CN219697296U

CN219697296U - Energy storage system, energy conversion system and power grid

Info

Publication number: CN219697296U
Application number: CN202223355305.3U
Authority: CN
Inventors: 柏浩峰; 张自驰; A·瑟德尔布罗姆; 孟乐轩; P·努瓦塞特
Original assignee: Hitachi Energy Switzerland AG
Current assignee: Hitachi Energy Co ltd
Priority date: 2022-12-14
Filing date: 2022-12-14
Publication date: 2023-09-15
Anticipated expiration: 2032-12-14
Also published as: DE202023100748U1

Abstract

The present disclosure relates to a bypass circuit for a capacitor-based energy storage system. The energy storage system includes a plurality of interconnected capacitors forming a capacitor bank and a bypass circuit disposed across the capacitor bank and configured to discharge the capacitor bank. The bypass circuit includes: a set of bypass switches configured to connect the bypass circuit across the capacitor bank and thereby bypass the capacitor bank; a resistor; and a resistor bypass switch configured to bypass the resistor. According to an advantageous aspect of the present disclosure, the bypass circuit further comprises a threshold switch arranged in series with the resistor, the threshold switch being configured to close when the voltage of the capacitor bank exceeds a threshold voltage. The present disclosure also relates to a system comprising the above energy storage system and a converter operatively coupled thereto, and a grid system comprising the above system.

Description

Energy storage system, energy conversion system and power grid

Technical Field

The present disclosure relates to an energy storage system suitable for use with an energy storage equipped static synchronous compensator (E-STATCOM). More specifically, the present disclosure relates to an improved bypass circuit for such an energy storage system, an E-STATCOM comprising such an energy storage system and an electrical grid comprising such an E-STATCOM.

Background

Due to its ability to provide active and reactive power support and other services related to power quality, E-STATCOM, i.e. an energy storage system (energy storage system, ESS) integrated with a static synchronous compensator (STATCOM), is considered as a promising option for improving the voltage and frequency stability of renewable energy dominant grids.

The ESS used in an E-STATCOM system may include a capacitor bank configured to charge or discharge according to the requirements of the grid in which they are installed. To properly address the charge or discharge requirements, the capacitor-based ESS in an E-STATCOM system can typically remain idle in an intermediate state of charge (SoC). Thus, the risk of overcharging the capacitor in the ESS is reduced.

ESS conventionally include protection circuits, such as bypass circuits, that are configured to bypass one or more capacitors (e.g., that are disposed into a module or cabinet in the ESS) in the event of a failure or malfunction of the capacitors or the entire cabinet. As part of the bypass procedure, discharge resistors may be connected into the bypass circuit to release energy from the bypassed capacitors, thereby making them safe for maintenance or replacement.

It is desirable to improve the operating efficiency of ESS used with converters such as E-STATCOM in order to increase the overall efficiency of the electrical grid in which such E-STATCOM is installed.

Disclosure of Invention

It is an implementation of a portion of the present disclosure that maintaining an ESS in an intermediate SoC in an idle state may disadvantageously underutilize the energy storage capacity of the ESS. Thus, according to the presently disclosed system, the ESS may remain at or near full SoC while mitigating the risk of the ESS being overcharged.

That is, in particular, according to one aspect of the present disclosure, an energy storage system is provided that includes a plurality of interconnected capacitors forming a capacitor bank and a bypass circuit disposed across the capacitor bank, the bypass circuit configured to discharge the capacitor bank. In some exemplary embodiments, the capacitor bank includes a plurality of supercapacitors connected in series and configured to provide the DC link voltage to the modular multilevel converter MMC.

The bypass circuit includes: a set of bypass switches configured to connect the bypass circuit across the capacitor bank and thereby bypass the capacitor bank; a resistor; and a resistor bypass switch configured to bypass the resistor.

According to a particularly advantageous aspect of the present disclosure, the bypass circuit further comprises a threshold switch arranged in series with the resistor, the threshold switch being configured to close when the voltage of the capacitor bank exceeds a threshold voltage (such as a maximum expected state of charge SoC of the capacitor bank).

According to some examples, the threshold switch comprises an insulated gate bipolar transistor IGBT. Additionally or alternatively, the group bypass switch and/or the resistor bypass switch comprise mechanical switches.

In an example embodiment, the energy storage system further comprises a control unit configured for operative communication with the group bypass switch and/or the resistor bypass switch.

The control unit may also be configured to be in operative communication with the threshold switch and to close the threshold switch in response to a request for a balancing operation of the capacitor bank.

