US-12627215-B2 - Cascaded multi-port converter and three-phase medium-voltage input system

US12627215B2US 12627215 B2US12627215 B2US 12627215B2US-12627215-B2

Abstract

A cascaded multi-port converter and a three-phase medium-voltage input system. Input terminals of the module units are cascaded. In each module unit: input ends of the high-voltage conversion units are cascaded, a magnetic core of a multi-winding transformer is wound with multiple primary windings and at least one secondary winding, an output end of each high-voltage conversion unit is connected to a corresponding primary winding, and the secondary winding is connected to an input end of a corresponding low-voltage rectifying unit. Therefore, the windings of the multiple high-voltage conversion units share the magnetic core, and the number of the multi-winding transformers and the number of the low-voltage rectifying units can be reduced, thereby reducing the volume, weight, and costs of the cascaded multi-port converter.

Inventors

Jiacai ZHUANG
Jun Xu
Yue Dong

Assignees

SUNGROW POWER SUPPLY CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20210906
Priority Date: 20200930

Claims (18)

1 . A cascaded multi-port converter, comprising: a plurality of module units and a plurality of low-voltage rectifying units, wherein each of the plurality of module units comprises at least one multi-winding transformer and a plurality of high-voltage conversion units; input ends of the plurality of module units are cascaded, and two terminals of the cascaded module units serve as two ports of an input end of the cascaded multi-port converter; in each of the plurality of module units: input ends of the plurality of high-voltage conversion units are cascaded, two terminals of the cascaded high-voltage conversion units serve as two ports of an input end of said module unit, a magnetic core of a multi-winding transformer is wound with a plurality of primary windings and at least one secondary winding, an output end of each of the plurality of high-voltage conversion units is connected to a corresponding primary winding, and the secondary winding is connected to an input end of a corresponding low-voltage rectifying unit; the number of the plurality of low-voltage rectifying units is less than the number of all secondary windings, and a plurality of secondary windings independent from each other share one of the plurality of low-voltage rectifying units, wherein the plurality of secondary windings independent from each other do not affect each other during operation.
2 . The cascaded multi-port converter according to claim 1 , wherein the plurality of secondary windings independent from each other comprise at least one of: secondary windings of different multi-winding transformers; and secondary windings on different magnetic columns in one multi-winding transformer.
3 . The cascaded multi-port converter according to claim 1 , wherein the plurality of secondary windings independent from each other are connected in series to an input end of the shared low-voltage rectifying unit; or the plurality of secondary windings independent from each other are connected in parallel to the input end of the shared low-voltage rectifying unit.
4 . The cascaded multi-port converter according to claim 1 , wherein output ends of the corresponding low-voltage rectifying units are connected to each other through a bus, to ensure that at least one secondary winding in at least one multi-winding transformer is indirectly connected to a secondary winding in at least one of the other multi-winding transformers.
5 . The cascaded multi-port converter according to claim 4 , wherein at least one secondary winding in each multi-winding transformer is indirectly connected to a secondary winding in each of other multi-winding transformers through the corresponding low-voltage rectifying unit and the bus.
6 . The cascaded multi-port converter according to claim 4 , wherein secondary windings connected to each other through the bus are connected to an external power supply through the bus.
7 . The cascaded multi-port converter according to claim 4 , wherein in each of multi-winding transformers that are connected to the low-voltage rectifying units connected to each other through the bus, a secondary winding in each module unit is indirectly connected to a secondary winding in each of other multi-winding transformers through the bus.
8 . The cascaded multi-port converter according to claim 4 , further comprising at least one additional redundant module unit, wherein each secondary winding of the redundant module unit independently outputs through a corresponding low-voltage rectifying unit.
9 . The cascaded multi-port converter according to claim 1 , further comprising a plurality of multi-port multiplexing units for combining inputs thereof in serial and/or parallel connection, wherein input ends of each of the plurality of multi-port multiplexing units are respectively connected to output ends of different low-voltage rectifying units.
10 . The cascaded multi-port converter according to claim 9 , wherein at least one of the plurality of multi-port multiplexing units comprises: a multi-input coupling branch; or a multi-input coupling branch and a converter provided at a rear stage of the multi-input coupling branch.
11 . The cascaded multi-port converter according to claim 10 , wherein the multi-input coupling branch comprises at least one of: a multi-input series structure, a multi-input parallel structure, and a multi-input series-parallel switching structure.
