Single-stage high-frequency isolated ac-dc converter

Abstract

This invention provides a single-stage high-frequency isolated AC-DC converter, relating to the field of converter technology. The single-stage high-frequency isolated AC-DC converter of this application includes an input inductor, an output inductor, a first intermediate capacitor, a second intermediate capacitor, a transformer, a freewheeling circuit, and a bridgeless structure. The bridgeless structure includes four connection terminals: the first connection terminal is unidirectionally connected to the second connection terminal, and the fourth connection terminal is unidirectionally connected to the first connection terminal; bidirectional conduction or disconnection can be achieved between the second and third connection terminals, and between the third and fourth connection terminals. By controlling the operating states of the four connection terminals in the bridgeless structure, power factor correction and rectification functions are achieved. This single-stage high-frequency isolated AC-DC converter of this application is a converter that achieves rectification and power factor correction functions through a single-stage energy conversion, using fewer components and fewer sampling circuits, resulting in lower equipment cost and smaller size. Simultaneously, single-stage energy conversion improves operating efficiency.

Description

Technical Field

[0001] This invention relates to the field of converter technology, and specifically to a single-stage high-frequency isolated AC-DC converter. Background Technology

[0002] Harmonic content generated by the operation of nonlinear devices such as power electronics can negatively impact power grid quality, while power factor issues in electrical equipment can exacerbate energy waste. To effectively reduce harmonics, improve power quality, enhance the power factor, and save energy, applications with high power demands, such as electric vehicle charging, data center and communication base station power supply, require power factor correction (PFC) functionality in converters, typically employing isolated PFC converters.

[0003] An isolated PFC converter typically consists of two stages. The first stage is an AC / DC converter, whose main function is to improve the power factor of the circuit and reduce the harmonic content of the input current, thereby reducing the interference of the converter to the power grid. The second stage is a DC / DC converter, which contains a high-frequency transformer to achieve safe and reliable power supply. The main functions of the second stage converter are generally twofold: first, to achieve electrical isolation between the input voltage and the output voltage; and second, to adjust and stabilize the output voltage according to the load requirements.

[0004] However, isolated PFC converters have lower power density. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides a single-stage high-frequency isolated AC-DC converter, which solves the technical problem of low power density in existing isolated PFC converters.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] In a first aspect, the present invention provides a single-stage high-frequency isolated AC-DC converter, comprising an input inductor, an output inductor, a first intermediate capacitor, a second intermediate capacitor, a transformer, a freewheeling circuit, and an improved bridgeless structure;

[0010] The bridgeless structure includes four connection ends. The first connection end is unidirectionally connected to the second connection end, and the fourth connection end is unidirectionally connected to the first connection end. There are three working states between the second and third connection ends: working state one, the second connection end is connected to the third connection end; working state two, the third connection end is connected to the second connection end; and working state three, disconnected. There are also three working states between the third and fourth connection ends: working state one, the third connection end is connected to the fourth connection end; working state two, the fourth connection end is connected to the third connection end; and working state three, disconnected.

[0011] The first connection terminal of the bridgeless structure is connected to the first terminal of the AC power supply via an input inductor; the third connection terminal of the bridgeless structure is connected to the second terminal of the AC power supply; the second connection terminal of the bridgeless structure is connected to the first terminal of the primary side of the transformer via a first intermediate capacitor; and the fourth connection terminal of the bridgeless structure is connected to the second terminal of the primary side of the transformer.

[0012] The first terminal of the secondary side of the transformer is connected to the first output terminal of the converter; the second terminal of the secondary side of the transformer is connected to the second output terminal of the converter via the second intermediate capacitor and the output inductor; the common terminal of the second intermediate capacitor and the output inductor is connected to the first terminal of the secondary side of the transformer via a freewheeling circuit.

[0013] By controlling the operating states between the four connection terminals in the bridgeless structure, the single-stage high-frequency isolated AC-DC converter achieves power factor correction and rectification functions.

[0014] Preferably, the transformer is a two-ended transformer.

[0015] Preferably, the freewheeling circuit includes a diode, and the diode is connected in the following ways: the anode of the diode is connected to the common terminal of the second intermediate capacitor and the output inductor, or the cathode of the diode is connected to the common terminal of the second intermediate capacitor and the output inductor.

[0016] Preferably, a diode is connected between the first connection end and the second connection end of the bridgeless structure or controlled by a switching device to achieve unidirectional conduction;

[0017] The fourth connection terminal of the bridgeless structure is connected to the first connection terminal by a diode or controlled by a switching device to achieve unidirectional conduction;

[0018] The bridgeless structure is connected between the second and third connection terminals by a switching transistor or a bidirectional thyristor with a reverse parallel freewheeling diode to achieve three working states.

