Direct current network, direct current distributor and method for establishing a direct current network

Abstract

Direct current network (1 ) of modular construction, comprising a number of direct current distributors (2) detachably connected by cables, arranged to electrically supply one or more direct current consumers connectable to the direct current distributor (2), such as chargers (3) and batteries (4), from an external alternating current source (5) or from an external direct current source, such as batteries (4) and hydrogen fuel cells (6). The direct current distributors (2) are portable and have identically equipped high-voltage circuits (7), the outputs (8) of which are electrically and mechanically equivalent to connectable units, whereby the direct current distributors (2) are interchangeable with each other and can be interconnected for expansion of the direct current network (1) by adding direct current distributors (2).

Description

[0001] Direct current network, direct current distributor and method for establishing a direct current network

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The invention relates to a direct current network of modular construction, a direct current distributor and a method for establishing a temporary direct current network that can be easily adapted to varying charging power needs.

[0004] BACKGROUND OF THE INVENTION AND PROBLEMS THAT THE INVENTION INTENDS TO SOLVE

[0005] Like other industries, the construction and civil engineering sector needs to become climate neutral. Part of achieving climate neutrality in the construction industry is to electrify the machinery and the transportation to and from the workplaces. With current technology, this is possible, but electrification also means that the industry greatly increases its power requirement from the electricity grid. The problem is that this is happening at the same time as other industries also intend to electrify their operations. The current power pool within the public electricity grid is not large enough to allow the connection of fast-charging infrastructure directly to the electricity grid. In addition, it will be very expensive for the electricity grid owner to expand the electricity grid for the short and intensive consumption that fast-charging of battery-powered vehicles entails.

[0006] Current electrically powered work vehicles are charged with a power of up to 150 kW, which means that a current of about 250 A is continuously drawn from the power grid every time a charging station is operated at maximum power. If charging times are to be reduced, the power needs to increase further. Power levels of 300 kW up to 600 kW at each charging station are not an inconceivable scenario in the future, especially for charging trucks. The mains connection for each individual fast charger that is directly connected to the power grid then needs to handle currents of 500 A up to 1000 A if it is operated on a mains voltage of 400 VAC. This will be very expensive and will involve lengthy permitting processes. In addition, the idea is that the work machines should be charged during the time when the machines are not being used, i.e. during breaks and during the evening / night. Most of the vehicles therefore risk being charged at the same point of time. The risk is that the electricity grid will not be able to handle that power unless there is some form of intermediate storage that evens out the chargers' power consumption from the grid. The construction industry is a sector that mainly works in projects. Each project consists of a number of different phases: ground work, foundation work, construction of the frame, facade, interior, and so on. Once the project is completed, the same power requirement no longer exists. The power requirement is temporary and also changes between the phases of the project. A well-suited solution to this problem must be flexible, modular and cost-effective. It must also be easy to install without the current power grid at the workplace needing to undergo any major modifications.

[0007] Last but not least, the main cost of a construction project is not the machinery, or the equipment. What costs companies money is when the project is at a standstill. The construction industry, as well as other industries, depends on a stable cash flow. Any delays in the form of stationary machinery will be a greater cost to companies compared to the investments required to establish a fast charging infrastructure. If charging cannot be handled smoothly, the electrification of companies' work machines may become economically unsustainable.

[0008] SUMMARY OF THE INVENTION

[0009] The object of the present invention is to design a system that allows the customer to establish a microgrid in the form of a DC grid that works in parallel, but disconnected from the 400 V (typical) AC grid that is found in workplaces today. Since the DC grid works in parallel with the AC grid, a developer only needs to make minimal adjustments to the existing electrical infrastructure. The system then becomes practical for the developer to deploy. The grid should use DC instead of AC, as DC is easier to control, expand, requires fewer cables and offers a more energy-efficient way to transfer energy.

[0010] This object is achieved by a direct current network designed in accordance with appended claim 1.

[0011] The object is also achieved by a direct current distributor in accordance with appended claim 13.

[0012] The object is nevertheless achieved by a method according to claim 14.

[0013] Briefly, the invention provides a direct current network (DC network) of modular construction, comprising a number of direct current distributors (DC nodes) detachably connected by cables, arranged to electrically supply one or more direct current consumers, such as chargers and batteries, connectable to the DC node from an external alternating current source (AC network) or from an external direct current source, such as solar, wind, hydrogen, V2G, etc.), whereby the DC nodes are portable and are characterized by comprising equally equipped high-voltage circuits whose outputs to connectable units are electrically and mechanically equivalent, whereby the DC nodes are mutually interchangeable and interconnectable for expansion of the DC network by adding DC nodes.

[0014] In other words, a central aspect of the invention is that DC distribution connections are constructed in the same way and may be interchanged without modification and may be added to each other, in different numbers and configurations, for dimensioning the DC network to the current need. The DC distributors form nodes in the DC network, DC nodes, which may be interconnected in a serial, meshed or parallel network configuration. The term DC node should be understood as a junction point in a power network structure that supplies and distributes direct current (DC) to charging stations and batteries connected to the DC network. The DC nodes also form interfaces to the external AC network with which the DC network may communicate in both directions for receiving energy or for outputting stored energy via a connected, preferably separate AC / DC converter.

[0015] The high-voltage circuit of DC node has a number of outputs for connecting external units. Each of the outputs includes a charging circuit, switch, current sensor, high-voltage detector, high-voltage connector. The number of outputs may be varied within the scope of the invention. In the exemplary embodiment, the DC node is described with six outputs, which is considered to be an advantageous dimensioning of the DC node with respect to external dimensions, weight and flexibility in designing DC networks for different needs, especially in the construction industry.

[0016] In this context, it should be noted that the outputs from the high-voltage circuit may nevertheless have additional components in addition to those listed above. Thus, each output from the high-voltage circuit in the DC node is preferably also assigned an earth fault sensor.

[0017] The high-voltage circuit of the DC node preferably comprises a capacitor bank associated with one or more discharge resistors. The purpose and advantages of this arrangement of the high-voltage circuit are more clearly apparent from the detailed explanation of the exemplary embodiment below.

