EP3925047A1

EP3925047A1 - Electric grid and method for operating an electric grid

Info

Publication number: EP3925047A1
Application number: EP19778837.5A
Authority: EP
Inventors: Yi Zhu; Shivansh BATRA; Thomas Beckert; feng DU; Michael Hein
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; EP3925048A1; EP3925045A1; US20220200274A1; WO2020200492A1; EP3928405A1; WO2020200493A1; WO2020200494A1; CN114128072A; US20220166214A1; CN114207975A; CN114207976A; EP3925046A1; US20220200275A1; US20220172914A1; CN113892219A

Abstract

The invention relates to an electric grid (1000), comprising feed-ins (1010... 1013), loads (1050... 1055), and a distribution grid (2000) which is arranged therebetween and comprises at least one busbar (200) and at least one device (2010... 2016) for opening or closing a DC circuit, said device 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 opens the DC circuit by means of the trigger unit if a fault current is detected by the fault current detector, and the precharging device restores the voltage on the busbar prior to closing the electric switch. Each of the feed-ins can be individually electrically separated by means of one of the devices for opening or closing a DC circuit.

Description

description

Electrical network and method of operating an electrical network

The invention relates to an electrical network and a method for operating an electrical network.

Direct current distribution networks offer advantages over alternating current distribution networks, especially when feeding in renewable energy sources in parallel to other network feeds, through lower costs and higher energy efficiency. When using renewable energy sources, for example through a photovoltaic module, a direct current / alternating current / direct current converter can be replaced by a simple direct current / direct current converter. Batteries as energy storage devices can be connected more easily and capacitor banks directly to the system without additional converters.

Regulated and unregulated rectifiers can be used for connecting and feeding in from an AC network (alternating current). Active Front End (AFE) technology is preferred for feeding energy from AC sources or for recirculating energy when braking energy is recovered from motors: while with Active Front End (AFE) devices, the AC side of the network is stabilized and thus the network as a whole factory quality is compensated with a reactive energy supply, the braking energy from the motors can be fed to the distribution system.

However, direct current networks also have challenges in terms of protection against short circuits or other sources of error. In an exemplary direct current network corresponding to the illustration in Figure 1 with feeds 1010;

1011; 1012; 1013 and consumers 1050; 1051; 1052; 1053;

1054 and a distribution network 2000 in between classic electro-mechanical protective devices (e.g. molded case circuit breakers, MCCB), these lose their selectivity due to the fast self-protection functions of the power electronics in the AC / DC converters. In the illustration of Figure 1, for example, the feeds 1010; 1011 AC power source via Active Front Ends (AFE) 1020; 1021 fed into the system.

Freewheeling diodes can not be sufficiently protected by the self-protection of the transducers and fuses on the AC side, as severe damage may orkommen by electric current due to a possible voltage reversal at LRC oscillations in the fault path _V. This is particularly noticeable when the Active Front End (AFE) is not connected to the power rail in a short-circuit-proof manner. Likewise, after the IGBTs have been switched off, the diodes can act as uncontrolled rectifiers. The fault current is supplied from the alternating current side and may not be able to be switched off quickly enough by the fuses and thus destroy the diodes.

The discharge of a capacitor bank or of direct current intermediate circuits (DC links) during a serious fault scenario generates extremely high current peaks which flow within periods of ms (milliseconds). Classic electro-mechanical switches are not fast enough to switch off such a fault current. The weakest infeed or consumer path, with the lowest nominal current, in such a system with several infeeds then has the highest ratio of maximum short-circuit current to nominal current.

The main problems of a DC distribution system are the possible destruction of free-wheeling diodes due to a voltage reversal, capacitive discharge and the selectivity of the protective devices for the active front ends (AFE). In addition, there are capacitors in each converter

(AC-DC or DC-DC) or inverter (DC-AC) on the DC side, this for feeders and consumers.