[0019] The bridgeless structure connects a reverse parallel freewheeling diode or a bidirectional thyristor between the third and fourth connection terminals to achieve three operating states.

[0020] Secondly, the present invention provides a single-stage high-frequency isolated AC-DC converter, comprising three single-phase AC-DC converters, each of which includes an input inductor, an output inductor, a first intermediate capacitor, a second intermediate capacitor, a transformer, a freewheeling circuit, and a bridgeless structure.

[0021] The bridgeless structure includes four connection ends. The first connection end is unidirectionally connected to the second connection end, and the fourth connection end is unidirectionally connected to the first connection end. There are three working states between the second and third connection ends: working state one, the second connection end is connected to the third connection end; working state two, the third connection end is connected to the second connection end; and working state three, disconnected. There are also three working states between the third and fourth connection ends: working state one, the third connection end is connected to the fourth connection end; working state two, the fourth connection end is connected to the third connection end; and working state three, disconnected.

[0022] The first connection terminal of the bridgeless structure is connected to the second terminal of the input inductor; the second connection terminal of the bridgeless structure is connected to the first terminal of the primary side of the transformer via the first intermediate capacitor; the fourth connection terminal of the bridgeless structure is connected to the second terminal of the primary side of the transformer.

[0023] The first terminal of the secondary side of the transformer is connected to the first output terminal of the single-phase AC-DC converter; the second terminal of the secondary side of the transformer is connected to the second output terminal of the single-phase AC-DC converter via the second intermediate capacitor and the output inductor; the common terminal of the second intermediate capacitor and the output inductor is connected to the first terminal of the secondary side of the transformer via a freewheeling circuit.

[0024] The first terminals of the input inductors in the three single-phase AC-DC converters are connected to the first terminals of the three-phase AC power supplies A, B, and C, respectively, and the second terminals of the three-phase AC power supplies A, B, and C are connected together.

[0025] The third connection terminals of the bridgeless structures in the three single-phase AC-DC converters are connected together.

[0026] The first output terminals of the three single-phase AC-DC converters are connected together as the first output terminal of a single-stage high-frequency isolated AC-DC converter; the second output terminals of the three single-phase AC-DC converters are connected together as the second output terminal of a single-stage high-frequency isolated AC-DC converter.

[0027] By controlling the operating states between the four connection terminals in the bridgeless structure, the single-stage high-frequency isolated AC-DC converter achieves power factor correction and rectification functions.

[0028] Preferably, the transformer is a two-ended transformer.

[0029] Preferably, the freewheeling circuit includes a diode, and the diode is connected in the following ways: the anode of the diode is connected to the common terminal of the second intermediate capacitor and the output inductor, or the cathode of the diode is connected to the common terminal of the second intermediate capacitor and the output inductor.

[0030] Preferably, the common terminal where the second terminals of the three-phase AC power supply A, B, and C are connected together, and the common terminal of the third connection terminal of the bridgeless structure in the three single-phase AC-DC converters are both grounded, serving as the N line of the three-phase four-wire system.

[0031] Preferably, in each single-phase AC-DC converter:

[0032] The first and second connection terminals of the bridgeless structure are connected by a diode or controlled by a switching device to achieve unidirectional conduction.

[0033] The fourth connection terminal of the bridgeless structure is connected to the first connection terminal by a diode or controlled by a switching device to achieve unidirectional conduction;

[0034] The bridgeless structure is connected between the second and third connection terminals by a switching transistor or a bidirectional thyristor with a reverse parallel freewheeling diode to achieve three working states.

[0035] The bridgeless structure connects a reverse parallel freewheeling diode or a bidirectional thyristor between the third and fourth connection terminals to achieve three operating states.

[0036] Preferably, all three single-phase AC-DC converters adopt a modular design.

[0037] (III) Beneficial Effects

[0038] This invention provides a single-stage high-frequency isolated AC-DC converter. Compared with the prior art, it has the following advantages:

[0039] The single-stage high-frequency isolated AC-DC converter in this application is a converter that can achieve rectification and power factor correction functions through a single-stage energy conversion. It uses fewer components and fewer sampling circuits, resulting in lower equipment cost and smaller size. At the same time, the single-stage energy conversion improves operating efficiency. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 The circuit diagram of an existing two-stage PFC converter;

[0042] Figure 2 The circuit diagram of an existing SEPIC single-stage converter;

[0043] Figure 3 This is a circuit diagram of the single-stage high-frequency isolated AC-DC converter in Example 1;

[0044] Figure 4 for Figure 3 The circuit diagram shown is the first specific circuit diagram of the circuit framework diagram;

[0045] Figure 5 for Figure 3 The second specific circuit diagram shown in the circuit framework diagram;

[0046] Figure 6 for Figure 4 The circuit diagram shown is a schematic diagram of the first operating mode.