[0018] In addition to the high-voltage circuit, the DC node also includes a low-voltage circuit with a low-voltage battery that is charged by the high-voltage circuit via a DC / DC converter. The low-voltage circuit of the DC node drives a system for communication and control of the connected units of the DC network.

[0019] The control of the DC node is divided into an energy management system (EMS) and a component monitoring system (PLC). Of these systems, the EMS system provides communication between the DC node and the units connected to it; between the DC node and the cloud / internet; between the DC node and other DC nodes in the DC network; and between the DC node and the operator via a human-machine interface (HMI). The PLC system, on the other hand, monitors the function of the switches, over-voltage protector and sensors in the high-voltage circuit of the DC node.

[0020] The mobility in the DC network is guaranteed by encapsulating the DC node's high-voltage circuit and outputs in a box module that may be rolled, lifted or carried on site, for example by a hand-held pallet truck, forklift or wheel loader / construction crane, as applicable. This allows a civil engineering company or a construction company, for example, to have a storage of DC nodes and cabling from which the desired number is lifted into the civil engineering site or the construction site for connection to a DC network of the desired extent - both horizontally and vertically in projects that cover several floors.

[0021] As previously mentioned, the DC nodes of the DC network can be interconnected in a serial (b), meshed (c) or parallel (d) configuration. In one configuration, at least one DC node is connected to at least two external AC sources via an AC / DC converter module with mutually isolated connection points for each external AC source and with a common connection to the DC node. Other possible configurations are described below in the detailed description of exemplary embodiments.

[0022] A central component of the DC network is the DC distributor (DC node) which is designed to establish a temporary DC network by connecting to an AC source via an AC / DC converter. The DC node comprises a high-voltage circuit and a low-voltage circuit arranged in a portable enclosure, wherein the high-voltage circuit has a number of outputs for connecting external units such as an AC / DC converter module, vehicle charger, batteries and other DC sources, wherein each output is equipped with a charging circuit, a switch, a current sensor, a high- voltage detector and a high-voltage connector.

[0023] In another aspect of the invention, a method for establishing a local direct current network is provided comprising: • providing of a number of equally equipped, portable high-voltage circuits (DC nodes) for direct current, each designed to electrically supply one or more DC consumers (such as chargers, batteries) connectable to a DC node, from an external AC source or from an external DC source (such as solar, hydrogen, V2G, etc.),

[0024] • interconnection via a cable of two or more DC nodes,

[0025] • connection of external DC consumers (chargers, batteries) to the DC nodes, and

[0026] • connecting at least one DC node to at least one external AC network via an AC / DC converter.

[0027] The method may include interconnecting DC nodes in a serial (b), meshed (c) or parallel (d) configuration for horizontal and / or vertical extension of the DC network. In one embodiment, the method involves connecting at least one DC node to at least two external AC sources via an AC / DC converter module with mutually isolated connection points for each external AC source and with a common connection to the DC node.

[0028] BRIEF DESCRIPTION OF DRAWINGS

[0029] Embodiments of the invention will now be explained in detail and in connection with the attached schematic drawings, of which

[0030] Fig. 1 shows a system diagram of a direct current network, hereinafter also referred to as a DC network, of modular construction based on mutually connectable DC nodes,

[0031] Fig. 2 shows a circuit diagram of a high-voltage circuit included in the DC node,

[0032] Fig. 3 shows a block and flow diagram of the DC network control,

[0033] Fig. 4 shows a functional diagram of the DC node control system,

[0034] Fig. 5 shows a simplified system diagram of a vehicle charging module connectable to the DC network,

[0035] Fig. 6 shows a simplified system diagram of an AC / DC converter module connectable to the DC network,

[0036] Fig. 7 shows a simplified system diagram of an alternative AC / DC converter module connectable to the DC network,

[0037] Fig. 8 shows a simplified system diagram of a battery module connectable to the DC network,

[0038] Fig. 9 shows a simplified system diagram of a hydrogen or fuel cell module connectable to the DC network,

[0039] Fig. 10A-10D show alternative configurations of modularly constructed DC networks based on the DC node, Fig. 11 shows a flow chart of the control of a network configuration based on standalone DC nodes,

[0040] Fig. 12A-B show flow charts of the control of DC nodes connected in a meshed network configuration,

[0041] Fig. 13 is an example of the design of a DC network based on DC nodes for a construction site,

[0042] Fig. 14 is an example of the design of a DC network based on DC nodes for a civil construction site,

[0043] Fig. 15 is an example of a load curve and available power from an apartment building serving a DC network,

[0044] Fig. 16 shows a first alternative embodiment of the DC node enclosure, and

[0045] Fig. 17 shows a second alternative embodiment of the DC node enclosure.

[0046] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0047] The DC network 1 includes a DC node 2 which has a central role. The DC node 2 is an interconnecting unit, i.e. a connection unit comprising electronics the task of which is to control the other units that are connected to the DC node. Units that can be connected to the DC nodes are chargers 3 for work vehicles, battery modules 4, AC / DC converter modules 5' which are connected to an AC network, fuel cell modules 6 and other DC nodes 2. The AC network may be an AC network found at the construction site, a local network operated by some form of generator solution or one, or more, external connections from adjacent properties or facilities.

[0048] Each DC node 2 is an individual unit that is separate from the remaining units that are connected to the DC node 2 within the DC network 1. All units within the DC network have their own encapsulation, container or similar enclosure. What connects the units are two, or more, DC cables, a ground conductor and possibly low-voltage cabling.

[0049] A DC cabling is connected to the high-voltage circuit 7 of the DC node and comprises two electrical poles: a positive and a negative pole of the DC network voltage. The ground conductor runs parallel to the DC conductors and is responsible for diverting the current in the event of a ground fault. The primary task of the low-voltage cabling is to handle communication between the connected units and the DC node as well as between two interconnected DC nodes.

[0050] Fig. 2 shows the system diagram of the high-voltage circuit 7 found in the DC node 2. The high-voltage circuit constitutes the high-voltage part of the DC network and acts as an interface to the units connected to the system. In the exemplary embodiment, the high- voltage circuit 7 consists of six outputs 8 each equipped with a switch 10, a current sensor 11 , a charging circuit 9 and a high-voltage connector 13 out to the units connected to the DC node. The DC node may be designed with different numbers of outputs that are dimensioned for different power levels and voltages. What defines the DC node is that all outputs within the same module are equivalent and interchangeable.

