EP4241357A1

EP4241357A1 - A power distribution arrangement

Info

Publication number: EP4241357A1
Application number: EP20803517.0A
Authority: EP
Inventors: Ritwik MAJUMDER
Original assignee: Hitachi Energy Switzerland AG
Current assignee: Hitachi Energy Ltd
Priority date: 2020-11-05
Filing date: 2020-11-05
Publication date: 2023-09-13
Also published as: WO2022096106A1

Abstract

A power distribution arrangement (100), for distributing AC power to a plurality of loads requiring AC power, is disclosed. The power distribution arrangement (100) comprises a power distribution substation (10) comprising a plurality of transformers (11, 12), each of the transformers (11, 12) being connected or connectable to at least one power source providing AC power. The power distribution arrangement (100) comprises a plurality of switches (1-6, 60-68), a plurality of buses (13-15), and a plurality of feeders (41-47). Each of the feeders (41-47) is selectively and controllably connectable to at least one of the loads and to at least one of the transformers (11, 12), respectively, via one or more of the buses (13-15), by means of at least some of the switches (1-6, 60-68). The power distribution arrangement (100) comprises a DC transmission line (70), which at one end is selectively and controllably connectable to the respective ones of the feeders (41-47) via at least one bus (15), via a converter (71), by means of at least one of the switches (1-6, 60-68), and at another end thereof is connected or connectable to another power distribution substation. The power distribution arrangement (100) comprises at least one control unit (90, 96, 116) configured to control any power transfer in the DC transmission line (70) between the at least one bus (15) and the other power distribution substation. At least one energy storage system, ESS, (110) is connected to at least one of the DC transmission line (70) and the converter (71). The at least one ESS (110) is configured to selectively and controllably supply power to the DC transmission line (70) or absorb power from the DC transmission line (70). The at least one control unit (90, 96, 116) is configured to control the at least one ESS (110) to supply power to the DC transmission line (70) or absorb power from the DC transmission line (70).

Description

A POWER DISTRIBUTION ARRANGEMENT

TECHNICAL FIELD

The present invention relates to a power distribution arrangement for distributing alternating current (AC) power to a plurality of loads requiring AC power, and a method in such a power distribution arrangement.

BACKGROUND

An electrical power distribution system may employ connection schemes or topologies of so-called feeders for connecting one or more electrical substations to one or more areas which may include a plurality of consumers of power. The feeders may be referred to as distribution feeders. The electrical substation(s), which in the following may be referred to simply as substation(s), may change the voltage level by decreasing the voltage level. The substation(s) may for example change the voltage level from a relatively high transmission voltage level, used in an electrical power transmission system connected to the electrical power distribution system, to a medium or relatively low distribution voltage level, used in the electrical power distribution system. The substation(s) may provide further functionality in addition to changing voltage level. The feeders may connect transformers, e.g., distribution transformers, in the substation(s) with the one or more areas or consumers of power, for distribution of power from the substation(s) to the one or more areas or consumers of power. Each or any of the feeders may for example comprise one or more overhead lines and/or cables. The loading in a feeder may vary with time. The variation of loading in a feeder with time may depend on variation in power requirement of one or more areas or consumers of power to which the feeder is connected. The variation of loading in a feeder with time may also depend on the type of load the one or more areas or consumers of power comprise or constitute - for example residential load, commercial load, or industrial load. Each feeder may have a certain power rating, which may be defined as the highest allowed power transfer level in the feeder.

SUMMARY

In an electrical power distribution arrangement there may be a plurality of feeders for connecting a substation to one or more geographical areas to which alternating current (AC) power is distributed, which one or more geographical areas may include a plurality of consumers of power. The substation may include one or more transformers, each of which may be connected or connectable (e.g., selectively and controllably connectable) to at least one power source providing AC power. The one or more geographical areas or the consumers of power may be referred to as a plurality loads, each of which may require AC power. Each of the feeders may be selectively and controllably connectable to at least one of the loads and to at least one of the transformers, respectively, via one or more buses (or busbars, bus sections, or bus parts). By means of switches, one or more of the feeders may be selectively and controllably connected or disconnected to or from the one or more of the buses in order to connect or disconnect the one or more feeders to or from at least one of the transformers. Thereby, AC power can be distributed to the loads via the feeders. The loading in the feeders may be changing continuously, and based on the loading in the feeders, switches may be opened and closed to achieve different loading at the transformers. The switches may for example be opened and closed such that loading in the respective ones of the transformers becomes more balanced between the transformers. Such opening and closing of the switches - in order to connect or disconnect one or more feeders to or from the transformers - may in the context of the present application be referred to as feeder reconfiguration (or feeder configuration, depending on when the opening and closing of the switches is carried out). By providing a relatively large number of buses and switches - in comparison to the number of transformers and feeders - and configuring the connections between the transformers and feeders via the buses and switches to allow for many different ways of connecting different feeders with different transformers - a relatively high flexibility in feeder reconfiguration may be achieved. However, at least in some applications an even higher flexibility in feeder reconfiguration may be desired or even required.

In view of the foregoing, a concern of the present invention is to provide a power distribution arrangement for distributing alternating current AC power to a plurality of loads requiring AC power, which power distribution arrangement employ feeders, and which power distribution arrangement may allow for a relatively high flexibility in feeder reconfiguration.

To address at least one of this concern and other concerns, a power distribution arrangement and a method in a power distribution arrangement in accordance with the independent claims are provided. Preferred embodiments are defined by the dependent claims.

According to a first aspect of the present invention, a power distribution arrangement is provided. The power distribution arrangement is for distributing AC power to a plurality of loads requiring AC power. The AC power requirement of any load may vary with time. The power distribution arrangement may comprise a substation, e.g., a power distribution substation, which may comprise a plurality of transformers. Each of the transformers may be connected or connectable to at least one power source providing AC power. The power distribution arrangement may comprise a plurality of switches, a plurality of buses (or busbars, bus sections, or bus parts), and a plurality of feeders. Each of the feeders may be selectively and controllably connectable to at least one of the loads and to at least one of the transformers, respectively, via one or more of the buses. At least some of the switches may be configured to selectively and controllably connect or disconnect one or more of the feeders to or from the one or more of the buses in order to connect or disconnect the one or more feeders to or from at least one of the transformers. The power distribution arrangement may comprise a direct current (DC) transmission line. The DC transmission line may at one end thereof be selectively and controllably connectable to the respective ones of the feeders via at least one bus, via a converter configured to convert DC power to AC power, or vice versa. The DC transmission line may at another (or the other) end thereof be connected or connectable to another substation, e.g., another power distribution substation. At least one of the switches may be configured to selectively and controllably connect or disconnect the DC transmission line to or from the at least one bus in order to connect or disconnect the DC transmission line to or from the feeders. The power distribution arrangement may comprise at least one control unit. The at least one control unit may be communicatively connected with the DC transmission line. The at least one control unit may be configured to control any power transfer in the DC transmission line between the at least one bus and the other power distribution substation. The power distribution arrangement may comprise at least one energy storage system (ESS), which may be connected to at least one of the DC transmission line and the converter. The at least one ESS may be configured to selectively and controllably supply power to the DC transmission line or absorb power from the DC transmission line (e.g., absorb power from any power transfer in the DC transmission line). The at least one control unit may be configured to control the at least one ESS to supply power to the DC transmission line or absorb power from the DC transmission line (e.g., absorb power from any power transfer in the DC transmission line).

By the providing of the DC transmission line, which at one end thereof may selectively and controllably connectable to the respective ones of the feeders via at least one bus, and by the switches being controllable in order to selectively connect or disconnect one or more of the feeders to or from at least one of the transformers via one or more of the buses and to selectively connect or disconnect the DC transmission line to or from one or more of the feeders via the at least one bus, feeder reconfiguration may be carried out while utilizing or taking into account any power transfer in the DC transmission line between the at least one bus and the other power distribution substation.

By providing additional power transfer capability via the DC transmission line, in addition to power transfer capability from the power sources providing AC power via the transformers, an increased flexibility in feeder reconfiguration may be facilitated or allowed. For example, an operator of the power distribution arrangement, or of a power distribution system of which the power distribution arrangement may be a part of, can utilize the power transfer capability in the DC transmission line in order to achieve more flexibility in reconfiguration of feeders. Furthermore, an additional increase in flexibility in feeder reconfiguration may be facilitated or allowed by the providing of the at least one ESS, which may be connected to at least one of the DC transmission line and the converter and may be configured to selectively and controllably supply power to the DC transmission line or absorb power from any power transfer in the DC transmission line. Accordingly, the at least one ESS may provide an additional degree of freedom in the controlling of power transfer capability in the DC transmission line, which may be utilized or taken into account in reconfiguration of feeders, whereby an even higher flexibility in reconfiguration of feeders may be achieved.

Depending on the circumstances, power may be supplied to the DC transmission line by the at least one ESS, based on the measure of the available energy in the at least one ESS and the power supply rating of the at least one ESS, or power from any power transfer in the DC transmission line may be absorbed by the at least one ESS (e.g., for subsequent use in supplying power to the DC transmission line if and when needed). For example, during certain conditions there may be a surplus in available power from the transformers, and power from any power transfer in the DC transmission line may then be absorbed by the at least one ESS. In other words, if there is available power headroom in the transformers to transfer more power (e.g., to the feeders), power from any power transfer in the DC transmission line may be absorbed by the at least one ESS.

By carrying out feeder reconfiguration while utilizing or taking into account any power transfer in the DC transmission line between the at least one bus and the other power distribution substation, the power transfer reliability to the loads may become relatively high. Further, it may allow for or enable for increasing the power transfer to one or more of the loads (e.g., as a result in increased power demand at the load(s)) without or with only relatively small investments in transformer and feeder capacity (e.g., to increase their power ratings) being required.

