DE102013102461A1 - Method for determining the state of charge of a rechargeable battery - Google Patents

Abstract

The invention relates to a method for determining the state of charge of an accumulator, wherein a functional relationship between the state of charge and the open circuit voltage of the accumulator is determined empirically, wherein in the determination of the functional relationship of the initially fully charged accumulator is discharged with defined charges and at several discharge stages of the accumulator open-circuit voltages are measured, wherein the measured no-load voltages are assigned after the measurements of charge states of the accumulator, and determined after determining the functional relationship, during operation of the accumulator on the basis of the functional relationship, the state of charge from an estimated open circuit voltage, wherein in determining the functional relationship between the state of charge and the open circuit voltage in a first phase of the accumulator is gradually discharged at constant currents until a limit voltage below is stepped, and then in a second phase, the current is reduced in a further step and the battery is further discharged until a threshold current is exceeded. The invention also relates to a device for carrying out such a method, wherein the device comprises at least one accumulator, a controller for controlling or regulating the stored and stored power, a computing unit for determining the state of charge of the accumulator and a data memory, wherein in the data memory the Data of the functional relationship between the state of charge and the open circuit voltage are stored and the arithmetic unit has access to the data memory.

Description

The invention relates to a method for determining the state of charge of an accumulator, wherein a functional relationship between the state of charge and the open circuit voltage of the accumulator is determined empirically, wherein in the determination of the functional relationship of the initially fully charged accumulator is discharged with defined charges and at several discharge stages the battery idle voltages are measured, the measured no-load voltages are assigned after the measurements of charge states of the accumulator, and determined after determining the functional relationship, during operation of the accumulator on the basis of the functional relationship, the state of charge from an estimated open circuit voltage. The invention also relates to a device for carrying out such a method.

The determination of the state of charge of a rechargeable battery is often essential for the use of the rechargeable battery. When the accumulator is to be used for the provision of control power, the state of charge determination may help to operate the accumulator in a particularly economical manner. For the provision of control power, the accumulators used must be made relatively large, since they must be able to take up or deliver some considerable energy for certain periods of time.

Both the generation and the consumption of energy can lead to unplanned fluctuations in power grids. These can arise on the energy producer side, for example, in that a power plant or part of the power grid fails or, for example, in the case of renewable energies such as wind, that the energy production is higher than predicted. Consumers may also experience unexpectedly high or low consumption. For example, the failure of a portion of the grid, which cuts off some consumers from the power supply, can lead to a sudden reduction in power consumption.

This generally results in power network fluctuations due to unplanned and / or short-term variations in power generation and / or consumption. For example, the desired AC frequency in Europe is 50,000 Hz. Such desired AC frequencies are also referred to as nominal frequencies. A reduction of consumption compared to a (forecast) plan leads to an increase of the grid frequency with power generated according to the forecast by the energy producers, as well as to an increase of the electricity production compared to the plan with correspondingly predicted consumption. On the other hand, a reduction in the output of the energy producers compared to the plan with correspondingly forecast consumption leads to a reduction in the grid frequency, as well as to an increase in consumption compared to the forecast consumption and correspondingly scheduled generation.

For reasons of network stability, it is necessary to keep these deviations within a defined range. For this purpose, depending on the amount and direction of the deviation, it is necessary to provide specifically positive control power by connecting additional generators or switching off consumers, or negative balancing power by shutting down generators or adding consumers. There is a general need for economic and efficient provision of these balancing services, where the requirements for the capacities to be kept available and the dynamics of the balancing power sources or control power sinks can vary depending on the characteristics of the electricity grid.

In Europe, for example, there is a set of rules ("UCTE Handbook"), which describes three different categories of control power. This also defines the respective requirements for the control power types. The types of balancing power differ, among other things, in the demands on the dynamics and the duration of the service provision. In addition, they are used differently with respect to the boundary conditions. Primary control power (PRL), regardless of the location of the fault, is to be delivered across Europe from all embedded sources, essentially in proportion to the actual frequency deviation. The maximum positive power (feed into the grid) is to be provided at frequency deviations of minus 200 mHz and (absolute) lower, the maximum negative power is to be provided at frequency deviations of plus 200 mHz and above. With regard to the dynamics, it must be ensured that the (maximum) power has to be provided evenly within 30 seconds from the idle state. On the other hand, secondary control power (SRL) and minute reserve power (MR) are to be provided in the power supplies in which the fault has occurred. Their task is to compensate for the disturbance as quickly as possible and thus to ensure that the grid frequency is back within the desired range as quickly as possible, preferably at the latest after 15 minutes. In terms of dynamics, lower requirements are placed on the SRLs and MRLs (5 or 15 minutes to full service delivery after activation).

