Bidirectional AC / DC conversion circuit

Abstract

The utility model relates to a bidirectional AC / DC conversion circuit, which comprises a battery, a first bidirectional DC conversion circuit, a second bidirectional DC conversion circuit, a first bus capacitor, a second bus capacitor and an inverter circuit, the high-voltage side of the first bidirectional DC conversion circuit is connected with the first bus capacitor in parallel, the high-voltage side of the second bidirectional DC conversion circuit is connected with the second bus capacitor in parallel, the first bus capacitor is connected with the second bus capacitor in series, and the output ends of the first bus capacitor and the second bus capacitor are connected with the input end of the inverter circuit. And the output end of the inverter circuit is used for outputting an inverter signal. The secondary conversion circuit realizes power conversion of a traditional energy storage inverter, reduces the number of stages of the conversion circuit and the number of elements, and reduces the cost. And the soft switching resonance technology is adopted, so that higher efficiency is achieved, the power density of the whole machine is improved, and the product has higher market competitiveness.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photovoltaic new energy and battery energy storage, and in particular to a bidirectional AC-DC conversion circuit. BACKGROUND

[0002] The energy storage inverter can realize bidirectional conversion from the battery to AC. If the battery is low-voltage 48V and the AC is three-phase 400Vac, the conversion topology generally has three stages, including a first stage of open-loop LLC fixed boost ratio, a second stage of BUCK / BOOST for realizing closed-loop voltage regulation, and a third stage of three-level inverter for realizing DC-AC. In addition, the three-phase AC output has the problem of unbalanced power of each phase, i.e., unbalanced load, which may cause large fluctuations in the voltage of the bus capacitor in series connection, and thus a fourth stage of conversion, i.e., a voltage balance bridge circuit (including two switching tubes and an inductor) is added.

[0003] As can be seen from the above topology of the energy storage inverter, there are four stages in total, and both switching elements and magnetic elements are relatively large, which not only leads to high cost of the energy storage inverter, but also reduces the conversion efficiency from the battery to AC. SUMMARY

[0004] The embodiment of the present application provides a bidirectional AC-DC conversion circuit to solve the problem of the existing energy storage inverter requiring four-stage conversion circuit, which leads to many elements in the conversion circuit and high cost.

[0005] In order to achieve the above purpose, in an embodiment, a bidirectional AC-DC conversion circuit is provided, which comprises a battery, a first bidirectional DC conversion circuit, a second bidirectional DC conversion circuit, a first bus capacitor, a second bus capacitor, and an inverter circuit. The low-voltage side of the first bidirectional DC conversion circuit and the low-voltage side of the second bidirectional DC conversion circuit are connected to the battery end. The high-voltage side of the first bidirectional DC conversion circuit is connected in parallel with the first bus capacitor. The high-voltage side of the second bidirectional DC conversion circuit is connected in parallel with the second bus capacitor. The first bus capacitor and the second bus capacitor are connected in series. The output end of the first bus capacitor and the output end of the second bus capacitor are connected to the input end of the inverter circuit. The output end of the inverter circuit is used for outputting an inverter signal.

[0006] In an embodiment, the first bidirectional DC conversion circuit and the second bidirectional DC conversion circuit are both bidirectional low-voltage isolation conversion circuits,

[0007] The first bidirectional DC conversion circuit comprises a first low-voltage side half-bridge circuit, a first isolation transformer and a first high-voltage side half-bridge circuit, the input end of the first low-voltage side half-bridge circuit is connected with the battery, the output end of the first low-voltage side half-bridge circuit is connected with the input end of the first isolation transformer, the output end of the first isolation transformer is connected with the input end of the first high-voltage side half-bridge circuit, and the output end of the first high-voltage side half-bridge circuit is connected with the first bus capacitor in parallel.

[0008] The second bidirectional DC conversion circuit comprises a second low-voltage side half-bridge circuit, a second isolation transformer and a second high-voltage side half-bridge circuit, the input end of the second low-voltage side half-bridge circuit is connected with the battery, the output end of the second low-voltage side half-bridge circuit is connected with the input end of the second isolation transformer, the output end of the second isolation transformer is connected with the input end of the second high-voltage side half-bridge circuit, and the output end of the second high-voltage side half-bridge circuit is connected with the second bus capacitor in parallel.

[0009] In an embodiment, the inverter circuit is a T-type three-level inverter circuit, which comprises a first-phase T-type inverter circuit, a second-phase T-type inverter circuit and a third-phase T-type inverter circuit, the input end of the first-phase T-type inverter circuit is connected with the output end of the first bus capacitor and the second bus capacitor, the first-phase T-type inverter circuit is connected in parallel with the second-phase T-type inverter circuit, and the second-phase T-type inverter circuit is connected in parallel with the third-phase T-type inverter circuit.

[0010] In an embodiment, the first bidirectional DC conversion circuit comprises a first low-voltage side full-bridge circuit, a first isolation transformer and a first high-voltage side full-bridge circuit, the input end of the first low-voltage side full-bridge circuit is connected with the battery, the output end of the first low-voltage side full-bridge circuit is connected with the input end of the first isolation transformer, the output end of the first isolation transformer is connected with the input end of the first high-voltage side full-bridge circuit, and the output end of the first high-voltage side full-bridge circuit is connected with the first bus capacitor in parallel.

[0011] The second bidirectional DC conversion circuit comprises a second low-voltage side full-bridge circuit, a second isolation transformer and a second high-voltage side full-bridge circuit, the input end of the second low-voltage side full-bridge circuit is connected with the battery, the output end of the second low-voltage side full-bridge circuit is connected with the input end of the second isolation transformer, the output end of the second isolation transformer is connected with the input end of the second high-voltage side half-bridge circuit, and the output end of the second high-voltage side half-bridge circuit is connected with the second bus capacitor in parallel.

[0012] In an embodiment, the first bidirectional DC conversion circuit comprises: a first low-voltage side full-bridge circuit, a first isolation transformer, a first high-voltage side half-bridge circuit, an input end of the first low-voltage side full-bridge circuit is connected with the battery, an output end of the first low-voltage side full-bridge circuit is connected with an input end of the first isolation transformer, an output end of the first isolation transformer is connected with an input end of the first high-voltage side half-bridge circuit, and an output end of the first high-voltage side half-bridge circuit is connected with the first bus capacitor in parallel.

[0013] The second bidirectional DC conversion circuit comprises: a second low-voltage side full-bridge circuit, a second isolation transformer, a second high-voltage side half-bridge circuit, an input end of the second low-voltage side full-bridge circuit is connected with the battery, an output end of the second low-voltage side half-bridge circuit is connected with an input end of the second isolation transformer, an output end of the second isolation transformer is connected with an input end of the second high-voltage side half-bridge circuit, and an output end of the second high-voltage side half-bridge circuit is connected with the second bus capacitor in parallel.

[0014] In an embodiment, the inverter circuit can also be a type I three-level inverter circuit or an ANPC three-level inverter circuit, wherein,

[0015] The type I three-level inverter circuit comprises: a first phase type I inverter circuit, a second phase type I inverter circuit, and a third phase type I inverter circuit, an input end of the first phase type I inverter circuit is connected with output ends of the first bus capacitor and the second bus capacitor, the first phase type I inverter circuit is connected in parallel with the second phase type I inverter circuit, and the second phase type I inverter circuit is connected in parallel with the third phase type I inverter circuit.

