Method for starting a system from a standby mode

Abstract

The invention relates to a method for starting a system (1) from a waiting state, having at least one battery inverter (10), at least one energy store (12), and at least one STATCOM (20), wherein the system (1) is connected, via a transformer (30) and a disconnecting switch (40), which is on the network side when viewed from the transformer (30), to a higher-level sub-network (100) with a higher nominal voltage than the nominal voltage (Unom) of the system (1), and the disconnecting switch (40) is open at the beginning of the method. The method has the steps of setting the system voltage (Usys) to a starting voltage (U1), which is less than half the nominal voltage of the system, by means of the at least one battery inverter; closing the disconnecting switch (40) so that the system (1) is connected to the higher-level sub-network (100); increasing the system voltage (Usys) in the system to the nominal voltage (Unom) by means of the at least one battery inverter (10); and stabilizing network parameters of the system (1) and the higher-level network (100) by means of the at least one STATCOM (20). The invention also relates to a system for stabilizing a power network which is designed to carry out the method.

Description

[0001] 24-101-P-WO-1-submitted version

[0002] METHOD FOR STARTING A SYSTEM FROM STANDBY MODE

[0003] Technical field of the invention

[0004] Method for starting a system from standby mode and a system for stabilizing a power grid.

[0005] Problem statement

[0006] In recent years, the number of synchronous machines, such as turbines in hydroelectric or coal-fired power plants, that feed electrical power into a power grid has declined sharply due to the decommissioning of conventional power plants with such synchronous machines. Synchronous machines automatically maintain grid parameters such as the grid frequency and the nominal grid voltage relatively constant. With the decommissioning of these synchronous machines, this stabilization of grid parameters is lost. Consequently, there is an increased need for systems that can improve grid stability in a power grid. In particular, the stabilization of the grid frequency and the nominal grid voltage is required for this purpose.

[0007] There are systems that provide grid stabilization functions, such as a so-called Statcom. However, in the event of a complete power grid failure, restarting these systems takes a long time. The restoration of the power grid is therefore delayed, leading to inconvenience for people and losses for industrial companies in the service area.

[0008] German patent application DE 102016 105662 A1 discloses a method for the black start of a wind farm after a grid outage. The wind farm is started in island mode to generate electrical energy and feed it into the power grid. The patent covers the steps for activating the wind farm and feeding power into the grid to enable the restoration of grid operation. Grid stabilization functions are not included.

[0009] Document US 2022 / 0209540 A1 describes a method for re-establishing a power supply network using an energy storage system, a converter, and other components. The disclosed process involves first disconnecting the connection to the grid, then charging the export line and activating individual components of the wind farm before reconnecting to the grid. The system's operation is dependent on wind conditions. 24-101-P-WO-2-submitted version

[0010] Object of the invention

[0011] This leads to the task of providing a procedure for a system that enables the system to quickly stabilize an energy supply network after a power outage.

[0012] Technical solution

[0013] This problem is solved by the subject matter of the main claim. Sub-claims define aspects of the invention, and dependent claims define further developments of the invention.

[0014] The main claim discloses a method for starting a system from a standby mode with at least one battery inverter, at least one energy storage device and at least one Statcom, wherein the system is connected via a transformer and a disconnect switch, which is arranged on the grid side of the transformer, to a higher-level subnetwork with a higher nominal voltage than the nominal voltage of the system, wherein the disconnect switch is open at the beginning of the method.

[0015] The method further shows a setting of a system voltage to a starting voltage that is less than half the nominal grid voltage by the at least one battery inverter, a closing of the disconnect switch so that the system is connected to the higher-level subnetwork, a raising of the system voltage in the system to nominal voltage by the at least one battery inverter, and a stabilization of grid parameters of the system and the higher-level grid by the at least one Statcom.

[0016] The main claim discloses a method for transitioning a system in a subnetwork, comprising at least one battery inverter with at least one energy storage device and at least one Statcom, from standby mode to regular operation. Due to the at least one Statcom, which is preferably equipped with supercapacitors, the system is suitable for stabilizing a supply network connected to the system. This means, in particular, that the at least one Statcom in the system includes controls that support a connected supply network in maintaining and adhering to certain parameter limits, such as frequency and voltage. This is generally achieved by absorbing and supplying reactive and / or active power. Furthermore, the method shows that the system, prior to the filing of the version 24-101-P-WO-3,

[0017] System voltage at start voltage in a state of charge in which the capacities of at least one Statcom are charged or the charge is maintained by active power provision by the at least one battery inverter, and optionally by setting the nominal voltage as the system voltage by the at least one battery inverter, thereby enabling the operation of operating equipment such as cooling.