In the power grids operated so far, a large part of the control power is provided by conventional power plants, in particular coal and nuclear power plants. Two fundamental problems result from this. On the one hand, the conventional power plants providing control power are not operated at full load and thus maximum efficiencies, but slightly below them in order to be able to provide positive control power if required, possibly over a theoretically unlimited period of time. On the other hand, with increasing expansion and preferential use of renewable energies, fewer and fewer conventional power plants are in operation, which is often the prerequisite for the provision of balancing services.

For this reason, approaches have been developed to increase the use of energy storage devices such as accumulators in order to store negative control power and provide it as positive control power when needed. This has the advantage that the same energy, which was taken from the power grid as a negative control power at a first time, can be provided as a positive control power at a second time, without having to be regenerated. For this purpose, the most accurate possible knowledge of the state of charge of a battery used for this purpose is important.

It is from the WO 2010 042 190 A2 and the JP 2008 178 215 A known to use energy storage to provide positive and negative control power. When the grid frequency leaves a range around the desired grid frequency, either energy is provided from the energy store or added to the energy store to regulate the grid frequency. Also the DE 10 2008 046 747 A1 proposes to operate an energy storage in an island power network such that the energy storage is used to compensate for consumption peaks and consumption minima. The disadvantage hereof is that the energy stores do not have the necessary capacity to compensate for a longer disturbance or a plurality of disturbances rectified with respect to the frequency deviation one after the other.

In the article "Optimizing a Battery Energy Storage System for Primary Frequency Control" by Oudalov et al., In IEEE Transactions on Power Systems, Vol. 3, August 2007 , the capacity of a rechargeable battery is determined according to technical and operational constraints, so that it can provide primary control power according to the European standards ("UCTE Handbook"). It turns out that due to the injection and Ausspeicherverluste long-term recharging of the energy storage at longer intervals is inevitable. Nevertheless, it may happen at short notice or temporarily, that the energy storage is already fully charged and therefore must be searched for another consumption option. The article suggests a (limited use) of resistors. However, this leads to an energy destruction and usually a devaluation of energy. Despite this measure, the energy storage with a full-load runtime of 1.6 hours is still comparatively large, at least significantly larger than it meets the minimum requirements of the "UCTE Handbooks". The comparatively high capacities are associated with corresponding investment costs and make the use of energy storage often uneconomical. By accurately determining the current state of charge of an accumulator during operation to provide control power, the state of charge of the accumulator can be more accurately adjusted. Possibilities for this are for example from the US 7,839,027 B2 as well as the WO 2010 042 190 A2 known. As a result, only a smaller capacity must be kept available, which can reduce costs.

Accumulators can absorb or release energy very quickly, making them basically suitable for providing PRL. A disadvantage, however, is that very large capacities of the batteries must be provided in order to deliver the control power over a longer period or repeatedly. However, very large capacity batteries are also very expensive.

Due to the losses during storage and withdrawal of energy takes place at a statistically symmetric deviation of the mains frequencies from the setpoint by the operation sooner or later emptying of the energy storage, such as a rechargeable battery. It is therefore necessary to recharge the energy storage more or less regularly targeted. It may be necessary to pay for this charging current separately.

From the US 7,839,027 B2 as well as the WO 2010 042 190 A2 a method for providing control power with an energy storage is known. In this case, in the times in which no control power is needed, so loaded or discharged within a dead band to the nominal frequency of the power frequency of the energy storage in order to achieve a desired output state of charge. The disadvantage of this is that the state of charge of an accumulator can only be determined with limited accuracy. In addition, the different accumulators age with time and with the duration of use. As a result, the state of charge of the accumulator can not be determined exactly. Furthermore, it is disadvantageous that, if the frequency is outside the deadband for a long time, the energy store is still heavily charged or discharged. So it still has a big one Capacity (energy storage capacity) of the energy storage are kept.

Another disadvantage of the prior art is the fact that at least temporarily in the deadband no control power is provided or the power grid is even charged with a counterproductive power to adjust the state of charge of the energy storage.

From an article by Michael Roscher and Dirk Sauer (Journal of Power Sources 196 (2011) 331-336) entitled "Dynamic Electric Behavior and Open-Circuit-Voltage Modeling of LiFePO4-based Lithium Ion Secondary Batteries" a generic method for determining the state of charge (SoC ") of an accumulator is known in which a characteristic of the state of charge of the accumulator in dependence on an open circuit voltage (open circuit voltage" OCV ") is determined by the accumulator step by step is discharged with always the same charge quantities and after each discharge and a sufficient relaxation time, the open circuit voltage of the battery is measured. Subsequently, the current state of charge of the accumulator during operation can be determined with the help of an equivalent circuit diagram, whereby also different influences on the capacity and the state of charge of the accumulator can be considered. For the details of this procedure, reference is made to the aforementioned article by Roscher and Sauer.

