Energy storage system

Abstract

An energy storage unit including a first unit terminal and a second unit terminal, an energy storage element having a first element terminal and a second element terminal, wherein the second element terminal is connected to the second unit terminal, and a protection circuit including a first pyrotechnic switch connected between the first unit terminal and the first element terminal and a second pyrotechnic switch connected between the first unit terminal and the second unit terminal.

Description

Technical Field

[0001] The present invention generally relates to energy storage systems, and energy storage units of energy storage systems. Background Art

[0002] An energy storage system (ESS) is a system for storing electrical energy in large quantities. The energy storage system is usually connected to (or capable of being connected to) an energy distribution network to deliver electric power to the grid when needed.

[0003] Energy storage systems typically include energy storage units, which in medium voltage (MV) or high voltage (HV) systems are connected in series to voltage levels up to several tens of kilovolts or even higher. Common rated voltages of such energy storage (ES) units are in the low voltage (LV) range. To meet power and / or energy requirements, ES units are usually also connected in parallel. The series- and parallel-connected ES units form an ESS.

[0004] To protect the ES units from safety-related events (such as thermal runaway or overvoltage), it is necessary to disconnect the ES units from the rest of the ESS. For an ESS operating at a relatively high voltage level, such as in an MV system, such a disconnection is not insignificant because voltage stress may occur. To be suitable for high voltage and high current, the typical mechanical switches used today are large and expensive. Summary of the Invention

[0005] In view of the above, an object of the present invention is to reduce the volume and structural complexity of switches in the prior art.

[0006] To solve at least this problem, an energy storage unit and a method are provided according to the independent claims. Preferred embodiments are defined by the dependent claims.

[0007] According to a first aspect of the present invention, there is provided an energy storage unit including a first unit terminal and a second unit terminal, an energy storage element having a first element terminal and a second element terminal (wherein the second element terminal is connected to the second unit terminal), and a protection circuit (including a first pyrotechnic switch connected between the first unit terminal and the first element terminal and a second pyrotechnic switch connected between the first unit terminal and the second unit terminal). Thereby, a more compact switch solution is obtained.

[0008] The first pyrotechnic switch may have a closed primary state and an open secondary state, while the second pyrotechnic switch may have an open primary state and a closed secondary state. Thus, in the first state, the energy storage element is connected to the first unit terminal and the second unit terminal, and in the second state, the energy storage element is disconnected from the first unit terminal and the second pyrotechnic switch is connected to the first unit terminal and the second unit terminal, thereby bypassing the energy storage element.

[0009] The energy storage unit may include a control unit connected to the first pyrotechnic switch and the second pyrotechnic switch, wherein the control unit is arranged to switch the first pyrotechnic switch and the second pyrotechnic switch from the primary state to the secondary state.

[0010] The control unit may be arranged to perform the switching with an adjustable time delay between the switchings.

[0011] According to a second aspect of the present invention, there is provided an energy storage system including a plurality of the above-mentioned energy storage units, wherein the energy storage units are connected in series.

[0012] The energy storage system may include a plurality of energy storage groups connected in parallel, wherein each energy storage group includes a plurality of energy storage units connected in series.

[0013] The energy storage system may be connected to an AC / DC converter, which in turn is connected to an energy distribution network.

[0014] According to a third aspect of the present invention, there is provided a method of controlling an energy storage unit having a first unit terminal and a second unit terminal, the method comprising:

[0015] - providing an energy storage element having a first element terminal and a second element terminal for the energy storage unit, and a protection circuit including a first pyrotechnic switch and a second pyrotechnic switch;

[0016] - connecting the second element terminal to the second unit terminal;

[0017] - connecting the first pyrotechnic switch between the first unit terminal and the first element terminal;

[0018] - connecting the second pyrotechnic switch between the first unit terminal and the second unit terminal; and

[0019] - controlling the switching of the first pyrotechnic switch and the second pyrotechnic switch.

[0020] The first pyrotechnic switch may have a closed primary state, and the second pyrotechnic switch may have an open primary state.

[0021] Thus, the controlling the switching of the first switch and the second switch may include:

[0022] - Control the second pyrotechnic switch to change its state to a closed secondary state; and

[0023] After a time delay, control the first switch to change its state to an open secondary state. Alternatively, the switching order can be reversed, i.e., switch the first pyrotechnic switch to the secondary state and then, after an adjustable time delay, switch the second pyrotechnic switch to the secondary state. The time delay can be adjustable. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

[0025] Figure 1 is a schematic diagram of an energy storage system according to an embodiment of the present invention.

[0026] Figure 2 is Figure 1 a schematic diagram of a part of the system shown.