In further example embodiments, the energy storage system further comprises: a second capacitor bank configured to provide a power supply for operation of the bypass circuit; and a second bypass circuit disposed across the second capacitor bank, the second bypass circuit configured to discharge the second capacitor bank. In such an embodiment, the capacitor bank is configured to provide a power supply for operation of the second bypass circuit. That is, the capacitor bank may advantageously act as an auxiliary power source for modules (i.e., capacitor modules) and/or switches associated with another capacitor bank.

According to a further aspect of the present disclosure, there is provided an energy conversion system comprising: an energy storage system substantially as described above; and a converter operatively coupled to the energy storage system, the converter configured to provide energy from the energy storage system to the power grid and/or from the power grid to the energy storage system.

For example, the converter may be a static synchronous compensator STATCOM operatively coupled to the ESS to form an energy storage equipped STATCOM, i.e., E-STATCOM. In another example, the converter may be a Static VAR Compensator (SVC) or another type of converter.

According to yet further aspects of the present disclosure, there is provided an electrical grid comprising an energy conversion system as described above, i.e. having an ESS operatively coupled with an energy storage system.

It should therefore be appreciated that in accordance with the presently disclosed method, the capacitor bank may remain at or near full SoC in an idle state, avoiding the risk of overcharging the capacitor. Therefore, the effective energy storage capacity of the energy storage system can be doubled compared to the comparative example in which the capacitor bank maintains the 50% charge amount in the idle state. From another perspective, the use of supercapacitors is advantageously reduced.

In addition, the presently disclosed technology is relatively inexpensive to implement and can be retrofitted into existing systems. Accordingly, aspects of the present disclosure are advantageously easy to implement, but significantly improve the efficiency of the ESS, and thus any power grid in which the ESS may be installed and operated.

Drawings

One or more embodiments will be described, by way of example only, with reference to the following drawings, in which:

FIG. 1 schematically illustrates an energy storage system according to an aspect of the present disclosure;

FIG. 2 schematically illustrates an example modification of the energy storage system illustrated in FIG. 1;

FIG. 3 schematically illustrates another example modification of the energy storage system illustrated in FIG. 1;

FIG. 4 graphically illustrates a state of charge of an energy storage system during operation and a state of charge of an energy storage system according to a comparative example, in accordance with aspects of the present disclosure; and

fig. 5 schematically illustrates a power grid system including a system according to an aspect of the present disclosure.

Detailed Description

The present disclosure is described below by way of a number of illustrative examples. It should be understood that the examples are for purposes of illustration and explanation only and are not intended to limit the scope of the present disclosure. Rather, the scope of the present disclosure is defined by the appended claims. In addition, while examples may be presented in the form of individual embodiments, it will be appreciated that the utility model also encompasses combinations of the embodiments described herein.

Fig. 1 schematically illustrates an Energy Storage System (ESS) 100 that includes a plurality of interconnected capacitors 112 that form a capacitor bank 110. Capacitor bank 110 includes one or more capacitors 112, which may be supercapacitors according to some embodiments. The capacitors 112 in the capacitor bank 110 are shown connected in series in fig. 1, but it should be understood that in some embodiments, the capacitors 112 may additionally or alternatively be connected in parallel.

For example, the capacitors 112 may be connected in both series and parallel, wherein two or more of the capacitors 112 are connected in parallel to form a pair or group of capacitors, which group parallel connected capacitors may then be connected in series with one or more other group capacitors, and vice versa. According to some embodiments, capacitor 112 may be configured to provide a DC link voltage for the modular multilevel converter MMC.

The ESS 100 further includes a bypass circuit 120. The bypass circuit 120 is arranged across the capacitor bank 110 such that the capacitor bank 110 can be bypassed. The bypass circuit 120 includes a bank bypass switch 124. The bank bypass switch 124 is configured to connect the bypass circuit 120 across the capacitor bank 110 and thereby bypass the capacitor bank 110.

The bypass circuit further includes a resistor 122. The resistance in the resistor 122 may be configured to be low enough that when the resistor 122 is connected, the operating current of the ESS 100 does not risk overcharging the capacitor 112. Resistor 122 may be bypassed using a resistor bypass switch 126 connected across resistor 122. As shown in fig. 1, resistor bypass switch 126 is connected in series with bank bypass switch 124 such that together they can provide a bypass path that bypasses both capacitor bank 110 and resistor 122. The bank bypass switch 124 and/or the resistor bypass switch 122 may comprise mechanical switches.