In the Roscher and Sauer method, the SOC-OCV characteristic is generated by a constant discharge of 1C to the turn-off voltage, assuming a fixed capacity of the cell (40 Ah). The electrical equivalent circuit used here uses constant parameters Rs, Rp, Cp for resistors or impedances and for the capacitive components. The open circuit voltage is adjusted during the SOC determination in each step. For continuous charge state determination, a Coulomb counting is performed, which takes place exclusively via a current measurement. Subsequently, a correction step takes place with the aid of the electrical model to the state of charge determined by means of Coulomb counting, in order to determine the actual state of charge of the accumulator.

A disadvantage of this method is that in the determination of the SoC-OCV characteristic, ie the state of charge no-load voltage characteristic, inaccuracies may occur, since this characteristic depends on the temperature and the aging of the battery, so that an exact determination of the current state of charge is only conditionally possible. The inaccuracies lead in practice to the fact that the accumulator is not optimally controlled or regulated. In the case of the provision of control power, an unnecessarily large capacity of the accumulator must be kept in order to compensate for the possible errors in the use of the state of charge no-load voltage characteristic and always have sufficient capacity to provide and absorb the control power.

The object of the invention is therefore to overcome the disadvantages of the prior art. In view of the prior art, it is a particular object of the present invention to provide a technically improved method for determining the state of charge of a rechargeable battery, so that a more precise state of charge-dependent control in the provision of control power is possible. In particular, previously disregarded charge components of the accumulator should be taken into account in order to determine a more accurate charge state open-circuit voltage characteristic, in particular less dependent on the temperature and age of the battery. As a result, inter alia, a smaller dimensioning of the accumulator is possible because for each possible error in the determination of the state of charge, a corresponding capacity of the accumulator must be kept.

A further object of the invention is to be seen in that, in particular when using galvanic elements, such as accumulators, the capacity of the energy store for cost reasons should be as low as possible in order to provide the required control power.

In addition, the process should be able to be carried out with as few process steps as possible, whereby they should be simple and reproducible.

Other tasks not explicitly mentioned emerge from the overall context of the following description, the exemplary embodiments and the claims.

These and other non-explicitly stated objects, which, however, are readily derivable or deducible from the contexts discussed hereinabove, are solved by a method having all the features of claim 1. Advantageous modifications of the inventive method for providing control power for a power network, in which at least one connected to the power grid energy storage power supply to the power grid as needed and / or absorbs power from the power grid as needed, are placed in the dependent claims 2 to 14 under protection. Furthermore, claim 15 has an apparatus for carrying out such a method to the object, while expedient modifications of this device are provided in the subclaims 16 to 18 under protection.

Accordingly, the present invention is achieved by a method for determining the state of charge of a rechargeable battery, wherein a functional relationship between the state of charge and the open circuit voltage of the rechargeable battery is determined empirically, wherein in the determination of the functional relationship the initially fully charged rechargeable battery is discharged with defined charges and in the case of a plurality of discharge stages of the accumulator, open-circuit voltages are measured, the measured open-circuit voltages being assigned to charging states of the accumulator following the measurements, and, after the functional relationship has been established, determined during operation of the accumulator on the basis of the functional relationship, the charge state is determined from an estimated open circuit voltage, wherein in determining the functional relationship between the state of charge and the open-circuit voltage in a first phase of the accumulator stepwise entla with constant currents is the until a threshold voltage is exceeded, and then in a second phase, the current is reduced in a further step and the battery is further discharged until a threshold current is exceeded.

It can be provided that the no-load voltage, which is measured at the last discharge stage after reaching the lowest current, preferably after reaching the limit current, a state of charge of 0% is assigned and the open circuit voltage, which is measured at fully charged accumulator, a state of charge of 100% is assigned.

It can also be provided that the accumulator comprises a plurality of galvanic cells connected in parallel and / or connected in series.

Such an arrangement is particularly well suited for larger accumulators for the provision of control energy.

The inventive method may also be characterized in that it is used in the provision of control power by the accumulator, preferably in the provision of primary control power and / or secondary control power.

Inventive methods can also be characterized in that the limit voltage of a lithium-based galvanic cell of the accumulator is between 1 V and 10 V, preferably between 3 V and 4.2 V, particularly preferably at 3 V.

Furthermore, it can be provided that the limiting current intensity of a lithium-based galvanic cell of the accumulator is between 0.1 A and 10 A, preferably between 0.5 A and 3 A, particularly preferably 1 A.

The preferred galvanic lithium-ion cells, which are particularly well suited for the implementation of methods according to the invention, operate up to these limiting voltages and limiting current strengths.

