Energy storage system and device for intermediate storage of electrical energy

Abstract

Energy storage and conversion device (1) for converting electrical energy from a low-voltage network (3) with voltages less than 1000 V to a medium-voltage network (103) with voltages greater than 1000 V and vice versa, and for storing electrical energy in a flow battery arrangement (20, 120) and for discharging the energy stored in the flow battery arrangement (20, 120), comprising: - the flow battery arrangement (20, 120) with hydraulic connecting lines (24, 124) for exchanging electrolyte from storage tanks (31, 32, 131, 132) to battery cells (7, 8, 107, 108) and back, - a first bidirectionally operable voltage converter device (10) for connection to the low-voltage network (3) and to the flow battery arrangement (20, 120) comprising a first AC / DC converter (2), - a second bidirectionally operable voltage converter device (110) for connection to the medium voltage network (103) and to the flow battery arrangement (20,120) comprising a second AC / DC converter (102), characterized in that the device (1) has an electrical connection (25, 26) and / or a hydraulic connection (24) of both AC / DC converters (2, 102) on its DC side (23) and that the first AC / DC converter (2) is designed to convert energy from the low-voltage network (3) to charge the flow battery arrangement (20, 120) and to convert energy from the flow battery arrangement (20, 120) to feed it into the low-voltage network (3) and that the second AC / DC converter (102) is designed to convert energy from the medium-voltage network (103) to charge the flow battery arrangement (20, 120) and to convert energy from the flow battery arrangement (20, 120) to feed it into the medium-voltage network (103).

Description

The invention relates to an energy storage and conversion device for converting electrical energy from a low-voltage grid having voltages of less than 1000 V into a medium-voltage grid having voltages of more than 1000 V and vice versa, and for storing and discharging electrical energy in electrochemical energy stores.A similar arrangement is described, for example, in DE 10 2008 030 342 A1.Alternative energies are becoming increasingly important. The problem with alternative energies, such as solar energy or wind power, is that the times of energy generation cannot be influenced and excess energy must be temporarily stored, so that it is available at times when no energy can be generated. It is therefore necessary to use energy storage systems. Energy storage systems, however, are subject to losses which should be avoided.A flow battery or an electrochemical energy converter for a flow battery, in particular a redox flow battery with a circulation arrangement for electrolytes and electrolyte lines for supplying and discharging one or more electrolytes from a storage tank to the electrochemical energy converter and further back into the respective storage tank in the form of a circulatory process, is suitable as energy storage, wherein the electrochemical energy converter comprises at least one reaction cell having two electrodes and an ion-conducting membrane, preferably a multiplicity of individual cells connected together electrically. These are preferably supplied with electrolytes in parallel and each have an inlet region for introducing the electrolyte into the reaction cell and an outlet region for discharging the electrolyte from the reaction cell. In order to be able to convert electrical energy particularly efficiently in such an electrochemical energy store, a highly efficient reaction cell is required, which is also called a flow battery stack or stack. In addition, high-efficiency voltage converters are required. The voltage converters are connected to the electrodes of the flow battery stacks.The voltage converters are currently usually designed for a low-voltage power supply system with voltages of less than 1000 V. The storage capacity of flow battery arrangements is, however, comparable to power plants which are also connected to a medium-voltage grid with voltages greater than 1000 V. It would therefore make sense to connect a flux battery arrangement not only via a transformer which converts the high voltages of the medium-voltage grid into the low voltages of a low-voltage grid, but also to provide a voltage converter with which the flux battery arrangement can be connected directly to a medium-voltage grid. However, since the voltage levels of a medium-voltage grid are very far apart from those of a low-voltage grid, it is not possible to use the same voltage converter for both grids. As a result, losses occur in the transformer. In addition, this transformer is very expensive, since it must additionally be designed for a high reactive power.US 2015 / 0 001 931 A1 discloses an energy storage system in which an energy storage is connected to an intermediate circuit network, from which the energy is distributed by means of a transformer in each case to the voltage levels of two different power supply networks.AT 509 888 A4 discloses an energy storage system in which an energy store can be charged and discharged using a plurality of bidirectionally operable current transformer devices. The current transformer