Control unit and method for managing idle time in battery energy storage system

Abstract

A control unit and method for managing idle time in a battery energy storage system, where the battery energy storage system includes a primary high voltage battery pack, an auxiliary battery pack, and a bidirectional DC-DC circuit connecting the primary high voltage battery pack and the auxiliary battery pack to facilitate energy transfer therebetween, and wherein the control unit is configured to: monitor an idle time and a state of charge (SoC) of the main high voltage battery pack, wherein the idle time reflects a time period during which the SoC remains unchanged; and initiate a charging alternating mode in response to the idle time of the primary high voltage battery pack exceeding a predetermined duration, wherein the charging alternating mode involves alternating between energy transfer from the primary high voltage battery pack to the secondary battery pack and energy transfer from the secondary battery pack to the primary high voltage battery pack.

Description

Technical Field

[0001] This disclosure generally relates to management strategies for battery energy storage systems. In a specific aspect, this disclosure relates to a control unit and method for managing idle time in a battery energy storage system. This disclosure is applicable to battery energy storage systems, such as those used for grid storage and other types of battery-powered applications. Although this disclosure may be described with respect to specific battery energy storage systems, it is not limited to any particular battery energy storage system. Background Technology

[0002] Battery energy storage systems (BESS) are used in a wide range of applications, including grid support, intermittent renewable energy, generator sets, and energy storage for electric vehicles and ships. A common problem with all these systems is the degradation of lithium-ion batteries, which is often exacerbated by the battery being idle at a high state of charge (SoC), thus adversely affecting battery life and overall performance.

[0003] Therefore, improved management strategies are needed to mitigate the negative impacts of prolonged idle periods, especially during high state of charge (SoC). These idle times, which are often unavoidable due to varying energy demands in applications such as grid storage and transportation, must be addressed to improve efficiency and extend the lifespan of battery storage systems. Summary of the Invention

[0004] According to a first aspect of this disclosure, a control unit for managing a battery energy storage system is disclosed. The battery energy storage system includes a main high-voltage battery pack, an auxiliary battery pack, and a bidirectional DC-DC circuit connecting the main high-voltage battery pack and the auxiliary battery pack to facilitate energy transfer between the two battery packs. The control unit is configured to monitor the idle time of the main high-voltage battery pack, wherein the idle time reflects a period of time during which the state of charge (SoC) remains constant. The control unit is also configured to initiate a charging alternation mode in response to the idle time of the main high-voltage battery pack exceeding a predetermined duration, wherein the charging alternation mode involves alternating between energy transfer from the main high-voltage battery pack to the auxiliary battery pack and energy transfer from the auxiliary battery pack to the main high-voltage battery pack. The first aspect of this disclosure seeks to extend battery life by actively managing the charge level of the main high-voltage battery. Technical advantages may include reducing battery performance degradation by preventing the SoC from remaining constant for extended periods.

[0005] Optionally, in some examples, including at least one preferred example, the predetermined duration depends on the SoC. Technical advantages may include the ability to adjust the predetermined duration to be shorter at high SoC levels (where degradation is more severe) and longer at low SoC levels (where degradation is less severe).

[0006] Optionally, in some examples, including at least one preferred example, the bidirectional DC-DC circuit includes: a first bidirectional DC-DC converter that connects the main high-voltage battery pack to a DC bus; and a second bidirectional DC-DC converter that connects the auxiliary battery pack to the DC bus, thereby facilitating energy transfer between the two battery packs via the DC bus. Technical advantages may include the ability to control the energy transfer between the two battery packs when they are connected via the DC bus.

[0007] Optionally, in some examples, including at least one preferred example, the bidirectional DC-DC circuit includes: a first bidirectional inverter that connects the main high-voltage battery pack to an AC bus; and a second bidirectional inverter that connects the auxiliary battery pack to the AC bus, thereby facilitating energy transfer between the two battery packs via the AC bus. Technical advantages may include the ability to control the energy transfer between the two battery packs when they are connected via the AC bus.

[0008] Optionally, in some examples, including at least one preferred example, the bidirectional DC-DC circuit includes: a first bidirectional DC-DC converter connecting the main high-voltage battery pack to a first DC bus; a first bidirectional inverter connecting the first DC bus to an AC bus; a second bidirectional DC-DC converter connecting the auxiliary battery pack to a second DC bus; and a second bidirectional inverter connecting the second DC bus to the AC bus, thereby facilitating energy transfer between the two battery packs via the first DC bus, the AC bus, and the second DC bus. Technical advantages may include the ability to control energy transfer between the two battery packs when they are connected via both the AC bus and the DC bus.

[0009] Optionally, in some examples, including at least one preferred example, the bidirectional DC-DC circuit includes multiple power converters to facilitate energy transfer between the two battery packs via one or more AC and / or DC buses.

[0010] Optionally, in some examples, including at least one preferred example, the battery storage system further includes a bidirectional inverter configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid and on-site electrical loads. The control unit is further configured to monitor AC grid data, including power demand indicators, and to switch to a grid-assisted charging alternation mode in response to the power demand indicators falling below a predetermined threshold. This grid-assisted charging alternation mode involves alternating between energy transfer from the AC grid to the main high-voltage battery and energy transfer from the main high-voltage battery to the on-site electrical loads. Technical advantages may include improved grid stability during periods of low demand, in addition to reducing battery degradation.

[0011] Optionally, in some examples, including at least one preferred example, the battery storage system further includes a bidirectional inverter configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid and field electrical loads. The control unit is further configured to switch to a grid-assisted charging alternating mode in response to the SoC dropping below a predetermined SoC threshold. Technical advantages may include improved system reliability by avoiding extremely low SoC levels.

[0012] Optionally, in some examples, including at least one preferred example, the field electrical load includes a heating, ventilation, and air conditioning (HVAC) system configured to maintain an optimal temperature range within the battery energy storage system. Technical advantages may include utilizing discharge cycles to maintain the optimal temperature range within the battery energy storage system.

[0013] Optionally, in some examples, including at least one preferred example, the control unit is configured to initiate a discharge cycle of the main high-voltage battery pack in response to, for example, power demand from the AC grid. The control unit can also be configured to initiate a charging cycle of the main high-voltage battery pack based on AC grid conditions. Technical advantages may include improved grid stability by coordinating charging and discharging cycles according to the AC grid conditions.

[0014] Optionally, in some examples, including at least one preferred example, the battery energy storage system further includes a generator. The control unit is configured to switch to a generator-assisted charging alternation mode in response to a drop in the System of Computation (SoC) below a predetermined SoC threshold. This generator-assisted charging alternation mode involves alternating between energy transfer from the generator to the main high-voltage battery and energy transfer from the main high-voltage battery to the field electrical load. Technical advantages may include reduced reliance on auxiliary battery packs, as the generator (e.g., a fuel cell, solar array, or internal combustion engine generator) can support energy transfer to the main high-voltage battery pack.

