Patent Description:
DC distribution systems have gained significant interest in the recent years due to emerging DC applications such as EV charging and data centers, among others. Such distribution systems use one common DC bus that is typically fed by a single source converter and backed up with a single energy storage system. However, in case of a malfunction of either the source converter or the energy storage system, a reliable operation of the DC distribution system is not possible anymore.

<NPL> describes a ring bus architecture of a DC microgrid. <CIT> D2 describes an electric vehicle charging system, where electric power may be supplied by one or more conventional power sources, such as a utility grid, an energy storage or renewable sources. Electric power from a power source is then converted using a first electric converter and supplied to a ring bus, or conductive ring. <CIT> describes a power electronics system for charging at least one electrically operated vehicle, wherein the power electronics system has at least three modules each having at least one terminal pair with DC output, at least one rectifier; at least one AC input, at least one DC link and a number of switching elements, in which the respective DC outputs of the at least three modules can be connected selectively by means of the switching elements.

The following abbreviations are used in this disclosure:.

An objective of the invention may be to provide an improved DC distribution system.

The problem is solved by the subject-matter of the independent claims. Embodiments are provided by the dependent claims, the following description and the accompanying figures.

The described embodiments similarly pertain to the DC distribution system, the use of DC bus ring structure, and the first and a second method for distributing power in a DC distribution system. Synergetic effects may arise from different combinations of the embodiments although they might not be described in detail.

Further on, it shall be noted that all embodiments of the present invention concerning a method, might be carried out with the order of the steps as described, nevertheless this has not to be the only and essential order of the steps of the method. The herein presented methods can be carried out with another order of the disclosed steps without departing from the respective method embodiment, unless explicitly mentioned to the contrary hereinafter.

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.

According to a first aspect, a DC distribution system is provided that comprises a plurality of power consumer clusters each comprising at least one power consumer. The power consumer clusters are arranged as a ring structure with a common LV-DC ring bus. Each power consumer is connected to the LV-DC ring bus. The DC distribution system further comprises a plurality of normal-open ring switches. Each power consumer cluster is separated from its adjacent power consumer clusters by one of the normal-open ring switches. Each power consumer cluster is fed by a MV-DC/DC converter, which in turn is fed by an AC/DC converter connected to a MV-AC grid.

A normal-open switch is a switch that, without taking any measure, is open or off. That is, it normally does not conduct current as long as it is actively closed, e.g. by applying a control voltage.

The term power consumer refers to, for example, a vehicle-charging device such as an EV charging station or charging post, also known as Electric Vehicle Supply Equipment EVSE, although the vehicle charger does not consume the power itself but supplies power to a vehicle. Therefore, the DC distribution system may be a system for an EV charging facility. The power consumer can further be, for example a cluster of servers in a data center. Therefore, the DC distribution system may also be a system for a data center. However, the DC distribution system may also be used in other applications.

The MV-DC/DC converter converts the medium voltage provided by the AC/DC converter into low voltage. Therefore, the voltage of the DC ring bus is a low voltage, which is typically in the range of <NUM> V - <NUM> kV.

The normal-open ring switches separate the LV-DC ring bus into sections, wherein each power consumer cluster is associated to one of these sections.

In other words, the formation of clusters is proposed. Clusters may be, for example, server clusters in case of data centers and charging pole clusters in case of EV charging. The clusters are fed from independent source converters and have their individual energy storage systems. Further, a ring structure with normally-off switches that can be closed is proposed to enable a continuation of the operation of a cluster even if its source converter and energy storage has malfunctioned, as described in the following embodiments.

According to an embodiment, each AC/DC converter feeds one or more MV-DC/DC converters over a common MV-DC bus.

The AC/DC converter is connected to the MV-AC grid and converts the MV-AC into MV-DC, which is output to the common MV-DC bus. The voltage at the MV-DC bus is the input for, for example, two DC/DC converters, each of which outputs the converted voltage to one section of the LV-DC ring bus.

