Method for operating a subgrid in the case of decoupling of the subgrid from the power supply grid

Abstract

The invention relates to a method for operating a system having a battery converter connected between a battery and a subgrid and at least one further converter connected between a power generation unit and / or a load and the subgrid. A supply grid can be connected to the subgrid via a grid disconnector. The method comprises the following steps: feeding in power generated by the at least one further converter; feeding in the power generated in grid-following mode when the grid disconnector is closed; and separating the supply grid from the subgrid by opening the grid disconnector. Subsequently in the method, battery power is fed in by the battery converter in grid-forming mode, wherein the battery power fed in comprises active power and / or reactive power, and power generated is fed in by the at least one further converter in grid-forming mode, wherein the power generated fed in comprises active power and / or reactive power. Once the voltage and the frequency are adjusted by the grid-forming type of feeding in to be within a predetermined value range after the separation, the battery power is fed in in grid-forming mode and the power generated is fed in in grid-following mode, so that the voltage and the frequency within the subgrid are maintained within a predetermined value range.

Description

[0001] describe This invention relates to a method for operating energy systems.

[0002] question In light of climate change, efforts are underway to replace fossil fuel power generation with renewable energy sources. The most widely distributed renewable energy sources are wind and solar power. Solar power, like wind, can also be converted into electricity through private photovoltaic (PV) systems. This electricity is either generated for domestic consumption or fed into the public power grid. To ensure the stability of the power grid and its sub-grids (e.g., individual local grids or large estates), efforts are being made to enable these sub-grids to decouple from the main grid and become self-sufficient in the event of a fault.

[0003] To address this, German publication DE 10 2012 023 424 A1 discloses an energy distribution device having at least one energy source and at least one electrical storage device, wherein the device can be isolated from the power grid and operate as an islanded grid. In islanded operation, the single inverter in the device operates in a voltage regulation and grid-connected manner. The inverter must supply all values ​​of the device independently, thus requiring a high apparent power, which leads to high cost.

[0004] German publication DE 10 2019 116 254 A1 discloses a power generation device with at least two inverters that can selectively operate in voltage injection or current injection mode. In voltage injection mode, one, more, or all inverters can establish an islanded grid or act as part of a grid to the upper-level grid. Task allocation is not disclosed, therefore the structure of all inverters is equally complex.

[0005] German publication DE 10 2017 112 491 A1 illustrates a similar operating method for wind power generation equipment.

[0006] The problem here is that, when decoupled from the power grid, the loads in the subgrid must be powered through the stable operation of the subgrid.

[0007] Technical solutions This problem is solved by the method of operation according to the main claim. The subject matter of the dependent claims constitutes an improvement according to the invention.

[0008] According to the method of operating the system of the present invention, the system comprises: a battery converter connected between the battery and the subgrid; and at least one additional converter connected between the generator unit and / or the load and the subgrid. The method discloses the following steps: feeding generated power through an additional converter; feeding generated power in a grid-connected manner when the grid disconnect switch is closed; and separating the power supply grid from the sub-grid by disconnecting the grid disconnect switch. After separation, battery power is fed into the sub-grid in a grid-connected manner through a battery converter, wherein the fed battery power includes active power and / or reactive power; and generated power is fed into the sub-grid in a grid-connected manner through at least one additional converter, wherein the fed generated power includes active power and / or reactive power. The method is characterized in that once the voltage and frequency are regulated to a predetermined range through grid-connected feeding after separation, battery power is fed into the sub-grid in a grid-connected manner, and generated power is fed into the sub-grid in a grid-connected manner, so that the voltage and frequency within the sub-grid remain within the predetermined range.

[0009] Here, the system refers to a subgrid, such as a rural distribution network. The battery converter is equipped with batteries, also known as a community energy storage unit (Quartierspeicher). Additionally, the system includes other converters, power supply units (e.g., photovoltaic equipment), and / or loads connected to the subgrid via these converters. Furthermore, the system can be connected to the power grid via a grid disconnect switch. While connected to the power grid, the system or subgrid can draw power from and feed it back into the power grid.

