Single-stage isolated AC-DC converter

Abstract

The invention provides a single-stage isolation type AC-DC converter which comprises a power grid side interface, a power grid voltage adjusting unit, a filtering unit, an active clamping control unit, an AC side rectifying unit, an intermediate DC voltage adjusting unit, a transformer, a secondary side rectifying unit, an output voltage adjusting unit and an output side interface. An active clamping control unit is additionally arranged in a single-stage isolation type AC-DC converter, the active clamping control unit is connected between an AC side rectification unit and a primary side coil of a transformer, and a first connection point in the active clamping control unit is connected with a second connection point in a power grid voltage regulation unit. The single-stage isolation type AC-DC converter can process energy corresponding to leakage inductance generated by a transformer excitation inductor Lm through the active clamping control unit, voltage spikes are avoided, the phase of input current is made to be consistent with the phase of power grid voltage, correction of the power factor of the input current and low-current harmonic operation are achieved, and the power factor of the input current is corrected. The circuit is simple in structure and low in cost.

Description

Technical Field

[0001] The present application relates to the field of electrical technology, and in particular to a single-stage isolated AC-DC converter. Background Art

[0002] With the upgrading of industries and the electrification of industrial equipment, more and more power electronic charging equipment, such as electric vehicle charging equipment, lighting systems, data center power supplies, etc., are connected to traditional power grids in large quantities. Therefore, AC-DC converters are needed. Since the AC side of traditional AC-DC converters uses uncontrolled rectifier circuits, it brings complex spectrum voltage and current harmonics to the power grid, resulting in higher power transmission costs and may also cause system overvoltage and overcurrent faults. Among them, AC-DC converters with grid-side input current power factor correction (PFC) function can reduce the impact of voltage and current harmonics on the grid side.

[0003] In the prior art, an AC-DC converter with a grid-side input current PFC function generally has a two-stage structure. The front stage adopts an AC-DC converter that meets IEC and other electrical equipment standards and can achieve input current unity power factor and low current harmonic control effects. The rear stage adopts a DC-DC converter that can control the output side to operate at constant voltage or constant current. Generally, the DC-DC converter is an isolated topology structure, which leads to high cost of the two-stage AC-DC converter. In addition, since the front-stage AC-DC converter is generally a hard switch, the loss is increased.

[0004] Single-stage AC-DC converters have the advantages of fewer components and low cost. However, some current single-stage AC-DC converters implement the PFC function through frequency conversion and phase shifting of the DC-DC circuit structure in the converter. The relationship between the control quantity and the grid-connected current is strongly nonlinear, so no special grid-connected current control is performed on them, and the current harmonic control effect is poor. In order to achieve grid-connected current harmonic control, some generally need to adopt closed-loop control of the grid-connected current, which requires adding a current detection circuit to the circuit and an additional grid-connected current control algorithm to the controller, resulting in a complex structure of the AC-DC converter. Summary of the invention

[0005] The present application provides a single-stage isolated AC-DC converter to solve the technical problems mentioned in the background technology.

[0006] The present application provides a single-stage isolated AC-DC converter, comprising: a grid-side interface, a grid voltage regulating unit, a filtering unit, an active clamping control unit, an AC-side rectifying unit, an intermediate DC voltage regulating unit, a transformer, a secondary-side rectifying unit, an output voltage regulating unit, and an output-side interface;

[0007] The grid voltage regulating unit is connected to both ends of the grid side interface, the filtering unit is connected between the grid voltage regulating unit and the AC side rectifier unit, the active clamping control unit is connected between the AC side rectifier unit and the primary side coil of the transformer, and a first connection point inside the active clamping control unit is connected to a second connection point inside the grid voltage regulating unit, the intermediate DC voltage regulating unit is connected in parallel with the active clamping control unit, the secondary side coil of the transformer is connected to the secondary side rectifier unit, and the output voltage regulating unit and the output side interface are both connected between the secondary side rectifier unit and the midpoint of the secondary side coil.

[0008] Optionally, the active clamping control unit includes: a clamping subunit, a first active switch subunit, and a second active switch subunit, one end of the clamping subunit, the first active switch subunit, and the second active switch subunit are connected in series in sequence, and the other end of the clamping subunit is also connected to the AC side rectifier unit and one end of the primary side coil, the first connection point is located between the first active switch subunit and the second active switch subunit, and the first connection point, the second connection point and the other end of the primary side coil are interconnected to form an equipotential point or an equipotential point.

[0009] Optionally, the first active switch sub-unit and the second active switch sub-unit each include at least one of the following: a MOS tube, an IGBT, or a SiC switch tube.

[0010] Optionally, a duty cycle of the first active switch subunit and the second active switch subunit during operation is less than or equal to 0.5.

[0011] Optionally, the first active switch subunit and the second active switch subunit are not in the on state at the same time.