[0047] Figure 7 for Figure 4 The circuit diagram shown is a schematic diagram of the second operating mode.

[0048] Figure 8 for Figure 4 The circuit diagram shown is a schematic diagram of the third working mode.

[0049] Figure 9 This is the first circuit diagram of the three-phase single-stage high-frequency isolated AC-DC converter in Example 2;

[0050] Figure 10 This is a second circuit diagram of the three-phase single-stage high-frequency isolated AC-DC converter in Example 2;

[0051] Figure 11 This is the third circuit diagram of the three-phase single-stage high-frequency isolated AC-DC converter in Example 2;

[0052] Figure 12 This is the fourth circuit diagram of the three-phase single-stage high-frequency isolated AC-DC converter in Example 2;

[0053] Figure 13 for Figure 12 The circuit diagram shown is a schematic diagram of operating mode one and operating mode seven.

[0054] Figure 14 for Figure 12 The circuit diagram shown is a schematic diagram of operating mode two and operating mode six.

[0055] Figure 15 for Figure 12The circuit diagram shown is a schematic diagram of operating mode three and operating mode five.

[0056] Figure 16 for Figure 12 The circuit diagram shown is a schematic diagram of the fourth operating mode.

[0057] Figure 17 This is a schematic diagram of the simulation results. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] It should be noted that, for ease of description, the IGBT is used to represent the controllable (on and off) switching transistor in the embodiments of this invention, but the switching transistor in this invention is not limited to IGBT. An IGBT will be used as an example. The first terminal of the IGBT refers to the collector, the second terminal to the emitter, and the control terminal to the gate. A drive control signal is applied to the control terminal of each switching transistor in the embodiments of this invention. For simplicity, this will not be elaborated further. The power switching transistor in the embodiments of this invention can also be implemented using other controllable switching transistor devices besides IGBT, such as MOSFET.

[0060] This application provides a single-stage high-frequency isolated AC-DC converter, which solves the technical problem of low power density in existing isolated PFC converters. It enables rectification and power factor correction functions with only one stage of energy conversion, uses fewer components and fewer sampling circuits, and improves power density.

[0061] The technical solution in this application is to solve the above-mentioned technical problems, and the general idea is as follows:

[0062] Existing two-stage PFC converters mainly use a front-stage PFC circuit plus a rear-stage isolated DC / DC converter, such as Figure 1 As shown, the front-end is typically a three-phase bridge uncontrolled rectifier circuit. The input is AC voltage, and the rectifier circuit consists of six diodes. The output is connected to a boost converter to achieve AC / DC conversion and power factor correction. The back-end commonly uses an LLC converter or a phase-shifted full-bridge converter to achieve DC / DC conversion, controlling the output voltage within the required range. This two-stage structure, which uses PFC rectification followed by buck-boost, results in complex circuit control, an increased number of switching devices, lower efficiency, lower power density, larger size, and higher cost.

[0063] In existing technologies, although there are also SEPIC single-stage converters, such as Figure 2 As shown, the transformer in the circuit is a flyback transformer. When the primary winding is on, energy is stored in the transformer core; only when the primary winding is off is the stored energy transferred to the secondary winding. This energy storage and transfer method makes the saturation characteristics of the transformer core a key factor affecting power capacity. As the input power increases, the primary current also increases accordingly, and the magnetic flux density of the core easily reaches saturation, thus preventing the transformer from storing more energy and limiting the power limit of the entire circuit.

[0064] Meanwhile, this "store energy first, release energy later" unilateral current mode requires the magnetic core to have sufficient energy storage capacity. To avoid the magnetic core from saturating during energy storage, an air gap (air gap) needs to be opened in the magnetic core. However, the existence of the air gap makes it difficult for the magnetic lines of force to be completely constrained by the magnetic core, and some magnetic lines of force will leak to the outside of the magnetic core, forming leakage flux, and thus generating leakage inductance.

[0065] As described above, the flyback transformer used in existing single-stage converters limits power and causes transformer leakage inductance problems.

[0066] To address the problems existing in the aforementioned two-stage PFC converter and SEPIC single-stage converter, this invention proposes a single-stage high-frequency isolated AC-DC converter. This converter, employing a single-stage energy conversion, can achieve rectification and power factor correction functions. It uses fewer components, reduces the number of corresponding sampling and driving circuits, resulting in lower equipment cost, smaller size, and higher power density. Furthermore, this converter uses a double-ended transformer, eliminating the mode where current flows through the primary side but not the secondary side. Since the transformer does not perform energy storage, theoretically, the air gap can be made very small, and the magnetizing inductance can be large. Therefore, the leakage inductance and size of the transformer in this topology are reduced, and its power is not limited by the converter itself.

