clamping module 204 includes a first capacitor C1 and a first switch tube Q1, wherein the first end of the first capacitor C1 is connected to the second end of the first inductor L1, the second end of the first capacitor C1 is connected to the first electrode of the first switch tube Q1, and the second electrode of the first switch tube Q1 is connected to the first switch module 202.

[0077] The second clamping module 205 includes a second capacitor C2 and a second switch tube Q2, wherein a first end of the second capacitor C2 is connected to a second end of the third inductor L3, a second end of the second capacitor C2 is connected to a first electrode of the second switch tube Q2, and a second electrode of the second switch tube Q2 is connected to the second switch module 203.

[0078] In this embodiment, the flyback converter 200 adopts an active clamp bidirectional topology structure with low transmission loss, which can further improve the overall power transmission efficiency of the DC-DC conversion circuit.

[0079] In one embodiment, Figure 3 As shown, the present application also provides an AC-DC conversion system, which includes an AC-DC conversion circuit 20, a control circuit 30 and a DC-DC conversion circuit 10 provided in any of the above embodiments.

[0080] The DC side of the AC-DC conversion circuit 20 is respectively connected to the second DC terminal 110 of the isolated DC-DC converter 100 and the first DC terminal 210 of the flyback converter 200, and the control circuit 30 is respectively connected to the AC-DC conversion circuit 20 and the flyback converter 200.

[0081] The AC side of the AC-DC conversion circuit 20 is used to receive an AC signal, and the AC-DC conversion circuit 20 is used to convert the AC signal and the first voltage. The AC-DC conversion circuit 20 can be a circuit structure that can perform AC-DC conversion, such as a full-bridge PFC (power factor correction circuit) topology structure or a half-bridge PFC topology structure. The control circuit 30 is used to control the working state of the AC-DC conversion circuit 20 and / or the flyback converter 200 according to the working mode of the AC-DC conversion system to change the first voltage and / or the fourth voltage; wherein the fourth voltage is the sum of the second voltage and the third voltage.

[0082] The working modes of the AC-DC conversion system include a forward working mode and a reverse working mode.

[0083] In the forward working mode, the AC-DC conversion circuit 20 converts the AC signal into a first voltage and transmits it to the DC-DC conversion circuit 10, and the DC-DC conversion circuit 10 converts the first voltage into a fourth voltage. The control circuit 30 can control the working state of the AC-DC conversion circuit 20 to change the first voltage, and control the working state of the flyback converter 200 to change the third voltage, thereby changing the fourth voltage.

[0084] In the reverse working mode, the DC-DC conversion circuit 10 converts the fourth voltage into the first voltage and transmits it to the AC-DC conversion circuit 20, and the AC-DC conversion circuit 20 converts the first voltage into an AC signal. The control circuit 30 can control the working state of the flyback converter 200 to change the value of the third voltage. When the fourth voltage is stable, the third voltage changes, and the second voltage also changes accordingly. Since the first voltage is proportional to the second voltage, the first voltage changes accordingly with the second voltage, thereby realizing dynamic adjustment of the first voltage.

[0085] In the embodiment of the present application, the AC-DC conversion system includes an AC-DC conversion circuit 20, a control circuit 30 and a DC-DC conversion circuit 10. The DC side of the AC-DC conversion circuit 20 is respectively connected to the second DC terminal 110 of the isolated DC-DC converter 100 and the first DC terminal 210 of the flyback converter 200, and the control circuit 30 is respectively connected to the AC-DC conversion circuit 20 and the flyback converter 200. The DC-DC conversion circuit 10 includes an isolated DC-DC converter 100, a flyback converter 200 and a control circuit 30, the first DC terminal 210 of the flyback converter 200 is connected in parallel with the second DC terminal 110 of the isolated DC-DC converter 100, and the third DC terminal 220 of the flyback converter 200 is connected in series with the fourth DC terminal 120 of the isolated DC-DC converter 100. When the AC-DC conversion system is in the forward working mode, the AC signal remains stable, and the working state of the AC-DC conversion circuit 20 can be controlled by the control circuit 30 to change the first voltage so that the second voltage changes accordingly, thereby ensuring that the isolated DC-DC conversion circuit 10 transmits most of the power; further, the working state of the flyback converter 200 is controlled by the control circuit 30 to change the third voltage, thereby realizing dynamic adjustment of the fourth voltage formed by the superposition of the third voltage and the second voltage. When the AC-DC conversion system is in the reverse working mode, the fourth voltage remains stable, and the working state of the flyback converter 200 can be adjusted by the control circuit 30 to change the third voltage so that the second voltage changes, and the first voltage will change accordingly with the second voltage, thereby realizing dynamic adjustment of the first voltage.