[0012] Optionally, the grid voltage regulating unit includes: a first voltage regulating subunit and a second voltage regulating subunit, and parameters of the first voltage regulating subunit are consistent with parameters of the second voltage regulating subunit;

[0013] The first voltage regulating subunit and the second voltage regulating subunit are connected in series at two ends of the grid-side interface, and the second connection point is located between the first voltage regulating subunit and the second voltage regulating subunit.

[0014] Optionally, the filtering unit includes: a first filtering subunit and a second filtering subunit, and parameters of the first filtering subunit are consistent with parameters of the second filtering subunit;

[0015] The first filtering subunit is connected between the positive end of the grid side interface and the AC side rectifying unit, and the second filtering subunit is connected between the positive end of the grid side interface and the AC side rectifying unit;

[0016] The first filtering subunit works in coordination with the first voltage regulating subunit, and the second filtering subunit works in coordination with the second voltage regulating subunit, and the coordinated work includes filtering harmonics greater than or equal to a target frequency in the alternating current connected through the grid-side interface, wherein the target frequency is greater than or equal to a smaller switching frequency between a switching frequency of the first active switching subunit and a switching frequency of the second active switching subunit.

[0017] Optionally, the first voltage regulating subunit includes: at least one first capacitor, the positive end of the first capacitor is connected to the positive end of the grid side interface, and the negative end of the first capacitor is connected to the second grid voltage regulating unit and the active clamping control unit.

[0018] Optionally, the second grid voltage regulation subunit includes: at least one second capacitor, the positive end of the second capacitor is connected to the negative end of the first capacitor and the active clamping control unit, and the negative end of the second capacitor is connected to the negative end of the grid side interface.

[0019] Optionally, the first filtering subunit includes: at least one first filtering inductor;

[0020] At least one of the first filter inductors works in cooperation with at least one of the first capacitors.

[0021] Optionally, the second filtering subunit includes: at least one second filtering inductor;

[0022] At least one of the second filtering inductors works in cooperation with at least one of the second capacitors.

[0023] Optionally, it also includes: an output voltage frequency conversion control unit, which is connected to the output voltage regulation unit and the active clamping control unit, and is used to regulate the output voltage of the output voltage regulation unit by controlling the active clamping control unit.

[0024] Optionally, it also includes: an overvoltage and undervoltage protection circuit, which is connected to the grid side interface and the output voltage frequency conversion control unit, and is used to control the use status of the output voltage frequency conversion control unit according to the grid voltage.

[0025] The single-stage isolated AC-DC converter provided in the present application includes: a grid-side interface, a grid voltage regulating unit, a filtering unit, an active clamping control unit, an AC-side rectifier unit, an intermediate DC voltage regulating unit, a transformer, a secondary-side rectifier unit, an output voltage regulating unit and an output-side interface. By adding an active clamping control unit to the single-stage isolated AC-DC converter, wherein the active clamping control unit is connected between the AC-side rectifier unit and the primary-side coil of the transformer, and a first connection point inside the active clamping control unit is connected to a second connection point inside the grid voltage regulating unit, the single-stage isolated AC-DC converter can process the energy corresponding to the leakage inductance generated by the transformer excitation inductance Lm through the active clamping control unit, avoid voltage spikes, and make the phase of the input current consistent with the phase of the grid voltage, thereby realizing the correction of the power factor of the input current and lower current harmonic operation, and the circuit structure is simple and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 A schematic diagram of the structure of a single-stage isolated AC-DC converter provided in one embodiment of the present application;

[0028] Figure 2 A structural diagram of a single-stage isolated AC-DC converter provided in another embodiment of the present application;

[0029] Figure 3 A circuit diagram of a single-stage isolated AC-DC converter provided in one embodiment of the present application;

[0030] Figure 4 For Figure 3 The circuit diagram shown corresponds to the working process diagram of the single-stage isolated AC-DC converter under the grid voltage cycle;

[0031] Figure 5 For Figure 3 The circuit diagram shown corresponds to a working process diagram of a single-stage isolated AC-DC converter under a switching cycle;

[0032] Figure 6 A structural diagram of an output voltage frequency conversion control unit provided in one embodiment of the present application;

[0033] Figure 7This is a structural diagram of a single-stage isolated AC-DC converter provided in yet another embodiment of the present application. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application is clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work also fall within the scope of protection of the present application.

[0035] In the charging application scenario of power electronic systems, for example, electric vehicles need to be connected to the power grid through an AC-DC converter and charged after AC-DC conversion. However, since the AC side of the traditional AC-DC converter uses an uncontrolled rectifier circuit, it will bring complex spectrum voltage and current harmonics to the power grid, resulting in increased power transmission costs and possible overvoltage and overcurrent faults in the system. Therefore, AC-DC converters with PFC functions are widely used.