[0010] Here, the battery converter and battery are used to stabilize the subgrid. Excess energy generated in the subgrid (e.g., through photovoltaics) can be stored in the battery and withdrawn from the energy storage at other times (e.g., during evening periods when PV power is low) without burdening the upstream power grid. The system according to the invention initially operates in normal mode, where an additional converter feeds generated power into the subgrid. The power feed is grid-connected. This means that generated power is fed into the subgrid in the form of active and / or reactive power. Grid-connected feeding means that the generated power is divided into active and reactive power so that the grid parameters of the subgrid (i.e., voltage and frequency) remain within permissible ranges. During this period, fault monitoring is continuously performed on the power grid and the subgrid. If a fault is detected, it is treated as a fault condition, and the power grid is isolated from the subgrid by disconnecting the grid disconnect switch.

[0011] The fault condition can be a fault in the power grid, or it can be an overload in the subgrid.

[0012] For example, a fault in the power grid can be caused by a short circuit or a transformer failure near the power grid. In this situation, power can no longer be drawn from the power grid. Instead, a rapid voltage drop will occur in the power grid, and without proper countermeasures, this voltage drop will cause a voltage drop in the subgrid, making it impossible to supply power to the load.

[0013] An overload condition describes a situation where a power supply unit feeds excessive active power into the subgrid via an additional converter. In systems with synchronous motors, this excessive active power can cause the system frequency to rise. The power generation units in the subgrid according to the invention are primarily not synchronous motors. Furthermore, the subgrid is connected to the upstream power grid, ensuring that the frequency within the subgrid does not rise even under subgrid overload conditions. Therefore, the additional converter does not perform active power limiting. Active power can be supplied from the subgrid to the power grid via transformers until the design limits of the transformers or other grid operating devices are reached. However, once the limits of the transformers or other grid operating devices are reached, an overload condition occurs.

[0014] In any fault condition, the subgrid is disconnected from the generation grid by disconnecting the isolating switch. Specifically, in the event of an overload, the subgrid is disconnected from the supply grid to protect the grid's operating equipment. Subsequently, the battery converter feeds power stored in the batteries into the subgrid in a grid-connected manner, or absorbs energy from the subgrid in a grid-connected manner. Here, "grid-connected manner" means that the battery converter injects power into the batteries in a voltage-regulated manner, ensuring that the frequency and voltage are supported, and that generation and consumption are consistent. Furthermore, the battery power fed in includes active power and / or reactive power depending on grid parameters such as voltage and frequency in the subgrid.

[0015] After being disconnected from the power grid, additional converters feed in the generated power in a grid-connected manner. Specifically, this grid-connected feeding is necessary because the load operates continuously throughout the entire time period, and the battery converter and other converters stabilize the subgrid as an islanded grid. Through this method of disconnecting the subgrid from the power grid, the subgrid can operate self-sufficiently using the battery power fed in by the battery converter and the generated power fed in by the other converters. However, when the fed-in power is high, the frequency may increase, causing the other converters to reduce their fed-in power or increase their power consumption.

[0016] Once disconnected from the power grid, the voltage and frequency of the subgrid are regulated to a predetermined range, and the battery converter is in grid-connected feed-in mode, ensuring that the voltage and frequency within the subgrid remain within the predetermined range.

[0017] "Grid-connected" should be understood as the converter (also called an inverter) being synchronized to the existing power grid and following it in terms of frequency and voltage. The converter follows the grid as quickly as its regulation allows. Furthermore, grid-connected converters are current-source type. "Grid-supported" means that grid-supported converters can differ from the existing grid in phase (where frequency is indirectly affected by phase shift) and / or voltage. Therefore, grid-supported converters can influence the existing grid. Multiple grid-supported voltage-source converters, with appropriate regulation, can maintain or construct a grid. Grid-supported converters can independently construct and maintain a grid. When constructing a grid, the converter can determine the frequency and voltage of the grid to be constructed.

[0018] According to the implementation method, the operation method further includes: in the event of subgrid overload, the frequency of the subgrid is predetermined by the battery converter, wherein the overload is determined by the separation in step C.

[0019] In this embodiment, operation under overload conditions is further specified. Specifically, this embodiment specifies that the battery converter sets the frequency of the subgrid so that another converter reduces or increases its power according to a predetermined frequency. Here, the other converter follows the frequency / power specifications of relevant standards (e.g., VDE-AR-N 4105 or VDE-AR-N 4110). In this case, the grid disconnect switch is connected to a sensing device that can determine the overload. Here, the sensing device is not limited to a specific technology.

