Cascaded Multiport Converter and Three-Phase Medium-Voltage Input System

Abstract

The present application discloses a cascaded multi-port converter and a three-phase medium voltage input system. The input terminals of each modular unit are cascaded, with both cascaded ends serving as the input terminal ports of the cascaded multi-port converter. In the modular unit, the input terminals of each high-voltage conversion unit are cascaded, with both cascaded ends serving as the input terminal ports of the modular unit. The output terminals of each high-voltage conversion unit are respectively connected to the corresponding primary windings of each multi-winding transformer. As the output terminals of the modular unit, each secondary winding of each multi-winding transformer is respectively connected to the input terminal of a corresponding low-voltage rectifier unit. Multiple primary windings and multiple secondary windings are wound around the magnetic core of the multi-winding transformer, so that the windings of multiple high-voltage conversion units share the magnetic core. This reduces the number of multi-winding transformers in the cascaded multi-port converter and the number of low-voltage rectifier units accordingly, thereby reducing the volume, weight and cost of the cascaded multi-port converter.

Description

Technical Field

[0001] This application claims the priority of a Chinese patent application filed with the China National Intellectual Property Administration on September 30, 2020, with the application number 202011059741.9 and the invention title "Cascaded Multi-port Converter and Three-phase Medium Voltage Input System", and all its contents are incorporated herein by reference.

[0002] This application relates to the technical field of power electronics, and more specifically, particularly to a cascaded multi-port converter and a three-phase medium voltage input system.

Background Art

[0003] Traditional DC charging piles generally use a power frequency step-down transformer to reduce the medium voltage to the commercial power supply voltage, for example, 380V in China, and then use a power supply module to convert the commercial power supply voltage into a DC voltage that can be used by electric vehicles, such as 200 - 1000Vdc, to charge the electric vehicle. As shown in Figure 1, the primary winding of the power frequency transformer is connected to the primary side high voltage power supply, the secondary winding of the power frequency transformer is respectively connected to the AC side of each DC charging pile module, and the DC side of each DC charging pile module (Vout1, Vout2... Voutn in Figure 1) is connected to the charging port of the power supply module. Due to the needs of safety regulations, when allowing simultaneous charging of multiple vehicles, it is necessary to insulate between the input and output of the power supply module. Therefore, not only is it necessary to provide the power frequency transformer in front of each DC charging pile module, but also an isolated DC / DC converter (Isolated D / D in Figure 1) needs to be further provided after the AC / DC converter (A / D in Figure 1) in the DC charging pile module. As a result, this solution has defects such as self-loss during the night and large volume.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, a solution using a cascaded power electronics transformer has been proposed. As shown in FIG. 2, each module (module 1, module 2... module m in FIG. 2) includes a first AC / DC converter (A / D-P1, A / D-P1... A / D-Pm in FIG. 2), a DC / AC converter (D / A-P1, D / A-P1... D / A-Pm in FIG. 2), a transformer, and a second AC / DC converter (A / D-S12, A / D-S22... A / D-Sm2 in FIG. 2). The output terminals of each module are connected in parallel as a DC bus bar, and then connected to the charging port of the power module by each isolated DC / DC converter (isolated DC / DC1, isolated DC / DC2... isolated DC / DCn in FIG. 2). To ensure safe charging, insulation must exist between each charging port. Therefore, in order to meet the requirements of the input voltage, by cascading a large number of modules, the output voltage of each cascaded module (i.e., the first AC / DC converter) becomes the corresponding safety voltage. In this solution, due to the large number of cascaded modules, the volume, weight, and cost of the converter increase.

[0005] In view of this, the embodiments of the present application provide a cascaded multi-port converter and a three-phase medium voltage input system, so as to reduce the number of cascaded modules, and further reduce the volume, weight, and cost of the cascaded multi-port converter.

Means for Solving the Problem

[0006] The first aspect of the present invention discloses a cascaded multi-port converter, which includes a plurality of module units and a plurality of low-voltage rectifier units. Each of the module units includes at least one multi-winding transformer and a plurality of high-voltage conversion units. The input terminals of each of the module units are cascaded, and both ends of the cascade function as both ports of the input terminal of the cascaded multi-port converter. In the module unit, the input ends of the high-voltage conversion units are cascaded, and both ends of the cascade function as two ports of the input end of the module unit. A plurality of primary windings and at least one secondary winding are wound around the magnetic core in the multi-winding transformer. The output end of each high-voltage conversion unit is respectively connected to the corresponding primary winding, and the secondary winding is connected to the corresponding input end of the corresponding low-voltage rectification unit.

[0007] Preferably, the number of the low-voltage rectification units is equal to the total number of all the secondary windings, and each secondary winding is connected to the input end of each low-voltage rectification unit in a one-to-one correspondence.

[0008] Preferably, the number of the low-voltage rectification units is smaller than the total number of all the secondary windings, and a plurality of independent secondary windings share the same low-voltage rectification unit.

[0009] Preferably, a plurality of independent secondary windings include secondary windings of different multi-winding transformers and / or secondary windings on different magnetic columns in the same multi-winding transformer.

[0010] Preferably, a plurality of independent secondary windings are connected in series to the input end of the shared low-voltage rectification unit or connected in parallel to the input end of the shared low-voltage rectification unit.

[0011] Preferably, the output ends of the corresponding low-voltage rectification units are connected to share a bus bar, so that at least one secondary winding exists in each multi-winding transformer, and there is an indirect connection relationship with the corresponding secondary winding in at least one other multi-winding transformer.

[0012] Preferably, at least one secondary winding exists in each multi-winding transformer, and there is an indirect connection relationship with the corresponding secondary winding in each other multi-winding transformer through the corresponding low-voltage rectification unit and the common bus bar.

[0013] Preferably, each of the secondary windings connected to share a bus bar is further connected to an external power source by a common bus bar.

[0014] Preferably, in each multi-winding transformer to which a low-voltage rectification unit connected to share a bus bar is connected, each secondary winding inside each of the module units realizes an indirect bus bar sharing connection with other corresponding secondary windings.

[0015] Preferably, it further includes at least one additional redundant module unit, Each secondary winding in the redundant module unit outputs independently by a corresponding low-voltage rectification unit.

[0016] Preferably, it further includes a plurality of multi-port multiplexing units, Each input end of the multi-port multiplexing unit is respectively connected to a corresponding output end of a different low-voltage rectification unit.

[0017] Preferably, the multi-port multiplexing unit includes a multi-input coupling branch, or a multi-input coupling branch and a converter at a subsequent stage thereof.

[0018] Preferably, the multi-input coupling branch is at least one of a multi-input series connection structure, a multi-input parallel connection structure, and a multi-input series-parallel connection switching structure.

[0019] Preferably, when the multi-port multiplexing unit includes a multi-input coupling branch and a converter at a subsequent stage thereof, and the multi-input coupling branch includes the multi-input series-parallel connection switching structure, All switches in the multi-input series-parallel connection switching structure are bidirectional switches.

[0020] Preferably, when the converter is a unidirectional converter, in the multi-input series-parallel connection switching structure, the bidirectional switch connected to the positive or negative electrode of the input end is replaced by a diode.