[0067] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0068] Example 1:

[0069] This embodiment proposes a single-phase, single-stage high-frequency isolated AC-DC converter, such as... Figure 3 As shown, it includes an input inductor L1, an output inductor L2, a first intermediate capacitor C1, a second intermediate capacitor C2, a transformer, a freewheeling circuit, and an improved bridgeless structure.

[0070] The bridgeless structure includes four switches. The common terminal of the first and second switches serves as the second connection terminal of the bridgeless structure; the common terminal of the first and third switches serves as the first connection terminal; the common terminal of the second and fourth switches serves as the third connection terminal; and the common terminal of the third and fourth switches serves as the fourth connection terminal. The first connection terminal is unidirectionally connected to the second connection terminal (i.e., the first switch is unidirectionally connected), and the fourth connection terminal is unidirectionally connected to the first connection terminal (i.e., the third switch is unidirectionally connected). There are three operating states between the second and third connection terminals: operating state one, the second connection terminal is connected to the third connection terminal; operating state two, the third connection terminal is connected to the second connection terminal; and operating state three, open (i.e., the second switch can be bidirectionally connected or open). Similarly, there are three operating states between the third and fourth connection terminals: operating state one, the third connection terminal is connected to the fourth connection terminal; operating state two, the fourth connection terminal is connected to the third connection terminal; and operating state three, open (i.e., the fourth switch can be bidirectionally connected or open).

[0071] The first connection terminal of the bridgeless structure is connected to the first terminal of the AC power supply via the input inductor L1; the third connection terminal of the bridgeless structure is connected to the second terminal of the AC power supply; the second connection terminal of the bridgeless structure is connected to the first terminal of the primary side of the transformer via the first intermediate capacitor; and the fourth connection terminal of the bridgeless structure is connected to the second terminal of the primary side of the transformer.

[0072] The first terminal of the secondary side of the transformer is connected to the first output terminal of the single-stage high-frequency isolated AC-DC converter; the output inductor L2 is connected to the second output terminal; the common terminal of the second intermediate capacitor C2 and the output inductor L2 is connected to the first terminal of the secondary side of the transformer via a freewheeling circuit; by controlling the working state between the four connection terminals in the bridgeless structure, the power factor correction and rectification functions are realized.

[0073] The transformer in this embodiment is a double-ended transformer. In a double-ended transformer, energy transfer is achieved through bidirectional current drive, without relying entirely on the magnetic core to store energy. Therefore, the air gap can be designed to be smaller, thereby effectively reducing the transformer size and reducing the impact of parasitic parameters such as leakage inductance.

[0074] In the specific implementation process, a load is connected between the first output terminal and the second output terminal. In this embodiment, an RC load is selected as the load.

[0075] In practical implementation, the first and third switches can be implemented using diodes for unidirectional conduction. Alternatively, they can be controlled by switches, switching transistors, or other devices to achieve unidirectional conduction. The second and fourth switches can be implemented using switching transistors with reverse parallel freewheeling diodes, such as IGBTs or MOSFETs with reverse parallel freewheeling diodes. Of course, other devices capable of achieving the above three operating states, such as bidirectional thyristors, can also be used.

[0076] In practical implementation, a diode is selected for the freewheeling circuit. This diode can be connected in two ways, such as... Figure 4 As shown, the diode anode is connected to the common terminal of the second intermediate capacitor C2 and the output inductor L2, and the cathode is connected to the first terminal on the secondary side of the transformer. Another connection method is as follows... Figure 5 As shown, the diode cathode is connected to the common terminal of the second intermediate capacitor C2 and the output inductor L2, and the anode is connected to the second terminal of the transformer's secondary side. The output inductor L2 is connected to the first output terminal. The common terminal of the second intermediate capacitor C2 and the output inductor L2 is connected to the second terminal of the transformer's secondary side via a freewheeling circuit. It should be noted that other devices can be used for the freewheeling circuit, such as a reverse-conducting thyristor, IGBT, or MOSFET (with the addition of a corresponding drive circuit). The difference between the two variations is that the second intermediate capacitor C2 and the output inductor L2 are located at the positive and negative terminals of the output voltage, respectively.

[0077] The following is based on Figure 4 Taking a single-phase, single-stage high-frequency isolated AC-DC converter as an example, modal analysis is performed:

[0078] The modes of a single-phase, single-stage topology are mainly divided into continuous current mode and discontinuous current mode. Taking an input voltage greater than zero as an example, when the input voltage is negative, the analysis can be referenced to the analysis when the input voltage is positive. The continuous current mode is determined by... Figure 6 and Figure 7 Composition, the discontinuous current mode is mainly composed of Figure 6 , Figure 7 and Figure 8 Composition. It should be noted that the switching transistor has a built-in anti-parallel diode, but for the sake of convenience, in the modal analysis, the switching transistor's turn-off refers to the turn-off of the transistor in the switching transistor. Whether the diode is conducting or cut off will be explained separately in the modal analysis. Similarly, the switching transistor's conduction refers to the transistor being conducting.