In Figure 2 possible positions of errors 1500; 1501; 1502; 1503; 1504; 1505; 1506; 1507; 1508 shown in a distribution network. Even a fault on the consumer side of a motor without feedback can be fed from both directions: Current can flow from the feeders and from other branches of the consumer and through the discharge of DC links (direct current intermediate circuit capacitors), which are typically used in direct current to alternating current inverters. Therefore, when planning a network, it must be taken into account that power converters such as Active Front Ends (AFE) are connected to a DC busbar 200 in a short-circuit-proof manner. Otherwise, two protective devices are necessary, as shown in FIG. 3B.

The main problem with electrical direct current networks is the increased number and capacity of the capacitors in the system. With low fault resistances, this means that these capacitors discharge within 2 to 3 ms (milliseconds), together with extremely high current peaks. Due to a voltage reversal, a high current is generated through the freewheeling diodes within the same period of time. In order to prevent damage to the cables and the free-wheeling diodes, the fault current must be interrupted very quickly. This is also necessary if selectivity to the power converters is to be created. Due to the nature of the electro-mechanical switches, their switching time to open is at least several ms (milliseconds). The discharge of the capacitors and the associated voltage drop on the distribution 2000 has already taken place. Therefore, a Solution based only on electro-mechanical switches does not lead to protection of such a direct current network.

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

The object is achieved by the electrical network according to claim 1. Advantageous embodiments are given in claims 2 to 12 under. The object according to the invention is also achieved by a method for operating an electrical network according to claim 13. An advantageous embodiment is specified in dependent claim 14.

The electrical network according to claim 1 is equipped with feeders, consumers and a distribution network arranged therebetween with at least one busbar as well as 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 trip unit,

- a pre-loader, and

- a control unit for automatic closing of the

electrical switch after pre-charging,

wherein upon detection of a fault current through the fault current detection of the electrical switch by means of the Auslöseein unit opens the DC circuit and the pre-charging device restores the voltage on the busbar before closing the electrical switch, the feeds each by means of one of the devices for opening or

Closing a direct current circuit can be separated electrically individually.

The advantage here is that a reduced number of semiconductor switches can be used in the network, so that Costs are minimized as well as power losses, since these are only used for feeds, energy storage and large motor loads with power feedback. In the event of a fault, the fault current can be interrupted very quickly by means of the circuit breaker within a few, typically 10 ps (microseconds), and the fault can then be isolated at a relatively slow speed. This allows electro-mechanical electrical switches to be used in the rest of the system. Since, in the event of a fault, all feeds are immediately disconnected from the grid, the responsible electro-mechanical electrical switches only have to interrupt a significantly reduced fault current, and in certain applications they can even switch off. This enables the electro-mechanical switches to be dimensioned much smaller compared to electro-mechanical switches in conventional networks.

In one embodiment, individual loads can each be electrically isolated individually by means of one of the devices for opening or closing a direct current circuit, and the distribution network arranged between them includes electro-mechanical switches for isolating faults.

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

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

In a further refinement, the at least one device further comprises a control unit for limiting a switch-on transient. This control unit can keep the high transient current at power-up below the shutdown thresholds of the device.

In a further embodiment, the pre-charging device restores the voltage on the busbar after a first wait. Alternatively, the pre-charger restores voltage to the bus bar upon receiving a command. The pre-charging device can receive the command via the communication unit.

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 automatically

Close the electrical switch this after restoring a voltage on the busbar above a threshold value.

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

In a further embodiment, the devices for opening or closing a DC circuit are arranged on power converters with high capacity, capacitor banks as energy storage, photovoltaic systems, batteries or consumers with feedback depending on the size of the DC link (DC link) and on the rest Positions the electro-mechanical switches.

The method for operating an electrical network according to claim 13 comprises the steps

- In the event of a fault, quick opening within ps (microseconds) of all devices (close to the feeds) for opening or closing a DC circuit to disconnect all feeds (including all energy sources and all regenerative systems);

- After opening the devices, only electro-mechanical switches close to the fault are opened within ms (milliseconds) to isolate the fault; and then

- automatic closing of the opening devices

or closing a DC circuit. In a further embodiment, the method according to the invention comprises the further step:

- if an error is still detected after the devices for opening or closing a DC circuit have been automatically closed, final opening of the devices for opening or closing a DC circuit at the feeders.

