EP4706147A1

EP4706147A1 - Energy storage system and method for operation of an energy storage system

Info

Publication number: EP4706147A1
Application number: EP23764272.3A
Authority: EP
Inventors: Anandababu CHAKRAVARTULA; Govind AVINASH REDDY; Vinothkumar KANNAN; Ying-Jiang Hafner; Anil BHARADWAJ
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2023-08-29
Filing date: 2023-08-29
Publication date: 2026-03-11
Also published as: WO2025045351A1; CN121794862A

Abstract

An energy storage system (1) is specified, comprising - at least one energy storage module (2) configured to be connected to a power transmission system (3), - a resistor (4) connected in series to the at least one energy storage module (2), and - a switch (5) connected in parallel to the resistor (4), and the switch and the resistor (4) are configured to be connected to an electrical reference potential (10), wherein - the at least one energy storage module (2) comprises an energy storage block (6), and - the at least one energy storage module (2) comprises a half-bridge module (7) electrically connected to the energy storage block (6). Further, a method for operation of an energy storage system is provided.

Description

P2023,0967 WO E / P230076WO01 August 29, 2023 - 1 - Description ENERGY STORAGE SYSTEM AND METHOD FOR OPERATION OF AN ENERGY STORAGE SYSTEM The present disclosure relates to an energy storage system and a method for operation of an energy storage system. A high voltage direct current, HVDC, transmission is typically used to integrate remotely located renewable energy-based power generating units, RPGU, to an alternating current, AC, grid. An inertia support is becoming an additional requirement due to large-scale power electronic integration of the renewable power into an AC grid. However, considering an inherent overload capability of a converter in a HVDC transmission system, it is a prudent choice to have an energy storage capacity integrated on a DC side while retaining a chopper operation in the same structure to handle excess energy. Embodiments of the disclosure relate to an energy storage system, which has an improved functionality. A further embodiment relates to a method for operation of an energy storage system. This is achieved by the subject-matter of the independent claims. Further embodiments are evident from the dependent claims and the following description. An energy storage system is described. Exemplarily, the energy storage system is connected to an electrical power grid via a power transmission system. In particular, the energy storage system is configured to reduce energy P2023,0967 WO E / P230076WO01 August 29, 2023 - 2 - imbalances of the electrical power grid. In particular, the energy storage system is configured to receive an electrical current from the electrical power grid as well as to provide an electrical current to the electrical power grid. According to an embodiment, the energy storage system comprises at least one energy storage module configured to be connected to a power transmission system. Exemplarily, the power transmission system is, for example, configured to be connected to an energy source and/or an energy load. The at least one energy storage module is configured to receive an electrical current from the power transmission system as well as to provide energy to the power transmission system, in particular independently from one another. Exemplarily, the energy storage system comprises a plurality of energy storage modules. For example, the plurality of energy storage modules is connected in series. Exemplarily, the energy storage modules are spaced apart from one another. In particular, the energy storage modules are spaced apart from the power transmission system. Each energy storage module is configured to receive an electrical current from the power transmission system as well as to provide energy to the power transmission system, in particular independently from one another. According to the embodiment, the energy storage system comprises a resistor connected in series to the at least one energy storage module. Exemplarily, the resistor is configured to receive an electrical current from the power transmission system. The resistor is, for example, a single resistor or comprises a plurality of sub-resistors forming P2023,0967 WO E / P230076WO01 August 29, 2023 - 3 - the resistor. The sub-resistors are connected in series and/or in parallel. According to the embodiment, the energy storage system comprises a switch connected in parallel to the resistor, and the switch and the resistor are configured to be connected to an electrical reference potential. Exemplarily, the resistor and the switch are arranged between the at least one energy storage module and the electrical reference potential in series. The electrical reference potential is, in particular, a ground potential, i.e., a ground. For example, the switch is configured to bypass the resistor when the switch is in a closed state. The switch is, for example, configured to transmit the electrical current when the switch is in the closed state. The switch is, for example, configured to transmit the electrical current through the resistor when the switch is in an open state. If the energy storage system comprises the plurality of energy storage modules, the energy storage modules are connected in series. For example, the resistor and the switch, the energy storage modules and an inductor device are connected between the electrical reference potential, and the power transmission system in series, in particular in the order indicated. According to the embodiment of the energy storage system, the at least one energy storage module comprises an energy storage block. The energy storage block is, for example, an electrical energy accumulator which is configured to store and release electric energy. The energy storage block is, for example, at least one of a battery module and a supercapacitor. The energy storage block comprises, for P2023,0967 WO E / P230076WO01 August 29, 2023 - 4 - example, at least two terminals, a first terminal and a second terminal. In particular, the terminals differ from one another from their polarity. If the energy storage is a battery, the terminals comprise an anode terminal and a cathode terminal. If the energy storage is a supercapacitor, the terminals comprise a positive terminal and a negative terminal. In particular, electric energy is stored in an electric field between the terminals. The energy storage block can further comprise a plurality of electrical storage cells being connected to one another. For example, the electrical storage cells are connected in series and/or in parallel to one another. According to the embodiment of the energy storage system, the at least one energy storage module comprises a half-bridge module electrically connected to the energy storage block. In particular, the half-bridge module comprises power semiconductor devices being arranged in a half-bridge arrangement. In particular, the half-bridge module comprises solely two power semiconductor devices, each comprising one power switching device. Advantageously, with using a half-bridge module in the energy storage system for the energy storage