[0079] Working mode as Figure 6 As shown, switches S1 and S2 are simultaneously turned on. The power supply charges the input inductor through diode D1 and switch S1. The primary capacitor of the transformer is connected in series with switches S1 and S2, the transformer, and the secondary capacitor of the transformer, jointly charging the load and the output inductor. The transformer is charging and discharging simultaneously; the transformer does not have an energy storage function.

[0080] Working mode two such as Figure 7 As shown, when switches S1 and S2 are simultaneously turned off, the diode connected in reverse parallel to S2 is turned on. The current in the input inductor flows through diode D1, the primary capacitor of the transformer, the transformer, the secondary capacitor of the transformer, and the freewheeling diode D3. The current in the output inductor flows through diode D3 and the load freewheeling.

[0081] Working Mode Three Figure 8 As shown, there is no change in the current flow direction between the primary and secondary sides of the transformer. The diode connected in reverse parallel to S2 continues to conduct. The current of the input inductor flows through diode D1, the primary capacitor of the transformer, the transformer, the secondary capacitor of the transformer, and the freewheeling diode D3. However, the current of the output inductor L2 enters discontinuous mode, and the energy of the output inductor L2 is completely released. The load is continued to be powered by the filter capacitor.

[0082] When the input voltage is greater than zero, it can be seen from the above modes that the first switch is single-phase conducting and is in power frequency conduction mode, the third switch is off, the second switch operates in modes one and three, and the fourth switch operates in modes one and two; when the input voltage is less than zero, the third switch is single-phase conducting and is in power frequency conduction mode, the first switch is off, the second switch operates in modes one and two, and the fourth switch operates in modes one and three.

[0083] Example 2:

[0084] This embodiment proposes a three-phase single-stage high-frequency isolated AC-DC converter, which includes three single-phase AC-DC converters. Each single-phase AC-DC converter includes an input inductor, an output inductor, a first intermediate capacitor, a second intermediate capacitor, a transformer, a freewheeling circuit, and a bridgeless structure.

[0085] The bridgeless structure includes four switches. The common terminal of the first and second switches serves as the second connection terminal of the bridgeless structure; the common terminal of the first and third switches serves as the first connection terminal; the common terminal of the second and fourth switches serves as the third connection terminal; and the common terminal of the third and fourth switches serves as the fourth connection terminal. The first connection terminal is unidirectionally connected to the second connection terminal (i.e., the first switch is unidirectionally connected), and the fourth connection terminal is unidirectionally connected to the first connection terminal (i.e., the third switch is unidirectionally connected). There are three operating states between the second and third connection terminals: operating state one, the second connection terminal is connected to the third connection terminal; operating state two, the third connection terminal is connected to the second connection terminal; and operating state three, open (i.e., the second switch can be bidirectionally connected or open). Similarly, there are three operating states between the third and fourth connection terminals: operating state one, the third connection terminal is connected to the fourth connection terminal; operating state two, the fourth connection terminal is connected to the third connection terminal; and operating state three, open (i.e., the fourth switch can be bidirectionally connected or open).

[0086] The first connection terminal of the bridgeless structure is connected to the second terminal of the input inductor; the second connection terminal of the bridgeless structure is connected to the first terminal of the primary side of the transformer via the first intermediate capacitor; the fourth connection terminal of the bridgeless structure is connected to the second terminal of the primary side of the transformer.

[0087] The first terminal of the secondary side of the transformer is connected to the first output terminal of the single-phase AC-DC converter; the second terminal of the secondary side of the transformer is connected to the second output terminal of the single-phase AC-DC converter via the second intermediate capacitor and the output inductor; the common terminal of the second intermediate capacitor and the output inductor is connected to the first terminal of the secondary side of the transformer via a freewheeling circuit.

[0088] The first terminals of the input inductors in the three single-phase AC-DC converters are connected to the first terminals of the three-phase AC power supplies A, B, and C, respectively, and the second terminals of the three-phase AC power supplies A, B, and C are connected together.

[0089] The third connection terminals of the bridgeless structures in the three single-phase AC-DC converters are connected together.

[0090] The first output terminals of three single-phase AC-DC converters are connected together as the first output terminal of a single-stage high-frequency isolated AC-DC converter; the second output terminals of three single-phase AC-DC converters are connected together as the second output terminal of a single-stage high-frequency isolated AC-DC converter; power factor correction and rectification functions are achieved by controlling the operating state between the four connection terminals in the bridgeless structure.

