Energy storage system, and method for operating the energy storage system

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 at least one energy storage module (2), and a switch (5) connected in parallel to the resistor (4), wherein the switch and resistor (4) are configured to be connected to a reference potential (10), and at least one energy storage module (2) comprises an energy storage block (6), and at least one energy storage module (2) comprises a half-bridge module (7) electrically connected to the energy storage block (6). Furthermore, a method for operating the energy storage system is provided.

Description

Technical Field

[0001] The present disclosure relates to an energy storage system and a method of operating an energy storage system.

Background Art

[0002] High voltage direct current (HVDC) transmission is commonly used to integrate a remotely located renewable energy-based power generating unit (RPGU) into an alternating current (AC) grid. Inertia support is becoming an additional requirement for large-scale power electronics integration of renewable power into the AC grid. However, considering the inherent overload capacity of the converters in the HVDC transmission system, it is a wise choice to incorporate energy storage capabilities on the DC side while maintaining the chopper operation within the same structure to handle excess energy.

Summary of the Invention

Means for Solving the Problems

[0003] Embodiments of the present disclosure relate to an energy storage system with improved functionality. Further embodiments relate to a method of operating an energy storage system.

[0004] This is achieved by the subject matter of the independent claims. Further embodiments are apparent from the dependent claims and the following description.

[0005] An energy storage system will be described. Exemplarily, the energy storage system is connected to a power grid via a power transmission system. In particular, the energy storage system is configured to reduce the energy imbalance of the power grid. In particular, the energy storage system is configured to receive current from the power grid and provide current to the power grid.

[0006] According to one 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 configured to be connected, for example, to an energy source and / or energy load. The at least one energy storage module is configured, in particular, independently of each other, to receive current from the power transmission system and to supply energy to the power transmission system.

[0007] Exemplary, an energy storage system comprises multiple energy storage modules. For example, the energy storage modules are connected in series. Exemplary, 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 current from and supply energy to the power transmission system, particularly independently of each other.

[0008] According to this embodiment, the energy storage system comprises a resistor connected in series with at least one energy storage module. Exemplarily, the resistor is configured to receive current from a power transmission system. The resistor is, for example, a single resistor or comprises a plurality of sub-resistors that form a resistor. The sub-resistors are connected in series and / or in parallel.

[0009] According to this embodiment, the energy storage system comprises a switch connected in parallel with a resistor, and the switch and resistor are configured to be connected to a reference potential. Exemplarily, the resistor and switch are arranged in series between at least one energy storage module and the reference potential. The reference potential is, in particular, the ground potential, i.e., earth. For example, the switch is configured to bypass the resistor when the switch is closed. The switch is configured to transmit current when the switch is closed, for example. The switch is configured to transmit current through the resistor when the switch is open, for example.

[0010] When an energy storage system comprises multiple energy storage modules, the energy storage modules are connected in series. For example, resistors and switches, energy storage modules, and inductor elements are connected in series between the reference potential and the power transmission system, in the order specifically shown.

[0011] According to this embodiment of the energy storage system, at least one energy storage module comprises an energy storage block. The energy storage block is, for example, an electrical energy accumulator configured to store and release electrical energy. The energy storage block is, for example, at least one of a battery module and a supercapacitor. The energy storage block comprises, for example, at least two terminals, namely a first terminal and a second terminal. In particular, these terminals have opposite polarities. If the energy storage is a battery, these terminals comprise an anode terminal and a cathode terminal. If the energy storage is a supercapacitor, these terminals comprise a positive terminal and a negative terminal. In particular, electrical energy is stored in the electric field between these terminals.

[0012] The energy storage block may further comprise multiple electrical storage cells connected to one another. For example, the electrical storage cells may be connected to one another in series and / or in parallel.

[0013] According to this embodiment of the energy storage system, at least one energy storage module comprises a half-bridge module electrically connected to an energy storage block. In particular, the half-bridge module comprises power semiconductor elements arranged within a half-bridge mechanism. Specifically, the half-bridge module comprises only two power semiconductor elements, each of which comprises one power switching element.

[0014] Advantageously, the number of power electronics components required can be reduced by using half-bridge modules within the energy storage system for all energy storage modules. This, advantageously, leads to a reduction in the cost and footprint of the energy storage system. In particular, the use of half-bridge modules reduces the overall size, complexity, and cost of the system.

[0015] In particular, compared to other configurations such as the full-bridge mechanism, the half-bridge mechanism has the advantage of having lower switching losses. Therefore, reduced power loss and improved efficiency are achieved.

[0016] In short, the energy storage system can maintain chopper operation within the same structure to handle excess energy, while its energy storage capacity is integrated into the DC side of the transmission system. This means that the energy storage system is advantageously configured to provide inertial support in the power grid when needed. At the same time, the energy storage system is also advantageously configured to provide DC chopper functionality to comply with the fault ride-through (FRT) requirements of the power grid.