module, in particular all the energy storage modules, a number of required power electronic devices can be reduced. This advantageously leads to reduced costs and footprint of the energy storage system. In particular, the use of the half-bridge module reduces the overall size, complexity, and cost of the system. In particular, compared to other configurations like a full- bridge arrangement, the half-bridge arrangement has P2023,0967 WO E / P230076WO01 August 29, 2023 - 5 - advantageously lower switching losses. Therefore, a lower power dissipation and improved efficiency is achieved. In sum, an energy storage capacity of the present energy storage system is integrated on the DC side of the power transmission system while a chopper operation can be retained in the same structure to handle excess energy. This is that the energy storage system is advantageously configured to provide inertia support during need at the electrical power grid. At the same time, the energy storage system is also advantageously configured to provide a DC chopper functionality to comply with fault ride through, FRT, requirement of the electrical power grid. According to a further embodiment of the energy storage system, the half-bridge module comprises a first power switching device and a second power switching device. In particular, the half-bridge module comprises solely two power switching devices. Exemplarily, the power switching devices, i.e. the first power switching device and the second power switching device, is configured to provide a control over a polarity and a magnitude of the electrical current applied to the energy storage block dependent on a switching state. Further, the power switching devices are configured to bypass the energy storage block dependent on the switching state. Each of these power switching devices are exemplarily formed of a semiconductor power switch, in particular comprising a metal-oxide-semiconductor field-effect transistor, MOSFET, an insulated gate bipolar transistor, IGBT, a gallium nitride, GaN, high electron mobility transistor, HEMT, and/or an integrated gate-commutated thyristor, IGCT. The IGBT has, for example, three terminals, a gate terminal, an emitter terminal and a collector terminal. Analogously, the MOSFET P2023,0967 WO E / P230076WO01 August 29, 2023 - 6 - has, for example, three terminals, a gate terminal, a source terminal and a drain terminal. Exemplarily, the first power switching device is a low side switch and the second power switching device is a high side switch for the energy storage block. According to a further embodiment of the energy storage system, the first power switching device and the second power switching device are connected in series. In particular, the first power switching device and the second power switching device are connected by a first bridge node. The first bridge node is, for example, characteristic for a common connection point where the first power switching device and the second power switching device are connected in series. Exemplarily, the collector terminal of the first power switching device and the emitter terminal of the second power switching device are connected by the first bridge node. According to a further embodiment of the energy storage system, the at least one energy storage module comprises a further energy storage block. The further energy storage block is, for example, a further electrical energy accumulator which is configured to store and release electric energy. The further energy storage block is, for example, at least one of a further battery module and a further supercapacitor. The further energy storage block comprises, for example, at least two further terminals, a further first terminal and a further second terminal. In particular, the further terminals differ from one another from their polarity similar to the terminal of the energy storage block. P2023,0967 WO E / P230076WO01 August 29, 2023 - 7 - According to a further embodiment of the energy storage system, the at least one energy storage module comprises a switching module. For example, the switching module comprises further power switching devices, arranged between the energy storage block and the further energy storage block. In operation of a typical energy storage system with typical energy storage modules, e.g. a super capacitor current varies between non-zero and zero at switching frequency of each energy storage block of the typical energy storage modules that are inserted and bypassed, respectively, during operation. Therefore, a current switching, between a zero and non-zero value, frequency of the super capacitor is equal to the typical energy storage module output voltage switching frequency. Generally, if the current switching, between a zero and non-zero valve, frequency of a super capacitor is higher than 2 Hz then a capacitance reduces predominantly and eventually the available stored energy. Generally, to limit a peak to peak current ripple, the effective current switching frequency of the typical energy storage modules is increased by proportionately increasing the number of energy storage modules with a reduced average voltage of the respective energy storage blocks. However, the energy storage system with the at least one energy storage module, which in particular comprises the switching module, advantageously can integrate the energy storage modules with a HVDC network, exemplarily on the DC- side. Also, such energy storage modules can provide a DC chopper functionality and/or energy support to the power transmission system. P2023,0967 WO E / P230076WO01 August 29, 2023 - 8 - Advantageously, the proposed configuration can achieve a higher switching frequency and transmit power to the power transmission system and vice-versa with low current ripple, compared to typical energy storage modules. A modularity and a redundancy of the configuration is high. A design optimization of the energy storage system in terms of number of energy storage modules and/or an inductor size is possible. This topology can be employed for HVDC transmission system interconnections without dc chopper functionality as well. Consequently, the use of such an energy storage module further has advantageously a comparatively low footprint. According to a further embodiment of the energy storage system, the switching module comprises a third power switching device, a fourth power switching device and a fifth power switching device. Exemplarily, the power switching devices, i.e. the third power switching device, the fourth power switching device and the fifth power switching device, are configured to provide a control over a polarity and a magnitude of the electrical current applied to the further energy storage block and in particular configured to provide a control over a polarity and a magnitude of the electrical current applied to the energy storage block dependent on the switching state. Exemplarily, the third power switching device is a low side switch and the fourth power switching device is a high side switch for the further energy storage block. Each of these power switching devices are exemplarily formed of a semiconductor power switch, in particular comprising an IGBT, a MOSFET, a HEMT, and/or