[0015] According to a second aspect of this disclosure, a battery energy storage system is disclosed. The battery energy storage system includes: a main high-voltage battery pack; an auxiliary battery pack; and a bidirectional DC-DC circuit connected to the main high-voltage battery pack and the auxiliary battery pack and configured to facilitate energy transfer between the two battery packs; and a control unit according to a first aspect of this disclosure. The second aspect of this disclosure seeks to extend battery life by actively managing the charging level of the main high-voltage battery. Technical advantages may include reducing battery performance degradation by preventing the SoC from remaining unchanged over long periods.

[0016] Optionally, in some examples, including at least one preferred example, the battery energy storage system further includes a bidirectional inverter configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid and on-site electrical loads. Technical advantages may include improved grid stability during periods of low demand, in addition to reducing battery degradation.

[0017] Optionally, in some examples, including at least one preferred example, the battery energy storage system further includes a generator. Technical advantages may include reduced reliance on auxiliary battery packs, as the generator (e.g., a fuel cell, solar array, or internal combustion engine generator) can support energy transfer to the main high-voltage battery pack.

[0018] According to a third aspect of this disclosure, a method for managing a battery energy storage system is disclosed. The battery energy storage system includes a main high-voltage battery pack, an auxiliary battery pack, and a bidirectional DC-DC circuit connecting the main high-voltage battery pack and the auxiliary battery pack to facilitate energy transfer between the two battery packs. The method includes monitoring, S1, an idle time of the main high-voltage battery pack, wherein the idle time reflects a period of time during which the state of charge (SoC) remains constant. The method also includes initiating, S2, a charging alternation mode in response to the idle time of the main high-voltage battery pack exceeding a predetermined duration, wherein the charging alternation mode involves alternating between energy transfer from the main high-voltage battery pack to the auxiliary battery pack and energy transfer from the auxiliary battery pack to the main high-voltage battery pack. The third aspect of this disclosure seeks to extend battery life by actively managing the charge level of the main high-voltage battery. Technical advantages may include reducing battery performance degradation by preventing the SoC from remaining constant for extended periods.

[0019] Optionally, in some examples, including at least one preferred example, the predetermined duration depends on the SoC. Technical advantages may include the ability to adjust the predetermined duration to be shorter at high SoC levels (where degradation is more severe) and longer at low SoC levels (where degradation is less severe).

[0020] Optionally, in some examples, including at least one preferred example, the bidirectional DC-DC circuit includes: a first bidirectional DC-DC converter that connects the main high-voltage battery pack to a DC bus; and a second bidirectional DC-DC converter that connects the auxiliary battery pack to the DC bus, thereby facilitating energy transfer between the two battery packs via the DC bus. Technical advantages may include the ability to control the energy transfer between the two battery packs when they are connected via the DC bus.

[0021] Optionally, in some examples, including at least one preferred example, the bidirectional DC-DC circuit includes: a first bidirectional inverter that connects the main high-voltage battery pack to an AC bus; and a second bidirectional inverter that connects the auxiliary battery pack to the AC bus, thereby facilitating energy transfer between the two battery packs via the AC bus. Technical advantages may include the ability to control the energy transfer between the two battery packs when they are connected via the AC bus.

[0022] Optionally, in some examples, including at least one preferred example, the bidirectional DC-DC circuit includes: a first bidirectional DC-DC converter connecting the main high-voltage battery pack to a first DC bus; a first bidirectional inverter connecting the first DC bus to an AC bus; a second bidirectional DC-DC converter connecting the auxiliary battery pack to a second DC bus; and a second bidirectional inverter connecting the second DC bus to the AC bus, thereby facilitating energy transfer between the two battery packs via the first DC bus, the AC bus, and the second DC bus. Technical advantages may include the ability to control energy transfer between the two battery packs when they are connected via both the AC bus and the DC bus.

[0023] Optionally, in some examples, including at least one preferred example, the bidirectional DC-DC circuit includes multiple power converters to facilitate energy transfer between the two battery packs via one or more AC and / or DC buses. Technical advantages may include the ability to control the energy transfer between the two battery packs when they are connected via one or more AC and / or DC buses.

[0024] Optionally, in some examples, including at least one preferred example, the battery energy storage system further includes a bidirectional inverter configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid and on-site electrical loads. The method further includes monitoring AC grid conditions, including power demand indicators; and switching to a grid-assisted charging alternation mode in response to the power demand indicator falling below a predetermined threshold, wherein the grid-assisted charging alternation mode alternates between energy transfer from the AC grid to the main high-voltage battery and energy transfer from the main high-voltage battery to the on-site electrical loads. Technical advantages may include improved grid stability during low-demand periods, in addition to reducing battery degradation.

[0025] Optionally, in some examples, including at least one preferred example, the battery storage system further includes a bidirectional inverter configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid and field electrical loads. The method further includes switching S4-B to the grid-assisted charging alternating mode in response to the SoC dropping below a predetermined SoC threshold. Technical advantages may include improved system reliability by avoiding extremely low SoC levels.

[0026] Optionally, in some examples, including at least one preferred example, the method further includes initiating a discharge cycle of the main high-voltage battery pack in response to, for example, power demand from the AC grid. The method may also include initiating a charging cycle of the main high-voltage battery pack based on the AC grid conditions. Technical advantages may include improved grid stability by coordinating charging and discharging cycles according to the AC grid conditions.

[0027] Optionally, in some examples, including at least one preferred example, the battery energy storage system further includes a generator, and the method further includes switching to a generator-assisted charging alternation mode in response to a drop in the SoC below a predetermined SoC threshold. This generator-assisted charging alternation mode involves alternating between energy transfer from the generator to the main high-voltage battery and energy transfer from the main high-voltage battery to the field electrical load. Technical advantages may include reduced reliance on auxiliary battery packs, as the generator (e.g., a fuel cell, solar cell array, or internal combustion engine generator) can support energy transfer to the main high-voltage battery pack.

[0028] Those skilled in the art will understand that the disclosed aspects, examples (including any preferred examples), and / or appended claims can be appropriately combined with each other. Additional features and advantages are disclosed in the following description, claims, and drawings, and will be apparent in part to those skilled in the art or recognized by practicing this disclosure as described herein.

[0029] This document also discloses computer systems, control units, code modules, computer-implemented methods, computer-readable media, and computer program products related to the technical advantages discussed above. Attached Figure Description

[0030] The examples are described in more detail below with reference to the accompanying drawings.