The bypass circuit 120 also includes a threshold switch 128. The threshold switch 128 is arranged in series with the resistor 122 and is configured to close when the voltage of the capacitor bank 110 exceeds a threshold voltage. The threshold voltage may, for example, correspond to a maximum expected state of charge (SoC) of the capacitor bank 110. In some example embodiments, the threshold switch 128 may include an Insulated Gate Bipolar Transistor (IGBT).

During normal operation, resistor bypass switch 126 and bank bypass switch 124 are open. When the voltage of capacitor 112 is above the threshold voltage, threshold switch 128 is closed, such that current bypasses capacitor bank 110 and is instead redirected through resistor 122. Such an arrangement may be referred to as a "chopper resistor" or "brake chopper". When the voltage of the capacitor 112 is below the threshold voltage, the threshold switch 128 is turned off. The upper and lower limits of the threshold voltage may be the same value, or the upper and lower limits of the threshold voltage may be different.

In the event of a failure or malfunction within the capacitor bank 110, a two-step bypass procedure will be initiated and the bank bypass switch 124 will close, as part of the first step, causing the capacitor bank 110 to discharge through the resistor. After this, as a second step, resistor bypass switch 126 will close so that both capacitor bank 110 and resistor 122 are bypassed.

A communication and control system (not shown) may be connected (either wired or wireless) to the group bypass switch 124 and the resistor bypass switch 126 to control and monitor the opening and closing of the switches 124, 126 and thereby implement such a 2-step bypass procedure.

In the event of a failure or malfunction of the threshold switch 128, a two-step bypass procedure may be implemented to mitigate the risk of the capacitor bank 110 being overcharged without the function of the threshold switch 128.

This arrangement also provides for faster module level balancing than can be provided by a single Capacitor Management System (CMS). If the capacitors 112 are unbalanced such that the capacitor within the capacitor bank 110 has a higher SoC than the remaining capacitors 112 within the capacitor bank 110, the threshold switch 128 may be closed to discharge the capacitor 112 having the highest SoC.

The introduction of the threshold switch 128 advantageously allows the capacitor bank 110 to be at a higher SoC in the idle state than a comparative example in which only the bank bypass switch 126 and the resistor bypass switch 124 are provided, as additional charging power may be redirected through the resistor 122 as described above. Moreover, the use of (super) capacitors 112 may be advantageously reduced, as the number of charge and discharge cycles may be reduced. Thus, the operational life of the ESS 100 may be extended.

Fig. 2 schematically illustrates a variation of an Energy Storage System (ESS) 100 for which like-numbered components mentioned above with respect to fig. 1 may be at least identical or similar in their function, and thus these components are not discussed in detail.

The ESS 100 shown in fig. 2 includes an additional capacitor bank 110 connected in parallel with the capacitor bank 110. The additional capacitor bank 110 may be the same as, similar to, or different from the other (first) capacitor banks 110 (e.g., regarding the number of capacitors 112 and/or their interconnections), and is not limited to being connected in parallel with the first capacitor bank 110, but may be connected in series. If more than two capacitor banks 110 are included in the ESS 100, they may be connected in both parallel and series using pairs or groups of parallel connected capacitor banks, which groups are then connected in series, and vice versa. By modularizing the ESS 100 in this manner, failures and faults in any particular capacitor bank 110 may be advantageously isolated and contained (i.e., physically and/or electrically).

According to the example shown in fig. 2, two capacitor banks 110 use the same bypass circuit 120. However, fig. 3 schematically illustrates another variation of the EES 100, which is similarly configured as the ESS 100 illustrated in fig. 1 and 2, including an additional bypass circuit 120. The two capacitor banks 110 depicted are each connected to one bypass circuit 120 such that each of the capacitor banks 110 may be individually bypassed by the respective bypass circuit 120. According to such an arrangement, advantageous redundancy is provided for powering the switches 124, 126, 128 in each bypass circuit 120.

Fig. 4 shows a graph 400 illustrating a state of charge (SoC) of an energy storage system, such as ESS 100 discussed above, over time (t) during operation, shown as line 401. Graph 400 also shows the SoC of the energy storage system during operation according to the comparative example, such as line 402.

Graph 400 begins at a time period 410 where the corresponding ESS is in an idle state. Referring to the respective lines 401 and 402, it can be seen that in this example, the ESS according to aspects of the present disclosure remains in a maximum (max.) state of charge, while the ESS according to the comparative example remains in an intermediate state of charge (about 50%), or half between the minimum and maximum states of charge.

During time period 420, a request for power may be issued, and thus the ESS may be discharged before returning to the idle state during a subsequent time period 430.