[0021] Preferably, the high-voltage conversion unit includes a DC / AC converter and a first AC / DC converter. The AC side of the first AC / DC converter functions as the input end of the high-voltage conversion unit. The DC side of the first AC / DC converter is connected to the DC side of the DC / AC converter. The AC side of the DC / AC converter functions as the output end of the high-voltage conversion unit.

[0022] Preferably, the first AC / DC converter has a full-bridge type structure or a half-bridge type structure.

[0023] Preferably, the low-voltage rectification unit includes a second AC / DC converter. The AC side of the second AC / DC converter functions as the input end of the low-voltage rectification unit. The DC side of the second AC / DC converter functions as the output end of the low-voltage rectification unit.

[0024] Preferably, the structure composed of the DC / AC converter and the second AC / DC converter is any one of a dual active bridge structure, an LLC structure, and a CLLC structure by corresponding windings.

[0025] The second aspect of the present invention discloses a three-phase medium-voltage input system, which includes three phase units. The phase unit includes an inductor and the cascade type multi-port converter described in the first aspect of the present invention. The tip of the input end of each phase unit is connected to the medium-voltage grid. The tail end of the input end of each phase unit is connected. In the phase unit, the tip of the input end of the cascade-type multi-port converter is connected to one end of the inductor, the other end of the inductor functions as the tip of the input end of the phase unit, and the tail end of the input end of the cascade-type multi-port converter functions as the tail end of the input end of the phase unit.

[0026] The third aspect of the present invention discloses a three-phase medium-voltage input system, including an MMC converter and N DC conversion units, where the DC conversion units include an inductor and a cascade-type multi-port converter according to any one of the first aspects of the present invention, and N is a positive integer. The tip of the input end of each of the DC conversion units is connected to the positive pole of the DC side of the MMC converter. The tail end of the input end of each of the DC conversion units is connected to the negative pole of the DC side of the MMC converter. The AC side of the MMC converter is connected to a medium-voltage grid. In the DC conversion unit, the tip of the input end of the cascade-type multi-port converter is connected to one end of the inductor, the other end of the inductor functions as the tip of the input end of the DC conversion unit, and the tail end of the input end of the cascade-type multi-port converter functions as the tail end of the input end of the DC conversion unit. In the DC conversion unit, the first AC / DC converter of the cascade-type multi-port converter is replaced by two direct-through lead wires.

Advantages of the Invention

[0027] As can be seen from the above technical solution, in the cascade-type multi-port converter provided by the present invention, the input ends of the module units are cascaded, and both ends of the cascade function as both ports of the input end of the cascade-type multi-port converter. In the module unit, the input ends of the high-voltage conversion units are cascaded, and both ends of the cascade function as both ports of the input end of the module unit. The output ends of the high-voltage conversion units are respectively connected to the corresponding primary windings in each multi-winding transformer. As the output end of the module unit, each secondary winding in each multi-winding transformer is respectively connected to the input end of the corresponding low-voltage rectification unit. Since a plurality of primary windings and a plurality of secondary windings are wound around the magnetic core in the multi-winding transformer, the windings of the plurality of high-voltage conversion units share the magnetic core, reducing the number of multi-winding transformers in the cascade-type multi-port converter and correspondingly reducing the number of low-voltage rectification units, thereby reducing the volume, weight and cost of the cascade-type multi-port converter. To clearly explain the technical solutions of the embodiments of the present application or the prior art, the following briefly introduces the necessary drawings for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. On the premise that those skilled in the art do not perform labor worthy of inventive step, based on the structures shown in these drawings, other drawings can be obtained.

Brief Description of the Drawings

[0028]

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Embodiments for Carrying Out the Invention

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the drawings of the embodiments of the present invention are hereinafter combined to clearly and completely describe the technical solutions of the embodiments of the present invention. Obviously, the described embodiments are only some, rather than all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the protection scope of the present invention.

[0030] In this application, the terms "comprising", "including", or any other variation thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, method, article, or apparatus. Unless otherwise limited, the elements defined by the phrase "comprising ○○" do not exclude the presence of other like elements in the process, method, article, or apparatus that comprises the element.

[0031] In the prior art, due to the large number of cascade modules, to solve the problem of increasing the volume, weight, and cost of the converter, embodiments of the present invention provide a cascade-type multi-port converter.

[0032] Referring to FIG. 3, the cascade-type multi-port converter includes a plurality of module units (module 1 to module m in FIG. 3) and a plurality of low-voltage rectification units (A / D-S11 to A / D-S1n, A / D-S21 to A / D-S2n, and A / D-Sm1 to A / D-Smn in FIG. 3). The module unit includes at least one multi-winding transformer and a plurality of high-voltage conversion units (taking the first high-voltage conversion unit of module 1 as an example, including A / D-P11 and D / A-P11 in FIG. 3).

[0033] The input ends of each module unit are cascaded, and both ends of the cascade function as the two ports of the input end of the cascade-type multi-port converter. Specifically, as shown in FIG. 3, the tip of the input end of Module 1 is connected to one end of the primary high-voltage power supply as the tip of the input end of the cascade-type multi-port converter, the tail end of the input end of Module 1 is connected to the tip of the input end of Module 2, and the tail end of the input end of Module 2 is connected to the tip of the input end of Module 3. By analogy, the tail end of the input end of Module m-1 is connected to the tip of the input end of Module m, and the tail end of the input end of Module m is connected to the other end of the primary high-voltage power supply as the tail end of the input end of the cascade-type multi-port converter.

[0034] Here, the number m of module units is not specifically limited and may be determined according to the actual situation, and all fall within the protection scope of this application.

[0035] In the module unit, the input ends of each high-voltage conversion unit are cascaded, and both ends of the cascade function as the two ports of the input end of the module unit. A plurality of primary windings and at least one secondary winding are wound around the magnetic core in the multi-winding transformer. The output end of each high-voltage conversion unit is respectively connected to the corresponding primary winding in the corresponding multi-winding transformer, and the secondary winding is connected to the corresponding input end of the corresponding low-voltage rectification unit.

[0036] That is, the primary side of one multi-winding transformer may be connected to a plurality of high-voltage conversion units, the secondary side of one multi-winding transformer may be connected to one low-voltage rectification unit, or the secondary side of one multi-winding transformer may be connected to a plurality of low-voltage rectification units (as shown in FIG. 3). Furthermore, the voltage across both ends of the high-voltage conversion unit in the cascade-type multi-port converter is controlled to be smaller than the corresponding threshold value.

[0037] Taking the module 1 in FIG. 3 as an example for explanation, the module 1 in FIG. 3 includes i high-voltage conversion units, and A / D-P1b and D / A-P1b form the b-th high-voltage conversion unit, where 0 < b ≤ i.

[0038] Specifically, the tip of the input end of the first high-voltage conversion unit functions as the tip of the input end of module 1, the tail end of the input end of the first high-voltage conversion unit is connected to the tip of the input end of the second high-voltage conversion unit, the tail end of the input end of the second high-voltage conversion unit is connected to the tip of the input end of the third high-voltage conversion unit, and by analogy, the tail end of the input end of the (i - 1)-th high-voltage conversion unit is connected to the tip of the input end of the i-th high-voltage conversion unit, and the tail end of the input end of the i-th high-voltage conversion unit functions as the tail end of the input end of module 1.