[0027] Figure 3 is a flowchart of a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be described below with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. However, the present invention can be embodied in many different forms and should not be construed as limited to the embodiments described herein; rather, these embodiments are provided by way of example so that this disclosure will convey the scope of the present invention to those skilled in the art.

[0029] Figure 1 is a schematic diagram of an ESS according to an embodiment of the present invention. The ESS1 can be connected to (or capable of being connected to) the power grid 5 through, for example, an AC / DC converter 4. According to an embodiment of the present invention, the ESS1 includes a plurality of energy storage units (ESUs) 3 connected in series. The ESUs 3 connected in series can be considered to form an ESU group 2. The ESS1 can include two or more ESU groups 2 connected in parallel. The ESU groups 2 are all connected to the DC link 16. The DC side of the AC / DC converter 4 is also connected to the DC link 16.

[0030] Each ESU 3 includes a first unit terminal 6, a second unit terminal 7, and an energy storage element (ESE) 8. Each of the first unit terminal 6 and the second unit terminal 7 can be connected in series with another ESU 3 or with the DC link 16, depending on the position of the ESU 3 in the ESU 2 group. The ESE 8 includes a first element terminal 9 and a second element terminal 10. The second element terminal 10 is connected to the second unit terminal 7. The output voltage of the ESU 3, i.e., the voltage between the first unit terminal 6 and the second unit terminal 7, can be in the LV range or in the MV range. The output of the ESS1 can be quite high and, for example, higher than 1.5 kV.

[0031] The ESU also includes a protection circuit that includes a first pyrotechnic switch 11 connected between the first unit terminal 6 and the first element terminal 9, and a second pyrotechnic switch 12 connected between the first unit terminal 6 and the second unit terminal 7. The first pyrotechnic switch 11 can have a closed primary state and an open secondary state, and the second pyrotechnic switch 12 can have an open primary state and a closed secondary state. In other words, during normal operation, the first pyrotechnic switch 11 is closed and the second pyrotechnic switch 12 is open.

[0032] As understood by those skilled in the art, a pyrotechnic switch is a switch that uses a pyrotechnic charge to open or close the internal contacts of the switch. The pyrotechnic charge stores the energy for the opening or closing operation in the form of a chemical compound and releases the energy through an electrical trigger signal. In contrast, a switch commonly used in the current environment includes an electromagnetic switch that uses the energy from an electromagnetic element (such as a coil) to open or close the contacts. Due to the much higher energy density and power density of the pyrotechnic charge compared to those of the electromagnetic element, the pyrotechnic switch has a significantly smaller volume and good current handling ability. However, the pyrotechnic charge is a one-time-use element, and thus the pyrotechnic switch must be replaced after switching. For energy storage system failures, the one-time operation is acceptable for some severe and non-repeating system failures. Therefore, the pyrotechnic switch is advantageous for the protection of the energy storage system.

[0033] Therefore, compared with the prior art solutions, the first pyrotechnic switch 11 and the second pyrotechnic switch 12 have the advantage of reducing the cost and physical volume of the ESU 3.

[0034] The energy storage unit 3 may further include a control unit 14 connected to the first pyrotechnic switch 11 and the second pyrotechnic switch 12, wherein the control unit 14 is arranged to control the states of the first pyrotechnic switch 11 and the second pyrotechnic switch 12. More specifically, in order to switch the first pyrotechnic switch 11 and the second pyrotechnic switch 12 from the primary state to the secondary state, the control unit 14 triggers the pyrotechnic actuators inside each of the first pyrotechnic switch 11 and the second pyrotechnic switch 12. The control unit 14 may be arranged inside the ESU 3, and the control unit 14 may in turn be connected to an external controller 15 by a wired or wireless connection.

[0035] See Figure 3 , an embodiment of a method of controlling the ESU 3 may include, for example, the following operations. First, in block 31, the ESU 3 is arranged by providing an ESE 8 having a first element terminal 9 and a second element terminal 10, and then, in block 32, the ESU 3 is arranged by providing a protection circuit for the ESE 8 including a first pyrotechnic switch 11 and a second pyrotechnic switch 12. Assuming that the energy storage system 1 is connected to the power grid 5 and feeding energy to the power grid, the pyrotechnic switches of the ESU 3 are in their primary state. This means that the ESE 8 delivers electric power to the unit terminals 6, 7 of the ESU 3 via its element terminals 9, 10 and through the first pyrotechnic switch 11. The method may further include connecting the second element terminal 10 to the second unit terminal 7 (block 33); connecting the first pyrotechnic switch 11 between the first unit terminal 6 and the first element terminal 9 (block 34); and connecting the second pyrotechnic switch 12 between the first unit terminal 6 and the second unit terminal 7 (block 35). In addition, in block 36, the method may include controlling the switching of the first pyrotechnic switch and the second pyrotechnic switch 12.

