WO2010069405A1

WO2010069405A1 - Battery energy storage system, and method

Info

Publication number: WO2010069405A1
Application number: PCT/EP2008/068075
Authority: WO
Inventors: Bertil Nygren; Falah Hosini; Gerhard Brosig; Gunnar Russberg; Jan R. Svensson; Willy Hermansson
Original assignee: Abb Research Ltd
Priority date: 2008-12-19
Filing date: 2008-12-19
Publication date: 2010-06-24

Abstract

The invention relates to a battery energy storage system (20) comprising at least one battery unit 13_i, which in turn comprises one or more battery modules 12₁,..., 12_n. The battery energy storage system (20) further comprises a battery management unit (17) managing the at least one battery unit 13_i. The battery energy storage system (20) is characterized by means (22, 23, 21) for powering the battery management unit (17) by one or more of the battery modules 12₁,..., 12_n of the at least one battery unit 13_i. The invention also relates to a corresponding method.

Description

Battery energy storage system, and method

Field of the invention

The invention relates generally to the field of electric power transmission systems, and in particular to battery storages for use in such power systems.

Background of the invention

Electric power systems need to provide electric power in a reliable fashion. Therefore such systems often comprise backup devices, for example in form of DC power sources. The backup devices may provide power for evening out fluctuations, shortages etc.

An example of such a device, usable as a backup, is a battery energy storage as illustrated in figure 1. The battery energy storage 1 comprises a number of series- and/or parallel- connected battery cells arranged in battery modules 2_±. The battery modules 2_± in turn are series- and/or parallel- connected to form a battery unit 3_± and several battery units 3i, 32,..., 3_n may be series-connected to form a battery string 4_1# In large battery energy storage systems, several such battery strings 4i,..., ^_±,..., 4_m are connected in parallel between negative and positive busbars. The battery strings 4i,..., 4i,..., 4_m are connected to a load, for example a converter system 5, which in turn is connected to a power network. Circuit breakers 6_xa, 6_xb may further be arranged between each battery string and the respective busbars.

The battery energy storage 1 further comprises one or more battery management unit(s) (BMU, not illustrated in figure 1) performing a number of different tasks. Among other things, the battery management unit measures different parameters such as battery currents, cell- and battery voltages, temperature, battery state-of-charge, and performs cell balancing, handles internal communication between battery modules and handles communication in order to send and receive data from an overall system controller. Each battery unit 3_X may be provided with a respective battery management unit, or one battery management unit may serve several battery units 3i, 32,..., 3_n.

The battery management unit needs electrical power, for example in the range of 5 - 12 VDC, 10 - 20 W. The electrical power is supplied from external sources, connected to the battery management unit.

In a large battery energy storage, such as the one described above, the battery units 3i, 32,..., 3_n will be on high electrical potential, which electrical potential may differ between the different battery units 3i, 32,..., 3_n. The external power supplies to the battery management units therefore need to be isolated.

Such large battery energy storage comprises many battery units 3i, 32,..., 3_n and a corresponding large number of isolated external power supplies are therefore required. The need for reliable isolation increases the cost of the system and also renders it more complex. Therefore, it is desirable to render the powering of the battery management units less complicated and less expensive.

Summary of the invention

It is an object of the invention to overcome or at least alleviate the above-mentioned problems. In particular, it is an object of the invention to provide improved means for powering battery management units.

It is another object of the invention to enable a less complex and more cost-efficient powering of a battery management unit. These objects, among others, are achieved by a battery energy storage system and by a method as claimed in the appended independent claims.

In accordance with the invention, a battery energy storage system is provided comprising at least one battery unit. The at least one battery unit in turn comprises one or more battery modules. The battery energy storage system further comprises a battery management unit, which manage the at least one battery unit. The battery energy storage system is characterized by means for powering the battery management unit by one or more of the battery modules of the at least one battery unit. By means of the invention, a cost-efficient powering of battery management units is provided, wherein the need for expensive and cumbersome isolations are eliminated or at least minimized. As the battery management unit draws its required power supply from the terminals of the battery unit that it manages, the need for isolation is minimized. As an additional advantage, other devices of the power system in which the battery unit is used may also be powered by the power source.