[0086] In one embodiment, the control circuit 30 includes a first control module 310 , a second control module 320 and a third control module 340 .

[0087] The first control module 310 is connected to the flyback converter 200, and is used to output a first control signal to the flyback converter 200 according to the fourth voltage reference value and the fourth voltage when the working mode of the AC-DC conversion system is the forward working mode, so as to change the third voltage of the third DC terminal 220 of the flyback converter 200. In the forward working mode, the electrical signal flows from the AC side to the DC side of the AC-DC conversion circuit 20. The first control signal can be a PWM (pulse width modulation) signal.

[0088] The first control module 310 may adopt a PI (proportional integral) control method to feedback-regulate the third voltage according to the fourth voltage reference value and the fourth voltage, so that the fourth voltage can reach the fourth voltage reference value. Figure 4As shown, the first control module 310 may include a first subtractor and a first PI controller. The voltage difference between the fourth voltage reference value and the fourth voltage may be obtained through the first subtractor, and the voltage difference may be used as the input of the first PI controller to obtain the first control signal. The first control module 310 may adjust the duty cycle of the flyback converter 200 through the first control signal, so that the third voltage of the third DC terminal 220 of the flyback converter 200 changes.

[0089] The second control module 320 is connected to the AC-DC conversion circuit 20, and is used to obtain a power ratio allocation table, and when the working mode of the AC-DC conversion system is the forward working mode, output a second control signal to the AC-DC conversion circuit 20 according to the fourth voltage reference value, the power ratio allocation table and the AC signal to change the first voltage. The second control signal can be a PWM (pulse width modulation) signal. The power ratio allocation table represents the power ratio of the isolated DC-DC converter 100 and the flyback converter 200. For example, when the fourth voltage is in the range of 32V-62V, the power ratio allocation table is as follows: Figure 5 When setting the power proportion of the isolated DC-DC converter 100 and the power proportion of the flyback converter 200, it is necessary to consider the withstand voltage level of each component in the AC-DC conversion system to avoid the first voltage or the fourth voltage exceeding the withstand voltage level of the component, causing the component to be damaged and affecting the stability and safety of the entire system. Figure 5 When the fourth voltage is 48V, the power share of the isolated DC-DC converter 100 is 92.7% at the maximum. However, after the fourth voltage is higher than 48V, the power share of the isolated DC-DC converter 100 decreases. This is because the first voltage is proportional to the second voltage. If the second voltage continues to increase, it may cause the first voltage to exceed the withstand voltage level of the component (such as the power tube).

[0090] Furthermore, if Figure 6 As shown, the second control module 320 may include a first power distribution unit 321 and a first voltage adjustment unit 322. The first power distribution unit 321 may be used to obtain a power ratio allocation table, and determine a first voltage reference value according to the power ratio allocation table and the fourth voltage reference value. Specifically, the first power distribution unit 321 includes a power coefficient regulator, a limiter and a multiplier, and the power coefficient regulator may be used to determine a second voltage reference value according to the power ratio allocation table and the fourth voltage reference value. The limiter may be used to limit the amplitude of the second voltage reference value. The multiplier may be used to determine the first voltage reference value according to the second voltage reference value and the transformation ratio N of the isolated DC-DC converter 100.