[0051] To meet the requirements for functionality and security of DC node, all DC nodes will contain the following components (see Fig. 2):

[0052] Current sensors, see reference numerals 11 in Fig. 2: The DC node must be able to measure the current flowing through each output from the high-voltage circuit. The DC node must measure the current to ensure that the current does not exceed the maximum value for which the cables are dimensioned. The system should also be able to detect at which of the outputs a fault has occurred, after a fault has occurred. Furthermore, the system should be able to determine whether the measured power from connected external units corresponds to the current measured at the output. Such a function is important to facilitate the system in detecting if the communication between the units and the node has been manipulated. It is an important function for the cyber security of the system. All this is done by a dedicated current sensor mounted on the positive pole of each output.

[0053] Ground fault sensors, see reference numeral 16 in Fig. 2: The DC node must be able to detect any ground faults. This is done most simply and safely by means of a ground fault sensor mounted on each output of the high-voltage circuit. The sensor measures the current leaving one pole and ensures that an equal current flows in the opposite direction in the opposite pole. If this is not the case, an electrical fault has occurred.

[0054] Voltage sensors, see reference numeral 27 in Fig. 2: The voltage sensor of the DC node is responsible for monitoring the voltage of the DC grid. The voltage is an important part of the control of the DC grid as it is directly related to the difference between the power entering the DC grid and the power going out to the units. In the same way as for the current sensor, the value from the voltage sensor may be used to filter incorrect measurement values or to detect suspected cyber attacks.

[0055] Switches / contactors, see reference numeral 10 in Fig. 2: The main purpose of the switch, or contactor, is to break the connection between the high-voltage circuit and the output. In the event of an electrical fault, during maintenance and movement of a group of units connected to the DC network, this makes it possible to break the current to a particular unit while at the same time the other units may remain connected to the DC network. The switch allows units to be replaced, maintained and moved without affecting the operation of the remaining network. The switch may comprise one or more contactors or switches connected in series. The switch can be located only on the positive pole or on both poles.

[0056] Charging circuits, see reference numeral 9 in Fig. 2: All batteries, AC / DC converters, hydrogen cells or chargers (via V2G) should have the ability to charge the grid to the correct voltage. The capacitor bank 14 is the unit that stabilizes the grid and needs to be charged safely. The problem is that the capacitor will act as a short circuit during the initial stage when the circuit is turned on. A resistor is used to charge the circuit safely as it limits the amount of current when the capacitor bank is charged. A switch is mounted in series with the resistor so that the connection between the DC grid and the unit can be broken.

[0057] Discharge resistors, see reference numeral 15 in Fig. 2: One or more discharge resistors are connected in parallel with the capacitor bank 14. The purpose of the discharge resistors is to automatically discharge the capacitor bank in the event of an interruption in the control system of DC node, or if the overvoltage protection fails. The discharge resistors are included in the circuit for safety reasons.

[0058] Low-voltage battery, see reference numeral 18 in Fig. 2: The function of the low-voltage battery is to power the low-voltage system that is part of the DC node. The low-voltage battery may also be used to power the low-voltage system of the connected units. The primary task of the low-voltage battery is to act as a backup to the power supply of the control system if the system is in a standby mode for a longer period of time. The low-voltage battery will primarily be charged through an isolated DC / DC converter that pulls power from the high- voltage circuit of the DC network.

[0059] High-voltage detectors, see reference numeral 12 in Fig. 2: The system must clearly indicate when the high-voltage circuit is charged and when an output is energized. Each high-voltage detector will indicate both to the control system and visually to the environment through diodes that the circuit is energized. The control system may then detect if contactors / s witches are stuck in a closed position when they should be open. The system may then shut down and order the discharge of the capacitor bank.

[0060] High-voltage connector, see reference numeral 13 in Fig. 2: Standardized high-voltage connector to which units can be connected. The high-voltage connector acts as an interface between the DC node and the cable to each unit, or to another DC node within the DC network.

[0061] Over-voltage protector, see reference numeral 26 in Fig. 2: The over-voltage protector consists of at least one switch and at least one power resistor. The switch is turned on and off by the DC node in order to regulate the voltage by burning off power when the power surplus in the system becomes too high. The over-voltage protector, unlike the discharge resistor, will actively regulate the voltage in the system and is a central part of the voltage regulation of the DC network.

[0062] Capacitor bank, see reference numeral 14 in Fig. 2: The function of the capacitor bank is to filter the incoming current to the DC network. It also acts as a short-term energy storage and counteracts rapid changes in the DC network voltage. The capacitor bank is important to ensure that the network voltage does not collapse during rapid changes in the power flows of the DC network. Without the capacitor bank, the DC network cannot regulate its voltage.

[0063] Fuses, see reference numeral 28 in Fig. 2: The function of the fuse is to act as an additional safety measure if the switch is unable to interrupt the fault current at an output.

[0064] The high-voltage circuit shown in Fig. 2 includes the components required to meet the functional requirements of the DC node. Additional components, such as filters or magnetic elements, may be added to meet EMC (electromagnetic compatibility) requirements. Fig. 2 should therefore be considered as a system diagram of the DC node.

[0065] Fig. 16 illustrates the intended physical appearance of the DC node with cabling connected to some outputs. The box-shaped enclosure 100 includes holes 101 at, for example, the corners of the box, where lifting units can engage by mounting, for example, its loops to lift the DC node into place. Alternatively, there are also holes 101 in the bottom of the box that a pallet truck, forklift, tractor or crane, for example, can use to move the DC node. Fig. 16 should be seen as a conceptual illustration. The placement of connectors, the doors of the enclosure, etc. are preliminary and can be determined when the DC node and the other components of the DC network are selected and integrated into the design. An alternative design of the DC node housing is shown in Fig. 17.

[0066] The DC node will be designed in a way that allows for easy repair and maintenance. All components that have a shorter lifespan should be easily accessible. The DC node does not need to be optimized for the smallest possible weight or size. Instead, it can be optimized for maintenance and be easy to mass produce. The design should be easily adapted to accommodate more or fewer outputs from the high-voltage circuit. The design should allow components from different manufacturers to be used when one manufacturer is unable or unwilling to supply components at a favorable price. This is the very reason why the system has been divided: the performance and weight of each module and DC node do not need to be optimized as the modules weigh less because the system has been divided.