[0017] According to a further embodiment of the energy storage system, the half-bridge module comprises a first power switching element and a second power switching element. In particular, the half-bridge module comprises only two power switching elements. Exemplarily, the power switching elements, i.e., the first power switching element and the second power switching element, are configured to control the polarity and magnitude of the current applied to the energy storage block depending on the switching state. Furthermore, the power switching elements are configured to bypass the energy storage block depending on the switching state. Exemplarily, each of these power switching elements is formed by a semiconductor power switch, which includes, in particular, 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 commutation thyristor (IGCT). An IGBT has, for example, three terminals, i.e., a gate terminal, an emitter terminal, and a collector terminal. Similarly, a MOSFET has, for example, three terminals, i.e., a gate terminal, a source terminal, and a drain terminal.

[0018] For example, the first power switching element is a low-side switch for the energy storage block, and the second power switching element is a high-side switch for the energy storage block.

[0019] According to a further embodiment of the energy storage system, a first power switching element and a second power switching element are connected in series. In particular, the first power switching element and the second power switching element are connected by a first bridge node. The first bridge node is characterized, for example, by a common connection point where the first power switching element and the second power switching element are connected in series. Exemplarily, the collector terminal of the first power switching element and the emitter terminal of the second power switching element are connected by the first bridge node.

[0020] According to a further embodiment of the energy storage system, 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 configured to store and release electrical energy. The further energy storage block is, for example, at least one of a further battery module and a further supercapacitor.

[0021] The further energy storage block comprises, for example, at least two further terminals, namely a further first terminal and a further second terminal. In particular, these further terminals, like the terminals of the energy storage block, have opposite polarities.

[0022] According to a further embodiment of the energy storage system, at least one energy storage module comprises a switching module. For example, the switching module comprises an additional power switching element positioned between an energy storage block and a further energy storage block.

[0023] For example, during the operation of a typical energy storage system with typical energy storage modules, the supercapacitor current fluctuates between non-zero and zero at the switching frequency of each energy storage block of the typical energy storage modules that are inserted and bypassed during operation. Therefore, the current switching frequency of the supercapacitor between zero and non-zero is equal to the output voltage switching frequency of the typical energy storage module. Generally, if the current switching frequency of the supercapacitor between zero and non-zero is higher than 2 Hz, the capacitance decreases, and ultimately the available stored energy decreases. Generally, to limit peak-to-peak current ripple, the effective current switching frequency of the typical energy storage module is increased by proportionally increasing the number of energy storage modules as the average voltage of each energy storage block decreases.

[0024] However, an energy storage system having at least one energy storage module with a switching module, in particular, can advantageously incorporate an energy storage module having an HVDC network, illustratively on the DC side. Further, such an energy storage module can provide a DC chopper function and / or energy support to a power transmission system.

[0025] Advantageously, the proposed configuration can achieve a higher switching frequency compared to a general energy storage module, and can transmit power to a power transmission system with a low current ripple, and vice versa. The modularity and redundancy of the said configuration are high. Optimization of the design of the energy storage system in terms of the number of energy storage modules and / or the inductor size is possible. This topology can be used for HVDC transmission system interconnection even without a DC chopper function.

[0026] As a result, the use of such an energy storage module is further advantageously of a relatively low footprint.

[0027] According to a further embodiment of the energy storage system, the switching module comprises a third power switching element, a fourth power switching element, and a fifth power switching element. Illustratively, the power switching elements, namely the third power switching element, the fourth power switching element, and the fifth power switching element, are configured to control the polarity and magnitude of the current applied to a further energy storage block, and in particular, are configured to control the polarity and magnitude of the current applied to the energy storage block according to the switching state.

[0028] Exemplary, a third power switching element is a low-side switch for further energy storage blocks, and a fourth power switching element is a high-side switch for further energy storage blocks. Each of these power switching elements is exemplary formed from a semiconductor power switch, which includes, in particular, IGBTs, MOSFETs, HEMTs, and / or IGCTs.

[0029] According to a further embodiment of the energy storage system, a third power switching element, a fourth power switching element, and a fifth power switching element are connected in series. In particular, the third power switching element and the fourth power switching element are connected by a second bridge node. The second bridge node is characterized, for example, at a common connection point where the third power switching element and the fourth power switching element are connected in series. Exemplarily, the collector terminal of the third power switching element and the emitter terminal of the fourth power switching element are connected by the second bridge node.

[0030] In particular, the fourth and fifth power switching elements are connected by a third bridge node. The third bridge node is characterized, for example, by a common connection point where the fourth and fifth power switching elements are connected in series. Exemplarily, the collector terminal of the fourth power switching element and the emitter terminal of the fifth power switching element are connected by the third bridge node.