devices are connected in parallel to a single current distribution network.The object of the present invention is to provide a device which is suitable for converting electrical energy from a low-voltage grid having voltages of less than 1000 V into a medium-voltage grid having voltages of more than 1000 V and vice versa, and for storing electrical energy in a flow battery arrangement and for discharging the energy stored in the flow battery arrangement, and is firstly more cost-effective and secondly operates more energy-efficiently than conventional energy converters.The object is achieved by the subject matter of claim 1 and the subordinate claims. Advantageous further developments of the invention are found in the dependent claims and in the following description.The object is achieved by a device according to claim 1.To achieve the object, an energy storage and conversion device is proposed which is suitable, and in particular also set up, for converting electrical energy from a low-voltage grid having voltages of less than 1000 V into a medium-voltage grid having voltages of more than 1000 V and vice versa, and for storing electrical energy in a flux battery arrangement and for discharging the energy stored in the flux battery arrangement. This has:the flow battery arrangement having hydraulic connecting lines for exchanging electrolyte from storage tanks to battery cells and back,a first bidirectionally operable voltage converter device for connection to the low-voltage power supply system and to the flow battery arrangement, having a first AC / DC converter,a second bidirectionally operable voltage converter device for connection to the medium voltage network and to the flow battery arrangement, comprising a second AC / DC converter.The device has an electrical connection and / or a hydraulic connection of both AC / DC converters on its DC side. By DC side is meant all components connected to the DC terminal of the AC / DC converters. These can be: an intermediate circuit at the DC-side output of the AC / DC converters, the connections from the voltage converter devices to the flow battery arrangement or arrangements and the hydraulic connections of the flow battery arrangement(s).By means of this connection, the flux battery arrangement can be charged or discharged independently of the voltage level without the energy having to be dissipated through a transformer, which is usually used to change the voltage level.The flow battery arrangement can be constructed in a stationary manner. Very large amounts of energy can thus be stored economically and efficiently.One voltage converter device each can be connected to one flow battery arrangement each. Very large amounts of energy can thus be stored economically and efficiently.In particular, the hydraulic connection of both AC / DC converters on their DC side can be dispensed with. Very large amounts of energy can thus be stored flexibly and efficiently.The connection can be provided as an electrical connection of both AC / DC converters on their DC side, which respectively connects intermediate circuits of the voltage converter device. An intermediate circuit is a connection point within the voltage converter device, at which a DC voltage is present and via which the power is transported. Energy stores, in particular in the form of individual or a plurality of capacitors, can be connected to the intermediate circuit. They can buffer small amounts of energy in comparison with the amounts of energy in the flow battery arrangement and smooth the voltage and damp short-term disturbances.The connection can be provided as an electrical connection of both AC / DC converters on their DC side, which respectively connects the connection terminals of the voltage converter device to the flow battery arrangement. Thus, very large amounts of energy can be stored cost-effectively, flexibly and efficiently.The voltage converter devices may be connected to a single flow battery arrangement. Very large amounts of energy can thus be stored economically and efficiently.The connection can be designed as an exclusively hydraulic connection of both AC / DC converters on their DC side. No additional electrical connection is then provided. Very large amounts of energy can thus be stored economically and efficiently.The flow battery arrangement and the AC / DC converters can each be accommodated individually or together in a unit having the dimensions of a vessel. Thus, very large amounts of energy can be stored cost-effectively, flexibly and efficiently.Between an AC / DC converter and the flow battery arrangement, a bidirectional DC / DC converter can be provided. Thus, very large amounts of energy can be stored cost-effectively, flexibly and efficiently.The low-voltage network can be a network with exclusively regenerative power generators from the group of solar, wind, and water energy. Decentralized regenerative energies can thus be stored directly decentralized and do not have to be transferred first into the medium voltage level by the transformer. The same applies to excesses in the medium-voltage network.A transformer can additionally be provided between the medium-voltage grid and the low-voltage grid. If too little energy is present in a power