[0091] The power factor regulator may store a power ratio allocation table, and the power factor regulator may determine the power ratio of the isolated DC-DC converter 100 according to the fourth voltage reference value by looking up the table, and calculate the second voltage reference value according to the power ratio and the fourth voltage reference value. Considering the withstand voltage level of the device, a limiter is set to limit the amplitude of the second voltage reference value to prevent the amplitude of the converted first voltage from exceeding the withstand voltage level of the device. Afterwards, the first voltage reference value may be determined by a multiplier according to the second voltage reference value and the transformation ratio of the isolated DC-DC converter 100.

[0092] Further, the first voltage regulating unit 322 can be used to determine the duty cycle of the second control signal according to the first voltage reference value and the AC signal to change the first voltage. The first voltage regulating unit can perform feedback regulation on the first voltage by means of PI control. For example, please continue to refer to Figure 6 The first voltage regulating unit 322 may include a second subtractor and a second PI controller, and the voltage difference between the first voltage reference value and the first voltage may be obtained through the second subtractor, and the voltage difference may be used as an input of the second PI controller to obtain a second control signal. The duty cycle of the AC-DC conversion circuit 20 may be adjusted based on the second control signal. Optionally, the duty cycle and phase of the second control signal may also be adjusted based on the AC signal on the AC side of the AC-DC conversion circuit 20 to improve the power factor of the AC-DC conversion circuit 20.

[0093] The third control module 330 is connected to the flyback converter 200, and is used to obtain the power proportion allocation table, and when the working mode of the AC-DC conversion system is the reverse working mode, output the first control signal to the flyback converter 200 according to the fourth voltage, the power proportion allocation table and the first voltage to change the third voltage. In the reverse working mode, the electrical signal flows from the DC side of the AC-DC conversion circuit 20 to the AC side.

[0094] Specifically, Figure 7As shown, the third control module 330 includes a second power distribution unit 331 and a second voltage adjustment unit 332. The second power distribution unit 331 can be used to obtain a power proportion allocation table, and determine a first voltage reference value according to the power proportion allocation table and the fourth voltage. The second voltage adjustment unit 332 can be used to adjust the duty cycle of the first control signal according to the first voltage reference value and the first voltage to change the third voltage. Exemplarily, the second power distribution unit 331 may include a second power coefficient regulator, a second limiter, and a second multiplier, and the second power coefficient regulator can be used to determine the second voltage reference value according to the power proportion allocation table and the fourth voltage. The limiter can limit the amplitude of the second voltage reference value. The multiplier can determine the first voltage reference value according to the second voltage reference value and the transformation ratio of the isolated DC-DC converter 100. The second voltage adjustment unit 332 may include a third subtractor and a third PI controller, and the voltage difference between the first voltage reference value and the first voltage can be obtained by the third subtractor, and the voltage difference is used as the input of the third PI controller to obtain the first control signal. The third module 330 may adjust the duty cycle of the flyback converter 200 based on the first control signal to change the third voltage.

[0095] In this embodiment, when the AC-DC conversion system is in the forward working mode, the third voltage of the flyback converter 200 is controlled by the first control module, so as to realize dynamic adjustment of the fourth voltage, and the first voltage of the AC-DC conversion circuit 20 is controlled by the second control module according to the power proportion allocation table, so as to ensure that the isolated DC-DC conversion circuit 10 transmits most of the power, and the flyback converter 200 transmits a small part of the power, thereby ensuring the forward transmission efficiency of the AC-DC conversion system. When the AC-DC conversion system is in the reverse working mode, the third voltage of the flyback converter 200 is controlled by the third control module according to the power proportion allocation table, and on the basis of ensuring that the isolated DC-DC conversion circuit 10 transmits most of the power, and the flyback converter 200 transmits a small part of the power, the dynamic adjustment of the first voltage is realized, thereby ensuring the reverse transmission efficiency of the AC-DC conversion system.

[0096] In one embodiment, Figure 8 and Fig. 9 As shown, the control circuit 30 further includes a ripple compensation module 340. The ripple compensation module 340 is respectively connected to the first control module 310, the third control module 330, and the flyback converter 200, and is used to obtain the feedback current of the third DC terminal 220, and adjust the duty cycle of the first control signal according to the feedback current so that the voltage ripple of the third voltage is inverted with the voltage ripple of the second voltage.