[0016] In an embodiment, the first low-voltage side half-bridge circuit comprises: a first resonant capacitor, a second resonant capacitor, a low-voltage side first switch tube, and a low-voltage side second switch tube, the first resonant capacitor and the second resonant capacitor are connected in series, the low-voltage side first switch tube and the low-voltage side second switch tube are connected in series, and the series-connected first resonant capacitor and second resonant capacitor are connected in parallel with the series-connected low-voltage side first switch tube and low-voltage side second switch tube.

[0017] The first high-voltage side half-bridge circuit comprises: a fifth resonant capacitor, a sixth resonant capacitor, a high-voltage side first switch tube, and a high-voltage side second switch tube, the high-voltage side first switch tube and the high-voltage side second switch tube are connected in series, the fifth resonant capacitor and the sixth resonant capacitor are connected in series, and the series-connected high-voltage side first switch tube and high-voltage side second switch tube are connected in parallel with the series-connected fifth resonant capacitor and sixth resonant capacitor.

[0018] The first isolation transformer comprises: a low-voltage side, a first resonant inductor, a second resonant inductor, a high-voltage side, an input end of the low-voltage side is connected to the first low-voltage side half-bridge circuit, the first resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the first high-voltage side half-bridge circuit in series with the second resonant inductor.

[0019] The second low-voltage side half-bridge circuit comprises: a third resonant capacitor, a fourth resonant capacitor, a low-voltage side third switch tube and a low-voltage side fourth switch tube, the third resonant capacitor is connected in series with the fourth resonant capacitor, and the low-voltage side third switch tube is connected in series with the low-voltage side fourth switch tube; and the third resonant capacitor and the fourth resonant capacitor connected in series are connected in parallel with the low-voltage side third switch tube and the low-voltage side fourth switch tube connected in series.

[0020] The second high-voltage side half-bridge circuit comprises: a seventh resonant capacitor, an eighth resonant capacitor, a high-voltage side third switch tube and a high-voltage side fourth switch tube, the high-voltage side third switch tube is connected in series with the high-voltage side fourth switch tube, the seventh resonant capacitor is connected in series with the eighth resonant capacitor, and the high-voltage side third switch tube and the high-voltage side fourth switch tube connected in series are connected in parallel with the seventh resonant capacitor and the eighth resonant capacitor connected in series.

[0021] The second isolation transformer comprises: a low-voltage end, a third resonant inductor, a fourth resonant inductor, a high-voltage side, an input end of the low-voltage end is connected to the second low-voltage side half-bridge circuit, the third resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the second high-voltage side half-bridge circuit in series with the fourth resonant inductor.

[0022] In an embodiment, the first low-voltage side full-bridge circuit comprises: a low-voltage side first switch tube, a low-voltage side second switch tube, a low-voltage side fifth switch tube and a low-voltage side sixth switch tube, the low-voltage side first switch tube is connected in series with the low-voltage side second switch tube, the low-voltage side fifth switch tube is connected in series with the low-voltage side sixth switch tube, and the low-voltage side first switch tube and the low-voltage side second switch tube connected in series are connected in parallel with the low-voltage side fifth switch tube and the low-voltage side sixth switch tube connected in series.

[0023] The first high-voltage side full-bridge circuit comprises: a high-voltage side first switch tube, a high-voltage side second switch tube, a high-voltage side fifth switch tube, a high-voltage side sixth switch tube and a second capacitor, the high-voltage side first switch tube is connected in series with the high-voltage side second switch tube, the high-voltage side fifth switch tube is connected in series with the high-voltage side sixth switch tube, the high-voltage side first switch tube and the high-voltage side second switch tube connected in series are connected in parallel with the high-voltage side fifth switch tube and the high-voltage side sixth switch tube connected in series, and the high-voltage side first switch tube and the high-voltage side second switch tube connected in parallel are connected in parallel with the second capacitor.

[0024] The first isolation transformer comprises: a low-voltage side, a first resonant capacitor, a first resonant inductor, a second resonant inductor, a third resonant capacitor, a high-voltage side, the low-voltage side is connected to the first low-voltage side full-bridge circuit in series after being connected with the first resonant capacitor, the first resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the first high-voltage side full-bridge circuit in series after being connected with the second resonant inductor and the third resonant capacitor.

[0025] The second low-voltage side full-bridge circuit comprises: a low-voltage side third switch tube, a low-voltage side fourth switch tube, a low-voltage side seventh switch tube and a low-voltage side eighth switch tube, the low-voltage side third switch tube is connected in series with the low-voltage side fourth switch tube, the low-voltage side seventh switch tube is connected in series with the low-voltage side eighth switch tube, and the low-voltage side third switch tube and the low-voltage side fourth switch tube connected in series are connected in parallel with the low-voltage side seventh switch tube and the low-voltage side eighth switch tube connected in series.

[0026] The second high-voltage side full-bridge circuit comprises: a high-voltage side third switch tube, a high-voltage side fourth switch tube, a high-voltage side seventh switch tube, a high-voltage side eighth switch tube and a third capacitor, the high-voltage side third switch tube is connected in series with the high-voltage side fourth switch tube, the high-voltage side seventh switch tube is connected in series with the high-voltage side eighth switch tube, the high-voltage side third switch tube and the high-voltage side fourth switch tube connected in series are connected in parallel with the high-voltage side seventh switch tube and the high-voltage side eighth switch tube connected in series, and the high-voltage side third switch tube and the high-voltage side fourth switch tube connected in parallel are connected in parallel with the third capacitor.

[0027] The second isolation transformer comprises: a low-voltage end, a second resonant capacitor, a third resonant inductor, a fourth resonant inductor, a fourth resonant capacitor and a high-voltage side, the input end of the low-voltage side is connected to the second low-voltage side full-bridge circuit in series after being connected with the second resonant capacitor, the third resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the second high-voltage side full-bridge circuit in series after being connected with the fourth resonant inductor and the fourth resonant capacitor.

[0028] In an embodiment, the first low-voltage side full-bridge circuit comprises: a low-voltage side first switch tube, a low-voltage side second switch tube, a low-voltage side fifth switch tube and a low-voltage side sixth switch tube, the low-voltage side first switch tube is connected in series with the low-voltage side second switch tube, the low-voltage side fifth switch tube is connected in series with the low-voltage side sixth switch tube, and the low-voltage side first switch tube and the low-voltage side second switch tube connected in series are connected in parallel with the low-voltage side fifth switch tube and the low-voltage side sixth switch tube connected in series.

[0029] The first high-voltage side half-bridge circuit comprises: a fifth resonant capacitor, a sixth resonant capacitor, a high-voltage side first switch tube and a high-voltage side second switch tube, the high-voltage side first switch tube is connected in series with the high-voltage side second switch tube, the fifth resonant capacitor is connected in series with the sixth resonant capacitor, and the high-voltage side first switch tube and the high-voltage side second switch tube connected in series are connected in parallel with the fifth resonant capacitor and the sixth resonant capacitor connected in series.

[0030] The first isolation transformer comprises a low-voltage side, a first resonant capacitor, a high-voltage side, a first resonant inductor and a second resonant inductor, the low-voltage side is connected to the first low-voltage side full-bridge circuit in series after being connected with the first resonant capacitor, the first resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the first high-voltage side half-bridge circuit in series after being connected with the second resonant inductor.