[0036] Among them, the AC-DC converter with PFC function includes a two-stage AC-DC converter and a single-stage AC-DC converter. For the two-stage AC-DC converter, the front stage adopts an AC-DC converter that meets the standards of electrical equipment such as IEC and can achieve input current unity power factor and low current harmonic control effect, and the rear stage adopts a DC-DC converter that can control the output side to operate at constant voltage or constant current. The front-stage AC-DC converter is a hard switch, and the rear-stage DC-DC converter is an isolated topology structure, which leads to high loss and high cost of the two-stage AC-DC converter; for the single-stage AC-DC converter, the PFC function is realized by methods such as frequency conversion and phase shifting of the DC-DC circuit structure in the converter, and the relationship between the control quantity and the grid-connected current is strongly nonlinear. Generally, the grid-connected current harmonics are not controlled, resulting in poor current harmonic control effect. Even if the grid-connected current harmonics are controlled, the AC-DC converter structure is complicated due to the need to use a current detection circuit and additionally add a grid-connected current control algorithm.

[0037] Therefore, there is a lack of an AC-DC converter with a simple structure, low cost and soft switching function on the market. In order to solve the technical problems existing in the prior art, this application proposes a single-stage isolated AC-DC converter, by adding an active clamping control unit on the DC side of the AC-DC converter, and connecting the active clamping control unit to the grid voltage regulation unit, and absorbing the transformer excitation inductance L through the active clamping control unit. mThe energy corresponding to the leakage inductance generated reduces the voltage spike in the circuit, and transmits the input current through the grid side interface to the active clamping control unit through the grid voltage regulation unit, thereby controlling the sinusoidal change of the input current through the active clamping control unit, so that the phase of the input current connected through the grid side interface in the AC-DC converter can follow the phase change of the grid voltage, and the waveform is a sinusoidal voltage waveform with almost no harmonic components, that is, the single-stage isolated AC-DC converter provided in the present application can automatically realize the correction of the power factor of the input current and low current harmonic operation, and the circuit structure is simple and the cost is low.

[0038] Figure 1 This is a schematic diagram of the structure of a single-stage isolated AC-DC converter provided in one embodiment of the present application. Figure 1 As shown, the single-stage isolated AC-DC converter includes: a grid side interface 100, a grid voltage adjustment unit 120, a filter unit 130, an active clamping control unit 140, an AC side rectifier unit 150, an intermediate DC voltage adjustment unit 160, a transformer 170, a secondary side rectifier unit 180, an output voltage adjustment unit 190 and an output side interface 200;

[0039] The grid voltage regulating unit 120 is connected to both ends of the grid side interface 100, the filtering unit 130 is connected between the grid voltage regulating unit 120 and the AC side rectifier unit 150, the active clamping control unit 140 is connected between the AC side rectifier unit 150 and the primary side coil of the transformer 170, and the first connection point inside the active clamping control unit 140 is connected to the second connection point inside the grid voltage regulating unit 120, the intermediate DC voltage regulating unit 160 is connected in parallel with the active clamping control unit 140, the secondary side coil of the transformer 170 is connected to the secondary side rectifier unit 180, and the output voltage regulating unit 190 and the output side interface 200 are both connected between the secondary side rectifier unit 180 and the midpoint of the secondary side coil.

[0040] In this embodiment, the grid-side interface 100 is connected to the grid side and is used to input the electricity from the grid side into the AC-DC converter of the present application.

[0041] The grid voltage regulating unit 120 is used to regulate the input voltage connected through the grid side interface 100, mainly to stabilize the voltage and avoid large voltage fluctuations.

[0042] The filtering unit 130 is used to filter the input voltage and input current, wherein it works in conjunction with the grid voltage regulation unit 120 to filter the harmonics in the input voltage and input current that are greater than or equal to the target frequency, wherein the target frequency is not a fixed frequency, and its size is controlled by the active clamping control unit 140.

[0043] The active clamp control unit 140 is used to absorb the transformer excitation inductance L m The energy corresponding to the leakage inductance generated clamps the voltage input to the primary side of the transformer 170, and controls the phase of the input current connected through the grid side interface 100, so that the phase of the input current automatically follows the phase change of the grid voltage, and adjusts the output voltage of the output side interface 200.

[0044] The AC-side rectifier unit 150 is used to convert the AC power received through the grid-side interface 100 into DC power.

[0045] The intermediate DC voltage regulating unit 160 is used to filter the DC power obtained by the AC side rectifying unit 150, wherein the harmonics in the DC power having a frequency lower than the target frequency are mainly filtered.

[0046] The secondary side rectifier unit 180 is used to convert the alternating current output by the transformer 170 into direct current to obtain direct current.

[0047] The output voltage regulating unit 190 is used to filter the direct current obtained by the secondary side rectifying unit 180, wherein mainly the harmonics in the direct current having a frequency lower than the target frequency are filtered.

[0048] The output side interface 200 is used to connect to an external load and provide power to the external load.