supply, this can be supplied from the flux battery arrangement and with the transformer. The transformer no longer has to be dimensioned at this point for the absolute maximum apparent power which occurs and can thus be constructed in a more cost-effective and material-saving manner.The transformer can be designed for a reactive current below 50% of the maximum active current for which it is rated. Thus, very large amounts of energy can be stored cost-effectively, flexibly and efficiently.The device may have a controller which is designed to actuate the flow battery arrangement and the AC / DC converter or converters. The controller may be suitable for influencing the power flow direction of the AC / DC converter or converters. The controller may further include an interface to a data communication network such that the power flow direction may be affected depending on data from external data sources. Thus, very large amounts of energy can be stored cost-effectively, flexibly and efficiently.The controller may be configured to drive pumps for circulating electrolyte of the flow batteries. Thus, very large amounts of energy can be stored cost-effectively, flexibly and efficiently.Also disclosed is a method for converting electrical energy from a medium-voltage grid with voltages greater than 1000 V into a low-voltage grid with voltages less than 1000 V and vice versa, with the aid of:a flow battery arrangement,a first bidirectionally operable voltage converter device for connection to the low-voltage power supply system and to a flow battery arrangement, having a first AC / DC converter,a second bidirectionally operable voltage converter device for connection to the medium voltage network and to a flow battery arrangement having a second AC / DC converter,In this case, the energy is conducted from the medium-voltage grid into the low-voltage grid and vice versa via both AC / DC converters and in this case additionally energy is fed from a flow battery arrangement in one of the two grids or energy is fed from one of the two grids into a flow battery arrangement.With the described methods and devices, reactive current compensation can be provided for both networks. Reactive current can be provided by the voltage converter devices that can be operated bidirectionally.In addition, one or more bidirectionally operable voltage converter devices can be designed to supply high-frequency currents that are required on the respective grid. In addition, one or more bidirectionally operable voltage converter devices can be designed to compensate for high-frequency currents which occur as disturbances on the respective grid.With the methods and devices described, energy can be provided from one network to the other, stored from one network, and provided to the other network as needed. A required voltage level at the low voltage grid may be maintained when the medium voltage grid breaks down. Voltage interruptions in both networks can be compensated.For the features of the further development, an increase in efficiency is achieved not only by the individual measures, but in particular by cooperation of all measures. For example, if a controller can control not only the voltage converters but also the pumps for circulating the electrolyte, it can operate the voltage converters in a range more favorable for them than a controller can control only the voltage converters. The same applies to the selection of the energy flow direction into the storage, from the storage, into the low-voltage grid, from the low-voltage grid, into the medium-voltage grid, from the medium-voltage grid. The controller can have all relevant data stored in a memory in order to influence the control of the components in an efficiency-enhancing manner.Exemplary embodiments of the invention are illustrated in the schematic drawings and are explained in more detail in the following description. The following are shown: FIG. 1 shows a first energy storage and conversion device FIGS. 2 to 4 show alternative devicesFIG. 1 shows an energy storage and conversion device 1, which has two current conversion devices 10, 110. It is designed to convert electrical energy from a low-voltage grid 3 with voltages of less than 1000 V into a medium-voltage grid 103 with voltages of greater than 1000 V and vice versa. "and vice versa" here means that the device 1 is also designed to convert energy from a medium-voltage grid 103 with voltages of greater than 1000 V into a low-voltage grid 3 with voltages of less than 1000 V. The energy storage and conversion device 1 has a flow battery arrangement 20 and is designed for storing electrical energy in a flow battery arrangement 20 and for discharging the energy stored in the flow battery arrangement 20. The flow battery assembly 20 includes hydraulic connection lines 24. These are designed for the exchange of electrolyte from storage tanks 31, 32 to battery cells 7, 8, 107, 108 and back. Pumps 33, 34 are arranged in the hydraulic connecting lines 24 for circulating the electrolyte.In addition to the two current conversion devices 10, 110, further current conversion devices can be provided. One of these can be designed for a DC voltage grid of high voltage, for high-voltage transmission (HVDC).The medium voltage