[0039] In this embodiment, as shown in FIG. 3, the total number of high-voltage conversion units is i + j +... + k. In the prior art, the total number of each cascade unit on the high-voltage side is s. Since each cascade unit on the high-voltage side is voltage-divided, in the prior art, the total number of A / D units on the low-voltage side is much larger than the total number of low-voltage rectifier units in this embodiment. Furthermore, because many transformers are required, in this embodiment, a plurality of primary windings and a plurality of secondary windings are wound around the magnetic core in the multi-winding transformer. The primary windings corresponding to the plurality of high-voltage conversion units share the magnetic core, and each set of low-voltage rectifier units is coupled to the high-voltage conversion unit by magnetic circuit coupling, realizing the exchange of energy between the energy of the plurality of high-voltage conversion units and the energy of the plurality of low-voltage rectifier units, reducing the number of multi-winding transformers in the cascade-type multi-port converter, correspondingly reducing the number of low-voltage rectifier units, and reducing the volume, weight, and cost of the cascade-type multi-port converter.

[0040] In the above embodiment, the number of low-voltage rectifier units may or may not be equal to the total number of all secondary windings. Here, two situations where the number of low-voltage rectifier units is equal to the total number of all secondary windings and where the number of low-voltage rectifier units is smaller than the total number of all secondary windings will be described respectively: (1) The number of low-voltage rectification units is equal to the total number of all secondary windings, and each secondary winding is connected so as to correspond one by one to the input terminal of each low-voltage rectification unit.

[0041] That is, the input terminal of each low-voltage rectification unit is connected to only one secondary winding, that is, there is a one-to-one relationship between the secondary winding and the low-voltage rectification unit.

[0042] Specifically, as shown in FIG. 3, taking Module 1 as an example, the input terminal of the low-voltage rectification unit A / D-S11 is connected to the first secondary winding in Module 1, the input terminal of the low-voltage rectification unit A / D-S12 is connected to the second secondary winding in Module 1, and by analogy, the input terminal of the low-voltage rectification unit A / D-S1n is connected to the Nth secondary winding in Module 1. Here, the AC / DC side of each low-voltage rectification unit functions as its own input terminal, and the DC side functions as its own output terminal (Vout11~Vout1n, Vout21~Vout2n, and Voutm1~Voutmn in FIG. 3).

[0043] Here, if there are too many primary windings wound around the same magnetic column, the pressure difference between the multiple primary windings will become too large, increasing the difficulty of insulation design. If there are too few primary windings wound, the number of low-voltage rectification units will become too large. In response, the following solution is proposed, that is, a plurality of independent secondary windings share one low-voltage rectification unit in a series-parallel manner, improving the situation where the pressure difference between the multiple primary windings is too large and solving the problem that the number of low-voltage rectification units is too large. For details, refer to the following description.

[0044] (2) The number of low-voltage rectification units is smaller than the total number of all secondary windings, and a plurality of independent secondary windings share the same low-voltage rectification unit.

[0045] Here, based on whether any two secondary windings are independent, it can be determined whether the two secondary windings affect each other. If they affect each other, they are not independent; otherwise, they are independent. Generally, secondary windings in the same magnetic column affect each other, that is, secondary windings in different transformers do not affect each other and are independent, and secondary windings in different magnetic columns in the same transformer do not affect each other and are independent.

[0046] 1. In practical applications, as shown in FIG. 4, each module unit includes one multi-winding transformer, and the multi-winding transformer includes only one magnetic column. Secondary windings of different multi-winding transformers are independent of each other. For example, any one secondary winding in Module 1 is independent of secondary windings in Module 2 and Module 3. Secondary windings within the same module unit are not independent. For example, secondary windings within Module 1 are not independent. That is, a plurality of independent secondary windings include secondary windings of different multi-winding transformers. Therefore, each independent secondary winding can share one low-voltage rectification unit.

[0047] Specifically, the secondary winding TX-S11 in Module 1 and the secondary winding TX-S21 in Module 2 share the low-voltage rectification unit 11. The secondary winding TX-S12 in Module 1 and the secondary winding TX-S22 in Module 2 share the low-voltage rectification unit 12. By analogy, the secondary winding TX-S1n in Module 1 and the secondary winding TX-S2n in Module 2 share the low-voltage rectification unit 1n. By analogy, the secondary winding TX-Sx1 in Module x and the secondary winding TX-Sm1 in Module m share the low-voltage rectification unit (0.5m)1. The secondary winding TX-Sx2 in Module x and the secondary winding TX-Sm2 in Module m share the low-voltage rectification unit (0.5m)2. By analogy, the secondary winding TX-Sxn in Module x and the secondary winding TX-Smn in Module 2 share the low-voltage rectification unit (0.5m)n.

[0048] Note that, for the purpose of demonstrating by taking as an example that two independent secondary windings share the same low-voltage rectifying unit, the number of low-voltage rectifying units is 0.5m, and the number of low-voltage rectifying units is related to the number of independent secondary windings sharing the same low-voltage rectifying unit. In this case, the number of independent secondary windings sharing the same low-voltage rectifying unit may be 2a, where a is a positive integer. For example, 2a may be 2, 4, 6, 8, etc. Regarding the specific value of a, it is not specifically limited here and may be determined according to the actual situation, and all fall within the protection scope of this application. Of course, the number of independent secondary windings sharing the same low-voltage rectifying unit may also be other numerical values, and without elaborating one by one here, all fall within the protection scope of this application.

[0049] In actual application, in a system where a cascade-type multi-port converter is located, if only one cascade-type multi-port converter is included in the system, the secondary windings of different multi-winding transformers in the cascade-type multi-port converter are independent of each other. When at least two cascade-type multi-port converters are included in the system where the cascade-type multi-port converter is located and each cascade-type multi-port converter is connected to the system in the same way, the secondary windings of different cascade-type multi-port converters are independent of each other. Regarding its specific structure, without elaborating one by one here, it may be determined according to the actual situation, and all fall within the protection scope of this application.

[0050] Note that there is a good coupling between each winding of the same multi-winding transformer. When high-voltage insulation is required, the coupling between the windings of different magnetic columns in the same multi-winding transformer is significantly reduced. To avoid the problem of power imbalance caused thereby, the secondary windings in different magnetic columns of the same multi-winding transformer are made into independent secondary windings. That is, it is the following second situation.

[0051] 2. In actual applications, as shown in FIG. 5, each module unit includes a multi-winding transformer, the multi-winding transformer includes at least two magnetic columns, and the secondary windings in different magnetic columns in the same multi-winding transformer are independent windings. For example, among the secondary windings TX-SR11 to TX-SR1n in one magnetic column in Module 1, they are not independent and affect each other. Any one of the secondary windings TX-SR11 to TX-SR1n, the secondary windings TX-SL11 to TX-SL1n in another magnetic column in Module 1, and the secondary windings in Modules 2 and 3 are all independent, and the secondary windings in other magnetic columns are the same, so there is no need to elaborate here one by one.

