EP3925048A1

EP3925048A1 - Electric grid

Info

Publication number: EP3925048A1
Application number: EP19778838.3A
Authority: EP
Inventors: Yi Zhu
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2019-03-29
Filing date: 2019-09-13
Publication date: 2021-12-22
Also published as: WO2020200495A1; US20220020544A1; CN114175436A; WO2020200496A1; EP3925045A1; US20220200274A1; WO2020200492A1; EP3928405A1; WO2020200493A1; WO2020200494A1; CN114128072A; US20220166214A1; EP3925047A1; CN114207975A; CN114207976A; EP3925046A1; US20220200275A1; US20220172914A1; CN113892219A

Abstract

The invention relates to an electric grid (1000), comprising feed-ins (1010; 1011; 1012; 1013; 1014; 1015), loads (1050; 1051; 1052; 1053; 1054; 1055; 1056; 1057), and a distribution grid (2000) which is arranged therebetween and comprises at least one busbar (200; 200'; 200") and at least one device (2010; 2011) for opening or closing a DC circuit, said device (2010; 2011) comprising: - an electric switch (110) for opening or closing the DC circuit, - a fault current detector (120), - a trigger unit (130), - a precharging device (140), and - a control unit (150) for automatically closing the electric switch after the precharging process, wherein the electric switch (110) opens the DC circuit by means of the trigger unit (130) if a fault current is detected by the fault current detector (120), and the precharging device (140) restores the voltage on the busbar (200; 200'; 200") prior to closing the electric switch (110). Multiple loads (1050; 1051; 1052, 1053; 1054; 1055) can be individually electrically separated by means of a respective electromechanical switch (2020; 2021; 2022, 2023; 2024; 2025), and multiple loads (1050; 1051; 1052, 1053; 1054; 1055) can be electrically separated as a group by means of the at least one device (2010; 2011).

Description

description

Electrical network

The invention relates to an electrical network.

Direct current distribution networks offer advantages over alternating current distribution networks, especially when renewable energy sources are available in parallel to other feeds. On the one hand, direct current distribution networks can be built more cost-effectively and have a higher energy efficiency. When generating renewable energy, for example through photovoltaics, direct current to alternating current and alternating current to direct current converters can be replaced by simple direct current to direct current converters. When feeding in from batteries or capacitor banks as energy buffers, these can be coupled directly to the system without an additional converter.

When using Active Front End (AFE) converters, energy can be transferred back into the power grid, for example with renewable energy sources or with the braking energy of motors. Active Front End (AFE) converters can therefore stabilize the network and also increase the quality of AC networks through reactive power compensation.

DC distribution networks also bring problems with regard to electrical protection. In the event of a fault, charges from capacitor banks or direct current intermediate circuit capacitors (DC links) can generate extremely high current peaks, within a very short time of a few hundred ps (microseconds) to a few ms (milliseconds).

FIG. 1 shows a typical direct current distribution network 100 with feeds 1010; 1011; 1012; 1013; 1014; 1015 and consumers 1050; 1051; 1051; 1053. Between the Feeds 1010; 1011; 1012; 1013; 1014; 1015 and consumers 1050; 1051; 1051; 1053 a distribution network 2000 is arranged. This comprises a busbar 200 with which the feeds 1010; 1011; 1012; 1013; 1014; 1015 and consumer 1050; 1051; 1051; 1053 are electrically connected. For example, the feeds 1010; 1011 AC sources that are generated via Active Front End (AFE) converters 1020; 1021 are connected to the distribution network 2000. The direct current distribution network 100 can include, for example, further feeds such as feed 1012 from a photovoltaic module, feed 1013 as a battery, feed 1014 as a capacitor bank for energy storage or feed 1015 as a further type of feed with power converters.

In the distribution network 2000 there are protective devices 2050; 2051; 2052; 2053; 2054; 2055; 2056; 2057; 2058; 2059; 2060; 2061 arranged, which in the event of a fault feeds 1010; 1011; 1012; 1013; 1014; 1015 or consumer 1050; 1051; 1051; 1053 can electrically separate from the busbar 200.

In such a multiple feed system 1010; 1011;

1012; 1013; 1014; 1015, the branch with the smallest consumer is problematic. In order to achieve the selectivity of the various protective devices and the fast self-protection functions of the power electronics in the converters, the design of the direct current network is very challenging.