12 . The cascaded multi-port converter according to claim 11 , wherein in a case that the multi-port multiplexing unit comprises the multi-input coupling branch and the converter provided at the rear stage of the multi-input coupling branch, and the multi-input coupling branch comprises the multi-input series-parallel switching structure, switches in the multi-input series-parallel switching structure are bidirectional switches.
13 . The cascaded multi-port converter according to claim 12 , wherein in a case that the converter is an unidirectional converter, a bidirectional switch in the multi-input series-parallel switching structure connected to a positive electrode or a negative electrode of an input end of the multi-input series-parallel switching structure is replaced by a diode.
14 . The cascaded multi-port converter according to claim 1 , wherein a high-voltage conversion unit comprises a DC/AC converter and a first AC/DC converter, wherein an AC side of the first AC/DC converter serves 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 serves as an output end of the high-voltage conversion unit; and the first AC/DC converter is a full bridge structure, or a half bridge structure.
15 . The cascaded multi-port converter according to claim 14 , wherein each of the plurality of low-voltage rectifying units comprises a second AC/DC converter, wherein an AC side of the second AC/DC converter serves as an input end of said low-voltage rectifying unit; and a DC side of the second AC/DC converter serves as an output end of said low-voltage rectifying unit.
16 . The cascaded multi-port converter according to claim 15 , wherein the DC/AC converter and the second AC/DC converter through a corresponding winding form one of: a double active bridge structure, an inductor-inductor-capacitor (LLC) structure, and a capacitor-inductor-inductor-capacitor (CLLC) structure.
17 . A three-phase medium-voltage input system, comprising three phase units, and each of the three phase units comprising an inductor and a cascaded multi-port converter, wherein the cascaded multi-port converter comprises: a plurality of module units and a plurality of low-voltage rectifying units; each of the plurality of module units comprises at least one multi-winding transformer and a plurality of high-voltage conversion units; input ends of the plurality of module units are cascaded, and two terminals of the cascaded module units serve as two ports of an input end of the cascaded multi-port converter; in each of the plurality of module units: input ends of the plurality of high-voltage conversion units are cascaded, two terminals of the cascaded high-voltage conversion units serve as two ports of an input end of said module unit, a magnetic core of a multi-winding transformer is wound with a plurality of primary windings and at least one secondary winding, an output end of each of the plurality of high-voltage conversion units is connected to a corresponding primary winding, and the secondary winding is connected to an input end of a corresponding low-voltage rectifying unit; head ends of input ends of the three phase units are connected to a medium-voltage power grid; tail ends of the input ends of the three phase units are connected to each other; and for each of the three phase units, a head end of an input end of the cascaded multi-port converter is connected to an end of the inductor, another end of the inductor serves as a head end of an input end of said phase unit, and a tail end of the input end of the cascaded multi-port converter serves as a tail end of the input end of said phase unit.
18 . A three-phase medium-voltage input system, comprising an modular multilevel converter (MMC), and N direct-current conversion units, each of the N direct-current conversion units comprising an inductor and a cascaded multi-port converter, and N representing a positive integer, wherein the cascaded multi-port converter comprises: a plurality of module units and a plurality of low-voltage rectifying units; each of the plurality of module units comprises at least one multi-winding transformer and a plurality of high-voltage conversion units; input ends of the plurality of module units are cascaded, and two terminals of the cascaded module units serve as two ports of an input end of the cascaded multi-port converter; in each of the plurality of module units: input ends of the plurality of high-voltage conversion units are cascaded, two terminals of the cascaded high-voltage conversion units serve as two ports of an input end of said module unit, a magnetic core of a multi-winding transformer is wound with a plurality of primary windings and at least one secondary winding, an output end of each of the plurality of high-voltage conversion units is connected to a corresponding primary winding, and the secondary winding is connected to an input end of a corresponding low-voltage rectifying unit; head ends of input ends of the N direct-current conversion units are connected to a positive electrode of a DC side of the MMC; tail ends of the input ends of the N direct-current conversion units are connected to a negative electrode of the DC side of the MMC; an AC side of the MMC is connected to a medium-voltage power grid; for each of the N direct-current conversion units, a head end of an input end of the cascaded multi-port converter is connected to an end of the inductor, another end of the inductor serves as a head end of an input end of said direct-current conversion unit, and a tail end of the input end of the cascaded multi-port converter serves as a tail end of the input end of said direct-current conversion unit; and a first AC/DC converter of the cascaded multi-port converter in said direct-current conversion unit is replaced by two straight lines.