[0049] In terms of circuit structure, an active clamping control unit 140 is added, wherein the active clamping control unit 140 is connected between the AC side rectifier unit 150 and the primary side coil of the transformer 170. The active clamping control unit 140 can be used to control the excitation inductance L in the primary side coil of the transformer 170. m The energy corresponding to the generated leakage inductance is processed, and the voltage input to the primary side of the transformer 170 is clamped to avoid voltage spikes. In addition, the active clamping control unit 140 is also connected to the second connection point A2 inside the grid voltage regulating unit 120 through the internal first connection point A1. Since the phase of the current at the second connection point A2 can reflect the phase of the input current, the active clamping control unit 140 can obtain the phase of the input current. Therefore, under this connection relationship, the AC-DC converter provided in this embodiment uses fewer components and a simple circuit structure, realizes the consistency of the phase of the input current with the phase of the grid voltage, and realizes the correction of the power factor of the input current, reducing the harmonic impact of the AC-DC converter of this application on the grid.

[0050] Figure 1The working process of the AC-DC converter is as follows: the AC-DC converter is connected to the grid through the grid side interface 100 to obtain the input voltage input from the grid side, the input voltage is filtered through the grid voltage adjustment unit 120 and the filter unit 130, and the input voltage is stabilized by the grid voltage adjustment unit 120, and then the input voltage after stabilization and filtering is converted from AC to DC through the AC side rectifier unit 150 to obtain DC power.

[0051] Then, the active clamping control unit 140 converts the DC power into AC power that can be input into the transformer 170, and after being transformed by the transformer 170, the transformed AC power is obtained, and then the AC-DC conversion is performed through the secondary side rectifier unit 180 to obtain DC power. Finally, the DC power is processed by the output voltage regulation unit 190, for example, filtering, voltage stabilization, etc., and the processed DC power is transmitted to the external load through the output side interface 200.

[0052] Among them, Figure 1 In the topology of the AC-DC converter shown in FIG. 1 , an active clamping control unit 140 is added, and the active clamping control unit 140 is connected to the transformer 170, and the active clamping control unit 140 is connected in series with the intermediate DC voltage regulating unit 160. Therefore, when the AC-DC converter is used, the active clamping control unit 140 can adjust the excitation inductance L of the transformer 170. m The energy corresponding to the generated leakage inductance is processed, the voltage input to the transformer 170 is adjusted to avoid voltage spikes, and the phase of the input current is controlled to be consistent with the phase of the current in the power grid. The principle of adding the active clamping control unit 140 to make the AC-DC converter have the input current consistent with the current in the power grid is referred to below.

[0053] In this embodiment, the single-stage isolated AC-DC converter includes: a grid side interface 100, a grid voltage regulating unit 120, a filtering unit 130, an active clamping control unit 140, an AC side rectifier unit 150, an intermediate DC voltage regulating unit 160, a transformer 170, a secondary side rectifier unit 180, an output voltage regulating unit 190 and an output side interface 200. By adding an active clamping control unit 140 to the single-stage isolated AC-DC converter, wherein the active clamping control unit 140 is connected between the AC side rectifier unit 150 and the primary side coil of the transformer 170, and the first connection point inside the active clamping control unit 140 is connected to the second connection point inside the grid voltage regulating unit 120, so that the single-stage isolated AC-DC converter can control the transformer excitation inductance L through the active clamping control unit 140. mThe energy corresponding to the generated leakage inductance is processed to avoid voltage spikes and make the phase of the input current consistent with the phase of the grid voltage, thereby realizing the correction of the power factor of the input current and lower current harmonic operation, and the circuit structure is simple and the cost is low.

[0054] Figure 2 A structural diagram of a single-stage isolated AC-DC converter provided in another embodiment of the present application is shown in FIG. Figure 2 As shown, in Figure 1 On the basis of the illustrated embodiment, the active clamping control unit 140 includes: a clamping subunit 401, a first active switch subunit 402 and a second active switch subunit 403, one end of the clamping subunit 401, the first active switch subunit 402 and the second active switch subunit 403 are sequentially connected in series, and the other end of the clamping subunit 401 is also connected to the AC side rectifier unit 150 and one end of the primary side coil, the first connection point is located between the first active switch subunit 402 and the second active switch subunit 403, and the first connection point, the second connection point and the other end of the primary side coil are connected to each other to form an equipotential point or an equipotential point.

[0055] Specifically, the first active switch subunit 402 and the second active switch subunit 403 are not turned on at the same time, that is, when the first active switch subunit 402 is turned on, the second active switch subunit 403 is turned off; when the second active switch subunit 403 is turned on, the first active switch subunit 402 is turned off.

[0056] The duty cycles of the first active switch subunit 402 and the second active switch subunit 403 during operation need to be less than or equal to 0.5.

[0057] Among them, when the duty cycles of the first active switch subunit 402 and the second active switch subunit 403 during operation are equal and are 0.5, zero voltage switch (Zero Voltage Switch, referred to as ZVS switch) of the first active switch subunit 402 and the second active switch subunit 403 can be achieved. The specific principle is referred to below.