[0018] At the start of the process, the system is disconnected from the main power grid by the disconnect switch. In the first step, a starting voltage is established within the system by at least one battery inverter. Once this is achieved, the disconnect switch can be closed, connecting the system to the main sub-grid. Grid stabilization measures, such as the provision of reactive power by at least one Statcom, are already implemented at this stage.

[0019] Before the Statcom can provide power to perform grid-stabilizing operation, it is necessary to charge the short-term energy storage, preferably in the form of supercapacitors. Generally, such short-term storage devices discharge over time, so recharging is required during extended standby phases. According to this embodiment, this is achieved by increasing the voltage of the supercapacitors via a DC / DC converter in the Statcom and, optionally, to ensure secondary operations such as cooling, etc., by increasing the system voltage to the system's nominal voltage via the at least one battery inverter. Once the supercapacitors are recharged, i.e., have a preset voltage, the system voltage is reduced to the starting voltage, and the process continues with the closing of the disconnect switch.

[0020] When the disconnect switch is closed, at least one battery inverter increases the system voltage to nominal voltage, followed by stabilization of the system's and the higher-level network's network parameters by at least one Statcom.

[0021] In this way, the system can be safely and efficiently brought out of standby or waiting mode. Furthermore, the procedure enables the upstream power grid to be brought online. Due to the system's connection to the power grid, when the system voltage is increased to the nominal voltage, the voltage of the power grid is also increased and stabilized by at least one Statcom. In particular, the reactive power provided by at least one Statcom can balance or compensate for the reactive power requirements of transformer and line impedances, such as those of high-voltage lines. 24-101-P-WO-4-submitted version

[0022] In the event of a power grid outage, decentralized energy producers, such as home photovoltaic systems, disconnect from the grid. When the grid is restored by the system, these decentralized producers can reconnect and feed active and / or reactive power into the grid, thereby strengthening it. Consumers can then be gradually reconnected.

[0023] According to one embodiment of the method, the at least one Statcom provides network-stabilizing operation, in particular in the form of providing reactive power and, if necessary, active power peaks during the method.

[0024] As mentioned above, at least one Statcom stabilizes the power grid through grid-stabilizing operation. In particular, the provision of reactive power can compensate for line impedances, which is especially beneficial for the reconstruction of a power grid.

[0025] According to one embodiment of the method, the starting voltage is between 20% and 50% of the nominal voltage of the system, preferably at 44% of the nominal voltage of the system.

[0026] The starting voltage according to this embodiment is between 20% and 50% of the system's nominal voltage, but preferably at 44% of the system's nominal voltage. This results from the fact that, from 40% of the nominal voltage, the self-sufficiency of at least one Statcom device functions due to its design. Furthermore, the no-load losses of transformers, which are conventionally used in this voltage range of, for example, more than 110 kV, decrease to, for example, 20% of the nominal losses.

[0027] According to one embodiment of the method, the system is in a waiting state before the charging state, in which the system voltage is reduced to the starting voltage.

[0028] In standby mode, only the communication devices of at least one Statcom and at least one battery inverter are active, in order to determine whether a signal is sent indicating that the system needs to implement grid stabilization measures and that the power supply network needs to be restarted. Furthermore, selected status parameters are transmitted to a control center in standby mode.

[0029] According to one embodiment of the method, the at least one battery inverter provides sufficient active power to bring the frequency in the system and in the higher-level subnetwork closer to a nominal frequency. 24-101-P-WO-5- submitted version

[0030] In the European interconnected grid, the nominal frequency is 50 Hz and serves as an example below. With the disconnect switch closed, the battery inverter provides sufficient active power at a frequency of 50 Hz to prevent significant frequency drops when loads are connected to the grid. Furthermore, grid-following generators, such as power-sensing inverters or wind turbines, also connect to the grid when its parameters are close to the nominal values. Therefore, at least one battery inverter may initially need to provide 1 MW of active power to maintain the grid frequency at 50 Hz.If a 500 kW wind turbine is connected to the power grid, for loads with a consumption of 1 MW, it is only necessary that at least one battery inverter provides 500 kW, since the wind turbine feeds in the remaining required active power.

[0031] According to one embodiment of the method, the system has a medium voltage as its nominal voltage and the higher-level subnetwork has a high voltage as its nominal voltage.

[0032] The system can be designed for a medium voltage range, i.e., a nominal voltage between 1 kV and 60 kV. For this range, there are good options for battery connection via at least one battery inverter. Furthermore, operating equipment such as at least one battery inverter and at least one Statcom can be operated and maintained.