[0031] Figure 1 An example of a battery energy storage system is shown, which includes a main high-voltage battery pack, an auxiliary battery pack, a bidirectional DC-DC circuit, and a control unit.

[0032] Figure 2 An example is shown. Figure 1 The battery energy storage system further includes a bidirectional inverter configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid.

[0033] Figure 3A An example is shown. Figure 1 A battery energy storage system having a bidirectional DC-DC circuit, which includes two bidirectional DC-DC converters connected via a DC bus.

[0034] Figure 3B An example is shown. Figure 1 The battery energy storage system has a bidirectional DC-DC circuit, which includes two bidirectional inverters connected via an AC bus.

[0035] Figure 3C An example is shown. Figure 1 The battery energy storage system has a bidirectional DC-DC circuit, which includes two bidirectional DC-DC converters that connect the main battery and the auxiliary battery to two DC buses and two bidirectional inverters that connect the two DC buses to a common AC bus.

[0036] Figure 4 This is a flowchart of a method for managing battery energy storage systems.

[0037] Figure 5A The control unit is shown schematically.

[0038] Figure 5B An example of a computer program product is shown.

[0039] Figure 6 This is a schematic diagram of an exemplary computer system for implementing the examples disclosed herein, based on examples. Detailed Implementation

[0040] The detailed description set forth below provides information and examples of the disclosed technology in sufficient detail to enable those skilled in the art to practice this disclosure.

[0041] Figure 1 Figures 3 to 3 illustrate a first aspect of the present disclosure, which relates to a control unit 110 for managing battery energy storage systems 100, 200.

[0042] Figure 1 A control unit 110 is shown for managing battery energy storage systems 100 and 200, which include a main high-voltage battery pack 120, an auxiliary battery pack 140, and a bidirectional DC-DC circuit 130 connecting the main high-voltage battery pack 120 and the auxiliary battery pack 140 to facilitate energy transfer between the two battery packs. While the main high-voltage battery 120 is typically a lithium-ion battery pack with an output voltage between 300 volts and 800 volts, the output voltage may exceed this range depending on the specific design and requirements of the battery energy storage systems 100 and 200. The main high-voltage battery 120 is configured to store and provide electrical energy when needed. The auxiliary battery pack 140 can be a low-voltage or high-voltage battery. The bidirectional DC-DC circuit 130 converts the output voltages of the main high-voltage battery 120 and the auxiliary battery pack 140, thereby regulating the direction of energy transfer. This allows the bidirectional DC-DC circuit 130 to precisely control the charging and discharging current of the main high-voltage battery 120, ensuring efficient energy management and optimal system performance. It should be noted that if the main high-voltage battery pack 120 and the auxiliary battery pack 140 are directly connected without an AC or DC bus, the bidirectional DC-DC circuit 130 can be any type of bidirectional converter. However, if the batteries are connected via a bus, multiple power converters may be required, as discussed in later paragraphs.

[0043] Control unit 110 is configured to monitor the idle time of main high-voltage battery pack 120, where the idle time reflects the period during which the state of charge (SoC) remains constant. The SoC is typically obtained from the battery management system (BMS) of main high-voltage battery pack 120. Similarly, the idle time may also be obtained from the BMS, or calculated by control unit 110 by monitoring the duration for which the SoC is in a state that is neither charging nor discharging.

[0044] In response to the main high-voltage battery pack 120 being idle for an extended period, the control unit 110 is configured to initiate a charging alternation mode, wherein the charging alternation mode involves alternating between energy transfer from the main high-voltage battery pack 120 to the auxiliary battery pack 140 and energy transfer from the auxiliary battery pack 140 to the main high-voltage battery pack 120. This predetermined duration can vary significantly depending on the requirements of the battery storage systems 100, 200 and the frequency of charge and discharge cycles. For example, the duration for which the energy storage system remains in an idle mode is typically described by the storage ratio, which is defined as the sum of all idle time intervals over a specified time interval (e.g., 24 hours). For example, if the system remains idle for 12 hours per day, the storage ratio would be 50%. In some examples, it may also be required to maintain at least 50% storage ratio per day. Ideally, especially at high SoC levels, the storage ratio should be minimized to reduce degradation. However, factors such as electricity prices and load demand typically affect the duration of charging and discharging, and consequently, the storage ratio. Therefore, the storage ratio requirement and the frequency of charge and discharge cycles typically determine the predetermined duration, which can range from several minutes to several hours.

[0045] The predetermined duration can be fixed or it can vary depending on the SoC. The advantage of varying the predetermined duration based on the SoC is that it allows for shorter durations at higher SoC levels where battery degradation occurs more quickly, and longer durations at lower SoC levels where battery degradation is less severe.

[0046] In some examples, the battery energy storage systems 100, 200 further include a bidirectional inverter 250 configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid 260. The bidirectional inverter 250 converts the DC output voltage of the main high-voltage battery 120 and the AC voltage of the AC grid 260, thereby allowing precise regulation of energy flow in both directions.

[0047] Battery energy storage systems 100 and 200 may also include one or more electrical loads 170 that can be connected to an AC or DC bus. One or more electrical loads can be utilized during energy transfer from the main high-voltage battery 120 in grid-assisted charging alternating mode. In one example, one or more field electrical loads 270 include a heating, ventilation, and air conditioning (HVAC) system configured to maintain an optimal temperature range within the battery energy storage system.

[0048] The control unit 110 is further configured to monitor the AC grid condition, including power demand indicators, and to switch to a grid-assisted charging alternation mode in response to the power demand indicator falling below a predetermined threshold. The power demand indicator can be any metric reflecting the real-time balance between generation and demand. The predetermined threshold is set to ensure that the grid-assisted charging alternation mode is activated only when the AC grid power demand is sufficiently low, thereby maintaining grid stability. The grid-assisted charging alternation mode involves alternating between energy transfer from the AC grid 260 to the main high-voltage battery 120 and energy transfer from the main high-voltage battery 120 to the field electrical load 270. Sometimes, switching to the grid-assisted charging alternation mode has the advantage of providing operational benefits during periods of low demand when excess energy from the AC grid needs to be absorbed into the battery storage system or other energy storage solutions. Therefore, this approach not only reduces battery degradation but also helps maintain grid stability.

[0049] In some examples, battery storage systems 100, 200, and control unit 110 may also be configured to switch to the grid-assisted charging alternation mode in response to the SoC dropping below a predetermined SoC threshold. This ensures that the SoC does not drop to extremely low levels, thereby enhancing system reliability. For example, in one example, the predetermined SoC threshold may be set to 20% to ensure system reliability. However, this threshold can vary considerably depending on the specific storage requirements and capacity of battery storage systems 100, 200. Additionally, in some examples, the charging alternation mode may cease once the optimal storage SoC level (typically around 30% to 40%) is reached. In some examples, control unit 110 may be further configured to terminate the charging alternation mode in response to initiated use of the main high-voltage battery pack 120 (such as when the battery pack 120 needs to supply power to an external load).