[0097] The feedback current refers to the actual current of the third DC terminal 220, which carries ripple information. The ripple compensation module 340 can perform feedback adjustment on the duty cycle of the first control signal according to the ripple information carried on the feedback current, so that under the action of the first control signal, the voltage ripples of the third voltage generated by the third DC terminal 220 and the second voltage generated by the fourth DC terminal 120 of the flyback converter 200 are in anti-phase, so that the ripples of the fourth voltage formed by the superposition of the third voltage and the second voltage are offset.

[0098] Exemplarily, the ripple compensation module 340 may include a fourth subtractor, a fourth PI controller, and an adder. The current regulation amount of the flyback converter 200 may be obtained by the fourth subtractor, and the current regulation amount is used as the input of the fourth PI controller to obtain the duty cycle regulation amount of the first control signal, and the duty cycle regulation amount of the first control signal and the steady-state duty cycle of the flyback converter 200 are added by the adder to obtain the duty cycle of the flyback converter 200. The steady-state duty cycle D of the flyback converter 200 may be obtained by the first voltage U 1 and the third voltage U 3 The calculation results are:

[0099]

[0100] Wherein, n represents the transformation ratio of the flyback converter 200 , which can be reasonably set according to actual use requirements, and the embodiment of the present application does not limit this.

[0101] Optionally, a ripple compensation module 340 may be provided for each of the first control module 310 and the third control module 330 , or the first control module 310 and the third control module 330 may share a ripple compensation module 340 .

[0102] In this embodiment, by setting up a ripple compensation module 340, the voltage ripples of the third voltage generated by the third DC terminal 220 and the second voltage generated by the fourth DC terminal 120 are inverted, which can effectively reduce the voltage ripple of the fourth voltage formed by the superposition of the third voltage and the second voltage, thereby achieving power decoupling.

[0103] In one embodiment, Fig.10As shown, the DC-DC conversion circuit 10 also includes a bus capacitor 40. The bus capacitor 40 is respectively connected in parallel to the second DC terminal 110 of the isolated DC-DC converter 100, the first DC terminal 210 of the flyback converter 200, and the DC side of the AC-DC conversion circuit 20. In the traditional solution, considering that the bus capacitor needs to suppress the ripple of the second DC terminal 110 of the isolated DC-DC converter 100, thereby reducing the voltage ripple of the fourth DC terminal 120, it is usually necessary to select an electrolytic capacitor with a larger capacity as the bus capacitor. In the embodiment of the present application, since the third voltage output by the flyback converter 200 can be adjusted by the control circuit 300, the voltage ripple of the third voltage is opposite to the voltage ripple of the second voltage, which reduces the ripple on the fourth voltage formed by the superposition of the second voltage and the third voltage, that is, the ripple suppression requirement for the bus capacitor is reduced. Therefore, in addition to selecting an electrolytic capacitor as a bus capacitor, the embodiment of the present application can also select an aluminum capacitor, a ceramic capacitor, etc. with a small capacity but a long service life as a bus capacitor, thereby improving the service life of the entire DC-DC conversion circuit.

[0104] For example, the AC-DC conversion system of the present application may be equivalent to: Fig.11 The circuit structure shown.

[0105] Among them, the current source is the AC signal on the AC side, R s is the equivalent internal resistance of the subsequent circuit, R dc is the equivalent internal resistance of the isolated DC-DC converter, C in is the equivalent filter capacitor of the third DC terminal 220 and the fourth DC terminal 110 connected in series, C dc is the bus capacitance, n represents the transformer ratio, the third voltage output by the flyback converter 200 is in phase with the second voltage ripple, so the flyback converter 200 can be equivalent to a voltage-controlled voltage source, α is the voltage compensation coefficient, which is the ratio of the second voltage to the third voltage. By solving the equivalent circuit, the current i at the third DC terminal can be obtained. dc The peak-to-peak value of the ripple is related to C in , and bus capacitance C dc The relationship is:

[0106]

[0107] Among them, A is the effective value of the current source ripple, and the other parameters are:

[0108]

[0109]

[0110]

[0111]

[0112]

[0113] According to formula (2), when the voltage compensation coefficient α is 1, the current i at the third DC terminal can be completely eliminated. dc of ripple. Figure 12a-12b When the voltage compensation coefficient α=1, the current i dc Ripple peak-to-peak value and bus capacitance C dc , equivalent filter capacitor C in relationship diagram. Figure 13a-13b When the voltage compensation coefficient α=0.9, the current i dc Ripple peak-to-peak value and bus capacitance C dc , equivalent filter capacitor C in relationship diagram. Figure 14a-14b When the voltage compensation coefficient α=1, the peak-to-peak value of the bus voltage (i.e., the first voltage) ripple is equal to the bus capacitance C dc , equivalent filter capacitor C in relationship diagram. Figure 15a-Figure 15b When the voltage compensation coefficient α=0.9, the peak-to-peak value of the bus voltage ripple and the bus capacitance C dc , equivalent filter capacitor C in Observation Fig.12a and Fig.13a ,as well as Fig.14a and Fig.15a It can be seen that as the voltage compensation coefficient decreases, the current i dc The peak-to-peak value of the ripple will increase, but the peak-to-peak value of the bus voltage ripple will decrease.

[0114] like Fig.16 As shown, when the output range requirement of the fourth voltage is 32-62V, the voltage compensation coefficient α is selected as 0.999. The present application only requires a 60μF bus capacitor to achieve an effect that the ripple rate of the fourth voltage is only 1.2%. For the traditional two-stage topology, a 5500μF bus capacitor is required to achieve an effect that the ripple rate of the fourth voltage is 1.2%. It can be seen that the AC-DC conversion system of the present application can greatly reduce the DC voltage ripple on the DC side, realize power decoupling, and significantly reduce the capacitance requirement of the bus capacitor.

[0115] The AC-DC conversion system of the embodiment of the present application has the characteristics of high conversion efficiency, wide input and output range, and low voltage ripple rate, and can be applied to any occasions requiring AC-DC conversion, such as photovoltaic systems, energy storage converters, energy routers, power supplies, etc.

[0116] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic description of the above terms does not necessarily refer to the same embodiment or example.

[0117] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0118] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. An AC-DC conversion system, characterized in that: It includes an AC-DC conversion circuit, a control circuit and a DC-DC conversion circuit, wherein: The DC-DC conversion circuit includes an isolated DC-DC converter and a flyback converter, wherein a first DC terminal of the flyback converter is connected in parallel with a second DC terminal of the isolated DC-DC converter, and a third DC terminal of the flyback converter is connected in series with a fourth DC terminal of the isolated DC-DC converter; the isolated DC-DC converter is used to convert a first voltage of the second DC terminal with a second voltage of the fourth DC terminal; the flyback converter is used to convert the first voltage with a third voltage of the third DC terminal; the second voltage is greater than the third voltage; The DC side of the AC-DC conversion circuit is respectively connected to the second DC end of the isolated DC-DC converter and the first DC end of the flyback converter, the AC side of the AC-DC conversion circuit is used to receive an AC signal, and the AC-DC conversion circuit is used to convert the AC signal and the first voltage; The control circuit comprises: a first control module, connected to the flyback converter, and configured to output a first control signal to the flyback converter according to a fourth voltage reference value and the fourth voltage when the working mode of the AC-DC conversion system is a forward working mode, so as to change a third voltage at a third DC terminal of the flyback converter; wherein, in the forward working mode, the electrical signal flows from the AC side of the AC-DC conversion circuit to the DC side; a second control module connected to the AC-DC conversion circuit, configured to obtain a power proportion allocation table, and output a second control signal to the AC-DC conversion circuit according to the fourth voltage reference value, the power proportion allocation table and the first voltage to change the first voltage when the working mode of the AC-DC conversion system is a forward working mode; A third control module is connected to the flyback converter, and is used to obtain a power proportion allocation table, and when the working mode of the AC-DC conversion system is a reverse working mode, output the first control signal to the flyback converter according to the fourth voltage, the power proportion allocation table and the first voltage to change the third voltage; wherein, in the reverse working mode, the electrical signal flows from the DC side of the AC-DC conversion circuit to the AC side; wherein the fourth voltage is the sum of the second voltage and the third voltage.

