Patent Description:
As both production and consumption of electrical energy varies with time, stabilizing an electrical power grid may present a challenge. To compensate for various peaks in production and consumption, a modern electrical power grid may include various forms of energy storages in which energy produced during periods of lower demand may be at least temporally stored and later released during subsequent periods of higher demand. Such energy storages may include everything from large scale hydroelectric dams down to smaller battery banks.

As an alternative to rechargeable batteries, supercapacitors have presented themselves as a viable option. Due to their construction, supercapacitors may both accept and deliver charge faster than rechargeable batteries, and also survive more charging and discharging cycles. To allow for an increased storage capability, multiple supercapacitors may be connected together (in series and/or in parallel) to form large scale energy storage systems.

However, large scale energy storage based on supercapacitors may also present challenges in terms of both fault protection capabilities and ability to provide uninterrupted service even in the event of a fault.

An example of prior art may be found in <CIT> relating to an electric energy storage apparatus, a voltage equalization module and a voltage equalization method.

To at least partly overcome the above challenge, the present disclosure provides a module for use in an energy storage system and a method of operating the same, as defined by the independent claims. Further embodiments of the module, energy storage system and the method are defined by the dependent claims.

According to a first aspect of the present disclosure, a module for use in an energy storage system is provided, as defined in the independent claim <NUM>. Among others, the module includes a first terminal and a second terminal, via which the module may be connected to e.g. one or more other modules and/or to an electrical power grid. The module further includes a supercapacitor branch, including an arrangement of one or more supercapacitors. The module further includes a resistive bypass branch including at least a first bypass switch and a resistance connected in series. In the module, the supercapacitor branch and the resistive bypass branch are connected in parallel between the first terminal and the second terminal.

As used herein, the term "supercapacitor" refers to a capacitor having a capacitance value higher than normal capacitors, but with lower voltage limits. Such a supercapacitor bridges a gap between normal (electrolytic) capacitors and rechargeable batteries. A supercapacitor may also be referred to as an "ultracapacitor" or "Electrochemical Double Layer Capacitor (EDLC)".

If a fault (such as e.g. a short circuit across one or more of the supercapacitors in the supercapacitor branch) occurs within the module, the bypass switch may be closed such that a remaining energy of the supercapacitor branch may be discharged/burned via the resistance. By lowering or emptying the energy within the faulty module, the fault may be cleared and operation of e.g. an energy storage system in which the module forms part may at least temporally continue to operate as intended.

The module further includes a direct bypass branch including at least a second bypass switch. The direct bypass branch may also be connected in parallel with the supercapacitor branch and the resistive bypass branch, between the first terminal and the second terminal. Herein, the word "direct bypass branch" refers to a branch not relying on (or not including) a series connected resistance such as found in the resistive bypass branch.

The direct bypass branch is activated (by closing the second bypass switch) in order to completely bypass the module and the supercapacitor branch. This takes place e.g. after a sufficient energy has been discharged/burned via the resistance in the resistive bypass branch. It is envisaged e.g. to first close the first bypass switch, discharge energy via the resistance, and then bypass the module/supercapacitor branch by closing the second bypass switch once sufficient energy has been discharged. Herein, that a sufficient energy has been discharged/burned may e.g. correspond to a situation wherein the remaining energy in the supercapacitor branch is low energy such that the closing of the second bypass switch does not introduce any safety risk.

Herein, a "bypass switch" refers to a switch which is at least sufficient to close a circuit but not necessarily sufficient to open a circuit. Phrased differently, the bypass switch does not have to be a circuit breaker capable of breaking a high-current path.

In one or more embodiments, the module may be such that there is no fuse, or similar component, connected in series with the arrangement of the one or more supercapacitors and any one of the first terminal and the second terminal.

The present disclosure provides the insight that the use of supercapacitors instead of e.g. traditional rechargeable batteries may allow to avoid having to insert a fuse or similar within the supercapacitor branch, thereby providing a reduced complexity of the circuit(s) and e.g. a reduced cost of manufacturing.

In one or more embodiments, the module may be such that there is no switch or circuit breaker connected in series with the arrangement of one or more supercapacitors and any one of the first terminal and the second terminal. This may provide an additional reduction of circuit complexity and manufacturing cost.