Reconfiguration of the feeders may be initiated by an operator, or based on occurrence of a predefined type of event, such as, for example, that it is sensed that a fault is occurring in the DC transmission line, and/or that it is sensed that there is an overload in one or more of the transformers (e.g., if the loading in one or more of the transformers exceed the power ratings of the respective ones of that or those transformers). Such sensing may be for example be carried out by some component or entity that is configured to monitor the state of the power distribution arrangement or a power distribution system of which the power distribution arrangement may be a part. The component or entity may for example comprise a fault protection or detection unit which may be configured to monitor transmission lines in the power distribution arrangement or in a power distribution system of which the power distribution arrangement may be a part of and sense whether any fault occurs in the transmission lines. The providing of the DC transmission line and any required switch(es) and bus(es) may require relatively little changes in an existing power distribution arrangement employing feeders. The DC transmission line may for example comprise or be constituted by a Medium Voltage DC (MVDC) transmission line, which may be referred to as an MVDC link.

By the at least one ESS being connected to at least one of the DC transmission line and the converter, it may for example be meant that the at least one ESS may be substantially directly connected to the DC transmission line, or that the at least one ESS may be connected to the DC transmission line via the converter. As mentioned in the foregoing, the DC transmission line may at one end thereof be selectively and controllably connectable to the respective ones of the feeders via at least one bus, via the converter. The converter may for example be connected to the DC transmission line via a first terminal (e.g., a DC terminal) of the converter. The at least one ESS may for example be connected to a second terminal (e.g., a DC terminal) of the converter. In alternative or in addition, the at least one ESS may be connected to the DC transmission line via one or more DC buses of the DC transmission line.

The at least one control unit may be communicatively connected with the transformers, the feeders and the switches. The at least one control unit may be configured to control operation of the switches in order to selectively connect or disconnect one or more of the feeders to or from at least one of the transformers via one or more of the buses and to selectively connect or disconnect the DC transmission line to or from one or more of the feeders via the at least one bus. Thereby, AC power may be distributed to the loads via the feeders. The at least one control unit may be configured to control the operation of the switches based on: loading in and a power rating of the respective ones of the feeders, loading in and a power rating of the respective ones of the transformers, any power transfer in the DC transmission line from the other power distribution substation to the at least one bus, and a measure of the available energy in the at least one ESS and power supply rating of the at least one ESS.

By the at least one control unit being configured to control operation of the switches in order to selectively connect or disconnect one or more of the feeders to or from at least one of the transformers via one or more of the buses and to selectively connect or disconnect the DC transmission line to or from one or more of the feeders via the at least one bus, feeder reconfiguration can be carried out while utilizing or taking into account any power transfer in the DC transmission line from the other power distribution substation to the at least one bus, possibly caused or supplemented by power supplied to the DC transmission line by the at least one ESS, based on the measure of the available energy in the at least one ESS and the power supply rating of the at least one ESS. By providing additional power transfer capability via the DC transmission line, in addition to power transfer capability from the power sources providing AC power via the transformers, an increased flexibility in feeder reconfiguration may be achieved. For example, an operator of the power distribution arrangement, or of a power distribution system of which the power distribution arrangement may be a part of, can utilize the power transfer capability via the DC transmission line in order to be achieve more flexibility in reconfiguration of feeders.

The at least one ESS may for example comprise at least one battery ESS (BESS). For example in such a case, the measure of the available energy in the at least one ESS may for example comprise a state of charge of the at least one ESS (or at least on BESS).

In case there would be no power transfer in the DC transmission line from the other power distribution substation to the at least one bus, the at least one ESS may be used to supply power to the DC transmission line, such that power may still be transferred to the feeder(s) via the converter. The amount of power that may be supplied may be governed by the measure of the available energy in the at least one ESS and power supply rating of the at least one ESS. The at least one control unit may be configured to control the operation of the switches based on the power that may be supplied. For example, due to the DC transmission line being disconnected from the other power distribution substation at the end of the DC transmission line closest to the other power distribution substation, there may be no power transfer in the DC transmission line from the other power distribution substation to the at least one bus. Such a disconnection may for example have been made responsive to a fault in a converter via which the DC transmission line may be connected to the other power distribution substation being sensed, e.g., by some fault sensing system.

The power distribution arrangement may comprise several control units, such as, for example, at least three control units. For example, the power distribution arrangement may comprise a first control unit, a second control unit and a third control unit. The control units may be communicatively coupled with each other. The first control unit may for example be a control unit of, or relating to, the DC transmission line, and may be referred to as a DC transmission line control unit or controller, or a MVDC link controller. The first control unit may be communicatively connected with the DC transmission line, or with the converter, which may be considered as a part of the DC transmission line. The first control unit may be configured to control any power transfer in the DC transmission line between the at least one bus and the other power distribution substation. The second control unit may for example be a control unit of, or relating to, the switches and/or the power distribution substation, and may be referred to as a power distribution substation control unit or controller. The second control unit may be communicatively connected with the transformers, the feeders and the switches. The second control unit may be configured to control the operation of the switches. The third control unit may for example be a control unit of, or relating to, the at least one ESS, and may be referred to as an ESS control unit or controller. The third control unit may be communicatively connected with the at least one ESS. The third control unit may be configured to control the at least one ESS to supply power to the DC transmission line or absorb power from any power transfer in the DC transmission line. Such first, second and third control units will be described further in the following. Possibly, the respective controlling capabilities of any at least two of the first control unit, the second control unit and the third control unit may be realized in or implemented by a single control unit.

Each or any of the switches in the power distribution arrangement may for example comprise one or more so called transfer switches and/or circuit breakers. The one or more circuit breakers may for example comprise one or more sulfur hexafluoride (SFe) high- voltage circuit breakers and/or carbon dioxide (CO2) high-voltage circuit breakers.

The at least one power source providing AC power may for example comprise or be constituted by a power system, or a part of a power system. For example, each of the transformers may be selectively and controllably connectable to a power system providing AC power.

In the context of the present application, by a plurality loads requiring AC power, it may be meant a plurality of geographical areas to which AC power is distributed, or a plurality of consumers of AC power (which consumers may or may not be located in respective ones of the plurality of geographical areas).

In the context of the present application, by a feeder it is meant a conducting device, element, component, etc., such as one or more transmission lines, which connect(s) a substation with one or more loads for distribution or transfer of power to the one or more loads from the substation. A feeder, e.g., comprising one or more transmission lines, may for example comprise one or more overhead lines and/or cables.

In the context of the present application, by a power rating of a component, such as any of the feeders, any of the transformers, or the DC transmission line, it may be meant the highest allowed power transfer level in the component.

In the context of the present application, by a first component being communicatively connected with a second component, it is meant that the components are able to communicate via wired and/or wireless communication means or techniques, for example via any appropriate wired and/or wireless communication means or techniques as known in the art, for transmitting messages, instructions, data, commands, etc., from the first component to the second component and possibly vice versa. Wired communication means may for example comprise radio frequency (RF) communication, infrared communication (e.g., employing a communication link employing infrared light) or another type of free-space optical communication. Wireless communication means may for example comprise at least one optical waveguide, or optical transmission line (e.g., an optical fiber), and/or at least one electrical conductor (e.g., a cable or wire, e.g., a copper conductor or cable, or copper wire).

The power distribution arrangement may comprise at least one sensor, which may be configured to sense one or more properties or characteristics of one or more of the components of the power distribution arrangement. The at least one sensor may for example be configured to sense loading in each or any of the transformers, and/or sense loading in each or any of the feeders or in a part or segment of each or any of the feeders. The at least one control unit may be communicatively connected with the at least one sensor. Thereby, the at least one control unit may be configured to receive sensor data (e.g., data indicative of one or more properties or characteristics sensed by the at least one sensor).

In order to provide additional power transfer capability, the power distribution arrangement may comprise more than one DC transmission line. Each of the DC transmission lines may at one end thereof be selectively and controllably connectable to the respective ones of the feeders via at least one bus, via a converter configured to convert DC power to AC power, or vice versa. The DC transmission lines may at another (or the other) end thereof be connected or connectable to other substations, e.g., other power distribution substations. At least one of the switches may be configured to selectively and controllably connect or disconnect each of the DC transmission lines to or from the at least one bus in order to connect or disconnect the DC transmission line to or from the feeders. The at least one control unit may be configured to control the operation of the switches based on: loading in and a power rating of the respective ones of the feeders, loading in and a power rating of the respective ones of the transformers, and any power transfer in each of the DC transmission lines between the respective ones of the other power distribution substations and the at least one bus. Possibly, there could be provided at least one ESS for each DC transmission line. For each DC transmission line, the corresponding at least one ESS may be connected to at least one of the DC transmission line and the associated converter. For each DC transmission line, the corresponding at least one ESS may be configured to selectively and controllably supply power to the DC transmission line or absorb power from any power transfer in the DC transmission line. For each DC transmission line, the at least one control unit may be configured to control the corresponding at least one ESS to supply power to the DC transmission line or absorb power from any power transfer in the DC transmission line.

According to a second aspect of the present invention, a method in a power distribution arrangement is provided. The method is for distributing AC power to a plurality of loads requiring AC power. The power distribution arrangement may comprise a substation, e.g., a power distribution substation, which may comprise a plurality of transformers. Each of the transformers may be connected or connectable to at least one power source providing AC power. The power distribution arrangement may comprise a plurality of switches, a plurality of buses (or busbars, bus sections, or bus parts), and a plurality of feeders. Each of the feeders may be selectively and controllably connectable to at least one of the loads and to at least one of the transformers, respectively, via one or more of the buses. At least some of the switches may be configured to selectively and controllably connect or disconnect one or more of the feeders to or from the one or more of the buses in order to connect or disconnect the one or more feeders to or from at least one of the transformers. The power distribution arrangement may comprise a DC transmission line. The DC transmission line may at one end thereof be selectively and controllably connectable to the respective ones of the feeders via at least one bus, via a converter configured to convert DC power to AC power, or vice versa. The DC transmission line may at another (or the other) end thereof be connected or connectable to another substation, e.g., another power distribution substation. At least one of the switches may be configured to selectively and controllably connect or disconnect the DC transmission line to or from the at least one bus in order to connect or disconnect the DC transmission line to or from the feeders. The power distribution arrangement may comprise at least one ESS, which may be connected to at least one of the DC transmission line and the converter. The at least one ESS may be configured to selectively and controllably supply power to the DC transmission line or absorb power from the DC transmission line.

The method according to the second aspect of the present invention may comprise controlling any power transfer in the DC transmission line between the at least one bus and the other power distribution substation. The method according to the second aspect of the present invention may comprise controlling the at least one ESS to supply power to the DC transmission line or absorb power from the DC transmission line.