It can also be provided that the accumulator is discharged before reaching the limit voltage with a discharge rate (C rate) between 0.5 C and 2 C, preferably with 1 C and / or after reaching the threshold voltage and before falling below the limiting current with a decreasing Discharge rate (C rate) between C / 500 and 2 C, preferably between C / 100 and 1 C is discharged.

At these discharge rates, the last remainder of the charge contained in the accumulator can also be discharged in large part and in a defined manner in order to make the entire spectrum of the state of charge of the accumulator available for measuring the open-circuit voltage.

Preferably, it can also be provided that several parallel and / or series-connected accumulators are operated centrally controlled as a control power device, wherein the control power device receives as required from a power grid control power or outputs control power in the grid and the state of charge of the control power device from the sum of the charge states the accumulators is determined.

The inventive method is particularly well suited for determining the state of charge of accumulators in the provision of control energy and, conversely, leads to the fact that the capacity of the accumulator can be chosen small and is more cost-effective, since the state of charge can be estimated more accurately.

A further development of the invention may provide for the charge state to be taken into account in the case of a recording and / or delivery of power by the accumulator, in particular by the control power device, wherein the recorded and / or delivered power, in particular control power, is controlled or regulated as a function of the state of charge becomes.

According to a particularly preferred embodiment of the invention it can be provided that the accumulator used is a lithium-ion accumulator, a lead-sulfuric acid accumulator, a nickel-cadmium accumulator, a sodium-sulfur accumulator or a composite of at least two of these accumulators becomes.

These accumulators can be used particularly well for implementing methods according to the invention.

It can also be provided that the capacity of the rechargeable battery is at least 40 Ah, preferably at least 1 kAh, and / or the rechargeable battery stores at least an energy of at least 4 kWh, preferably at least 10 kWh, particularly preferably at least 50 kWh, very particularly preferably at least 250 kWh can.

These loads and capacities are particularly well suited for providing control power.

According to a particularly preferred variant of a method according to the invention it can be provided that the capacity of the accumulator as a function of the temperature of the galvanic cells of the accumulator and / or the current during charging and discharging of the accumulator is taken into account in the determination of the state of charge of the accumulator, wherein preferably the maximum state of charge as a function of the temperature of the galvanic cells of the accumulator and / or the current during charging and discharging of the accumulator due to a measurement of the temperature of the galvanic cells of the accumulator and / or the current during charging and discharging of the accumulator is determined.

Considering these additional variables leads to an improvement in the estimation of the state of charge of the accumulator.

Furthermore, in particularly preferred inventive method can also be provided that when determining the state of charge of the accumulator an equivalent circuit comprising at least one resistor and / or at least one capacitor for determining the open circuit voltage of the accumulator as a function of the temperature of the galvanic cells of the accumulator, the current direction and / or the discharge rate is taken into account.

With the aid of the equivalent circuit diagram an even more accurate and realistic estimation of the state of charge can be given.

Furthermore, it can be provided that the state of charge determined during operation is determined taking into account the estimated value of the open circuit voltage and / or an open circuit voltage which was or were determined in the previous determination of the open circuit voltage.

Particularly preferably, it can be provided that graphite or lithium titanium oxide, preferably Li ₂ Ti ₅ O ₁₂ , is used as the anode material of the galvanic cells of the rechargeable battery and lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide and / or lithium iron phosphoroxide is used as the cathode material of the galvanic cells of the rechargeable battery LiCoO ₂ , LiMn ₂ O ₄ , Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ , Li (Ni _0.85 Co _0.1 Al _0.05 ) O ₂ and / or LiFePO ₄ .

These electrode materials bring about highly calculable galvanic cells, to which methods of the invention are particularly well applicable.

In particular, the method can also be a method for providing primary control power and / or secondary control power.

This makes it possible to implement a method for determining the state of charge of an accumulator in an unpredictable manner, in which at least one energy storage connected to the power supply depending on its state of charge to the power grid supplies energy as needed and / or absorbs energy from the power grid as needed does not suffer from the disadvantages of conventional methods.

The economy of the operation of energy storage devices, such as accumulators, for the primary control power supply by avoiding inefficient charging states is improved by the inventive method, in particular a provision of primary control power is made possible with lower energy storage capacity.

In addition, the effect of the aging load can be determined more accurately by the method according to the invention.

As energy storage systems in particular with very limited memory size in question. In English-speaking countries, these are referred to inter alia as Limited Energy Storage Resources (LESRs).

In addition, the inventive method can be carried out very easily and inexpensively. Furthermore, the process can be carried out with relatively few process steps, the same being simple and reproducible.

According to a further advantageous embodiment of the method according to the invention can be provided that a bandwidth, within the state of charge of the accumulator by Charging or discharging can be changed to aim for a mean state of charge, proportional to a state of charge difference of the current state of charge of the accumulator is selected from a medium state of charge, in particular the bandwidth depends linearly on the state of charge state of charge of the current state of charge from the average state of charge.