In one or more embodiments, the module may be such that there is neither a fuse, switch nor circuit breaker connected in series with the arrangement of one or more supercapacitors and any one of the first terminal and the second terminal. This may provide even more reduction of complexity and manufacturing cost.

In one or more embodiments, the module may be such that the arrangement of one or more supercapacitors are connected directly between the first terminal and second terminal, i.e. without any other electrical components (such as switches, breakers, fuses, resistances, etc.) therebetween. This may provide an even further reduction of circuit complexity and manufacturing cost.

In one or more embodiments, the module may further include an array of diodes. In the array, each diode may be connected in reverse across at least one supercapacitor of the one or more supercapacitors.

Providing the array of diodes may for example prevent an excessive voltage from being applied across the supercapacitors during e.g. discharge when the first bypass switch is closed. An applied negative voltage may for example be limited by a forward voltage of the diodes.

In one or more embodiments, the arrangement of one or more supercapacitors may include two or more supercapacitors connected in series. It is envisaged that the number of supercapacitors may be selected to match e.g. a specific requirement in terms of storage voltage capacity, etc., and a higher such voltage may be obtained by series connection of multiple supercapacitors.

In one or more embodiments, the arrangement of one or more supercapacitors may include two or more supercapacitors connected in parallel. It is envisaged that the number of supercapacitors may be selected to match e.g. a specific requirement in terms of current supply capacity, etc., and a higher such current supply capacity may be obtained by parallel connection of multiple supercapacitors.

It is of course also envisaged to combine series and parallel connection of multiple supercapacitors. For example, a particular storage voltage may be obtained by a string of a particular number of supercapacitors connected in series. A particular current supply capacity may be obtained by a particular number of such strings connected in parallel. Other variations are of course also envisaged.

According to a second aspect of the present disclosure, a method of operating a module according to the first aspect (or according to any embodiment thereof) is provided, as defined in the independent claim <NUM>. Among others, the method includes detecting an occurrence of a fault associated with the one or more supercapacitors of the module. The method further includes lowering a remaining energy in the one or more supercapacitors by closing the first bypass switch, thereby discharging the one or more supercapacitors through/via the resistance.

As described earlier herein, such a method may provide for a reduction of a remaining energy in the supercapacitor branch of the module to be sufficiently reduced, such that the fault in the module may be hindered from negatively affecting other modules within the energy storage system.

The detection of the fault could for example be performed by a controller or similar, and/or based on supercapacitor internal diagnostics. For example, a short circuit fault may be detected by measuring a voltage across one or more supercapacitors, and indicated by a (sudden) decrease in such a voltage due to the short circuit. Generally herein, a "fault in the module" or a "fault associated with the one or more supercapacitors" may also include other faults than short circuits, such as for example loss of communication with e.g. a control unit, over-temperatures in the supercapacitors or in bus-bars, or similar. Other faults which may be handled by discharging the energy of the supercapacitors by closing the first bypass switch and using the resistance are also envisaged although not explicitly stated herein.

The method further includes determining whether the remaining energy in the one or more supercapacitors is below a certain threshold. The method may further include to, upon determining that the remaining energy is below the certain threshold, directly bypass the one or more supercapacitors by closing the second bypass switch.

In one or more embodiments, the fault may be a short-circuit across at least one of the one or more supercapacitors.

According to a third aspect of the present disclosure, an energy storage system is provided. The energy storage system includes a plurality of modules of the first aspect (or any embodiment thereof), and control means (e.g. a computer implemented controller) for controlling at least one of the modules in accordance with the method of the second aspect (or any embodiment thereof). Herein, it is envisaged that the "control means" includes all means necessary to both detect the fault, and to command and control e.g. the various bypass switches and similar.

In one or more embodiments, the energy storage system further includes at least a second plurality of modules according to the first aspect (or any embodiment thereof) connected in series. The first plurality of modules and the second plurality of modules are connected in parallel, as described earlier herein.

Further objects and advantages of the various embodiments of the present disclosure will be described below by means of exemplifying embodiments.

Exemplifying embodiments will be described below with reference to the accompanying drawings, in which:.

In the drawings, like reference numerals will be used for like elements unless stated otherwise. Unless explicitly stated to the contrary, the drawings show only such elements that are necessary to illustrate the example embodiments, while other elements, in the interest of clarity, may be omitted or merely suggested. As illustrated in the figures, the sizes of elements and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of the embodiments.