A classic mechanical electrical switch (Molded Case Circuit Breaker, MCCB) is not fast enough to interrupt the discharge of the capacitors in the event of a fault; they only become active after the maximum discharge. The consequence of this is that cables will be destroyed, that the IGBTs in the Active Front Ends (AFE) will be switched off by the self-protection functions, that the Active Front Ends (AFE) will function as uncontrolled rectifiers. Free-running diodes can blow if the AC side fuses are not fast enough. Furthermore is The problem is that the voltage on busbar 200 drops and all capacitors are discharged. A long recharge time delays the restart of the entire system after an error has been corrected.

When solid-state circuit breakers (SSCB) are used as protective devices, the problem is that they have high power losses and the high costs for them speak against the use of these protective devices alone.

It is therefore the object of the invention to provide an alternative electrical network available which overcomes the disadvantages be described.

This object is achieved according to the invention by the electrical network according to claim 1. Advantageous Ausgestaltun conditions of the electrical network according to the invention are specified in the subclaims.

The electrical network according to claim 1 has feeds, loads and a distribution network arranged between them with at least one busbar and with at least one device for opening or closing a direct current circuit, the device comprising:

- an electrical switch to open or close the DC circuit,

- a fault current detection,

- a trigger unit,

- a pre-loader, and

- a control unit for automatic closing of the

electrical switch after pre-charging,

wherein when a fault current is detected by the fault current detection, the electrical switch opens the DC circuit by means of the tripping unit and the pre-charging device restores the voltage on the busbar before the electrical switch is closed, with several consumers can be separated electrically individually by means of an electromechanical switch and several consumers as a group by means of the at least one device

can be separated electrically.

It is advantageous in the electrical network according to the invention that the number of electrical switches, for example solid-state switches, can be reduced and thus costs and power losses can be reduced as well. The fault current can be interrupted quickly within 10 ps (microseconds), whereby the fault itself can be isolated more slowly with conventional electromechanical switches. After the loads are disconnected from the infeeds very quickly in the event of a fault, the actual isolation of the fault takes place via the electromechanical switch with a reduced fault current or, in certain applications, even without current. As a result, the proposed electromechanical switches can be dimensioned much smaller in comparison to switches in conventional networks. Another advantage is that the voltage on the busbar 200 is maintained and the rest of the system, which is not affected by the fault, remains operational. Reloading the group is much faster than reloading the entire system.

In one embodiment, the electrical switch of the at least one device is a semiconductor switch.

In a further embodiment, the at least one device furthermore comprises a unit for communication.

The at least one device can furthermore comprise a control unit for a switch-on transient. This unit can suppress the switch-on transient.

In a further embodiment, the pre-charging device sets the voltage on the busbar according to a first Wait again. Alternatively, the pre-charger can restore voltage to the bus bar upon receiving a command. The pre-charging device can receive this command via the communication unit.

In one embodiment, the pre-charging device interrupts the pre-charging process if the voltage on the busbar does not rise, which indicates a fault that still exists.

In a further embodiment, the control unit automatically closes the electrical switch for automatic closing after a second waiting time. Alternatively, the control unit closes the electrical switch to automatically close it after restoration of a voltage on the busbar above a threshold value.

In a further embodiment, the electrical network is a direct current circuit.

The properties, features and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more clearly understandable in connection with the following description of the embodiments, which are explained in more detail in connection with the figures.

Show:

Figure 1: DC network with several feeds and

Consumers;

FIG. 2: electrical network according to the invention with several feeds and consumers; and

Figure 3: Device for opening or closing a direct current circuit. FIG. 2 shows an electrical network 1000 according to the invention. This network 1000 is provided with feeds 1010; 1011; 1012; 1013; 1014; 1015 and consumers 1050; 1051; 1052; 1053; 1054; 1055; 1056; 1057 and a distribution network 2000 arranged in between. The distribution network 2000 comprises busbars 200, 200 ', 200''to which the feeds 1010; 1011; 1012; 1013; 1014; 1015 and consumer 1050; 1051; 1052; 1053; 1054; 1055; 1056; 1057 are electrically connected.