[0052] Specifically, the secondary winding TX-SR11 in module 1 and the secondary winding TX-SL11 in module 1 share the low-voltage rectification unit 11. The secondary winding TX-SR12 in module 1 and the secondary winding TX-SL12 in module 1 share the low-voltage rectification unit 12. By analogy, the secondary winding TX-SR1n in module 1 and the secondary winding TX-SL1n in module 1 share the low-voltage rectification unit 1n. The secondary winding TX-SR21 in module 2 and the secondary winding TX-SL21 in module 2 share the low-voltage rectification unit 21. The secondary winding TX-SR22 in module 2 and the secondary winding TX-SL22 in module 2 share the low-voltage rectification unit 22. By analogy, the secondary winding TX-SR2n in module 2 and the secondary winding TX-SL2n in module 2 share the low-voltage rectification unit 2n. By analogy, the secondary winding TX-SRx1 in module x and the secondary winding TX-SLx1 in module x share the low-voltage rectification unit x1. The secondary winding TX-SRx2 in module x and the secondary winding TX-SLx2 in module x share the low-voltage rectification unit x2. By analogy, the secondary winding TX-SRxn in module x and the secondary winding TX-SLxn in module x share the low-voltage rectification unit xn. The secondary winding TX-SRm1 in module m and the secondary winding TX-SLm1 in module m share the low-voltage rectification unit m1. The secondary winding TX-SRm2 in module m and the secondary winding TX-SLm2 in module m share the low-voltage rectification unit m2. By analogy, the secondary winding TX-SRmn in module m and the secondary winding TX-SLmn in module m share the low-voltage rectification unit mn.

[0053] Note that FIG. 5 shows an example where two independent secondary windings share the same low-voltage rectification unit. In this case, the number of independent secondary windings sharing the same low-voltage rectification unit may be 2a, where a is a positive integer. For example, 2a can be 2, 4, 6, 8, etc. Regarding the specific value of a, it is not specifically limited here and can be determined according to the actual situation, all of which fall within the protection scope of this application. Of course, the number of independent secondary windings sharing the same low-voltage rectification unit may also be other values, and without elaborating one by one here, all of them fall within the protection scope of this application.

[0054] 3. In actual applications, combining FIGS. 4 and 5, as shown in FIG. 6, each module unit has its own multi-winding transformer, and each multi-winding transformer includes at least two magnetic columns. In this way, the cascade multi-port converter includes at least two multi-winding transformers each including at least two magnetic columns. The secondary windings on different magnetic columns in the same multi-winding transformer are independent windings, and the secondary windings of different multi-winding transformers are independent windings. For example, the secondary windings TX-SR11 to TX-SR1n in Module 1 are not independent and affect each other. Any one of the secondary windings TX-SR11 to TX-SR1n in Module 1, the secondary windings TX-SL11 to TX-SL1n in Module 1, and the secondary windings in Modules 2 and 3 are all independent, and the same is true for other magnetic columns, so there is no need to elaborate here one by one.

[0055] Specifically, the secondary windings TX-SR11 and TX-SL11 in module 1 and the secondary windings TX-SR21 and TX-SL21 in module 2 share the low-voltage rectification unit 11. By analogy, the secondary windings TX-SR12 and TX-SL12 in module 1 and the secondary windings TX-SR22 and TX-SL22 in module 2 share the low-voltage rectification unit 12. By analogy, the secondary windings TX-SR1n and TX-SL1n in module 1 and the secondary windings TX-SR2n and TX-SL2n in module 2 share the low-voltage rectification unit 1n. By analogy, the secondary windings TX-SRx1 and TX-SLx1 in module x and the secondary windings TX-SRm1 and TX-SLm1 in module m share the low-voltage rectification unit (0.5m)1. The secondary windings TX-SRx2 and TX-SLx2 in module x and the secondary windings TX-SRm2 and TX-SLm2 in module m share the low-voltage rectification unit (0.5m)2. By analogy, the secondary windings TX-SRxn and TX-SLxn in module x and the secondary windings TX-SRmn and TX-SLmn in module m share the low-voltage rectification unit (0.5m)n.

[0056] Note that FIG. 6 shows, as an example, four independent secondary windings sharing the same low-voltage rectification unit. In this case, the number of independent secondary windings sharing the same low-voltage rectification unit may be 4a, where a is a positive integer. For example, 4a can be 4, 8, etc. Regarding the specific value of a, it is not specifically limited here and can be determined according to the actual situation, and all fall within the protection scope of this application. Of course, the number of independent secondary windings sharing the same low-voltage rectification unit may also be other values, and there is no need to elaborate here one by one, and all fall within the protection scope of this application.

[0057] In each multi-winding transformer, each secondary winding of each multi-winding transformer is connected to the corresponding low-voltage rectification unit to ensure the consistency of the connection of the high-voltage conversion unit.

[0058] In the above three situations 1, 2, and 3, when multiple independent secondary windings share one low-voltage rectification unit, A plurality of independent secondary windings are connected in series to the input end of a shared low-voltage rectification unit (as shown in FIG. 7a, FIG. 7a shows, based on FIG. 4, an example of two independent secondary windings sharing one low-voltage rectification unit). Specifically, as shown in FIG. 7a, one end of the secondary winding TX-S11 is connected to the tip of the input end of the low-voltage rectification unit A / D-S11, the other end is connected to one end of the secondary winding TX-S21, and the other end of the secondary winding TX-S21 is connected to the tail end of the input end of the low-voltage rectification unit A / D-S11.

[0059] Alternatively, a plurality of independent secondary windings may be connected in parallel to the input end of a shared low-voltage rectification unit (as shown in FIG. 7b, FIG. 7b shows, based on FIG. 4, an example of two independent secondary windings sharing one low-voltage rectification unit). Specifically, as shown in FIG. 7b, one end of the secondary winding TX-S11 is connected to one end of the secondary winding TX-S21, the connection point is connected to the tip of the input end of the low-voltage rectification unit A / D-S11, the other end of the secondary winding TX-S11 is connected to the other end of the secondary winding TX-S21, and the connection point is connected to the tail end of the input end of the low-voltage rectification unit A / D-S11.

[0060] In this embodiment, a plurality of independent secondary windings share the same low-voltage rectification unit, thereby reducing the total number of low-voltage rectification units, improving the complexity and cost of the cascade-type multi-port converter, making the power density of the cascade-type multi-port converter higher, the cost lower, and the efficiency higher.

[0061] In any one of the above embodiments, the high-voltage conversion unit includes a DC / AC converter (each D / A in FIGS. 3 to 6) and a first AC / DC converter (each A / D in FIGS. 3 to 6).

[0062] The AC side of the first AC / DC converter functions as the input end of the high-voltage conversion unit, the DC side of the first AC / DC converter is connected to the DC side of the DC / AC converter, and the AC side of the DC / AC converter functions as the output end of the high-voltage conversion unit.

[0063] In actual application, as shown in FIG. 9a, the first AC / DC converter has a full-bridge structure, or, as shown in FIG. 9b, the first AC / DC converter has a half-bridge structure. Here, it is not specifically limited and can be determined according to the actual situation, and both fall within the protection scope of this application. Specifically, when the high-voltage side of the cascade multi-port converter is DC input, the second AC / DC converter can be removed and each DC / AC converter can be directly connected in series. In this case, the cascade of the second AC / DC converter may degenerate into the two connection wires in FIG. 9c.