[0031] The second low-voltage side full-bridge circuit comprises a low-voltage side third switch tube, a low-voltage side fourth switch tube, a low-voltage side seventh switch tube and a low-voltage side eighth switch tube, the low-voltage side third switch tube is connected in series with the low-voltage side fourth switch tube, the low-voltage side seventh switch tube is connected in series with the low-voltage side eighth switch tube, and the low-voltage side third switch tube and the low-voltage side fourth switch tube connected in series are connected in parallel with the low-voltage side seventh switch tube and the low-voltage side eighth switch tube connected in series.

[0032] The second high-voltage side half-bridge circuit comprises a seventh resonant capacitor, an eighth resonant capacitor, a high-voltage side third switch tube and a high-voltage side fourth switch tube, the high-voltage side third switch tube is connected in series with the high-voltage side fourth switch tube, the seventh resonant capacitor is connected in series with the eighth resonant capacitor, and the high-voltage side third switch tube and the high-voltage side fourth switch tube connected in series are connected in parallel with the seventh resonant capacitor and the eighth resonant capacitor connected in series.

[0033] The second isolation transformer comprises a low-voltage side, a second resonant capacitor, a high-voltage side, a third resonant inductor and a fourth resonant inductor, the input end of the low-voltage side is connected to the second low-voltage side full-bridge circuit in series after being connected with the second resonant capacitor, the third resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the second high-voltage side half-bridge circuit in series after being connected with the fourth resonant inductor.

[0034] In an embodiment, the first bidirectional direct current conversion circuit and the second bidirectional direct current conversion circuit are combined to form a first stage of the bidirectional alternating current-direct current conversion circuit, and the first bus capacitor, the second bus capacitor and the inverter circuit are combined to form a second stage of the bidirectional alternating current-direct current conversion circuit.

[0035] The bidirectional alternating current-direct current conversion circuit adopts a two-stage conversion circuit to realize power conversion of a three-phase energy storage inverter with a low-voltage battery input, the number of stages of the conversion circuit is reduced, the number of switching elements and magnetic elements is reduced, the switching elements of the bidirectional alternating current-direct current conversion circuit are all high-voltage elements, the driving circuit of each switching element and the voltage and current sampling circuit are reduced, the soft switching resonance technology is adopted to realize zero-voltage turn-on and zero-current turn-off, the bidirectional alternating current-direct current conversion circuit has higher efficiency and better EMC performance, the power density of the whole machine is improved, and the product has more market competitiveness. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the description of the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some of the embodiments of the present application, and all other drawings obtained by those skilled in the art without creative labor on the basis of these drawings also belong to the scope of protection of the present application.

[0037] Figure 1 is a schematic diagram of a bidirectional AC-DC conversion circuit of an embodiment of the present application;

[0038] Figure 2 is a T-type three-level inverter circuit diagram in an embodiment of the present application;

[0039] Figure 3 is a first-phase circuit diagram in a T-type three-level inverter circuit in an embodiment of the present application;

[0040] Figure 4 is a circuit diagram in which the inverter circuit is an I-type three-level inverter circuit in an embodiment of the present application;

[0041] Figure 5 is a schematic diagram in which the low-voltage side and the high-voltage side are both half-bridge circuits in an embodiment of the present application;

[0042] Figure 6 is a schematic diagram of current flow in the first stage of the discharging upper half cycle in an embodiment of the present application;

[0043] Figure 7 is a schematic diagram of current flow in the second stage of the discharging upper half cycle in an embodiment of the present application;

[0044] Figure 8 is a schematic diagram in which the low-voltage side and the high-voltage side are both full-bridge circuits in an embodiment of the present application;

[0045] Figure 9 is a schematic diagram in which the low-voltage side is a full-bridge circuit and the high-voltage side is a half-bridge circuit in an embodiment of the present application.

[0046] Explanation of reference numerals: 1, first bidirectional DC conversion circuit, 2, second bidirectional DC conversion circuit, 3, inverter circuit. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, and not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor also belong to the scope of protection of the present application.

[0048] It is to be understood that the application can assume various alternative embodiments, and that it is not limited to what is described in the specification. Rather, the specific examples of embodiment disclosed herein are illustrative of various embodiments of the present application. Thus, the scope of the present application should not be limited to the specific examples of embodiment described herein, but should be given the broadest interpretation of the appended claims possible in view of the specification as a whole.

[0049] It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on or connected to the other element or layer or intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element or layer, there are no intervening elements or layers present. It will also be understood that, when a term is used herein to describe a feature, it is intended to encompass both the feature and the absence of the feature. It will be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present application.

[0050] Spatially relative terms, such as "beneath", "below", "lower", "under", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. For example, if a device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0051] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0052] For a thorough understanding of the application, detailed descriptions will be given in the following description and specific embodiments will be illustrated to explain the technical solutions of the application. The preferred embodiments of the application are described in detail as follows. However, the application can have other embodiments in addition to these detailed descriptions.

[0053] In an embodiment, a bidirectional AC / DC conversion circuit is provided, comprising: a battery, a first bidirectional DC conversion circuit, a second bidirectional DC conversion circuit, a first bus capacitor, a second bus capacitor, an inverter circuit, the low-voltage side of the first bidirectional DC conversion circuit and the low-voltage side of the second bidirectional DC conversion circuit are connected to the battery end, the high-voltage side of the first bidirectional DC conversion circuit is connected in parallel with the first bus capacitor, the high-voltage side of the second bidirectional DC conversion circuit is connected in parallel with the second bus capacitor, the first bus capacitor and the second bus capacitor are connected in series, the output end of the first bus capacitor and the output end of the second bus capacitor are connected to the input end of the inverter circuit, and the output end of the inverter circuit is used to output an inverter signal.

[0054] In an embodiment, the first bidirectional DC conversion circuit and the second bidirectional DC conversion circuit are bidirectional low-voltage isolation conversion circuits. Figure 1 As shown in the figure, the original four-stage conversion circuit is replaced by the first bidirectional DC conversion circuit 1 and the second bidirectional DC conversion circuit 2, the battery charges and discharges the first bus capacitor C1 and the second bus capacitor C2 through the first bidirectional DC conversion circuit 1 and the second bidirectional DC conversion circuit 2 respectively, and the low-voltage voltage is boosted and converted, realizing the open-loop fixed boost ratio function of the first stage of the original four-stage energy storage inverter. At the same time, the voltage of the first bus capacitor C1 and the second bus capacitor C2 can also be adjusted respectively, realizing the closed-loop voltage regulation function of the second stage of the original four-stage energy storage inverter. The first bidirectional DC conversion circuit 1 and the second bidirectional DC conversion circuit 2 can also work alternately, which can reduce the current ripple value of the low-voltage battery and realize the voltage balance function of the fourth stage of the original four-stage energy storage inverter. In an embodiment, the first bidirectional DC conversion circuit and the second bidirectional DC conversion circuit are bidirectional low-voltage isolation conversion circuits. In an embodiment, the first bidirectional DC conversion circuit and the second bidirectional DC conversion circuit are bidirectional low-voltage isolation conversion circuits.

[0055] In an embodiment, the first bidirectional DC conversion circuit and the second bidirectional DC conversion circuit are bidirectional low-voltage isolation conversion circuits.

[0056] In an embodiment, the first bidirectional DC conversion circuit and the second bidirectional DC conversion circuit are bidirectional low-voltage isolation conversion circuits.