According to a third aspect of the present invention, a control unit for a power distribution arrangement is provided. The control unit comprises a processor configured to carry out a method according to the second aspect of the present invention. The control unit may be a control unit in a power distribution arrangement according to the first aspect of the present invention.

The control unit according to the third aspect of the present invention or any control unit in the power distribution arrangement according to the first aspect of the present invention may for example include or be constituted by any suitable central processing unit (CPU), microcontroller, digital signal processor (DSP), Application Specific Integrated Circuit (ASIC), Field Programmable Gate Array (FPGA), etc., or any combination thereof. The control unit according to the third aspect of the present invention or any control unit in the power distribution arrangement according to the first aspect of the present invention may optionally be capable of executing software instructions stored in a computer program product e.g. in the form of a memory. The memory may for example be any combination of read and write memory (RAM) and read only memory (ROM). The memory may comprise persistent storage, which for example can be a magnetic memory, an optical memory, a solid-state memory or a remotely mounted memory, or any combination thereof.

According to a fourth aspect of the present invention, a computer program is provided. The computer program comprises instructions, which when executed by one or more processors comprised in at least one control unit for a power distribution arrangement according to the first aspect of the present invention, cause the at least one control unit to perform the method according to the second aspect of the present invention.

According to a fifth aspect of the present invention, a processor-readable medium is provided. The processor-readable medium has a computer program loaded thereon, wherein the computer program comprises instructions, which when executed by one or more processors comprised in at least one control unit for a power distribution arrangement according to the first aspect of the present invention, cause the at least one control unit to perform the method according to the second aspect of the present invention.

Further objects and advantages of the present invention are described in the following by means of exemplifying embodiments. It is noted that the present invention relates to all possible combinations of features recited in the claims. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the description herein. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments of the present invention will be described below with reference to the accompanying drawings.

Each of Figures 1 to 5 is a schematic view of a power distribution arrangement according to one or more embodiments of the present invention.

Figure 6 is a flowchart illustrating a method in a power distribution arrangement according to one or more embodiments of the present invention.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate embodiments of the present invention, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

The present invention will now be described hereinafter with reference to the accompanying drawings, in which exemplifying embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments of the present invention set forth herein; rather, these embodiments are provided by way of example so that this disclosure will convey the scope of the present invention to those skilled in the art.

Figure 1 is a schematic view of a power distribution arrangement 100 according to one or more embodiments of the present invention. The power distribution arrangement 100 is for distributing alternating current (AC) power to a plurality of loads (not shown in Figure 1) requiring AC power. The AC power requirement of any of the loads may vary with time. The power distribution arrangement 100 comprises a substation 10, e.g., a power distribution substation. The substation 10 comprises a plurality of transformers. In accordance with the embodiment of the present invention illustrated in Figure 1, the substation 10 comprises two transformers 11, 12. However, it is to be understood that the substation 10 may comprise more than two transformers.

The power distribution arrangement 100 comprises a plurality of switches. In accordance with the embodiment of the present invention illustrated in Figure 1, the power distribution arrangement 100 comprises switches 1-6 and 60-68. It is to be understood that there may be more or fewer switches provided in the power distribution arrangement 100 than illustrated in Figure 1.

Each of the transformers 11, 12 is connected or connectable to at least one power source providing AC power (not shown in Figure 1). As indicated in Figure 1, each of the transformers 11, 12 may be selectively and controllably connectable to at least one power source by means of the switches 1 and 2, respectively.

The power distribution arrangement 100 comprises a plurality of buses (or bus sections, busbars, or bus parts). In accordance with the embodiment of the present invention illustrated in Figure 1, the power distribution arrangement 100 comprises three buses 15, 16, 17. However, it is to be understood that the power distribution arrangement 100 may comprise more or fewer buses than three.

The power distribution arrangement 100 comprises a plurality of feeders. In accordance with the embodiment of the present invention illustrated in Figure 1, the power distribution arrangement 100 comprises feeders 41-47. It is to be understood that there may be more or fewer feeders provided in the power distribution arrangement 100 than illustrated in Figure 1.

Generally, each of the feeders is selectively and controllably connectable to at least one of the loads and to at least one of the transformers, respectively, via one or more of the buses of the power distribution arrangement, by means of at least some of the switches of the power distribution arrangement.

Each of the feeders 41-47 is selectively and controllably connectable to at least one of the loads. Each of the ends of the feeders 41-47 with dashed lines is connected to one or more of the loads (not shown in Figure 1).

As illustrated in Figure 1, each of the feeders 41-47 is selectively and controllably connectable to at least one of the loads and to at least one of the transformers 11, 12, respectively, via one or more of the buses 13, 14, 15. The switches 3-6 and 60-67 are configured to selectively and controllably connect or disconnect one or more of the feeders 41-47 to or from the one or more of the buses 13, 14, 15 in order to connect or disconnect the one or more feeders 41-47 to or from at least one of the transformers 11, 12. For example, the switches 1, 2, 3, 4 and 5 may be normally-closed switches, and the switch 6 may be a normally-open switch.

As illustrated in Figure 1, the feeders 43 and 44 may be connected to either the transformer 11 or the transformer 12, or to both of the transformers 11 and 12, depending on whether the respective ones of the switches 3, 4, 5 and 6 are open or closed.

The power distribution arrangement 100 comprises a direct current (DC) transmission line 70. The DC transmission line 70 is at one end thereof selectively and controllably connectable to the respective ones of the feeders 41-47 via at least one bus, via a converter 71 configured to convert DC power to AC power, or vice versa. As illustrated in Figure 1, in accordance with the illustrated embodiment of the present invention, the DC transmission line 70 is at one end thereof selectively and controllably connectable to at least the feeders 45-47 via the bus 15. The DC transmission line 70 may for example comprise or be constituted by a Medium Voltage DC (MVDC) transmission line, which may be referred to as an MVDC link.

It is to be understood that the DC transmission line 70 could be selectively and controllably connectable to at least some of the feeders via more than one bus. Further, the DC transmission line 70 may be connected or connectable between different buses (or bus sections) of the power distribution arrangement 100. These aspects relating to the DC transmission line 70 may be applied or implemented in any one of the embodiments of the present invention disclosed herein.

The DC transmission line 70 is at the other end thereof connected or connectable to another substation, e.g., another power distribution substation (not shown in Figure 1).

Generally, at least one of the switches is configured to selectively and controllably connect or disconnect the DC transmission line 70 to or from the at least one bus in order to connect or disconnect the DC transmission line 70 to or from the feeders 41-47. As illustrated in Figure 1, in accordance with the illustrated embodiment of the present invention, the switch 68 is configured to selectively and controllably connect or disconnect the DC transmission line 70 to or from the bus 15 in order to connect or disconnect the DC transmission line 70 to or from the feeders 41-47.

Further in accordance with the illustrated embodiment of the present invention, a transformer 72 is connected between the converter 71 and the switch 68. The transformer 72 may be omitted.

Generally, at least some of the feeders may be selectively and controllably connectable to at least one of the transformers by means of a plurality of buses connected or connectable in series. The DC transmission line may be selectively and controllably connectable to at least one of the buses that are connected or connectable in series. In accordance with the embodiment of the present invention illustrated in Figure 1, the buses 15, 16, 17 are connected or connectable in series, and the DC transmission line 70 is selectively and controllably connected or connectable to the bus 15.

It is to be understood that the configuration (e.g., interconnections) of feeders, buses and switches illustrated in Figure 1 is according to an example and for illustrating principles of one or more embodiments of the present invention. The configuration (e.g., interconnections) of feeders, buses and switches could be different, for example such as illustrated in any one of Figures 2 to 5.

The power distribution arrangement 100 comprises a first control unit 90. The first control unit 90 may be communicatively connected with the DC transmission line 70. The first control unit 90 is configured to control any power transfer in the DC transmission line 70 between the at least one bus and the other power distribution substation. The first control unit 90 is at least configured to control any power transfer in the DC transmission line 70 from the other power distribution substation to the at least one bus, and possibly also any power transfer in the DC transmission line 70 from the at least one bus to the other power distribution substation. To that end, the first control unit 90 may be communicatively connected with the converter 71. The first control unit 90 may be a control unit of, or relating to, the DC transmission line 70, and may be referred to as a DC transmission line control unit or controller.

In the context of the present application, by a first component being communicatively connected with a second component (e.g., the first control unit 90 being communicatively connected with the DC transmission line 70 or the converter 71), it is meant that the components are able to communicate via wired and/or wireless communication means or techniques, for example via any appropriate wired and/or wireless communication means or techniques as known in the art, for transmitting messages, instructions, data, commands, etc., from the first component to the second component and possibly also vice versa. Wired communication means may for example comprise radio frequency (RF) communication, infrared communication (e.g., employing a communication link employing infrared light) or another type of free-space optical communication. Wireless communication means may for example comprise at least one optical waveguide, or optical transmission line (e.g., an optical fiber), and/or at least one electrical conductor (e.g., a cable or wire, e.g., a copper conductor or cable, or copper wire).

The power distribution arrangement 100 comprises a second control unit 96. The second control unit 96 may be communicatively connected with the first control unit 90, the transformers 11, 12, the feeders 41-47 and at least some of the switches 1-6 and 60-68.

The power distribution arrangement 100 may comprise at least one sensor (not shown in Figure 1), which for example may be configured to sense loading in each or any of the transformers 11, 12, and/or sense loading in each or any of the feeders 41-47 or in a part or segment of each or any of the feeders 41-47. The second control unit 96 may be communicatively connected with the at least one sensor. Thereby, the second control unit 96 may be configured to receive sensor data (e.g., data indicative of one or more properties or characteristics sensed by the at least one sensor, such as loading in each or any of the transformers 11, 12 and in each or any of the feeders 41-47 or in a part or segment of each or any of the feeders 41-47. Such at least one sensor may be applied or included in any one of the embodiments of the present invention disclosed herein.