network 103 is shown in FIG. 1 as an AC voltage network. However, a direct voltage network of high voltage, for high voltage transmission (HVDC), can also be provided here. The current transformer device 110 is then designed for a DC voltage network with voltages above 1000 V.The first current transformer device 10 has a first voltage converter 2 which can be connected to a single-phase or polyphase low-voltage power supply system 3 with voltages of less than 1000 V. The first voltage converter 2 can be designed as an in particular bidirectional AC / DC converter. It is connected to a first intermediate circuit 4, to which a third and a fourth voltage converter 5, 6 are in turn connected. The voltage converters 5, 6 can be designed, for example, as bidirectional DC / DC converters. They can each convert more than 5 kW of power. More than the two voltage converters 5, 6 shown can be connected to the intermediate circuit 4. The voltage converters 5, 6 can each be connected to one or more electrochemical energy converters, so-called battery cells 7, 8, wherein in the exemplary embodiment shown the voltage converter 5 is connected to the electrochemical energy converter 7 and the voltage converter 6 is connected to the electrochemical energy converter 8.The voltage at the first intermediate circuit 4 can be significantly higher than the voltage at the battery cells 7, 8.Furthermore, the current transformer device 10 can have a first controller 11 which is connected both to the first voltage converter 2 and to the voltage converters 5, 6 and is configured to control these. In particular, the first controller 11 can be configured to control the power flow, in particular the direction of the power flow, in the voltage converters 5, 6. In this case, the first controller 11 can actuate the voltage converters 5, 6 in such a way that, for example, energy is transferred from the electrochemical energy converter 7 via the voltage converter 5, the intermediate circuit 4 and the voltage converter 6 into the electrochemical energy converter 8, or vice versa. During this transfer, the first controller 11 may shut down the voltage converter 2. Furthermore, the first controller 11 can actuate the voltage converters 2, 5, 6 in such a way that a power flow from the power supply network 3 via the voltage converter 2, the intermediate circuit 4 and the voltage converters 5, 6 into the electrochemical energy converters 7 to 10 takes place. The first controller 11 can also control only one of the voltage converters 5, 6, so that, for example, only energy transfer into the battery cell 7 takes place. Furthermore, the first controller 11 can control the power flow in such a way that, for example, energy stored in the battery cell 7 is fed into the power supply network 3 via the voltage converter 5, the intermediate circuit 4 and the voltage converter 2.Furthermore, the first controller 11 may have a first control terminal 17 for connecting at least one energy storage peripheral device.In addition, the first controller 11 may have a first signal input 18 for detecting one or more of the following process parameters:temperature of the electrolyte,pressure of the electrolyteflow rate of the electrolytefill level of the electrolyte in the storage tank 31, 32.In addition, the first controller 11 may have a first port 19 for graphically displaying the process parameters, the power flow direction, the power flow quantity and / or the energy quantity.Because the voltage converter 2 can be switched off and energy transfer between the battery cells 7, 8 is made possible, the energy efficiency of the current transformer device 1 can be further increased. The controller may be configured to control one or more of the following energy storage peripherals depending on the power flow direction of the voltage converter specified by the controller:pumps 33, 34 for circulating the electrolyte,a flow controller for controlling the electrolyte flow rate,temperature control for adjusting the electrolyte temperature,pressure control for adjusting electrolyte pressure.In this case, the controller can have at least one control connection for connecting at least one of these energy storage peripheral devices.The second current transformer device 110 has a second voltage converter 102, which can be connected to a single-phase or polyphase medium-voltage network 103 with voltages greater than 1000 V. The second power conversion device 110 may include the same components as the first power conversion device 10. Expediently, these have been represented with the reference signs increased by 100 in each case. It thus shows104 the second intermediate circuit;105, 106 fifth and sixth voltage converters, in particular DC / DC converters;107, 108 battery cells or electrochemical energy converters;111 second controller;117 second control terminal;118 second signal input;119 second terminal;In each of the two intermediate circuits 4, 104, an intermediate circuit capacitor 9, 109 can be provided for intermediate storage and smoothing.The two voltage converters, in particular the two AC / DC converters 2, 102, have an AC side in the direction of the low-voltage grid 3 and of the medium-voltage grid 103 and a DC side 23. The DC side 23 comprises the