[0057] ​​The first bidirectional direct current conversion circuit comprises a first low-voltage side half-bridge circuit, a first isolation transformer and a first high-voltage side half-bridge circuit, the input end of the first low-voltage side half-bridge circuit is connected with the battery, the output end of the first low-voltage side half-bridge circuit is connected with the input end of the first isolation transformer, the output end of the first isolation transformer is connected with the input end of the first high-voltage side half-bridge circuit, and the output end of the first high-voltage side half-bridge circuit is connected with the first bus capacitor in parallel.

[0058] The second bidirectional direct current conversion circuit comprises a second low-voltage side half-bridge circuit, a second isolation transformer and a second high-voltage side half-bridge circuit, the input end of the second low-voltage side half-bridge circuit is connected with the battery, the output end of the second low-voltage side half-bridge circuit is connected with the input end of the second isolation transformer, the output end of the second isolation transformer is connected with the input end of the second high-voltage side half-bridge circuit, and the output end of the second high-voltage side half-bridge circuit is connected with the second bus capacitor in parallel.

[0059] The low-voltage isolation conversion circuit can effectively prevent mutual interference and influence of current, voltage and signal, avoid voltage impact, electromagnetic interference or signal distortion between different circuits and provide an additional safety barrier to protect equipment and personnel safety.

[0060] In the embodiment, the low-voltage isolation conversion circuit is used to process the signal, isolate the input signal and the output signal and convert the signal according to the circuit requirement to meet the requirement of the bidirectional AC / DC conversion circuit, the high-voltage side and the low-voltage side both adopt the half-bridge circuit, the structure is simple and compact, the occupied space is small, the number of used switching tubes is small, the cost is low, the switching elements used in the two bidirectional direct current conversion circuits are high-voltage elements, the element loss is reduced, the cost is reduced, the soft switching resonance technology is used to realize zero-voltage turn-on and zero-current turn-off, the bidirectional AC / DC conversion circuit has higher efficiency and better performance.

[0061] In an embodiment, the inverter circuit is a T-type three-level inverter circuit, which comprises a first-phase T-type inverter circuit, a second-phase T-type inverter circuit and a third-phase T-type inverter circuit, the input end of the first-phase T-type inverter circuit is connected with the output end of the first bus capacitor and the second bus capacitor, the first-phase T-type inverter circuit is connected in parallel with the second-phase T-type inverter circuit, and the second-phase T-type inverter circuit is connected in parallel with the third-phase T-type inverter circuit.

[0062] In the embodiment, the first bus capacitor and the second bus capacitor are connected in parallel with the first-phase T-type inverter circuit, the second-phase T-type inverter circuit and the third-phase T-type inverter circuit. Figure 2As shown, the T-type three-level inverter circuit can provide three different output levels, i.e. positive level, zero level and negative level. Such multi-level output helps better control the load voltage, reduce the resonant voltage, and improve the stability of the inverter circuit. Taking the first phase as an example, as shown in the figure, when the switch tube Figure 3 is turned on, is turned on, is turned off, is turned off, the output level is positive; when is turned off, is turned off, is turned on, is turned on, is turned off, the output level is zero; when is turned off, is turned off, is turned on, is turned on, the output level is negative. The positive and negative switching of the voltage is realized by setting the on and off of the switch tube, wherein the output phase voltage of each phase is , wherein θ= , θ is the frequency of the alternating current, t is the time, is the angular frequency, Mac is the modulation ratio of the alternating current, and different phase voltage values can be output by adjusting Mac.

[0063] The inverter circuit of the embodiment adopts the T-type three-level inverter circuit, so that the output voltage waveform is closer to the sine wave, which helps reduce the harmonic content and improve the quality of electric energy. Moreover, the switching device works under lower voltage stress under the same output voltage, reduces the conduction loss of the switching device, and improves the efficiency. The control strategy of the T-type three-level inverter circuit is simpler than that of some other multi-level topologies. By controlling the states of the two main switches and the two auxiliary switches, the level switching can be realized, so that the circuit design and implementation are more convenient.

[0064] In an embodiment, the first bidirectional DC conversion circuit can further include a first low-voltage side full-bridge circuit, a first isolation transformer, and a first high-voltage side full-bridge circuit. The input end of the first low-voltage side full-bridge circuit is connected to the battery. The output end of the first low-voltage side full-bridge circuit is connected to the input end of the first isolation transformer. The output end of the first isolation transformer is connected to the input end of the first high-voltage side full-bridge circuit. The output end of the first high-voltage side full-bridge circuit is connected in parallel to the first bus capacitor.

[0065] The second bidirectional DC conversion circuit can further include a second low-voltage side full-bridge circuit, a second isolation transformer, and a second high-voltage side half-bridge circuit, wherein an input end of the second low-voltage side full-bridge circuit is connected with the battery, an output end of the second low-voltage side full-bridge circuit is connected with an input end of the second isolation transformer, an output end of the second isolation transformer is connected with an input end of the second high-voltage side half-bridge circuit, and an output end of the second high-voltage side half-bridge circuit is connected with the second bus capacitor in parallel.

[0066] The high-voltage side and the low-voltage side of the bidirectional DC conversion circuit both adopt the full-bridge circuit, which can effectively control the current flow direction, reduce energy loss, quickly adjust the operation state, and has a large output power range, and is suitable for high-power and low-voltage boosting working scenarios.

[0067] The first bidirectional DC conversion circuit and the second bidirectional DC conversion circuit of the embodiment adopt the full-bridge circuit structure, have high working efficiency, can effectively reduce energy loss, can realize positive and negative polarity switching of the power supply, can flexibly control voltage and current, are suitable for circuits with bidirectional current control, have good current and heat management capabilities, can adapt to high-power and high-frequency applications, improve the reliability of the circuit, have certain anti-unbalance capability, and have a large power range.

[0068] In an embodiment, the first bidirectional DC conversion circuit can further include a first low-voltage side full-bridge circuit, a first isolation transformer, and a first high-voltage side half-bridge circuit, wherein an input end of the first low-voltage side full-bridge circuit is connected with the battery, an output end of the first low-voltage side full-bridge circuit is connected with an input end of the first isolation transformer, an output end of the first isolation transformer is connected with an input end of the first high-voltage side half-bridge circuit, and an output end of the first high-voltage side half-bridge circuit is connected with the first bus capacitor in parallel.

[0069] The second bidirectional DC conversion circuit can further include a second low-voltage side full-bridge circuit, a second isolation transformer, and a second high-voltage side half-bridge circuit, wherein an input end of the second low-voltage side full-bridge circuit is connected with the battery, an output end of the second low-voltage side half-bridge circuit is connected with an input end of the second isolation transformer, an output end of the second isolation transformer is connected with an input end of the second high-voltage side half-bridge circuit, and an output end of the second high-voltage side half-bridge circuit is connected with the second bus capacitor in parallel.

[0070] The first bidirectional DC conversion circuit and the second bidirectional DC conversion circuit of the embodiment adopt the full-bridge circuit structure, have high working efficiency, can effectively reduce energy loss, can realize positive and negative polarity switching of the power supply, can flexibly control voltage and current, are suitable for circuits with bidirectional current control, have good current and heat management capabilities, can adapt to high-power and high-frequency applications, improve the reliability of the circuit, have certain anti-unbalance capability, and have a large power range.

[0071] In one embodiment, the inverter circuit may also be a type I three-level inverter circuit or an ANPC three-level inverter circuit.

