System with an energy storage unit and method in such a system

Abstract

A system (10) is disclosed that includes a plurality of energy storage units (1) and at least one voltage balancing unit (2, 8). Each voltage balancing unit (2, 8) is associated with at least one of the energy storage units (1). The at least one voltage balancing unit (2, 8) is connected to the energy storage units (1) and configured, when activated, to reduce the voltage of at least one of the energy storage units (1) whose voltage exceeds a threshold voltage level to below the threshold voltage level, on condition that the voltage of at least one of the energy storage units (1) associated with the at least one voltage balancing unit (2, 8) exceeds the threshold voltage level. The system (10) includes at least one control and / or processing unit (6) that is configured to monitor the amount of time that the at least one voltage balancing unit (2, 8) is activated or has been activated, when the at least one voltage balancing unit (2, 8) is activated and the voltage of at least one of the energy storage units (1) associated with the at least one voltage balancing unit (2, 8) exceeds the threshold voltage level.

Description

[Technical Field]

[0001] Technical Field The present invention relates to a system comprising an energy storage unit, such as a capacitor, and to a method in such a system. [Background technology]

[0002] background Electrical parameters of an electrical energy storage unit, such as equivalent series resistance (ESR) and capacity (e.g., energy rating), can change significantly from the beginning of the life of the electrical energy storage unit to the end of the life of the electrical energy storage unit. The electrical energy storage unit may comprise or consist of, for example, one or more batteries or ultracapacitors.

[0003] For example, in applications where a large number of electrical energy storage units may be used, such as power transmission, distribution, and power generation applications, it is useful to have an indication of the life or state of health (SOH) of an electrical energy storage unit to know when an electrical energy storage unit needs to be replaced due to aging of the electrical energy storage unit, and to know which electrical energy storage units need to be replaced.

[0004] The SOH of an electric energy storage unit can often be estimated by offline measurements of the electric energy storage unit's ESR and capacity or based on a model of the electric energy storage unit's aging (or lifetime) using historical data of the electric energy storage unit (e.g., historical data regarding the electric energy storage unit's voltage, temperature, etc.). Offline measurements are performed while the device, system, etc. containing the electric energy storage unit is shut down. If there are a large number of electric energy storage units, offline measurements may require a significant amount of time, during which the device, system, etc. containing the electric energy storage unit is offline. The accuracy of an electric energy storage unit SOH estimation based on a model of the electric energy storage unit's aging or lifetime may strongly depend on the accuracy of the model used. Relatively time-consuming calculations and relatively large data storage may also be required. Either of these methods of estimating the SOH of an electric energy storage unit may be less efficient in large-scale electric energy storage applications and may require estimating the SOH of a very large number of electric energy storage units. Summary of the Invention [Problem to be solved by the invention]

[0005] overview In view of the above, it is an interest of the present invention to provide a means that allows or facilitates relatively easily providing an indication of which energy storage units of a plurality of energy storage units require maintenance or replacement due to their aging. [Means for solving the problem]

[0006] To address this and / or other concerns, a system and a method therein 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, a system is provided. The system may include a plurality of energy storage units. Each energy storage unit may be selectively charged with electrical energy supplied to the energy storage unit and capable of discharging electrical energy stored in the energy storage unit. Each energy storage unit may be associated with a threshold voltage level. The system may include at least one detection unit configured to detect (e.g., at least) a voltage of each of the energy storage units. The system may include at least one voltage balancing unit. Each voltage balancing unit may be associated with at least one of the energy storage units. The at least one voltage balancing unit may be connected to the energy storage units. When activated, the at least one voltage balancing unit may be configured to reduce the voltage of at least one of the energy storage units whose voltage exceeds the threshold voltage level to be below the threshold voltage level, provided that the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level. The system may include at least one control and / or processing unit. The at least one control and / or processing unit may be configured to monitor the amount of time that the at least one voltage balancing unit is activated or has been activated when the at least one voltage balancing unit is activated and a voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds a threshold voltage level.

[0008] According to a second aspect of the present invention, a method is provided in a system. The system may include a plurality of energy storage units. Each energy storage unit may be selectively charged with electrical energy supplied to the energy storage unit and capable of discharging electrical energy stored in the energy storage unit. Each energy storage unit may be associated with a threshold voltage level. The system may include at least one voltage balancing unit. Each voltage balancing unit may be associated with at least one of the energy storage units. The at least one voltage balancing unit may be connected to the energy storage units. When activated, the at least one voltage balancing unit may be configured to, on a condition that the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level, reduce the voltage of at least one of the energy storage units whose voltage exceeds the threshold voltage level to below the threshold voltage level.

[0009] The method according to the second aspect of the present invention may include monitoring the amount of time that the at least one voltage balancing unit is activated or has been activated when the at least one voltage balancing unit is activated and the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds a threshold voltage level.