[0067] The low-voltage system of the DC node may be categorized into four main functional categories: communication, power supply, control, monitoring and control system. Fig. 4 shows the relationship between each functional category of the low-voltage system of the DC node, where the arrows indicate how the parts of the low-voltage system interact.

[0068] The intelligence of the DC grid is located in the control system of the DC node, see Fig. 3 and Fig. 4. The control system is responsible for the safety functions of the system, for controlling the power consumption of the units and for monitoring the system during operation. The control system found in each DC node is divided into two parts: an EMS 20 and a PLC 21 (Fig. 4).

[0069] EMS stands for “Energy Management System” and represents the software responsible for less time-critical tasks that require greater computing power.

[0070] PLC stands for “Programmable Logic Controller” and is the software that, combined with the hardware, is responsible for time-critical tasks that primarily relate to the safety functions included in the DC node.

[0071] EMS

[0072] • Less time-critical tasks include the following:

[0073] • Planning - how the user will be guaranteed the power they need at the time they want to charge.

[0074] • Monitoring - the DC node shall be responsible for ensuring the connection between the connected units and that the DC node is properly equipped. It shall also be able to detect if the traffic between a connected unit and the DC node has been manipulated.

[0075] • Communication - the EMS handles communication between the connected units, the cloud via the internet, the user, the remaining DC grid and the DC node.

[0076] • Control - the EMS shall be responsible for the control of the connected units and systems of the DC node within the DC node. The control of the system may be based on the EMS's own planning algorithm or commands from another EMS within the network, see below how the network is controlled when two or more DC nodes are interconnected.

[0077] Each DC node must be able to work independently or within a cluster of DC nodes. In addition, the system must be able to be controlled in environments with poor internet connectivity. Each DC node has the ability to independently plan how the resources of the DC network should be used. The software should have the ability to autonomously predict how and when the vehicles need to be charged, handle unexpected outages of parts of the DC network and be able to plan for movements or maintenance of parts of the DC network. Al (Al - artificial intelligence / machine learning) supplemented with traditional programming is currently good enough to handle the above-mentioned situations. By adding a traditional optimization algorithm to the system, the system will be able to optimize the use of the system's resources in real time.

[0078] When the system connects new units or expands the DC network by connecting a new DC node, the remaining DC nodes need to determine whether the connection has been made correctly. This can be done by comparing the currents and voltages that the newly connected DC node measures with those measured by the previously connected DC node. If a sufficiently large difference is measured, there are three different likely scenarios: the new DC node is faulty, the connection between the DC nodes is faulty, or a malicious actor has manipulated the communication between the DC nodes. The sensors within the DC node enable the system to locate on which output a fault has occurred in the event of an electrical fault. If the fault occurs after the switch of the high-voltage circuit, the fault can be isolated and the remaining part of the DC network can continue to be powered. The DC node handles the communication between the DC node and the remaining system, the cloud, or the user through an HMI (Human Machine Interface). The communication will primarily take place through a physical Ethernet cable or wirelessly via WiFi, or a 4G / 5G connection.

[0079] The communication between the units, the remaining DC nodes and the DC node comprises:

[0080] • Order: when and how the unit or system should be activated.

[0081] • Configuration: the EMS must be able to detect which type of unit that is connected, what technical characteristics the unit has, or what the rest of the network looks like. The information should be used to plan the operation of the DC network, and to set how the connected unit should act within the DC network. This could, for example, be how quickly the unit regulates its power. • Status: the status of the units, or the system, is important information for the real-time planning of the system.

[0082] The communication between the DC node and the cloud is performed for the following purposes:

[0083] • Software update: the software installed in the system must be able to be updated. This should be done either through the cloud or through a physical connection to the EMS.

[0084] • Obtaining software packages for specific units: Units from different manufacturers will behave differently. The EMS must be able to obtain the software package required to control the unit. The system can be updated before a mission. There may be situations where the system must be able to handle units from other manufacturers.

[0085] • Remote control: in some situations, it may be necessary to control the system via the cloud. The ability to connect to the system to support the customer must be available.

[0086] The communication between the user and the DC node should be managed via an HMI and allow the user to perform the following actions:

[0087] - Report a planned move or outage: the user should have the opportunity to report a planned move or outage of a unit or part of the DC network.

[0088] - Define the system design: the DC network must know which units are connected to the DC network and the design of the DC network. The software of the DC node should automatically be able to detect how the system is connected. If an error has occurred, the user must be able to correct the error.

[0089] - Report abnormal charging patterns: during parts of a construction site, the construction site may require machines to be charged up to 100% when work is to be performed during which it may be difficult to charge the machine. Such charging differs from how the battery should usually be charged in order not to degrade the battery's capacity to an excessive extent. Typically, the battery should fluctuate between 20% and 80% in charge, then it will last for a longer time.

[0090] PLC

[0091] Time-critical tasks refer to any of the following tasks: • Reading sensor data: the sensor data that the system obtains will be used in two ways: monitoring the system and the safety functions contained in the software of the control system.

[0092] • Control: the task of the PLC is to obtain commands from the EMS and convert these into control signals, for example to the contactors.

[0093] • Safety-related functions: the system must be able to react quickly to any potential faults that may occur within the system.

[0094] The sensors of the DC node will generate a large amount of data, data that will be handled by the control system and converted into information that the EMS can use in decision-making. In order for the system not to lose any data, all sensor data should be processed by the PLC. In addition, a fast reading of sensor data enables the PLC to react quickly to any faults within the network.

[0095] The control of the contactors and over-voltage protector of the DC node shall be handled by the PLC. This relieves the EMS and gives the PLC the ability to react to all faults that may occur within the DC node and on any of the outputs of the DC node. All safety-related tasks within the control system will be given high priority by the control system. The damage caused by the fault is minimized if the fault can be detected and the system reacts quickly to the fault.