[0050] In some examples, control unit 110 can be configured to initiate a discharge cycle of the main high-voltage battery pack 120 in response to power demand, such as from the AC grid. Control unit 110 can also initiate a charging cycle of the main high-voltage battery pack 120 based on AC grid conditions. The advantage of this approach is improved grid stability by coordinating charging and discharging cycles according to AC grid conditions.

[0051] In some examples, the battery energy storage systems 100, 200 further include a generator. The control unit can be configured to switch to a generator-assisted charging alternation mode in response to a drop in the System Capacity (SoC) below a predetermined SoC threshold. The generator-assisted alternation mode involves alternating between energy transfer from the generator to the main high-voltage battery 120 and energy transfer from the main high-voltage battery 120 to the field electrical load 270. The generator can be a fuel cell, a solar array, an internal combustion engine generator, or any other type of power source. The advantage of this approach is reduced reliance on auxiliary battery packs, as the generator can assist in transferring energy to the main high-voltage battery pack, thus providing additional support when needed.

[0052] Figures 3A to 3C The implementation of the bidirectional DC-DC circuit 130 is of particular interest when the main high-voltage battery pack 120 and the auxiliary battery pack 140 are connected via a bus. Typically, a DC or AC bus maintains a fixed voltage, thus requiring multiple power converters when two battery packs are connected via the bus. Therefore, in the general case of energy transfer via the bus, the bidirectional DC-DC circuit 130 includes multiple power converters to facilitate energy transfer between the two battery packs 120 and 140.

[0053] Figure 3A It shows Figure 1 The battery energy storage system includes two battery packs 120 and 140 connected via a DC bus. A bidirectional DC-DC circuit 130 includes a first bidirectional DC-DC converter 321 that connects the main high-voltage battery pack 120 to the DC bus DC1; and a second bidirectional DC-DC converter 341 that connects the auxiliary battery pack 140 to the DC bus DC1, thereby facilitating energy transfer between the two battery packs 120 and 140 via the DC bus DC1. This implementation is particularly useful in multi-battery systems where multiple battery packs are connected via a DC bus. In such cases, one of the battery packs can be designated as the auxiliary battery 140, and this designation can be dynamically reallocated to other battery packs as needed. Therefore, any battery pack can assume the role of the auxiliary battery pack 140 at any time, enabling more flexible and adaptive management of the battery energy storage system.

[0054] Figure 3B An example is shown. Figure 1The battery energy storage system includes two battery packs 120 and 140 connected via an AC bus. A bidirectional DC-DC circuit 130 includes a first bidirectional inverter 322 that connects the main high-voltage battery pack 120 to the AC bus AC1; and a second bidirectional inverter 342 that connects the auxiliary battery pack 140 to the AC bus AC1, thereby facilitating energy transfer between the two battery packs 120 and 140 via the AC bus AC1. This implementation is particularly useful in multi-battery systems where multiple battery packs are connected via an AC bus. In such cases, one of the battery packs can be designated as the auxiliary battery 140, and this designation can be dynamically redistributed to other battery packs as needed. Therefore, any battery pack can assume the role of the auxiliary battery pack 140 at any time, enabling more flexible and adaptive management of the battery energy storage system.

[0055] Figure 3C It shows Figure 1 The battery energy storage system includes two battery packs 120 and 140 connected via two DC buses and a common AC bus. The bidirectional DC-DC circuit 130 includes: a first bidirectional DC-DC converter 321 connecting the main high-voltage battery pack 120 to a first DC bus DC1; a first bidirectional inverter connecting the first DC bus DC1 to the AC bus AC1; a second bidirectional DC-DC converter 341 connecting the auxiliary battery pack 140 to a second DC bus DC2; and a second bidirectional inverter connecting the second DC bus DC2 to the AC bus AC1, thereby facilitating energy transfer between the two battery packs 120 and 140 via the first DC bus DC1, the AC bus AC1, and the second DC bus DC2. This implementation is particularly useful in multi-battery systems where multiple battery packs are connected via a common AC bus.

[0056] Figure 1 Figure 3 also shows a second aspect of the present disclosure, which relates to battery energy storage systems 100 and 200. Figure 1 Battery energy storage systems 100 and 200 are shown. The battery energy storage systems 100 and 200 include: a main high-voltage battery pack 120; an auxiliary battery pack 140; a bidirectional DC-DC circuit connecting the main high-voltage battery pack 120 and the auxiliary battery pack 140 and configured to facilitate energy transfer between the two battery packs; and a control unit according to a first aspect of this disclosure. Figure 2The battery energy storage systems 100 and 200 are shown to further include a bidirectional inverter 250 configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid 260. In some examples, the battery energy storage systems 100 and 200 may further include a generator, such as a fuel cell, a solar cell array, or an internal combustion engine generator. It should be noted that any of the foregoing aspects associated with the control unit 110 also apply to the battery energy storage systems 100 and 200.

[0057] Figure 4 A third aspect of this disclosure is illustrated, relating to a method for managing battery energy storage systems 100, 200. The method includes monitoring an idle time S1 and initiating a charging alternation mode S2. Any of the foregoing aspects relating to the control unit 110 and the battery energy storage systems 100, 200 are also applicable to this method.

[0058] The method includes monitoring the idle time and state of charge (SoC) of the main high-voltage battery pack 120, wherein the idle time reflects the period during which the SoC remains constant. The SoC is typically obtained directly from the battery management system (BMS) of the main high-voltage battery pack 120. Alternatively, the idle time can be obtained directly from the BMS or indirectly by determining the duration for which the SoC is in a state that is neither charging nor discharging.

[0059] The method also includes initiating a S2 charging alternation mode in response to the idle time of the main high-voltage battery pack 120 exceeding a predetermined duration, wherein the charging alternation mode involves alternating between energy transfer from the main high-voltage battery pack 120 to the auxiliary battery pack 140 and energy transfer from the auxiliary battery pack 140 to the main high-voltage battery pack 120. As previously described, the predetermined duration can vary significantly depending on the requirements of the battery storage systems 100, 200 and the frequency of charge and discharge cycles. In some examples, the predetermined duration can be fixed or can vary depending on the SoC. The advantage of varying the predetermined duration based on the SoC is that it allows for a shorter duration at higher SoC levels where battery degradation occurs more rapidly and a longer duration at lower SoC levels where battery degradation is less severe.