[0091] The transformer in this embodiment is a double-ended transformer. The load is connected between the first and second output terminals of the single-stage high-frequency isolated AC-DC converter. In this embodiment, the load is an RC load.

[0092] In practical implementation, the first and third switches in the three single-phase AC-DC converters can be implemented using diodes for unidirectional conduction. Alternatively, they can be controlled by switches, switching transistors, or other devices to achieve unidirectional conduction. The second and fourth switches can be implemented using switching transistors with reverse parallel freewheeling diodes, such as IGBTs or MOSFETs with reverse parallel freewheeling diodes. Of course, other devices capable of achieving the above three operating states, such as bidirectional thyristors, can also be used.

[0093] In practical implementation, a diode is selected for the freewheeling circuit. This diode can be connected in two ways, such as... Figure 9 As shown, the diode cathode is connected to the common terminal of the second intermediate capacitor and the output inductor, and the anode is connected to the second terminal on the secondary side of the transformer. Another connection method is as follows... Figure 10 As shown, the diode anode is connected to the common terminal of the second intermediate capacitor C2 and the output inductor L2, and the cathode is connected to the first terminal of the secondary side of the transformer. It should be noted that other devices can also be used in the freewheeling circuit, such as a reverse-conducting thyristor, IGBT, or MOSFET (with the addition of a corresponding drive circuit).

[0094] It should be noted that, in practical implementation, this three-phase single-stage high-frequency isolated AC-DC converter can be used as a three-phase four-wire single-stage high-frequency isolated AC-DC converter, such as... Figure 11 , 12 As shown, the common terminal of the second terminals of the three-phase AC power supply A, B, and C connected together, and the common terminal of the third connection terminal of the bridgeless structure in the three single-phase AC-DC converters are both grounded, serving as the N line of the three-phase four-wire system.

[0095] In practice, each single-phase AC-DC converter adopts a modular design, with each phase controlled independently.

[0096] A three-phase single-stage high-frequency isolated AC-DC converter topology is composed of three single-phase AC-DC converter topologies, therefore their operating modes are similar, and thus the main approach is to select... Figure 12 The three-phase four-wire single-stage high-frequency isolated AC-DC converter shown is analyzed in continuous current mode. Other topology variations can be easily derived by referring to the following operating conditions.

[0097] The order of the three-phase voltage magnitudes changes every 30° phase shift of the three-phase input voltage. Therefore, the three-phase input voltage can be divided into 12 sectors every 30° within one cycle, taking Va>Vb>0>Vc as an example:

[0098] Working mode as Figure 13 As shown, with switches S1-S6 off, the input inductance of phase A flows through diode D1, the primary capacitor of the transformer, the transformer itself, the secondary capacitor of the transformer, and freewheeling diode D7. The output inductance of phase A flows through freewheeling diode D7 and the load. The input inductance of phase B flows through diode D3, the primary capacitor of the transformer, the transformer itself, the secondary capacitor of the transformer, and freewheeling diode D8. The output inductance of phase B flows through freewheeling diode D8 and the load. The input inductance of phase C flows through diode D6, the primary capacitor of the transformer, the transformer itself, the secondary capacitor of the transformer, and freewheeling diode D9. The output inductance of phase C flows through freewheeling diode D9 and the load. From the mode diagram, it can be seen that the mode of the primary diodes of the transformer is mainly determined by the direction of the input voltage.

[0099] Working mode two such as Figure 14 As shown: the modes of phases A and B remain unchanged, and the switches S5 and S6 of phase C are turned on first. The power supply of phase C charges the input inductor of phase C through diode D6 and switch S6. The primary capacitor of the transformer is connected in series with the secondary capacitor of the transformer through switches S5 and S6, the transformer, and the secondary capacitor of the transformer, and together they charge the load and the output inductor.

[0100] Working Mode Three Figure 15As shown: Phase B's mode remains unchanged. Switches S5 and S6 in phase C are turned on. The phase C power supply charges the phase C input inductor via diode D6 and switch S6. The primary capacitor of the transformer is connected in series with switches S5 and S6, the transformer itself, and the secondary capacitor, collectively charging the load and output inductor. Switches S1 and S2 in phase A are turned on. The phase A power supply charges the phase A input inductor via diode D1 and switch S1. The primary capacitor of the transformer is connected in series with switches S1 and S2, the transformer itself, and the secondary capacitor, collectively charging the load and output inductor.