[0031] According to a further embodiment of the energy storage system, a fourth power switching element and a fifth power switching element are connected in parallel to the energy storage block. For example, the fourth power switching element is connected to the first terminal, in particular by a second bridge node. For example, the fifth power switching element is connected to the second terminal, in particular by a connection on the opposite side of the third bridge node. The connection of the fifth power switching element on the opposite side of the third bridge node is characteristic, for example, at the collector terminal of the fifth power switching element.

[0032] According to a further embodiment of the energy storage system, a third power switching element and a fourth power switching element are connected in parallel to a further energy storage block. For example, the third power switching element is connected to a further first terminal, particularly by a connection on the opposite side of the second bridge node. The connection of the third power switching element on the opposite side of the second bridge node is characteristic, for example, at the emitter terminal of the third power switching element. For example, the fourth power switching element is connected to a further second terminal, particularly by the third bridge node.

[0033] According to a further embodiment of the energy storage system, a first power switching element and a second power switching element are connected in parallel to a switching module. For example, the first power switching element is connected to a third power switching element, particularly by a connection of the first power switching element on the opposite side of the first bridge node, to a connection of the third power switching element on the opposite side of the second bridge node. The connection of the first power switching element on the opposite side of the first bridge node is, for example, characteristic of the emitter terminal of the first power switching element. Furthermore, exemplary, the second power switching element is connected to a second terminal and a fifth power switching element, particularly by a connection of the second power switching element on the opposite side of the first bridge node, to a connection of the fifth power switching element on the opposite side of the third bridge node. The connection of the second power switching element on the opposite side of the first bridge node is, for example, characteristic of the collector terminal of the second power switching element.

[0034] Exemplary, the first bridge node is connected to the power transmission system via an inductor element, and the connection point of the first power switching module on the opposite side of the first bridge node is connected to a reference potential via resistors and switches.

[0035] If the energy storage system comprises multiple energy storage modules, the energy storage module closest to the power transmission system is connected to the power transmission system via an inductor element by a first bridge node. Furthermore, the energy storage module closest to the resistors and switches is connected to the resistors and switches, for example, by a connection point of a first power switching module located on the opposite side of the first bridge node.

[0036] According to a further embodiment of the energy storage system, a first power switching element and a second power switching element are connected in parallel to the energy storage block. For example, the first power switching element is connected to a first terminal, particularly by a connector on the opposite side of the first bridge node. Furthermore, exemplary, the second power switching element is connected to a second terminal, particularly by a connector on the opposite side of the first bridge node.

[0037] For example, the first bridge node is connected to the power transmission system via an inductor element, and the connection point of the third power switching module, opposite the second bridge node, is connected to a reference potential via resistors and switches.

[0038] If the energy storage system comprises multiple energy storage modules, the energy storage module closest to the power transmission system is connected to the power transmission system via an inductor element by a first bridge node. Furthermore, the energy storage module closest to the resistors and switches is connected to the resistors and switches, for example, by a connection point of a third power switching module located opposite the second bridge node.

[0039] According to a further embodiment of the energy storage system, at least one energy storage module comprises a further half-bridge module comprising a sixth power switching element and a seventh power switching element. Exemplarily, the power switching elements, i.e., the sixth and seventh power switching elements, are configured to control the polarity and magnitude of the current applied to the further energy storage block or, in particular, to the energy storage block and the further energy storage block, depending on the switching state. Each of these power switching elements is exemplary formed by a semiconductor power switch, the semiconductor power switch includes, in particular, IGBTs, MOSFETs, HEMTs and / or IGCTs.

[0040] According to a further embodiment of the energy storage system, a sixth power switching element and a seventh power switching element are connected in series. In particular, the sixth power switching element and the seventh power switching element are connected by a fourth bridge node. The fourth bridge node is characterized, for example, at a common connection point where the sixth power switching element and the seventh power switching element are connected in series. Exemplarily, the collector terminal of the sixth power switching element and the emitter terminal of the seventh power switching element are connected by the fourth bridge node.

[0041] According to a further embodiment of the energy storage system, a further half-bridge module is connected in parallel to the switching module. For example, a sixth power switching element is connected to a further first terminal and a third power switching element, particularly by a connection on the opposite side of the fourth bridge node, to a connection of the third power switching element on the opposite side of the second bridge node. The connection of the sixth power switching element on the opposite side of the fourth bridge node is characteristic, for example, to the emitter terminal of the sixth power switching element.

[0042] Furthermore, exemplary, the seventh power switching element is connected to the fifth power switching element, particularly by a connection of the seventh power switching element on the opposite side of the fourth bridge node, to a connection of the fifth power switching element on the opposite side of the third bridge node. The connection of the seventh power switching element on the opposite side of the fourth bridge node is characteristic, for example, the collector terminal of the seventh power switching element.

[0043] According to a further embodiment of the energy storage system, further half-bridge modules are connected in parallel to further energy storage blocks. For example, a sixth power switching element is connected to a further first terminal, particularly by a connector on the opposite side of the fourth bridge node. Furthermore, exemplary, a seventh power switching element is connected to a further second terminal, particularly by a connector on the opposite side of the fourth bridge node.