The distribution network 2000 comprises on the one hand devices 2010; 2011 for opening or closing a DC circuit and further electromechanical switches 2020; 2021;

2022; 2023; 2024; 2025. Furthermore, there are 2000 protective devices in the distribution network 2050; 2051; 2052; 2053; 2054; 2055; 2056; 2057; 2058; 2059 included.

Multiple consumers 1050; 1051; 1052; 1053; 1054; 1055; 1056; 1057 of the electrical network 1000 according to the invention each form a group. For example, consumers 1050; 1051; 1052 a first group. A second group is made up of consumers 1053; 1054; 1055 formed.

Each of these consumers 1050; 1051; 1052, 1053; 1054; 1055 is with an electromechanical switch 2020; 2021; 2022, 2023; 2024; 2025 can be separated from the distribution network 2000 in the event of a fault. Load 1050 is assigned to electromechanical switch 2020, load 1051 to electromechanical switch 2021 and load 1052 to electromechanical switch 2022. Electromechanical switch 2020; 2021; 2022 are electrically connected to a first busbar 200 ′, which in turn is electrically connected to a device 2010 for opening or closing a direct current circuit with the busbar 200 of the distribution network 2000.

The same applies to the second group of consumers 1053; 1054; 1055. Consumer 1053 is via the electromechanical Switch 2023 connected to the second busbar 200 ″. Consumer 1054 by means of the electromechanical switch 2024 with the second busbar 200 ″ and consumer 1055 by means of the electromechanical switch 2025 also with the second busbar 200 ″. This second busbar 200 ″, in turn, is electrically connected to a device 2011 for opening or closing a direct current circuit with the busbar 200 of the distribution network 2000.

The functioning of the electrical network 1000 according to the invention is discussed on the basis of an exemplary fault in the connection between the consumer 1050 and the electromechanical switch 2020. This fault is detected by the device 2010 for opening or closing a direct current circuit and also by the electromechanical switch 2020. Due to the faster tripping behavior of the device 2010 for opening or closing a direct current circuit, the device 2010 is opened immediately and thus prevents a further flow of current in the direction of the fault from the other feeds.

In the meantime, the electromechanical switch 2020 will also trip to isolate the fault. A fast-switching electromechanical switch 2020 is preferred for this purpose, the switching time of which is in the range of several ms (milliseconds). The device 2010 for opening or closing a direct current circuit can now be switched on again either for a fixedly defined period of time or on the basis of a command which indicates that the fault has been eliminated.

The device 2010 for opening or closing a direct current circuit can recharge the first busbar 200 ′ by means of the pre-charging device 140 and then be switched on again. If the device 2010 for opening or closing a direct current circuit continues to detect a fault current, this device 2010 can again open and remain open. The advantage of this method is that the feeds and consumers in the remaining part of the electrical network 1000 that are not affected by the fault can continue to be operated and do not show any failure. The consumers in the group with the error have a brief failure, depending on the switch-off speed of the associated electromechanical switch and the time it takes to switch the device on again to open or close a DC circuit. The downtime should be limited to a few 10 ms (milliseconds). Uninterruptible power supplies (UPS) can be provided for very sensitive consumers whose power should not be interrupted. Other consumers should be able to survive these short downtimes, as these downtimes have already been standard.

In Figure 3, the device 2010; 2011 to open or close a DC circuit with at least one busbar 200; 200 '; 200 ''. The device 2010; 2011 includes an electrical switch 110 for opening or closing the DC circuit, a fault current detection 120, a tripping unit 130 and a pre-charging device 140, with the electrical switch 110 opening the DC circuit by means of the tripping unit 130 when a fault current is detected by the fault current detection 120 and wherein the pre-charging device 140 before closing the electrical switch 110, the voltage on the busbar 200; 200 '; 200 ''. For automatic closing, the device 2010; 2011 ei ne control unit 150 is provided, which can automatically close the electrical switch 110 after the precharge.

The electrical switch 110 of the device 2010; 2011 can be a solid-state switch or a semiconductor switch, for example. For example, it can be a Acting semiconductor switches based on silicon (Si), silicon carbide (SiC) or gallium nitride (GaN).