[0072] The type I three-level inverter circuit includes: a first-phase type I inverter circuit, a second-phase type I inverter circuit, and a third-phase type I inverter circuit. The input terminal of the first-phase type I inverter circuit is connected to the output terminals of the first bus capacitor and the second bus capacitor. The first-phase type I inverter circuit and the second-phase type I inverter circuit are connected in parallel. The second-phase type I inverter circuit and the third-phase type I inverter circuit are connected in parallel.

[0073] Among them, such as Figure 4 The diagram illustrates the applicable scenario for a Type I three-level inverter circuit. Both the low-voltage and high-voltage sides of the first and second bidirectional DC-DC converters are half-bridge circuits. The output phase voltage of each phase in the Type I three-level inverter circuit remains constant. , where θ= θ is the frequency of the alternating current, and t is the time. ω is the angular frequency, and MAC is the AC modulation ratio. Adjusting MAC can output different phase voltage values, but the tube's withstand voltage is always half voltage, reducing switching losses by more than half, making it suitable for high-power inverter scenarios.

[0074] The inverter circuit in this embodiment can significantly increase the output voltage while the devices are subjected to the same voltage, making it more suitable for medium-voltage frequency converters. It effectively reduces the harmonic content of the output waveform, improves power quality, and meets the higher demands of power applications. The Type I three-level inverter circuit also provides a more flexible control strategy, which can be flexibly adjusted according to different load characteristics and operating conditions to optimize system performance.

[0075] In one embodiment, the first low-voltage side half-bridge circuit includes: a first resonant capacitor, a second resonant capacitor, a low-voltage side first switch, and a low-voltage side second switch. The first resonant capacitor and the second resonant capacitor are connected in series, the low-voltage side first switch and the low-voltage side second switch are connected in series, and the series-connected first resonant capacitor and the series-connected second resonant capacitor are connected in parallel with the series-connected low-voltage side first switch and the low-voltage side second switch.

[0076] The first high-voltage side half-bridge circuit includes: a fifth resonant capacitor, a sixth resonant capacitor, a first high-voltage side switch transistor, and a second high-voltage side switch transistor. The first high-voltage side switch transistor and the second high-voltage side switch transistor are connected in series. The fifth resonant capacitor and the sixth resonant capacitor are connected in series. The first high-voltage side switch transistor and the second high-voltage side switch transistor connected in series are connected in parallel with the fifth resonant capacitor and the sixth resonant capacitor connected in series.

[0077] The first isolation transformer comprises a low-voltage side, a first resonant inductor, a second resonant inductor, and a high-voltage side, an input end of the low-voltage side is connected to the first low-voltage side half-bridge circuit, the first resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the first high-voltage side half-bridge circuit in series with the second resonant inductor.

[0078] The second low-voltage side half-bridge circuit comprises a third resonant capacitor, a fourth resonant capacitor, a low-voltage side third switch tube, and a low-voltage side fourth switch tube, the third resonant capacitor is connected in series with the fourth resonant capacitor, the low-voltage side third switch tube is connected in series with the low-voltage side fourth switch tube, and the third resonant capacitor and the fourth resonant capacitor connected in series are connected in parallel with the low-voltage side third switch tube and the low-voltage side fourth switch tube connected in series.

[0079] The second high-voltage side half-bridge circuit comprises a seventh resonant capacitor, an eighth resonant capacitor, a high-voltage side third switch tube, and a high-voltage side fourth switch tube, the high-voltage side third switch tube is connected in series with the high-voltage side fourth switch tube, the seventh resonant capacitor is connected in series with the eighth resonant capacitor, and the high-voltage side third switch tube and the high-voltage side fourth switch tube connected in series are connected in parallel with the seventh resonant capacitor and the eighth resonant capacitor connected in series.

[0080] The second isolation transformer comprises a low-voltage end, a third resonant inductor, a fourth resonant inductor, and a high-voltage side, an input end of the low-voltage end is connected to the second low-voltage side half-bridge circuit, the third resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the second high-voltage side half-bridge circuit in series with the fourth resonant inductor.

[0081] In the embodiment, the topology structure of the energy storage inverter is the same during discharging and charging, and the operation principle is completely symmetrical. The specific circuit principle topology structure diagram is shown in FIG. 1. Figure 5 The first bidirectional direct current conversion circuit and the second bidirectional direct current conversion circuit are both half-bridge circuits, the low-voltage side is connected to the battery end, the high-voltage side is connected to the first bus capacitor and the second bus capacitor respectively and The inverter circuit is a T-shaped three-level inverter circuit, the input end of which is connected to the output end of the first bus capacitor and the second bus capacitor and After filtering by inductors , , and capacitors , , , an industrial frequency alternating current sine wave is output, and the two bidirectional direct current conversion circuits have the same resonant parameters Lm, Lr, and Cr, the resonant frequency , and the output voltage gain Where N is the transformer turns ratio, and M is the voltage turns ratio of the resonant network adjusted by changing the PWM operating frequency of the bidirectional DC-DC converter circuit.

[0082] In this embodiment, since the second stage is a common three-level inverter circuit, its working principle will not be described here; only the working principle of the first stage conversion will be introduced:

[0083] When the battery discharges, in the first stage of the first half of a PWM switching cycle, such as Figure 6 As shown, switches S1, Q1, S4, and Q4 are on, while switches S2, Q2, S3, and Q3 are off. At this time, the current in the first bidirectional DC-DC converter circuit flows through switch S1, the low-voltage side of the transformer, and the resonant capacitor. After passing through the transformer, the current flows through the resonant capacitor. , Switch Q1, first bus capacitor and resonant capacitor The current in the second bidirectional DC-DC converter circuit passes through the resonant capacitor. The current flows through the transformer's low-voltage side and the switching transistor S4, and then through the resonant capacitor after passing through the transformer. , Resonant capacitor Second bus capacitor and switching transistor Q4;

[0084] In the second phase of the first half-cycle, switches S2, Q2, S3, and Q3 are turned off, while switches S1, Q1, S4, and Q4 remain off. Since the resonant inductor current cannot change abruptly, the current direction of Lr remains unchanged, as shown in the diagram. Figure 7 As shown, the body diodes of S2 and S4 are conducting at this time, which provides the conditions for S2 and S4 to achieve zero-voltage turn-on. At the same time, the high-voltage side natural current drops to 0, achieving zero-current turn-off.

[0085] In the second half of the cycle, the switching transistors and current paths of the first and second bidirectional DC-DC converter circuits are exactly opposite. When the three-phase output load is unbalanced, the voltages of the upper and lower capacitors are not equal. By adjusting the PWM frequency of the upper and lower switching transistors and adjusting the voltage transformation ratio M, the voltage values ​​of the upper and lower bus capacitors can be adjusted.

[0086] In one embodiment, the first low-voltage side full-bridge circuit includes: a low-voltage side first switch, a low-voltage side second switch, a low-voltage side fifth switch, and a low-voltage side sixth switch. The low-voltage side first switch and the low-voltage side second switch are connected in series, the low-voltage side fifth switch and the low-voltage side sixth switch are connected in series, and the series-connected low-voltage side first switch and low-voltage side second switch are connected in parallel with the series-connected low-voltage side fifth switch and low-voltage side sixth switch.