[0096] Communication

[0097] The communication within and out from the DC network should be handled through wired or wireless communication. Initially, the DC node should be able to handle four different communication channels:

[0098] • The units: the DC node needs to communicate with the units connected to the respective output. The communication will include the status of the unit, commands from the DC node to the unit and feedback from the unit back to the DC node.

[0099] • Cloud: the system is designed to establish communication via the internet. The communication shall be used primarily for updating software, for necessary software packages to deploy specific units, for remotely configuring the system and / or for diagnostics.

[0100] • HMI: the user needs the possibility to interact with the system through a user interface, or HML The HMI of the system should be used when planning a system move, to diagnose the system, or to perform manual updates.

[0101] • Other DC nodes: each DC node must be capable of communicating with other DC nodes that are connected to the DC node. The communication between the connected DC nodes is handled in the same way as the communication to other connected units, as in both cases the same connection is used. The communication between the units and the remaining DC nodes should be handled in the same way - a wired connection is established between the interconnected units.

[0102] The connection should run alongside the high-voltage cable. The reason for using a physical connection as the main communication method is that it allows the system to easily determine which units are connected to each respective output. The system can then automatically identify the layout of the DC network. The DC node can then autonomously adapt the control to the components that are connected to its outputs.

[0103] The cloud is a collective name for the resources and systems that the DC node connects to via an internet connection. During system operation, it is important that the customer gets a complete picture of the system's energy use. Each respective DC node should compile the power flows that occur via the network and communicate the measured values to the cloud. The cloud compiles the data and gives the customer a complete picture of the system's instantaneous energy levels, how much energy that has been consumed, when the energy was consumed, etc. All KPIs (key performance indicators) are important to the customer as the customer needs to know how and when the charging stations are used to invoice subcontractors or the transport companies that use the charger.

[0104] Diagnostics is an important aspect of fault detection; diagnostics require access to the data that the system collects. Through continuous data collection, fault detection may be improved, and the planning algorithms that are used to manage energy planning may also be improved. Through effective data collection, the system's software can be improved until it is able to handle the situations that may arise during, for example, a construction project. Subsequently, all data may be used to predict when a product needs to be maintained or repaired. All forms of data that the system can collect are valuable for the customer, the company and the further development of smart energy systems.

[0105] The user must interact with the system easily. The construction industry often works according to schedules that are continuously updated through digital tools. If the application developed for the DC grid resembles their tools, the industry can quickly adopt the solution. The main features that an application should have are the following:

[0106] The user should be offered a visual overview of how the system is connected and the current status of each unit. • In the event of any errors, they should be communicated in a simple but detailed manner. What has happened, where in the DC network the system has detected the error and how it can be fixed.

[0107] • The user should also be given the opportunity to plan any possible movements of the system. The movement of the specific components should be reported.

[0108] The control and monitoring of the low-voltage system includes all sensors, contactors and over-voltage protector that are part of the DC node. The measurements of interest to the system are the output currents on each output, the ground fault sensor, the voltage sensor and the voltage detectors that send back a feedback when they have detected a voltage. Other measurements of interest are the air temperature of the DC node, which is used to estimate the temperature of the over-voltage protector, the discharge resistor and the capacitor bank. In addition, a cooling system may be needed to regulate the temperature of the DC node during operation.

[0109] All safety-related functions need to have some form of feedback. The system should detect when a contactor is closed through the high-voltage detector and through feedback from the contactor indicating its position: closed or open.

[0110] Finally, each system needs some form of fire detector and interlocking loop that prevents the high-voltage system from being energized when it should remain de-energized. Alternatively, a switch may be arranged in the low-voltage system, followed by several relays that indicate the status of the safety-critical functions.

[0111] The system needs some form of power supply to the low-voltage system. A preferred solution is for each DC node to draw power directly from the high-voltage circuit through an isolated DC / DC converter.

[0112] The control system of the DC node needs to function also when the high-voltage circuit is discharged, hence the low-voltage battery that is connected to the power supply of the low- voltage system. If the low-voltage battery has a charge, the system can always start.

[0113] The DC node forms the interface between the units that are connected to the DC network. A unit is a module whose task is to fulfill one any of the following functions:

[0114] • Charger 3: The function of the module is to charge a battery-powered vehicle with power obtained via the DC node to which the unit is connected. • AC / DC converter module 5': The function of the module is to convert alternating current to direct current. The module must be able to feed power from the construction site's AC network to the DC network or from the DC network to the AC network. The AC / DC converter module acts as an intermediary between the DC network and the “construction site's electricity”, or alternatively to an external AC connection to the construction site.

[0115] • Battery 4: The function of the module is to temporarily store the energy that is obtained from the energy sources of the DC grid. The battery's task is to cover the high power consumption of the charger when charging a vehicle. The battery does this by discharging its stored power over a short period of time.

[0116] • Hydrogen storage 6: The function of the module is primarily to supplement the energy obtained via the AC / DC converter module. If the workplace lacks a grid connection, the entire energy of the DC grid may be obtained from hydrogen storage.

[0117] One or more units of the same type can be connected to one of the DC node outputs. When several units are connected to one output, it is called a unit group. Unit groups of all types of units may occur, but it is most likely that batteries and hydrogen storages are present in unit groups. Hydrogen storages are generally poorly adapted to deliver high power and since each output is adapted to the power required for vehicle charging, it may be of interest to connect several smaller units in parallel to each output. Batteries connected in unit groups may be of interest if the system capacity needs to be increased but not its total power. In this case, two battery modules may be connected to the same output. The energy storage capacity of the output has then been doubled, while at the same time the combined power that the unit group can deliver to the DC node remains the same.

[0118] A microgrid in the form of a DC grid may consist of one or more interconnected DC nodes 2. What defines the DC grid is that it has an energy source in the form of a connection such as an AC source 5 to an external power grid, hydrogen storage 6 and / or local production of energy in the form of a generator or solar cells, or a battery 4 that is replaced at regular intervals. In addition, a load is required that is to be supplied with power. The load may be in the form of a vehicle charger 3, or may belong to the AC part of the grid.