[0020] Battery converters and other converters can autonomously detect disconnection from the power grid via sensors (e.g., a change in frequency after disconnection, thus an indicator of overload), or switches can notify the battery converters and other converters of the disconnection via appropriate communication (e.g., a PLC (Power Line Communication) via power cable) or a dedicated communication connection. Alternatively or additionally, battery converters and converters can also autonomously detect disconnection by measuring electrical parameters (frequency and voltage) at their respective grid connection points.

[0021] According to the implementation method, the operation method further includes increasing the frequency set by the battery converter relative to a predetermined value range of the frequency to reduce the active power fed in by the additional converter.

[0022] This implementation specifies how to reduce active power in the subgrid. To this end, an additional converter is equipped with regulation that sets the input active power based on the frequency of the grid (in this case, the subgrid). By setting the frequency in the subgrid to a higher than the nominal frequency of the corresponding grid in the region (e.g., 50Hz in Europe) via a battery converter, the active power input by the additional converter is reduced. Additionally, with such a higher frequency, the power drawn from the subgrid by controllable loads can also be increased by either increasing the power of these loads or by activating them from a specific frequency. This eliminates overload conditions and establishes power balance in the subgrid.

[0023] According to the implementation method, the operation method further includes: setting a frequency set by the battery converter so that there is no longer an overload in the subgrid, wherein the voltage and frequency are then adjusted to a predetermined value range.

[0024] This implementation specifies how long the adjustment should be maintained under overload conditions. Specifically, the frequency set by the battery converter is kept increasing relative to the nominal frequency until the overload is no longer present and power balance is achieved in the subgrid. Once the battery converter must output power to the subgrid because the power output of the generating equipment in the subgrid is no longer sufficient, the battery converter automatically readjusts the frequency of the subgrid to a predetermined range, specifically to the nominal frequency.

[0025] According to the implementation, the system is also connected to the power grid via a decoupling reactor, and the operation method further includes: in the event of a grid fault, providing or absorbing active power by a battery converter to keep the frequency in the subgrid within a predetermined range; and before disconnection, providing so much reactive power by another converter, independent of the position of the grid disconnecting switch, to keep the voltage within a predetermined range (e.g., the other converter may follow a static reactive power target value, or set its reactive power according to voltage changes as specified in standards such as VDE-AR-N 4105).

[0026] In the event of a grid failure, the voltage of the power grid drops to zero. The subgrid must remain connected to the power grid for a predetermined period to support it, preventing the power grid from collapsing due to the lack of generating equipment during even brief failures. To prevent the voltage in the subgrid from dropping to zero, additional reactive power is supplied through a separate converter to maintain the voltage within a predetermined range. The working principle is as follows: by feeding reactive power into the subgrid, a voltage difference is generated across the decoupling reactor. Therefore, the subgrid voltage can differ from the grid voltage.

[0027] During the period of grid failure and disconnection from the power grid, the battery converter mainly feeds active power into the subgrid, and may also feed reactive power, so as to continue to supply active power to the load and support the voltage in the subgrid.

[0028] Therefore, the overall advantage of this implementation is that even in the event of a grid failure and when the subgrid is (not yet) isolated from the power supply grid, it can still maintain voltage and supply active power to the load; that is, the subgrid continues to operate as if in normal operating mode without experiencing its own failure. Here, the frequency in the subgrid is supported by the grid-type feed of battery power, and the voltage in the subgrid is supported by the reactive power feed of the generator power from another converter. Here, the reactive power used for voltage support comes from the other converter and the battery converter. The battery converter provides the additional dynamic reactive power share required to maintain voltage.

[0029] According to the implementation method, the operation method further includes: an additional converter providing reactive power so that the voltage at the decoupling reactor in the subgrid is higher or lower than the voltage on the grid side.

[0030] As mentioned earlier, in the event of a grid fault, additional converters also provide reactive power, resulting in a voltage drop across the decoupling reactor. In this case, the voltage in the subgrid may be higher than the grid voltage. In special circumstances, the voltage on the load side of the subgrid may also be lower than the grid voltage, for example, when an overvoltage occurs in the grid.

[0031] According to the implementation method, the operation method further includes: determining the power grid fault by measuring device, and / or determining the power grid fault by disconnecting the power grid disconnecting switch.