In this case, calculations are carried out which, although complicating the method, also lead to the fact that the state of charge of the accumulator changes greatly only in the case of large deviations and thus causes an expedient return of the state of charge to the mean state of charge.

Furthermore, it can be provided that the state of charge of the accumulator is determined continuously, wherein preferably the output from the accumulator to the power grid control power is regulated in dependence on the state of charge.

A further embodiment of the method according to the invention can provide that outside the bandwidth control power is provided as desired by the power grid operator and / or the amount of control power with respect to the frequency deviation in regions antiproportional to the frequency deviation of the grid frequency is provided, preferably linear to the frequency deviation.

A further embodiment of the invention can provide that, in the event of a change in the required control power, the time after the change, after which a control power is provided by the energy store, is selected as a function of the current state of charge of the battery.

It can be provided that the time is in a time interval between the change in the required control power and a maximum time after the change, in particular, the time interval in the case of provision of primary control power is 30 seconds.

By striving for an average desired state of charge or an average desired energy content of the accumulator, the use of such a rechargeable battery can be used in a surprisingly advantageous manner for the provision of control power for a power grid, without requiring, for example, accumulators with larger capacities. As a result, the disadvantages of conventional energy producers and energy consumers, which usually have to be operated at partial load for the provision of control power, can be avoided. The state of charge in the case of accumulators corresponds to the state of charge (SOC).

The object of the invention is also achieved by a device for carrying out such a method, wherein the device comprises at least one accumulator, a controller for controlling or regulating the stored and stored power, a computing unit for determining the state of charge of the accumulator and a data memory, wherein in the data memory, the data of the functional relationship between the state of charge and the open-circuit voltage are stored and the arithmetic unit has access to the data memory.

It can be provided that the accumulator is connected to a power supply in such a way that power can be fed into the power grid and removed from the power supply system by the device.

It can also be provided that the device comprises an ammeter for determining the current intensity and preferably also the current direction of the current stored in the accumulator and the current flowing out of the accumulator and / or at least one thermocouple for determining the temperature of at least one galvanic element of the accumulator.

According to a development of the device according to the invention it can be provided that the accumulator is a lithium-ion accumulator, a lead-sulfuric acid accumulator, a nickel-cadmium accumulator, a sodium sulfide accumulator and / or a Li-ion accumulator and / or is a composite of at least two of these accumulators.

Furthermore, it can be provided that the device comprises a device for measuring the state of charge of the at least one accumulator and / or a device for measuring the frequency deviation of the network frequency from the nominal frequency and a data memory, wherein in the data memory preferably the average state of charge of the energy storage is stored, wherein the controller has access to the data memory and is designed to control the output and energy absorbed by the energy storage and control function depending on the state of charge of the energy store and / or the frequency deviation.

The invention is based on the surprising finding that, by means of a discharge step or a plurality of additional discharge steps at a reduced discharge current intensity, it is also possible to discharge the last remnants of the capacity of the accumulator and thus enable a much more accurate determination of the open circuit voltage of the discharged state of charge.

While with previous methods only the open circuit voltages at charge states between 100% and a state of charge well above 0% determine, with the method according to the invention, a lower state of charge than previously included in the characteristic. From this realization of the invention it also follows that the capacity of the accumulator can be chosen lower and it can succeed with a method according to the invention particularly well to keep the capacity of the accumulator small.

In preferred embodiments of the invention, several accumulators are pooled and operated in accordance with the method of the invention. The size of the accumulators within the pool can vary.

In contrast to the previously known methods, a method according to the invention can be carried out by using a variable capacitance of the galvanic cells or the accumulator depending on the C-rate and the temperature. As a result, the calculated SOC reflects the actually removable capacity in the current operating state.

In the method according to the invention, it is particularly advantageous that the SOC-OCV characteristic which is generated over a CV step until reaching a threshold voltage, preferably below 3 V, is produced. This has the advantage that 0% SOC is uniquely defined regardless of the temperature of the accumulator and the C rate. In addition, the calculated SOC reflects the actual extractable capacity.

The equivalent circuit, as proposed by Roscher and Sauer, is calculated using a series-connected virtual resistance Rs and a virtual parallel connection of a capacitor Cp and a resistor Rp. According to the invention, it can now be particularly preferred for the electrical equivalent circuit to use a parameter Rs which is determined as a function of temperature, SOC and C rate. Rp and Cp, on the other hand, are constant. This results in a consideration of the current operating state of the accumulator. According to the invention, changes in the internal resistance due to aging can thus be taken into account.

The parameters Rs and the open circuit voltage of the equivalent electrical circuit diagram can be adjusted according to the invention in each step. The error of the estimated voltage (U_ estimation) determines the adaptation.