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

Show:

Figure 1: electrical network with feeds, consumers and distribution network;

Figure 2: electrical network with feeds and ver

users and possible mistakes;

Figures 3A and 3B: electrical network with feeds and

Consumers in the distribution network and protective equipment;

Figure 4: inventive electrical network with a

feeds, consumers and distribution network; and

Figure 5: Device for opening or closing a direct current circuit.

In Figure 1, an exemplary direct current network is Darge presents with the current flows under nominal conditions. A feed 1010; 1011; 1012; 1013 are over a distribution network 2000 with a busbar 200 with loads 1050; 1051; 1052; 1053; 1054 connected. Feeds 1010; 1011 can be, for example, AC power sources that have an Active Front End (AFE) 1020; 1021 are connected to the distribution network 2000. Here, the currents can flow bidirectionally into or out of the distribution network 2000. A feed 1012 can be a photovoltaic system, for example, feed 1013 a different type with power converters. With these feeds 1012; 1013, only a unidirectional current flow in the direction of the distribution network 2000 is possible.

The same applies to the consumers, some consumers enable a unidirectional and others a bidirectional current flow to the network 2000. For example, consumer 1050 can be an ohmic load that only allows a unidirectional current flow in its direction. The same applies to motors without power feedback, for example consumer 1052. The consumer 1051; 1053; 1054 can be, for example, motors with power feedback, a capacitor bank as an energy store or a battery, with these consumers allowing a bidirectional flow of current to and from the distribution network.

In Figure 2, the electrical network of Figure 1 is Darge presents with feeds 1010; 1011; 1012; 1013, consumers 1050; 1051; 1052; 1053; 1054 and a distribution network 2000 arranged between them, the possible error locations of errors 1500; 1501; 1502; 1503; 1504; 1505; 1506; 1507; 1508 are drawn. For example, a fault can occur between consumer 1050 and busbar 200 at the fault location of fault 1504.

In Figures 3A and 3B, the electrical network of Figures 1 and 2 is again shown, the distribution network 200 protection devices 2050; 2051; 2052; 2053; 2054; 2055; 2056; 2057; 2058; 2059; 2060; 2061; 2062; 2063; 2064; 2065; 2066 include. Depending on which error 1500; 1501; 1502; 1503; 1504; 1505; 1506; 1507; 1508 are to be intercepted accordingly, the protective devices can be arranged in the distribution network 2000.

FIG. 4 shows the electrical network 1000 according to the invention with feeds 1010; 1011; 1012; 1013, consumers 1050; 1051; 1052; 1053; 1054; 1055 and a distribution network 2000 arranged therebetween with at least one busbar 200 and with at least one device 2010; 2011; 2012; 2013; 2014; 2015; 2016 to open or close a

DC circuit.

The feeds 1010; 1011; 1012; 1013 can each with means of one of the devices 2010; 2011; 2012; 2013 for opening or closing a DC circuit individually

be separated electrically. The device 2010; 2011; 2012; 2013 for opening or closing a DC circuit are each arranged between the feed and the busbar 200.

Furthermore, individual consumers 1052; 1054;

1055 by means of one of the devices 2014; 2015; 2016 can be individually electrically disconnected or disconnected from the busbar 200 for opening or closing a DC circuit. The distribution network 2000 arranged in between also includes conventional electro-mechanical switches 2020 for isolating faults; 2021; 2022; 2023; 2024; 2025; 2026; 2027; 2028; 2029; 2030. Individual outgoing feeders with consumers 1053, which contain intermediate circuit capacitances but cannot be fed back, can be protected on busbar 200 with an electro-mechanical switch and close to the consumer with a diode.

The devices for opening or closing a direct current circuit are dependent on power converters with high capacity, capacitor banks as energy storage, photovoltaic systems, batteries or consumers with feedback of the size of the DC link (DC link) is arranged.