an IGCT. P2023,0967 WO E / P230076WO01 August 29, 2023 - 9 - According to a further embodiment of the energy storage system, the third power switching device, the fourth power switching device and the fifth power switching device are connected in series. In particular, the third power switching device and the fourth power switching device are connected by a second bridge node. The second bridge node is, for example, characteristic for a common connection point where the third power switching device and the fourth power switching device are connected in series. Exemplarily, the collector terminal of the third power switching device and the emitter terminal of the fourth power switching device are connected by the second bridge node. In particular, the fourth power switching device and the fifth power switching device are connected by a third bridge node. The third bridge node is, for example, characteristic for a common connection point where the fourth power switching device and the fifth power switching device are connected in series. Exemplarily, the collector terminal of the fourth power switching device and the emitter terminal of the fifth power switching device are connected by the third bridge node. According to a further embodiment of the energy storage system, the fourth power switching device and the fifth power switching device are connected in parallel to the energy storage block. For example, the fourth power switching device is connected to the first terminal, in particular with the second bridge node. For example, the fifth power switching device is connected to the second terminal, in particular with a connection facing away from the third bridge node. The connection of the fifth power switching device facing away P2023,0967 WO E / P230076WO01 August 29, 2023 - 10 - from the third bridge node is characteristic, for example, for the collector terminal of the fifth power switching device. According to a further embodiment of the energy storage system, the third power switching device and the fourth power switching device are connected in parallel to the further energy storage block. For example, the third power switching device is connected to the further first terminal, in particular with a connection facing away from the second bridge node. The connection of the third power switching device facing away from the second bridge node is characteristic, for example, for the emitter terminal of the third power switching device. For example, the fourth power switching device is connected to the further second terminal, in particular with third bridge node. According to a further embodiment of the energy storage system, the first power switching device and the second power switching device are connected in parallel to the switching module. For example, the first power switching device is connected to the third power switching device, in particular with a connection of the first power switching device facing away from the first bridge node to the connection of the third power switching device facing away from the second bridge node. The connection of the first power switching device facing away from the first bridge node is characteristic, for example, for the emitter terminal of the first power switching device. Further, exemplarily, the second power switching device is connected to the second terminal and the fifth power switching device, in particular with a connection of the second power switching device facing away from the first bridge node to the connection of the P2023,0967 WO E / P230076WO01 August 29, 2023 - 11 - fifth power switching device facing away from the third bridge node. The connection of the second power switching device facing away from the first bridge node is characteristic, for example, for the collector terminal of the second power switching device. Exemplarily, the first bridge node is connected to the power transmission system via the inductor device and the connection of the first power switching module facing away from the first bridge node is connected to the electrical reference potential via the resistor and the switch. If the energy storage system comprises a plurality of energy storage modules, the energy storage module closest to the power transmission system is connected to the power transmission system via the inductor device by the first bridge node. Further, the energy storage module closest to the resistor and the switch is connected to the resistor and the switch, for example, by the connection of the first power switching module facing away from the first bridge node. According to a further embodiment of the energy storage system, the first power switching device and the second power switching device are connected in parallel to the energy storage block. For example, the first power switching device is connected to the first terminal, in particular with the connection facing away from the first bridge node. Further, exemplarily, the second power switching device is connected to the second terminal, in particular with the connection facing away from the first bridge node. Exemplarily, the first bridge node is connected to the power transmission system via the inductor device and the P2023,0967 WO E / P230076WO01 August 29, 2023 - 12 - connection of the third power switching module facing away from the second bridge node is connected to the electrical reference potential via the resistor and the switch. If the energy storage system comprises a plurality of energy storage modules, the energy storage module closest to the power transmission system is connected to the power transmission system via the inductor device by the first bridge node. Further, the energy storage module closest to the resistor and the switch is connected to the resistor and the switch, for example, by the connection of the third power switching module facing away from the second bridge node. According to a further embodiment of the energy storage system, the at least one energy storage module comprises a further half-bridge module comprising a sixth power switching device and a seventh power switching device. Exemplarily, the power switching devices, i.e. the sixth power switching device and the seventh power switching device, are configured to provide a control over a polarity and a magnitude of the electrical current applied to the further energy storage block or in particular to the energy storage block and the further energy storage block dependent on the switching state. Each of these power switching devices are exemplarily formed of a semiconductor power switch, in particular comprising an IGBT, a MOSFET, a HEMT, and/or an IGCT.. According to a further embodiment of the energy storage system, the sixth power switching device and the seventh power switching device are connected in series. In particular, the sixth power switching device and the seventh power switching device are connected by a fourth bridge node. The fourth bridge node is, for example, characteristic for a P2023,0967 WO E / P230076WO01 August 29, 2023 - 13 - common connection point where the sixth power switching device and the seventh power switching device are connected in series. Exemplarily, the collector terminal of the sixth power switching