2. The AC-DC conversion system according to claim 1, characterized in that: The control circuit further comprises: The ripple compensation module is respectively connected to the first control module, the third control module and the flyback converter, and is used to obtain the feedback current of the third DC terminal, and adjust the duty cycle of the first control signal according to the feedback current so that the voltage ripple of the third voltage is inverse to the voltage ripple of the second voltage.

3. The AC-DC conversion system according to claim 1, characterized in that: The second control module includes: a first power allocation unit, configured to obtain the power proportion allocation table, and determine a first voltage reference value according to the power proportion allocation table and the fourth voltage reference value; The first voltage regulating unit is used to determine the duty cycle of the second control signal according to the first voltage reference value and the first voltage, so as to change the first voltage.

4. The AC-DC conversion system according to claim 3, characterized in that: The first power distribution unit comprises: A power factor regulator, configured to determine the second voltage reference value according to the power proportion allocation table and the fourth voltage reference value; a limiter, used for limiting the amplitude of the second voltage reference value; A multiplier is used to determine the first voltage reference value according to the second voltage reference value and the transformation ratio of the isolated DC-DC converter.

5. The AC-DC conversion system according to claim 1, characterized in that: The third control module comprises: a second power allocation unit, configured to obtain the power proportion allocation table, and determine the first voltage reference value according to the power proportion allocation table and the fourth voltage; The second voltage regulating unit is used to adjust the duty cycle of the first control signal according to the first voltage reference value and the first voltage to change the third voltage.

6. The AC-DC conversion system according to claim 1, characterized in that: The AC-DC conversion system further comprises: The bus capacitor is connected in parallel with the second DC end of the isolated DC-DC converter, the first DC end of the flyback converter, and the DC side of the AC-DC conversion circuit respectively.

7. The AC-DC conversion system according to claim 1, characterized in that: The flyback converter comprises a transformer module, a first switch module, a first clamp module, a second switch module, and a second clamp module, wherein the primary side of the transformer module is connected to the first clamp module and the first switch module respectively, and the secondary side of the transformer module is connected to the second clamp module and the second switch module respectively; The voltage transformation module is used to convert the first voltage and the third voltage; The first clamping module is used to suppress the voltage spike on the primary side of the transformer module, recover leakage inductance energy, or realize zero voltage switching of the first switch module under specific conditions; The second clamping module is used to suppress the voltage spike on the secondary side of the transformer module, recover leakage inductance energy, or realize zero voltage switching of the second switch module under specific conditions.

8. The AC-DC conversion system according to claim 7, characterized in that: The transformer module includes a first inductor, a second inductor, a third inductor and a transformer, wherein the first end of the primary winding of the transformer is respectively connected to the first end of the first inductor and the first end of the second inductor, the second end of the primary winding of the transformer is respectively connected to the second end of the second inductor, the first end of the first clamping module and the first end of the first switch module, the first end of the secondary winding of the transformer is connected to the first end of the third inductor, and the second end of the secondary winding of the transformer is respectively connected to the first end of the second clamping module and the first end of the second switch module; The first clamping module includes a first capacitor and a first switch tube, wherein the first end of the first capacitor is connected to the second end of the first inductor, the second end of the first capacitor is connected to the first electrode of the first switch tube, and the second electrode of the first switch tube is connected to the first switch module; The second clamping module includes a second capacitor and a second switch tube, wherein the first end of the second capacitor is connected to the second end of the third inductor, the second end of the second capacitor is connected to the first electrode of the second switch tube, and the second electrode of the second switch tube is connected to the second switch module.

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