The Coulomb counting is carried out according to the invention particularly preferably based on the last final SOC value, which has been corrected by calculations from electrical model. The final correction step is carried out via the electrical model to the determined by the Coulomb counting open circuit voltage and thus determines the final Leerlausspannung.

Since a final SOC value has already been corrected, measurement errors are not integrated by a method according to the invention. In addition, the correction step remains small over the entire period since the Coulomb Counting step is already based on the last corrected SOC value (final SOC).

In the following, embodiments of the invention will be explained with reference to a schematically illustrated figure and with reference to eight diagrams, without, however, limiting the invention. Showing:

1 : a schematic representation of a device according to the invention for determining the state of charge of an accumulator and for providing control energy;

2 : a diagram of the accuracy of the SOC estimate with -1 A current measurement error using the algorithm of Roscher and Sauer;

3 : A SOC estimation accuracy diagram with +1 A current measurement error using the Roscher and Sauer algorithm;

4 FIG. 4 is a diagram of the accuracy of the SOC estimate with -1 A current measurement error using the algorithm according to the invention; FIG.

5 FIG. 3 is a SOC estimation accuracy diagram with +1 A current measurement error using the algorithm of the invention; FIG.

6 : A SOC estimation accuracy chart with -5 A current measurement error using the Roscher and Sauer algorithm;

7 : A SOC estimation accuracy diagram with +5 A current measurement error using the Roscher and Sauer algorithm;

8th FIG. 4 is a SOC estimation accuracy diagram with -5 A current measurement error using the algorithm of the invention; FIG. and

9 FIG. 5 is a graph of accuracy of the SOC estimate with +5 A current measurement error using the algorithm of the invention.

1 shows a schematic representation of a device according to the invention 1 for determining the state of charge of a rechargeable battery 2 and to provide control energy. The accumulator 2 is from a control system 3 controlled and supervised. The accumulator 2 is connected to a power grid 4 connected to the intake and delivery of control energy. The stored and stored energy is measured with an ammeter 5 measured. The ammeter 5 is with the guidance system 3 connected. In the control system 3 a program is executed, so that a method according to the invention of the control system 3 is carried out. The control system 3 also controls the current intensity of the stored and stored control power from the power grid 4 in the accumulator 2 ,

For determining the state of charge of the accumulator 2 is in a data memory of the control system 3 a relationship between the open circuit voltage of the accumulator 2 and the state of charge of the accumulator 2 saved. In addition, the stored and stored control power and other factors can additionally be taken into account in order to determine the state of charge of the battery 2 during operation.

The relationship between the open circuit voltage of the battery and the state of charge was determined as follows. First, the accumulator 2 fully charged, in which case it is charged up to an upper cut-off voltage and then further to a turn-off current. Subsequently, a certain period of time, for example half an hour is waited without the accumulator 2 is operated during this time. Then the open circuit voltage of the accumulator 2 determined and assigned to this open circuit voltage of state of charge 100%. Subsequently, the accumulator 2 discharged in defined steps with constant current and after similar waiting times again determines the open circuit voltage. When a threshold voltage of, for example, 50 V is reached, the current intensity of the discharge is reduced and as long as further no-load voltages are measured until a limit current intensity is undershot. The last measured no-load voltage is assigned a charge state of 0%. The idle voltages measured therebetween are assigned the corresponding intermediate values of the state of charge, with the percentage of a discharge from the accumulator 2 taken by the current and the time over which the current was discharged taken into account.

The corresponding value pairs or the reference curve and the mathematical relationship, which can be generated by a mathematical fit from the value pairs, is stored in the memory of the control system 2 deposited and for determining the state of charge of the accumulator 2 used. In this case, other known methods for determining the state of charge can be used.

When delivering control power to the mains 4 or when receiving control power from the mains 4 can the state of charge of the accumulator 2 be considered by this is determined using the method described. For example, control power can be delivered only at a greater frequency deviation of the mains frequency when the state of charge of the accumulator 2 is too low and it can be recorded control power only at a greater frequency deviation of the mains frequency when the state of charge of the accumulator 2 is too high. This can increase the capacity of the accumulator 2 lower than if a more inaccurate method of determining the state of charge were used.

In the 2 to 9 are diagrams of the accuracy of the SOC estimation with different current measurement errors using well-known algorithms according to Roscher and Sauer ( 2 . 3 . 6 and 7 ), and according to a method of the invention ( 4 . 5 . 8th and 9 ). The diagrams show the frequency of a measured deviation as a function of the percentage error. The deviation is due to a measurement error in the determination of the current and is for -1A ( 2 and 4 ) and + 1A ( 3 and 5 ) as well as for -5A ( 6 and 8th ) and + 5A ( 7 and 9 ) shown in the diagrams.