intermediate circuits 4, 104, the DC / DC converters 5, 6, 105, 106, the battery cells 7, 8, 107, 108 and the hydraulic connecting lines 24.The energy storage and conversion device 1 can have a higher-order controller 121 which actuates the two controllers 11, 111. However, the higher-level controller 121 can also partially or completely replace the two controllers 11, 111.The controllers 11, 111, 121 can be designed to actuate the flow battery arrangement 20 and the AC / DC converters 2, 102 and can be suitable for influencing their power flow direction. In this case, the controllers 11, 111, 121 can have an interface 127 to a data communication network 128, with the result that the power flow direction can be influenced as a function of data from external data sources 129.All voltage converters 2, 102, 5, 6, 105, 106 can have a transformer for galvanic isolation.In the case of flux batteries, the battery cells or electrochemical energy converters 7, 8, 107, 108 are also referred to as cell stacks. They frequently consist of a stack of a plurality of energy converters through which the electrolyte flows in parallel and which are electrically connected in series, so that a voltage of 30 to 80 V is present at the connections of a stack depending on the state of charge.All voltage converters 2, 102, 5, 6, 105, 106 can have electrically controllable switches, such as transistors, for example, in order to be able to convert voltage from DC voltage to AC voltage and vice versa. In particular, they may comprise bridge circuits constructed from transistors. Inverters may be operated at frequencies above the audible range, particularly above 20 kHz.All voltage converters 2, 102, 5, 6, 105, 106 can have nonlinear passive components, such as diodes, zener diodes, and varistors.Transistors and diodes may be made of various semiconductor materials such as Si, Ge, SiC, GaN.All voltage converters 2, 102, 5, 6, 105, 106 may have overvoltage-suppressing circuit components, such as snubber circuits.All voltage converters 2, 102, 5, 6, 105, 106 can have filters, in particular dissipative filters, for suppressing interference.All the voltage converters 2, 102, 5, 6, 105, 106 can have temperature sensors which have connections to the controller or controllers 11, 111, 121 for monitoring or regulating the temperature of the voltage converters or of individual components thereof.All voltage converters 2, 102, 5, 6, 105, 106 can have means for cooling, such as air cooling or liquid cooling. The electrolyte can also be used for cooling.All voltage converters 2, 102, 5, 6, 105, 106 can have coils, chokes and inductances for storing electrical energy in the form of an impressed current. These components also serve for smoothing current and can filter electromagnetic interference.All voltage converters 2, 102, 5, 6, 105, 106 can have capacitors for storing energy in the form of voltage. These components also serve for smoothing voltage and can filter electromagnetic interference.All controllers 11, 111, 121 may include volatile and nonvolatile data memories, logic devices, programmable logic devices, display devices, and wireless and wired interfaces.In FIG. 1, the battery cells or electrochemical energy converters 7, 8, 107, 108 are hydraulically connected in parallel. They can also be connected individually or in groups in series.FIG. 2 differs from FIG. 1 in the additional connecting line 25 which connects the two intermediate circuit voltages 4, 104 of the two current transformer devices 10, 110. In FIG. 2, an arrangement is shown in which an electrical connection 25 and a hydraulic connection 24 are provided on the DC side 23 of both AC / DC converters 2, 102.FIG. 3 differs from FIG. 2 in the replacement of the connecting line 25 by the connecting line 26 which connect the DC voltages at the battery cells or electrochemical energy converters 7, 8, 107, 108. In FIG. 3, an arrangement is shown in which an electrical connection 25 and a hydraulic connection 24 are provided on the DC side 23 of both AC / DC converters 2, 102.FIG. 4 differs from FIG. 2 in the separation of the hydraulic connection 24 on the DC side. Two additional storage tanks 131 and 132 and two additional pumps 133 and 134 are now provided in a second flow battery assembly 120. In FIG. 4, an arrangement is shown in which an electrical connection 26 and no hydraulic connection 24 are provided on the DC side 23 of both AC / DC converters 2, 102. The first flow battery assembly 20 has a first hydraulic connection 224 and the second flow battery assembly 120 has a second hydraulic connection 124. Both hydraulic connections 224, 124 are not in contact with each other.FIGS. 1-4 are non-exhaustive or restrictive. Further devices 1 with further combinations of connections 24, 25, 26 can be provided.The controllers 11, 111, 121 may be configured to maintain data communication with external data sources. In particular, they can have connection to a smart grid functionality. The energy storage and conversion devices described are highly suitable for providing or compensating energy which is just being urgently required or just being advantageous to store, particularly quickly, flexibly, energy-efficiently and cost-effectively in accordance with requirements.