device and the emitter terminal of the seventh power switching device are connected by the fourth bridge node. According to a further embodiment of the energy storage system, the further half-bridge module is connected in parallel to the switching module. For example, the sixth power switching device is connected to the further first terminal and the third power switching device, in particular with a connection facing away from the fourth bridge node, in particular with a connection of the sixth power switching device facing away from the fourth bridge node to the connection of the third power switching device facing away from the second bridge node. The connection of the sixth power switching device facing away from the fourth bridge node is characteristic, for example, for the emitter terminal of the sixth power switching device. Further, exemplarily, the seventh power switching device is connected to the fifth power switching device, in particular with a connection of the seventh power switching device facing away from the fourth bridge node to the connection of the fifth power switching device facing away from the third bridge node. The connection of the seventh power switching device facing away from the fourth bridge node is characteristic, for example, for the collector terminal of the seventh power switching device. According to a further embodiment of the energy storage system, the further half-bridge module is connected in P2023,0967 WO E / P230076WO01 August 29, 2023 - 14 - parallel to the further energy storage block. For example, the sixth power switching device is connected to the further first terminal, in particular with the connection facing away from the fourth bridge node. Further, exemplarily, the seventh power switching device is connected to the further second terminal, in particular with the connection facing away from the fourth bridge node. Exemplarily, the sixth power switching device is a low side switch and the seventh power switching device is a high side switch for the further energy storage block. For example, the first bridge node is connected to the power transmission system via an inductor device and the fourth bridge node is connected to the electrical reference potential via the resistor and the switch. If the energy storage system comprises a plurality of energy storage modules, the energy storage module closest to the power transmission system is connected to the power transmission system by the first bridge node. Further, the energy storage module closest to the resistor and the switch is connected to the resistor and the switch by the fourth bridge node. According to a further embodiment of the energy storage system, the at least one energy storage module exclusively comprises the half-bridge module electrically connected to the energy storage block. If the energy storage system comprises the plurality of energy storage modules, all the energy storage modules exemplarily comprise exclusively one half-bridge module. P2023,0967 WO E / P230076WO01 August 29, 2023 - 15 - Advantageously, such an energy storage system has particularly reduced costs and a reduced footprint with respect to full bridge topologies. In this embodiment, the energy storage module closest to the resistor and the switch is connected to the resistor and the switch by the connection of the first power switching device facing away from the first bridge node. In this case, the energy storage module closest to the power transmission system is connected to the power transmission system via the inductor device by the first bridge node. Alternatively, in this embodiment, the energy storage module closest to the resistor and the switch is connected to the resistor and the switch by the first bridge node. In this case, the energy storage module closest to the power transmission system is connected to the power transmission system via the inductor device by the connection of the second power switching device facing away from bridge node. According to a further embodiment of the energy storage system, the switch is a high speed switch. In particular, the switch is a mechanical high speed switch. According to a further embodiment of the energy storage system, an inductor device is arranged between the power transmission system and the at least one energy storage module, in particular the energy storage module closest to the power transmission system. In particular, the inductor device is arranged in series between the power transmission system and the energy storage module closest to the power transmission system. P2023,0967 WO E / P230076WO01 August 29, 2023 - 16 - Advantageously, the electrical current provided to the power transmission system and/or by the power transmission system is regulated by the inductances to a suitable level. According to a further embodiment of the energy storage system, the power transmission system is a direct current, DC, transmission system. For example, the power transmission system is a high voltage DC transmission system configured to be connected to an alternating current, AC, power grid. According to a further embodiment of the energy storage system, the energy storage system further comprises a control system. Exemplarily, the control system comprises a plurality of control units which can be controlled by a master control unit. The control units can be arranged within at least one of the energy storage modules, the resistor, the switch and the inductor device. Further, at least some of the control units are, for example, located externally. According to a further embodiment of the energy storage system, the control system is configured to control the at least one energy storage module, in particular each energy storage module. According to a further embodiment of the energy storage system, the control system is configured to control the switch. In particular, the control system is configured to switch the two power switching devices of each energy storage module. Exemplarily, the controller is configured to control the energy storage modules and the switch independently from one another. P2023,0967 WO E / P230076WO01 August 29, 2023 - 17 - The control system can further comprise sensing units configured to sense the electrical current and/or a voltage of the half-bridge module, the resistor, the switch, the inductor device and/or the energy storage block. According to a further embodiment of the energy storage system, the power transmission system is configured to be connected to at least one renewable energy source. The renewable energy source is formed of, for example, a wind farm, a solar farm and/or a hydroelectric power plant. A further embodiment relates to a method for operation of an energy storage system having at least two energy storage modules connected in series, in particular, an energy storage system described herein above. Therefore, the features as described in connection with the method are also applicable for the energy storage system and vice versa. According to an embodiment, the method comprises a first mode configured to provide energy to the energy storage system. This is that the first mode is in particular an energization mode. Exemplarily, the energy storage modules are charged