Description

This application is a national stage filing under 35 U.S.C. 371 of International Patent Application Serial No. PCT/CN2021/116650, filed Sep. 6, 2021, which claims priority to Chinese Patent Application No. 202011059741.9, entitled “CASCADED MULTI-PORT CONVERTER AND THREE-PHASE MEDIUM-VOLTAGE INPUT SYSTEM”, filed on Sep. 30, 2020 with the China National Intellectual Property Administration. The contents of these applications are incorporated herein by reference in their entireties. FIELD The present disclosure relates to the technical field of power electronics, and in particular, to a cascaded multi-port converter and a three-phase medium-voltage input system. BACKGROUND A conventional direct-current (DC) charging pile typically first converts a medium voltage to a mains voltage, for example, 380V in China, through a power-frequency step-down transformer, and then converts the mains voltage to a DC voltage, for example, 200 Vdc to 1000 Vdc for an electric vehicle through a power module, to charge the electric vehicle. As shown in FIG. 1, a primary winding of a power-frequency transformer is connected to a primary side high-voltage power supply, a secondary winding of the power-frequency transformer is connected to an alternating-current (AC) side of each DC charging pile module respectively, and a DC side (including Vout1, Vout2 . . . and Voutn shown in FIG. 1) of each DC charging pile module is connected to a charging port of the power module. Due to the requirements of safety regulations, in situations where multiple vehicles are allowed to be charged simultaneously, an input of the power module is required to be isolated from an output of the power module. Therefore, not only the power-frequency transformer is required to be arranged at a front stage of each DC charging pile module, but also an isolated DC/DC converter (such as isolated D/D shown in FIG. 1) is required to be arranged at a rear stage of an AC/DC converter (such as A/D shown in FIG. 1) in each DC charging pile module. As a result, the solution has defects such as self-loss at night and large volume. Therefore, a cascaded power electronic transformer is provided in the conventional technology. As shown in FIG. 2, each module unit (such as, a module unit 1, a module unit 2 . . . or a module unit m shown in FIG. 2) includes a first AC/DC converter (such as, A/D-P1, A/D-P2 . . . or A/D-Pm shown in FIG. 2), a DC/AC converter (such as, D/A-P1, D/A-P2 . . . or D/A-Pm shown in FIG. 2), a transformer and a second AC/DC converter (such as, A/D-S12, A/D-S22 . . . or A/D-Sm2 shown in FIG. 2). An output end of each module unit is connected in parallel into a DC bus, and then connected to the charging port of the power module through an isolated DC/DC converter (including isolated DC/DC1, isolated DC/DC2 . . . isolated DC/DCn shown in FIG. 2). The charging ports are required to be isolated from each other, to ensure the safety of charging. In order to meet requirements of an input voltage, a large number of module units are required to be cascaded, and an output voltage of each cascaded module (i.e., the first AC/DC converter) is a safety voltage. In this solution, the large number of the cascaded modules results in the increase of the volume, weight and cost of the converter. SUMMARY In view of the above, a cascaded multi-port converter and a three-phase medium-voltage input system are provided according to embodiments of the present disclosure, which are used to reduce the number of cascaded modules units, to reduce the volume, weight and cost of the cascaded multi-port converter. A cascaded multi-port converter is provided according to a first aspect of the present disclosure. The cascaded multi-port converter includes multiple module units and multiple low-voltage rectifying units. Each of the multiple module units includes at least one multi-winding transformer and multiple high-voltage conversion units. Input ends of the multiple module units are cascaded, and two terminals of the cascaded module units serve as two ports of an input end of the cascaded multi-port converter. In each of the multiple module units: input ends of the multiple high-voltage conversion units are cascaded, two terminals of the cascaded high-voltage conversion units serve as two ports of an input end of said module unit, a magnetic core of a multi-winding transformer is wound with multiple primary windings and at least one secondary winding, an output end of each of the multiple high-voltage conversion units is connected to a corresponding primary winding, and the secondary winding is connected to an input end of a corresponding low-voltage rectifying unit. In an embodiment, the number of the multiple low-voltage rectifying units is the same as the number of all secondary windings, and all secondary windings are connected to input ends of the multiple low-voltage rectifying units in one-to-one correspondence. In an embodiment, the number of the multiple low-voltage rectifyi