[0101] Working Mode Four Figure 16 As shown: In phase C, switches S5 and S6 are turned on. The phase C power supply charges the phase C input inductor via diode D6 and switch S6. The primary capacitor of the transformer is connected in series with switches S5 and S6, the transformer itself, and the secondary capacitor, collectively charging the load and output inductor. In phase A, switches S1 and S2 are turned on. The phase A power supply charges the phase A input inductor via diode D1 and switch S1. The primary capacitor of the transformer is connected in series with switches S1 and S2, the transformer itself, and the secondary capacitor, collectively charging the load and output inductor. In phase B, switches S3 and S4 are turned on. The phase B power supply charges the input inductor via diode D3 and switch S3. The primary capacitor of the transformer is connected in series with switches S1 and S2, the transformer itself, and the secondary capacitor, collectively charging the load and output inductor.

[0102] Operating mode five is the same as operating mode three, operating mode six is ​​the same as operating mode two, and operating mode seven is the same as operating mode one. Therefore, there are mainly these seven modes in a power grid sector. The operating modes of other sectors are similar to the above modes and can be derived through analysis.

[0103] The following is about... Figure 12 The three-phase single-stage high-frequency isolated AC-DC converter shown was simulated and verified:

[0104] The circuit parameters in Table 1 were selected for functional simulation verification of the three-phase topology. The simulation aimed to demonstrate the basic functions, and the quantitative relationships reflected in the parameter settings were not fixed. The simulation results are as follows: Figure 17 As shown.

[0105] Table 1 Circuit Parameters

[0106]

[0107] Simulation results show that the power factor correction and rectification functions of this topology can be achieved well.

[0108] In summary, compared with existing technologies, it has the following beneficial effects:

[0109] 1. The embodiments of the present invention employ a converter that achieves rectification and power factor correction functions through single-stage energy conversion. This requires fewer components, reduces the number of corresponding sampling and driving circuits, resulting in lower equipment cost, smaller size, and increased power density. Simultaneously, single-stage energy conversion improves operating efficiency.

[0110] 2. The proposed three-phase single-stage high-frequency isolated AC-DC converter adopts a modular design, consisting of three independent single-phase AC-DC converter units. In this topology, there is no coupling between the three phases, which significantly simplifies the system control complexity and facilitates efficient control.

[0111] 3. The topology of the single-stage high-frequency isolated AC-DC converter eliminates the bus capacitor in the traditional structure, fundamentally avoiding the lifespan bottleneck caused by the aging of the bus capacitor, and significantly improving the long-term operational reliability and service life of the converter.

[0112] 4. Since the three-phase topology is directly composed of three decoupled single-phase circuits, when the input power supply voltage exhibits phase interleaving, the output terminals of the three-phase circuit will produce the same phase interleaving, which will greatly reduce the voltage ripple, and thus greatly reduce the filter capacitor.

[0113] 5. In the topology of a single-stage high-frequency isolated AC-DC converter, the transformer does not serve as an energy storage device. A double-ended transformer can be used. In a double-ended transformer, energy transfer is achieved through bidirectional current drive, without relying entirely on the magnetic core to store energy. Therefore, the air gap can be designed to be extremely small, thereby effectively reducing the transformer size and reducing the impact of parasitic parameters such as leakage inductance.

[0114] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0115] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A single-stage high-frequency isolated AC-DC converter, characterized in that, It includes an input inductor, an output inductor, a first intermediate capacitor, a second intermediate capacitor, a transformer, a freewheeling circuit, and an improved bridgeless structure; The bridgeless structure includes four connection ends. The first connection end is unidirectionally connected to the second connection end, and the fourth connection end is unidirectionally connected to the first connection end. There are three working states between the second and third connection ends: working state one, the second connection end is connected to the third connection end; working state two, the third connection end is connected to the second connection end; and working state three, disconnected. There are also three working states between the third and fourth connection ends: working state one, the third connection end is connected to the fourth connection end; working state two, the fourth connection end is connected to the third connection end; and working state three, disconnected. The first connection terminal of the bridgeless structure is connected to the first terminal of the AC power supply via an input inductor; the third connection terminal of the bridgeless structure is connected to the second terminal of the AC power supply; the second connection terminal of the bridgeless structure is connected to the first terminal of the primary side of the transformer via a first intermediate capacitor; and the fourth connection terminal of the bridgeless structure is connected to the second terminal of the primary side of the transformer. The first terminal of the secondary side of the transformer is connected to the first output terminal of the converter; the second terminal of the secondary side of the transformer is connected to the second output terminal of the converter via the second intermediate capacitor and the output inductor; the common terminal of the second intermediate capacitor and the output inductor is connected to the first terminal of the secondary side of the transformer via a freewheeling circuit. By controlling the operating states between the four connection terminals in the bridgeless structure, the single-stage high-frequency isolated AC-DC converter achieves power factor correction and rectification functions.

2. The single-stage high-frequency isolated AC-DC converter as described in claim 1, characterized in that, The transformer is a two-ended transformer.