to a predetermined voltage, e.g. to a nominal voltage. According to the embodiment, the method comprises a second mode configured to keep the energy storage system in an idle state. In particular, the second mode is configured to keep the energy storage system in the idle mode. In the second mode, the energy storage modules are configured to provide a predetermined pole voltage, e.g. matching a voltage of the transmission system. P2023,0967 WO E / P230076WO01 August 29, 2023 - 18 - According to the embodiment, the method comprises a third mode configured to provide energy to the power transmission system. According to the embodiment, the method comprises a fourth mode configured to dissipate energy from the power transmission system. In the fourth mode, the total power of the transmission system is diverted into the resistor. According to the embodiment of the method, each energy storage module can be inserted or bypassed by the half-bridge module in the serial connection. According to a further embodiment of the method, the energy storage modules are bypassed when the first power switching device is in a closed state and the second power switching device is in an open state. According to a further embodiment of the method, a predetermined number of the energy storage modules are inserted in the serial connection for charging the energy storage blocks of the inserted energy storage modules, and while providing energy to the energy storage system, the switch is in an open state for a first time interval and a closed state for a second time interval dependent on a voltage of the power transmission system. This method stage is characteristic for the first method stage, i.e. a charging of the energy storage system. According to a further embodiment of the method, a predetermined number of the energy storage modules are inserted in the serial connection and a further predetermined P2023,0967 WO E / P230076WO01 August 29, 2023 - 19 - number of the energy storage modules are bypassed in the serial connection such that a voltage of the inserted energy storage modules equals a voltage of the power transmission system, and the switch is in the closed state. This method stage is characteristic for the second method stage, i.e. an idle state of the energy storage system. According to a further embodiment of the method, a predetermined number of energy storage modules are inserted in the serial connection dependent on a predetermined voltage such that a voltage of the inserted energy storage modules is larger than a voltage of the power transmission system, and the switch is in the closed state. This method stage is characteristic for the third method stage, i.e. a discharge of the energy storage system. According to a further embodiment of the method, all energy storage modules are bypassed in the serial connection, and the switch is in an open state. This method stage is characteristic for the fourth method stage, i.e. an energy dissipation through the resistor of the energy storage system. The accompanying Figures are included to provide a further understanding. In the Figures, elements of the same structure and/or functionality may be referenced by the same reference signs. It is to be understood that the embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale. P2023,0967 WO E / P230076WO01 August 29, 2023 - 20 - Figure 1 schematically shows a schematic view of an energy storage system according to an exemplary embodiment. Figures 2, 3, 4, 5, 6 and 7 each schematically shows a schematic view of an energy storage module of an energy storage system according to an exemplary embodiment. Figures 8, 9 and 10 schematically show a bypass mode and an insertion mode of an energy storage module of an energy storage system according to an exemplary embodiment. The energy storage system 1 according to the exemplary embodiment of Figure 1 comprises a plurality of energy storage modules 2. The energy storage modules 2 are connected in series to one another and are arranged between a power transmission system 3 and an electrical reference potential 10. A resistor 4 and a switch 5 are arranged between the energy storage modules 2 and the electrical reference potential 10. The resistor 4 and the switch 5 are connected in parallel. The switch 5 is a high speed switch 5 and is configured to bypass the resistor 4 when in the closed state. An inductor device 8 comprising at least one inductance is arranged between the energy storage modules 2 and the power transmission system 3 in series. The potentials U_d, U_{ch_v}, U_{o_v} and a current I_ch are indicated accordingly in Figure 1. The potential Ud is defined between the power transmission system 3 and the electrical reference potential 10, the potential Uch_v between terminals of the outer energy storage modules 2 and the potential Uo_v between P2023,0967 WO E / P230076WO01 August 29, 2023 - 21 - two terminals of each energy storage module 2. The current Ich is the current fed from the power transmission system 3 in direction to the energy storage modules 2 or in direction from the energy storage modules 2 to the power transmission system 3. In particular, each energy storage module 2 comprises an energy storage block 6, and each energy storage module 2 comprises a half-bridge module 7 electrically connected to the energy storage block 6 being described more detailed in connection with Figures 2 to 7. By using the energy storage modules 2 comprising the half- bridge modules 7, the inductor device 8 and the resistor 4 with the switch 5 connected in series, a dual functionality of energy support and FRT grid code compliance is advantageously achieved. Exemplarily, the energy storage modules 2 are grouped in a plurality of arms, e.g. two arms as indicated exemplarily in Figure 1, namely a first arm 11 and a second arm 12. For example, a number of energy storage modules 2 in the second arm is designed for a maximum dc link voltage to the power transmission system 3 whereas a number of energy storage modules 2 in the first arm 11 is designed to cater to the energy needs of the connected electrical power grid 9. In particular, the energy storage modules 2 can be sorted in the whole arm for achieving an energy storage module 2 balancing. In particular, each energy storage module 2 can be inserted or bypassed by the half-bridge module 7 as described more detailed in connection with Figures 8, 9 and 10. Thus, such P2023,0967 WO E / P230076WO01 August 29, 2023 - 22 - an energy storage system 1 of Figure 1 can be operated in several different modes. A first mode is configured to provide energy to the energy storage system 1, i.e. being an energization mode or charging mode. In the first mode, a predetermined number of energy storage modules 2 are inserted in the serial connection for charging the energy storage blocks 6 of the inserted energy storage modules 2, and while providing energy to the energy storage system 1, the switch 5 is in an open state for a first time interval and in the closed state for a second time interval dependent on a voltage of the power transmission system 3. Exemplarily, the energy storage modules 2 in the first arm 11 and the second arm 12 are inserted. In this first mode, the energy storage