[0010] For each or any voltage balancing unit, an indication (e.g., a signal) that at least one of the energy storage units with which the voltage balancing unit is associated requires maintenance or replacement may be provided (e.g., generated) based at least on the amount of time the voltage balancing unit has been activated. For example, the at least one control and / or processing unit may be configured to determine, for each or any voltage balancing unit, that the amount of time the voltage balancing unit has been activated exceeds a threshold amount of time and provide the indication based at least on the determination. According to another example, the at least one control and / or processing unit may alternatively or additionally be configured, for each or any voltage balancing unit, to compare the amount of time the voltage balancing unit has been activated with the amount of time at least one of the other voltage balancing units has been activated and provide the indication based at least on the comparison. Thus, an indication may be provided to a voltage balancing unit based on a comparison of its relative operating time or activation time compared to the other voltage balancing units. Such comparison may be performed repeatedly, e.g., continuously.

[0011] According to another example, the at least one control and / or processing unit may alternatively or additionally be configured to determine, for each or any voltage balancing unit, a difference between the amount of time the voltage balancing unit is activated and the amount of time at least one of the other voltage balancing units is activated, and determine whether the difference exceeds a threshold difference. An indication may be provided based on determining whether the difference exceeds the threshold difference. Thus, an indication may be provided for a voltage balancing unit based on any drift between the amount of time the voltage balancing unit is activated and the amount of time at least one of the other voltage balancing units is activated. The threshold difference may, for example, be defined in terms of a multiple of the amount of time at least one of the other voltage balancing units is activated. The threshold difference may, for example, be two or three times or more the amount of time at least one of the other voltage balancing units is activated. For example, if it is determined that the amount of time that a voltage balancing unit has been activated is greater than or equal to X times the amount of time that at least one of the other voltage balancing units has been activated (X>1, e.g., 2 or 3), an indication may be provided that at least one of the energy storage units with which the voltage balancing unit is associated requires maintenance or replacement. The operations of determining (for each or any voltage balancing unit) the difference between the amount of time that the voltage balancing unit has been activated and the amount of time that at least one of the other voltage balancing units has been activated, determining whether the difference exceeds a threshold difference, and providing an indication based on the determination of whether the difference exceeds the threshold difference may be performed repeatedly, e.g., continuously.

[0012] Thus, embodiments of the present invention may facilitate or enable relatively easy provision of an indication of which energy storage units in a system require maintenance or replacement due to aging, by monitoring the use of at least one voltage balancing unit.

[0013] The at least one control and / or processing unit may be configured to monitor the amount of time the at least one voltage balancing unit has been activated, for example, by integrating or summing the amount of time the at least one voltage balancing unit has been activated. The amount of time the at least one voltage balancing unit has been activated may be referred to as an overvoltage switch-on time of at least one of the energy storage units associated with the at least one voltage balancing unit. The switch-on time of the at least one voltage balancing unit may be considered an indication of the SOH of at least one of the energy storage units with which the voltage balancing unit is associated relative to other energy storage units.

[0014] By monitoring the use of at least one voltage balancing unit according to the above-described first and second aspects of the present invention, it is possible to reduce or eliminate the need for (offline) measurements of the ESR and capacity (e.g., capacitance) of the energy storage unit and to reduce the complexity of the degradation or lifespan of the energy storage unit. Namo Without requiring or requiring little diagnostics, it is possible to provide an indication of which energy storage units in the system require maintenance or replacement, and in some cases an indication of the state of health of the energy storage units.

[0015] For systems with multiple energy storage units, it is useful to be able to obtain an indication of which energy storage units in the system require maintenance or replacement, and potentially an indication of the SOH of the energy storage units, in order to limit maintenance costs, maintain the energy rating of the system, and ensure safe operation of the system.

[0016] The threshold amount of time may be a fixed period (e.g., a fixed number of hours) established, for example, by experiments and / or simulations to investigate the aging of an energy storage unit (e.g., the type of energy storage unit used in the system). However, the threshold amount of time may not be fixed (e.g., not a fixed period of time). According to another example, the threshold amount of time may be the relative difference between the longest period for which the voltage balancing unit has been activated (e.g., monitored) and the shortest period for which the voltage balancing unit has been activated (e.g., monitored). Several voltage balancing units may be provided in a system, and one voltage balancing unit may be associated with one or more of the energy storage units.

[0017] The at least one control and / or processing unit may be configured to determine, for each voltage balancing unit, a curve (or function) of the time that the at least one voltage balancing unit is activated or has been activated as a function of time, and to provide an indication that at least one of the energy storage units with which the voltage balancing unit is associated requires maintenance or replacement based on at least one of the slope of the curve at a point on the curve and the shape of the curve. The curve may, for example, be determined based on interpolation between multiple values ​​of the time that the at least one voltage balancing unit is activated or has been activated at different times or for different periods of time.