According to an embodiment, the DC distribution system comprises a plurality of energy storages, wherein each power consumer cluster comprises at least one of the plurality of energy storages, and wherein each energy storage is connected to the LV-DC ring bus.

An energy storage may be a battery storage, which is also commonly known as Battery Energy Storage System (BESS), or may be photovoltaic and/or fuel cells. The energy storage may be used, for example, to reduce of the grid peak consumption and the MV-AC to LV-DC converter power rating. Different types may be contained in the same system. Furthermore, each cluster may accommodate one or several energy storages.

According to an embodiment, the DC distribution system comprises a plurality of energy storage or consumer switches; wherein each power consumer and each energy storage are connected to the LV-DC ring bus via an energy storage or consumer switches.

Using an energy storage switch for the energy storage and a consumer switch for a consumer, a faulty energy storage or power consumer can be disconnected. Further, for example, a power consumer not in use or under maintenance can be disconnected. The switches are arranged between the LV-DC ring bus and DC/DC converters associated with the power consumers or the energy storage.

According to an embodiment, the DC distribution system comprises a plurality of LV-DC/DC converters, each arranged between an energy storage or consumer switch and the battery or consumer.

These LV-DC/DC converters are the converters mentioned in the explanation of the previous embodiment.

According to an embodiment, the power consumer is a vehicle charging post or a cluster of servers in a data center. However, the types of power consumers in the power consumer clusters are not limited to the mentioned.

According to an embodiment, the DC distribution system further comprises AC/DC converter switches and MV-DC/DC converter switches. Each AC/DC converter is connected via one of the AC/DC converter switches to an MV-AC grid, and each MV-DC/DC converter is connected to the LV-DC ring bus via one of the MV-DC/DC converter switches. The AC/DC converter switches and/or the MV-DC/DC converter switches are self-operated or controlled.

These switches may be used to disconnect a faulty converter from the subsequent stage or from the LV-DC bus. "Self-operated" means that they switch themselves if the switches are, for example, reacting to local overcurrent. "Controlled" means, that a controller may control the switches.

According to an embodiment, the DC distribution system further comprises a controller configured to switch any of the MV-DC/DC converter switches, the energy storage or consumer switches and/or the normal-open ring switches.

According to an embodiment, the controller is configured, in case of a malfunction of a MV-DC/DC converter associated with a power consumer cluster, to open the MV-DC/DC converter switch over which the MV-DC/DC converter is connected to the LV-DC ring bus, and to close a normal-open ring switch that connects the power consumer cluster to a neighboring power consumer cluster.

In other words, the controller disconnects the faulty MV-DC/DC converter from its LV-DC bus ring section by opening the corresponding switch, and connects the neighboring LV-DC bus ring section and thus the two adjacent clusters by closing the normal-open ring switch. The controller may connect one neighboring LV-DC bus ring section or both neighboring LV-DC bus ring sections. This applies also for the following embodiments.

According to an embodiment, the controller is configured, in case of a malfunction of an AC/DC converter to open the AC/DC converter switch and/or the MV-DC/DC converter switches of MV-DC/DC converters fed by the AC/DC converter and over which the MV-DC/DC converters are connected to the LV-DC ring bus, and to close the normal-open ring switches that connect the power consumer clusters associated with the MV-DC/DC converters to the neighboring power consumer clusters.

In other words, the controller disconnects the faulty AC/DC converter and the subsequent DC/DC converter stages from their LV-DC bus ring sections by opening the corresponding switches, and connects the LV-DC bus ring section adjacent to these faulty sections by closing the normal-open ring switch between these sections and the adjacent section. Also the normal-open ring switch between the faulty sections may be closed.

According to an embodiment, the controller is configured, in case of a malfunction of an energy storage of an associated power consumer cluster to open the energy storage switch of the malfunctioning energy storage and to close the LV-DC ring switches to the power consumer clusters neighboring the associated power consumer cluster so that the associated power consumer cluster is supported by the energy storages of the neighboring power consumer clusters.