Real time waveforms of voltages and currents of accumulators were used as data for the generation of the diagrams, in particular, as they are suitable for the provision of control power (PRL or SRL). The voltage and current profiles were recorded over a period of about 10 hours. The accumulator was charged and discharged several times. The SOC-OCV characteristics according to the methods of Roscher and Sauer and according to the method of the invention were determined on the basis of the accumulator used. The exact state of charge could also be accurately determined in the laboratory thanks to subsequent state of charge determinations as well as controlled charging and discharging of the accumulator. As a result, the state of charge determined with the various methods could be compared with the actual state of charge of the accumulator.

It can be seen that with the conventional methods according to Roscher and Sauer ( 2 . 3 . 6 and 7 ) greater deviations than with a method according to the invention ( 4 . 5 . 8th and 9 ). The larger deviations are in the diagrams after the 2 . 3 . 6 and 7 highlighted by the oval encirclements on the x-axis (error).

At a measuring error of the current measurement of 1 A ( 2 and 3 ) and the method of Roscher and Sauer results in a maximum estimation error of 18%. At a measuring error of the current measurement of 1 A ( 4 and 5 ) and a method according to the invention results in a maximum estimation error of about 5.3%. Here, 99% of the estimated values are at an estimation error of less than 5%.

At a measurement error of the current measurement of 5 A ( 6 and 7 ) and the method of Roscher and Sauer results in a maximum estimation error of 18%. At a measurement error of the current measurement of 5 A ( 8th and 9 ) and a method according to the invention results in a maximum estimation error of about 8%. In this case, 93% of the estimated values are at an estimation error of less than 5%.

The higher systematic errors of the Roscher and Sauer models are due, among other things, to the fact that in determining the SOC-OCV characteristic curve, the complete discharge of the accumulator is not correctly detected, but the capacity of the accumulator is underestimated.

For details on the regulation of balancing power and the exchange of information with network operators, see the Forum Netztechnik / Netzbetrieb im VDE (FNN) "TransmissionCode 2007" from November 2009 directed.

The features of the invention disclosed in the foregoing description, as well as the claims, figures and embodiments may be essential both individually and in any combination for the realization of the invention in its various embodiments.

LIST OF REFERENCE NUMBERS

1

Device for controlling or regulating the state of charge

2

accumulator

3

Control system / control

4

power grid

5

ammeter

P

power

t

Time

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2010042190 A2 [0009, 0010, 0013]
• JP 2008178215 A [0009]
• DE 102008046747 A1 [0009]
• US 7839027 B2 [0010, 0013]

Cited non-patent literature

• "Optimizing a Battery Energy Storage System for Primary Frequency Control" by Oudalov et al., In IEEE Transactions on Power Systems, Vol. 3, August 2007 [0010]
• Michael Roscher and Dirk Sauer (Journal of Power Sources 196 (2011) 331-336) entitled "Dynamic Electric Behavior and Open-Circuit-Voltage Modeling of LiFePO4-based Lithium Ion Secondary Batteries" [0015]
• VDE (FNN) "TransmissionCode 2007" of November 2009 [0095]

Claims (18)