[0044] For example, the sixth power switching element is a low-side switch for an additional energy storage block, and the seventh power switching element is a high-side switch for an additional energy storage block.

[0045] For example, the first bridge node is connected to the power transmission system via an inductor element, and the fourth bridge node is connected to a reference potential via resistors and switches.

[0046] If the energy storage system comprises multiple energy storage modules, the energy storage module closest to the power transmission system is connected to the power transmission system by a first bridge node. Furthermore, the energy storage module closest to the resistors and switches is connected to the resistors and switches by a fourth bridge node.

[0047] According to a further embodiment of the energy storage system, at least one energy storage module comprises only a half-bridge module electrically connected to an energy storage block. If the energy storage system comprises multiple energy storage modules, each energy storage module comprises, exemplary, only one half-bridge module.

[0048] Advantageously, such energy storage systems are low-cost and have a low footprint, especially compared to full-bridge topologies.

[0049] In this embodiment, the energy storage module closest to the resistor and switch is connected to the resistor and switch by a connection of the first power switching element located opposite 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 an inductor element by the first bridge node.

[0050] Alternatively, in this embodiment, the energy storage module closest to the resistor and switch is connected to the resistor and switch by a first bridge node. In this case, the energy storage module closest to the power transmission system is connected to the power transmission system via an inductor element by a connection of a second power switching element located opposite the bridge node.

[0051] According to a further embodiment of the energy storage system, the switch is a high-speed switch. In particular, the switch is a high-speed mechanical switch.

[0052] According to a further embodiment of the energy storage system, an inductor element is arranged between the power transmission system and at least one energy storage module, in particular the energy storage module closest to the power transmission system. Specifically, the inductor element is arranged in series between the power transmission system and the energy storage module closest to the power transmission system.

[0053] Advantageously, the current supplied to and from the power transmission system is regulated to a suitable level by the inductance.

[0054] 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.

[0055] 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 controllable by a master control unit. These control units may be located within at least one of the energy storage module, resistors, switches, and inductor elements. Furthermore, at least some of the control units are located externally, for example.

[0056] According to a further embodiment of the energy storage system, the control system is configured to control at least one energy storage module, in particular each energy storage module.

[0057] According to a further embodiment of the energy storage system, the control system is configured to control switches. In particular, the control system is configured to switch two power switching elements of each energy storage module. Exemplaryly, the controller is configured to control the energy storage modules and switches independently of each other.

[0058] The control system may further include a sensing unit configured to detect the current and / or voltage of the half-bridge module, resistors, switches, inductor elements, and / or energy storage blocks.

[0059] 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, which may be, for example, a wind power plant, a solar power plant, and / or a hydroelectric power plant.

[0060] Further embodiments relate to a method for operating an energy storage system having at least two energy storage modules connected in series, in particular the energy storage system described herein. Thus, the features described in connection with the above method are also applicable to the energy storage system, and vice versa.

[0061] According to one embodiment, the method includes a first mode configured to supply energy to an energy storage system, wherein the first mode is specifically an energizing mode. Exemplarily, the energy storage module is charged to a predetermined voltage, for example, a nominal voltage.

[0062] According to this embodiment, the method includes 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 idle mode. In the second mode, the energy storage module is configured to provide a predetermined pole voltage that matches, for example, the voltage of a transmission system.

[0063] According to this embodiment, the method includes a third mode configured to supply energy to a power transmission system.

[0064] According to this embodiment, the method includes a fourth mode configured to dissipate energy from the power transmission system. In the fourth mode, the total power of the transmission system is distributed to resistors.

[0065] According to this embodiment of the method described above, each energy storage module can be inserted into or bypassed by a half-bridge module in a series connection.

[0066] According to a further embodiment of the above method, the energy storage module is bypassed when the first power switching element is in a closed state and the second power switching element is in an open state.

[0067] According to a further embodiment of the above method, a predetermined number of energy storage modules are inserted in series to charge the energy storage blocks of the inserted energy storage modules, and while energy is being supplied to the energy storage system, the switch is open for a first time interval and closed for a second time interval, depending on the voltage of the power transmission system.

[0068] This method step is characterized by the first method step, namely the charging of the energy storage system.

[0069] According to a further embodiment of the above method, a predetermined number of energy storage modules are inserted in series such that the voltage of the inserted energy storage modules is equal to the voltage of the power transmission system, a further predetermined number of energy storage modules are bypassed in series, and the switch is closed.

[0070] This method stage is characteristic of the second method stage, namely the idle state of the energy storage system.

[0071] According to a further embodiment of the above method, a predetermined number of energy storage modules are inserted in series according to a predetermined voltage such that the voltage of the inserted energy storage modules is greater than the voltage of the power transmission system, and the switch is in the closed state.

[0072] This method step is characteristic of the third method step, namely the discharge of the energy storage system.