In accordance with an embodiment of the invention, the means for powering the battery management unit comprises a voltage divider, connected at one end to a pole of the battery unit and at another end to the other pole of the battery unit, wherein an output of the voltage divider is connected to the battery management unit. Readily available components can thus be used for enabling the supply of power to the battery management unit from the batteries that it manages.

In accordance with another embodiment of the invention, an output of the voltage divider is connected to the battery management unit via a DC/DC converter, wherein the DC/DC converter output is connected at one end to the output of the voltage divider and at another end to the battery management unit. The addition of a DC/DC converter enables the use of the invention for systems using even higher voltages.

In accordance with still another embodiment of the invention, the battery energy storage system further comprises a circuit breaker and the DC/DC converter output is further connected to this circuit breaker. The battery unit thereby also powers the circuit breaker, and an improvement of powering of other auxiliary electronics is provided.

In accordance with still another embodiment of the invention, the battery energy storage system further comprises a system controller connected to the battery management unit and arranged to control the battery energy storage system. Further features such as balancing the state-of-charge of the battery units by controlling the current magnitude drawn from the different battery units for powering the battery management unit is thereby provided.

The invention is also related to a corresponding method for powering a battery unit, whereby advantages similar to the above are achieved.

Brief description of the drawings

Figure 1 illustrates a known battery energy storage.

Figures 2a and 2b illustrate a battery energy storage system in accordance with the invention.

Figure 3 illustrates the battery energy storage system of figure 2 in a first embodiment of the invention.

Figure 4 illustrates the battery energy storage system of figure 2 in a second embodiment of the invention. Figure 5 illustrates the battery energy storage system of figure 2 in a third embodiment of the invention.

Figure 6 illustrates the battery energy storage system of figure 2 in a fourth embodiment of the invention.

Detailed description of embodiments of the invention

The same reference numerals are used throughout the description for denoting same or similar parts.

Figure 2a illustrates a battery unit 13_X of a battery energy storage system 20 in accordance with the invention. The battery unit 13_X comprises a number of series- and/or parallel- connected battery modules 12i, ..., 12_n, which in turn comprises a number of battery cells 14i, 14₂,..., 14_m. Several such battery units 13i may be series- and/or parallel-connected in various configurations to form a battery energy storage. Figure 2b illustrates several battery units 13i, 132,..., 13_n connected in series and forming a battery string IS₁. Several such battery strings 15_X may be connected in parallel. The battery energy storage is thus similar to the one described in connection with figure 1, and is suitable for use as a backup energy storage for a power converter connected to a electric power system.

The battery energy storage system 20 further comprises a battery management unit 17, managing the battery unit 13_X. In the figure the battery management unit 17 is shown as managing a single battery unit 13_X. It is realized that it is desirable to minimize the number of battery management units, and the battery management unit 17 could alternatively be arranged to manage a whole battery string comprising a number of battery units 13i,..., 13_n. However, in the following the battery management unit 17 is described as managing the single battery unit 13_X. In accordance with the invention, the battery management unit 17 is powered by one or more of the battery modules 12_X of battery unit 13_X that it manages. The power can thus be taken from a single battery module 12_X of the battery unit 13_X or from the total battery unit IS₁.

Figure 3 illustrates the battery energy storage system 20 and a first embodiment on how to power the battery management unit 17. A voltage divider 22 is provided, in conventional manner comprising two resistors Rl, R2 connected in series. It is noted that the resistors Rl and R2 may be any combination of series and/or parallel-connected resistors. The voltage divider 22 is arranged connected between the positive and negative poles, or terminals, of the battery unit IS₁. In particular, one end of the voltage divider 22 is connected to a first pole of the battery unit 13_X and another end is connected to the other pole of the battery unit IS₁.