The power distribution arrangement 100 comprises an energy storage system (ESS) 110. The ESS 110 is connected to at least one of the DC transmission line 70 and the converter 71. According to the embodiment of the present invention illustrated in Figure 1, the ESS 110 is connected to the DC transmission line 70. The ESS 110 is configured to selectively and controllably supply power to the DC transmission line 70 or absorb power from the DC transmission line 70 (e.g., absorb power from any power transfer in the DC transmission line 70). Although only one ESS is illustrated in Figure 1, it is to be understood that the power distribution arrangement 100 (or a power distribution arrangement according to any other embodiment of the present invention) could comprise in principle any number of ESSs, which may be interconnected with each other. For example, there could be provided at least two ESSs, which may comprise at least a first ESS and a second ESS connected with the first ESS.

In accordance with the embodiment of the present invention illustrated in Figure 1, the ESS 110 is connected to the DC transmission line 70 via a converter 111, which for example, as indicated in Figure 1, comprise a DC-DC converter. It is to be understood that the illustrated connection of the ESS 110 with the DC transmission line 70 via a converter 111 is according to an example. Generally, the ESS 110 may be connected to at least one of the DC transmission line 70 and the converter 71 via one or more intermediate components, wherein the one or more intermediate components may include a converter configured to convert AC power to DC power, or a DC-DC converter (the latter case being illustrated in Figure 1). It is however not required that the ESS 110 is connected to at least one of the DC transmission line 70 and the converter 71 via one or more intermediate components; the ESS 110 may possibly be directly connected to at least one of the DC transmission line 70 and the converter 71 (i.e. without any intermediate component such as a converter). A direct connection of the ESS 110 to at least one of the DC transmission line 70 and the converter 71 may be feasible for example at relatively low voltages (e.g., at about 1 kV or less).

The power distribution arrangement 100 comprises a third control unit 116. The third control unit 116 may be communicatively connected with the first control unit 90 and/or with the second control unit 96. The third control unit 116 is configured to control the ESS 110 to supply power to the DC transmission line 70 or absorb power from the DC transmission line 70 (e.g., absorb power from any power transfer in the DC transmission line 70). The third control unit 116 may be a control unit of, or relating to, the ESS 110, and may be referred to as an ESS control unit or controller.

Each of the first control unit 90, the second control unit 96 and the third control unit 116 may be configured so as to be capable of wireless and/or wired communication, for example using any wireless and/or wired communication means or technique as known in the art.

The second control unit 96 is configured to control operation of at least some of the switches 1-6 and 60-68 in order to selectively connect or disconnect one or more of the feeders 41-47 to or from at least one of the transformers 11, 12 via one or more of the buses 13-15 and to selectively connect or disconnect the DC transmission line 70 to or from one or more of the feeders 41-47 via the at least one bus (e.g., the bus 15). Thereby, AC power is distributed to the loads via the feeders 41-47.

The second control unit 96 is configured to control the operation of the switches based on: loading in and a power rating of the respective ones of the feeders 41-47, loading in and a power rating of the respective ones of the transformers 11, 12, any power transfer in the DC transmission line 70 from the other power distribution substation to the at least one bus (e.g., the bus 15), and a measure of the available energy in the ESS 110 and power supply rating of the ESS 110. The second control unit 96 may be a control unit of, or relating to, the switches and/or the power distribution substation 10, and may be referred to as a power distribution substation control unit or controller.

As indicated in Figure 1, the ESS 110 may for example comprise a battery ESS (BESS). In case the ESS 110 is including or is constituted by a BESS, the measure of the available energy in the ESS 110 may for example comprise a state of charge of the ESS 110. It is however to be understood that the ESS 110 is not limited to include or be constituted by a BESS. In alternative or in addition, the ESS 110 may comprise another or other types of ESSs, such as, for example, a capacitor-based ESS.

Even if the first control unit 90, the second control unit 96 and the third control unit 116 are described herein as separate control units, the respective controlling capabilities of any of at least two of (or all of) the first control unit 90, the second control unit 96 and the third control unit 116 could be realized or implemented by a single control unit.

The second control unit 96 may be configured to receive, possibly continually or continuously, data or information regarding loading in the feeders 41-47 and loading in the transformers 11, 12 from another entity, which for example may comprise another control unit or a controller, or a sensor. The sensor, which may be comprised in the power distribution arrangement 100, may be configured to sense loading in each or any of the transformers 11, 12, and/or sense loading in each or any of the feeders 41-47. The second control unit 96 may be communicatively connected with the sensor or other entity for receiving, possibly continually or continuously, data or information regarding loading in the feeders 41-47 and loading in the transformers 11, 12.

The second control unit 96 may be configured to receive, possibly continually or continuously, data or information regarding the measure of the available energy in the ESS 110, for example from the ESS 110 or the third control unit 116.

Further to the foregoing description, by providing additional power transfer capability via the DC transmission line 70, in addition to power transfer capability from the power sources providing AC power via the transformers 11, 12, an increased flexibility in feeder reconfiguration may be achieved. For example, an operator of the power distribution arrangement 100, or of a power distribution system of which the power distribution arrangement 100 may be a part of, can utilize the power transfer capability via the DC transmission line 70 in order to achieve more flexibility in reconfiguration of the feeders 41- 47. Furthermore, an additional increase in flexibility in feeder reconfiguration may be facilitated or allowed by the providing of the ESS 110, which is connected to at least one of the DC transmission line (as illustrated in Figure 1) and the converter, and which is configured to selectively and controllably supply power to the DC transmission line 70 or absorb power from any power transfer in the DC transmission line 70. Accordingly, the ESS 110 may provide an additional degree of freedom in the controlling of power transfer capability in the DC transmission line 70, which may be utilized or taken into account in reconfiguration of the feeders 41-47, whereby an even higher flexibility in reconfiguration of the feeders 41-47 may be achieved.

As mentioned in the foregoing, there could for example be provided at least two ESSs, which may comprise at least a first ESS and a second ESS connected with the first ESS. At least one control unit of the power distribution arrangement 100 (for example, the third control unit 116) or a power distribution arrangement according to any one of the embodiments of the present invention disclosed herein may be configured to, based on a measure of the available energy in the first ESS and power supply rating of the first ESS and a measure of the available energy in the second ESS and power supply rating of the second ESS, control the first ESS to supply power to the second ESS or absorb power from the second ESS, or control the second ESS to supply power to the first ESS or absorb power from the first ESS.

At least one control unit of the power distribution arrangement 100 may be configured to, based on an indication that the DC transmission line 70 is disconnected from the other power distribution substation (not shown in Figure 1) at the end of the DC transmission line 70 closest to the other power distribution substation: control the ESS 110 to supply power to the DC transmission line 70 based on the measure of the available energy in the ESS 70 and power supply rating of the ESS 110, and control the operation of the switches based on: loading in and a power rating of the respective ones of the feeders, loading in and a power rating of the respective ones of the transformers 11, 12, and power transfer in the DC transmission line 70 caused by the ESS 110 supplying power to the DC transmission line 70. For example, the third control unit 116 may be configured to control the ESS 110 to supply power to the DC transmission line 70 based on the measure of the available energy in the ESS 70 and power supply rating of the ESS 110, and the second control unit 96 may be configured to control the operation of the switches based on: loading in and a power rating of the respective ones of the feeders, loading in and a power rating of the respective ones of the transformers 11, 12, and power transfer in the DC transmission line 70 caused by the ESS 110 supplying power to the DC transmission line 70. Such control of the ESS 110 and the operation of the switches may be applied in any one of the embodiments of the present invention disclosed herein. The at least one control unit (e.g., the second control unit 96 and/or the third control unit 116) may for example be configured to receive or retrieve the indication that the DC transmission line 70 is disconnected from the other power distribution substation at the end of the DC transmission line closest to the other power distribution substation, e.g., from a fault sensing system and/or a controller or control unit for controlling operation of the other power distribution substation.

At least one control unit of the power distribution arrangement 100 may be configured to control any power transfer in the DC transmission line 70 from the other power distribution substation to the at least one bus (e.g., the bus 15) based on a selected power transfer reference value, or power transfer setpoint. That least one control unit may be configured to control the operation of the switches further based on the power transfer reference value and a power rating of the DC transmission line 70. The at least one control unit may be communicatively connected with another control unit that is associated with the other power distribution substation. The at least one control unit may be configured to receive an indication of the selected power transfer reference value from the other control unit.

For example, the first control unit 90 may be configured to control any power transfer in the DC transmission line 70 from the other power distribution substation (not shown in Figure 1) to the at least one bus (e.g., the bus 15) based on a selected power transfer reference value, or power transfer setpoint. The second control unit 96 may be configured to control the operation of the switches further based on the power transfer reference value, and possibly also based on a power rating of the DC transmission line 70. The first control unit 90 and/or the second control unit 96 may be communicatively connected with another control unit (not shown in Figure 1) which may be associated with the other power distribution substation (also not shown in Figure 1). The other control unit may be configured to control operation of the other power distribution substation. The first control unit 90 and/or the second control unit 96 may be configured to receive an indication of the selected power transfer reference value from the other control unit. Such control of the operation of the switches may be applied in any one of the embodiments of the present invention disclosed herein. The indication of the selected power transfer reference value from the other control unit may be constituted by a request for a certain power transfer reference value from the other control unit, to be used for controlling power transfer in the DC transmission line 70 between the other power distribution substation and the at least one bus (e.g., the bus 15) by the first control unit 90.

The converter 71 may be configured so as to be capable of controlling power flow of the converter 71 at least with respect to the contributions from active power or reactive power to the apparent power of the power flow at an AC terminal of the converter 71. At least one control unit of the power distribution arrangement 100 may be configured to set limits for the active power and the reactive power, respectively, of the power flow of the converter 71, based on a limit for current of the converter 71, any power transfer in the DC transmission line 70 from the other power distribution substation to the at least one bus (e.g., the bus 15), the measure of the available energy in the ESS 110 and the power supply rating of the ESS 110.