[0073] According to a further embodiment of the above method, in a series connection, all energy storage modules are bypassed and the switch is open.

[0074] This method step is characterized by the fourth method step, namely, energy dissipation through the resistors of the energy storage system.

[0075] The attached drawings are included for further understanding. In the drawings, elements of the same structure and / or function may be referred to by the same reference numerals. It should be understood that the embodiments shown in the drawings are illustrative and not necessarily drawn to scale. [Brief explanation of the drawing]

[0076] [Figure 1]This is a schematic diagram of an energy storage system according to an exemplary embodiment. [Figure 2] This is a schematic diagram of an energy storage module of an energy storage system according to an exemplary embodiment. [Figure 3] This is a schematic diagram of an energy storage module of an energy storage system according to an exemplary embodiment. [Figure 4] This is a schematic diagram of an energy storage module of an energy storage system according to an exemplary embodiment. [Figure 5] This is a schematic diagram of an energy storage module of an energy storage system according to an exemplary embodiment. [Figure 6] This is a schematic diagram of an energy storage module of an energy storage system according to an exemplary embodiment. [Figure 7] This is a schematic diagram of an energy storage module of an energy storage system according to an exemplary embodiment. [Figure 8] This diagram schematically shows the bypass mode and insertion mode of the energy storage module of an energy storage system according to an exemplary embodiment. [Figure 9] This diagram schematically shows the bypass mode and insertion mode of the energy storage module of an energy storage system according to an exemplary embodiment. [Figure 10] This diagram schematically shows the bypass mode and insertion mode of the energy storage module of an energy storage system according to an exemplary embodiment. [Modes for carrying out the invention]

[0077] The energy storage system 1 according to an exemplary embodiment shown in Figure 1 comprises a plurality of energy storage modules 2. The energy storage modules 2 are connected in series with each other and are located between the power transmission system 3 and the reference potential 10.

[0078] A resistor 4 and a switch 5 are positioned between the energy storage module 2 and the reference potential 10. The resistor 4 and switch 5 are connected in parallel. Switch 5 is a fast switch and is configured to bypass the resistor 4 when it is closed.

[0079] An inductor element 8 containing at least one inductance is arranged in series between the energy storage module 2 and the power transmission system 3.

[0080] Accordingly, the potential U d ,U ch_v ,U o_v and current I ch This is shown in Figure 1. Potential U d This is defined between the power transmission system 3 and the reference potential 10, and the potential U ch_v This is defined between the terminals of the outer energy storage module 2, and the potential U o_v The current I is defined between two terminals of each energy storage module 2. ch This is the current supplied from the power transmission system 3 to the energy storage module 2 or from the energy storage module 2 to the power transmission system 3.

[0081] In particular, each energy storage module 2 includes an energy storage block 6, and each energy storage module 2 includes a half-bridge module 7 electrically connected to the energy storage block 6, which will be explained in more detail in relation to Figures 2 to 7.

[0082] Advantageously, dual functionality of energy support and FRT grid code compliance is achieved by using an energy storage module 2 with a half-bridge module 7, an inductor element 8, and a resistor 4 with a switch 5 connected in series.

[0083] For example, the energy storage module 2 is grouped into multiple arms, for instance, two arms as illustrated in Figure 1, namely the first arm 11 and the second arm 12. For instance, the number of energy storage modules 2 in the second arm is designed to match the maximum DC link voltage to the power transmission system 3, while the number of energy storage modules 2 in the first arm 11 is designed to meet the energy needs of the connected power grid 9. In particular, the energy storage modules 2 can be sorted across the entire arm to achieve balance among the energy storage modules 2.

[0084] In particular, as will be explained in more detail in relation to Figures 8, 9, and 10, each energy storage module 2 can be inserted into or bypassed by the half-bridge module 7. Thus, such an energy storage system 1 as shown in Figure 1 can be operated in several different modes.

[0085] The first mode is configured to supply energy to the energy storage system 1, i.e., it is an energizing mode or a charging mode. In the first mode, a predetermined number of energy storage modules 2 are inserted in series to charge the energy storage block 6 of the inserted energy storage modules 2, and while supplying energy to the energy storage system 1, the switch 5 is open for a first time interval and closed for a second time interval, depending on the voltage of the power transmission system 3. Exemplarily, energy storage modules 2 are inserted in the first arm 11 and the second arm 12.

[0086] In this first mode, the energy storage modules 2 are charged to their nominal voltages. In particular, switch 5 is initially open to allow control of the charging of the inserted energy storage modules 2 during the first time interval. Furthermore, in the second time interval, i.e., after the first time interval, switch 5 is closed when the total voltage approaches the DC link voltage to facilitate the boost operation. Charging control is performed to increase the voltage in each energy storage module 2 to its corresponding nominal value.