[0087] The first high-voltage side full-bridge circuit includes: a high-voltage side first switch, a high-voltage side second switch, a high-voltage side fifth switch, a high-voltage side sixth switch, and a second capacitor. The high-voltage side first switch and the high-voltage side second switch are connected in series, the high-voltage side fifth switch and the high-voltage side sixth switch are connected in series, the series-connected high-voltage side first switch and high-voltage side second switch are connected in parallel with the series-connected high-voltage side fifth switch and sixth switch, and then connected in parallel with the second capacitor.

[0088] The first isolation transformer includes: a low-voltage side, a first resonant capacitor, a first resonant inductor, a second resonant inductor, a third resonant capacitor, and a high-voltage side. The low-voltage side is connected in series with the first resonant capacitor and then connected to the first low-voltage side full-bridge circuit. The first resonant inductor is connected in parallel with the high-voltage side. The high-voltage side is connected in series with the second resonant inductor and the third resonant capacitor and then connected to the second high-voltage side full-bridge circuit.

[0089] The second low-voltage side full-bridge circuit includes: a low-voltage side third switch, a low-voltage side fourth switch, a low-voltage side seventh switch, and a low-voltage side eighth switch. The low-voltage side third switch and the low-voltage side fourth switch are connected in series, the low-voltage side seventh switch and the low-voltage side eighth switch are connected in series, and the series-connected low-voltage side third switch and the low-voltage side fourth switch are connected in parallel with the series-connected low-voltage side seventh switch and the low-voltage side eighth switch.

[0090] The second high-voltage side full-bridge circuit includes: a high-voltage side third switch, a high-voltage side fourth switch, a high-voltage side seventh switch, a high-voltage side eighth switch, and a third capacitor. The high-voltage side third switch and the high-voltage side fourth switch are connected in series, the high-voltage side seventh switch and the high-voltage side eighth switch are connected in series, the series-connected high-voltage side third switch and the high-voltage side fourth switch are connected in parallel with the series-connected high-voltage side seventh switch and the high-voltage side eighth switch, and then connected in parallel with the third capacitor.

[0091] The second isolation transformer includes: a low-voltage side, a second resonant capacitor, a third resonant inductor, a fourth resonant inductor, and a fourth resonant capacitor; a high-voltage side, wherein the input terminal of the low-voltage side is connected in series with the second resonant capacitor and then connected to the second low-voltage side full-bridge circuit; the third resonant inductor is connected in parallel with the high-voltage side; and the high-voltage side is connected in series with the fourth resonant inductor and the fourth resonant capacitor and then connected to the second high-voltage side full-bridge circuit.

[0092] Among them, such as Figure 8 As shown, both the low-voltage side and high-voltage side of the first and second bidirectional DC-DC converters are full-bridge circuits, but the resonant capacitor value is twice that of the half-bridge circuit. The output voltage gain remains unchanged. The bidirectional AC-DC conversion circuit of the embodiment is suitable for a high-power and low-voltage boosting scenario.

[0093] In an embodiment, the first low-voltage side full-bridge circuit comprises a low-voltage side first switch tube, a low-voltage side second switch tube, a low-voltage side fifth switch tube, and a low-voltage side sixth switch tube, the low-voltage side first switch tube and the low-voltage side second switch tube are connected in series, the low-voltage side fifth switch tube and the low-voltage side sixth switch tube are connected in series, and the series-connected low-voltage side first switch tube and the low-voltage side second switch tube are connected in parallel with the series-connected low-voltage side fifth switch tube and the low-voltage side sixth switch tube.

[0094] The first high-voltage side half-bridge circuit comprises a fifth resonant capacitor, a sixth resonant capacitor, a high-voltage side first switch tube, and a high-voltage side second switch tube, the high-voltage side first switch tube and the high-voltage side second switch tube are connected in series, the fifth resonant capacitor and the sixth resonant capacitor are connected in series, and the series-connected high-voltage side first switch tube and the high-voltage side second switch tube are connected in parallel with the series-connected fifth resonant capacitor and the sixth resonant capacitor.

[0095] The first isolation transformer comprises a low-voltage side, a first resonant capacitor, a high-voltage side, a first resonant inductor, and a second resonant inductor, the low-voltage side and the first resonant capacitor are connected in series and then connected to the first low-voltage side full-bridge circuit, the first resonant inductor and the high-voltage side are connected in parallel, and the high-voltage side and the second resonant inductor are connected in series and then connected to the first high-voltage side half-bridge circuit.

[0096] The second low-voltage side full-bridge circuit comprises a low-voltage side third switch tube, a low-voltage side fourth switch tube, a low-voltage side seventh switch tube, and a low-voltage side eighth switch tube, the low-voltage side third switch tube and the low-voltage side fourth switch tube are connected in series, the low-voltage side seventh switch tube and the low-voltage side eighth switch tube are connected in series, and the series-connected low-voltage side third switch tube and the low-voltage side fourth switch tube are connected in parallel with the series-connected low-voltage side seventh switch tube and the low-voltage side eighth switch tube.

[0097] The second high-voltage side half-bridge circuit comprises a seventh resonant capacitor, an eighth resonant capacitor, a high-voltage side third switch tube, and a high-voltage side fourth switch tube, the high-voltage side third switch tube and the high-voltage side fourth switch tube are connected in series, the seventh resonant capacitor and the eighth resonant capacitor are connected in series, and the series-connected high-voltage side third switch tube and the high-voltage side fourth switch tube are connected in parallel with the series-connected seventh resonant capacitor and the eighth resonant capacitor.

[0098] The second isolation transformer comprises a low-voltage side, a second resonant capacitor, a high-voltage side, a third resonant inductor, and a fourth resonant inductor, an input end of the low-voltage side and the second resonant capacitor are connected in series and then connected to the second low-voltage side full-bridge circuit, the third resonant inductor and the high-voltage side are connected in parallel, and the high-voltage side and the fourth resonant inductor are connected in series and then connected to the second high-voltage side half-bridge circuit.

[0099] In the above embodiment, the first bidirectional AC-DC conversion circuit and the second bidirectional DC-DC conversion circuit are combined to form a first stage of the bidirectional AC-DC conversion circuit, and the first bus capacitor, the second bus capacitor and the inverter circuit are combined to form a second stage of the bidirectional AC-DC conversion circuit. Figure 9 As shown in the above embodiment, the low-voltage side of the first bidirectional AC-DC conversion circuit and the low-voltage side of the second bidirectional DC-DC conversion circuit are full-bridge circuits, and the high-voltage side of the first bidirectional AC-DC conversion circuit and the high-voltage side of the second bidirectional DC-DC conversion circuit are half-bridge circuits. The circuit is suitable for high-power and high-voltage scenarios.

[0100] In an embodiment, the first bidirectional DC-DC conversion circuit and the second bidirectional DC-DC conversion circuit are combined to form a first stage of the bidirectional AC-DC conversion circuit, and the first bus capacitor, the second bus capacitor and the inverter circuit are combined to form a second stage of the bidirectional AC-DC conversion circuit.

[0101] In the above embodiment, the bidirectional AC-DC conversion circuit of the second stage can complete the power conversion of the traditional four-stage energy storage inverter, the first stage is two bidirectional DC-DC conversion circuits, the second stage is an inverter circuit and two bus capacitors, and the two bidirectional DC-DC conversion circuits of the first stage use soft switching resonance technology to realize zero-voltage turn-on and zero-current turn-off, which has higher efficiency and better electromagnetic compatibility compared with traditional hard switching current.