[0018] Each voltage balancing unit may be switchable between an active state (i.e., a state in which it is activated) and an inactive state (i.e., a state in which it is not activated). The at least one control and / or processing unit may alternatively be referred to as at least one processor. Each or any of the energy storage units may alternatively be referred to as an energy storage cell. Each or any of the voltage balancing units may alternatively be referred to as a voltage balancing circuit.

[0019] Each or any voltage balancing unit may comprise, for example, one or more so-called bleeder resistors or bleeder circuits. The reduction of the voltage of the energy storage units as described above may be performed, for example, by bleed resistors / circuits in the voltage balancing units. Thus, each or any voltage balancing unit may be configured to reduce the voltage of at least one of the energy storage units associated with the voltage balancing unit by one or more bleeder resistors or bleeder circuits that may be included in the voltage balancing unit. However, it is contemplated that the reduction of the voltage of the energy storage units as described above may alternatively or additionally be performed by means other than bleeder resistors or bleeder circuits.

[0020] A method according to a second aspect of the present invention may include activating the at least one voltage balancing unit or keeping the at least one voltage balancing unit activated if the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds a threshold voltage level, and deactivating or not activating the at least one voltage balancing unit if the voltage of none of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level.

[0021] A method according to a second aspect of the present invention includes activating at least one voltage balancing unit or keeping at least one voltage balancing unit activated if a voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds a threshold voltage level, and activating at least one voltage balancing unit or keeping at least one voltage balancing unit activated if none of the energy storage units associated with the at least one voltage balancing unit has a voltage above a threshold voltage level. VoltageThe method may include keeping the at least one voltage balancing unit activated or activating the at least one voltage balancing unit if the voltage of at least one of the energy storage units associated with the balancing unit is within a selected voltage range below a threshold voltage level, and deactivating or not activating the at least one voltage balancing unit otherwise.

[0022] According to a third aspect of the present invention there is provided a computer program comprising instructions which, when executed by one or more processors comprised in or constituting a control and / or processing unit, cause the control and / or processing unit to carry out a method according to the second aspect of the present invention.

[0023] According to a fourth aspect of the present invention there is provided a processor-readable medium having a computer program loaded thereon, the computer program comprising instructions which, when executed by one or more processors comprised in or constituting a control and / or processing unit, cause the control and / or processing unit to carry out a method according to the second aspect of the present invention.

[0024] Each or any of the control and / or processing units may include or be configured by, for example, any suitable central processing unit (CPU), microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA), etc., or any combination thereof. Each or any of the control and / or processing units may optionally execute software instructions stored, for example, in a computer program product in the form of a memory. The memory may be, for example, any combination of read-write memory (RAM) and read-only memory (ROM). The memory may comprise persistent storage, which may be, for example, magnetic memory, optical memory, solid-state memory, or remotely mounted memory, or any combination thereof.

[0025] Each or any of the one or more processors may comprise, for example, a CPU, microcontroller, DSP, ASIC, FPGA, etc., or any combination thereof.

[0026] The processor-readable medium may include, for example, but not limited to, non-volatile memory, a hard disk drive, a compact disc (CD), flash memory, magnetic tape, a universal serial bus (USB) memory device, a memory such as a Zip drive, a digital versatile disc (DVD) or a floppy disk, or any other suitable type of processor-readable means or processor-readable (digital) medium.

[0027] Further objects and advantages of the present invention will be described below by way of exemplary embodiments. It should be noted that the present invention relates to all possible combinations of the features set forth in the claims. Further features and advantages of the present invention will become apparent upon review of the appended claims and the description herein. Those skilled in the art will understand that different features of the present invention can be combined to create embodiments other than those described herein.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic diagram of a system according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram of a system according to one embodiment of the present invention. [Figure 3] 1 is a schematic flow chart illustrating a method according to one embodiment of the present invention. [Figure 4] 1 is a schematic flow chart illustrating a method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] All figures are schematic, not necessarily to scale, and generally show only those parts necessary to elucidate embodiments of the invention; other parts may be omitted or merely suggested.

[0031] Detailed Description The present invention will now be described with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments of the invention set forth herein; rather, these embodiments are provided as examples so that this disclosure will convey the scope of the invention to those skilled in the art.

[0032] FIG. 1 is a schematic diagram of a system 10 according to one embodiment of the present invention. The system 10 includes a plurality of energy storage units 1. Each energy storage unit 1 is selectively capable of being charged with electrical energy supplied to the energy storage unit 1 and discharging electrical energy stored in the energy storage unit 1. Thus, the energy storage units 1 may be referred to as electrical energy storage units. It should be understood that the number of energy storage units 1 shown in FIG. 1 is exemplary, and that the system 10 may include fewer or more energy storage units than shown in FIG. 1. The system 10 may, in principle, include any number of energy storage units, such as tens or hundreds or more energy storage units.