[0032] In this embodiment, a grid fault is determined by a measuring device and / or by disconnecting a grid disconnect switch. The determination by the measuring device is designed to first identify the grid fault using a sensor. Subsequently, a dedicated signal is sent to the grid disconnect switch, battery converter, and other converters, notifying these components as well. The grid disconnect switch will then disconnect the subgrid from the power grid after a predetermined time. The battery converter and other converters activate the regulation described in the above embodiment. Alternatively or supplementarily, the grid disconnect switch may also be equipped with a corresponding sensor to detect the grid fault. The battery converter and other converters then determine the grid fault either by disconnecting themselves or by obtaining relevant information through a communication channel. Combinations are also possible. For example, the measuring device can activate regulation for a grid fault, wherein disconnecting the grid disconnect switch terminates the regulation and initiates islanded grid operation.

[0033] According to the implementation method, the operation method further includes: the battery converter and the other converter include regulation, which has different inertia from each other, or different settings in terms of amplitude inertia (related to reactive power) or phase inertia (related to active power).

[0034] In the event of a grid fault or islanded grid operation, the operation of the battery converter and the other converter differs. Taking the other converter as an example, in the event of a grid fault, it initially only modifies and feeds reactive power into the sub-grid to maintain voltage. If the grid disconnect switch is now disconnected, the other converter begins to feed reactive power in a grid-connected manner (according to its characteristic curve (also known as the reactive power static characteristic)). To avoid side effects from a sudden switch from pure reactive power feeding to other feeding methods, the regulation of the other converter is equipped with higher inertia, ensuring that the feed change is gradual. This means that when the voltage drops, the other converter begins to feed reactive power into the sub-grid to maintain the voltage across the decoupling reactor. Here, the reactive power regulation of the other converter is equipped with such inertia that when the voltage returns to normal, it does not immediately stop feeding reactive power, but rather gradually reduces the amount of reactive power fed in. In contrast, in the event of a grid failure, the battery converter primarily supplies active power to the loads in the subgrid, and only secondarily feeds in the differential reactive power required to maintain voltage.

[0035] According to the implementation of the above operating method, the battery converter and other converters include regulation with different inertia from each other.

[0036] In this implementation, the battery converter and other converters have different inertia. In this way, in the event of a grid fault or overload, the battery converter and other converters can perform different tasks. For example, the battery converter can provide active power through high phase inertia, while other converters can provide reactive power due to high amplitude inertia.

[0037] According to an embodiment of the operating method of the present invention, the inertia of the battery converter and other converters differs in the setting of amplitude inertia with respect to reactive power and phase inertia with respect to active power.

[0038] In this embodiment, the battery converter and other converters have different inertia. In this way, in the event of a grid fault or overload, the battery converter and other converters can perform different tasks. For example, the battery converter can provide active power with high phase inertia, while other converters can provide reactive power due to high amplitude inertia. According to the embodiment, the operating method also includes regulating the battery converter to have different inertia depending on the operating mode.

[0039] In the post-grid failure operating mode, it is crucial that the battery converter can quickly supply active power to new loads in the subgrid. To this end, in the event of a grid failure, the battery converter possesses increased inertia, thus maintaining voltage and frequency. This smooths out fluctuations in the feed from other converters. For example, when the frequency in the subgrid set by the battery converter increases relative to a predetermined range of frequencies in the subgrid, the active power feed from other converters decreases rapidly. Thanks to its high inertia, the battery converter can compensate for any potentially low active power in the subgrid and correspondingly reduce the frequency again until equilibrium is reached.

[0040] According to the above implementation of the operating method, in the event of a grid fault, the regulation of the battery converter has high inertia in terms of both amplitude and phase inertia.

[0041] In this implementation, the battery converter provides both active and reactive power during a fault, independent of the frequency and voltage parameters occurring in the subgrid under fault conditions. Therefore, the battery converter can maintain the subgrid. It is important to emphasize that the power supply grid can be, for example, a medium-voltage grid or a high-voltage grid. Furthermore, the power supply grid can be any other grid, i.e., a grid into which electrical power can be fed and from which electrical power can be obtained.

[0042] Furthermore, power grid disconnect switches and bypass switches can be designed as different or the same type of switch. Both switches can be relays or other electromechanical switches. Generally, power grid disconnect switches and bypass switches are required to be equipped with their own measuring electronics or be controllable by a controller, and to be able to switch safely and in compliance with standards, or to possess such switching capability. In particular, these switches are medium-voltage switches and are part of medium-voltage switchgear.