The output voltage Ui of the voltage divider 22 is preferably only a fraction of the input voltage U_bu over the battery unit 13_X, in order to obtain a sufficiently stable output voltage that does not vary too much with the varying load of the battery unit IS₁. However, the output voltage Ui from the voltage divider 22 needs in most cases be stepped down further, and a DC/DC converter 23 is therefore preferably provided. As an example, the voltage U_bu over the battery unit 13_X lies within the range of 450 - 750 V, and the output voltage Ui from the voltage divider 22 could for example be in the range of 48 - 140 V or some other suitable voltage matching the chosen DC/DC converter. The battery management unit 17 will most often require a supply voltage U2 in the range of 5 - 24 VDC, for example 5, 12 or 24 VDC, and the DC/DC converter 23 is chosen accordingly. The DC/DC converter 23 is thus connected to the output from the voltage divider 22 and further to one of the poles of the battery unit IS₁. The output of the DC/DC converter 23 is connected to the battery management unit 17, providing the required supply voltage U₂. The needed supply voltage for the battery management unit 17 is thus provided from the battery unit 13_X itself, via the voltage divider 22 and the DC/DC converter 23. To feed the battery management unit 17 with power from the battery unit 13_X that it manages, thus requires only the addition of the voltage divider 22 and the DC/DC converter 23, which is a more cost-efficient solution than the prior art solutions described earlier.

It is noted that the battery energy storage system 20 in accordance with the invention may also include circuit breakers 16_xa, 16_xb, such as corresponding to the circuit breakers 6a, 6b mentioned with reference to prior art illustrated in figure 1. Such circuit breakers 16_xa, 16_xb also require power. In accordance with an embodiment of the invention, the circuit breakers 16_xa, 16_xb are also powered by means of power from battery module (s) 12_X of the battery unit 13_X. The DC/DC converter 23 output is therefore also connected to the nearest circuit breaker 16_X. As the circuit breaker 16_X close to the battery unit 13_X will be on about the same potential as the battery unit 13_X itself, or at least differing less than about 1 kV in potential, this power supply connection will need only a small isolation. The circuit breakers 16_xa, 16_xb may be of an electromechanical type or they may be solid state devices such as transistors, IGBTs

(insulated-gate bipolar transistor) or turn-off thyristors.

Yet other devices or auxiliary electronics of the power system may also be powered by the described power source arrangement, using the battery unit 13_X. As an additional example of such devices, cooling fans used for cooling the batteries can be mentioned.

Figure 4 illustrates the solution of figure 3, with the addition of a load control device 24. The function of the load control device 24 is to keep the current I_p0Wer supply constant, for example a few mA, giving sufficient power for the power supply of the battery management unit 17 and possibly other auxiliary devices. In particular, as mentioned briefly earlier, the output from the voltage divider 22 is not fixed, but varies as the load varies, i.e. varies as the battery module 12_X or battery unit 13_X voltage varies, this being the case as the battery is discharged or charged. The load control device 24 ensures that the current I_pOwer supply is a constant current within the voltage span of the battery unit IS₁. It is noted that the load control device 24 does not need to be a separate device. That is, the functionality of the load control device 24 may alternatively be included and integrated into the DC/DC converter itself.

Figure 5 illustrates the battery energy storage system 20 and yet another embodiment on how to power the battery management unit 17. In particular, the voltage divider 23 of the first embodiment is omitted, and the DC/DC converter 22 is connected directly between the positive and negative poles of the battery unit 13_X. This embodiment thus provides a solution requiring fewer components and is thus more cost-efficient, although the DC/DC converter 22 has to be dimensioned so as to handle the whole, possibly large, voltage step-down.

Figure 6 illustrates still another embodiment of the invention. The embodiment of figure 5 is here complemented with a load control device 24 having the function described earlier, i.e. keeping the current I_pOwer supply constant. Again, it is noted that the load control device 24 does not need to be a separate device, but can be integrated into the DC/DC converter, as mentioned above in connection with figure 4.

The DC/DC converter 23 and/or the load control device 24 is/are designed in such a way that the current drawn from the battery unit 13_X always has a constant current within the voltage span of the battery unit IS₁. Typically, the power needed for the battery management unit 17 could be in the order of 2OW, which corresponds to a need of a current of 25- 45 mA from the battery unit IS₁.