By the converter 71 being configured to be capable of controlling power flow of the converter at least with respect to the contributions from active power or reactive power to the apparent power of the power flow at the AC terminal of the converter 71, the converter 71 can for example be controlled to make room for an increased contribution from active power to the apparent power of the power flow at the AC terminal of the converter 71 with a corresponding reduction in the contribution from reactive power to the apparent power of the power flow at the AC terminal of the converter 71 (since the apparent power is limited, e.g., by a limit for current of the converter 71). By the at least one control unit being configured to set limits for the active power and the reactive power, respectively, of the power flow of the converter 71, based on a limit for current of the converter 71, any power transfer in the DC transmission line 70 from the other power distribution substation to the at least one bus (e.g., the bus 15), the measure of the available energy in the ESS 110, and the power supply rating of the ESS 110, the active power flow capacity of the converter 71 may be increased (at the expense of reactive power capacity of the converter 71) in order to be able to fully or increasingly be able to utilize the available energy in the ESS 110, which may further facilitate increasing flexibility in feeder reconfiguration. Such configuration and setting of limits for the active power and the reactive power, respectively, of the power flow of the converter 71 may be applied in any one of the embodiments of the present invention disclosed herein.

In the context of the present application, the expression “power flow of the converter” encompasses contributions from active power and/or reactive power to the apparent power of the power flow at an AC terminal of the converter, such as active power flowing through the converter, etc. At least one control unit of the power distribution arrangement 100 may be configured to compare loadings in the feeders 41-47 with the power ratings of the respective ones of the feeders 41-47, and further to compare loadings in the transformers 11, 12 with the power ratings of the respective ones of the transformers 11, 12, and further to control the operation of the switches based on the comparisons, such that loading in the respective ones of the transformers 11, 12 becomes more balanced between the transformers 11, 12.

The second control unit 96, for example, may be configured to control the operation of at least some of the switches 1-6 and 60-68 such that loading in the respective ones of the transformers 11, 12 becomes more balanced between the transformers 11, 12. For example, the second control unit 96 may be configured to compare loadings in the feeders 41- 47 with the power ratings of the respective ones of the feeders 41-47, and further to compare loadings in the transformers 11, 12 with the power ratings of the respective ones of the transformers 11, 12, and further to control the operation of the switches based on the comparisons such that loading in the respective ones of the transformers 11, 12 becomes more balanced between the transformers 11, 12. Such control of the operation of the switches may be applied in any one of the embodiments of the present invention disclosed herein.

At least a part of the power distribution arrangement 100 may be comprised in, or constitute, a power distribution grid. The power distribution grid could further comprise, e.g., the power source(s) providing AC power and/or the other power distribution substation mentioned in the foregoing.

At least one control unit of the power distribution arrangement 100 (for example, the third control unit 116) may be configured to, based on an indication regarding at least one requirement of the power distribution grid with respect to at least one of current, voltage and frequency of the power distribution grid, control the ESS 110 to supply power to the DC transmission line 70 based on the measure of the available energy in the ESS 110 and power supply rating of the ESS 110 so as to comply with, or come closer to complying with, the at least one requirement of the power distribution grid. Such control of the ESS 110 may be applied in any one of the embodiments of the present invention disclosed herein.

The at least one control unit (e.g., the third control unit 116) may for example be configured to receive or retrieve the at least one requirement of the power distribution grid with respect to at least one of current, voltage and frequency of the power distribution grid, e.g., from a power distribution grid controller.

The indication regarding at least one requirement of the power distribution grid with respect to at least one of current, voltage and frequency of the power distribution grid may for example be based on a measurement of at least one of current, voltage and frequency of the power distribution grid. The measurement may be carried out on the AC side of the power distribution arrangement 100, for example by means of one or more sensors for sensing current, voltage and/or frequency as known in the art. The at least one requirement of the power distribution grid with respect to at least one of current, voltage and frequency of the power distribution grid may for example comprise or relate to at least one of: voltage regulation requirement in the power distribution grid, frequency regulation requirement in the power distribution grid, a black start of the power distribution grid, one or more ancillary services related to operating reserves for the power distribution grid, or electrical power quality of power supplied by the power distribution grid.

Voltage regulation requirement and/or frequency regulation requirement may be according to some established criteria or specifications.

In the context of the present application, ancillary services should be understood as services for the power distribution grid (e.g., provided by the power distribution grid), beyond generation and transmission of power, that facilitate continuous power flow so that distribution of power by the power distribution grid will meet the demand and that facilitate or enable stability and security of the power distribution grid.

Further, electrical power quality of power supplied by the power distribution grid should in the context of the present application be understood as a measure of the extent to which at least voltage and frequency of the power distribution grid conform to some predefined or established criteria or specifications.

For example, the at least one requirement of the power distribution grid with respect to at least one of current, voltage and frequency of the power distribution grid may include a requirement regarding electrical power quality of power supplied by the power distribution grid. The DC transmission line 70 and the ESS 110 may be configured such that they can be operated in a plurality of modes, including a grid forming mode. At least one control unit of the power distribution arrangement 100 (for example, the first control unit 90 and the third control unit 116) may be configured to control the DC transmission line 70 and the ESS 110 to operate in the grid forming mode so as to comply with, or come closer to complying with, the requirement regarding electrical power quality of power supplied by the power distribution grid. For example, the first control unit 90 may be configured to control the DC transmission line 70 to operate in the grid forming mode and the third control unit 116 may be configured to control the ESS 110 to operate in the grid forming mode so as to comply with, or come closer to complying with, the requirement regarding electrical power quality of power supplied by the power distribution grid. The operation of the DC transmission line 70 and the ESS 110 in grid forming mode may be with respect to the AC side of the power distribution arrangement 100, where the DC transmission line 70 and possibly also the ESS 110 can provide grid forming functionality to the AC grid, such as, for example, create grid voltage, act as sink for balancing or attracting harmonics, provide or contribute to inertia, support grid voltage in case of occurrence of a fault, etc. The second control unit 96 may be configured to control the operation of the switches to selectively connect or disconnect the DC transmission line 70 to or from one or more of the feeders 41-47 via the at least one bus (e.g., the bus 15) further based on an indication whether there is a fault occurring in the DC transmission line 70. The second control unit 96 may be configured to receive an indication whether there is a fault occurring in the DC transmission line 70 from a fault protection or detection unit (not shown in Figure 1) which may be configured to monitor transmission lines, e.g., in the power distribution arrangement 100, or in a power distribution system of which the power distribution arrangement 100 may be a part of for occurrence of faults. In the event of a fault occurring in a transmission line, the fault protection unit may trip, or open, circuit breakers located at each end of the transmission line may be tripped, or opened, in order to disconnect the transmission line in which a fault occurs from other parts the power distribution arrangement 100 or the power distribution system. Such fault protection or detection units are known in the art. In overhead lines, a majority of the faults which may occur are temporary or transient faults, and may for example be due to lightning strike and/or flashover. In cables, virtually all of the faults that may occur may be permanent faults, which for example may be due to a short- circuit between conductors. On a condition that there is a fault occurring in the DC transmission line 70, the second control unit 96 may be configured to disconnect the DC transmission line 70 from the at least one bus (e.g., the bus 15). On a condition that there is no fault occurring in the DC transmission line 70, the second control unit 96 may be configured to selectively connect or disconnect the DC transmission line 70 to or from one or more of the feeders 41-47 via the at least one bus (e.g., the bus 15). Such control based on an indication whether there is a fault occurring in the DC transmission line 70 may be applied in any one of the embodiments of the present invention disclosed herein.

The loading in one or more of the transformers 11, 12 may exceed the power ratings of the respective ones of that or those transformers 11, 12, such that that or those transformers 11, 12 are overloaded. In that event, the second control unit 96 may be configured to control the operation of the switches so as to disconnect one or more of the feeders 41-47 from the overloaded transform er(s) 11, 12 via one or more of the buses and connect that or those feeders to one or more transformers 11, 12 that are not overloaded (if such is/are available) via one or more of the buses and/or connecting the DC transmission line 70 to that or those feeders via the at least one bus (e.g., the bus 15). Such control of the operation of the switches may be applied in any one of the embodiments of the present invention disclosed herein.

At least one control unit, e.g., the first control unit 90, may be configured to control any power transfer in the DC transmission line 70 from the at least one bus (e.g., the bus 15) to the other power distribution substation. At least one control unit, e.g., the first control unit 90 and/or the second control unit 96, may be configured to determine, based on the loading in and the power rating of the respective ones of the feeders 41-47 and the loading in and the power rating of the respective ones of the transformers 11, 12, whether there is a deficit in available power from the transformers 11, 12, so that there is need for power to be transferred in the DC transmission line 70 to the at least one bus (e.g., the bus 15), or if there is a surplus in available power from the transformers 11, 12, so that power can be transferred in the DC transmission line 70 to the other power distribution substation.

On a condition that there is a deficit in available power from the transformers 11, 12, at least one control unit, e.g., the first control unit 90, may be configured to control transfer of power in the DC transmission line 70 so as to transfer power from the other power distribution substation to the at least one bus (e.g., the bus 15). In alternative or in addition, on a condition that there is a deficit in available power from the transformers 11, 12, at least one control unit, e.g., the third control unit 116, may be configured to, based on the measure of the available energy in the ESS 110 and power supply rating of the ESS 110, control the ESS 110 to supply power to the DC transmission line 70.

On a condition that there is a surplus in available power from the transformers 11, 12, at least one control unit, e.g., the first control unit 90, may be configured to control transfer of power in the DC transmission line 70 so as to transfer power from the at least one bus (e.g., the bus 15) to the other power distribution substation. In alternative or in addition, on a condition that there is a surplus in available power from the transformers 11, 12, at least one control unit, e.g., the third control unit 116, may be configured to, based on the measure of the available energy in the ESS 110 and power supply rating of the ESS 110, control the ESS 110 to absorb power from the DC transmission line 70. A condition that there is a surplus in available power from the transformers 11, 12 means that there is available power headroom in the transformers 11, 12 to transfer more power (e.g., to the feeders).

Such control of transfer of power in the DC transmission line 70 and control of the ESS 110 to supply power to or absorb power from the DC transmission line 70 based on whether there is a surplus or a deficit in available power from the transformers 11, 12 may be applied in any one of the embodiments of the present invention disclosed herein.

Figure 2 is a schematic view of a power distribution arrangement 200 according to one or more embodiments of the present invention. The power distribution arrangement 200 illustrated in Figure 2 is in part similar to the power distribution arrangement 100 illustrated in Figure 1, and the same reference numerals in Figure 2 and in Figure 1 denote the same or similar components, having the same or similar function.