[0033] As shown in Figure 1, multiple energy storage units 1 may be connected in series. A series connection of energy storage units as shown in Figure 1 may be referred to as a string of energy storage units. However, it should be understood that multiple energy storage units 1 may be interconnected in some other manner.

[0034] As indicated by the symbols on the energy storage units 1 in FIG. 1 , each or any of the energy storage units 1 may comprise a capacitor (or several capacitors). The capacitor may comprise, for example, one or more so-called supercapacitors, which may also be referred to as ultracapacitors. However, it should be understood that the energy storage units do not necessarily have to comprise capacitors, and other or other types of energy storage units may also be considered. For example, alternatively or additionally, each or any of the energy storage units 1 may comprise one or more batteries.

[0035] System 10 includes at least one sensing unit, shown generally at 7 in FIG. 1 . The at least one sensing unit 7 senses (e.g., at least) the voltage of each of the energy storage units 1. For example, the at least one sensing unit 7 may be configured to sense, for each of the energy storage units 1, the voltage across any capacitors and / or batteries of the energy storage units 1. The at least one sensing unit 7 may include one or more sub-units, each configured to sense the voltage of one or more of the energy storage units 1. For example, there may be an equal number of energy storage units and sub-units in system 10, and each sub-unit may be configured to sense a respective voltage of the energy storage units. In some cases, the at least one sensing unit 7 may be configured to sense one or more electrical parameters of the electrical energy storage units 1 other than their voltage.

[0036] Each energy storage unit 1 may be associated with a threshold voltage level. The threshold voltage level may be fixed or may vary. For example, for each energy storage unit 1, the threshold voltage may vary and may include or consist of the difference between the voltage of the energy storage unit 1 and the average voltage of the energy storage unit 1 (e.g., the average voltage of the voltages of all the energy storage units 1). According to another example, for each energy storage unit 1, the threshold voltage may be fixed and may include or consist of an upper voltage limit for the voltage of the energy storage unit 1. The upper voltage limit for the voltage of the energy storage unit 1 may be, for example, a nominal voltage level set to a level at which sufficient functionality of the energy storage unit 1 can be expected when the voltage of the energy storage unit 1 does not exceed the nominal voltage level, or a nominal voltage level set to a level at which premature degradation of the energy storage unit 1 is not expected to occur. The upper voltage limit for the voltage of the energy storage unit 1 may be set or provided, for example, by the supplier or manufacturer of the energy storage unit 1.

[0037] 1, the system 10 includes a plurality of voltage balancing units 2, each associated with a respective one of the energy storage units 1. It should be understood that the number of voltage balancing units 2 shown in FIG. 1 is exemplary, and the system 10 may include fewer or more voltage balancing units 2 than shown in FIG.

[0038] In general, system 10 may include at least one voltage balancing unit, each voltage balancing unit associated with at least one of the energy storage units 1. The at least one voltage balancing unit may be connected to the energy storage units 1 and configured, when activated, to reduce the voltage of at least one of the energy storage units 1 whose voltage exceeds the threshold voltage level to below the threshold voltage level, provided that the voltage of at least one of the energy storage units 1 associated with the at least one voltage balancing unit exceeds the threshold voltage level.

[0039] According to the embodiment of the present invention shown in FIG. 1, each voltage balancing unit 2, when activated, is configured to balance the voltage of the energy storage unit 1 associated with the voltage balancing unit 2 (i.e., the energy storage unit 1 On condition that the threshold voltage level (of the voltage storage unit 1) is exceeded, the voltage of the energy storage unit 1 is reduced to below the threshold voltage level.

[0040] Reducing the voltage of the energy storage unit 1 may be performed, for example, by a bleed resistor / circuit of the voltage balancing unit 2. For example, according to an embodiment of the present invention further shown in FIG. 1 , each voltage balancing unit 2 may include a switch 4, a bleeder resistor 3, and a control unit 5. As shown in FIG. 1 , the switch 4 and the bleeder resistor 3 may be connected in series, and the series connection of the switch 4 and the bleeder resistor 3 may be connected in parallel to the energy storage unit 1 with which the voltage balancing unit 2 is associated. The control unit 5 may be communicatively coupled to the switch 4 and may be configured to control the operation of the switch 4, for example, to selectively control the switch 4 to switch between an open or non-conductive state in which no or substantially no current is conducted through the switch 4, and a closed or conductive state in which the switch 4 conducts current. While a wired communication coupling between the control unit 5 and the switch 4 of each of the voltage balancing units 2 is shown in FIG. 1 , it should be understood that the control unit 5 and the switch 4 of each or any of the voltage balancing units 2 may be communicatively coupled using any wired and / or wireless communication means. It will be appreciated that reducing the voltage of the energy storage unit 1 as described above may alternatively or additionally be performed by means other than a bleeder resistor or bleeder circuit.