[0043] The present invention will now be described with reference to the accompanying drawings, wherein: Figure 1 A system according to the present invention is shown. Figure 2 The operating method according to the present invention is shown. Figure 3 An operating method according to an embodiment of the present invention is shown, and Figure 4 An operating method according to another embodiment of the present invention is shown.

[0044] The accompanying drawings are described in detail below.

[0045] Figure 1System 1 according to the present invention is shown. System 1 includes a subgrid connected to the power grid 10 via a grid disconnect switch 12 and a decoupling reactor 16. Optionally, the decoupling reactor 16 may be bridged via a bypass switch 18 connected in parallel therewith.

[0046] Battery converter 20 is connected to the subgrid. Battery 22 is connected to battery converter 20. Battery converter 20 can transfer electrical power from battery 22 to the subgrid. Similarly, battery converter 20 can transfer electrical power from the subgrid to battery 22.

[0047] In addition, additional converters 24 and 26 are connected to the subgrid. These additional converters 24 and 26 can be, for example, converters for supplying power to loads (e.g., in an electrolysis unit) or converters for operating power generation equipment (e.g., in a residential photovoltaic system). Furthermore, the additional converters 24 and 26 can also be designed as battery converters. Generally, converters 24 and 26 are capable of feeding power into and / or drawing power from the subgrid. Furthermore, loads 28 can be connected to the subgrid. These loads 28 are preferably designed as AC loads.

[0048] Figure 2 A method of operation according to the invention for the system described above is shown. The method begins at step 100, where generated power is fed into the subgrid by additional converters 24, 26. Here, as specified in step 102, the generated power is fed into the subgrid in a grid-connected manner. This means that the voltage and frequency of the fed-in generated power correspond to a predetermined voltage and frequency of the subgrid. Step 102 is maintained until proceeding to step 104. In step 104, the subgrid is disconnected from the power supply grid. This disconnection is achieved by disconnecting the grid disconnect switch 12.

[0049] If the subgrid is disconnected from the power grid in step 104, the method proceeds to step 106. In step 106, battery power from battery 22 (connected to battery converter 20) is fed into the subgrid via battery converter 20 in a grid-like manner. The battery power fed into the subgrid from battery 22 connected to battery converter 20 includes active power and / or reactive power.

[0050] Step 108 is performed after or concurrently with step 106. In step 108, generated power is fed into the subgrid via at least one of the additional converters 24 and 26, wherein the fed-in generated power includes active power and / or reactive power. Steps 106 and 108 are performed until, after the subgrid is disconnected from the power grid 10, the voltage and frequency are regulated to a predetermined range via a grid configuration of battery converter 20 and at least one additional converter 24 or 26. Once this has occurred, the method proceeds to step 200.

[0051] In step 200, the battery power from the battery 22 connected to the battery converter 20 is fed into the subgrid in a grid-connected manner through the battery converter 20 and the generated power through at least one other converter 24, 26, so that the voltage and frequency in the subgrid are maintained within a predetermined range.

[0052] Figure 3 An embodiment of the operating method according to the invention for a system based on the invention is shown below. Figure 2 The differences in the operating method according to the present invention described herein. Here, Figure 3 The operating method according to the invention shown herein involves determining an overload condition in the subgrid. Here, steps 100 and 102 are... Figure 2 The operating method according to the invention described herein is the same. In step 104a, an overload in the subgrid is determined via a suitable measuring device (connected to the grid disconnect switch 12) or by the switch itself (which has such a measuring device). After disconnecting the subgrid from the power supply grid 10 in step 104a, the method continues to step 106a.

[0053] In step 106a, the battery converter 20 predetermines the frequency of the subgrid by feeding battery power into the subgrid in a grid-like manner. After or simultaneously with step 106a, the following is performed: Figure 2 Step 108 as described in the document. The method is as follows: Figure 2 The description ends at step 200.

[0054] Figure 4 Another embodiment of the operating method according to the invention for the system according to the invention is shown below. Only the following shows the method with respect to... Figure 2 The differences in the operating method according to the present invention described herein. Here, Figure 4 The operating method shown according to the invention relates to determining the situation where there is a grid fault in the power supply grid 10.