In other words, the controller disconnects the faulty energy storage from its LV-DC bus ring section by opening the corresponding switch, and connects the LV-DC bus ring section adjacent to these faulty section by closing the normal-open ring switch between the faulty section and the adjacent section.

According to an embodiment, the controller is configured, in case of a malfunction of an energy storage of an associated power consumer cluster to open the energy storage switch of the malfunctioning energy storage and to switch the MV-DC /DC converters having the same common MV-DC bus such that a neighboring energy storage connected to these MV-DC /DC converters provides power over these MV-DC /DC converters and the common MV-DC bus to the associated power consumer cluster that comprises the malfunctioning energy storage. The MV-DC /DC converters may be bi-directional converters.

In other words, the controller disconnects the faulty energy storage. Instead of closing the normal-open ring switch between the faulty ring bus section and the neighboring section, the path via the MV-DC/DC converter pair is used, that are linked together by a common MV-DC bus, and which are supplied by the same AC/DC converter.

Further switches may be arranged between the AC/DC converter and the MV-DC/DC converters, i.e. one MV-side switch for each MV DC/DC converter. In case one of the MV-DC/DC converters fails (e.g. to short), this would allow further operation of the AC/DC converter and the other DC/DC converter, which works properly. Furthermore, this would allow maintenance of one MV-DC/DC converter without shutting down the AC/DC and the other DC/DC converter.

According to a further aspect, a use of a DC bus ring structure with power consumer clusters is provided. The power consumer clusters comprise a power consumer and an energy storage in a DC distribution system. The power consumer clusters are separated by switches and each power consumer cluster is fed by an associated MV-DC/DC converter.

An AC/DC converter may feed two or more MV-DC/DC converters over a common MV-DC bus.

According to a further aspect, a method for distributing power in a DC distribution system is provided, wherein the method comprises the following steps. In a first step, a malfunctioning power providing device connected to a section of the LV-DC ring bus is detected. In a second step, the power providing device is disconnected from the section of the LV-DC ring bus. In a third step, a normal-open LV-DC ring bus switch connecting the section of the LV-DC ring bus to a neighboring section of the LV-DC ring bus is closed.

The steps of the method may be performed by the controller of the DC distribution system. A disconnection of switches in case of a malfunction of a converter or an energy storage may be, for example, alternatively performed by a switch itself.

According to an aspect, a further method for distributing power in a DC distribution system is provided, wherein the further method comprises the following steps. In a first step, a malfunctioning energy storage connected to a section of the LV-DC ring bus is detected. In a second step, the energy storage is disconnected from the section of the LV-DC ring bus. In a third step, power of a neighboring energy storage is conducted a MV-DC/DC converter, a common DC bus, and a MV-DC/DC converter, wherein the common DC bus is connected to an MV-AC/DC connector feeding MV-DC/DC converter and the MV-DC/DC converter.

The steps of the further method may be performed by the controller of the DC distribution system.

The controller may comprise circuits without programmable logics or may be or comprise a micro controller, a field programmable gate array (FPGA), an ASIC, a Complex Programmable Logic Devices (CPLD), or any other programmable logic devices known to person skilled in the art.

The controller may perform the steps of the method according to a computer program element that may be part of a computer program, but which can also be an entire program by itself. For example, the computer program element may be used to update an already existing computer program to get to the present invention. The computer program and/or computer program element may be stored on a computer readable medium. The computer readable medium may be seen as a storage medium, such as for example, a USB stick, a CD, a DVD, a data storage device, a hard disk, or any other medium on which a program element as described above can be stored.

These and other features, aspects and advantages of the present invention will become better understood with reference to the accompanying figure and the following description.