[0033] The main subnetwork, or power supply network, is conventionally a high-voltage network with a high voltage as its nominal voltage. A voltage above 60 kV is usually considered high voltage, although the classification varies.

[0034] One aspect of the invention shows a system for stabilizing a power grid with at least one battery inverter, at least one energy storage device and at least one Statcom, wherein the system is connected via a disconnect switch and a transformer to a higher-level subnetwork with a higher nominal voltage than the nominal voltage of the system, which is operated using a method according to one of claims 1 to 7.

[0035] The system shown in this aspect reveals all the advantages and functionalities of the method used for operation.

[0036] According to one embodiment of the system, the rated power of each battery inverter is at least 1 MVA and the rated power of each Statcom is at least 1 MVA. 24-101-P-WO-6-submitted version

[0037] Classifying the individual components helps in dimensioning a system. Furthermore, to ensure sufficiently high stabilization capacity, it is advisable that each battery inverter, particularly for providing active power and charging the supercapacitors of the Statcoms, and each Statcom, for providing reactive power and compensating for active power or frequency fluctuations, have a sufficiently high apparent power output.

[0038] According to one embodiment of the system, the transformer can be disconnected on both sides by opening the disconnect switch and a second disconnect switch in order to avoid the no-load losses of the transformer in standby mode.

[0039] Decoupling the transformer increases the system's efficiency. By avoiding no-load losses, the standby state can be maintained for longer without the battery being completely discharged.

[0040] According to one embodiment of the system, the transformer is configured to be switched on by closing the second disconnect switch when the standby state is to be exited.

[0041] Switching on the transformer when the system voltage is low prevents inrush currents, thus avoiding current spikes and imbalances in the system components. High inrush currents would occur, in particular, if the transformer were only switched on at the system's nominal voltage.

[0042] According to one embodiment of the system, the inrush current when closing the disconnect switch to the superimposed subnetwork is reduced by the fact that the starting voltage is lower than the nominal voltage and the system is configured to be able to ride through the closing of the disconnect switch like an FRT (Fault Ride Through) event.

[0043] Similar to the previous embodiment, a low system voltage can prevent faults or damage to system components. Furthermore, it is possible to treat the closing of the disconnect switch as a fault ride-through (FRT) event, in which the at least one battery inverter and the at least one Statcom continue their operation without being disturbed by anomalous grid parameters such as voltage dips or frequency changes. In this way, the closing of the disconnect switch can be compensated for without impairing the stabilizing operation of the system.

[0044] According to one embodiment of the system, the system is configured such that all system components are powered by their respective self-supply at start-up voltage, 24-101-P-WO-7-submitted version

[0045] They can be operated at nominal voltage and at a voltage higher than the nominal voltage.

[0046] The system should be capable of operating in a standby or waiting mode to be operational as quickly as possible when a higher-level power supply needs to be restored. This requires the basic operation of certain components, such as communication equipment, to detect that a higher-level power supply needs to be restored. Other components that should operate at startup voltage include battery inverters, the battery, Statcom, switchgear, communication systems, measurement technology, air conditioning, and monitoring equipment. Furthermore, the operation of these components should be guaranteed even at voltages higher than the startup voltage. In particular, the components should also function at a system voltage as high as the system's nominal voltage.

[0047] According to one embodiment of the system, at least one Statcom is configured to communicate with a communication device outside the system when the system is in standby mode.

[0048] This allows at least one Statcom to be made operational in a very short time. This requires the basic operation of some facilities, such as communication equipment, to detect that a higher-level power supply network is to be restored.

[0049] According to one embodiment of the system, the power electronics of the at least one Statcom are configured to be switched off in standby mode, and the power electronics of the at least one battery inverter are configured to be operated in standby mode in order to set the starting voltage.

[0050] The power electronics of at least one Statcom can be switched off in standby mode to avoid losses, thus increasing system efficiency and allowing the standby mode to be maintained for a longer period using the batteries of at least one battery inverter. In standby mode, the at least one battery inverter continues to provide a low voltage to power components such as communication equipment and maintain operation.

[0051] SHORT DESCRIPTION OF FIGURES 24-101-P-WO-8-submitted version

[0052] The invention will now be further explained and described with reference to exemplary embodiments shown in the figures.

[0053] Fig. 1 shows a schematic, exemplary system with an energy supply network.

[0054] Fig. 2 shows a diagram of the time course of voltage and power values ​​during a process run, and

[0055] Fig. 3 shows a diagram following Fig. 2, depicting a time course of voltage and power values ​​during a process sequence.