[0060] In some examples, the main high-voltage battery pack 120 and the auxiliary battery pack 140 are connected via a DC bus or an AC bus. Typically, the DC or AC bus maintains a fixed voltage, thus requiring multiple power converters when the two battery packs are connected via the bus. Therefore, in the general case of energy transfer via the bus, the bidirectional DC-DC circuit 130 includes multiple power converters to facilitate energy transfer between the two battery packs 120, 140. It should be noted that any of the foregoing aspects related to the implementation of the bidirectional DC-DC circuit 130 also applies to the third aspect of this disclosure.

[0061] In some examples, battery storage systems 100, 200 further include a bidirectional inverter 250 configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid 260 and field electrical loads 270. The method further includes monitoring the AC grid condition (S3), which includes a power demand indicator; and switching (S4-A) to a grid-assisted charging alternation mode in response to the power demand indicator falling below a predetermined threshold. This grid-assisted charging alternation mode alternates between energy transfer from the AC grid 260 to the main high-voltage battery 120 and energy transfer from the main high-voltage battery 120 to the field electrical loads 270. Sometimes, switching to the grid-assisted charging alternation mode has the advantage of providing operational benefits during periods of low demand when excess energy from the AC grid needs to be absorbed into the battery storage system or other energy storage solutions. Therefore, this approach not only reduces battery degradation but also helps maintain grid stability.

[0062] In some examples, battery storage systems 100, 200 further include a bidirectional inverter 250 configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid 260 and field electrical loads 270. The method further includes switching S4-B to the grid-assisted charging alternation mode in response to the SoC dropping below a predetermined SoC threshold. This ensures that the SoC does not drop to extremely low levels, thereby enhancing system reliability. For example, in one example, the predetermined SoC threshold may be set to 20% to ensure system reliability. However, this threshold can vary considerably depending on the specific storage requirements and capacity of the battery storage systems 100, 200. Additionally, in some examples, the charging alternation mode may cease once the optimal storage SoC level (typically around 30% to 40%) is reached. In some examples, the method may further include terminating the charging alternation mode in response to initiated use of the main high-voltage battery pack 120 (such as when the battery pack 120 needs to supply power to an external load).

[0063] In some examples, including at least one preferred example, the method further includes initiating a discharge cycle of the main high-voltage battery pack 120 in response to, for example, power demand from the AC grid. The method may also include initiating a charging cycle of the main high-voltage battery pack 120 based on AC grid conditions. The advantage of this method is that it improves grid stability by coordinating charging and discharging cycles according to AC grid conditions.

[0064] In some examples, the battery storage systems 100 and 200 further include a generator, and the method further includes switching to a generator-assisted charging alternation mode in response to a drop in the System of Computation (SoC) below a predetermined SoC threshold. This generator-assisted charging alternation mode involves alternating between energy transfer from the generator to the main high-voltage battery 120 and energy transfer from the main high-voltage battery 120 to the field electrical load 270. The generator can be a fuel cell, a solar array, an internal combustion engine generator, or any other type of power source. The advantage of this approach is reduced reliance on auxiliary battery packs, as the generator can assist in transferring energy to the main high-voltage battery pack, thus providing additional support when needed.

[0065] Figure 5A The components of a control unit 110, representing aspects of the discussion and methods disclosed herein, are schematically shown in terms of multiple functional units. This control unit 110 may generally be included in battery energy storage systems 100, 200. Processing circuitry 510 is provided using any combination of one or more suitable central processing units such as CPUs, multiprocessors, microcontrollers, digital signal processors (DSPs), etc., capable of executing software instructions stored in a computer program product, for example, in the form of a storage medium 520. Processing circuitry 510 may further be provided as at least one application-specific integrated circuit (ASIC) or field-programmable gate array (FPGA).

[0066] Specifically, the processing circuit 510 is configured to cause the control unit 110 to perform a set of operations or steps, such as the method discussed in conjunction with FIG3. For example, the storage medium 520 may store the set of operations, and the processing circuit 510 may be configured to retrieve the set of operations from the storage medium 520 to cause the control unit 110 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuit 510 is thereby arranged to perform the methods disclosed herein.

[0067] Storage medium 520 may also include a permanent storage device, which may be, for example, any or a combination of magnetic storage, optical storage, solid-state storage, or even remotely mounted storage.

[0068] The control unit 110 may further include an interface 530 for communicating with at least one external system, such as a main high-voltage battery pack 120, an auxiliary battery pack 140, a bidirectional DC-DC circuit 130, a bidirectional inverter 250, an AC grid 260, etc. Thus, the interface 530 may include one or more transmitters and receivers, including analog and digital components, and a suitable number of ports for wired or wireless communication.

[0069] Processing circuitry 510 controls the general operation of control unit 110 (e.g., by sending data and control signals to interface 530 and storage medium 520, by receiving data and reports from interface 530, and by retrieving data and instructions from storage medium 520). Other components of the control node and their related functionality are omitted to avoid obscuring the concepts presented herein.

[0070] Figure 5B An example of a computer program product is shown. A computer-readable medium 560 carrying a computer program 570 includes program code means for performing the steps of the methods described above when the program product is run on a computer or on the processing circuitry 510 of the control unit 110.

[0071] Figure 6 This is a schematic diagram of a computer system 600 for implementing the examples disclosed herein. The computer system 600 is adapted to execute instructions from a computer-readable medium to perform these and / or any of the functions or processes described herein. The computer system 600 may be connected (e.g., networked) to other machines in a LAN (Local Area Network), LIN (Local Internet Protocol), automotive network communication protocols (e.g., FlexRay), intranet, extranet, or the Internet. Although only a single device is shown, the computer system 600 may include any collection of devices that individually or jointly execute a set (or more sets) of instructions to perform any or more of the methods discussed herein. Therefore, any reference in this disclosure and / or claims to computer systems, computing systems, computer devices, computing apparatus, control systems, control units, electronic control units (ECUs), processor devices, processing circuitry, etc., includes references to one or more such devices to individually or jointly execute a set (or more sets of instructions) to perform any or more of the methods discussed herein. For example, a control system may include a single control unit or multiple control units connected to or otherwise communicatively coupled to each other, such that any functions performed can be distributed among the control units as needed. Furthermore, such devices can communicate with each other or with other devices through various system architectures, such as directly or via a controller area network (CAN) bus.