Claims

Energy storage and conversion device (1) for converting electrical energy from a low-voltage grid (3) with voltages of less than 1000 V into a medium-voltage grid (103) with voltages of more than 1000 V and vice versa, and for storing electrical energy in a flow battery arrangement (20, 120) and for discharging the energy stored in the flow battery arrangement (20, 120), comprising: - the flow battery arrangement (20, 120) with hydraulic connecting lines (24, 124) for exchanging electrolyte from storage tanks (31, 32, 131, 132) to battery cells (7, 8, 107, 108) and back, - a first bidirectionally operable voltage conversion device (10) for connection to the low-voltage grid (3) and to the flow battery arrangement (20, 120) comprising a first AC / DC converter (2), a second bidirectionally operable voltage converter device (110) for connection to the medium voltage grid (103) and to the flow battery arrangement (20, 120), having a second AC / DC converter (102), characterized in that the device (1) has an electrical connection (25, 26) and / or a hydraulic connection (24) of both AC / DC converters (2, 102) on its DC side (23), and in that the first AC / DC converter (2) is designed to convert energy from the low voltage grid (3) in order to charge the flow battery arrangement (20, 120) and to convert energy from the flow battery arrangement (20, 120) in order to conduct it into the low voltage grid (3), and in that the second AC / DC converter (102) is designed to convert energy from the medium voltage grid (103) in order to charge the flow battery arrangement (20, 120), and to convert energy from the flow battery arrangement (20, 120) to conduct it into the medium voltage network (103).Device according to claim 1, characterised in that the flow battery arrangement (20, 120) is constructed in a stationary manner.Device according to one of the preceding claims, characterized in that one voltage converter device (10, 110) each is connected to one flow battery arrangement (20, 120) each.Device according to one of the preceding claims 1 or 2, characterized in that both voltage converter devices (10, 110) are connected to a flow battery arrangement (20).Device according to one of the preceding claims, characterized in that the flow battery arrangement (20) and the two AC / DC converters (2, 102) are each accommodated individually or together in a unit which has the dimensions of a shipping container.Device according to one of the preceding claims, characterized in that the low-voltage network (3) is a network with exclusively regenerative power generators from the group of solar, wind, water energy.Device according to one of the preceding claims, characterized in that the device additionally has a transformer between the medium-voltage network (103) and the low-voltage network (3), and in that in this case in particular the transformer is designed for a reactive current below 50% of the maximum active current for which it is rated.Device according to one of the preceding claims, characterized in that the device has a controller (11, 111, 121) which is designed to actuate the flow battery arrangement (20) and the AC / DC converter (2, 102) and is suitable for influencing the power flow direction thereof, and in particular has an interface (127) to a data communication network (128), such that the power flow direction can be influenced as a function of data from external data sources (129).Device according to one of the preceding claims, characterized in that the controller (11, 111, 121) is designed to drive pumps for circulating electrolyte of the flow batteries.

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