[0087] In particular, in the first mode, each of the half-bridge modules 7 of one or more of the energy storage modules 2 is configured so that its respective energy storage block 6 receives electrical energy from the power transmission system 3, and the resistor 4 is bypassed via the switch 5. Energy storage modules 2 that are not configured to receive electrical energy from the power transmission system 3 are configured so that their respective energy storage blocks 6 are bypassed.

[0088] The second mode is configured to keep the energy storage system 1 in an idle state, i.e., the idle mode. In the second mode, a predetermined number of energy storage modules 2 are inserted in series, a further predetermined number of energy storage modules 2 are bypassed in series, and the switch 5 is closed, such that the voltage of the inserted energy storage modules 2 is equal to the voltage of the power transmission system 3. 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.

[0089] 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. Switch 5 remains closed during the second mode.

[0090] The third mode is configured to provide energy to the power transmission system 3, i.e., it is an energy support mode. In the third mode, a predetermined number of energy storage modules 2 are inserted in series according to a predetermined voltage, such that the voltage of the inserted energy storage modules 2 is greater than the voltage of the power transmission system 3, and the switch 5 is closed. Exemplarily, energy storage modules 2 in the first arm 11 and energy storage modules 2 in the second arm 12 are inserted.

[0091] In particular, in the third mode, the half-bridge module 7 of each energy storage module 2 is configured such that the energy storage block 6 of each energy storage module 2 discharges electrical energy to the power transmission system 3 to achieve a predetermined voltage. Energy storage modules 2 that do not discharge electrical energy are configured, for example, so that their respective energy storage blocks 6 are bypassed.

[0092] The 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 series connection, and switch 5 is open.

[0093] In particular, in the fourth mode, the half-bridge module 7 of each energy storage module 2 is configured to bypass the energy storage block 6, and the switch 5 is open so that the resistor 4 dissipates electrical energy from the power transmission system 3.

[0094] In short, in the event of a DC fault, the energy storage module 2 can bypass its disconnector with zero current and open, thereby achieving fault tolerance. Overall, the proposed topology of the energy storage system 1 is advantageous in that it has an optimal design in terms of the number of energy storage modules 2 and the inductor size.

[0095] Each energy storage module 2 according to the exemplary embodiment shown in 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 module 7 comprises a first power switching element 13 and a second power switching element 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.

[0096] The first power switching element 13 is connected to the first terminal 16 by a connector on the opposite side of the first bridge node 15. The second power switching element 14 is connected to the second terminal 17 by a connector on the opposite side of the first bridge node 15.

[0097] The energy storage modules 2 in Figure 2 are interconnected via a first bridge node 15 and a first terminal 16 having a connection on the opposite side of the first bridge node 15. In this case, the first bridge node 15 is connected to the connection of a first power switching element 13 on the opposite side of the first bridge node 15 of a directly adjacent energy storage module 2 facing the power transmission system 3. Furthermore, the connection of the first power switching element 13 on the opposite side of the first bridge node 15 is connected to the first bridge node 15 of a directly adjacent energy storage module 2 facing the reference potential 10.

[0098] The energy storage module 2 in Figure 3 is interconnected with the first bridge node 15 via a second terminal 17 having a connection on the opposite side of the first bridge node 15. In this case, the first bridge node 15 is connected to a connection on the opposite side of the first bridge node 15 of a directly adjacent energy storage module 2 facing the reference potential 10. Furthermore, the connection on the opposite side of the first bridge node 15 of the second power switching element 14 is connected to the first bridge node 15 of a directly adjacent energy storage module 2 facing the power transmission system 3.

[0099] Each energy storage module 2 according to the exemplary embodiments shown in Figures 4, 5, 6, and 7 comprises an additional energy storage block 18 and a switching module 21, in addition to the exemplary embodiments shown in Figures 2 and 3. The switching module 21 comprises a third power switching element 22, a fourth power switching element 23, and a fifth power switching element 24 connected in series. The third power switching element 22 and the fourth power switching element 23 are connected in series via a second bridge node 25, and the fourth power switching element 23 and the fifth power switching element 24 are connected in series via a third bridge node 26.

[0100] In Figure 4, the first power switching element 13 is connected to the connection of the third power switching element 22, which is on the opposite side of the second bridge node 25, by a connection on the opposite side of the first bridge node 15. The second power switching element 14 is connected to the connection of the second terminal 17 and the connection of the fifth power switching element 24, which is on the opposite side of the third bridge node 26, by a connection on the opposite side of the first bridge node 15.

[0101] The fourth power switching element 23 and the fifth power switching element 24 are connected in parallel to the energy storage block 6. The fourth power switching element 23 is connected to the first terminal 16 by the second bridge node 25. The fifth power switching element 24 is connected to the second terminal 17 and to the connection of the second power switching element 14 on the opposite side of the first bridge node 15 by a connection on the opposite side of the third bridge node 26.