<FIG> shows a DC distribution system <NUM> according to an embodiment. The DC distribution system <NUM> comprises a plurality of power consumer clusters <NUM> each comprising a plurality of n power consumers <NUM>. The power consumer clusters <NUM> further each comprise an energy storage <NUM> and LV-DC/DC converters <NUM> for supplying the consumers <NUM> and the energy storage <NUM> with power at appropriate voltages and currents. The DC/DC converters <NUM> for the energy storage are bi-directional such that they can receive power from the common LV-DC ring bus <NUM> but also provide power over the common LV-DC ring bus <NUM> to the consumers <NUM>. The DC/DC converters for the consumers can be bidirectional as well in order to allow vehicle-to-grid support. Therefore, also the MV-DC/DC converter <NUM> and the MV AC/DC converter <NUM> can be bidirectional. "MW" stands for Megawatt in the figures.

The LV-DC/DC converters <NUM> for the power consumers <NUM> and energy storages <NUM> are each connected via a switch <NUM> to the DC bus <NUM>. The switches <NUM> are also referred to as "energy storage or consumer switches" in this disclosure to enable a distinction to other switches in the power distribution system <NUM>. Of course, an energy storage switch <NUM> refers to a switch that connects a LV-DC/DC converter <NUM> of an energy storage <NUM> to the DC bus <NUM>. Correspondingly, a consumer switch <NUM> refers to a switch that connects a DC/DC converter <NUM> of a power consumer <NUM> to the DC bus <NUM>. A power consumer <NUM>, or consumer <NUM> for short, is, for example, a vehicle charging post or a cluster of servers in a data center, but may further be any other power consumer consuming power at similar magnitudes. An energy storage <NUM> may be based, for example on a battery that is suitable to deliver power to these power consumers <NUM>. However, also other power delivering devices or systems such as photovoltaic systems or fuel cells may be used additionally or instead. All such devices or systems are understood under the term "energy storage" in this disclosure. The energy storages <NUM> are useful, for example, for reducing the grid peak consumption and the MV-AC to LV-DC converter power rating.

Each of the power consumers <NUM> and each of the energy storages <NUM> are coupled via the energy storage or consumer switches <NUM> to the LV-DC bus <NUM>, which is arranged as ring bus <NUM> and therefore referred to in the present disclosure as LV-DC ring bus <NUM> or as "ring bus" <NUM> for short. The ring bus <NUM> is divided into sections separated by switches <NUM> that are normally open, and therefore herein referred to as normal-open ring switches <NUM>. The devices of one power consumer cluster <NUM>, i.e. power consumers <NUM> and energy storage <NUM>, are connected to one section of the ring bus <NUM>. Due to the ring structure, every power consumer cluster <NUM> has two neighboring power consumer clusters.

Each cluster <NUM> is supplied by a MV-DC/DC converter <NUM>, which again is supplied by an AC/DC converter <NUM> that is connected to the MV-AC grid. That is, each MV-DC/DC converter <NUM> is coupled via an MV-DC/DC converter switch to one section of the ring bus <NUM>. The AC/DC converter <NUM> is coupled over a common MV-DC bus <NUM> to one, two or more MV-DC/DC converters <NUM>, such that the AC/DC converter <NUM> supplies one, two or more power consumer clusters. In the common MV-DC bus <NUM>, there are MV-DC bus switches <NUM> between the AC/DC converters <NUM> and the MV-DC/DC converters <NUM>. The AC/DC converter <NUM> may be coupled over a switch <NUM>, herein referred to as AC/DC switch <NUM> to the MV-AC grid <NUM>.

Although the switches <NUM>, <NUM>, <NUM>, <NUM> may be realized as manual switches or connectors, the switches are preferably self-operated or controllable switches. The switches may be realized as relays or as transistors or any other electronically switchable devices. The DC distribution system <NUM> may therefore comprises a controller <NUM>. The controller <NUM> may also be responsible for controlling the MV-DC/DC converters <NUM>, which may be operated be-directional. The dashed lines in <FIG> indicate control lines. The DC distribution system <NUM> may further comprise failure detection circuits that detect an outage or malfunction of a power supplying device such as the MV-DC/DC converters or the energy storages. Converters or energy storages having outages, defects, malfunctions or which are under maintenance are referred to as malfunctioning or faulty devices for short in this disclosure. In the case of faulty energy storages or faulty power consumers, it is understood that either the power consumer <NUM> may be faulty or the DC/DC converter <NUM> connected to the power consumer <NUM> or energy storage <NUM>. For the definition of "power consumer" it is referred to the explanation above describing the first aspect.