[0058] Furthermore, since one end of the clamping subunit 401, the first active switch subunit 402, and one end of the second active switch subunit 403 are sequentially connected in series, the other end of the clamping subunit 401 is also connected to the AC side rectifier unit 150 and one end of the primary side coil, and the other end of the second active switch subunit is also connected to one end of the primary side coil, and the first connection point is the connection point between the first active switch subunit 402 and the second active switch subunit 403, and the first connection point, the second connection point, and the other end of the primary side coil are connected to each other. An equipotential point or an equipotential point is formed, that is, a loop is formed by the first connection point, the first active switch subunit 402, and the primary side coil, and the clamp subunit 401 is connected in series in the loop; a loop is formed by the first connection point, the second active switch subunit 403, and the primary side coil, so that the direct current rectified by the AC side rectifier unit 150 can be converted into alternating current and input to the primary side coil by turning on and off the first active switch subunit 402 and the second active switch subunit 403, and the transformer excitation inductance L m The energy corresponding to the generated leakage inductance is transferred to the clamping subunit 401, avoiding voltage spikes and realizing automatic correction of the input current power factor, so that the phase of the input current is consistent with the phase of the grid voltage, reducing the harmonics of the input current, thereby reducing the adverse impact on the grid.

[0059] The output voltage of the output terminal interface can be adjusted by adjusting the switching frequency of the first active switch subunit 402 and the second active switch subunit 403 .

[0060] Optional, such as Figure 3 As shown, the clamping subunit may include at least one active clamping capacitor Cr.

[0061] Optional, such as Figure 3 As shown, the first active switch subunit 402 and the second active switch subunit 403 each include at least one of the following: a MOS transistor, an IGBT, or a SiC switch transistor.

[0062] Further, such as Figure 2 As shown, the grid voltage regulating unit 120 includes: a first voltage regulating subunit 201 and a second voltage regulating subunit 202, and the parameters of the first voltage regulating subunit 201 are consistent with the parameters of the second voltage regulating subunit 202;

[0063] The first voltage regulating subunit 201 and the second voltage regulating subunit 202 are connected in series at two ends of the grid-side interface 100 , and the second connection point is located between the first voltage regulating subunit 201 and the second voltage regulating subunit 202 .

[0064] Specifically, the first voltage regulating subunit 201 and the second voltage regulating subunit 202 are connected in series at both ends of the grid side interface 100, and are used to stabilize and divide the input voltage, wherein the second connection point is located between the first voltage regulating subunit 201 and the second voltage regulating subunit 202, and the parameters of the first voltage regulating subunit 201 and the second voltage regulating subunit 202 are consistent, so that the first voltage regulating subunit and the second voltage regulating subunit 202 each obtain half of the AC component.

[0065] Optionally, the first voltage regulating subunit 201 includes at least one first capacitor C f1 , when the first capacitor C f1 When the number is greater than 1, the plurality of first capacitors C f1 The first capacitors C f1 The positive end of the overall structure is connected to the positive end of the grid side interface 100, and the negative end is connected to the second connection point to form an equipotential point or equipotential point, wherein the negative end is also connected to the second grid voltage regulation unit 120 and the active clamping control unit 140.

[0066] Accordingly, the second voltage regulating subunit 202 includes at least one second capacitor C f2 , when the second capacitor C f2 When the number is greater than 1, the plurality of second capacitors C f2 The second capacitors C f2 The positive end of the integral structure is connected to the second connection point to form an equipotential point or an equipotential point, and the negative end is connected to the negative end of the grid-side interface 100 .

[0067] It should be noted that the structure of the first voltage regulating subunit 201 and the structure of the second voltage regulating subunit 202 may be the same or different, as long as the parameters of the two are equal.

[0068] Further, such as Figure 2 As shown, the filtering unit 130 includes: a first filtering subunit 301 and a second filtering subunit 302, and the parameters of the first filtering subunit 301 are consistent with the parameters of the second filtering subunit 302;

[0069] The first filtering subunit 301 is connected between the positive end of the grid side interface 100 and the AC side rectifying unit 150, and the second filtering subunit 302 is connected between the positive end of the grid side interface 100 and the AC side rectifying unit 150;

[0070] The first filtering subunit 301 works in coordination with the first voltage regulating subunit 201, and the second filtering subunit 302 works in coordination with the second voltage regulating subunit 202. The coordinated work includes filtering harmonics greater than or equal to a target frequency in the alternating current connected through the grid-side interface 100, wherein the target frequency is greater than or equal to the smaller switching frequency between the switching frequency of the first active switching subunit 402 and the switching frequency of the second active switching subunit 403.

[0071] Specifically, one end of the first filtering subunit 301 is connected to the positive end of the first voltage regulating subunit 201 and the grid side interface 100, and the other end is connected to the AC side rectifier unit 150, and works in coordination with the first voltage regulating subunit 201. Similarly, one end of the second filtering subunit 302 is connected to the positive end of the second voltage regulating subunit 202 and the grid side interface 100, and the other end is connected to the AC side rectifier unit 150, and works in coordination with the second voltage regulating subunit 202, and jointly filters the harmonics greater than or equal to the target frequency in the AC power connected to the grid side interface 100, and inputs the filtered AC power into the AC side rectifier unit 150.

