US-12620902-B2 - Bi-directional medium voltage to low voltage converter topology

US12620902B2US 12620902 B2US12620902 B2US 12620902B2US-12620902-B2

Abstract

A bi-directional medium voltage converter topology includes an n-pulse line-interphase-transformer, LIT; a plurality of bi-directional medium voltage, MV converters connected to the LIT on an AC side thereof and connected in parallel on a DC side thereof; a bi-directional multi-stage DC/DC converter connected to the plurality of bi-directional MV converters; and a bi-directional low voltage, LV, DC/DC converter; wherein the multi-stage DC/DC converter and the LV DC/DC converter are connected to each other galvanically insulated.

Inventors

Uwe DROFENIK
Francisco Canales
Daniel Rothmund

Assignees

ABB E-mobility B.V.

Dates

Publication Date: 20260505
Application Date: 20220810
Priority Date: 20210813

Claims (9)

1 . A bi-directional medium voltage converter topology, comprising: a multi-pulse line-interphase-transformer (LIT) connected to a three-phase grid; a plurality of bi-directional medium voltage (MV) converters connected to the multi-pulse LIT on an alternating current (AC) side and connected in parallel on a direct current (DC) side; and a medium-voltage to low-voltage (MV-to-LV) DC-to-DC (DC/DC) converter with an AC interface, wherein the MV-to-LV DC/DC converter comprises: a bi-directional multi-stage converter connected to the plurality of bi-directional MV converters; and a bi-directional low voltage (LV) converter; wherein the bi-directional multi-stage converter and the bi-directional LV converter are connected to each other but galvanically insulated via one or more medium frequency transformers (MFTs); wherein the bi-directional multi-stage converter comprises a plurality of switch cells connected in series; wherein an upper cell of the plurality of switch cells is connected to a first end of a primary transformer coil of one of the one or more MFTs, and a second end of the primary transformer coil of the one of the one or more MFTs is connected to a lower cell of the plurality of switch cells; and wherein secondary transformer coils of the one or more MFTs are connected in parallel when there is more than one MFT of the one or more MFTs.
2 . The bi-directional medium voltage converter topology according to claim 1 , wherein each converter of the plurality of bi-directional MV converters comprises active switches, and wherein the active switches are a combination of: an insulated-gate bipolar transistors (IGBT) and a diode; an IGBT and a thyristor; or an IGBT and an anti-parallel transistor.
3 . The bi-directional medium voltage converter topology according to claim 1 , wherein each converter of the plurality of bi-directional MV converters comprises active switches, and wherein at least one of the active switches comprises a metal-insulator-semiconductor field-effect transistor (MOSFET).
4 . The bi-directional medium voltage converter topology according to claim 1 , wherein each converter of the plurality of bi-directional MV converters is operated at a low frequency.
5 . The bi-directional medium voltage converter topology according to claim 1 , wherein pulse number of the multi-pulse LIT comprises 12, 18, 24, 36 or 48.
6 . The bi-directional medium voltage converter topology according to claim 1 , wherein each of the plurality of switch cells comprises a combination of a transistor and one of an antiparallel diode, a thyristor or a further transistor; and wherein the bi-directional multi-stage converter further comprises capacitors that are arranged in parallel to one or more of the plurality of switch cells.
7 . The bi-directional medium voltage converter topology according to claim 1 , wherein the upper cell is connected via a capacitor or via an inductor to the first end of the primary transformer coil of the one of the one or more MFTs.
8 . The bi-directional medium voltage converter topology according to claim 1 , wherein the bi-directional medium voltage converter topology is configured to simulate a pulse LIT concurrently with the operation of the multi-pulse LIT and to use results of the simulation for generating control signals for switches of the plurality of bi-directional MV converters.
9 . A bi-directional medium voltage converter topology, comprising: a multi-pulse line-interphase-transformer (LIT) connected to a three-phase grid; a plurality of bi-directional medium voltage (MV) converters connected to the multi-pulse LIT on an alternating current (AC) side and connected in parallel on a direct current (DC) side; and a medium-voltage to low-voltage (MV-to-LV) DC-to-DC (DC/DC) converter with an AC interface, wherein the MV-to-LV DC/DC converter comprises: a bi-directional multi-stage converter connected to the plurality of bi-directional MV converters; and a bi-directional low voltage (LV) converter; wherein the bi-directional multi-stage converter and the bi-directional LV converter are connected to each other but galvanically insulated via one or more medium frequency transformers (MFTs); wherein the bi-directional multi-stage converter comprises a plurality of switch cells connected in series; wherein each of the plurality of switch cells is connected to a corresponding first end of a primary transformer coil of a corresponding MFT of the one or more MFTs, and a lower side of each switch cell of the plurality of switch cells is connected to a corresponding second end of the primary transformer coil of the corresponding MFT of the one or more MFTs; and wherein secondary transformer coils of the one or more MFTs are connected in parallel when there is more than one MFT of the one or more MFTs.