[0055] Here, steps 100 and 102 are related to... Figure 2The operating method is the same as described in the previous section. In step 104b, a grid fault in the power supply grid 10 is determined via a suitable measuring device (connected to the grid disconnect switch 12) or by the grid disconnect switch 12 itself (which has such a measuring device). After the subgrid is disconnected from the power supply grid 10 in step 104b, the method continues to step 106b.

[0056] In step 106b, battery power from battery 22 is provided by battery converter 20. Here, battery power is provided in a grid-like manner, ensuring that the frequency in the subgrid remains within a predetermined range. Step 108b is performed simultaneously with step 106b. In step 108b, such a large amount of reactive power is fed into the subgrid via additional converters 24 and 26, ensuring that the voltage remains within a predetermined range according to a suitable characteristic curve or through its grid-like characteristics (amplitude inertia). This method is as follows... Figure 2 The description ends at step 200.

[0057] Reference tag list 10 Power Grid 12 power grid disconnect switches 14 Transformers 16 Decoupling Reactors 18 bypass switches 20-cell battery converter 22 batteries 24 converter 26 converters 100-200 steps.

Claims

1. A method of operating a system, the system comprising: a battery converter (20) connected between a battery (22) and a subgrid; and at least one additional converter (24, 26) connected between a power generation unit and / or a load and the subgrid. in, The power grid can be connected to the subgrid via a grid disconnect switch (12), and the operation method includes the following steps: The power generation is fed into (100) through at least one additional converter (24, 26). When the grid disconnect switch (12) is closed, the generated power is fed into (102) in a grid-connected manner. By disconnecting the power grid disconnect switch (12), the power supply grid (10) is separated from the sub-grid (104). The battery power is fed into the subgrid in a grid-like manner via the battery converter (20) in a grid-like manner (106), wherein the fed-in battery power includes active power and / or reactive power. The generated power is fed into (108) the grid via at least one additional converter (24, 26), wherein the fed-in generated power includes active power and / or reactive power, and Its features are, Once separated (104), the voltage and frequency are adjusted to the predetermined value range by feeding in a grid-connected manner (106, 108), and the battery power (200) is fed in a grid-connected manner, and the power generation power is fed in a grid-connected manner, so that the voltage and frequency in the subgrid are maintained within the predetermined value range.

2. The operating method according to claim 1, comprising, in the event of an overload in the subgrid, setting (106a) the frequency of the subgrid via the battery converter (20), wherein, The overload is determined by separating the power supply grid from the subgrid (104).

3. The operating method according to claim 2, wherein, The set frequency is increased relative to the predetermined value range of the frequency to reduce the active power fed into the additional converters (24, 26).

4. The operating method according to claim 3, wherein, The frequency set by the battery converter is maintained at an increased rate until there is no longer an overload in the subgrid, wherein the voltage and frequency are then adjusted to the predetermined value range.

5. The operating method according to claim 1, wherein, The system is also connected to the power grid via a decoupling reactor (16), and the operation method includes: In the event of a grid fault, active power is supplied (106b) or absorbed via the battery converter (20) to maintain the frequency in the subgrid within the predetermined value range, and Independent of the location of the grid disconnect switch (12), so much reactive power is provided (108b) by the additional converters (24, 26) that the voltage is maintained within the predetermined value range.

6. The operating method according to claim 5, wherein, The additional converters (24, 26) and the battery converter (20) provide reactive power such that the voltage at the decoupling reactor (16) in the subgrid is higher or lower than the voltage on the grid side.

7. The operating method according to any one of claims 5 or 6, wherein, The grid fault is determined by measuring devices and / or by disconnecting the grid disconnect switch (12).

8. The operating method according to any one of claims 5 to 7, wherein, The battery converter (20) and the other converters (24, 26) include regulation with different inertia from each other.

9. The operating method according to claim 8, wherein, The inertia of the battery converter (20) and the other converters (24, 26) differs in the setting of the magnitude inertia with respect to reactive power and in the setting of the phase inertia with respect to active power.

10. The operating method according to any one of the preceding claims, wherein, The regulation of the battery converter (20) has different inertia depending on the operating mode.

11. The operating method according to claim 10, wherein, In the event of a grid fault, the regulation of the battery converter (20) exhibits an increase in inertia in terms of both amplitude and phase inertia.

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