[0072] Among them, the target frequency should be greater than or equal to the smaller switching frequency of the switching frequency of the first active switch subunit 402 and the switching frequency of the second active switch subunit 403. In the present application, the switching frequency of the first active switch subunit 402 is equal to the switching frequency of the second active switch subunit 403, thereby removing the harmonics in the alternating current that are greater than or equal to the switching frequency of the first active switch subunit 402 or the switching frequency of the second active switch subunit 403, thereby ensuring the operation of the AC-DC converter.

[0073] Optionally, the first filtering subunit 301 includes: at least one first filtering inductor L f1 , when the first filter inductor L f1 When the number is greater than 1, the first filter inductors L f1 The second filter subunit 302 includes: at least one second filter inductor L f2 , when the second filter inductor L f2 When the number is greater than 1, the second filter inductor L f2 They can be connected in series, in parallel, or in series and in parallel.

[0074] It should be noted that the structure of the first filtering subunit 301 and the structure of the second filtering subunit 302 may be the same or different, as long as the parameters of the two are consistent.

[0075] Below, a specific embodiment is used to demonstrate that the AC-DC converter provided by the present application can realize automatic correction of the input current power factor, and the phase of the input current is consistent with the phase of the grid voltage, and the current harmonics are extremely small.

[0076] like Figure 3 As shown, the circuit structure includes: a single-phase grid power supply u g , i.e., the grid voltage connected to the grid-side interface 100; the AC-side filter inductor L f1 and L f2 , corresponding to the first filter inductor and the second filter inductor respectively; the AC side filter capacitor C f1 and C f2 , corresponding to the first capacitor and the second capacitor respectively; the AC side rectifier unit 150 composed of the AC side rectifier diodes D1, D2, D3, and D4; the active clamping capacitor Cr, the MOSFET switch tubes S1 and S2, constitute the active clamping control unit 140; the intermediate DC bus capacitor C dc , namely, the intermediate DC voltage regulating unit 160; the transformer Tx; the secondary side rectifying unit 180 composed of the secondary side rectifying diodes D5 and D6; the DC output side bus capacitor C out , that is, the output voltage regulating unit 190; the equivalent output resistance load R load , that is, the output side interface.

[0077] The primary side of the transformer Tx includes a resonant inductor Lr and a magnetizing inductor Lm.

[0078] It should be noted that for u g , L f1 and L f2 , C f1 and C f2 , D1, D2, D3, D4, Cr, S1 and S2, Tx, D5, D6, C out , R load , for L f1 and L f2 , C f1 and C f2 As mentioned above, it can contain multiple components. For other components, take D1 as an example. Figure 3 There is only one diode in the diagram, but in fact the branch where D1 is located may contain multiple diodes, or a circuit module or integrated unit including other components, which can realize the function corresponding to D1.

[0079] in, Figure 3 Point c is the first connection point, and point e is the second connection point.

[0080] for Figure 3As can be seen from the above, the switch tubes S1 and S2 cannot be turned on at the same time, and the duty cycle of the switch tubes S1 and S2 needs to be less than or equal to 0.5. When the switch tubes S1 and S2 are the same and complementary, that is, the duty cycle of the switch tubes S1 and S2 is the same, both 0.5, the single-stage isolated AC-DC converter shown in the present application can achieve ZVS conduction. Therefore, the duty cycle of the switch tubes S1 and S2 is the same, both 0.5, as an example. At this time, the working process of the single-stage isolated AC-DC converter provided by the present application under the power grid cycle is Figure 4 , where T grid is the grid voltage cycle.

[0081] According to Kirchhoff's voltage law KVL or the principle of the flyback circuit of the reference active clamp:

[0082] UCr=-Udc Formula (1)

[0083] Among them, U Cr and U dc They are the clamping capacitor voltage u Cr and the intermediate DC bus capacitor voltage u dc The average value of is the DC component. Figure 3 The first capacitor C f1 , the first filter inductor L f1 , diode D1 to the loop composed of clamping capacitor Cr and switch tube S1. Since the duty cycle of switch tube S1 is 0.5, the following formula can be obtained:

[0084] UCf1=0.5UCr=-0.5Udc formula (2)

[0085] Among them, U Cf1 is the filter capacitor voltage u Cf1 At the same time, due to L f1 =L f2 , C f1 =C f2 , and u Cf1 +u Cf2 =u g In practical applications, a passive EMI filter is generally added to the grid-side interface 100 of the single-phase isolated AC-DC converter. It is considered that under ideal conditions, the EMI filter can completely absorb the current ripple on the first filter inductor and the second filter inductor without changing the phase of the current fundamental wave. Therefore, the expressions of the first capacitor voltage and the second capacitor voltage can be further approximately derived as follows:

[0086] uCf1=0.5ug-0.5Udc

[0087] uCf2=0.5ug+0.5Udc formula (3)