[0064] The above low-voltage rectification unit includes a second AC / DC converter. The AC side of the second AC / DC converter functions as the input end of the low-voltage rectification unit, and the DC side of the second AC / DC converter functions as the output end of the low-voltage rectification unit.

[0065] In addition, the structure composed of the DC / AC converter and the second AC / DC converter may be the dual active bridge structure in FIG. 10a, the LLC structure in FIG. 10b, or even the CLLC structure in FIG. 10c through the corresponding windings. Of course, it may also be other structures, and details are not elaborated here one by one. Regarding the structure composed of the DC / AC converter and the second AC / DC converter through the corresponding windings, it is not specifically limited here and can be determined according to the actual situation, and all fall within the protection scope of this application.

[0066] Preferably, in any one of the above embodiments, the cascade multi-port converter further includes a plurality of multi-port multiplexing units (multi-port multiplexing unit 1, multi-port multiplexing unit 2... multi-port multiplexing unit n in FIGS. 3 to 6).

[0067] Each input terminal of the multiport multiplexing unit is respectively connected to the corresponding output terminal of a different low-voltage rectifying unit. Specifically, taking Figure 3 as an example, the first input terminal of the multiport multiplexing unit 1 is connected to the output terminal Vout11 of the low-voltage rectifying unit A / D-S11, the second input terminal of the multiport multiplexing unit 1 is connected to the output terminal Vout21 of the low-voltage rectifying unit A / D-S21, and by analogy, the m-th input terminal of the multiport multiplexing unit 1 is connected to the output terminal Voutm1 of the low-voltage rectifying unit A / D-Sm1. Since the same applies to the multiport multiplexing units 2 to n, for the sake of brevity, each of them is within the protection scope of this application and will not be elaborated here one by one.

[0068] In addition, the secondary winding of each multi-winding transformer realizes the busbar shared connection of at least one set of secondary windings through the corresponding multiport multiplexing unit. In practical applications, in each multi-winding transformer, through the corresponding low-voltage rectifying unit and the common busbar, each secondary winding and the corresponding secondary winding in other multi-winding transformers realize an indirect busbar shared connection. Figures 3 to 6 all show, by way of example, that there is an indirect busbar shared connection for all the secondary windings of each multi-winding transformer. Since the structure where there is a busbar shared connection only for some of the secondary windings in each multi-winding transformer is similar to the structure in Figures 3 to 6, for the sake of brevity, each of them is within the protection scope of this application and will not be elaborated here one by one.

[0069] In practical applications, the multiport multiplexing unit includes a multi-input coupling branch, or a multi-input coupling branch and a converter at its subsequent stage.

[0070] The multi-input coupling branch is at least one of a multi-input series connection structure, a multi-input parallel connection structure, and a multi-input series-parallel connection switching structure.

[0071] Here, the multi-input series connection structure is shown in FIG. 11a. FIG. 11a shows an example of 2 inputs. Since the other numbers of inputs are the same, there is no need to elaborate here one by one, and all of them fall within the protection scope of this application. The multi-input parallel connection structure is shown in FIG. 11b. FIG. 11b shows an example of 2 inputs. Since the other numbers of inputs are the same, there is no need to elaborate here one by one, and all of them fall within the protection scope of this application. The multi-input series-parallel connection switching structure is shown in FIG. 11c. A switch is provided between the input end and the output end, and a switch is also provided between the two input ends. Specifically, the positive electrode of the input end SHn is connected to the positive electrode of the output end SOUTn, the negative electrode of the input end SHn is connected to the negative electrode of the output end SOUTn by the first switch, the negative electrode of the input end SHn is further connected to the positive electrode of the input end SLn by the second switch, the positive electrode of the input end SLn is further connected to the positive electrode of the output end SOUTn by the third switch, and the negative electrode of the input end SLn is connected to the negative electrode of the output end SOUTn. FIG. 11c shows an example of 2 inputs. Specifically, since the other numbers of inputs are the same, there is no need to elaborate here one by one, and all of them fall within the protection scope of this application. When using the structure of FIG. 11c for the input coupling branch, the series-parallel connection switching of the connection unit can be realized, and the requirement for the gain range of the previous-stage converter can be reduced.

[0072] In practical applications, the multi-port multiplexing unit includes a multi-input coupling branch and a converter at its subsequent stage. When the multi-input coupling branch includes a multi-input series-parallel connection switching structure, if the converter is a bidirectional converter, all the switches in the multi-input series-parallel connection switching structure are bidirectional switches, that is, switches that allow current to flow in both directions. If the converter is a unidirectional converter, all the switches in the multi-input series-parallel connection switching structure may be bidirectional switches, and instead of some of the bidirectional switches, diodes may be used. For example, the switches connected to the positive electrodes of each input end or the switches connected to the negative electrodes of each input end can be replaced.

[0073] The subsequent-stage converter includes an inductor and a capacitor. Both ends of the capacitor are connected to the positive and negative electrodes of the output end of the multi-port multiplexing unit.

[0074] Specifically, as shown in FIG. 11d, the positive electrode of the input terminal SHn is sequentially connected to the negative electrode of the input terminal SHn by the first switch and the second switch. One end of the inductor is connected to the connection point between the first switch and the second switch, and the other end is respectively connected to one end of the capacitor and the positive electrode of the output terminal SOUTn. The negative electrode of the input terminal SHn is further connected to the connection point between the third switch and the fourth switch. The positive electrode of the input terminal SLn is sequentially connected to the negative electrode of the input terminal SLn by the third switch and the fourth switch. The negative electrode of the input terminal SLn is further connected to the other end of the capacitor and the negative electrode of the output terminal SOUTn. As for the transformer, since the converter itself at the rear stage of the multi-input coupling branch can realize the adjustment of the gain, when the structure of FIG. 10d is used for the multi-port multiplexing unit, the requirement for the gain range of the front-stage converter can be further reduced, and the continuous adjustment of the voltage can be realized.

[0075] When the multi-port multiplexing unit is a one-way conversion, its structure may further be the structure of FIG. 11e. Replace the first switch and the fourth switch with diodes. Regarding the specific connection relationship, there is no need to elaborate here one by one, and all of them fall within the protection scope of this application. It may also be the structure of FIG. 11f. Replace the second switch and the third switch with diodes. Regarding the specific connection relationship, there is no need to elaborate here one by one, and all of them fall within the protection scope of this application. By using two diodes instead of two switches, the cost can be further reduced.

[0076] Here, for the situation of multi-input single-output, several solutions in FIGS. 11a to 11f can be combined to obtain flexible and various solutions. FIGS. 12a to 12c show several 6-input / 1-output structures. The structure in FIG. 12a first uses the structure in FIG. 11b to connect three modules in parallel, and then cascades the units connected in parallel by the structure in FIG. 11d. The structure in FIG. 12b first connects three modules in parallel by the structure in FIG. 11b, and then realizes the series connection switching of the units connected in parallel by the structure in FIG. 11c. The structure in FIG. 12c first connects module units in pairs in parallel by the structure in FIG. 11b, and then adopts a solution of three-stage cascade output using the structure in FIG. 11d. Regarding other combination methods, there is no need to elaborate here one by one, and all of them fall within the protection scope of this application. The number of inputs is not specifically limited either and can be determined according to the actual situation, and all of them fall within the protection scope of this application.