The electrical network 1000 according to the invention can be operated using the following method:

- in the event of an error, quick opening within ps (microseconds) of all devices 2010; 2011; 2012; 2013; 2014; 2015; 2016 for opening or closing a direct current circuit to disconnect all feeds 1010; 1011; 1012; 1013;

- after opening the devices 2010; 2011; 2012;

2013; 2014; 2015; 2016 Open only electro-mechanical switches close to the fault location (one or more of 2020; 2021; 2022; 2023; 2024; 2025; 2026; 2027; 2028; 2029;

2030) within ms (milliseconds) to isolate the fault; and then

- automatic closing of devices 2010; 2011;

2012; 2013; 2014; 2015; 2016 for opening or closing a DC circuit.

The method according to the invention can furthermore comprise the step:

- if after the automatic closing of the devices

2010; 2011; 2012; 2013; 2014; 2015; 2016 to open or

Closing a DC circuit continues to detect a fault, finally opening the devices 2010; 2011; 2012; 2013; 2014; 2015; 2016 to open or

Closing a DC circuit.

In the event of an error, the following happens:

The Devices 2010; 2011; 2012; 2013; 2014; 2015; 2016 to open or close a direct current circuit and the electro-mechanical switch in the vicinity of the fault detect the fault at the same time. All fixtures 2010;

2011; 2012; 2013; 2014; 2015; 2016 to open or close a DC circuit switch off immediately to a to prevent further feeding of the fault by the infeeds. In the meantime, the nearest electro-mechanical switch turns off to isolate the fault. For this purpose, an electro-mechanical switch with fast switching properties in the range of a few ms (milliseconds) is preferred. The Active Front Ends (AFE) are still in operation. The devices for opening or closing a direct current at the infeeds wait a fixed time or until they receive a command to close again. The voltage on busbar 200 is recharged through devices 2010; 2011; 2012; 2013; 2014; 2015; 2016 for opening or closing a DC circuit. The devices for opening or closing the feeds are closed and, if necessary, a switch-on transient is run through. The devices for opening or closing a direct current circuit on the loads and on the photovoltaics, battery or capacitor bank will close as soon as the voltage on the busbar 200 is restored. If the devices for opening or closing a direct current on the feeders still detect a fault, they are switched off again and remain off.

In Figure 5, the inventive device 2010; 2011; 2012; 2013; 2014; 2015; 2016 shown for opening or closing a DC circuit with at least one busbar 200. The device 2010; 2011; 2012; 2013; 2014; 2015; 2016 includes an electrical switch 110 for opening or closing the DC circuit, a fault current detection 120, a triggering unit gate driver 130 and a pre-charging device 140, with the electrical switch 110 using the tripping unit 130 when a fault current is detected by the fault current detection 120 the DC circuit opens and the pre-charging device 140 restores the voltage on the busbar 200 before the electrical switch 110 is closed. The device according to the invention is also used for automatic closing 2010; 2011; 2012; 2013; 2014; 2015; 2016 a control unit 150 is provided which can automatically close the electrical switch 110 after the pre-charge.

The electrical switch 110 of the inventive device 2010 Vorrich; 2011; 2012; 2013; 2014; 2015; 2016 can be a semiconductor switch, for example. For example, it can be a semiconductor switch based on silicon (Si), based on silicon carbide (SiC) or based on gallium nitride (GaN).

As shown in Figure 5, the inventive device before 2010; 2011; 2012; 2013; 2014; 2015; 2016 further comprise a unit 180 for communication. This unit 180 for communication can receive commands from a superordinate control unit and / or devices 2010 arranged in a distribution network 2000; 2011; 2012; 2013; 2014; 2015; Coordinate 2016.

Furthermore, the device according to the invention 2010;

2011; 2012; 2013; 2014; 2015; 2016 include a control unit 160 for limiting the switch-on transient. For example, the controller 160 can control the high transient current at power-on below the power-off thresholds from the device 2010; 2011; 2012; 2013; 2014; 2015; 2016 hold.

The inventive device 2010; 2011; 2012; 2013;

2014; 2015; 2016 can furthermore comprise a measuring unit 170 for measuring current and / or voltage values.