[0088] When the single-stage isolated AC-DC converter operates at the positive peak of the input voltage, that is, u g =U g In a single-stage isolated AC-DC converter switching cycle Ts (t0-t5), its working process is as follows Figure 5 As shown:

[0089] t1~t2: gate-source driving voltage u of switch tube S2 gs2 From zero to positive, the switch tube S2 is turned on. At this time, the first filter inductor L f1 Through D1 and S2 to the intermediate DC bus capacitor C dc Discharge, its first inductor current i Lf1 When the switch tube S2 is turned on, the first inductor current i Lf1 Provides reverse current to achieve ZVS turn-on of S2;

[0090] t2~t3: At this time, the switch tube S2 is still turned on, but the first filter inductor current i Lf1 is zero, so D1 is turned off and D2 is turned on. Cf1 is negative, the first capacitor C f1 The first filter inductor L is supplied via D2 and S2. f1 Reverse charging;

[0091] t3~t5: In the dead time, the second filter inductor L f2 Through D4 and S1 to the intermediate DC bus capacitor C dc At the same time, the first filter inductor L f1 The current also changes from zero to positive. In this process, when the drain-source voltage u of the switch tube S1 ds1 It gradually decreases to zero until its reverse diode is turned on, realizing ZVS turn-on of the switch tube S1.

[0092] Therefore, the single-stage isolated AC-DC converter of the present application can achieve zero voltage conduction of the relevant switch tubes, ie, the switch tubes S1 and S2.

[0093] Wherein, without considering the charging and discharging time of the parasitic capacitance corresponding to the switch tubes S1 and S2, the expression of the first capacitor voltage in the single-stage isolated AC-DC converter within the switching period Ts can be obtained as follows:

[0094]

[0095] Among them, according to Figure 2 and Figure 3 It can be seen that according to formula (4), u Cf1 After that, you can get u g .

[0096] Since the intermediate DC bus capacitor C dc Generally, a larger bus capacitor is used, and it can be approximately considered that the DC voltage output by the AC side rectifier unit 150 changes very little within a grid voltage cycle, that is, u dc ≈U dc ,u Cr ≈U Cr =-U dc Therefore, the first filter inductance L in the switching period Ts can be further obtained f1 Current i Lf1 The expression is as follows:

[0097]

[0098] Among them, I pk is the peak value of the filter inductor current, which can be derived from formula (5). Since the duty cycle is 0.5, t3 = 0.5Ts, t5 = Ts. Since the current waveform is continuous, formula (6) can be obtained as follows:

[0099]

[0100] As can be seen from the above, in actual applications, a passive EMI filter is generally added to the grid-side interface 100 of a single-phase isolated AC-DC converter. It is assumed that under ideal conditions, the EMI filter can completely absorb the current ripple on the first filter inductor and the second filter inductor without changing the phase of the current fundamental wave. It can be approximately obtained that the input current and the average current of the first filter inductor and then the second filter inductor within a switching cycle Ts are equal. Therefore, the AC side input current i can be obtained by formula (5) and formula (6): g The expression is:

[0101]

[0102] Among them, U g is the amplitude of the grid voltage, and ω is the angular frequency of the grid voltage. When the single-phase isolated AC-DC converter operates stably at a power point, Ts, U g and L f1 are all constants, which shows that the input current of the topological structure adopted in the present application can not only automatically follow the phase change of the grid voltage, but its current waveform is also an ideal sinusoidal voltage waveform with almost no harmonic components. Therefore, the proposed topological structure does not need to add additional high-frequency current detection circuits and complex control loops, and can further reduce costs compared to traditional AC-DC converters.

[0103] Optional, such as Figure 6As shown, the single-stage isolated AC-DC converter also includes: an output voltage frequency conversion control unit, which is connected to the output voltage adjustment unit 190 and the active clamping control unit 140 and is used to adjust the output voltage of the output voltage adjustment unit 190 by controlling the active clamping control unit 140.

[0104] Specifically, the output voltage frequency conversion control unit is connected to the output voltage regulating unit 190 to obtain the DC output voltage u of the output voltage regulating unit 190. out and compare it with the output voltage given value u outref Compare and get the error signal Δu out . out The input is sent to the PI controller, and the voltage loop is tracked without static error through the PI controller. The PI controller outputs the switching frequency adjustment, which is added to the rated switching frequency fr to obtain the switching frequency fs of the converter. Then, the pulse frequency modulation (PFM) module obtains the switching signals of the switch tubes S1 and S2 according to the switching frequency fs to achieve closed-loop control of the DC output voltage.

[0105] Optional, such as Figure 7 As shown, the single-stage isolated AC-DC converter also includes: an overvoltage and undervoltage protection circuit, which is connected to the grid side interface 100 and the output voltage frequency conversion control unit, and is used to control the use status of the output voltage frequency conversion control unit according to the grid voltage.