[0077] Here, each of the above corresponding embodiments can ensure that each set of low-voltage rectification units is directly coupled by the corresponding high-voltage conversion unit. However, since the energy balance of each high-voltage conversion unit cannot be guaranteed, in actual applications, when there is at least one low-voltage rectification unit in each module unit that maintains a bus bar shared connection at the output end with the low-voltage rectification unit corresponding to another module unit, there is at least one of the secondary windings in each multi-winding transformer. There is an indirect connection relationship between the corresponding secondary winding in each other multi-winding transformer and the corresponding low-voltage rectification unit and the common bus bar, thereby realizing the energy balance of each high-voltage conversion unit and low-voltage rectification unit with the characteristic of bus bar sharing.

[0078] As shown in FIGS. 8a to 8d, FIG. 8a is a schematic diagram in which a part shares a bus bar and the other part outputs independently. Specifically, as shown in FIG. 8a, Vout11, Vout21... Voutm1 are connected to share the bus bar, Vout12, Vout22... Voutm2 are connected to share the bus bar,..., Vout1i, Vout2i... Voutmi are connected to share the bus bar, and the remaining secondary windings are all independently output by the corresponding low-voltage rectification units. For example, Vout1(i + 1), Vout2(i + 1)... Voutm(i + 1) are independently output, Vout1(i + 2), Vout2(i + 2)... Voutm(i + 2) are independently output,..., Vout1n, Vout2n... Voutmn are independently output. Of course, it may also be a situation where all bus bars are shared (not shown), and here, without going into details one by one, all are within the protection scope of this application.

[0079] Taking the example that each module unit has four secondary windings and each secondary winding is assigned an independent low-voltage rectification unit, each module unit corresponds to the output terminals of four low-voltage rectification units. The situation where a part shares a bus bar and the other part outputs independently is as follows: that is, only three output terminals are respectively connected to the corresponding input terminals of three multi-port multiplexing units, and the remaining other output terminals of each module unit are respectively connected to the output terminals of the corresponding multi-port multiplexing units. Thereby, a bus bar sharing connection of at least one set of secondary windings and an independent output of at least one set of secondary windings are realized. The situation where all bus bars are shared is as follows: that is, the four output terminals are respectively connected to the corresponding input terminals of the four multi-port multiplexing units, and the output terminals of other low-voltage rectification units are also connected to the corresponding input terminals of these four multi-port multiplexing units. That is, the output terminals of the four low-voltage rectification units of each module unit and the output terminals of the four low-voltage rectification units of other module units respectively correspond and are connected to share the bus bar.

[0080] To facilitate the description, in the special situation of FIG. 8b, the realization method of the energy balance will be described.

[0081] Specifically, as shown in FIG. 8b (taking the case where the number of secondary windings in FIG. 8b is 2 and the number of module units is 3 as an example), one secondary winding in module 1 is connected to the AC side of the low-voltage rectifier unit A / D-S11, and another secondary winding in module 1 is connected to the AC side of the low-voltage rectifier unit A / D-S12. The DC side of the low-voltage rectifier unit A / D-S11 functions as its own output terminal Vout11, and the DC side of the low-voltage rectifier unit A / D-S12 functions as its own output terminal Vout12. One secondary winding in module 2 is connected to the AC side of the low-voltage rectifier unit A / D-S21, and another secondary winding in module 2 is connected to the AC side of the low-voltage rectifier unit A / D-S22. The DC side of the low-voltage rectifier unit A / D-S21 functions as its own output terminal Vout21, and the DC side of the low-voltage rectifier unit A / D-S22 functions as its own output terminal Vout22. One secondary winding in module 3 is connected to the AC side of the low-voltage rectifier unit A / D-S31, and another secondary winding in module 3 is connected to the AC side of the low-voltage rectifier unit A / D-S32. The DC side of the low-voltage rectifier unit A / D-S31 functions as its own output terminal Vout31, and the DC side of the low-voltage rectifier unit A / D-S32 functions as its own output terminal Vout32.

[0082] The output terminals Vout11 of the low-voltage rectifier unit A / D-S11, Vout21 of the low-voltage rectifier unit A / D-S21, and Vout31 of the low-voltage rectifier unit A / D-S31 are connected to share a busbar, that is, each corresponding secondary winding in different multi-winding transformers realizes an indirect busbar sharing connection through the corresponding low-voltage rectifier unit, and the output terminals Vout12 of the low-voltage rectifier unit A / D-S12, Vout22 of the low-voltage rectifier unit A / D-S22, and Vout32 of the low-voltage rectifier unit A / D-S32 output independently.

[0083] Specifically, the arrow line in Fig. 8b indicates the energy flow direction when only the output terminal Vout12 of the low-voltage rectification unit A / D-S12 needs to output energy. The high-voltage conversion units of Modules 2 and 3 respectively provide 1 / 3 of the total output energy to the common busbar through the low-voltage rectification unit sharing their busbar, and then 2 / 3 of the energy is transmitted from the output terminal Vout11 of Module 1 to the output terminal Vout12 of the low-voltage rectification unit A / D-S12. The high-voltage conversion unit of Module 1 directly provides another 1 / 3 of the energy to the output terminal Vout12 of the low-voltage rectification unit A / D-S12, thereby ensuring the energy balance of the high-voltage conversion unit.

[0084] In actual application, each secondary winding connected in a way that shares the busbar may be further connected to an external power source through the common busbar. As shown in Fig. 8c and Fig. 8d, the output terminal Vout11 of the low-voltage rectification unit A / D-S11, the output terminal Vout21 of the low-voltage rectification unit A / D-S21, and the output terminal Vout31 of the low-voltage rectification unit A / D-S31 are connected to the DC power source DC through the common busbar.

[0085] Fig. 8c shows that when the low-voltage busbar, that is, the common busbar, provides and inputs separate energy, the high-voltage conversion units provide similar energy respectively, and the common busbar on the low-voltage side provides the balance of separate energy. Fig. 8d provides a more extreme situation where the high-voltage conversion units do not provide energy, and the independently output energy is completely provided from the separate energy input on the low-voltage side.

[0086] Here, Figs. 8a to 8c all have a connection relationship where some share the busbar. The connection relationship where all share the busbar and its working principle are similar to the descriptions corresponding to Figs. 8a to 8c, so they will not be elaborated here one by one, and all fall within the protection scope of this application.

[0087] Here, the low-voltage rectification unit is bidirectional. In the above content, its AC side is marked as the input terminal, and its DC side is marked as the output terminal.

[0088] In this embodiment, the energy harmonic of multiple sets of low-voltage rectification units is realized by a common bus bar, thereby ensuring the energy balance of the high-voltage conversion unit, reducing the complexity of the system, reducing the number of low-voltage rectification units, and the common low-voltage bus bar provided to the system provides convenience for other energy access. For example, the realization of photovoltaic energy storage and charging coupling can enhance the multiplicity of the system. When ensuring the bus bar sharing of at least one set of low-voltage rectification units, the other sets of low-voltage rectification units are independent of some of the low-voltage rectification units, thereby realizing the energy balance of each high-voltage conversion unit and low-voltage rectification unit with the characteristics of bus bar sharing.