The LV-DC ring <NUM> is a complete ring. That is, if all normal-open ring switches <NUM> would be closed, all section of the ring would be galvanically connected to each other. By providing a complete ring, any power consumer cluster <NUM> and any substructure fed by an AC/DC converter has two neighbors such that in case of faults or malfunctions, the according neighboring power consumer clusters <NUM> or AC/DC substructures can supply the power consumer clusters <NUM> or substructures, where a fault or malfunction in a power supplying device occurred.

In <FIG>, the reference signs for the converters, switches, power consumers and clusters are drawn only once representative for all corresponding devices in the DC distribution system. In the following <FIG> and <FIG>, individual devices are identified by specific reference signs.

<FIG> and <FIG> show examples of malfunctioning devices in the DC distribution systems and how to partially or completely offset the negative effect on the power consumer clusters or power consumers, respectively.

<FIG>, shows an example, where one MV-DC/DC converter <NUM> of the MV-DC/DC converters <NUM> is faulty or malfunctioning. The MV-DC/DC converter <NUM> supplies the power consumer cluster <NUM>. If this converter <NUM> is malfunctioning, switch <NUM> is opened to disconnect the converter <NUM> from the section <NUM> of the common LV-DC ring bus <NUM>. Since the power consumer cluster <NUM> is not provided with power from the MV-DC/DC converter <NUM> anymore and the energy storage may not be sufficient to replace the outage, switches <NUM> and <NUM> are closed such that power is provided from the neighboring ring bus sections <NUM> and <NUM>. In case that the sections <NUM> and <NUM> are already utilized to capacity, the total available power could be shared such each of the power consumer clusters <NUM>, <NUM>, and <NUM> has a share of <NUM>/<NUM> of the total available power at his disposal.

The switches <NUM>, <NUM> may be mechanical or electro-mechanical switches or connectors that are switched manually, however, preferably they are controlled by controller <NUM>. The DC distribution system <NUM> may comprise one or more fault detection circuits (not shown in the figures) that communicate with the controller <NUM>, so that a fully automatic switching is achieved. The DC distribution systems may further comprise means to distribute power between the sections. For example, a section may be prioritized such that only a distinct amount of power is shared with other sections or that power is only shared if a predetermined capacity utilization is not exceeded. For example, section <NUM> may only be connected to section <NUM> if the capacity utilization of power of section <NUM> is below <NUM>%.

In embodiments, only one neighbor may be connected to the section <NUM> or cluster <NUM>, respectively. In other embodiments, more neighboring sections than the direct neighbor sections <NUM>, <NUM> may be connected together. The decision for adding more neighbors may be based on priorities or on the actual required power in the single sections.

The principle presented above can also be applied in case of a malfunction of one of the AC/DC converter <NUM>, where ring bus switches <NUM>, <NUM>, and <NUM> are closed so that power can be provided by sections <NUM> and <NUM>.

The MV-DC bus switch <NUM> arranged between the AC/DC converter <NUM> and the MV-DC/DC converter <NUM> allow further operation of the AC/DC converter <NUM> and the other DC/DC converter <NUM>, which works properly, in case MV-DC/DC <NUM> converter fails (e.g. to short or due to maintenance).

<FIG> shows an example, where one energy storage <NUM> is faulty. The faulty energy storage is part of the power consumer cluster <NUM> of ring bus section <NUM>, to which consumers <NUM> and <NUM> are connectable and which is supplied by MV-DC/DC converter <NUM>, which is again supplied by AC/DC converter <NUM>. Energy storage or consumer switch <NUM> is open to disconnect the faulty energy storage <NUM> from the LV-DC ring bus section <NUM>. In order to offset the effect of the outage, there are two principal options.