[0041] System 10 includes a control and / or processing unit 6. Control and / or processing unit 6 may be referred to as an energy storage management unit. System 10 may include multiple control and / or processing units. In general, control and / or processing unit 6 may be configured to monitor the amount of time that at least one voltage balancing unit is activated or activated when at least one voltage balancing unit is activated and the voltage of at least one of the energy storage units 1 associated with the at least one voltage balancing unit exceeds a threshold voltage level. Monitoring may be performed, for example, by integrating or summing the amount of time that at least one voltage balancing unit is activated or activated.

[0042] According to the embodiment of the invention shown in FIG. 1, the control and / or processing unit 6 determines, for each voltage balancing unit 2, when the voltage balancing unit 2 is activated and the voltage of the energy storage unit 1 associated with the voltage balancing unit 2 (that energy storage unit 1 If a threshold voltage level (of the voltage balancing unit 2) is exceeded, the voltage balancing unit 2 is configured to monitor the amount of time that the voltage balancing unit 2 is activated or has been activated.

[0043] Generally, the control and / or processing unit 6 controls the voltage balancing for each voltage balancing unit 2. Chemical knit 2 may be configured to provide an indication that at least one of the associated energy storage units requires maintenance or replacement based at least on a determination that the amount of time that the voltage balancing unit 2 has been activated exceeds a threshold amount of time.

[0044] 1 , each voltage balancing unit 2 is associated with a respective energy storage unit 1. The control and / or processing unit 6 may be configured to provide, for each voltage balancing unit 2, an indication that the energy storage unit 1 with which the voltage balancing unit 2 is associated requires maintenance or replacement based at least on determining that the amount of time the voltage balancing unit 2 has been activated exceeds a threshold amount of time. As mentioned above, the threshold amount of time may be a fixed period of time. However, that is not required, and the threshold amount of time need not be a fixed period of time.

[0045] The at least one sensing unit 7 may be communicatively coupled to the control and / or processing unit 6. Although a wired communication coupling between the at least one sensing unit 7 and the control and / or processing unit 6 is shown in Figure 1, it should be understood that the at least one sensing unit 7 and the control and / or processing unit 6 may be communicatively coupled using any wired and / or wireless communication means.

[0046] The control unit 5 of the voltage balancing unit 2 may be omitted. In that case, the switches 4 of the voltage balancing unit 2 may be communicatively coupled (e.g., directly communicatively coupled) to the control and / or processing unit 6, and the control and / or processing unit 6 may be configured to control the operation of the switches 4 (e.g., individually).

[0047] As mentioned above, the control and / or processing unit 6 may be configured to monitor when the voltage of at least one of the energy storage units 1 associated with the at least one voltage balancing unit exceeds a threshold voltage level and when the at least one voltage balancing unit is activated, the amount of time the at least one voltage balancing unit is activated or has been activated.

[0048] According to one control scheme, the control and / or processing unit 6 may generally be configured to activate at least one voltage balancing unit or keep at least one voltage balancing unit activated if the voltage of at least one of the energy storage units 1 associated with the at least one voltage balancing unit exceeds a threshold voltage level, and to deactivate or not activate at least one voltage balancing unit if the voltage of none of the energy storage units 1 associated with the at least one voltage balancing unit exceeds the threshold voltage level. According to the embodiment of the invention shown in FIG. 1, the control and / or processing unit 6 may be configured, for each voltage balancing unit 2, to activate or keep the voltage balancing unit 2 activated if the voltage of the energy storage unit 1 associated with the voltage balancing unit 2 exceeds the threshold voltage level, and to deactivate or not activate the voltage balancing unit 2 if the voltage of the energy storage unit 1 associated with the voltage balancing unit 2 does not exceed the threshold voltage level. This control scheme is further described below with reference to FIG. 3.

[0049] According to other control schemes, the control and / or processing unit 6 may generally be configured to activate at least one voltage balancing unit or keep at least one voltage balancing unit activated if the voltage of at least one of the energy storage units 1 associated with the at least one voltage balancing unit exceeds a threshold voltage level. The control and / or processing unit 6 may generally be further configured to activate at least one voltage balancing unit if the voltage of at least one of the energy storage units 1 associated with the at least one voltage balancing unit is within a selected voltage range below the threshold voltage level (e.g., within a selected voltage range just below the threshold voltage level) if none of the energy storage units 1 associated with the at least one voltage balancing unit has a voltage above the threshold voltage level, and not activate the at least one voltage balancing unit otherwise. According to the embodiment of the present invention shown in FIG. 1, the control and / or processing unit 6 may be configured, for each voltage balancing unit 2, to activate at least one voltage balancing unit or keep at least one voltage balancing unit activated if the voltage of at least one of the energy storage units 1 associated with the at least one voltage balancing unit exceeds a threshold voltage level. The control and / or processing unit 6 may be further configured, for each voltage balancing unit 2, to activate the voltage balancing unit 2 if the voltage of at least one of the energy storage units 1 associated with the voltage balancing unit 2 is within a selected voltage range below the threshold voltage level if the energy storage units 1 associated with the voltage balancing unit 2 have a voltage that does not exceed the threshold voltage level, and not to activate the voltage balancing unit 2 otherwise. This control scheme is further described below with reference to FIG. 4.