modules 2 are charged to their nominal voltage. In particular, the switch 5 is initially in the open state to allow a controlled charging of the inserted energy storage modules 2 in the first time interval. Further, in the second time interval, i.e. after the first time interval, the switch 5 is closed when the total voltage is closer to the dc link voltage to facilitate a boosting operation. The controlled charging is performed to build up the voltage in each of the energy storage modules 2 to a corresponding nominal value. In particular, in the first mode, the half-bridge modules 7 of one or more of the energy storage modules 2 are each configured such that the respective energy storage blocks 6 receive electrical energy from the power transmission system 3, and the resistor 4 is bypassed via the switch 5. The energy storage modules 2 not being configured for receiving electrical energy from the power transmission system 3 are P2023,0967 WO E / P230076WO01 August 29, 2023 - 23 - configured such that the respective energy storage blocks 6 are bypassed. A second mode is configured to keep the energy storage system 1 in an idle state, i.e. being an idle mode. In the second mode a predetermined number of energy storage modules 2 are inserted in the serial connection and a further predetermined number of energy storage modules 2 are bypassed in the serial connection such that a voltage of the inserted energy storage modules 2 equals a voltage of the power transmission system 3, and the switch 5 is in the closed state. Exemplarily, the energy storage modules 2 in the first arm 11 are bypassed and the energy storage modules 2 in the second arm 12 are inserted. In this second mode, the configuration generates a predetermined pole voltage by using the second arm 12. In the second mode, there is no exchange of current and/or power with the power transmission system 3. The switch 5 remains in the closed state during the second mode. A third mode is configured to provide energy to the power transmission system 3, i.e. being an energy support mode. In the third mode a predetermined number of energy storage modules 2 are inserted in the serial connection dependent on a predetermined voltage such that a voltage of the inserted energy storage modules 2 is larger than a voltage of the power transmission system 3, and the switch 5 is in the closed state. Exemplarily, the energy storage modules 2 in the first arm 11 and the energy storage modules 2 in the second arm 12 are inserted. P2023,0967 WO E / P230076WO01 August 29, 2023 - 24 - In particular, in the third mode, the half-bridge modules 7 of the respective energy storage modules 2 are configured such that the energy storage blocks 6 of the respective energy storage modules 2 discharge electrical energy to the power transmission system 3 such that the predetermined voltage is achieved. The energy storage modules 2 not discharging electrical energy are, for example, configured such that the respective energy storage blocks 6 are bypassed. A fourth mode is configured to dissipate energy from the power transmission system 3. In the fourth mode, all energy storage modules 2 are bypassed in the serial connection, and the switch 5 is in the open state. In particular, in the fourth mode, the half-bridge modules 7 of the respective energy storage modules 2 are configured such that the energy storage blocks 6 are bypassed and the switch 5 in the open state such that the resistor 4 dissipates electrical energy from the power transmission system 3. In sum, in case of DC faults, the energy storage modules 2 can bypass and open its disconnectors at current zero thereby achieve fault immunity. Overall, the proposed energy storage system 1 topology has advantageously an optimal design in terms of number of energy storage modules 2 and inductor size. Each energy storage module 2 according to the exemplary embodiment of Figures 2 and 3 comprises an energy storage block 6 and a single half-bridge module 7 electrically connected to the energy storage block 6. The half-bridge P2023,0967 WO E / P230076WO01 August 29, 2023 - 25 - module 7 comprises a first power switching device 13 and a second power switching device 14 connected in series via a first bridge node 15. The energy storage block 6 comprises a first terminal 16 and a second terminal 17. The first power switching device 13 is connected to the first terminal 16 with a connection facing away from the first bridge node 15. The second power switching device 14 is connected to the second terminal 17 with a connection facing away from the first bridge node 15. Energy storage modules 2 of Figure 2 are interconnected via the first bridge node 15 and the first terminal 16 with the connection facing away from the first bridge node 15. In this case, the first bridge node 15 is connected to a connection of a first power switching device 13 facing away from a first bridge node 15 of a directly neighboring energy storage module 2 facing the power transmission system 3. Further, the connection of the first power switching device 13 facing away from the first bridge node 15 is connected to a first bridge node 15 of a directly neighboring energy storage module 2 facing the electrical reference potential 10. Energy storage modules 2 of Figure 3 are interconnected via the second terminal 17 with the connection facing away from the first bridge node 15 and the first bridge node 15. In this case, the first bridge node 15 is connected to a connection of a second power switching device 14 facing away from a first bridge node 15 of a directly neighboring energy storage module 2 facing the electrical reference potential 10. Further, the connection of the second power switching device 14 facing away from the first bridge node 15 is connected to a first bridge node 15 of a directly neighboring P2023,0967 WO E / P230076WO01 August 29, 2023 - 26 - energy storage module 2 facing the power transmission system 3. Each energy storage module 2 according to the exemplary embodiment of Figures 4, 5, 6 and 7 comprises in addition to the exemplary embodiments of Figures 2 and 3 a further energy storage block 18 and a switching module 21. The switching module 21 comprises a third power switching device 22, a fourth power switching device 23 and a fifth power switching device 24 connected in series. The third power switching device 22 and the fourth power switching device 23 are connected in series via a second bridge node 25 and the fourth power switching device 23 and the fifth power switching device 24 are connected in series via a third bridge node 26. In Figure 4, the first power switching device 13 is connected with a connection facing away from the first bridge node 15 to a connection of the third power switching device 22 facing away from the second bridge node 25. The second power switching device 14 is connected with a connection facing away from the first bridge node 15 to the second terminal 17 and a connection of the fifth power switching device 24 facing away from the third bridge node 26. The fourth power switching device 23 and the fifth power switching device 24 are connected in parallel to the energy storage block 6. The fourth power switching device 23 is connected with the second