[0119] Fig. 5 shows a simplified system diagram of a vehicle charger 3. The charger consists of one or more parallel-connected DC / DC converters controlled by a PLC. The PLC communicates in three directions: the DC node to which the charger is connected, the internal control system of the vehicle and the DC / DC converters located in the charger 3. The vehicle supplies the PLC with a desired voltage and current. The PLC commands the DC / DC converters to generate the desired voltage and current out to the vehicle. The PLC then communicates the power consumed by the charger back to its DC node which commands AC / DC converters, batteries or other nodes within the network to cover the power consumption of the charger.

[0120] The charger 3 may also contain filters, switches and a cooling system, to name a few subsystems that are not shown in the system diagram depicted in Fig. 5.

[0121] The AC / DC converter module 5' may be designed in alternative ways: a module where all AC / DC converters share a common connection to the same AC network, and a module where each respective AC / DC converter is connected to different AC network connections 5. All connections in alternative two should be mutually isolated to enable the unit to connect to different AC connections that do not share a common fuse to the network. A simplified system diagram is shown for both alternatives in Fig. 6 and 7.

[0122] Just like the charger, the AC / DC converter module 5' will also contain a PLC that coordinates the combined power of the AC / DC converters with the DC node to which the unit belongs. The biggest difference between the two concepts is that the DC node and the AC / DC converter module in the second alternative must know what power it can deliver or consume from the respective grid connection. This therefore requires cooperation between the connection and the DC grid. Preferably, the communication takes place wirelessly or via the internet via the responsible electricity grid company.

[0123] Fig. 8 shows a simplified system diagram of a battery module 4. The converter of the module is controlled by a PLC that communicates with the DC node. In addition to the PLC, the module contains a BMS, short for “Battery Management System”, which monitors the battery.

[0124] Fig. 9 shows a simplified system diagram of a hydrogen or fuel cell module 6. The converter of the module is controlled by a PLC which communicates with the DC node.

[0125] Fig. 1 is an example of how a DC network on a construction site can be designed. The example comprises all types of units that may be included in the DC network and consists of interconnected DC nodes. Each DC node has a vehicle charger and an energy storage, but differs in three different ways in which the DC node is supplied with energy. A first DC node has an AC / DC converter module 5' that is only connected to an AC connection, i.e. the construction site's own construction electricity. A second DC node is supplied with energy by a fuel cell powered by hydrogen. A third DC node is supplied with energy by the alternative for AC / DC converter module 5' according to Fig. 7. This DC node fetches power from several different separate connections to one or more AC networks or sources 5.

[0126] All DC nodes within the DC network shown in Fig. 1 have the ability to share power among themselves. The ability to share power between the DC nodes enables the DC nodes to borrow power from the batteries connected to any of the other DC nodes, or to share a common energy source. All DC nodes can always cover the power needs of another DC node if, for example, one of the DC node's energy storage or energy sources were to fail. The power is limited by how much power the DC node's output and the lines between the DC nodes are dimensioned for. In this way, the network becomes robust.

[0127] The DC network can connect the DC nodes through four different basic connections: standalone, series, meshed or parallel. The DC network may thereafter consist of various combinations of several basic connections. Fig. 10A-D show the four possible basic connections that the DC network can use. The DC nodes of the DC network are represented by squares and a line between the DC nodes represents a connection.

[0128] The stand-alone network configuration, see Fig. 10A and Fig. 11 , is the simplest type of connection. Here, each DC node with connected units stands alone. No internal connection is made between the DC nodes found at the workplace. Hence, each DC node needs its own energy source, energy storage and charger. The control and planning are entirely handled by the individual DC node, i.e. the DC node always acts as a local leader within the DC network. The DC nodes in a stand-alone system must still communicate as they need to coordinate their power consumption if they draw power from a common energy source.

[0129] Advantages of a stand-alone network configuration include:

[0130] • Robust against faults, faults in the remaining DC nodes do not affect the individual DC node.

[0131] • This requires fewer cables within the DC network. More cables within the construction site may mean more complicated logistics as the cables must be planned along the movement of the machines and protected against possible injuries caused by squeezing.

[0132] • All of the DC node's outputs can be used to connected units.

[0133] In a serial network configuration, see Fig. 10B, the DC nodes are connected in series. This enables the DC nodes to move power within the DC network to compensate for a failure of one or more energy sources, batteries, or to prepare for a change in the DC network. The network has now become more flexible and resilient to the failure of units within the network. One DC node will now act as a leader and the remaining DC nodes serve as followers. Each DC node is now responsible for the safety-related functions for the units that are part of the DC node and forwards orders that come from the system leader.

[0134] Advantages of a serial network configuration include:

[0135] • Robust against fault within any of the units. The respective DC node can now isolate the faulty unit and “borrow” power from the remaining DC nodes. The system becomes more resilient against faults within, in particular, the battery modules and the AC / DC converter module.

[0136] • The network can share one or more common energy sources. See for example DC node 2 in Fig. 10B which can be adapted to handle charging only and instead obtain energy from the two other DC nodes.

[0137] • Each battery module and energy source can be utilized more efficiently when it is used by multiple DC nodes to supply the chargers with the necessary energy.

[0138] In a meshed network configuration, see Fig. 10C and Fig. 12A and 12B, each DC node within the DC network is connected to at least two other DC nodes, which are also interconnected.

[0139] A mesh consists of at least three DC nodes where all DC nodes have at least one connection to the other DC nodes. This means that the power flow between each DC node always has two possible paths under normal operating conditions. In the same way as in the series- connected configuration, the meshed network configuration will consist of a leading DC node and the remaining DC nodes act as followers.

[0140] Advantages of a meshed network configuration include:

[0141] • The advantages of the meshed network are similar to the series connection in that the network becomes robust against failure of units. In addition, the DC network will also become robust against faults in the connection between the DC nodes and within any of the DC nodes. If a DC node fails, the connection will instead act as a series connection.

[0142] • The power that can be shared via the DC nodes has now been doubled, each DC node can now cover up to two batteries. The DC node may also choose to draw power from both of the DC nodes, or from just one of the DC nodes; the power flow can be optimized. • The DC grid can now choose to use only one energy source without the DC grid becoming less robust against disturbances within the grid. The energy source can now be utilized optimally.