[0072] Computer system 600 may include at least one computing device or electronic device capable of including firmware, hardware, and / or executing software instructions to implement the functionality described herein. Computer system 600 may include processing circuitry 602 (e.g., processing circuitry including one or more processor devices or control units), memory 604, and system bus 606. Computer system 600 may include at least one computing device having processing circuitry 602. System bus 606 provides an interface for system components (including, but not limited to, memory 604 and processing circuitry 602). Processing circuitry 602 may include any number of hardware components for performing data or signal processing or for executing computer code stored in memory 604. Processing circuitry 602 may, for example, include a general-purpose processor, a special-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), circuitry containing processing components, a set of distributed processing components, a set of distributed computers configured to perform processing, or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. Processing circuitry 602 may also include computer-executable code that controls the operation of the programmable device.

[0073] System bus 606 can be any of several types of bus architectures, which can further interconnect to a memory bus (with or without a memory controller), a peripheral bus, and / or a local bus using any of a variety of bus architectures. Memory 604 can be one or more means for storing data and / or computer code to perform or facilitate the methods described herein. Memory 604 may include database components, object code components, script components, or other types of information structures for supporting the various activities described herein. Any distributed or local memory device may be used in conjunction with the systems and methods of this specification. Memory 604 may be communicatively connected to processing circuitry 602 (e.g., via circuitry or any other wired, wireless, or network connection) and may include computer code for performing one or more processes described herein. Memory 604 may include non-volatile memory 608 (e.g., read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), etc.) and volatile memory 610 (e.g., random access memory (RAM)), or any other medium that can be used to carry or store desired program code in the form of machine-executable instructions or data structures and can be accessed by a computer or other machine having processing circuitry 602. Basic Input / Output System (BIOS) 612 may be stored in non-volatile memory 608 and may include basic routines that facilitate the transfer of information between elements within computer system 600.

[0074] Computer system 600 may also include or be coupled to a non-transitory computer-readable storage medium such as storage device 614, which may include, for example, an internal or external hard disk drive (HDD) (e.g., Enhanced Integrated Drive Electronics (EIDE) or Serial Advanced Technology Accessory (SATA)), an HDD for storage (e.g., EIDE or SATA), flash memory, etc. Storage device 614 and other drives associated with computer-readable and computer-usable media can provide non-volatile storage of data, data structures, computer-executable instructions, etc.

[0075] Hard-coded or soft-coded computer code may be provided in the form of one or more modules. Modules may be implemented as software and / or hard-coded in circuitry to fully or partially implement the functionality described herein. These modules may be stored in storage device 614 and / or volatile memory 610, which may include operating system 616 and / or one or more program modules 618. All or part of the examples disclosed herein may be implemented as a computer program 620 stored on a transient or non-transitory computer-usable or computer-readable storage medium (e.g., a single medium or multiple media) such as storage device 614, which includes complex programming instructions (e.g., complex computer-readable program code) that cause processing circuitry 602 to perform the actions described herein. Thus, the computer-readable program code of computer program 620 may include software instructions for implementing the functionality of the examples described herein when executed by processing circuitry 602. In some examples, storage device 614 may be a computer program product (e.g., a readable storage medium) on which computer program 620 is stored, wherein at least a portion of computer program 620 may be loadable (e.g., loaded into a processor) for implementing the functionality of the examples described herein when executed by processing circuitry 602. Processing circuitry 602 may serve as a controller or control system for implementing the functionality of computer system 600 described herein.

[0076] Computer system 600 may include an input device interface 622 configured to receive input and selections to be transmitted to computer system 600, such as from a keyboard, mouse, touch-sensitive surface, etc., when executing instructions. Such input devices can be connected to processing circuitry 602 via input device interface 622 coupled to system body 606, but can also be connected via other interfaces, such as parallel ports, IEEE 1394 serial ports, Universal Serial Bus (USB) ports, IR interfaces, etc. Computer system 600 may include an output device interface 624 configured to forward output to, for example, a display, video display unit (e.g., a liquid crystal display (LCD) or cathode ray tube (CRT)). Computer system 600 may include a communication interface 626 suitable for communicating with a network, as needed or as required.

[0077] The actions described in any exemplary aspect of this document are described to provide examples and discussion. These actions may be performed by hardware components, may be embodied in machine-executable instructions to cause a processor to perform these actions, or may be performed by a combination of hardware and software. Although a particular order of method actions may be shown or described, the order of actions may differ. Furthermore, two or more actions may be performed simultaneously or partially simultaneously.

[0078] Example 1: A control unit 110 for managing a battery energy storage system 100, wherein the battery energy storage system 100, 200 includes: a main high-voltage battery pack 120, an auxiliary battery pack 140, and a bidirectional DC-DC circuit connecting the main high-voltage battery pack 120 and the auxiliary battery pack 140 to facilitate energy transfer between the two battery packs; and wherein the control unit 110 is configured to: monitor the idle time and state of charge (SoC) of the main high-voltage battery pack 120, wherein the idle time reflects a period of time during which the SoC remains unchanged; and initiate a charging alternation mode in response to the idle time of the main high-voltage battery pack 120 exceeding a predetermined duration, wherein the charging alternation mode involves alternating between energy transfer from the main high-voltage battery pack 120 to the auxiliary battery pack 140 and energy transfer from the auxiliary battery pack 140 to the main high-voltage battery pack 120.

[0079] Example 2: Control unit 110 as described in Example 1, wherein the predetermined duration depends on the SoC of the main high voltage battery pack 120.

[0080] Example 3: The control unit 110 as described in any one of Examples 1 to 2, wherein the bidirectional DC-DC circuit 130 includes: a first bidirectional DC-DC converter 321 that connects the main high-voltage battery pack 120 to the DC bus DC1; and a second bidirectional DC-DC converter 341 that connects the auxiliary battery pack 140 to the DC bus DC1, thereby facilitating energy transfer between the two battery packs 120 and 140 via the DC bus DC1.

[0081] Example 4: The control unit 110 as described in any one of Examples 1 to 2, wherein the bidirectional DC-DC circuit 130 includes: a first bidirectional inverter 322 that connects the main high-voltage battery pack 120 to the AC bus AC1; and a second bidirectional inverter 342 that connects the auxiliary battery pack 140 to the AC bus AC1, thereby facilitating energy transfer between the two battery packs 120 and 140 via the AC bus AC1.

[0082] Example 5: The control unit 110 as described in any one of Examples 1 to 2, wherein the bidirectional DC-DC circuit 130 includes: a first bidirectional DC-DC converter 321 that connects the main high-voltage battery pack 120 to a first DC bus DC1; a first bidirectional inverter 322 that connects the first DC bus DC1 to an AC bus AC1; a second bidirectional DC-DC converter 341 that connects the auxiliary battery pack 140 to a second DC bus DC2; and a second bidirectional inverter 342 that connects the second DC bus DC2 to an AC bus AC1, thereby facilitating energy transfer between the two battery packs 120 and 140 via the first DC bus DC1, the AC bus AC1, and the second DC bus DC2.