bridge node 25 to the first terminal 16. The fifth power switching device 24 is connected with the connection facing away from the third bridge node 26 to the second terminal 17 and the connection of the second P2023,0967 WO E / P230076WO01 August 29, 2023 - 27 - power switching device 14 facing away from the first bridge node 15. Further, the third power switching device 22 and the fourth power switching device 23 are connected in parallel to the further energy storage block 18. The third power switching device 22 is connected with a connection facing away from the second bridge node 25 to a connection of the further first terminal 19. The fourth power switching device 23 is connected with the third bridge node 26 to the further second terminal 20. A connection in direction to the power transmission system 3 is provided via the first bridge node 15. A connection in direction to the electrical reference potential 10 is provided via the connection of the first power switching device 13 facing away from the first bridge node 15. In Figure 5, in particular in contrast to the each energy storage module 2 of Figure 4, the first power switching device 13 and the second power switching device 14 are connected in parallel to the energy storage block 6. The first power switching device 13 is connected with a connection facing away from the first bridge node 15 to the first terminal 16 and the second bridge node 25. The second power switching device 14 is connected with a connection facing away from the first bridge node 15 to the second terminal 17 and a connection of the fifth power switching device 24 facing away from the third bridge node 26. A connection in direction to the power transmission system 3 is provided via the first bridge node 15. A connection in direction to the electrical reference potential 10 is P2023,0967 WO E / P230076WO01 August 29, 2023 - 28 - provided via the connection of the third power switching device 22 facing away from the second bridge node 25. The energy storage module 2 according to Figure 6 has in addition to the energy storage module 2 of Figure 4 a further half-bridge module 27 comprising a sixth power switching device 28 and a seventh power switching device 29 connected in series. The sixth power switching device 28 and the seventh power switching device 29 are connected in series via a fourth bridge node 30. The further half-bridge module 27 is connected in parallel to the switching module 21. A connection of the sixth power switching device 28 facing away from the fourth bridge node 30 is connected to the further first terminal 19 and a connection of the third power switching device 22 facing away from the second bridge node 25. A connection of the seventh power switching device 29 facing away from the fourth bridge node 30 is connected to a connection of the fifth power switching device 24 facing away from the third bridge node 26. The energy storage module 2 according to Figure 7 has in addition to the energy storage module 2 of Figure 5 a further half-bridge module 27 as described in connection with Figure 6. In contrast to Figure 6, the further half-bridge module 27 of Figure 7 is connected in parallel to the further energy storage block 18. A connection of the sixth power switching device 28 facing away from the fourth bridge node 30 is connected to the further first terminal 19 and a connection of the third power switching device 22 facing away from the second bridge node 25. A connection of the seventh power switching device 29 facing away from the fourth bridge node P2023,0967 WO E / P230076WO01 August 29, 2023 - 29 - 30 is connected to the further second terminal 20 and the third bridge node 26. For Figures 6 and 7, a connection in direction to the power transmission system 3 is provided via the first bridge node 15. Further, a connection in direction to the electrical reference potential 10 is provided via the fourth bridge node 30. Figures 8, 9 and 10 describe an insertion and a bypass of an energy storage module 2 according to the exemplary embodiment of Figure 4. In particular, the energy storage modules 2 are located exemplarily in the first arm 11 of Figure 1 and are generally operated in a bypass mode and an insertion mode. The following description is also applicable to the energy storage modules 2 of different embodiments accordingly. In Figure 8, the bypass mode is described. The energy storage module 2 is bypassed when the first power switching device 13 is in a switching state characteristic for a closed state and the second power switching device 14 is in a switching state characteristic for an open state. In the closed state, the power switching device is configured to transmit electrical current. Accordingly, in the open state, the power switching device is configured to block electrical current. In bypass mode state, an output voltage of the energy storage module 2 is zero and an electrical current through the energy storage block 6 and the further energy storage block 18 is also zero. In Figures 9 and 10, the insertion mode is described. The energy storage module 2 is inserted when the second power P2023,0967 WO E / P230076WO01 August 29, 2023 - 30 - switching device 14 is in the closed state and the first power switching device 13 is in the open state. Dependent on a switching state of the switching module 21, the energy storage module 2 can output two different output voltages. This is that two different voltage levels at the output of each energy storage module 2 can be advantageously realized. If the third power switching device 22 and the fifth power switching device 24 are each in the closed state and the fourth power switching device 23 is in the open state, the energy storage block 6 and the further energy storage block 18 are connected in parallel, as shown in Figure 9. This is that the output voltage of the energy storage module 2 is equal to the voltage across the energy storage block 6 and the further energy storage block 18. In this configuration, electrical current flowing through the energy storage block 6 and the further energy storage block 18 is half of the energy storage module 2 output electrical current. If the fourth power switching device 23 is in the closed state and the third power switching device 22 and the fifth power switching device 24 are each in the open state, the energy storage block 6 and the further energy storage block 18 are connected series, as shown in Figure 10. In this configuration, the output voltage of the energy storage module 2 is equal to a sum of the voltage across each the energy storage block 6 and the further energy storage block 18, carrying the output electrical current of the energy storage module 2. Advantageously, the energy storage module 2 with two distinct output voltages is instrumental while supporting energy to the power transmission system 3. Moreover, the energy storage P2023,0967 WO E / P230076WO01 August 29, 2023 - 31 - block 6 and the further energy storage block 18 carry a non- zero electrical current, thereby allowing the switches of the switching module 21 to operate at higher the switching frequency without losing available stored energy in the energy storage block 6 and the further energy storage block 18.