The pre-charger 140 can restore the voltage on the busbar 200 after a first waiting period. Alternatively, the pre-charger 140 restores voltage to the busbar 200 upon 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 automatically close it after a second waiting time. Likewise, the control unit 150 can automatically close the electrical switch

110 close this after restoration of a voltage on the busbar 200 above a threshold value. To this end, the control unit 150 can receive the voltage values on the busbar 200 from the measuring unit 170 in order to automatically close an electrical switch 110.

Claims

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

1011; 1012; 1013), consumers (1050; 1051; 1052; 1053; 1054; 1055) and an intermediate distribution network (2000) with at least one busbar (200) and with at least one device (2010; 2011; 2012; 2013; 2014; 2015 ; 2016) for opening or closing a direct current circuit, the device comprising (2010; 2011; 2012; 2013; 2014; 2015; 2016)

- 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 the automatic

Closing the electrical switch (110) after the pre-charge,

wherein when a fault current is detected by the fault current detection (120), the electrical switch (110) opens the DC circuit by means of the tripping unit (130) and the pre-charging device (140) before the electrical switch (110) closes the voltage on the busbar ( 200) restores,

d u r c h e k e n n n n e n t, that the feeds (1010; 1011; 1012; 1013) can each be electrically isolated by means of one of the devices (2010; 2011; 2012; 2013) for opening or closing a direct current circuit.

2. Electrical network (1000) according to claim 1, wherein an individual consumer (1052; 1054; 1055) can be individually electrically isolated by means of one of the devices (2014; 2015; 2016) for opening or closing a direct current circuit, as well as the one in between arranged distribution network (2000) electro-mechanical switches

(2020; 2021; 2022; 2023; 2024; 2025; 2026; 2027; 2028; 2029; 2030) includes to isolate faults.

3. Electrical network (1000) according to claim 1 or 2, where the electrical switch (110) of the at least one device (2010; 2011; 2012; 2013; 2014; 2015; 2016) is a semiconductor switch.

4. Electrical network (1000) according to claim 1, 2 or 3, wherein the at least one device (2010; 2011; 2012; 2013; 2014; 2015; 2016) further comprises a unit (180) for communication.

5. Electrical network (1000) according to one of the preceding claims, wherein the at least one device (2010; 2011; 2012; 2013; 2014; 2015; 2016) further comprises a control unit (160) for limiting a switch-on transient.

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

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

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

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 9, wherein the control unit (150) for automatic closing of the electrical switch (110) closes this after restoration of a voltage on the Sam melschiene (200) above a threshold value.

11. Electrical network (1000) according to one of the preceding claims, wherein the electrical network (1000) is a direct current circuit.

12. Electrical network (1000) according to one of the preceding claims, wherein the devices (2010; 2011; 2012; 2013; 2014; 2015; 2016) for opening or closing a DC circuit on power converters with high capaci ity, capacitor banks as energy storage systems, photovoltaic systems , Batteries or consumers with feedback are arranged depending on the size of the direct current intermediate circuit (DC link) and the electromechanical switches (2020; 2021; 2022; 2023; 2024; 2025; 2026; 2027; 2028) in the remaining positions ; 2029; 2030).

13. Method of operating an electrical network

(1000) according to one of the preceding claims,

- in the event of an error, quick opening within ps

(Micro seconds) of all devices (2010; 2011; 2012; 2013; 2014; 2015; 2016) for opening or closing a

DC circuit for disconnecting all feeds (1010; 1011; 1012; 1013);

- after opening the devices (2010; 2011;

2012; 2013; 2014; 2015; 2016) Only open electro-mechanical switches close to the fault location (one or more of 2020; 2021; 2022; 2023; 2024; 2025; 2026; 2027; 2028;

2029; 2030) within ms (milliseconds) to isolate the fault; and then

- automatic closing of the devices (2010;

2011; 2012; 2013; 2014; 2015; 2016) to open or Closing a DC circuit.

14. Method of operating an electrical network

(1000) according to claim 13 with the further step:

- If after the automatic closing of the devices (2010; 2011; 2012; 2013; 2014; 2015; 2016) for opening or closing a direct current circuit an error is still detected at the infeeds (1010; 1011; 1012; 1013), final opening the devices (2010; 2011; 2012; 2013; 2014; 2015; 2016) to open or

Closing a DC circuit.