[0050] As described above, according to the embodiment of the present invention shown in FIG. 1 , each voltage balancing unit 2 is associated with a respective one of the energy storage units 1. However, a voltage balancing unit 2 does not need to be associated with only one energy storage unit 1. In some cases, one voltage balancing unit 2 may be associated with several energy storage units 1. An example of this is described below with reference to FIG. 2 . Generally, one of the voltage balancing units may be associated with a set of energy storage units 1 including at least two of the plurality of energy storage units 1. When activated, one of the voltage balancing units may be configured to, on condition that the voltage of at least one of the energy storage units 1 in the set of energy storage units 1 exceeds a threshold voltage level, reduce the voltage of the energy storage unit 1 in the set of energy storage units 1 whose voltage exceeds the threshold voltage level to be below the threshold voltage level. The control and / or processing unit 6 may be configured to monitor the amount of time that one of the voltage balancing units has been activated or activated when one of the voltage balancing units is activated and the voltage of at least one of the energy storage units 1 in the set of energy storage units 1 exceeds the threshold voltage level. Further, the control and / or processing unit 6 may be configured to provide (e.g., generate) an indication (e.g., a signal) that the energy storage units 1 in the set of energy storage units 1 each require replacement based at least on a determination that the amount of time that one of the voltage balancing units has been activated exceeds a threshold amount of time.

[0051] FIG. 2 is a schematic diagram of a system 10 according to one embodiment of the present invention. The system 10 shown in FIG. 2 is similar to the system 10 shown in FIG. 1 , and the same reference numerals in FIGS. 1 and 2 indicate the same or similar components having the same or similar functions. However, in contrast to the system 10 shown in FIG. 1 , the system 10 shown in FIG. 2 includes a voltage balancing unit 8 associated with several energy storage units 1. According to the embodiment of the present invention shown in FIG. 2 , the voltage balancing unit 8 is associated with a set of energy storage units 1 that includes two of the energy storage units 1. However, the voltage balancing unit 8 can, in principle, be associated with any number of energy storage units 1 that may be included in the system 10. Thus, the set of energy storage units 1 can, in principle, include any number of energy storage units 1 that may be included in the system 10. The system 10 shown in FIG. 2 may include at least three energy storage units 1.

[0052] According to the embodiment of the present invention shown in FIG. 2 , the voltage balancing unit 8 may be configured, when activated, to reduce the voltage of the energy storage units 1 in the set of energy storage units 1 whose voltage exceeds the threshold voltage level to below the threshold voltage level, on the condition that the voltage of at least one of the energy storage units 1 in the set of energy storage units 1 exceeds the threshold voltage level. The control and / or processing unit 6 is configured to monitor the amount of time that the voltage balancing unit 8 is activated or has been activated, when the voltage balancing unit 8 is activated and the voltage of at least one of the energy storage units 1 in the set of energy storage units 1 exceeds the threshold voltage level. The control and / or processing unit 6 may be configured to provide an indication that the energy storage units 1 in the set of energy storage units 1 each require replacement based at least on the amount of time that the voltage balancing unit 8 has been activated. For example, the control and / or processing unit 6 may be configured to provide an indication that the energy storage units 1 in the set of energy storage units 1 each require replacement based at least on determining that the amount of time that the voltage balancing unit 8 has been activated exceeds the threshold amount of time.

[0053] FIG. 3 is a schematic flowchart illustrating a method 20 in a system according to one embodiment of the present invention. FIG. 4 is a schematic flowchart illustrating a method 30 in a system according to another embodiment of the present invention. In both methods 20 and 30 shown in FIGS. 3 and 4, respectively, the system includes a plurality of energy storage units. Each energy storage unit is selectively capable of being charged with electrical energy supplied to the energy storage unit and discharging electrical energy stored in the energy storage unit. Each energy storage unit is associated with a threshold voltage level. The system further includes at least one voltage balancing unit. Each voltage balancing unit is associated with at least one of the energy storage units. The at least one voltage balancing unit is connected to the energy storage units. When activated, the at least one voltage balancing unit is configured to reduce the voltage of at least one of the energy storage units whose voltage exceeds the threshold voltage level to below the threshold voltage level, provided that the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level.