The first option is similar to the one discussed in <FIG>. That is, the ring bus switches <NUM> and <NUM> are closed such that the neighboring bus ring sections <NUM> and <NUM> are galvanically connected to the ring bus section <NUM> with the faulty energy storage <NUM> indicated by the paths <NUM> and <NUM> in <FIG>. In this case, energy storages <NUM> and <NUM> of the neighboring clusters <NUM> and <NUM> are switched to section <NUM> to replace at least in parts the faulty energy storage <NUM>.

As a second option, path <NUM> over the MV-DC/DC converter <NUM>, the common MV-DC bus <NUM> and the MV-DC/DC converter <NUM> may be chosen for including the energy storage <NUM> into the power consumer cluster <NUM>. For this, the MV-DC/DC converter <NUM> may be designed bi-directional. Similarly, the MV-DC/DC converter <NUM> may be designed bi-directional for supporting a power flow from energy storage <NUM> to the cluster <NUM> in case of a malfunction of energy storage <NUM>. In the second option, sections <NUM> and <NUM> would still be separate, so that the interactions between the two sections <NUM>, <NUM> or clusters <NUM>, <NUM> can be kept low.

In embodiments, a combination of paths <NUM> and <NUM>, a combination of paths <NUM> and <NUM>, or one of the paths <NUM>, <NUM>, <NUM> may be chosen. With respect to the switching, similarly to the case presented in <FIG>, a controller <NUM> may be in charge of actuating the switches <NUM>, <NUM> and/or controlling the MV-DC/DC converter <NUM>. Alternatively, the switches can be operated manually by an operator on site or, for example, via a communication device that includes an appropriate application or any method known to a skilled person.

<FIG> shows a method <NUM> for distributing power in a DC distribution system <NUM> with a LV-DC ring bus <NUM> separated by normal-open LV-DC ring bus switches <NUM>, such as a system shown in <FIG> in combination with the fault case shown in <FIG> and/or <FIG>. The method <NUM> comprises the following steps: detecting <NUM> a malfunctioning power providing device <NUM>, <NUM> connected to a section <NUM>, <NUM> of the LV-DC ring bus <NUM>; disconnecting <NUM> the power providing device <NUM>, <NUM> from the section <NUM>, <NUM> of the LV-DC ring bus <NUM>; and closing <NUM> a normal-open LV-DC ring bus switch <NUM>, <NUM> connecting the section <NUM>, <NUM> of the LV-DC ring bus to a neighboring section <NUM>, <NUM> of the LV-DC ring bus <NUM>. The power providing device is, for example, a MV-DC/DC converter <NUM> or an energy storage <NUM>, but may also be a photovoltaic device or fuel cell. The last step of the method may further comprise closing a further normal-open LV-DC ring bus switch <NUM>, <NUM> connecting the section <NUM>, <NUM> of the LV-DC ring bus <NUM> to a further neighboring section <NUM>, <NUM> of the LV-DC ring bus.

Claim 1:
Direct Current, DC, distribution system (<NUM>) comprising
a plurality of power consumer clusters (<NUM>) each comprising at least one power consumer (<NUM>);
wherein
the power consumer clusters (<NUM>) are arranged as a ring structure with a common low voltage, LV, DC ring bus (<NUM>);
each power consumer (<NUM>) is connected to the LV-DC ring bus (<NUM>);
the DC distribution system (<NUM>) further comprises a plurality of normal-open ring switches (<NUM>);
each power consumer cluster (<NUM>) is separated from its adjacent power consumer clusters by one of the normal-open ring switches (<NUM>);
characterized in that
each power consumer cluster (<NUM>) is fed by a medium voltage, MV, DC/DC converter (<NUM>), which in turn is fed by a MV-AC/DC converter (<NUM>) connected to a MV-AC grid (<NUM>), wherein the MV-DC/DC converter is configured to convert the medium voltage provided by the AC/DC converter into low voltage.