With reference to the embodiments of figures 3 - 6, the battery energy storage system 20 comprises an overall system controller 21, controlling different functions of the system 20. For example, the system controller 21 controls the DC circuit breakers 16_X of the system, the one or more battery management units 17, communication within the system 20 etc. and also possible other auxiliary devices. The system controller 21 may be connected to the different parts of the battery energy storage system 20 in any suitable manner, for example by means of opto fiber cables. The connection between the system controller 21 and the battery management unit 17 is indicated by a line 28, and the connection between the system controller 21 and the DC circuit breaker 16_X is indicated by a line 29.

Further, the magnitude of the current I_p0Wer supply drawn from the battery unit 13_X can be controlled and set automatically from the system controller 21. That is, the system controller 21 comprises means for controlling the current I_pOwer supply/ such means for example being implemented as software. Communication means are also provided, illustrated at reference numeral 26 and 27, for controlling the current I_pOwer supply Specifically, communication means 26, 27 is provided between the system controller 21 and the load control device 24, and/or between the system controller 21 and the DC/DC converter 23. By means of the communication means 26, 27 the system controller 21 can provide control signals to the load control device 24 and/or the DC/DC converter 23 for controlling the current I_p0Wer supply

In normal operation the current drawn from the different battery units 13i,..., IS₁,..., 13_m (only one battery unit is shown in the figures 3-6) is set to be the same in all battery units

13i,..., 13!,..., 13_m. Thereby it is ensured that the discharged Ah

(Ampere-hour) are the same for all battery units 13_X, which in turn prolongs the service life of the battery units 13_X. In this way the power supply will not cause any unbalance between the battery units 13i,..., 13i,..., 13_m.

Since the current magnitude of the current drawn from the battery units 13i,..., 13χ,..., 13_m can be set individually for each battery unit, this current can also be used as a means for balancing the state-of-charge (SOC) between each battery unit. The system controller 21 keeps track of the SOC in each battery unit 13_X and if the SOC differs system controller 21 can give an order for providing a larger current from the battery unit with the highest SOC in order to adjust the SOC levels. Usually the balancing is made locally in each battery cell, within each battery module or within each battery unit, controlled by the respective battery management units, but by using this inventive power supply also as a balancing part, a kind of global balancing on battery system level can also be made. The balancing procedure is thereby more rapid and since it is controlled from the system controller 21, it can be made at any time during the battery operation or during the battery units idle times.

There is also provided means for internal communication in the battery unit 13_X. The battery management unit 17 performs several functional tasks, e.g. measure battery unit 13_X current, measure battery module 12_X and battery cell current and voltage, measure temperature of the battery cells and the battery unit 13_X, battery state-of-charge, battery cell balancing, and internal communication between battery modules 12_1# Communication means is provided for this end, illustrated in the figure at reference numeral 25.

In still another embodiment of the invention, the battery management unit 17 is provided with a functionality to go into a "sleep mode" status when it is not used. In the sleep mode, the battery management unit 17 has minimized power consumption. To accomplish the sleep mode status, only a small part of the battery management unit 17 is kept active instead of the complete battery management unit 17 system. The sleep mode functionality may be built into the battery management unit 17 internal control or may be controlled by the system controller 21. That is, the system controller 21 orders the battery management unit 17 into the sleep mode when appropriate. The system controller 21 may also in the same way set the load control device 24 and/or the DC/DC converter 23 in a sleep mode status. The sleep mode can be entered in idle mode of the energy storage and when it is only in stand-by. When the energy storage is set in active mode, the battery management unit 17, the load control device 24 and the DC/DC converter 23 are set active by a wake-up signal. By means of this sleep mode functionality the power consumption from the batteries is reduced to a minimum, which will enhance the battery service life.

The invention also provides a method for powering a battery management unit 17 as described above. The method comprises the step of supplying the battery management unit 17 with power from the battery unit 13_X. This can for example be accomplished by arranging a voltage divider 22 and/or a DC/DC converter 23 between the poles of the battery unit 13_X, as described above.

The method may comprise further steps, for example a step of drawing a constant current from the battery unit IS₁. This can for example be accomplished by means of the load control device 24 as described above or by the DC/DC converter 23.

As an example of yet another step, the system controller 21 controls the magnitude of the current drawn from the battery unit 13_X. The system controller 21 may also perform the step of balancing the state-of-charge between the battery units 13_X and/or between the battery modules 12i, 12₂,..., 12_n.