Compared to the power distribution arrangement 100 illustrated in Figure 1, the power distribution arrangement 200 illustrated in Figure 2 comprises a different number of feeders, and has a different configuration of feeders, buses and switches. The principles of controlling of the operation of the switches in the power distribution arrangement 200 illustrated in Figure 2 are similar to or the same as described with reference to the power distribution arrangement 100 illustrated in Figure 1.

The power distribution arrangement 200 comprises feeders 48 and 49, switches 1-6, 60-69, 76 and 77, and buses 16 and 17. It is to be understood that the number of feeders may be larger than illustrated in Figure 2, and that the number of switches and the number of buses may be smaller or larger than illustrated in Figure 2.

As illustrated in Figure 2, each of the feeders 48 and 49 is selectively and controllably connectable to at least one of the loads and to at least one of the transformers 11, 12, respectively, via one or more of the buses 16, 17. The switches 3-6 and 60-66, 69 and 76 are configured to selectively and controllably connect or disconnect one or more of the feeders 48 and 49 to or from the one or more of the buses 16, 17 in order to connect or disconnect the one or more feeders 48, 49 to or from at least one of the transformers 11, 12.

For example, the switches 1, 2, 3, 6, 63, 65 and 69 may be normally-closed switches, and the switches 4, 5, 64 and 66 may be normally-open switches.

Generally, at least some of the feeders may be are selectively and controllably connectable to at least one of the transformers by means of a plurality of buses connected or connectable in parallel. The DC transmission line may be selectively and controllably connectable to at least one of the buses that are connected or connectable in parallel. In accordance with the embodiment of the present invention illustrated in Figure 2, each of the feeders 48, 49 is selectively and controllably connectable to at least one of the transformers 11, 12 by means of the buses 16, 17 connected or connectable in parallel. The DC transmission line 70 is selectively and controllably connectable to each of the buses 16, 17 that are connected or connectable in parallel. Each of the feeders 48 and 49 is selectively and controllably connectable to either the bus 16 or the bus 17. The DC transmission line 70 is also selectively and controllably connectable to either the bus 16 or the bus 17.

Figure 3 is a schematic view of a power distribution arrangement 300 according to one or more embodiments of the present invention. The power distribution arrangement 300 illustrated in Figure 3 is in part similar to the power distribution arrangements 100 and 200 illustrated in Figures 1 and 2, respectively, and the same reference numerals in Figure 3 and in Figures 1 and 2 denote the same or similar components, having the same or similar function.

Compared to the power distribution arrangements 100 and 200 illustrated in Figures 1 and 2, respectively, the power distribution arrangement 300 illustrated in Figure 3 comprises a different number of feeders, and has a different configuration of feeders, buses and switches. The principles of controlling of the operation of the switches in the power distribution arrangement 300 illustrated in Figure 3 are similar to or the same as described with reference to the power distribution arrangement 100 illustrated in Figure 1.

The power distribution arrangement 300 comprises feeders 40 and 50-59, switches 1-6, 60-69, 76, 77, 81, 82 and 83, and buses 18-22. It is to be understood that the number of feeders, the number of switches, and the number of buses may be smaller or larger than illustrated in Figure 3.

For example, the switches 1, 2, 3, 4 and 83 may be normally-closed switches, and the switch 82 may be a normally-open switch.

As illustrated in Figure 3, the feeders 53 and 54 may be connected to either the transformer 11 or the transformer 12 or to both of the transformers 11 and 12, via the buses 18 and/or 19, depending on whether the respective ones of the switches 3, 4, 6, 61, 82 and 83 are open or closed.

In the power distribution arrangement 300 illustrated in Figure 3, some of the illustrated switches are included in the power distribution substation 10, and the other of the illustrated switches are arranged remote from the power distribution substation 10. Specifically, the switches 64-69, 76, 77, 81, 82 and 83 are arranged remote from the power distribution substation 10, while the other ones of the illustrated switches are included in the power distribution substation 10. The switches 64-69, 76, 77, 81, 82 and 83 may be considered as being comprised in one or more so called (remote) switch houses, remote from the power distribution substation 10. In the power distribution arrangements 100 and 200 illustrated in Figures 1 and 2, respectively, the illustrated switches may all be considered to be included in the power distribution substation 10.

Figure 4 is a schematic view of a power distribution arrangement 400 according to one or more embodiments of the present invention. The power distribution arrangement 400 illustrated in Figure 4 is in part similar to the power distribution arrangements 100, 200 and 300 illustrated in Figures 1, 2 and 3, respectively, and the same reference numerals in Figure 4 and in Figures 1, 2 and 3 denote the same or similar components, having the same or similar function.

Compared to the power distribution arrangements 100, 200 and 300 illustrated in Figures 1, 2 and 3, respectively, the power distribution arrangement 400 illustrated in Figure 4 comprises a different number of feeders, and has a different configuration of feeders, buses and switches. The principles of controlling of the operation of the switches in the power distribution arrangement 400 illustrated in Figure 4 are similar to or the same as described with reference to the power distribution arrangement 100 illustrated in Figure 1. The power distribution arrangement 400 comprises feeders 78-80, switches 1-6 and 60-69, and buses 23 and 24. It is to be understood that the number of feeders, the number of switches and the number of buses may be smaller or larger than illustrated in Figure 4.

As illustrated in Figure 4, in the power distribution arrangement 400, the feeders 78-80 are selectively and controllably connectable to the transformers 11, 12 by means of a ring main distribution system.

For example, the switches 1-4, 60 and 62-66 may be normally-closed switches, and the switch 61 may be a normally-open switch.

As illustrated in Figure 4, the feeders 78-80 may be connected to either the transformer 11 or the transformer 12 or to both of the transformers 11 and 12, via the buses 23 and/or 24, depending on whether the respective ones of the switches 3-6 and 60-66 are open or closed. Further, by changing a ring open point of the ring main distribution system, e.g., by opening or closing one or more of the switches 60-66, each of the feeders 78-80 may be connected to either the transformer 11 or the transformer 12.

Figure 5 is a schematic view of a power distribution arrangement 500 according to one or more embodiments of the present invention. The power distribution arrangement 500 illustrated in Figure 5 is in part similar to the power distribution arrangements 100, 200, 300 and 400 illustrated in Figures 1, 2, 3 and 4, respectively, and the same reference numerals in Figure 5 and in Figures 1, 2, 3 and 4 denote the same or similar components, having the same or similar function.

Compared to the power distribution arrangements 100, 200, 300 and 400 illustrated in Figures 1, 2, 3 and 4, respectively, the power distribution arrangement 500 illustrated in Figure 5 has a different configuration of feeders, buses and switches. The principles of controlling of the operation of the switches in the power distribution arrangement 500 illustrated in Figure 5 are similar to or the same as described with reference to the power distribution arrangement 100 illustrated in Figure 1.

The power distribution arrangement 500 comprises feeders 61 and 62 and buses 25 and 26. It is to be understood that the number of feeders may be larger than illustrated in Figure 5, and that the number of buses may be smaller or larger than illustrated in Figure 5. The switches of the power distribution arrangement 500 are not indicated by any reference numerals in Figure 5. The number of switches of the power distribution arrangement 500 may be smaller or larger than illustrated in Figure 5.

The power distribution arrangement 500 comprises a DC transmission line 70. The DC transmission line 70 is at one end thereof selectively and controllably connectable to the respective ones of the feeders 61, 62 via at least one bus, via a converter 71 configured to convert DC power to AC power, or vice versa. As illustrated in Figure 5, in accordance with the illustrated embodiment of the present invention, the DC transmission line 70 is at one end thereof selectively and controllably connectable to the feeders 61, 62 via the bus 26. The DC transmission line 70 may for example comprise or be constituted by an MVDC transmission line, which may be referred to as an MVDC link. The DC transmission line 70 is the other end thereof connected or connectable to another substation 95, e.g., another power distribution substation.

The first control unit 90 is configured to control any power transfer in the DC transmission line 70 between the at least one bus (e.g., the bus 26) and the other power distribution substation 95, including any power transfer in the DC transmission line 70 from the at least one bus (e.g., the bus 26) to the other power distribution substation 95. Similar to as described with reference to Figure 1, the first control unit 90 may be configured to control any power transfer in DC transmission line 70 between the power distribution substation 95 and the at least one bus (e.g., the bus 26) based on a selected power transfer reference value, or power transfer setpoint. The second control unit 96 may be configured to control the operation of the switches of the power distribution arrangement 500 based on the power transfer reference value, and possibly also based on a power rating of the DC transmission line 70.

The power distribution substation 95 comprises a transformer 75 connected or connectable to at least one power source providing AC power (not shown in Figure 5). However, similarly to the power distribution substation 10 of the power distribution arrangement 500, the power distribution substation 95 may comprise a plurality of transformers, each being connected or connectable to at least one power source providing AC power (not shown in Figure 5), even though only one such transformer 75 of the power distribution substation 95 is shown in Figure 5. Each of a plurality of transformers of the power distribution substation 95 may be selectively and controllably connectable to at least one power source providing AC power (not shown in Figure 5).

Similar to the power distribution arrangement 500, there may be provided a plurality of buses 27, 28 and a plurality of feeders 92, 93, which may be comprised in the power distribution substation 95 or at least be associated therewith.

It is to be understood that the number of feeders of or associated with the power distribution substation 95 may be larger than illustrated in Figure 5, and that the number of switches and the number of buses of or associated with the other power distribution substation 95 may be smaller or larger than illustrated in Figure 5. The switches of or associated with the power distribution substation 95 are not indicated by any reference numerals in Figure 5.

Each of the feeders 92, 93 of or associated with the power distribution substation 95 may be selectively and controllably connectable to at least one load and to at least one of the transformers, respectively, via one or more of the buses 27, 28. There is a loading in and a power rating of the respective ones of the feeders 92, 93, and a loading in and a power rating of the respective ones of the transformers of the other power distribution substation 95.

The DC transmission line 70 is at the other end thereof (i.e. at the power distribution substation 95 end) selectively and controllably connectable to the respective ones of the feeders 92, 93, via at least one bus (e.g., the bus 27), via a converter 73 configured to convert DC power to AC power, or vice versa. Further in accordance with the illustrated embodiment of the present invention, a transformer 74 is connected between the converter 73 and the bus 27. The transformer 74 may be omitted.