[0056] FIGURE DESCRIPTION

[0057] Figure 1 shows a schematic, exemplary system 1 with a power supply network 100. This system 1 includes a battery inverter 10 with battery 12 and a Statcom 20 with a supercapacitor 22 as a short-term storage device. It is also possible for a DC / DC converter to be arranged between the Statcom 20 and the supercapacitor 22, which is not shown here. Furthermore, the system 1 includes a transformer 30 and a disconnect switch 40 for the power supply network 100. A second disconnect switch 42 is also provided for disconnecting the transformer 30 to avoid losses.

[0058] It is expressly emphasized here that several battery inverters 10, each with one or more batteries 12, and several Statcoms 20, each with one or more supercapacitors 22 as short-term storage, may be present, and that the representation in Fig. 1 is merely schematic. Likewise, significantly different numbers of battery inverters 10 and Statcoms 20 may be present, such as two battery inverters 10 and a much higher number, for example forty, of Statcoms 20.

[0059] The power supply network 100 is schematically represented as lines with impedances. Because overhead power lines or high-voltage lines can bridge very long distances, lines in the power supply network 100 can be effectively represented schematically as impedances.

[0060] In Fig. 1, an additional transformer 50 and a generator or load 60 are connected to the energy supply network 100 as an example.

[0061] Fig. 2 shows a diagram with the voltage curves of the short-term storage devices or supercapacitors Ucap as a solid line, the system voltage Usys as a dashed line with long dashes, and the active power provided by the battery inverter 10. 24-101-P-WO-9- submitted version

[0062] Pbat is represented by a dashed line with short dashes. The horizontal axis represents the time axis, while the vertical axis merely serves to illustrate the progression.

[0063] On the left side, at the beginning of the diagram, system 1 is connected to a power supply network 100. The system voltage llsys is initially at nominal voltage Unorn. The level of the active line Pbat indicates that system 1 is feeding active power into the power supply network. At t1, a fault or similar event occurs in the power supply network 100, whereupon system 1 disconnects from the power supply network 100 by opening disconnect switch 40. System 1 is now in standby mode. A second disconnect switch 42 is also opened, thus disconnecting transformer 30.

[0064] If System 1 is disconnected from the power supply network 100, the available active power Pbat drops to a low value. The value of the active power Pbat is adjusted to the consumption of selected loads in System 1. In particular, communication equipment is supplied, and the no-load losses of the power converters of the at least one battery inverter 10 and the at least one Statcom 20 are compensated, so that System 1 can be quickly reactivated from standby mode. The system voltage Usys is reduced to a starting voltage U1. Due to discharge processes and similar factors, the supercapacitor voltage Ucap decreases continuously over time after time t1.

[0065] At time t2, a signal is given to restart the power supply network 100 and reactivate system 1 for this purpose. In response to this signal, at least one battery inverter 10 sets the nominal voltage Unom as the system voltage. At least one Statcom 20 recharges its supercapacitor, causing the supercapacitor voltage Ucap to rise again.

[0066] At time t3, all supercapacitors are charged. The active power required to maintain the operation of system 1 now decreases, as can be seen from the active power Pbat from time t3 onwards. It should be noted that the time intervals before t1, from t1 to t2, from t2 to t3, and after t3 are not to scale and can vary considerably. For example, minutes may pass between t2 and t3, while several days, such as three, may pass between t1 and t2.

[0067] The diagram in Fig. 3 continues the process illustrated in Fig. 2 and begins at time t3. The same differentiation of the lines from Fig. 2 is maintained. The information is now received that the power supply network 100 is to be connected to system 1. Consequently, the battery inverter 24-101-P-WO-10- (submitted version)

[0068] 10. The system voltage set in the system is reduced to the starting voltage U1 at time t4. After a short waiting period, during which the system 1 and its controls stabilize, the disconnect switch 40 is closed at time t5 and the connection between the system 1 and the power supply network 100 is restored.

[0069] At this point t5, at least one battery inverter provides 10 more active power Pbat. In addition, the supercapacitor voltage llcap drops sharply for a short time, which is due to the provision of active and reactive power that compensates for the grid impedances of the connected power supply network 100.

[0070] Between times t5 and t6, at least one battery inverter 10 continuously increases the system voltage llsys to the nominal voltage Unorn. Simultaneously, the voltage of the power supply network 100 is increased via the transformer 30. At time t6, the system voltage has reached the nominal voltage Unorn. It becomes clear that significantly less active power Pbat needs to be provided when the nominal voltage Unorn is reached, particularly because external generators supply some of the required active power. In this state, additional loads and generators connect to the power supply network 100. The at least one Statcom 20, which has been performing stabilizing operation since time t3, continues its stabilizing operation, thus compensating for network events and irregularities.