[0143] The parallel connection, see Fig. 10D, is a compromise between a series and a meshed network. Only one output is used to connect the nodes in the network as they share a common cable to which all DC nodes are connected. The control strategy works in a similar way to the meshed connection as power can always flow from two energy sources. The control must limit the combined power taken from both outputs so as not to exceed the maximum power of each output.

[0144] Advantages of a parallel connection

[0145] - A parallel connected DC network can, in the same way as the meshed network, share power between multiple nodes without the connection reserving more than one output on each DC node. The connection becomes resource-efficient and allows one node to supply multiple nodes with power.

[0146] - The connection requires fewer cables compared to a series-connected DC network or a meshed network. Fewer cables simplify workplace logistics.

[0147] The design of the DC network needs to be adapted to the conditions in and around the workplace. The main aspects that affect the design of the DC network are where the workplace is located, how many machines are to be charged and the customer's needs. The concept has been identified as suitable for application to two different types of workplaces: house construction and civil engineering construction.

[0148] Fig. 13 and Fig. 14 show how a DC network can be established at a construction site and a civil engineering site, respectively. In both figures, each DC node 2 within the DC network is represented by a black square. The local AC network is symbolically represented by a lightning bolt with the respective connection 5 to the DC node 2.

[0149] The problem for construction companies when they are going to build a house is the access to the energy required to charge the electric vehicles. The energy for the vehicles can be obtained from three types of sources:

[0150] Energy carriers in the form of diesel generators, hydrogen or batteries that are replaced at regular intervals. The workplace's own connection to the local electricity grid.

[0151] Surrounding electrical connections to the local electricity grid in the form of properties, charging stations or electrical terminals.

[0152] Fig. 13 illustrates how the construction site's own connection to the local electricity grid “a” may be complemented by the connections found in the buildings around the construction site. The grid is connected in series and consists of four DC nodes, of which DC node “b” is connected to an AC / DC converter module 5' in accordance with Fig. 6, DC node “c” is connected to an AC / DC converter module 5' in accordance with Fig. 7 and DC node “d” may, for example, include an external energy source in the form of a hydrogen storage. Another alternative is to exploit the opportunity that comes with V2G technology where electric cars are converted into a mobile energy storage. The batteries of the electric cars can be used to cover parts of the power needs of the work vehicles. This is a technology that is not yet mature, but may be an important piece of the puzzle in the future.

[0153] Fig. 14 illustrates how the DC node may be used to establish a DC network at a civil engineering site. What is common for this type of sites is that they are spread out over a larger geographical area. This means that the DC network must be able to work more scattered. In this example, the network is supplied with energy through two connections to the electricity grid and a hydrogen storage. The connections may be in the form of electrical terminals or properties spread out along the site.

[0154] The DC network of Fig. 14 is divided into two parts that operate independently of each other. Each DC node within the network comprises one or more chargers that are connected to the DC node and are placed in the vicinity of the machines it charges. Since the module does not contain an energy storage, its weight is significantly reduced as it only needs to contain the system that handles the charging of the vehicle; the charger then becomes mobile and the logistics of the charging infrastructure are made more efficient.

[0155] The construction industry is an industry that involves many risks. Large vehicles, dangerous operations and hot work pose a risk when batteries and hydrogen storages are to be placed on construction sites. The probability of a system being hit is higher if the system is located close to the machines. Batteries can be damaged and start to burn in the event of a collision. Therefore, from a work safety perspective, it is better to separate batteries and chargers. The hydrogen storage can be kept separate from the rest of the system and placed in a secured location using the same way of thinking. Since the DC network operates with a relatively high 11 operating voltage, the cables are reduced in size, which makes the longer electrical cables more manageable.

[0156] Fig. 11 illustrates the information flow between two parallel stand-alone microgrids that are interconnected to the same connection point to the local grid. Each DC node is responsible for the energy planning and control of the system units. The nodes coordinate their power consumption from the connection in order not to overload the connection point to the local grid from which the DC grid obtains its energy.

[0157] The difference between how the system is controlled in stand-alone operation and interconnected operation lies primarily in which node takes the leader role and which nodes assume a follower role. Leader means the node that takes overall responsibility for the operation planning of the DC grid, or a certain part of the DC grid. In simple terms, it is about when each battery module should deliver power and when the module should charge or when and how the AC / DC converter should draw power from the grid. Finally, the leader must predict when each charging station will consume its power, how much power is needed and what energy needs to be stored by the batteries of the DC grid to meet the power demand.

[0158] Fig. 12 illustrates how the system works in a meshed connection and how it reacts in the event of a node failure. In Fig. 12A, node 3 acts as the leader in the DC network and sends orders to the followers: nodes 1 and 2 how and when to activate their resources. In the example, the leader orders that the power stored in node 1's batteries shall be transferred to node 3 in preparation for an upcoming movement of node 3. In Fig. 12B, the system has been reconfigured after removal of node 3. Node 1 now acts as the leader for node 2 and the system is now connected in a series connection.

[0159] Fig. 3 illustrates the flow chart of how each DC node's controllers (EMS and PLC) work within the DC network. Tasks that are reserved for the leader node have been placed within the dashed rectangle. The remaining tasks are executed by all nodes within the network. The system needs to quickly detect and isolate the faults that occur within the DC network. Each DC node has a separate fault management that works independently of the algorithms that manage the planning of the system's operation. The DC node can then quickly detect that a fault has occurred and isolate the fault. The algorithms that manage the planning of the system's operation must then handle the new conditions that prevail in the system by replanning the system's operation. By utilizing the power pool of other properties, there is a great opportunity to reduce the need of one's own energy storages or fuel cells. A continuous communication between the construction site's internal DC network and the external connection enables the system to plan its power draw according to the typical power consumption of the external building. The system must also adapt its power consumption in real time so as not to affect the property owner's opportunities to draw power from his or her own grid connection. Power can then be shared from the system to the external building when the site is on standby, thus optimizing the electricity use between the properties. There are many possibilities for local DC networks.

[0160] There are three preliminary energy sources that can charge the energy storages: the construction site's own connection to the electricity grid, external energy sources such as hydrogen and diesel generators, and the electricity grid connection of other buildings. The first two sources are handled internally within the grid, but the latter requires the system to coordinate power consumption with the site's power consumption. Fig. 15 illustrates a load curve for, for example, a residential building. The lighter gray scale denotes the energy that can be obtained from the connection. The figure also shows how the stored energy in the system's energy storage may be used to minimize the host house's peak load and reduce the house's power fee. A synergy is created between the DC grid and the building to which the grid is connected.