3. The single-stage high-frequency isolated AC-DC converter as described in claim 1, characterized in that, The freewheeling circuit includes a diode, and the diode is connected in the following ways: the anode of the diode is connected to the common terminal of the second intermediate capacitor and the output inductor, or the cathode of the diode is connected to the common terminal of the second intermediate capacitor and the output inductor.

4. The single-stage high-frequency isolated AC-DC converter as described in any one of claims 1 to 3, characterized in that, The first and second connection terminals of the bridgeless structure are connected by a diode or controlled by a switching device to achieve unidirectional conduction. The fourth connection terminal of the bridgeless structure is connected to the first connection terminal by a diode or controlled by a switching device to achieve unidirectional conduction; The bridgeless structure is connected between the second and third connection terminals by a switching transistor or a bidirectional thyristor with a reverse parallel freewheeling diode to achieve three working states. The bridgeless structure connects a reverse parallel freewheeling diode or a bidirectional thyristor between the third and fourth connection terminals to achieve three operating states.

5. A single-stage high-frequency isolated AC-DC converter, characterized in that, It includes three single-phase AC-DC converters, each of which includes an input inductor, an output inductor, a first intermediate capacitor, a second intermediate capacitor, a transformer, a freewheeling circuit, and a bridgeless structure; The bridgeless structure includes four connection ends. The first connection end is unidirectionally connected to the second connection end, and the fourth connection end is unidirectionally connected to the first connection end. There are three working states between the second and third connection ends: working state one, the second connection end is connected to the third connection end; working state two, the third connection end is connected to the second connection end; and working state three, disconnected. There are also three working states between the third and fourth connection ends: working state one, the third connection end is connected to the fourth connection end; working state two, the fourth connection end is connected to the third connection end; and working state three, disconnected. The first connection terminal of the bridgeless structure is connected to the second terminal of the input inductor; the second connection terminal of the bridgeless structure is connected to the first terminal of the primary side of the transformer via the first intermediate capacitor; the fourth connection terminal of the bridgeless structure is connected to the second terminal of the primary side of the transformer. The first terminal of the secondary side of the transformer is connected to the first output terminal of the single-phase AC-DC converter; the second terminal of the secondary side of the transformer is connected to the second output terminal of the single-phase AC-DC converter via the second intermediate capacitor and the output inductor; the common terminal of the second intermediate capacitor and the output inductor is connected to the first terminal of the secondary side of the transformer via a freewheeling circuit. The first terminals of the input inductors in the three single-phase AC-DC converters are connected to the first terminals of the three-phase AC power supplies A, B, and C, respectively, and the second terminals of the three-phase AC power supplies A, B, and C are connected together. The third connection terminals of the bridgeless structures in the three single-phase AC-DC converters are connected together; The first output terminals of the three single-phase AC-DC converters are connected together as the first output terminal of a single-stage high-frequency isolated AC-DC converter; the second output terminals of the three single-phase AC-DC converters are connected together as the second output terminal of a single-stage high-frequency isolated AC-DC converter. By controlling the operating states between the four connection terminals in the bridgeless structure, the single-stage high-frequency isolated AC-DC converter achieves power factor correction and rectification functions.

6. The single-stage high-frequency isolated AC-DC converter as described in claim 5, characterized in that, The transformer is a two-ended transformer.

7. The single-stage high-frequency isolated AC-DC converter as described in claim 5, characterized in that, The freewheeling circuit includes a diode, and the diode is connected in the following ways: the anode of the diode is connected to the common terminal of the second intermediate capacitor and the output inductor, or the cathode of the diode is connected to the common terminal of the second intermediate capacitor and the output inductor.

8. The single-stage high-frequency isolated AC-DC converter as described in claim 5, characterized in that, The common terminal where the second terminals of the three-phase AC power supply A, B, and C are connected together, and the common terminal of the third connection terminal of the bridgeless structure in the three single-phase AC-DC converters are both grounded, serving as the N line of the three-phase four-wire system.

9. The single-stage high-frequency isolated AC-DC converter as described in any one of claims 5 to 8, characterized in that, In each single-phase AC-DC converter: The first and second connection terminals of the bridgeless structure are connected by a diode or controlled by a switching device to achieve unidirectional conduction. The fourth connection terminal of the bridgeless structure is connected to the first connection terminal by a diode or controlled by a switching device to achieve unidirectional conduction; The bridgeless structure is connected between the second and third connection terminals by a switching transistor or a bidirectional thyristor with a reverse parallel freewheeling diode to achieve three working states. The bridgeless structure connects a reverse parallel freewheeling diode or a bidirectional thyristor between the third and fourth connection terminals to achieve three operating states.

10. The single-stage high-frequency isolated AC-DC converter as described in any one of claims 5 to 8, characterized in that, The three single-phase AC-DC converters all adopt a modular design, with each phase controlled independently.

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