The method may include the further step of setting individually the current drawn from each battery module 12i,..., 12_n. That is, when using several battery modules, the current drawn from each respective battery module may differ, and the system controller 21 controls the current drawn from the battery modules individually, preferably so as to optimize the battery unit performance and maximize its service life.

Claims

1. A battery energy storage system (20) comprising at least one battery unit (IS₁), said at least one battery unit (IS₁) comprising one or more battery modules (H₁,..., 12_n) , said battery energy storage system (20) further comprising a battery management unit (17) managing said at least one battery unit (13_X), characterized by means (22, 23, 21) for powering said battery management unit (17) by one or more of said battery modules (12i,..., 12_n) of said at least one battery

2. The battery energy storage system (20) as claimed in claim

1, wherein said means for powering said battery management unit (17) comprises a voltage divider (22), connected at one end to a pole of said battery unit (13_∑) and at another end to the other pole of said battery unit (13_∑), wherein an output of said voltage divider (22) is connected to said battery management unit (17) .

3. The battery energy storage system (20) as claimed in claim

2, wherein said output of said voltage divider (22) is connected to said battery management unit (17) via a DC/DC converter (23) , said DC/DC converter (23) output being connected at one end to said output of said voltage divider (22) and at another end to said battery management unit (17) .

4. The battery energy storage system (20) as claimed in claim 3, further comprising a circuit breaker (16_X) and wherein said

DC/DC converter (23) output is further connected to said circuit breaker (16_X), whereby said circuit breaker (16_X) is powered by said battery unit (13J .

5. The battery energy storage system (20) as claimed in claim 1, wherein said means for powering said battery management unit (17) comprises a DC/DC converter (23), connected at one end to one pole of said battery unit (IS₁) and connected at another end to the other pole of said battery unit (IS₁) .

6. The battery energy storage system (20) as claimed in claim 5, further comprising a circuit breaker (IG₁) and wherein said DC/DC converter (23) output is further connected to said circuit breaker (16_X), whereby said circuit breaker (16_X) is powered by said battery unit (13J .

7. The battery energy storage system (20) as claimed in any of the preceding claims further comprising a system controller (21) connected to said battery management unit (17) and arranged to control said battery energy storage system (20) .

8. The battery energy storage system (20) as claimed in claim

7, wherein said system controller (21) comprises means for controlling the magnitude of current drawn from said battery

9. The battery energy storage system (20) as claimed in claim

8, comprising at least two battery units (13i,..., 13_n) , said system controller (21) further comprising means for balancing state-of-charge between each of said battery units (13i,..., 13_n) and/or each of said battery modules (H₁,..., 12_n) .

10. The battery energy storage system (20) as claimed in any of the preceding claims, said means (22, 23, 21) further being arranged to power additional devices connected to said battery unit (13J .

11. The battery energy storage system (20) as claimed in any of the preceding claims, comprising two or more parallel- connected battery strings (15i,..., 15_X, 15k), each battery string (15i,..., 15_X, 15k) in turn comprising one or more of said battery units (13_X) .

12. The battery energy storage system (20) as claimed in claim 11, wherein said battery strings (15i,..., 15_X, 15_k) are connected to a power converter of a high-voltage network.

13. The battery energy storage system (20) as claimed in any of the preceding claims, wherein said battery management unit

(17) is arranged to go into a sleep mode, in which said battery management unit (17) has minimized power consumption.

14. A method for powering a battery management unit (17) arranged to manage a battery unit (13_X) of a battery energy storage system (20) as claimed in any of claims 1-13, characterized by the step of:

- supplying said battery management unit (17) with power from said battery unit (13_X) .

15. The method as claimed in claim 14, comprising the further step of controlling the current drawn from said battery unit

(13_X) so as to be constant.

16. The method as claimed in claim 14 or 15, comprising the further step of setting individually the current drawn from each battery module (12i,..., 12_n) and/or each battery unit (13!,..., 13_n) .

17. The method as claimed in any of claim 13-16, comprising the further step of balancing the state-of-charge between said battery modules (12i,..., 12_n) and/or said battery units (13i,..., 13_n) .