[0161] The so-called “Vehicle 2 Grid” (V2G) technology is expected to become a central part of the regulation of the electricity grid once it becomes widespread. The technology means that each electric vehicle is transformed into a mobile power reserve that may be used to alleviate the effect of high and short-term loads on the electricity grid. The same concept can be used by connecting vehicle chargers directly to the DC node, thus reducing the need for the construction company to buy / rent its own energy storage. Instead, the power that is stored in the battery-powered vehicles is utilized. The technology enables a cheaper system and allows vehicle owners to capitalize on the power reserve that is stored in their vehicles.

[0162] Typically, an electric car charger is 11 to 22 kW. To cover the power of a 150 kW vehicle charger, approximately 7 to 14 vehicles are needed. The same figure to cover the power requirement for a 300 kW charger is 14 to 28 vehicles. The technology should be seen as a complement and not a replacement for the energy storage installed at the workplace.

[0163] The reason for using DC instead of AC is two-fold: fuel cells, batteries, and fast chargers will all operate on DC. If AC is used to move power between systems, more intermediate steps are needed during the charging in the form of all modules requiring an AC / DC converter, which means a more complicated system. It will also almost certainly mean higher losses and a higher system cost.

[0164] In general, it is easier to regulate DC networks. The DC network needs a control that maintains the voltage on the network and a capacitor bank that filters the current that goes into the network. The network can then be expanded more easily by connecting a larger capacitor bank to the network in the form of a new module. In this way, the DC network becomes easily scalable.

Claims

CLAIMS1. Direct current network (1 ) of modular construction, comprising a number of direct current distributors (2) detachably connected by cables, each arranged to electrically supply one or more direct current consumers connectable to the direct current distributor (2), such as chargers (3) and batteries (4), from an external alternating current source (5) or from an external direct current source such as batteries (4) and hydrogen fuel cells (6), whereby the direct current distributors (2) are portable and characterised by comprising identically equipped high-voltage circuits (7) whose outputs (8) to connectable units are electrically and mechanically equivalent, whereby the direct current distributors (2) are interchangeable with each other and can be connected to each other for expansion of the direct current network (1) by adding direct current distributors (2).

2. A direct current network according to claim 1 , wherein the high-voltage circuit (7) in the direct current distributor (2) has a number of outputs (8) for connecting external units, each output comprising a charging circuit (9), a switch (10), a current sensor (11 ), a high-voltage detector (12) and a high-voltage connector (13).

3. A direct current network according to claim 2, wherein the high-voltage circuit (7) in the direct current distributor (2) comprises a capacitor bank (14) associated with one or more discharge resistors (15).

4. A direct current network according to any one of the preceding claims, wherein each output (8) from the high-voltage circuit (7) in the direct current distributor (2) is assigned to an earth fault sensor (16).

5. A direct current network according to any one of the preceding claims, wherein the direct current distributor (2) comprises a low-voltage circuit (17) with a low-voltage battery (18) which is charged by the high-voltage circuit (7) via a DC / DC converter.

6. Direct current network according to claim 5, wherein the direct current distributor (2) comprises systems (20; 21) supplied by the low-voltage circuit (17) for communication and control.

7. Direct current network according to claim 6, wherein control of the direct current distributor (2) is divided into power distribution system (20) and component monitoring system (21).

8. The DC network according to claim 7, wherein the power distribution system (20) provides communication between the DC distributor (2) and the units (22; 3, 4, 5', 6) connected to it, between the DC distributor (2) and a cloud (23), between the DC distributor (2) and other DC distributors (2, 24) included in the DC network (1 ) and between the DC distributor (2) and the operator via a user interface (25).

9. Direct current network according to claim 7 or 8, wherein the component monitoring system (21) monitors the functionality of switches (10), over-voltage protector (26) and sensors (11 , 16, 27) included in the high-voltage circuit (7) of the direct current distributor.

10. A direct current network according to any one of the preceding claims, wherein the high-voltage circuit (7) and outputs (8) of the direct current distributor (2) are encapsulated in a box module (100) which can be rolled or carried.

11. A direct current network according to any one of the preceding claims, wherein direct current distributors (2) are interconnected in a serial (b), meshed (c) or parallel (d) configuration.

12. Direct current network according to any one of the preceding claims, wherein at least one direct current distributor (2) is connected to at least two external alternating current sources (5) via AC / DC converter module (5') with mutually isolated connection points for each external alternating current source (5) and with a common connection to the direct current distributor (2).

13. Direct current distributor (2) designed for establishing a temporary direct current network (1) by connection to an alternating current source (5) via an AC / DC converter, wherein the direct current distributor (2) comprises a high-voltage circuit (7) and a low-voltage circuit (17) arranged in a portable enclosure (100), wherein the high- voltage circuit (7) has a number of outputs (8) for connecting external units such as an AC / DC converter module (5'), vehicle charger (3), batteries (4) and other direct current sources (6), wherein each output (8) is equipped with a charging circuit (9), a switch (10), a current sensor (11), a high-voltage detector (12) and a high-voltage connector (13).

14. Method for establishing a local direct current network (1 ) comprising:- providing a number of identically equipped, portable high-voltage circuits (7) for direct current, each arranged to electrically supply one or more direct current consumers connectable to a direct current distributor (2) from an external alternating current source (5) or from an external direct current source (4, 6),- interconnection via a cable of two or more direct current distributors (2),- connecting external direct current consumers (3, 4) to the direct current distributors (2), and- connecting at least one direct current distributor (2) to at least one external alternating current source (5) via an AC / DC converter (5').

15. Method according to claim 14, comprising interconnecting direct current distributors (2) in serial (b), meshed (c) or parallel (d) configuration.

16. Method according to claim 15, according to which at least one direct current distributor (2) is connected to at least two external alternating current sources (5) via an AC / DC converter module with mutually isolated connection points for each external alternating current source (5) and with a common connection to the direct current distributor (2).

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