[0054] Referring to method 20 shown in FIG. 3 , at 21, it is checked whether the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds a threshold voltage level. If the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level, the method proceeds to 22, where the at least one voltage balancing unit is either left activated (if currently activated) or activated (if not currently activated). The at least one voltage balancing unit reduces the voltage of the at least one energy storage unit whose voltage exceeds the threshold voltage level to below the threshold voltage level. Subsequently, at 23, the amount of time that the at least one voltage balancing unit is activated or has been activated is monitored.

[0055] The method 20 further includes, at 24, checking for each voltage balancing unit whether the amount of time the voltage balancing unit has been activated exceeds a threshold amount of time.

[0056] If this is the case for any of the voltage balancing units, then at 25, for each of those voltage balancing units, an indication is provided that at least one of the energy storage units with which the voltage balancing unit is associated requires maintenance or replacement based at least on a determination that the amount of time the voltage balancing unit has been activated exceeds a threshold amount of time.

[0057] If the amount of time that the voltage balancing units have been activated does not exceed the threshold amount of time for any of the voltage balancing units, then method 20 returns to 21 .

[0058] If it is determined at 21 that the voltages of any of the energy storage units associated with the at least one voltage balancing unit do not exceed the threshold voltage level, then the at least one voltage balancing unit is deactivated (if currently activated) or not activated (if not currently activated) at 26. Method 20 then returns to 21.

[0059] Referring to method 30 shown in Figure 4, at 31, it is checked whether the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds a threshold voltage level. If the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level, the method proceeds to 32, where, if the at least one voltage balancing unit is activated, the amount of time the at least one voltage balancing unit has been activated is monitored. The at least one voltage balancing unit reduces the voltage of the at least one energy storage unit whose voltage exceeds the threshold voltage level to below the threshold voltage level.

[0060] The method 30 further includes, at 33, checking for each voltage balancing unit whether the amount of time the voltage balancing unit has been activated exceeds a threshold amount of time.

[0061] If this is the case for any of the voltage balancing units, then at 34, for each of those voltage balancing units, an indication is provided that at least one of the energy storage units with which the voltage balancing unit is associated requires maintenance or replacement based at least on a determination that the amount of time the voltage balancing unit has been activated exceeds a threshold amount of time. Method 30 then proceeds to 35, where at least one voltage balancing unit is activated (if not currently activated) or left activated (if currently activated). Based on the above, this is performed if the voltage of at least one of the energy storage units associated with at least one voltage balancing unit exceeds a threshold voltage level, which is checked at 31.

[0062] If, based on the check at 33, it is determined that for any voltage balancing unit, the amount of time the voltage balancing unit has been activated does not exceed the threshold amount of time, then method 30 proceeds to 35 without performing operation 34.

[0063] If, based on the check at 31, it is determined that none of the energy storage units associated with the at least one voltage balancing unit have a voltage above the threshold voltage level, method 30 proceeds to 36, where it is checked whether the voltage of at least one of the energy storage units associated with the at least one balancing unit is within a selected voltage range below the threshold voltage level. If so, method 30 proceeds to 35, where the at least one voltage balancing unit is either activated (if not currently activated) or left activated (if currently activated), as previously described. Method 30 then returns to 31.

[0064] If, based on the check at 36, it is determined that none of the energy storage units associated with the at least one balancing unit have a voltage within the selected voltage range that is below the threshold voltage level, method 30 proceeds to 37, where the at least one voltage balancing unit is deactivated (if currently activated) or not activated (if not currently activated). Method 30 then returns to 31.

[0065] In conclusion, a system is disclosed that includes a plurality of energy storage units and at least one voltage balancing unit. Each voltage balancing unit is associated with at least one of the energy storage units. The at least one voltage balancing unit is connected to the energy storage units and configured, when activated, to reduce the voltage of at least one of the energy storage units whose voltage exceeds a threshold voltage level to below the threshold voltage level, provided that the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds a threshold voltage level. The system also includes at least one control and / or processing unit configured to monitor the amount of time that the at least one voltage balancing unit has been activated or activated when the at least one voltage balancing unit is activated and the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level.

[0066] While the present invention has been illustrated in the accompanying drawings and in the foregoing description, such illustrations are to be considered illustrative or exemplary and not restrictive, and the present invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the dependent claims. In the appended claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. a plurality of energy storage units (1), each of which is selectively capable of being charged with electrical energy supplied to said energy storage unit and discharging electrical energy stored in said energy storage unit, and each of which is associated with a threshold voltage level; at least one sensing unit (7) configured to sense the voltage of each of said energy storage units; at least one voltage balancing unit (2, 8), each voltage balancing unit associated with at least one of the energy storage units, the at least one voltage balancing unit being connected to the energy storage units and configured, when activated, to, on a condition that the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level, reduce the voltage of at least one of the energy storage units whose voltage exceeds the threshold voltage level to be equal to or less than the threshold voltage level; at least one control and / or processing unit (6) configured to monitor whether the amount of time that the at least one voltage balancing unit has been activated exceeds a threshold amount of time when the at least one voltage balancing unit is activated and the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level; Equipped with the at least one control and / or processing unit is configured to: activate the at least one voltage balancing unit or keep the at least one voltage balancing unit activated if the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level; keep the at least one voltage balancing unit activated or activate the at least one voltage balancing unit if the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit is within a selected voltage range below the threshold voltage level if none of the energy storage units associated with the at least one voltage balancing unit has a voltage above the threshold voltage level; and deactivate or not activate the at least one voltage balancing unit otherwise.