As shown in Figure 3, the device 2010; 2011 further comprise a unit 180 for communication. This unit 180 for communication can receive commands from a higher-level control unit and / or devices 2010 arranged in a subnetwork 2000; Coordinate 2011.

Furthermore, the device 2010; 2011 include a control unit 160 for a switch-on transient. For example, the control unit 160 can suppress the switch-on transient.

The device 2010; 2011 can furthermore comprise a measuring unit 170 for measuring current and / or voltage values.

The pre-charger 140 can reduce the voltage on the bus bar 200; 200 '; 200 '' after an initial waiting period. Alternatively, the pre-charger 140 provides the voltage on the bus bar 200; 200 '; 200 '' after receiving a command. The command can be given to the precharge device 140 via the unit 180 for communication.

The control unit 150 for automatically closing the

electrical switch 110 can close this automatically after a second waiting time. Likewise, the control unit 150 can automatically close the electrical switch 110 after restoration of a voltage on the busbar 200; 200 '; 200 '' above a threshold value. For this purpose, the control unit 150 for the automatic closing of an electrical switch 110 can from the measuring unit 170 the voltage values on the busbar 200; 200 '; 200 '' received. If the voltage on the busbar 200; 200 '; 200 '' does not increase this indicates that the error has not yet been eliminated.

In this case, the pre-charging process must be interrupted.

The different components of the device 100 according to the invention are supplied with electrical energy via the power supply 190. The power supply 190 can be formed externally or internally.

Claims

1. Electrical network (1000) with feeds (1010;

1011; 1012; 1013; 1014; 1015), consumers (1050; 1051; 1052; 1053; 1054; 1055; 1056; 1057) and a distribution network (2000) arranged in between with at least one busbar (200; 200 '; 200' ') and with at least one device ( 2010; 2011) for opening or closing a direct current circuit, the device comprising (2010; 2011)

- an electrical switch (110) for opening or closing the direct current circuit,

- a fault current detection (120),

- a release unit (130),

- a pre-loading device (140), and

- A control unit (150) for automatic

Closing the electrical switch after the pre-charge, with the detection of a fault current by the fault current detection (120) the electrical switch (110) by means of the trip unit (130) opens the DC circuit and the pre-charging device (140) before closing the electrical The switch (110) restores the voltage on the busbar (200; 200 '; 200' '),

d a d u r c h e k e n n n z e i c h n e t, d a s s several consumers (1050; 1051; 1052, 1053; 1054; 1055) each by means of an electromechanical switch

(2020; 2021; 2022, 2023; 2024; 2025) can be separated electrically and several consumers (1050; 1051; 1052, 1053; 1054; 1055) as a group by means of the at least one device (2010; 2011) can be.

2. Electrical network (1000) according to claim 1, wherein the electrical switch (110) of the at least one device (2010; 2011) is a semiconductor switch.

3. Electrical network (1000) according to claim 1 or 2, where the at least one device (2010; 2011) des Wei direct comprises a unit (180) for communication.

4. Electrical network (1000) according to one of the preceding claims, wherein the at least one device (2010; 2011) further comprises a control unit (160) for suppressing the switch-on transient.

5. Electrical network (1000) according to one of the preceding claims, wherein the pre-charging device (140) restores the voltage on the busbar (200; 200 '; 200' ') after a first waiting time.

6. Electrical network (1000) according to one of the preceding claims 1 to 5, wherein the pre-charging device (140) restores the voltage on the busbar (200; 200 '; 200 ") after receiving a command.

7. The electrical network (1000) according to claim 6, wherein the pre-charging device (140) receives the command via the unit (180) for communication.

8. Electrical network (1000) according to one of the preceding claims, wherein the pre-charging device (140) interrupts the pre-charging process when the voltage on the Sam melschiene (200; 200 '; 200' ') does not increase, which on egg indicates a still existing error.

9. Electrical network (1000) according to one of the preceding claims, wherein the control unit (150) for automatic closing of the electrical switch (110) closes this automatically after a second waiting time.

10. Electrical network (1000) according to one of the preceding claims 1 to 8, wherein the control unit (150) for automatic closing of the electrical switch (110) this closes after restoration of a voltage on the collecting rail (200; 200 ';200'') above a threshold value.

11. Electrical network (1000) according to one of the preceding

Claims, wherein the electrical network (1000) is a DC circuit.