[0036] When a need to disconnect the ESE 8 occurs, the control unit 14 first switches the second pyrotechnic switch 12 to the secondary state, i.e., the control unit 14 closes the second pyrotechnic switch 12. Thereby, the ESE 8 is bypassed by virtue of the direct connection obtained between the first unit terminal 6 and the second unit terminal 7 by the second pyrotechnic switch 12. Then, after a short time delay, the control unit 14 switches the first pyrotechnic switch 11 to its secondary state, i.e., the control unit 14 opens the first pyrotechnic switch 11. Thereby, the ESE 8 is finally disconnected from the first unit terminal 6 and the second unit terminal 7, and thus, as a whole, disconnected from the ESS1. For different reasons, such as short circuit faults, overvoltage, overheating, aging, etc., bypassing / disconnecting the ESE 8 may be desired.

[0037] The operation of the control unit 14 to perform the switching of the first pyrotechnic switch 11 and the second pyrotechnic switch 12 can in turn be controlled by a control signal sent from an external controller 15 to the control unit 14. The time delay between closing the second pyrotechnic switch 12 and opening the first pyrotechnic switch 11 can be adjustable. For example, the time delay can be between 1 - 10 ms. However, other suitable time delays can also be used. The time delay can be set by the control unit 14. The adjustment of the time delay can be done by the operator directly or by providing an input to the control unit 14 through the external controller 15.

[0038] Alternatively, for use in certain applications, the switching sequence of the first pyrotechnic switch 11 and the second pyrotechnic switch 12 will be the reverse of the sequence described above. This means that first the control unit 14 will switch the first pyrotechnic switch 11 to the open state, and then after a time delay, the control unit 14 will switch the second pyrotechnic switch 12 to the closed state.

[0039] In addition, the control unit 14 can monitor the states of the pyrotechnic switches 11, 12 and send information about their states to the external controller 15.

[0040] When the first pyrotechnic switch and the second pyrotechnic switch have been switched to the secondary state, the AC / DC converter can control the voltage on the DC link to maintain the same DC voltage or reduce the DC voltage.

Claims

1. An energy storage system capable of being connected to an energy distribution network, the energy storage system (1) comprising a plurality of energy storage units (3) connected in series, one of the plurality of energy storage units comprising: a first unit terminal (6) and a second unit terminal (7), an energy storage element (8) having a first element terminal (9) and a second element terminal (10), wherein the second element terminal is connected to the second unit terminal, and a protection circuit, the protection circuit comprising a first pyrotechnic switch (11) connected between the first unit terminal and the first element terminal and a second pyrotechnic switch (12) connected between the first unit terminal and the second unit terminal, wherein the energy storage system is configured to provide an output voltage of more than 1.5 kV, wherein the first pyrotechnic switch has a closed primary state and an open secondary state, wherein the second pyrotechnic switch has an open primary state and a closed secondary state, wherein the energy storage unit comprises a control unit (14) connected to the first pyrotechnic switch and the second pyrotechnic switch, wherein the control unit is arranged to switch the first pyrotechnic switch and the second pyrotechnic switch from the primary state to the secondary state, and wherein the control unit is arranged to perform the switching with an adjustable time delay between the switchings.

2. The energy storage system according to claim 1, comprising a plurality of energy storage groups (2) connected in parallel, wherein each energy storage group comprises a plurality of energy storage units (3) connected in series.

3. The energy storage system according to claim 1 or 2, wherein the energy storage system (1) is connected to an AC / DC converter (4), and the AC / DC converter is in turn connected to the energy distribution network (5).

4. A method of controlling an energy storage system (1) capable of being connected to an energy distribution network (5), wherein the energy storage system is configured to provide an output voltage of more than 1.5 kV, and wherein the energy storage system comprises a plurality of energy storage units (3) connected in series, one of the plurality of energy storage units having a first unit terminal (6) and a second unit terminal (7), the method comprising: providing an energy storage element (8) having a first element terminal (9) and a second element terminal (10) for the energy storage unit, and a protection circuit comprising a first pyrotechnic switch (11) and a second pyrotechnic switch (12); connecting the second element terminal to the second unit terminal; connecting the first pyrotechnic switch between the first unit terminal and the first element terminal; connecting the second pyrotechnic switch between the first unit terminal and the second unit terminal; wherein the first pyrotechnic switch has a closed primary state, and wherein the second pyrotechnic switch has an open primary state, and controlling the switching of the first pyrotechnic switch and the second pyrotechnic switch comprises: Switch the second pyrotechnic switch to the closed secondary state and, after an adjustable time delay, switch the first switch to the open secondary state, or vice versa.

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