With reference to <FIG>, the concept of a module according to the present disclosure will now be described in more detail.

<FIG> schematically illustrates an example embodiment of a module <NUM> which may be included as part of an energy storage system (not shown). The module <NUM> includes a first terminal <NUM> and a second terminal <NUM>. The terminals <NUM> and <NUM> may for example be used to connect the module to one or more other modules, and/or to an electrical power grid, as part of the energy storage system.

A supercapacitor branch <NUM> is connected between the first terminal <NUM> and the second terminal <NUM> and includes an arrangement <NUM> including at least one supercapacitor <NUM>. In the module <NUM>, only a single supercapacitor <NUM> is illustrated in <FIG>, but it is envisaged that the arrangement <NUM> may include also more than one supercapacitor. If that is the case, the supercapacitors <NUM> in the arrangement <NUM> in the supercapacitor branch <NUM> may be connected in series and/or in parallel as needed to meet specific voltage and/or current supply requirements.

A resistive bypass branch <NUM> is also connected between the first terminal <NUM> and the second terminal <NUM>, i.e. in parallel with the supercapacitor branch <NUM>. The resistive bypass branch <NUM> includes a first bypass switch <NUM> and a resistance <NUM> which are connected in series as shown in <FIG>.

As described earlier herein, if a fault (such as e.g. a short circuit) occurs within the arrangement <NUM> of supercapacitors <NUM>, a remaining energy within the arrangement <NUM> may be drained/burned via the resistance <NUM> by closing the first bypass switch <NUM>. This procedure may continue at least until a remaining energy in the arrangement <NUM> is/goes below a certain threshold.

<FIG> schematically illustrates another example embodiment of a module <NUM>. In addition to the elements/components of the module <NUM> described with reference to <FIG>, the module <NUM> further includes a direct bypass branch <NUM> connected between the first terminal <NUM> and the second terminal <NUM>, and also in parallel with the supercapacitor branch <NUM> and the resistive bypass branch <NUM>. The direct bypass branch <NUM> includes a second bypass switch <NUM>. It is envisaged that the second bypass switch <NUM> may be closed once the remaining energy of the arrangement <NUM> has gone below the certain threshold (after draining/burning via the resistance <NUM> due to the closing of the first bypass switch <NUM>), and thereby fully bypass the module <NUM>. By so doing, in case of a fault, the module may be bypassed such that it does not interfere with the functionality of e.g. other modules in the energy storage system (not shown) of which the module <NUM> forms part.

With reference to <FIG>, it should be noted that a fault in the arrangement <NUM> of the modules <NUM> and <NUM> may thus be handled without the need for other components (such as fuses, additional switches, etc.) e.g. in series with the arrangement <NUM> within the supercapacitor branch <NUM>. This is a result of the insight that the use of supercapacitors <NUM> instead of e.g. traditional rechargeable batteries as means for energy storage allows to not include such additional components (such as e.g. fuses) in the circuit. As described earlier herein, leaving out such additional components may allow for a less complex circuitry, with e.g. a lower footprint, and with e.g. a reduced cost of manufacturing.

In some embodiments of the modules <NUM> and <NUM>, it is envisaged that there is at least no fuse connected in series with the arrangement <NUM> within the supercapacitor branch <NUM>. In some embodiments, it is envisaged that there is at least no switch (or circuit breaker) connected in series with the arrangement <NUM> within the supercapacitor branch <NUM>. In some embodiments, it is envisaged that there is neither a fuse nor a switch (or circuit breaker) connected in series with the arrangement <NUM> within the supercapacitor branch <NUM>. Within all such embodiments, "something not in series with the arrangement" is to be interpreted as there being no such "something" between the arrangement <NUM> and any of the first terminal <NUM> and the second terminal <NUM>. In some embodiments, the arrangement <NUM> of the one or more supercapacitors <NUM> may therefore be connected directly between the first terminal <NUM> and the second terminal <NUM>. Herein, "directly" of course includes there being e.g. connection wires, bus-bars or similar, but no additional electrical components such as resistors, switches, fuses, or similar.