2. 2. The system of claim 1, wherein the at least one control and / or processing unit is configured to provide, for each voltage balancing unit, an indication that the at least one of the energy storage units with which the voltage balancing unit is associated requires maintenance or replacement based at least on the amount of time the voltage balancing unit has been activated.

3. The at least one control and / or processing unit determines for each voltage balancing unit: determining that the amount of time the voltage balancing unit has been activated exceeds a threshold amount of time; a comparison between the amount of time the voltage balancing unit was activated and the amount of time at least one of the other voltage balancing units was activated; The system of claim 2 , configured to provide the indication based on at least one of:

4. The at least one control and / or processing unit determines for each voltage balancing unit: determining a difference between the amount of time the voltage balancing unit was activated and the amount of time at least one of the other voltage balancing units was activated; determining whether the difference exceeds a threshold difference; providing the indication based on the determination whether the difference exceeds the threshold difference. The system according to claim 2 or 3, configured to:

5. 5. The system of claim 1, wherein for each energy storage unit, the threshold voltage may vary, and wherein the threshold voltage comprises or is a difference between the voltage of the energy storage unit and an average voltage of the voltages of the energy storage units.

6. 5. The system of claim 1, wherein for each energy storage unit, the threshold voltage is fixed and the threshold voltage comprises or is an upper limit voltage of the voltage of the energy storage unit.

7. One of the voltage balancing units (8) is associated with a set of energy storage units including at least two of the plurality of energy storage units, and when activated, the one of the voltage balancing units is configured to balance the voltage of at least one of the energy storage units in the set of energy storage units to the threshold voltage level. and, on a condition that the threshold voltage level is exceeded, reducing the voltage of the energy storage unit in the set of energy storage units whose voltage exceeds the threshold voltage level to be equal to or less than the threshold voltage level; 7. The system of claim 1, wherein the at least one control and / or processing unit is configured to monitor the amount of time that the one of the voltage balancing units is activated or has been activated when the one of the voltage balancing units is activated and the voltage of at least one of the energy storage units in the set of energy storage units exceeds the threshold voltage level.

8. 8. The system of claim 7, wherein the at least one control and / or processing unit is configured to provide an indication that the energy storage units in the set of energy storage units each require replacement based at least on the amount of time that the one of the voltage balancing units has been activated.

9. The system of any one of claims 1 to 8, wherein each of the energy storage units comprises one or more of at least one capacitor and at least one battery.

10. 10. The system of claim 9, wherein the at least one sensing unit is configured to sense, for each of the energy storage units, a voltage across the at least one capacitor and / or the at least one battery of the energy storage unit.

11. The system of any one of claims 1 to 10, wherein the plurality of energy storage units are connected in series.

12. A method (20, 30) in a system, the system comprising a plurality of energy storage units, each energy storage unit being selectively capable of being charged with electrical energy supplied to the energy storage unit and discharging electrical energy stored in the energy storage unit, each energy storage unit being associated with a threshold voltage level, the system further comprising at least one voltage balancing unit, each voltage balancing unit being associated with at least one of the energy storage units, the at least one voltage balancing unit being connected to the energy storage units and configured, when activated, to reduce the voltage of at least one of the energy storage units whose voltage exceeds the threshold voltage level to be equal to or less than the threshold voltage level, on a condition that the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level, the method comprising: When the at least one voltage balancing unit is activated and the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level, monitoring (23, 32) whether the amount of time that the at least one voltage balancing unit has been activated or activated exceeds a threshold amount of time; activating the at least one voltage balancing unit or keeping the at least one voltage balancing unit activated (35) if the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit exceeds the threshold voltage level; if none of the energy storage units associated with the at least one voltage balancing unit have a voltage above the threshold voltage level; keeping the at least one voltage balancing unit activated or activating the at least one voltage balancing unit when the voltage of at least one of the energy storage units associated with the at least one voltage balancing unit is within a selected voltage range below the threshold voltage level (35); If not, deactivating or not activating the at least one voltage balancing unit (37). A method (20, 30) comprising:

13. A computer program comprising instructions which, when executed by one or more processors included in a control and / or processing unit (6), cause said control and / or processing unit to carry out the method according to claim 12.

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