[0089] Of course, in actual applications, it is necessary to exclude the possibility that there is no relationship of bus bar sharing connection at the output end between at least one additional redundant module unit and other module units. For example, it is the module m + 1 in FIG. 15, which can be determined according to its specific application environment, and all of them fall within the protection scope of this application.

[0090] In the cascaded multi-port converter provided by this embodiment, when viewed from the low-voltage side, each multi-winding transformer provides a secondary winding for its corresponding multiple low-voltage side outputs, and for each low-voltage rectification voltage connected to share the bus bar, the corresponding total output on the low-voltage side is provided by the multi-port multiplexing unit by aggregating the outputs of the corresponding high-voltage conversion units. When viewed from the high-voltage side, each high-voltage conversion unit is connected to the primary winding of the corresponding multi-winding transformer, ensuring that the energy of the output terminals of the multiple low-voltage sides (Vout1 to Vouti in FIGS. 3 to 6) all comes from the corresponding multiple high-voltage conversion units. Insulation can be easily realized between the multiple secondary windings, meeting the insulation needs. Also, the multiple low-voltage sides realize independent control of the total output voltage by the low-voltage rectification units or the low-voltage rectification units and the multi-port multiplexing units.

[0091] Embodiments of the present invention provide a three-phase medium-voltage input system. As shown in FIG. 13, it includes three phase units, and each phase unit includes an inductor and a cascaded multi-port converter provided by any one of the above embodiments.

[0092] The tip of the input end of each phase unit is directly connected to the medium-voltage grid, and the tail end of the input end of each phase unit is connected. Each phase unit is connected in the same way, so that the output energy on the low-voltage side of each phase unit is directly coupled to all units in the three-phase cascade system. In the phase unit, the tip of the input end of the cascaded multi-port converter is connected to one end of the inductor, the other end of the inductor functions as the tip of the input end of the phase unit, and the tail end of the input end of the cascaded multi-port converter functions as the tail end of the input end of the phase unit.

[0093] In practical applications, when the low-voltage rectifier unit of the cascaded multi-port in each phase unit is connected to a plurality of independent secondary windings, the low-voltage rectifier unit may be connected to independent secondary windings in different phase units, or may be connected to independent secondary windings in the same phase unit. For example, the first low-voltage rectifier unit is respectively connected to one secondary winding in the first phase unit and one secondary winding in the second phase unit, and these two secondary windings are independent. Here, without further elaboration, each secondary winding connected to the same low-voltage rectifier unit only needs to be independent, and it is not limited whether these secondary windings are from the same phase unit and whether they are from the same multi-winding transformer. For the specific connection relationship of each low-voltage rectifier unit, it can be determined according to the actual situation, and all fall within the protection scope of this application.

[0094] Here, all cascaded multi-port converters may share the same set of multi-port multiplexing units, or each cascaded multi-port converter may share its own set of multi-port multiplexing units.

[0095] In actual applications, the structures of each cascaded multi-port converter may be the same or different. The structure in FIG. 13 is only an example. For schematic diagrams using other structures for the cascaded multi-port converter respectively, reference may be made to the above embodiments.

[0096] For the specific structure and working principle of the cascaded multi-port converter, reference may be made to the above embodiments, and details will not be elaborated here, all of which fall within the protection scope of this application. Here, the cascaded multi-port converter may also be applied to other systems, and details will not be elaborated here, all of which fall within the protection scope of this application.

[0097] In this embodiment, a plurality of independent secondary windings share the same low-voltage rectification unit, thereby reducing the total number of low-voltage rectification units. As a result, the complexity and cost of the three-phase medium-voltage input system are improved, the power density of the three-phase medium-voltage input system becomes higher, the cost becomes lower, and the efficiency becomes higher.

[0098] The embodiment of the present invention provides a three-phase medium-voltage input system. As shown in FIG. 14, it includes an MMC converter and N DC conversion units. The DC conversion unit includes an inductor and the cascaded multi-port converter provided by any one of the above embodiments, where N is a positive integer.

[0099] The tip of the input end of each DC conversion unit is connected to the positive pole of the DC side of the MMC converter, and the tail of the input end of each DC conversion unit is connected to the negative pole of the DC side of the MMC converter. The AC side of the MMC converter is connected to the medium-voltage grid.

[0100] In the DC conversion unit, the tip of the input end of the cascaded multi-port converter is connected to one end of the inductor. The other end of the inductor functions as the tip of the input end of the DC conversion unit, and the tail of the input end of the cascaded multi-port converter functions as the tail of the input end of the DC conversion unit.

[0101] Here, the input terminals of each DC conversion unit are connected to the medium-voltage grid by an MMC converter. That is, on the high-voltage side, first, an MMC converter is used to construct a high-voltage DC busbar, and then, from the high-voltage DC busbar in a cascade manner, at least two ports exchange energy with low-voltage DC power supplies insulated from each other, and a plurality of ports all achieve direct energy coupling.

[0102] In the DC conversion unit, the first AC / DC converter of the cascade-type multi-port converter is replaced by two straight-through lead wires.

[0103] In practical applications, when the low-voltage rectification unit of the cascade-type multi-port of each DC conversion unit is connected to a plurality of independent secondary windings, the low-voltage rectification unit may be connected to the independent secondary windings of different DC conversion units, or may be connected to the independent secondary windings of the same DC conversion unit. For example, the first low-voltage rectification unit is respectively connected to one secondary winding of the first DC conversion unit and one secondary winding of the second DC conversion unit, and these two secondary windings are independent. Here, without going into details one by one, it is only necessary that each secondary winding connected to the same low-voltage rectification unit is independent, and it is not limited whether these secondary windings are from the same DC conversion unit and whether they are from the same multi-winding transformer. For the specific connection relationship of each low-voltage rectification unit, it can be determined according to the actual situation, and all fall within the protection scope of this application.

[0104] Here, all cascade-type multi-port converters may share the same set of multi-port multiplexing units, or each cascade-type multi-port converter may have its own set of multi-port multiplexing units.

[0105] In practical applications, the structures of each cascade-type multi-port converter may be the same or different. The structure in FIG. 14 is only an example. For schematic diagrams using other structures for each cascade-type multi-port converter respectively, reference may be made to the above embodiments.

[0106] For the specific structure and working principle of the cascaded multi-port converter, reference may be made to the above embodiments, and details are not elaborated here one by one, and all of them fall within the protection scope of the present application. Here, the cascaded multi-port converter may be applied to other systems, and details are not elaborated here one by one, and all of them fall within the protection scope of the present application.

[0107] In this embodiment, a plurality of independent secondary windings share the same low-voltage rectification unit, thereby reducing the total number of low-voltage rectification units, improving the complexity and cost of the N-phase medium-voltage input system, making the power density of the three-phase medium-voltage input system higher, the cost lower, and the efficiency higher.

[0108] The features described in each embodiment in this specification may be replaced or combined with each other. For the same or similar parts between each embodiment, reference may be made to each other. Each embodiment mainly explains the differences from other embodiments. In particular, for a system or an embodiment of a system, since it is basically similar to an embodiment of a method, its description is brief, and for related parts, reference may be made to some descriptions of the embodiment of the method. The systems and system embodiments described above are only schematic. The units described as the individual members may or may not be physically separated. The members shown as units may or may not be physical units, that is, they may be located in one place or distributed among multiple network units. According to actual needs, some or all of the modules can be selected to achieve the purpose of the solution of this embodiment. Those skilled in the art can understand and implement it without performing inventive labor.