Herein, a "bypass switch" is envisaged as being e.g. a disconnector, a circuit breaker or an electronic switch. As described earlier, such a bypass switch does not necessarily need to be able to break a larger current, in which case an electronic switch may be enough, reducing the need for more expensive and complex disconnectors and/or circuit breakers.

<FIG> schematically illustrates a further example embodiment of a module <NUM> (wherein any branch other than the supercapacitor branch <NUM> is not illustrated), which further includes an array <NUM> of diodes <NUM>. Each diode <NUM> is connected in reverse (with respect to polarity) across a respective supercapacitor <NUM>. As described earlier herein, the diode array <NUM> may help to prevent damage to the supercapacitors <NUM> due to a negative voltage which may appear during discharge of the supercapacitors <NUM> (via the resistance in the resistive bypass branch) during a fault. By connecting the diodes <NUM> in reverse across the supercapacitors <NUM>, the generated negative voltage during discharge may turn on the diodes <NUM> and prevent an amplitude of the negative voltage from increasing to more than a forward voltage of the diodes <NUM>.

<FIG> schematically illustrate further example embodiments of modules <NUM> and <NUM>, respectively. In the module <NUM>, the supercapacitor branch <NUM> includes two sub-branches <NUM> and <NUM>, each including a plurality of supercapacitors <NUM> connected in series. Each sub-branch <NUM> and <NUM> is further provided with a respective diode array <NUM> and <NUM>, each including diodes <NUM> connected in reverse across a respective supercapacitor <NUM>. In the module <NUM>, the supercapacitor branch <NUM> includes series-connected blocks of supercapacitors, wherein each block includes one or more parallel strings of series-connected supercapacitors <NUM>. For each block, a diode <NUM> of the diode array <NUM> is connected in reverse across the block. Here, each diode is connected in reverse across more than a single supercapacitor.

It is also envisaged that, if there are no diodes included, the supercapacitor branch of a module as described herein may still be configured as in the modules <NUM> and/or <NUM> (i.e. with two parallel sub-branches and/or with series connected blocks of parallel strings of series-connected supercapacitors). Other configurations of the supercapacitor branch <NUM> are also envisaged, wherein the supercapacitors <NUM> in the arrangement <NUM> are provided and connected in a way which meets required performance in e.g. terms of storage voltage and/or supply current. The idea of using at least a resistive bypass branch (and possibly also a direct bypass branch) applies to all such configurations of the supercapacitor branch <NUM> described in the embodiments shown in <FIG>.

A method of operating a module as described herein will now be described in more detail with reference to <FIG>.

<FIG> schematically illustrates a flow of an example embodiment of a method <NUM>. In a step S210, the method <NUM> includes detecting whether a fault associated with one or more supercapacitors in the module has occurred. If it is determined that no fault has occurred, the method <NUM> may continue to monitor the supercapacitors as indicated by the arrow <NUM>. If, on the other hand, it is determined that a fault has occurred, the method <NUM> may proceed as indicated by the arrow <NUM> to a further step S220.

Detecting the fault could for example be either from a supercapacitor cabinet/system, and may for example be based on current and/or voltage measurements, or e.g. by a battery management system (BMS) based on supercapacitor internal diagnostics. A voltage measurement may for example show a sudden decrease in voltage, which may indicate that e.g. a short circuit has occurred. Likewise, a current measurement may for example show a sudden increase in current, which may also indicate e.g. a short circuit fault. Whether a voltage is to be indicative of a fault may for example be figured out in accordance with specifications provided by a manufacturer of the supercapacitors, or similar. As described earlier herein, a fault is not necessarily required to be a short circuit fault. Other types of faults envisaged within the present disclosure include for example loss of BMS communication, supercapacitor over-temperatures, supercapacitor cabinet busbar over-temperatures, etc..

The step S220 includes lowering a remaining energy in the (one or more) supercapacitors of the module by closing the first bypass switch within the resistive bypass branch. By so doing, the supercapacitors may be discharged through the resistance of the resistive bypass branch, and the fault may thereby be handled without negatively affecting other modules within a same energy storage system.