[0102] Furthermore, the third power switching element 22 and the fourth power switching element 23 are connected in parallel to an additional energy storage block 18. The third power switching element 22 is connected to a connection at an additional first terminal 19 by a connection on the opposite side of the second bridge node 25. The fourth power switching element 23 is connected to an additional second terminal 20 by a third bridge node 26.

[0103] The connection to the power transmission system 3 is provided via the first bridge node 15. The connection to the reference potential 10 is provided via the connection of the first power switching element 13, which is located on the opposite side of the first bridge node 15.

[0104] In Figure 5, in particular, in contrast to the energy storage modules 2 in Figure 4, the first power switching element 13 and the second power switching element 14 are connected in parallel to the energy storage block 6. The first power switching element 13 is connected to the first terminal 16 and the second bridge node 25 by a connector on the opposite side of the first bridge node 15. The second power switching element 14 is connected to the second terminal 17 and the connector of the fifth power switching element 24 on the opposite side of the third bridge node 26 by a connector on the opposite side of the first bridge node 15.

[0105] The connection to the power transmission system 3 is provided via the first bridge node 15. The connection to the reference potential 10 is provided via the connection of the third power switching element 22, which is opposite the second bridge node 25.

[0106] The energy storage module 2 shown in Figure 6 has, in addition to the energy storage module 2 shown in Figure 4, a further half-bridge module 27 comprising a sixth power switching element 28 and a seventh power switching element 29 connected in series. The sixth power switching element 28 and the seventh power switching element 29 are connected in series via a fourth bridge node 30.

[0107] A further half-bridge module 27 is connected in parallel to the switching module 21. The connection point of the sixth power switching element 28, opposite the fourth bridge node 30, is connected to a further first terminal 19 and to the connection point of the third power switching element 22, opposite the second bridge node 25. The connection point of the seventh power switching element 29, opposite the fourth bridge node 30, is connected to the connection point of the fifth power switching element 24, opposite the third bridge node 26.

[0108] The energy storage module 2 shown in Figure 7 has, in addition to the energy storage module 2 shown in Figure 5, a further half-bridge module 27 as described in relation to Figure 6. In contrast to Figure 6, the further half-bridge module 27 in Figure 7 is connected in parallel to a further energy storage block 18. The connection of the sixth power switching element 28, opposite the fourth bridge node 30, is connected to a further first terminal 19 and to the connection of the third power switching element 22, opposite the second bridge node 25. The connection of the seventh power switching element 29, opposite the fourth bridge node 30, is connected to a further second terminal 20 and the third bridge node 26.

[0109] In Figures 6 and 7, the connection to the power transmission system 3 is provided via the first bridge node 15. Furthermore, the connection to the reference potential 10 is provided via the fourth bridge node 30.

[0110] Figures 8, 9, and 10 illustrate the insertion and bypass modes of the energy storage module 2 according to the exemplary embodiment of Figure 4. In particular, the energy storage module 2 is exemplary located within the first arm 11 in Figure 1 and generally operates in bypass and insertion modes. Therefore, the following description is also applicable to energy storage module 2 of different embodiments.

[0111] Figure 8 illustrates the bypass mode. When the first power switching element 13 is in a switching state characteristic of the closed state and the second power switching element 14 is in a switching state characteristic of the open state, the energy storage module 2 is bypassed. In the closed state, the power switching elements are configured to transmit current. Therefore, in the open state, the power switching elements are configured to block current.

[0112] In bypass mode, the output voltage of energy storage module 2 is zero, and the current flowing through energy storage block 6 and further energy storage block 18 is also zero.

[0113] Figures 9 and 10 illustrate the insertion mode. When the second power switching element 14 is in a closed state and the first power switching element 13 is in an open state, the energy storage module 2 is inserted. Depending on the switching state of the switching module 21, the energy storage module 2 can output two different output voltages. This is advantageous because it is possible to achieve two different voltage levels at the output of each energy storage module 2.

[0114] When the third power switching element 22 and the fifth power switching element 24 are both in the closed state and the fourth power switching element 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 means that the output voltage of the energy storage module 2 is equal to the voltage between the energy storage block 6 and the further energy storage block 18. In this configuration, the current flowing through the energy storage block 6 and the further energy storage block 18 is half the output current of the energy storage module 2.

[0115] When the fourth power switching element 23 is closed and the third power switching element 22 and the fifth power switching element 24 are each open, the energy storage block 6 and the further energy storage block 18 are connected in series as shown in Figure 10. In this configuration, the output voltage of the energy storage module 2 is equal to the sum of the voltages between the energy storage block 6 and the further energy storage block 18 that carry the output current of the energy storage module 2.

[0116] Advantageously, the energy storage module 2, having two separate output voltages, plays a crucial role in supplying energy to the power transmission system 3. Furthermore, the energy storage block 6 and the additional energy storage block 18 carry non-zero currents, thereby allowing the switching module 21 to operate at higher switching frequencies without losing the available stored energy in the energy storage block 6 and the additional energy storage block 18. [Explanation of symbols]

[0117] 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 element, 9 Power grid, 10 Reference potential, 11 First arm, 12 Second arm, 13 First power switching element, 14 Second power switching element, 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 element, 23 Fourth power switching element, 24 Fifth power switching element, 25 Second bridge node, 26 Third bridge node, 27 Further half-bridge module, 28 Sixth power switching element, 29 Seventh power switching element, 30 Fourth bridge node.