As illustrated in Figure 5, there may be a control unit 91 associated with the other power distribution substation 95. The control unit 91 may be configured to control operation of the power distribution substation 95 and any components associated with the power distribution substation 95 (e.g., any feeders and switches associated with the power distribution substation 95). The first control unit 90, the second control unit 96 and/or the third control unit 116 may be communicatively connected with the control unit 91. Further, as described with reference to Figure 1, each of the first control unit 90, the second control unit 96 and the third control unit 116 may be communicatively connected with at least one of the other ones of the first control unit 90, the second control unit 96 and the third control unit 116.

The principles of controlling of the operation of the switches of or associated with the power distribution substation 95 by the control unit 91 may or may not be similar to or the same as described with reference to the power distribution arrangement 100 illustrated in Figure 1. Thus, the control unit 91 may or may not be configured to carry out such controlling that the first control unit 90 and/or the second control unit 96 is or are capable of and as described in the foregoing with reference to the power distribution arrangement 100 illustrated in Figure 1.

As mentioned in the foregoing, the second control unit 96 may be configured to control the operation of the switches of the power distribution arrangement 500 based on the power transfer reference value. The second control unit 96 may be configured to receive an indication of the selected power transfer reference value from the control unit 91 or from any another component or element of the other power distribution substation 95, possibly via the first control unit 90.

At least one control unit of the power distribution arrangement 500 (for example, the first control unit 90) may be configured to determine possible power import and export ranges, for power transfer to the power distribution arrangement 500 from the other power distribution substation 95 and from the power distribution arrangement 500 to the other power distribution substation 95, respectively, based on the loading in and the power rating of the respective ones of the feeders of the power distribution arrangement 500 and the feeders of or associated with the other power distribution substation 95 and the loading in and the power rating of the respective ones of the transformers of the power distribution arrangement 500 and the transformers of the other power distribution substation 95, and further based on the measure of the available energy in the ESS 110 and the power supply rating of the ESS 110.

Thus, the possible power import and export ranges of the power distribution arrangement 500 may be determined taking into account the loading in and the power rating of the transformers and feeders at both ends of the DC transmission line 70, as well as the measure of the available energy in the ESS 110 and the power supply rating of the ESS 110.

The possible power import and export ranges determined by the at least one control unit of the power distribution arrangement 500, e.g., the first control unit 90, may be transmitted by, e.g., the first control unit 90, to the second control unit 96. The second control unit 96 may be configured to control the operation of the switches of the power distribution arrangement 500 based on the possible power import and export ranges. Determining possible power import and export ranges and control of the operation of the switches of the power distribution arrangement based on the possible power import and export ranges as described above may be applied in any one of the embodiments of the present invention disclosed herein.

Figure 6 is a flowchart illustrating a method 600 in a power distribution arrangement according to one or more embodiments of the present invention. The method 600 is for distributing AC power to a plurality of loads requiring AC power. The power distribution arrangement may comprise a substation, e.g., a power distribution substation, which may comprise a plurality of transformers. Each of the transformers may be selectively and controllably connectable to at least one power source providing AC power. The power distribution arrangement may comprise a plurality of switches, a plurality of buses (or busbars, bus sections, or bus parts), and a plurality of feeders. Each of the feeders may be selectively and controllably connectable to at least one of the loads and to at least one of the transformers, respectively, via one or more of the buses. At least some of the switches may be configured to selectively and controllably connect or disconnect one or more of the feeders to or from the one or more of the buses in order to connect or disconnect the one or more feeders to or from at least one of the transformers. The power distribution arrangement may comprise a DC transmission line. The DC transmission line may at one end thereof be selectively and controllably connectable to the respective ones of the feeders via at least one bus, via a converter configured to convert DC power to AC power, or vice versa. The DC transmission line may at another (or the other) end thereof be connected or connectable to another substation, e.g., another power distribution substation. At least one of the switches may be configured to selectively and controllably connect or disconnect the DC transmission line to or from the at least one bus in order to connect or disconnect the DC transmission line to or from the feeders. The power distribution arrangement may comprise at least one ESS, which may be connected to at least one of the DC transmission line and the converter. The at least one ESS may be configured to selectively and controllab ly supply power to the DC transmission line or absorb power from the DC transmission line.

The method 600 comprises, at 601, controlling any power transfer in the DC transmission line between the at least one bus and the other power distribution substation.

At 602, the at least one ESS is controlled to supply power to the DC transmission line or absorb power from the DC transmission line.

Optionally, at 603, operation of the switches is controlled in order to selectively connect or disconnect one or more of the feeders to or from at least one of the transformers via one or more of the buses and to selectively connect or disconnect the DC transmission line to or from one or more of the feeders via the at least one bus, whereby AC power is distributed to the loads via the feeders. The operation of the switches may be controlled based on: loading in and a power rating of the respective ones of the feeders, loading in and a power rating of the respective ones of the transformers, any power transfer in the DC transmission line from the other power distribution substation to the at least one bus, and a measure of the available energy in the at least one ESS and power supply rating of the at least one ESS. Step 603 may be omitted.

The method 600 may then end. The method 600 may however not end, and the step 602, and possibly also the step 601, and perhaps also the step 603, may be carried out repeatedly, e.g., over a period of time, as indicated by the line immediately before “end” going back to immediately after “start”. Accordingly, the method 600 may comprise or constitute a control loop for controlling any power transfer in the DC transmission line between the at least one bus and the other power distribution substation and for controlling the at least one ESS to supply power to the DC transmission line or absorb power from the DC transmission line, and possibly also for controlling operation of the switches, e.g., over a period of time. The method 600 may for example be initiated by an operator, or based on occurrence of a predefined type of event, such as, for example, that it is sensed that a fault is occurring in the DC transmission line, and/or that it is sensed that there is an overload in one or more of the transformers (e.g., if the loading in one or more of the transformers exceed the power ratings of the respective ones of that or those transformers). Thus, responsive to, e.g., it is sensed that a fault is occurring in the DC transmission line, and/or that it is sensed that there is an overload in one or more of the transformers, feeder reconfiguration may be carried out to achieve different loading at the transformers. In alternative or in addition, the method 600 may be initiated based on another or other types of events, such as, for example, that it is sensed that a fault is occurring in the at least one ESS. If it is sensed that a fault is occurring in the at least one ESS, the power transfer in the DC transmission line between the at least one bus and the other power distribution substation may be controlled to take into account, e.g., that the at least one ESS is not available, for example by changing a power transfer reference value, or power transfer setpoint, for transfer of power in the DC transmission line. The operation of the switches may then be controlled without utilizing the at least one ESS.

Controlling any power transfer in the DC transmission line between the at least one bus and the other power distribution substation, such as at 601, may comprise adjusting a power transfer reference value, or power transfer setpoint, for transfer of power in the DC transmission line between the at least one bus and the other power distribution substation.

Controlling the at least one ESS to supply power to the DC transmission line or absorb power from the DC transmission line, such as at 602, may comprise adjusting a power transfer reference value, or power transfer setpoint, for transfer of power from the at least one ESS to the DC transmission line or from the DC transmission line to the at least one ESS.

In conclusion, a power distribution arrangement, for distributing AC power to a plurality of loads requiring AC power, is disclosed. The power distribution arrangement comprises a power distribution substation comprising a plurality of transformers, each of the transformers being connected or connectable to at least one power source providing AC power. The power distribution arrangement comprises a plurality of switches, a plurality of buses, and a plurality of feeders. Each of the feeders is selectively and controllably connectable to at least one of the loads and to at least one of the transformers, respectively, via one or more of the buses, by means of at least some of the switches. The power distribution arrangement comprises a DC transmission line, which at one end is selectively and controllably connectable to the respective ones of the feeders via at least one bus, via a converter, by means of at least one of the switches, and at another end thereof is connected or connectable to another power distribution substation. The power distribution arrangement comprises at least one control unit configured to control any power transfer in the DC transmission line between the at least one bus and the other power distribution substation. At least one ESS is connected to at least one of the DC transmission line and the converter. The at least one ESS is configured to selectively and controllably supply power to the DC transmission line or absorb power from the DC transmission line. The at least one control unit is configured to control the at least one ESS to supply power to the DC transmission line or absorb power from the DC transmission line.

While the present invention has been illustrated in the appended drawings and the foregoing description, such illustration is to be considered illustrative or exemplifying and not restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the appended claims, the word “comprising” does not exclude other elements or steps, and the indefinite article ”a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

32 CLAIMS

1. A power distribution arrangement (100) for distributing alternating current,

AC, power to a plurality of loads requiring AC power, the power distribution arrangement comprising: a power distribution substation (10) comprising a plurality of transformers (11, 12), each of the transformers being connected or connectable to at least one power source providing AC power; a plurality of switches (1-6, 60-68); a plurality of buses (13-15); a plurality of feeders (41-47), each of which is selectively and controllably connectable to at least one of the loads and to at least one of the transformers, respectively, via one or more of the buses, wherein at least some of the switches are configured to selectively and controllably connect or disconnect one or more of the feeders to or from the one or more of the buses in order to connect or disconnect the one or more feeders to or from at least one of the transformers; a direct current, DC, transmission line (70), which at one end thereof is selectively and controllably connectable to the respective ones of the feeders via at least one bus (15), via a converter (71) configured to convert DC power to AC power, or vice versa, and at another end thereof is connected or connectable to another power distribution substation (95), wherein at least one of the switches is configured to selectively and controllably connect or disconnect the DC transmission line to or from the at least one bus in order to connect or disconnect the DC transmission line to or from the feeders; at least one control unit (90, 96, 116) configured to control any power transfer in the DC transmission line between the at least one bus and the other power distribution substation; and at least one energy storage system, ESS, (110) connected to at least one of the DC transmission line and the converter, the at least one ESS being configured to selectively and controllably supply power to the DC transmission line or absorb power from the DC transmission line; wherein the at least one control unit is configured to control the at least one ESS to supply power to the DC transmission line or absorb power from the DC transmission line. 33

2. A power distribution arrangement according to claim 1, wherein the at least one control unit is configured to control operation of the switches in order to selectively connect or disconnect one or more of the feeders to or from at least one of the transformers via one or more of the buses and to selectively connect or disconnect the DC transmission line to or from one or more of the feeders via the at least one bus, whereby AC power is distributed to the loads via the feeders; wherein the at least one control unit is configured to control the operation of the switches based on: loading in and a power rating of the respective ones of the feeders, loading in and a power rating of the respective ones of the transformers, any power transfer in the DC transmission line from the other power distribution substation to the at least one bus, and a measure of the available energy in the at least one ESS and power supply rating of the at least one ESS.