<FIG> schematically illustrates a flow of another example embodiment of a method <NUM>. In the method <NUM>, an additional step S230 includes determining whether the remaining energy in the (one or more) supercapacitors is below a certain threshold. If the remaining energy is determined to still be higher than the certain threshold, the method <NUM> may for example wait (as indicated by the arrow <NUM>) until the threshold is reached. If it is determined that the remaining energy is below the certain threshold, the method <NUM> may proceed (as indicated by the arrow <NUM>) to a step S240, in which the supercapacitors are then directly bypassed by closing the second bypass switch within a direct bypass branch as described earlier herein. The module may then be fully bypassed, and current no longer required to flow through the resistance of the resistive bypass branch of the module.

An energy storage system according to the present disclosure will now be described with reference to <FIG>.

<FIG> schematically illustrates an energy storage system <NUM>, including a plurality <NUM> of modules <NUM> connected in series. The system <NUM> also includes control means <NUM> (such as e.g. a computer implemented controller, or similar) for controlling at least one of the modules <NUM>. Although not illustrated in <FIG>, it is envisaged that the system also <NUM> includes means necessary for e.g. detecting whether a fault has occurred within a module <NUM>, and the control means <NUM> is thus such that the module <NUM> may be controlled in accordance with a method as described herein, for example any one of the methods <NUM> and <NUM> described above with reference to <FIG>. In some embodiments, it is envisaged that the control means <NUM> may instead form part of a module <NUM>, and i.e. that each module <NUM> may have its own internal control means <NUM>.

The system <NUM> may be connected e.g. to an electrical power grid <NUM>, in order to provide stabilization of the electrical power grid <NUM> in times when e.g. a demand for power is high. As an example, during times when a demand for power is lower, the energy storage system may receive power from the grid <NUM> in order to charge the supercapacitors in the modules <NUM>. During times when the demand for power on the grid <NUM> is higher, the increased demand may be compensated for by the system <NUM> instead providing power to the grid <NUM> from the supercapacitors of the modules <NUM>. If the electrical power grid <NUM> is an AC power grid, the connection to the electrical power grid <NUM> may be provided via an AC/DC conversion stage <NUM>. Although not explicitly shown in <FIG>, it is envisaged that such an AC/DC conversion stage <NUM> may, for control purposes, also be connected to the control means <NUM>.

As illustrated in <FIG>, the system <NUM> may also include at least one further plurality <NUM> of series-connected modules (as e.g. described herein). The further plurality <NUM> may be connected in series with the plurality <NUM>.

In summary, the use of supercapacitors may enable a faster stabilization (due to the faster response time in terms of charging/discharging of the supercapacitors compared to e.g. traditional rechargeable batteries), and also an increased reliability as supercapacitors may handle an increased number of such charging/discharging cycles. The modules, control method therefor, as well as the energy storage system as described herein, provide an improved reliability in that a fault (e.g. a short circuit) within a module may be properly handled, and the module even completely bypassed, such that the operation of the other modules are not negatively affected by the occurrence of such a fault, and such that the system as a whole may still be available thereafter. As each module has its own means of handling a fault (the one or more bypass branches), fault handling may be distributed within the energy storage system. Additionally, if used, one or more diodes as described in here provides further protection against negative voltages.

Although features and elements have been described above in particular combinations, each feature or element may be used alone without the other features and elements or in various combinations with or without other features and elements.

Claim 1:
A module (<NUM>) for use in an energy storage system, including:
a first terminal (<NUM>) and a second terminal (<NUM>);
a supercapacitor branch (<NUM>) including an arrangement (<NUM>) of one or more supercapacitors (<NUM>), and
a resistive bypass branch (<NUM>) including at least a first bypass switch (<NUM>) and a resistor (<NUM>) connected in series,
wherein the supercapacitor branch and the resistive bypass branch are connected in parallel between the first terminal and the second terminal;
further including a direct bypass branch (<NUM>) including at least a second bypass switch (<NUM>), wherein the direct bypass branch is also connected in parallel with the supercapacitor branch and the resistive bypass branch, between the first terminal and the second terminal;
characterized in that the direct bypass branch (<NUM>) does not rely on or include a series connected resistor and in that the first bypass switch is configured to, upon an occurrence of a fault associated with the one or more supercapacitors, be closed such that the one or more supercapacitors are discharged through the resistor, thereby lowering a remaining energy in the one or more supercapacitors;
wherein the second bypass switch is configured to subsequently be closed in order to directly bypass the one or more supercapacitors upon an occurrence of the remaining energy in the one or more supercapacitors being below a certain threshold.