During time period 440, an excess of power may be detected and the ESS may be charged. As seen in line 402, this charge power does not cause the ESS according to the comparative example to be overcharged (i.e., to exceed the maximum state of charge) because it begins from an idle state in the intermediate state of charge. However, as seen in line 401, in accordance with aspects of the present disclosure, the charging power is dissipated (as shown by the shading) rather than overcharging the ESS.

That is, during the period 440 in which charging power is provided to the ESS, the state of charge of the ESS may exceed the limit and thereby cause a switch (such as the threshold switch 128 discussed above) to close in accordance with aspects of the present disclosure. Thus, the charging power is directed to the resistor, thereby performing discharging. When the charging power subsides, the ESS may return to the idle state again at time period 450.

As will be readily appreciated from this graph 400, an ESS according to aspects of the present disclosure may maintain a larger SoC in an idle state and thus have a larger discharge capacity in situations where the grid requires a large amount of power. In addition, since the ESS is not charged for the period 440, the charging power is instead dissipated by the resistor, whereby the use of the supercapacitor is reduced. Thus, the operational lifetime of the supercapacitor can be advantageously prolonged.

Fig. 5 schematically illustrates a power grid system 500 in accordance with an aspect of the disclosure. The grid system 500 includes a (sub) system 501 that includes an ESS 100 such as described above that is operatively coupled to a converter 510. The converter 510 may be a static compensator (STATCOM), a Static VAR Compensator (SVC), or the like.

The converter 510 is configured to provide power to and from a power distribution network 520, such as an AC power distribution network. In the illustrated example, the ESS 100 discharges to the power distribution network 520 via the converter 510 and also charges from the power distribution network 520 via the converter 510, but it should be understood that there may also be a connection between the ESS 100 and the power distribution network 520 that is not via the converter 510.

Thus, the power distribution network 520 may advantageously be supported by the power from the ESS 100, and may, for example, provide excess power (e.g., caused by an excess of power generation) to the ESS 100 for storage and potential later use when the power is insufficient.

Although specific examples of operation have been discussed above, it should be understood that these examples are provided for illustrative purposes only and are not intended to limit the scope of the present disclosure. Indeed, any combination of the above-described examples should be considered to fall within the scope of the present disclosure. For the avoidance of doubt, the scope of the utility model is intended to be defined by the appended claims.

Claims

1. An energy storage system, comprising:

a plurality of interconnected capacitors, the plurality of interconnected capacitors forming a capacitor bank; and

a bypass circuit disposed across the capacitor bank and configured to discharge the capacitor bank;

wherein the bypass circuit comprises:

a bank bypass switch configured to connect the bypass circuit across the capacitor bank and thereby bypass the capacitor bank;

a resistor;

a resistor bypass switch configured to bypass the resistor; and

a threshold switch arranged in series with the resistor and configured to close when the voltage of the capacitor bank exceeds a threshold voltage.

2. The energy storage system of claim 1, wherein:

the capacitor bank includes a plurality of supercapacitors connected in series and configured to provide a DC link voltage to the modular multilevel converter MMC.

3. The energy storage system of claim 1 or 2, wherein:

the threshold switch comprises an insulated gate bipolar transistor IGBT.

4. The energy storage system of claim 1 or 2, wherein:

the set of bypass switches and/or the resistor bypass switch comprise mechanical switches.

5. The energy storage system of claim 1 or 2, wherein:

the threshold voltage corresponds to a maximum expected state of charge SoC of the capacitor bank.

6. The energy storage system of claim 1 or 2, further comprising:

a control unit configured for operative communication with the set of bypass switches and/or the resistor bypass switch.

7. The energy storage system of claim 6, wherein:

the control unit is further configured to be in operative communication with the threshold switch and to close the threshold switch in response to a request for balancing operation of the capacitor bank.

8. The energy storage system of any of claims 1-2 and 7, further comprising:

a second capacitor bank configured to provide a power supply for operation of the bypass circuit; and

a second bypass circuit disposed across the second capacitor bank, the second bypass circuit configured to discharge the second capacitor bank,

wherein:

the capacitor bank is configured to provide a power supply for operation of the second bypass circuit.

9. An energy conversion system, comprising:

the energy storage system of any one of the preceding claims; and

a converter is operatively coupled to the energy storage system and configured to provide energy from the energy storage system to an electrical grid and/or to provide energy from the electrical grid to the energy storage system.

10. The energy conversion system according to claim 9, wherein:

the converter is a static synchronous compensator STATCOM operatively coupled to the energy storage system to form an energy storage equipped STATCOM, i.e., E-STATCOM.

11. An electrical grid comprising the energy conversion system of claim 9 or 10.