[0083] Example 6: The control unit 110 as described in any one of Examples 1 to 5, wherein the battery energy storage system 100, 200 further includes a bidirectional inverter 250 configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid 260 and the field electrical load 270, wherein the control unit 110 is further configured to: monitor the AC grid condition, wherein the AC grid condition includes a power demand indicator; and switch to a grid-assisted charging alternation mode in response to the power demand indicator being lower than a predetermined threshold, wherein the grid-assisted charging alternation mode involves alternating between energy transfer from the AC grid 260 to the main high-voltage battery 120 and energy transfer from the main high-voltage battery 120 to the field electrical load 270.

[0084] Example 7: Control unit 110 as described in any one of Examples 1 to 6, wherein the battery energy storage system 100, 200 further includes a bidirectional inverter 250 configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid 260 and the field electrical load 270, wherein the control unit 110 is further configured to switch to the grid-assisted charging alternating mode in response to the SoC falling below a predetermined SoC threshold.

[0085] Example 8: Control unit 110 as described in any one of Examples 6 to 7, wherein the one or more field electrical loads 270 include a heating, ventilation and air conditioning (HVAC) system configured to maintain an optimal temperature range within the battery energy storage system 100, 200.

[0086] Example 9: Control unit 110 as described in any one of Examples 1 to 8, wherein the battery energy storage system 100, 200 further includes a generator, and wherein the control unit 110 is further configured to switch to a generator-assisted charging alternation mode in response to the SoC falling below a predetermined SoC threshold, wherein the generator-assisted charging alternation mode involves alternating between energy transfer from the generator to the main high-voltage battery 120 and energy transfer from the main high-voltage battery 120 to the field electrical load 270.

[0087] Example 10: A battery energy storage system 100, 200, wherein the battery energy storage system 100, 200 includes: a main high-voltage battery pack 120; an auxiliary battery pack 140; a bidirectional DC-DC circuit that connects the main high-voltage battery pack 120 to the auxiliary battery pack 140 and is configured to facilitate energy transfer between the two battery packs; and a control unit according to Example 1.

[0088] Example 11: Battery energy storage system 100, 200 as described in Example 10, wherein the battery energy storage system 100, 200 further includes: a bidirectional inverter 250 configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid 260 and the field electrical load 270; and a control unit according to any one of Examples 1 to 8.

[0089] Example 12: A battery energy storage system 100, 200 as described in any one of Examples 10 to 11, wherein the battery energy storage system 100, 200 further includes a generator and a control unit according to any one of Examples 1 to 9.

[0090] Example 13: A method for managing a battery energy storage system 100, 200, wherein the battery energy storage system 100, 200 includes: a main high-voltage battery pack 120, an auxiliary battery pack 140, and a bidirectional DC-DC circuit 130, the bidirectional DC-DC circuit connecting the main high-voltage battery pack 120 and the auxiliary battery pack 140 to facilitate energy transfer between the two battery packs; and wherein the method includes: monitoring S1 an idle time of the main high-voltage battery pack 120, wherein the idle time reflects a period of time during which the state of charge (SoC) remains unchanged; and initiating S2 a charging alternation mode in response to the idle time of the main high-voltage battery pack 120 exceeding a predetermined duration, wherein the charging alternation mode involves alternating between energy transfer from the main high-voltage battery pack 120 to the auxiliary battery pack 140 and energy transfer from the auxiliary battery pack 140 to the main high-voltage battery pack 120.

[0091] Example 14: The method as described in Example 13, wherein the predetermined duration depends on the SoC of the main high-voltage battery pack 120.

[0092] Example 15: The method of any one of Examples 13 to 14, wherein the bidirectional DC-DC circuit 130 includes a plurality of power converters 321, 322, 341, 342 to facilitate energy transfer between the two battery packs 120, 140 via one or more AC and / or DC buses AC1, DC1, DC2.

[0093] Example 16: The method of any one of Examples 13 to 15, wherein the battery energy storage system 100, 200 further includes a bidirectional inverter 250 configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid 260 and the field electrical load 270, wherein the method further includes: monitoring the AC grid condition, wherein the AC grid condition includes a power demand indicator; and switching S4-A to a grid-assisted charging alternation mode in response to the power demand indicator being below a predetermined threshold, wherein the grid-assisted charging alternation mode alternates between energy transfer from the AC grid 260 to the main high-voltage battery 120 and energy transfer from the main high-voltage battery 120 to the field electrical load 270.

[0094] Example 17: The method of any one of Examples 13 to 16, wherein the battery energy storage system 100, 200 further includes a bidirectional inverter 250 configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid 260 and the field electrical load 270, wherein the method further includes: switching S4-B to the grid-assisted charging alternation mode in response to the SoC falling below a predetermined SoC threshold.

[0095] Example 18: The method of any one of Examples 13 to 17, wherein the battery energy storage system 100, 200 further includes a generator, and wherein the method further includes switching to a generator-assisted charging alternation mode in response to a drop in SoC below a predetermined SoC threshold, wherein the generator-assisted charging alternation mode involves alternating between energy transfer from the generator to the main high-voltage battery 120 and energy transfer from the main high-voltage battery 120 to the field electrical load 270.

[0096] Example 19: A computer program product comprising program code that, when executed by processing circuitry, performs the method described in any one of Examples 13 to 18.

[0097] Example 20: A non-transitory computer-readable storage medium including instructions that, when executed by processing circuitry, cause the processing circuitry to perform the method described in any one of Examples 13 to 18.

[0098] The terminology used herein is for descriptive purposes only and is not intended to limit this disclosure. As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” are intended to also include the plural forms. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. It should also be understood that the terms “comprising” and / or “including” as used herein indicate the presence of the stated features, integers, actions, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components, and / or groups thereof.

[0099] It should be understood that although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of this disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0100] In this document, relative terms such as “below,” “above,” “upper,” “lower,” “horizontal,” or “vertical” may be used to describe the relationship between one element and another, as illustrated in the figures. It should be understood that these terms, along with those discussed above, are intended to cover different device orientations in addition to those depicted in the figures. It should be understood that when an element is referred to as “connected” or “coupled” to another element, the element may be directly connected or coupled to the other element, or there may be intermediate elements present. In contrast, when an element is referred to as “directly connected” or “directly coupled” to another element, there are no intermediate elements present.

[0101] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It should also be understood that, unless expressly defined herein, terms used herein shall be interpreted as having the same meaning as they have in the context of this specification and the relevant field, and not in an idealized or overly formal sense.

[0102] It should be understood that this disclosure is not limited to the aspects described above and shown in the accompanying drawings; rather, those skilled in the art will recognize that many changes and modifications can be made within the scope of this disclosure and the appended claims. Aspects have been disclosed in the drawings and description for illustrative purposes only and not for limiting purposes, and the scope of this disclosure is set forth in the appended claims.