[0106] Specifically, the overvoltage and undervoltage protection circuit is used to detect the grid voltage, and output the overvoltage and undervoltage protection enable signal Fen to the output voltage frequency conversion control unit according to the grid voltage. When the grid voltage is overvoltage or undervoltage, Fen is 0, and the output voltage frequency conversion control unit disconnects the switch tubes S1 and S2 according to the frequency conversion control method to protect the single-stage isolated AC-DC converter; when the grid voltage is normal, Fen is 1, and the output voltage frequency conversion control unit obtains the switching signal of the switch tube according to the frequency conversion control method to control the switch tubes S1 and S2 to be turned on and off.

[0107] Among them, the structure of the overvoltage and undervoltage protection circuit and the frequency conversion control method can refer to the existing technology and will not be repeated here.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, ordinary technicians in the field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A single-stage isolated AC-DC converter, characterized in that: include: A grid side interface, a grid voltage regulating unit, a filtering unit, an active clamping control unit, an AC side rectifier unit, an intermediate DC voltage regulating unit, a transformer, a secondary side rectifier unit, an output voltage regulating unit and an output side interface; The grid voltage regulating unit is connected to both ends of the grid side interface, the filtering unit is connected between the grid voltage regulating unit and the AC side rectifier unit, the active clamping control unit is connected between the AC side rectifier unit and the primary side coil of the transformer, and a first connection point inside the active clamping control unit is connected to a second connection point inside the grid voltage regulating unit, the intermediate DC voltage regulating unit is connected in parallel with the active clamping control unit, the secondary side coil of the transformer is connected to the secondary side rectifier unit, and the output voltage regulating unit and the output side interface are both connected between the secondary side rectifier unit and the midpoint of the secondary side coil.

2. The single-stage isolated AC-DC converter according to claim 1, characterized in that: The active clamping control unit includes: a clamping subunit, a first active switch subunit and a second active switch subunit, one end of the clamping subunit, the first active switch subunit and the second active switch subunit are connected in series in sequence, and the other end of the clamping subunit is also connected to the AC side rectifier unit and one end of the primary side coil, the first connection point is located between the first active switch subunit and the second active switch subunit, and the first connection point, the second connection point and the other end of the primary side coil are connected to each other to form an equipotential point or an equipotential point.

3. The single-stage isolated AC-DC converter according to claim 2, characterized in that: The first active switch sub-unit and the second active switch sub-unit each include at least one of the following: a MOS tube, an IGBT, or a SiC switch tube.

4. The single-stage isolated AC-DC converter according to claim 2 or 3, characterized in that: A duty cycle of the first active switch subunit and the second active switch subunit during operation is less than or equal to 0.

5.

5. The single-stage isolated AC-DC converter according to claim 2, characterized in that: The grid voltage regulating unit comprises: a first voltage regulating subunit and a second voltage regulating subunit, and the parameters of the first voltage regulating subunit are consistent with the parameters of the second voltage regulating subunit; The first voltage regulating subunit and the second voltage regulating subunit are connected in series at two ends of the grid-side interface, and the second connection point is located between the first voltage regulating subunit and the second voltage regulating subunit.

6. The single-stage isolated AC-DC converter according to claim 5, characterized in that: The filtering unit comprises: a first filtering subunit and a second filtering subunit, and the parameters of the first filtering subunit are consistent with the parameters of the second filtering subunit; The first filtering subunit is connected between the positive end of the grid side interface and the AC side rectifier unit, and the second filtering subunit is connected between the positive end of the grid side interface and the AC side rectifier unit; the first filtering subunit works in coordination with the first voltage regulating subunit, and the second filtering subunit works in coordination with the second voltage regulating subunit, and the coordinated work includes filtering harmonics greater than or equal to a target frequency in the AC power connected through the grid side interface, and the target frequency is greater than or equal to the smaller switching frequency of the switching frequency of the first active switch subunit and the switching frequency of the second active switch subunit.

7. The single-stage isolated AC-DC converter according to claim 6, characterized in that: The first voltage regulating subunit includes: at least one first capacitor, the positive end of the first capacitor is connected to the positive end of the grid-side interface, and the negative end of the first capacitor is connected to the second grid voltage regulating unit and the active clamping control unit.

8. The single-stage isolated AC-DC converter according to claim 6, characterized in that: The second grid voltage regulation subunit includes: at least one second capacitor, the positive end of the second capacitor is connected to the negative end of the first capacitor and the active clamping control unit, and the negative end of the second capacitor is connected to the negative end of the grid side interface.

9. The single-stage isolated AC-DC converter according to any one of claims 1 to 8, characterized in that: It also includes: an output voltage frequency conversion control unit, which is connected to the output voltage regulation unit and the active clamping control unit and is used to regulate the output voltage of the output voltage regulation unit by controlling the active clamping control unit.

10. The single-stage isolated AC-DC converter according to claim 9, characterized in that: Also includes: An overvoltage and undervoltage protection circuit is connected to the grid side interface and the output voltage frequency conversion control unit, and is used to control the use status of the output voltage frequency conversion control unit according to the grid voltage.

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