P2023,0967 WO E / P230076WO01 August 29, 2023 - 32 - Reference Signs 1 energy storage system 2 energy storage module 3 power transmission system 4 resistor 5 switch 6 energy storage block 7 half-bridge module 8 inductor device 9 electrical power grid 10 electrical reference potential 11 first arm 12 second arm 13 first power switching device 14 second power switching device 15 first bridge node 16 first terminal 17 second terminal 18 further energy storage block 19 further first terminal 20 further second terminal 21 switching module 22 third power switching device 23 fourth power switching device 24 fifth power switching device 25 second bridge node 26 third bridge node 27 further half-bridge module 28 sixth power switching device 29 seventh power switching device 30 fourth bridge node

Claims

P2023,0967 WO E / P230076WO01 August 29, 2023 - 33 - Claims 1. Energy storage system (1), comprising - at least one energy storage module (2) configured to be connected to a power transmission system (3), - a resistor (4) connected in series to the at least one energy storage module (2), and - a switch (5) connected in parallel to the resistor (4), and the switch and the resistor (4) are configured to be connected to an electrical reference potential (10), wherein - the at least one energy storage module (2) comprises an energy storage block (6), and - the at least one energy storage module (2) comprises a half-bridge module (7) electrically connected to the energy storage block (6). 2. Energy storage system (1) according to claim 1, wherein - the half-bridge module (7) comprises a first power switching device (13) and a second power switching device (14), and - the first power switching device (13) and the second power switching device (14) are connected in series. 3. Energy storage system (1) according to one of the claims 1 or 2, wherein - the at least one energy storage module (2) comprises a further energy storage block (18), and - the at least one energy storage module (2) comprises a switching module (21). 4. Energy storage system (1) according to claim 3, wherein P2023,0967 WO E / P230076WO01 August 29, 2023 - 34 - - the switching module (21) comprises a third power switching device (22), a fourth power switching device (23) and a fifth power switching device (24), and - the third power switching device (22), the fourth power switching device (23) and the fifth power switching device (24) are connected in series. 5. Energy storage system (1) according to claim 4, wherein - the fourth power switching device (23) and the fifth power switching device (24) are connected in parallel to the energy storage block (6), and - the third power switching device (22) and the fourth power switching device (23) are connected in parallel to the further energy storage block (18). 6. Energy storage system (1) according to claim 5, wherein - the first power switching device (13) and the second power switching device (14) are connected in parallel to the switching module (21), or - the first power switching device (13) and the second power switching device (14) are connected in parallel to the energy storage block (6). 7. Energy storage system (1) according to one of the claims 3 to 6, wherein - the at least one energy storage module (2) comprises a further half-bridge module (27) comprising a sixth power switching device (28) and a seventh power switching device (29), - the sixth power switching device (28) and the seventh power switching device (29) are connected in series. 8. Energy storage system (1) according to claim 7, wherein P2023,0967 WO E / P230076WO01 August 29, 2023 - 35 - - the further half-bridge module (27) is connected in parallel to the switching module (21), or - the further half-bridge module (27) is connected in parallel to the further energy storage block (18). 9. Energy storage system (1) according to one of the claims 1 or 2, wherein - the at least one energy storage module (2) exclusively comprises the half-bridge module (7) electrically connected to the energy storage block (6). 10. Energy storage system (1) according to one of the claims 1 to 9, wherein - the switch (5) is a mechanical high speed switch. 11. Energy storage system (1) according to one of the claims 1 to 10, wherein - an inductor device (8) is arranged between the power transmission system (3) and the at least one energy storage module (2). 12. Energy storage system (1) according to one of the claims 1 to 11, wherein - the power transmission system (3) is a direct current, DC, transmission system. 13. Energy storage system (1) according to one of the claims 1 to 12, wherein - the energy storage system (1) further comprises a control system, - the control system is configured to control the at least one energy storage module (2), and - the control system is configured to control the switch (5). P2023,0967 WO E / P230076WO01 August 29, 2023 - 36 - 14. Method for operation of an energy storage system (1) according to one of the claims 1 to 13 having at least two energy storage modules (2) connected in series, with - a first mode configured to provide energy to the energy storage system (1), - a second mode configured to keep the energy storage system (1) in an idle state, - a third mode configured to provide energy to the power transmission system (3), and - a fourth mode configured to dissipate energy from the power transmission system (3), wherein - each energy storage module (2) is inserted or bypassed by the half-bridge module (7) in the serial connection. 15. Method according to claim 14, wherein - the energy storage modules (2) are bypassed when the first power switching device (13) is in a closed state and the second power switching device (14) is in an open state. 16. Method according to one of the claims 14 or 15, wherein - the energy storage modules (2) are inserted when the first power switching device (13) is in an open state and the second power switching device (14) is in a closed state. 17. The method according to one of the claims 14 to 16, wherein - a predetermined number of the energy storage modules (2) are inserted in the serial connection for charging the energy storage blocks of the inserted energy storage modules (2), and - while providing energy to the energy storage system (1), the switch (5) is opened for a first time interval and closed P2023,0967 WO E / P230076WO01 August 29, 2023 - 37 - for a second time interval dependent on a voltage of the power transmission system (3). 18. The method according to one of the claims 14 or 17, wherein - a predetermined number of the energy storage modules (2) are inserted in the serial connection and a further predetermined number of the energy storage modules (2) are bypassed in the serial connection such that a voltage of the inserted energy storage modules (2) equals a voltage of the power transmission system (3), and - the switch (5) is closed. 19. The method according to one of the claims 14 to 18, wherein - a predetermined number of energy storage modules (2) are inserted in the serial connection dependent on a predetermined voltage such that a voltage of the inserted energy storage modules (2) is larger than a voltage of the power transmission system (3), and - the switch (5) is closed. 20. The method according to one of the claims 14 to 19, wherein - all energy storage modules (2) are bypassed in the serial connection, and - the switch (5) is open.