[0102] In the above embodiment, the first stage of the bidirectional AC-DC conversion circuit can realize the low-voltage boosting function of the first stage, the voltage regulating function of the second stage and the voltage balancing function of the fourth stage of the traditional four-stage energy storage inverter, and the second stage realizes the inversion from DC to AC, which reduces the number of circuit stages and components, reduces the cost and improves the conversion efficiency.

[0103] The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A bidirectional AC-DC conversion circuit, characterized by comprising: The application relates to a bidirectional AC-DC conversion circuit, which comprises a battery, a first bidirectional DC conversion circuit, a second bidirectional DC conversion circuit, a first bus capacitor, a second bus capacitor and an inverter circuit, wherein the low-voltage side of the first bidirectional DC conversion circuit and the low-voltage side of the second bidirectional DC conversion circuit are connected to the battery end, the high-voltage side of the first bidirectional DC conversion circuit is connected in parallel with the first bus capacitor, the high-voltage side of the second bidirectional DC conversion circuit is connected in parallel with the second bus capacitor, the first bus capacitor and the second bus capacitor are connected in series, the output end of the first bus capacitor and the output end of the second bus capacitor are connected to the input end of the inverter circuit, and the output end of the inverter circuit is used for outputting an inverter signal. The first bidirectional DC conversion circuit and the second bidirectional DC conversion circuit are both bidirectional low-voltage isolation conversion circuits, 2. The bidirectional AC-DC conversion circuit of claim 1, wherein, The first bidirectional DC conversion circuit comprises a first low-voltage side half-bridge circuit, a first isolation transformer and a first high-voltage side half-bridge circuit, the input end of the first low-voltage side half-bridge circuit is connected to the battery, the output end of the first low-voltage side half-bridge circuit is connected to the input end of the first isolation transformer, the output end of the first isolation transformer is connected to the input end of the first high-voltage side half-bridge circuit, and the output end of the first high-voltage side half-bridge circuit is connected in parallel with the first bus capacitor; The second bidirectional DC conversion circuit comprises a second low-voltage side half-bridge circuit, a second isolation transformer and a second high-voltage side half-bridge circuit, the input end of the second low-voltage side half-bridge circuit is connected to the battery, the output end of the second low-voltage side half-bridge circuit is connected to the input end of the second isolation transformer, the output end of the second isolation transformer is connected to the input end of the second high-voltage side half-bridge circuit, and the output end of the second high-voltage side half-bridge circuit is connected in parallel with the second bus capacitor. The inverter circuit is a T-type three-level inverter circuit, which comprises a first-phase T-type inverter circuit, a second-phase T-type inverter circuit and a third-phase T-type inverter circuit, the input end of the first-phase T-type inverter circuit is connected to the output end of the first bus capacitor and the output end of the second bus capacitor, the first-phase T-type inverter circuit is connected in parallel with the second-phase T-type inverter circuit, and the second-phase T-type inverter circuit is connected in parallel with the third-phase T-type inverter circuit.

3. The bidirectional AC-DC conversion circuit of claim 1, wherein, 4. The bidirectional AC-DC conversion circuit according to claim 2, wherein the first bidirectional DC conversion circuit further comprises a first low-voltage side full-bridge circuit, a first isolation transformer and a first high-voltage side full-bridge circuit, the input end of the first low-voltage side full-bridge circuit is connected to the battery, the output end of the first low-voltage side full-bridge circuit is connected to the input end of the first isolation transformer, the output end of the first isolation transformer is connected to the input end of the first high-voltage side full-bridge circuit, and the output end of the first high-voltage side full-bridge circuit is connected in parallel with the first bus capacitor. ​ ​ The second bidirectional DC conversion circuit further comprises a second low-voltage side full-bridge circuit, a second isolation transformer, and a second high-voltage side half-bridge circuit, an input end of the second low-voltage side full-bridge circuit is connected with the battery, an output end of the second low-voltage side full-bridge circuit is connected with an input end of the second isolation transformer, an output end of the second isolation transformer is connected with an input end of the second high-voltage side half-bridge circuit, and an output end of the second high-voltage side half-bridge circuit is connected with the second bus capacitor in parallel.

5. The bidirectional AC-DC conversion circuit of claim 2, wherein, The first bidirectional DC conversion circuit further comprises a first low-voltage side full-bridge circuit, a first isolation transformer, and a first high-voltage side half-bridge circuit, an input end of the first low-voltage side full-bridge circuit is connected with the battery, an output end of the first low-voltage side full-bridge circuit is connected with an input end of the first isolation transformer, an output end of the first isolation transformer is connected with an input end of the first high-voltage side half-bridge circuit, and an output end of the first high-voltage side half-bridge circuit is connected with the first bus capacitor in parallel. The second bidirectional DC conversion circuit further comprises a second low-voltage side full-bridge circuit, a second isolation transformer, and a second high-voltage side half-bridge circuit, an input end of the second low-voltage side full-bridge circuit is connected with the battery, an output end of the second low-voltage side half-bridge circuit is connected with an input end of the second isolation transformer, an output end of the second isolation transformer is connected with an input end of the second high-voltage side half-bridge circuit, and an output end of the second high-voltage side half-bridge circuit is connected with the second bus capacitor in parallel.

6. The bidirectional AC-DC conversion circuit of claim 1, wherein: The inverter circuit can also be an I-type three-level inverter circuit or an ANPC three-level inverter circuit, The I-type three-level inverter circuit comprises a first-phase I-type inverter circuit, a second-phase I-type inverter circuit, and a third-phase I-type inverter circuit, an input end of the first-phase I-type inverter circuit is connected with output ends of the first bus capacitor and the second bus capacitor, the first-phase I-type inverter circuit is connected in parallel with the second-phase I-type inverter circuit, and the second-phase I-type inverter circuit is connected in parallel with the third-phase I-type inverter circuit.

7. The bidirectional AC-DC conversion circuit of claim 2, wherein, The first low-voltage side half-bridge circuit comprises a first resonant capacitor, a second resonant capacitor, a low-voltage side first switch tube, and a low-voltage side second switch tube, the first resonant capacitor and the second resonant capacitor are connected in series, the low-voltage side first switch tube and the low-voltage side second switch tube are connected in series, and the series-connected first resonant capacitor and second resonant capacitor are connected in parallel with the series-connected low-voltage side first switch tube and low-voltage side second switch tube; The first high-voltage side half-bridge circuit comprises a fifth resonant capacitor, a sixth resonant capacitor, a high-voltage side first switch tube, and a high-voltage side second switch tube, the high-voltage side first switch tube and the high-voltage side second switch tube are connected in series, the fifth resonant capacitor and the sixth resonant capacitor are connected in series, and the series-connected high-voltage side first switch tube and high-voltage side second switch tube are connected in parallel with the series-connected fifth resonant capacitor and sixth resonant capacitor; The first isolation transformer comprises: a low-voltage side, a first resonant inductor, a second resonant inductor, a high-voltage side, an input end of the low-voltage side is connected to the first low-voltage side half-bridge circuit, the first resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the first high-voltage side half-bridge circuit in series with the second resonant inductor; The second low-voltage side half-bridge circuit comprises: a third resonant capacitor, a fourth resonant capacitor, a low-voltage side third switch tube and a low-voltage side fourth switch tube, the third resonant capacitor is connected in series with the fourth resonant capacitor, and the low-voltage side third switch tube is connected in series with the low-voltage side fourth switch tube; and the third resonant capacitor and the fourth resonant capacitor connected in series are connected in parallel with the low-voltage side third switch tube and the low-voltage side fourth switch tube connected in series. The second high-voltage side half-bridge circuit comprises: a seventh resonant capacitor, an eighth resonant capacitor, a high-voltage side third switch tube and a high-voltage side fourth switch tube, the high-voltage side third switch tube is connected in series with the high-voltage side fourth switch tube, the seventh resonant capacitor is connected in series with the eighth resonant capacitor, and the high-voltage side third switch tube and the high-voltage side fourth switch tube connected in series are connected in parallel with the seventh resonant capacitor and the eighth resonant capacitor connected in series. The second isolation transformer comprises: a low-voltage end, a third resonant inductor, a fourth resonant inductor, a high-voltage side, an input end of the low-voltage end is connected to the second low-voltage side half-bridge circuit, the third resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the second high-voltage side half-bridge circuit in series with the fourth resonant inductor.