Claims

1. Energy storage system (1), At least one energy storage module (2) configured to be connected to a power transmission system (3), A resistor (4) connected in series with at least one energy storage module (2), The system comprises a switch (5) connected in parallel to the resistor (4), and the switch and the resistor (4) are configured to be connected to a reference potential (10). The at least one energy storage module (2) comprises an energy storage block (6), The energy storage system (1) comprises at least one energy storage module (2) which includes a half-bridge module (7) electrically connected to the energy storage block (6).

2. The half-bridge module (7) comprises a first power switching element (13) and a second power switching element (14), The energy storage system (1) according to claim 1, wherein the first power switching element (13) and the second power switching element (14) are connected in series.

3. The at least one energy storage module (2) comprises a further energy storage block (18), The energy storage system (1) according to claim 1 or 2, wherein the at least one energy storage module (2) comprises a switching module (21).

4. The switching module (21) comprises a third power switching element (22), a fourth power switching element (23), and a fifth power switching element (24). The energy storage system (1) according to claim 3, wherein the third power switching element (22), the fourth power switching element (23), and the fifth power switching element (24) are connected in series.

5. The fourth power switching element (23) and the fifth power switching element (24) are connected in parallel to the energy storage block (6), The energy storage system (1) according to claim 4, wherein the third power switching element (22) and the fourth power switching element (23) are connected in parallel to the further energy storage block (18).

6. The first power switching element (13) and the second power switching element (14) are connected in parallel to the switching module (21). The energy storage system (1) according to claim 5, wherein the first power switching element (13) and the second power switching element (14) are connected in parallel to the energy storage block (6).

7. The at least one energy storage module (2) comprises a further half-bridge module (27) having a sixth power switching element (28) and a seventh power switching element (29), The energy storage system (1) according to any one of claims 3 to 6, wherein the sixth power switching element (28) and the seventh power switching element (29) are connected in series.

8. The further half-bridge module (27) is connected in parallel to the switching module (21), The energy storage system (1) according to claim 7, wherein the further half-bridge module (27) is connected in parallel to the further energy storage block (18).

9. The energy storage system (1) according to claim 1 or 2, wherein the at least one energy storage module (2) comprises only the half-bridge module (7) electrically connected to the energy storage block (6).

10. The energy storage system (1) according to any one of claims 1 to 9, wherein the switch (5) is a high-speed mechanical switch.

11. The energy storage system (1) according to any one of claims 1 to 10, wherein an inductor element (8) is arranged between the power transmission system (3) and the at least one energy storage module (2).

12. The energy storage system (1) according to any one of claims 1 to 11, wherein the power transmission system (3) is a direct current (DC) transmission system.

13. 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), The energy storage system (1) according to any one of claims 1 to 12, wherein the control system is configured to control the switch (5).

14. A method for operating an energy storage system (1) according to any one of claims 1 to 13, having at least two energy storage modules (2) connected in series, A first mode configured to supply 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 supply energy to the power transmission system (3), It has a fourth mode configured to dissipate energy from the power transmission system (3), A method wherein each energy storage module (2) is inserted into or bypassed by the half-bridge module (7) in the series connection.

15. The method according to claim 14, wherein the energy storage module (2) is bypassed when the first power switching element (13) is in a closed state and the second power switching element (14) is in an open state.

16. The method according to any one of claims 14 or 15, wherein the energy storage module (2) is inserted when the first power switching element (13) is in an open state and the second power switching element (14) is in a closed state.

17. In order to charge the energy storage block of the inserted energy storage module (2), a predetermined number of the energy storage modules (2) are inserted in the series connection, The method according to any one of claims 14 to 16, wherein while energy is being supplied to the energy storage system (1), the switch (5) is opened for a first time interval and closed for a second time interval, depending on the voltage of the power transmission system (3).

18. A predetermined number of energy storage modules (2) are inserted in the series connection such that the voltage of the inserted energy storage modules (2) is equal to the voltage of the power transmission system (3), and a further predetermined number of energy storage modules (2) are bypassed in the series connection. The method according to any one of claims 14 or 17, wherein the switch (5) is closed.

19. A predetermined number of energy storage modules (2) are inserted in the series connection according to a predetermined voltage such that the voltage of the inserted energy storage modules (2) is greater than the voltage of the power transmission system (3). The method according to any one of claims 14 to 18, wherein the switch (5) is closed.

20. In the aforementioned series connection, all energy storage modules (2) are bypassed. The method according to any one of claims 14 to 19, wherein the switch (5) is opened.

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