[0071] For example, such an event takes place at time t7, represented in this example by connecting a larger generator to the power supply network 100. Due to the switching on of one or more transformers that are upstream of the exemplary generator, and the further lines between the power supply network 100, there is a brief increase in reactive power demand, which is covered by at least one Statcom 20.

[0072] - 101 -P- WO submitted version

[0073] REFERENCE MARK LIST

[0074] System 0 Battery inverter 2 Battery 0 Statcom 2 Supercapacitor 0 Transformer 0 Disconnect switch 2 Second disconnect switch 0 Transformer 0 Generator / Load 0 Disconnect switch 00 Power supply network

Claims

24-101-P-WO-12- submitted version PATENT CLAIMS 1. Method for starting a system (1) from a standby state comprising at least one battery inverter (10), at least one energy storage device (12) and at least one Statcom (20), wherein the system (1) is connected via a transformer (30) and a disconnect switch (40) arranged on the grid side of the transformer (30) to a higher-level subnetwork (100) with a higher nominal voltage than the nominal voltage (Unorn) of the system (1), wherein the disconnect switch (40) is open at the beginning of the method, comprising the steps: Setting a system voltage (llsys) to a starting voltage (U 1) that is less than half the nominal voltage of the system, by means of at least one battery inverter (10), Closing the disconnect switch (40) so that the system (1) is connected to the higher-level subnetwork (100), Increasing the system voltage (llsys) in the system to nominal voltage (Unorn) by means of at least one battery inverter (10), and Stabilizing network parameters of the system (1) and the higher-level network (100) by means of at least one Statcom (20), - wherein the system is in a state of charge prior to setting the system voltage to start voltage, in which the capacities (22) of the at least one Statcom (20) are charged or receive charge by active power provision by the at least one battery inverter (10), and optionally is achieved by setting the nominal voltage to the system voltage by the at least one battery inverter (10).

2. Method according to claim 1, wherein the at least one Statcom (20) provides network stabilizing operation, in particular in the form of providing reactive power, optionally also short-term active power, during the method.

3. Method according to claim 1 or 2, wherein the starting voltage is between 20% and 50% of the nominal voltage of the system, preferably at 44% of the nominal voltage of the system.

4. Method according to claim 1, wherein 24-101-P-WO-13- submitted version the system is in a standby state before the charging state, in which the system voltage is reduced to the starting voltage.

5. Method according to one of the preceding claims, wherein the at least one battery inverter provides so much active power that a frequency in the system and in the higher-level subnetwork approaches a nominal frequency.

6. Method according to one of the preceding claims, wherein the system (1) has a medium voltage as nominal voltage and the higher-level subnetwork (100) has a high voltage as nominal voltage.

7. System for stabilizing a power grid with at least one battery inverter (10), at least one energy storage device (12) and at least one Statcom (20), wherein the system (1) is connected via a transformer (30) and a disconnect switch (40) arranged on the grid side from the transformer (30) to a higher-level sub-network (100) with a higher nominal voltage than the nominal voltage (Unorn) of the system (1), which is configured to be operated with a method according to one of claims 1 to 6.

8. System according to claim 7, wherein the rated power of each battery inverter (10) is at least 1 MVA and the rated power of each of the Statcoms (20) is at least 1 MVA.

9. System according to one of claims 7 to 8, wherein the transformer (30) can be disconnected on both sides by opening the disconnect switch (40) and a second disconnect switch (42) in order to avoid the no-load losses of the transformer (30) in the standby state.

10. System according to claim 9, wherein the transformer (30) is configured to be switched on by closing the second disconnect switch (42) when the standby state is to be exited.

11. System according to one of claims 7 to 10, wherein an inrush current when closing the disconnect switch (40) to the superimposed subnetwork (100) is reduced by the fact that the start voltage (U1) is lower than the nominal voltage (Unom) and the system is configured to be able to traverse the closing of the disconnect switch (40) like an FRT event.

12. System according to any one of claims 7 to 10, wherein the system (1) is configured such that all system components are powered by their respective self-supply at start voltage (U1), 24-101-P-WO-14-submitted version They can be operated at nominal voltage (Ilnom) and at a voltage higher than the nominal voltage.

13. System according to any one of claims 7 to 11, wherein the at least one Statcom (20) is configured to communicate with a communication device outside the system when the system (1) is in standby mode.

14. System according to any one of claims 7 to 12, wherein a power electronics of the at least one Statcom (20) is configured to be switched off in standby mode, and a power electronics of the at least one battery inverter (10) is configured to be operated in standby mode in order to provide the start voltage (U1).

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