Method for determining the state of charge of a rechargeable battery ( 2 ), wherein a functional relationship between the state of charge and the open circuit voltage of the accumulator ( 2 ) is determined empirically, wherein in determining the functional relationship of the initially fully charged accumulator ( 2 ) is discharged with defined charges and at several discharge stages of the accumulator ( 2 ), Whereby the measured open-circuit voltages are followed by the states of charge of the accumulator ( 2 ) and after determining the functional relationship, during operation of the accumulator ( 2 ) is determined based on the functional relationship of the state of charge from an estimated open circuit voltage, characterized in that in determining the functional relationship between the state of charge and the open circuit voltage in a first phase of the accumulator ( 2 ) is discharged stepwise at constant current levels until a limit voltage is exceeded, and then in a second phase, the current is reduced in a further step and the accumulator ( 2 ) is discharged further until a limit current is exceeded. A method according to claim 1, characterized in that the no-load voltage, which is measured at the last discharge stage after reaching the lowest current, preferably after reaching the limit current, a state of charge of 0% is assigned and the open circuit voltage, the fully charged accumulator ( 2 ), a state of charge of 100% is assigned. Method according to claim 1 or 2, characterized in that the accumulator ( 2 ) comprises a plurality of galvanic cells connected in parallel and / or connected in series. Method according to one of the preceding claims, characterized in that the limit voltage of a lithium-based galvanic cell of the accumulator ( 2 ) is between 1 V and 10 V, preferably between 3 V and 4.2 V, particularly preferably at 3 V. Method according to one of the preceding claims, characterized in that the limiting current intensity of a lithium-based galvanic cell of the accumulator ( 2 ) is between 0.1 A and 10 A, preferably between 0.5 A and 3 A, more preferably 1 A. Method according to one of the preceding claims, characterized in that the accumulator ( 2 ) is discharged before reaching the limit voltage at a discharge rate (C rate) between 0.5 C and 2 C, preferably with 1 C and / or after reaching the threshold voltage and before falling below the limiting current with a decreasing discharge rate (C rate) between C / 500 and 2 C, preferably between C / 100 and 1 C is unloaded. Method according to one of the preceding claims, characterized in that a plurality of parallel and / or series-connected accumulators ( 2 ) centrally controlled as a control power device ( 1 ), wherein the control power device is adapted from a power grid as required ( 4 ) Receives control power or in the power grid ( 4 ) Outputs control power and the state of charge of the control power device ( 1 ) from the sum of the states of charge of the accumulators ( 2 ) is determined. Method according to one of the preceding claims, characterized in that during a recording and / or delivery of power by the accumulator ( 2 ), in particular by the control power device ( 1 ), the state of charge is taken into account, wherein the recorded and / or delivered power, in particular control power, is controlled or regulated as a function of the state of charge. Method according to one of the preceding claims, characterized in that as accumulator ( 2 ) a lithium-ion battery ( 2 ), a lead-sulfuric acid secondary battery, a nickel-cadmium secondary battery, a sodium-sulfur secondary battery or a composite of at least two of these batteries ( 2 ) is used. Method according to one of the preceding claims, characterized in that the capacity of the accumulator ( 2 ) is at least 40 Ah, preferably at least 1 kAh and / or the accumulator ( 2 ) can store at least one energy of at least 4 kWh, preferably at least 10 kWh, particularly preferably at least 50 kWh, very particularly preferably at least 250 kWh. Method according to one of the preceding claims, characterized in that in determining the state of charge of the accumulator ( 2 ) the capacity of the accumulator ( 2 ) as a function of the temperature of the galvanic cells of the accumulator ( 2 ) and / or the current during charging and discharging of the accumulator ( 2 ), wherein preferably the maximum state of charge as a function of the temperature of the galvanic cells of the accumulator ( 2 ) and / or the current during charging and discharging of the accumulator ( 2 ) due to a measurement of the temperature of the galvanic cells of the accumulator ( 2 ) and / or the current during charging and discharging of the accumulator ( 2 ) is determined. Method according to one of the preceding claims, characterized in that in determining the state of charge of the accumulator ( 2 ) an equivalent circuit diagram comprising at least one resistor and / or at least one capacitor for determining the open circuit voltage of the accumulator ( 2 ) as a function of the temperature of the galvanic cells of the accumulator ( 2 ), the current direction and / or the discharge rate is taken into account. Method according to one of the preceding claims, characterized in that the determined during operation state of charge is determined taking into account the estimate of the open circuit voltage and / or an error of the open circuit voltage or was determined in the previous determination of the open circuit voltage or have been. Method according to one of the preceding claims, characterized in that as the anode material of the galvanic cells of the accumulator ( 2 ) Graphite or lithium titanium oxide, preferably Li ₂ Ti ₅ O ₁₂ is used and as the cathode material of the galvanic cells of the accumulator ( 2 Lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide and / or lithium iron phosphoroxide, preferably LiCoO ₂ , LiMn ₂ O ₄ , Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ , Li (Ni _0.85 Co _0.1 Al _0.05 ) O ₂ and / or LiFePO ₄ . Device for carrying out a method according to one of the preceding claims, characterized in that the device ( 1 ) at least one accumulator ( 2 ), a controller ( 3 ) for controlling or regulating the stored and stored power, a computing unit ( 3 ) for determining the state of charge of the accumulator ( 2 ) and a data memory, wherein in the data memory, the data of the functional relationship between the state of charge and the open-circuit voltage are stored and the arithmetic unit ( 3 ) has access to the data store. Apparatus according to claim 15, characterized in that the accumulator ( 2 ) to a power grid ( 4 ) connected by the device power in the power grid ( 4 ) and from the power grid ( 4 ) is removable. Device according to claim 15 or 16, characterized in that the device ( 1 ) an ammeter ( 5 ) for determining the current intensity and preferably also the current direction of the current in the accumulator ( 2 ) stored current and that from the accumulator ( 2 ) flowing out stream and / or at least one thermocouple for determining the temperature of at least one galvanic element of the accumulator ( 2 ). Device according to one of claims 15 to 17, characterized in that the accumulator ( 2 ) a lithium-ion battery ( 2 ), a lead-sulfuric acid accumulator, a nickel-cadmium accumulator, a sodium sulfide accumulator and / or a Li-ion accumulator and / or a composite of at least two of these accumulators ( 2 ).

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