Description

This patent application claims priority to European Patent Application No. 21191272.0, filed on Aug. 13, 2021, which is incorporated herein in its entirety by reference. FIELD OF THE DISCLOSURE The present invention relates to a bi-directional medium voltage converter topology, and a use of a bi-directional MV converter and a DC/DC converter employing medium frequency transformer in a LIT-based bi-directional medium voltage converter topology. BACKGROUND OF THE INVENTION For applications as renewables (PV solar, wind), storage (battery, hydrogen, fuel cells), large drives, EV charging and datacenter, where at least several Megawatt of electrical power are involved, the connection to the MV grid is done by a MV-to-LV AC/DC converter with galvanic insulation. BRIEF SUMMARY OF THE INVENTION In many of these applications, bi-directional power flow at low costs and with high efficiency is desirable. The described embodiments similarly pertain to the bi-directional medium voltage converter topology, the use of a bi-directional MV converter and a DC/DC converter employing medium frequency transformer in a LIT-based bi-directional medium voltage converter topology, and the use of a bi-directional medium voltage converter topology in a photovoltaic solar power plant, a wind farm, a storage for a battery, hydrogen, fuel cell, a drive, an electric vehicle charging device, or a datacenter. Synergetic effects may arise from different combinations of the embodiments although they might not be described in detail. Technical terms are used by their common sense. If a specific meaning is conveyed to certain terms, definitions of terms will be given in the following in the context of which the terms are used. The following abbreviations are used in this disclosure: MV medium voltage (typically 3 kV-50 kV)LV low voltage (typically up to 1 kV)MFT medium frequency transformer (operating at multiple times the mains frequency)EV electric vehicleHF high frequency (multiple times the mains frequency, e.g. 5 kHz-30 kHz)LIT line-interphase-transformer (provides phase-shifted three-phase systems without galvanic insulation)MLC multi-level converter (cell-based)PV photovoltaicAC Alternating CurrentDC Direct CurrentLIT line interphase transformer According to a first aspect, a bi-directional medium voltage converter topology is provided. The converter comprises an n-pulse line-interphase-transformer (LIT), a plurality of bi-directional medium voltage (MV) converters connected to the LIT on AC side and connected in parallel on DC side, a bi-directional multi-stage DC/DC converter connected to the plurality of bi-directional MV converters, and a bi-directional low voltage (LV) DC/DC converter; wherein the multi-stage DC/DC converter and the LV DC/DC converter are connected to each other galvanically insulated. The topology allows a bi-directional power flow with a significant reduction of size and cost yet in one single direction and a small footprint of the whole system due to employment of MFTs and LITs. The topology is suited for a very broad scope, i.e. for many different applications such as renewables energy applications, for example, photovoltaic/solar and wind energy plants, energy storage for batteries or hydrogen or fuel cells, large drives, EV charging and datacenters. The topology can be realized at low-cost, is simple, reliable and robust. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) FIG. 1 shows a bi-directional medium voltage converter topology in accordance with the disclosure. FIG. 2a shows a diagram of the bi-directional front-end employing a first semiconductor combination of the switches in accordance with the disclosure. FIG. 2b shows a diagram of the bi-directional front-end employing a second semiconductor combination of the switches in accordance with the disclosure. FIG. 2c shows a diagram of the bi-directional front-end employing a third semiconductor combination of the switches in accordance with the disclosure. FIG. 3a shows a diagram of a 12-pulse LIT in accordance with the disclosure. FIG. 3b shows a diagram of a 24-pulse LIT in accordance with the disclosure. FIG. 4a shows a first embodiment of the MV DC/DC converter in accordance with the disclosure. FIG. 4b shows a second embodiment of the MV DC/DC converter in accordance with the disclosure. FIG. 5 shows diagrams of realizations of the MV DC/DC converter in accordance with the disclosure. FIG. 6a shows a numerical circuit simulation of a unidirectional 18-pulse LIT rectifier in accordance with the disclosure. FIG. 6b shows a numerical circuit simulation of a bi-directional 18-pulse LIT rectifier. DETAILED DESCRIPTION OF THE INVENTION Corresponding parts are provided with the same reference symbols in all figures. FIG. 1 shows a bi-directional medium voltage converter topology 100 comprising an 18-pulse LIT 102, a plurality of bi-directional MV converters 104 . . . 106 connected to the LIT on AC side and connected in parallel on DC side, i.e. a