[0109] As will be more readily apparent to those skilled in the art, each of the exemplary units and algorithm steps described in combination with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both, and in the foregoing description, to clearly explain the interchangeability of hardware and software, each exemplary combination and step is described in accordance with its general functionality. Whether these functions are executed in hardware form or software form depends on the specific application of the technical solution and the design constraints. Those skilled in the art may use different methods to implement the described functions for each specific application, but such implementation does not exceed the scope of the present invention.

[0110] From the foregoing description of the disclosed embodiments, those skilled in the art can implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Accordingly, the present invention is not limited to these embodiments shown herein, but rather conforms to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cascade - type multi - port converter, comprising a plurality of module units and a plurality of low - voltage rectification units, wherein each of the module units includes at least one multi - winding transformer and a plurality of high - voltage conversion units, The input ends of each of the module units are cascaded, and both ends of the cascade function as both ports of the input end of the cascade - type multi - port converter, In the module unit, the input ends of each of the high - voltage conversion units are cascaded, and both ends of the cascade function as both ports of the input end of the module unit. A plurality of primary windings and a plurality of secondary windings are wound around the magnetic core of the multi - winding transformer. The output end of each of the high - voltage conversion units is respectively connected to the corresponding primary winding, and the secondary winding is connected to the corresponding input end of the corresponding low - voltage rectification unit, Between the output ends of the corresponding low - voltage rectification units, they are connected so as to share a bus bar. Thus, in at least one of the multi - winding transformers, there are a plurality of the secondary windings, and there is an indirect connection relationship with the corresponding secondary windings in at least one other multi - winding transformer respectively, In each of the at least one multi - winding transformer, there is no indirect connection relationship between the plurality of secondary windings, The number of the low - voltage rectification units is smaller than the total number of all the secondary windings, and a plurality of independent secondary windings share the same low - voltage rectification unit. A cascade - type multi - port converter characterized by this.

2. The cascade - type multi - port converter according to claim 1, wherein the plurality of independent secondary windings include secondary windings of different multi - winding transformers and / or secondary windings in different magnetic columns of the same multi - winding transformer.

3. The plurality of independent secondary windings are connected in series to the input end of the shared low-voltage rectifying unit or are connected in parallel to the input end of the shared low-voltage rectifying unit, and the cascade-type multi-port converter according to claim 1 is characterized thereby.

4. Each of the multi-winding transformers has at least one of the secondary windings, and there is an indirect connection relationship between the corresponding secondary winding in each of the other multi-winding transformers and the corresponding low-voltage rectifying unit and the common bus bar, and the cascade-type multi-port converter according to claim 3 is characterized thereby.

5. Each of the secondary windings connected to share a bus bar is further connected to an external power source by a common bus bar, and the cascade-type multi-port converter according to claim 3 is characterized thereby.

6. In each of the multi-winding transformers to which the low-voltage rectifying units connected to share a bus bar are connected, each of the secondary windings inside each of the module units realizes an indirect bus bar sharing connection with the corresponding other secondary windings, and the cascade-type multi-port converter according to claim 3 is characterized thereby.

7. Further includes at least one additional redundant module unit, Each of the secondary windings in the redundant module unit is independently output by the corresponding low-voltage rectifying unit, and the cascade-type multi-port converter according to claim 3 is characterized thereby.

8. Further includes a plurality of multi-port multiplexing units, Each input end of the multi-port multiplexing unit is respectively connected to the corresponding output end of a different low-voltage rectifying unit, and the cascade-type multi-port converter according to any one of claims 1 to 3 is characterized thereby.

9. The cascade type multi-port converter according to claim 8, wherein the multi-port multiplexing unit includes a multi-input combining branch, or a multi-input combining branch and a converter at a subsequent stage thereof.

10. The cascade type multi-port converter according to claim 9, wherein the multi-input combining branch is at least one of a multi-input series connection structure, a multi-input parallel connection structure, and a multi-input series-parallel connection switching structure.

11. When the multi-port multiplexing unit includes a multi-input combining branch and a converter at a subsequent stage thereof, and the multi-input combining branch includes the multi-input series-parallel connection switching structure, The cascade type multi-port converter according to claim 10, wherein all switches in the multi-input series-parallel connection switching structure are bidirectional switches.

12. When the converter is a unidirectional converter, in the multi-input series-parallel connection switching structure, a bidirectional switch connected to the positive or negative electrode of the input end is replaced by a diode. The cascade type multi-port converter according to claim 11.

13. The high-voltage conversion unit includes a DC / AC converter and a first AC / DC converter, An AC side of the first AC / DC converter functions as an input end of the high-voltage conversion unit, A DC side of the first AC / DC converter is connected to a DC side of the DC / AC converter, An AC side of the DC / AC converter functions as an output end of the high-voltage conversion unit. The cascade type multi-port converter according to any one of claims 1 to 3.

14. The cascade type multi-port converter according to claim 13, wherein the first AC / DC converter has a full-bridge type structure or a half-bridge type structure.

15. The low-voltage rectification unit includes a second AC / DC converter, the AC side of the second AC / DC converter functions as the input end of the low-voltage rectification unit, and the DC side of the second AC / DC converter functions as the output end of the low-voltage rectification unit. The cascade-type multi-port converter according to claim 13, characterized in that. **Claim 16** The structure composed of the DC / AC converter and the second AC / DC converter is any one of a dual active bridge structure, an LLC structure, and a CLLC structure by corresponding windings. The cascade-type multi-port converter according to claim 15, characterized in that. **Claim 17** A three-phase medium-voltage input system includes three phase units. The phase unit includes an inductor and a cascade-type multi-port converter according to any one of claims 1 to 16. The tip of the input end of each phase unit is connected to a medium-voltage grid, the tail end of the input end of each phase unit is connected, In the phase unit, the tip of the input end of the cascade-type multi-port converter is connected to one end of the inductor, the other end of the inductor functions as the tip of the input end of the phase unit, and the tail end of the input end of the cascade-type multi-port converter functions as the tail end of the input end of the phase unit. A three-phase medium-voltage input system, characterized in that. **Claim 18** A three-phase medium-voltage input system includes an MMC converter and N DC conversion units. The DC conversion unit includes an inductor and a cascade-type multi-port converter according to any one of claims 1 to 16, where N is a positive integer. The tip of the input end of each DC conversion unit is connected to the positive pole of the DC side of the MMC converter, the tail end of the input end of each DC conversion unit is connected to the negative pole of the DC side of the MMC converter, and the AC side of the MMC converter is connected to a medium-voltage grid. In the DC conversion unit, the tip of the input end of the cascade type multi-port converter is connected to one end of the inductor, the other end of the inductor functions as the tip of the input end of the DC conversion unit, and the tail end of the input end of the cascade type multi-port converter functions as the tail end of the input end of the DC conversion unit. A three-phase medium voltage input system, characterized in that in the DC conversion unit, the first AC / DC converter of the cascade type multi-port converter is replaced by two straight-through lead wires.

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