Claims

1. A control unit (110) for managing idle time in a battery energy storage system (100, 200), wherein the battery energy storage system (100, 200) comprises: Main high-voltage battery pack (120); Auxiliary battery pack (140); and a bidirectional DC-DC circuit (130) connecting the main high-voltage battery pack (120) to the auxiliary battery pack (140) to facilitate energy transfer between the two battery packs (120, 140), wherein the control unit (110) is configured to: The idle time and state of charge (SoC) of the main high-voltage battery pack (120) are monitored, wherein the idle time reflects the period during which the SoC remains unchanged; and In response to the idle time of the main high-voltage battery pack (120) exceeding a predetermined duration, a charging alternation mode is initiated, wherein the charging alternation mode involves alternating between energy transfer from the main high-voltage battery pack (120) to the auxiliary battery pack (140) and energy transfer from the auxiliary battery pack (140) to the main high-voltage battery pack (120).

2. The control unit (110) of claim 1, wherein the predetermined duration depends on the SoC of the main high-voltage battery pack (120).

3. The control unit (110) as claimed in any one of claims 1 to 2, wherein the bidirectional DC-DC circuit (130) comprises: A first bidirectional DC-DC converter (321) connects the main high-voltage battery pack (120) to the DC bus (DC1); And a second bidirectional DC-DC converter (341) that connects the auxiliary battery pack (140) to the DC bus (DC1), thereby facilitating energy transfer between the two battery packs (120, 140) via the DC bus (DC1).

4. The control unit (110) as claimed in any one of claims 1 to 2, wherein the bidirectional DC-DC circuit (130) comprises: A first bidirectional inverter (322) connects the main high-voltage battery pack (120) to the AC bus (AC1). And a second bidirectional inverter (342) that connects the auxiliary battery pack (140) to the AC bus (AC1), thereby facilitating energy transfer between the two battery packs (120, 140) via the AC bus (AC1).

5. The control unit (110) as claimed in any one of claims 1 to 2, wherein the bidirectional DC-DC circuit (130) comprises: A first bidirectional DC-DC converter (321) connects the main high-voltage battery pack (120) to a first DC bus (DC1); A first bidirectional inverter (322) that connects the first DC bus (DC1) to the AC bus (AC1); and a second bidirectional DC-DC converter (341) that connects the auxiliary battery pack (140) to the second DC bus (DC2); and a second bidirectional inverter (342) that connects the second DC bus (DC2) to the AC bus (AC1), thereby facilitating energy transfer between the two battery packs (120, 140) via the first DC bus (DC1), the AC bus (AC1), and the second DC bus (DC2).

6. The control unit (110) as claimed in any one of claims 1 to 5, wherein the battery energy storage system (100, 200) further includes a bidirectional inverter (250) configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid (260) and the field electrical load (270), wherein the control unit (110) is further configured to: Monitoring AC power grid conditions, including electricity demand indicators. In response to the power demand index falling below a predetermined threshold, the system switches to a grid-assisted charging alternation mode, wherein the grid-assisted charging alternation mode involves alternating between energy transfer from the AC grid (260) to the main high-voltage battery (120) and energy transfer from the main high-voltage battery (120) to the field electrical load (270).

7. The control unit (110) as claimed in any one of claims 1 to 6, wherein the battery energy storage system (100, 200) further includes a bidirectional inverter (250) configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid (260) and the field electrical load (270), wherein the control unit (110) is further configured to: In response to the SoC dropping below a predetermined SoC threshold, the system switches to the grid-assisted charging alternating mode.

8. A battery energy storage system (100, 200), wherein the battery energy storage system (100, 200) comprises: A main high-voltage battery pack (120); an auxiliary battery pack (140); a bidirectional DC-DC circuit connecting the main high-voltage battery pack (120) and the auxiliary battery pack (140) and configured to facilitate energy transfer between the two battery packs; and a control unit according to any one of claims 1 to 5.

9. The battery energy storage system (100, 200) as claimed in claim 8, wherein the battery energy storage system (100, 200) further comprises: A bidirectional inverter (250) configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid (260) and the field electrical load (270); and a control unit according to any one of claims 6 to 7.

10. A method for managing idle time in a battery energy storage system (100, 200), wherein the battery energy storage system (100, 200) comprises: Main high-voltage battery pack (120); Auxiliary battery pack (140); And a bidirectional DC-DC circuit (130) connecting the main high-voltage battery pack (120) to the auxiliary battery pack (140) to facilitate energy transfer between the two battery packs (120, 140), and wherein the method includes: Monitoring (S1) the idle time of the main high-voltage battery pack (120), wherein the idle time reflects the period during which the state of charge (SoC) remains unchanged; as well as In response to the idle time of the main high-voltage battery pack (120) exceeding a predetermined duration, a charging alternation mode is initiated (S2), wherein the charging alternation mode involves alternating between energy transfer from the main high-voltage battery pack (120) to the auxiliary battery pack (140) and energy transfer from the auxiliary battery pack (140) to the main high-voltage battery pack (120).

11. The method of claim 10, wherein the predetermined duration depends on the SoC of the main high-voltage battery pack (120).

12. The method of any one of claims 10 to 11, wherein the bidirectional DC-DC circuit (130) includes a plurality of power converters (321, 322, 341, 342) to facilitate energy transfer between the two battery packs (120, 140) via one or more AC and / or DC buses (AC1, DC1, DC2).

13. The method of any one of claims 10 to 12, wherein the battery energy storage system (100, 200) further comprises a bidirectional inverter (250) configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid (260) and the field electrical load (270), wherein the method further comprises: Monitoring (S3) AC grid conditions, wherein the AC grid conditions include power demand indicators. In response to the power demand index falling below a predetermined threshold, the system switches (S4-A) to a grid-assisted charging alternation mode, wherein the grid-assisted charging alternation mode alternates between energy transfer from the AC grid (260) to the main high-voltage battery (120) and energy transfer from the main high-voltage battery (120) to the field electrical load (270).

14. The method of any one of claims 10 to 13, wherein the battery energy storage system (100, 200) further comprises a bidirectional inverter (250) configured to facilitate energy transfer between the main high-voltage battery pack and the AC grid (260) and the field electrical load (270), wherein the method further comprises: In response to the SoC dropping below a predetermined SoC threshold, the system switches (S4-B) to the grid-assisted charging alternation mode.

15. A non-transitory computer-readable storage medium comprising instructions that, when executed by processing circuitry, cause the processing circuitry to perform the method as described in any one of claims 10 to 14.

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