3. A power distribution arrangement according to claim 2, wherein the at least one control unit is configured to, based on an indication that the DC transmission line is disconnected from the other power distribution substation at the end of the DC transmission line closest to the other power distribution substation: control the at least one ESS to supply power to the DC transmission line based on the measure of the available energy in the at least one ESS and power supply rating of the at least one ESS; and control the operation of the switches based on: loading in and a power rating of the respective ones of the feeders, loading in and a power rating of the respective ones of the transformers, and power transfer in the DC transmission line caused by the at least one ESS supplying power to the DC transmission line.

4. A power distribution arrangement according to claim 2 or 3, wherein the at least one control unit is configured to control any power transfer in the DC transmission line from the other power distribution substation to the at least one bus based on a selected power transfer reference value, and wherein the least one control unit is configured to control the operation of the switches further based on the power transfer reference value and a power rating of the DC transmission line.

5. A power distribution arrangement according to any one of claims 2-4, wherein the converter is configured so as to be capable of controlling power flow of the converter at least with respect to the contributions from active power or reactive power to the apparent power of the power flow at an AC terminal of the converter, wherein the at least one control unit is configured to set limits for the active power and the reactive power, respectively, of the power flow of the converter, based on a limit for current of the converter, any power transfer in the DC transmission line from the other power distribution substation to the at least one bus, the measure of the available energy in the at least one ESS and the power supply rating of the at least one ESS.

6. A power distribution arrangement according to any one of claims 2-5, wherein the at least one control unit is configured to control any power transfer in the DC transmission line from the at least one bus to the other power distribution substation; wherein the other power distribution substation comprises a plurality of transformers, each of the transformers being selectively and controllably connectable to at least one power source providing AC power, a plurality of buses, and a plurality of feeders, each of which is selectively and controllably connectable to at least one load and to at least one of the transformers, respectively, via one or more of the buses, wherein the DC transmission line at the other end thereof is selectively and controllably connectable to the respective ones of the feeders, via at least one bus, via a converter configured to convert DC power to AC power, or vice versa, wherein there is a loading in and a power rating of the respective ones of the feeders, a loading in and a power rating of the respective ones of the transformers; and wherein the at least one control unit is configured to determine possible power import and export ranges, for power transfer to the power distribution arrangement from the other power distribution substation and from the power distribution arrangement to the other power distribution substation, respectively, based on the loading in and the power rating of the respective ones of the feeders and the loading in and the power rating of the respective ones of the transformers, at both ends of the DC transmission line, and further based on the measure of the available energy in the at least one ESS and the power supply rating of the at least one ESS.

7. A power distribution arrangement according to any one of claims 2-5, wherein the at least one control unit is configured to control any power transfer in the DC transmission line from the at least one bus to the other power distribution substation; and wherein the at least one control unit is configured to determine, based on the loading in and the power rating of the respective ones of the feeders and the loading in and the power rating of the respective ones of the transformers, whether there is a deficit in available power from the transformers, so that there is need for power to be transferred in the DC transmission line to the at least one bus, or if there is a surplus in available power from the transformers, so that power can be transferred in the DC transmission line to the other power distribution substation; and wherein the at least one control unit is configured to, on a condition that there is a deficit in available power from the transformers: control transfer of power in the DC transmission line so as to transfer power from the other power distribution substation to the at least one bus; and/or based on the measure of the available energy in the at least one ESS and power supply rating of the at least one ESS, control the at least one ESS to supply power to the DC transmission line; and wherein the at least one control unit is configured to, on a condition that there is a surplus in available power from the transformers: control transfer of power in the DC transmission line so as to transfer power from the at least one bus to the other power distribution substation; and/or based on the measure of the available energy in the at least one ESS and power supply rating of the at least one ESS, control the at least one ESS to absorb power from the DC transmission line.

8. A power distribution arrangement according to any one of claims 2-7, wherein the at least one control unit is configured to compare loadings in the feeders with the power ratings of the respective ones of the feeders, and further to compare loadings in the transformers with the power ratings of the respective ones of the transformers, and further to control the operation of the switches based on the comparisons such that loading in the respective ones of the transformers becomes more balanced between the transformers.

9. A power distribution arrangement according to any one of claims 1-8, wherein the at least one ESS is directly connected to at least one of the DC transmission line and the converter.

10. A power distribution arrangement according to any one of claims 1-8, wherein the at least one ESS is connected to at least one of the DC transmission line and the converter via one or more intermediate components, wherein the one or more intermediate components include a converter configured to convert DC power to AC power, or vice versa, or a DC-DC converter.

11. A power distribution arrangement according to any one of claims 1-10, wherein the at least one control unit is configured to, based on an indication regarding at least one requirement of a power distribution grid, comprising at least a part of the power distribution arrangement, with respect to at least one of current, voltage and frequency of the power distribution grid, control the at least one ESS to supply power to the DC transmission line based on the measure of the available energy in the at least one ESS and power supply 36 rating of the at least one ESS so as to comply with, or come closer to complying with, the at least one requirement of the power distribution grid.

12. A power distribution arrangement according to claim 11, wherein the indication regarding at least one requirement of the power distribution grid with respect to at least one of current, voltage and frequency of the power distribution grid is based on a measurement of at least one of current, voltage and frequency of the power distribution grid.

13. A power distribution arrangement according to claim 11 or 12, wherein the at least one requirement of the power distribution grid with respect to at least one of current, voltage and frequency of the power distribution grid comprises or relates to at least one of: voltage regulation requirement in the power distribution grid, frequency regulation requirement in the power distribution grid, a black start of the power distribution grid, one or more ancillary services related to operating reserves for the power distribution grid, or electrical power quality of power supplied by the power distribution grid.

14. A power distribution arrangement according to any one claims 11-13, wherein the at least one requirement of the power distribution grid with respect to at least one of current, voltage and frequency of the power distribution grid includes a requirement regarding electrical power quality of power supplied by the power distribution grid, wherein the DC transmission line and the at least one ESS are configured such that they can be operated in a plurality of modes including a grid forming mode, and wherein the at least one control unit is configured to control the DC transmission line and the at least one ESS to operate in the grid forming mode so as to comply with, or come closer to complying with, the requirement regarding electrical power quality of power supplied by the power distribution grid.

15. A power distribution arrangement according to any one of claims 1-14, wherein the at least one ESS comprises at least one battery ESS, BESS, wherein the measure of the available energy in the at least one ESS comprises a state of charge of the at least one BESS.

16. A power distribution arrangement according to any one of claims 1-15, comprising at least two ESSs, comprising at least a first ESS and a second ESS connected with the first ESS, wherein the at least one control unit is configured to, based on a measure of the available energy in the first ESS and power supply rating of the first ESS and a measure of the available energy in the second ESS and power supply rating of the second ESS, control the first ESS to supply power to the second ESS or absorb power from the second ESS, or control the second ESS to supply power to the first ESS or absorb power from the first ESS. 37

17. A power distribution arrangement according to any one of claims 1-16, wherein at least some of the feeders are selectively and controllably connectable to at least one of the transformers by means of a plurality of buses (13-15) connected or connectable in series, and wherein the DC transmission line is selectively and controllably connectable to at least one of the buses that are connected or connectable in series.

18. A power distribution arrangement according to any one of claims 1-17, wherein at least some of the feeders are selectively and controllably connectable to at least one of the transformers by means of a plurality of buses (16, 17) connected or connectable in parallel, and wherein the DC transmission line is selectively and controllably connectable to at least one of the buses that are connected or connectable in parallel.

19. A power distribution arrangement according to any one of claims 1-18, wherein at least some of the feeders (78, 79, 80) are selectively and controllably connectable to the transformers by means of a ring main distribution system.

20. A method (600) in a power distribution arrangement for distributing alternating current, AC, power to a plurality of loads requiring AC power, the power distribution arrangement comprising a power distribution substation comprising a plurality of transformers, each of the transformers being connected or connectable to at least one power source providing AC power, a plurality of switches, a plurality of buses, and a plurality of feeders, each of which is selectively and controllably connectable to at least one of the loads and to at least one of the transformers, respectively, via one or more of the buses, wherein at least some of the switches are configured to selectively and controllably connect or disconnect one or more of the feeders to or from the one or more of the buses in order to connect or disconnect the one or more feeders to or from at least one of the transformers, wherein the power distribution arrangement further comprises a direct current, DC, transmission line, which at one end thereof is selectively and controllably connectable to the respective ones of the feeders via at least one bus, via a converter configured to convert DC power to AC power, or vice versa, and at another end thereof is connected or connectable to another power distribution substation, wherein at least one of the switches is configured to selectively and controllably connect or disconnect the DC transmission line to or from the at least one bus in order to connect or disconnect the DC transmission line to or from the feeders, and wherein the power distribution arrangement further comprises at least one energy storage system, ESS, connected to at least one of the DC transmission line and the converter, the at least one ESS being configured to selectively and controllably supply power to the DC transmission line or absorb power from the DC transmission line, the method comprising: 38 controlling (601) any power transfer in the DC transmission line between the at least one bus and the other power distribution substation; and controlling (602) the at least one ESS to supply power to the DC transmission line or absorb power from the DC transmission line.

21. A computer program comprising instructions, which when executed by one or more processors comprised in at least one control unit for a power distribution arrangement according to any of claims 1-19, cause the at least one control unit to perform the method of claim 20.

22. A processor-readable medium, having a computer program loaded thereon, wherein the computer program comprises instructions, which, when executed by one or more processors comprised in at least one control unit for a power distribution arrangement according to any of claims 1-19, cause the at least one control unit to perform the method of claim 20.