8. The bidirectional AC-DC conversion circuit of claim 4, wherein, The first low-voltage side full-bridge circuit comprises: a low-voltage side first switch tube, a low-voltage side second switch tube, a low-voltage side fifth switch tube and a low-voltage side sixth switch tube, the low-voltage side first switch tube is connected in series with the low-voltage side second switch tube, the low-voltage side fifth switch tube is connected in series with the low-voltage side sixth switch tube, and the low-voltage side first switch tube and the low-voltage side second switch tube connected in series are connected in parallel with the low-voltage side fifth switch tube and the low-voltage side sixth switch tube connected in series. The first high-voltage side full-bridge circuit comprises: a high-voltage side first switch tube, a high-voltage side second switch tube, a high-voltage side fifth switch tube, a high-voltage side sixth switch tube and a second capacitor, the high-voltage side first switch tube is connected in series with the high-voltage side second switch tube, the high-voltage side fifth switch tube is connected in series with the high-voltage side sixth switch tube, the high-voltage side first switch tube and the high-voltage side second switch tube connected in series are connected in parallel with the high-voltage side fifth switch tube and the high-voltage side sixth switch tube connected in series, and the high-voltage side first switch tube and the high-voltage side second switch tube connected in parallel are connected in parallel with the second capacitor. The first isolation transformer comprises: a low-voltage side, a first resonant capacitor, a first resonant inductor, a second resonant inductor, a third resonant capacitor and a high-voltage side, the low-voltage side is connected to the first low-voltage side full-bridge circuit in series with the first resonant capacitor, the first resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the first high-voltage side full-bridge circuit in series with the second resonant inductor and the third resonant capacitor. The second low-voltage side full-bridge circuit comprises a low-voltage side third switch tube, a low-voltage side fourth switch tube, a low-voltage side seventh switch tube and a low-voltage side eighth switch tube, the low-voltage side third switch tube is connected in series with the low-voltage side fourth switch tube, the low-voltage side seventh switch tube is connected in series with the low-voltage side eighth switch tube, and the low-voltage side third switch tube and the low-voltage side fourth switch tube connected in series are connected in parallel with the low-voltage side seventh switch tube and the low-voltage side eighth switch tube connected in series; The second high-voltage side full-bridge circuit comprises a high-voltage side third switch tube, a high-voltage side fourth switch tube, a high-voltage side seventh switch tube, a high-voltage side eighth switch tube and a third capacitor, the high-voltage side third switch tube is connected in series with the high-voltage side fourth switch tube, the high-voltage side seventh switch tube is connected in series with the high-voltage side eighth switch tube, the high-voltage side third switch tube and the high-voltage side fourth switch tube connected in series are connected in parallel with the high-voltage side seventh switch tube and the high-voltage side eighth switch tube connected in series, and the high-voltage side third switch tube and the high-voltage side fourth switch tube connected in parallel are connected in parallel with the third capacitor; The second isolation transformer comprises a low-voltage end, a second resonance capacitor, a third resonance inductor, a fourth resonance inductor, a fourth resonance capacitor and a high-voltage side, the input end of the low-voltage side is connected to the second low-voltage side full-bridge circuit in series with the second resonance capacitor, the third resonance inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the second high-voltage side full-bridge circuit in series with the fourth resonance inductor and the fourth resonance capacitor.

9. The bidirectional AC-DC conversion circuit of claim 5, wherein, The first low-voltage side full-bridge circuit comprises a low-voltage side first switch tube, a low-voltage side second switch tube, a low-voltage side fifth switch tube and a low-voltage side sixth switch tube, the low-voltage side first switch tube is connected in series with the low-voltage side second switch tube, the low-voltage side fifth switch tube is connected in series with the low-voltage side sixth switch tube, and the low-voltage side first switch tube and the low-voltage side second switch tube connected in series are connected in parallel with the low-voltage side fifth switch tube and the low-voltage side sixth switch tube connected in series; The first high-voltage side half-bridge circuit comprises a fifth resonance capacitor, a sixth resonance capacitor, a high-voltage side first switch tube and a high-voltage side second switch tube, the high-voltage side first switch tube is connected in series with the high-voltage side second switch tube, the fifth resonance capacitor is connected in series with the sixth resonance capacitor, and the high-voltage side first switch tube and the high-voltage side second switch tube connected in series are connected in parallel with the fifth resonance capacitor and the sixth resonance capacitor connected in series; The first isolation transformer comprises a low-voltage side, a first resonance capacitor, a high-voltage side, a first resonance inductor and a second resonance inductor, the low-voltage side is connected to the first low-voltage side full-bridge circuit in series with the first resonance capacitor, the first resonance inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the first high-voltage side half-bridge circuit in series with the second resonance inductor; The second low-voltage side full-bridge circuit comprises a low-voltage side third switch tube, a low-voltage side fourth switch tube, a low-voltage side seventh switch tube and a low-voltage side eighth switch tube, the low-voltage side third switch tube is connected in series with the low-voltage side fourth switch tube, the low-voltage side seventh switch tube is connected in series with the low-voltage side eighth switch tube, and the low-voltage side third switch tube and the low-voltage side fourth switch tube connected in series are connected in parallel with the low-voltage side seventh switch tube and the low-voltage side eighth switch tube connected in series; The second high-voltage side half-bridge circuit comprises a seventh resonant capacitor, an eighth resonant capacitor, a high-voltage side third switch tube, and a high-voltage side fourth switch tube, the high-voltage side third switch tube and the high-voltage side fourth switch tube are connected in series, the seventh resonant capacitor and the eighth resonant capacitor are connected in series, and the series-connected high-voltage side third switch tube and high-voltage side fourth switch tube are connected in parallel with the series-connected seventh resonant capacitor and eighth resonant capacitor; The second isolation transformer comprises a low-voltage side, a second resonant capacitor, a high-voltage side, a third resonant inductor, and a fourth resonant inductor, the input end of the low-voltage side is connected to the second low-voltage side full-bridge circuit after being connected in series with the second resonant capacitor, the third resonant inductor is connected in parallel with the high-voltage side, and the high-voltage side is connected to the second high-voltage side half-bridge circuit after being connected in series with the fourth resonant inductor.

10. The bidirectional AC-DC conversion circuit of claim 1, wherein, The first bidirectional direct current conversion circuit and the second bidirectional direct current conversion circuit constitute a first stage of the bidirectional alternating current-direct current conversion circuit, and the first bus capacitor, the second bus capacitor, and the inverter circuit constitute a second stage of the bidirectional alternating current-direct current conversion circuit.

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