WO2024074340A1

WO2024074340A1 - Energy storage system, method for operating an energy storage system, and use of an energy storage system

Info

Publication number: WO2024074340A1
Application number: PCT/EP2023/076464
Authority: WO
Inventors: Paul-Markus Schweizer-Berberich
Original assignee: Vitesco Technologies Germany Gmbh
Priority date: 2022-10-06
Filing date: 2023-09-26
Publication date: 2024-04-11
Also published as: DE102022210572A1

Abstract

The invention relates to an energy storage system (10) comprising an electrical energy store (20, 30), which has a first storage unit (20) composed of high-power cells (22) and a second storage unit (30) composed of high-energy cells (32). For improved usability of the specific advantages of the high-energy cells (22) and high-power cells (32) and thus improvement in the usage properties, the system (10) according to the invention also comprises: an energy transmission unit (40) in order to allow energy to be transmitted between the first storage unit (20) and the second storage unit (30); a connection device (50) for charging and discharging the electrical energy store (20, 30); a sensing device (60, 62, 64) for sensing operating parameters (soc-p, soc-e, il) of the electrical energy store (20, 30), which include at least a state parameter (soc-p) of the high-power cells (22) and a state parameter (soc-e) of the high-energy cells (32); and a control device (70) for controlling the energy transmission unit (40) according to a transmission algorithm which provides for control of the energy transmission unit (40) according to a transmission strategy depending on the sensed operating parameters (soc-p, soc-e, il), the transmission strategy providing for a specification of target values or target value ranges for a state of charge (soc-p) of the high-power cells (22) and for a state of charge (soc-e) of the high-energy cells (32). The invention also relates to an operating method and a use for a system (10) of this type.

Description

Energy storage system, method for operating an energy storage system and use of an energy storage system

The present invention relates to an energy storage system, a method for operating an energy storage system and a use of an energy storage system.

The field of the invention relates to the storage of energy. This plays a central role, for example, in connection with the generation of electrical energy from renewable energy sources such as photovoltaics, hydropower, wind power, etc., in order to enable the energy to be provided as needed regardless of when it is generated. Furthermore, the storage of energy plays a central role, for example in the automotive sector for supplying energy to an electric drive system of a vehicle such as a battery electric vehicle (BEV) or a hybrid electric vehicle (HEV).

In particular, in the aforementioned applications, electrical energy storage devices are typically used in which the energy is stored in a large number of rechargeable battery cells connected in parallel and/or in series. A serial connection of battery cells (or of several battery cells connected in parallel) advantageously enables the energy storage device (rechargeable battery) to be implemented with an electrical voltage at an electrical connection of the energy storage device that can be selected to be many times higher than the voltage of the individual battery cells.

In contrast, a parallel connection of battery cells (or of several battery cells connected in series) enables an increase in both the storage capacity (in terms of energy or electrical charge) and the "load capacity" of the energy storage device in terms of maximum electrical power or maximum electrical current when charging or discharging the energy storage device. One problem with the design of battery cells and the storage units formed with them is that a higher energy density generally goes hand in hand with a lower power density and, conversely, a higher power density goes hand in hand with a lower energy density. Based on this conflicting objectives, battery cells can often be classified as "high energy cells" (HEC) or "high performance cells" (HPC), depending on which of the two conflicting parameters, i.e. storage capacity or energy density (for HEC) on the one hand and resilience or power density (for HPC) on the other hand, can be considered comparatively good compared to other types of battery cells.

High-energy cells (HEC) are typically used to supply energy in a battery electric vehicle (BEV) in order to achieve a long range, whereas high-performance cells (HPC) are often more advantageous for use in a hybrid electric vehicle (HEV), e.g. to be able to store electrical energy with a high power during recuperation.

The respective other physical parameter from the pair "storage capacity" and "load capacity" must also be fulfilled by the electrical energy storage device, which in practice can disadvantageously lead to an unnecessary number of HECs having to be installed in order to achieve a desired load capacity or, conversely, an unnecessary number of HPCs having to be installed in order to achieve a desired storage capacity.

Compromises are often made, for example by choosing a battery cell design in which the parameters of load capacity and storage capacity are both "in the middle range". However, such cells are not ideally suited for most applications (since they are neither particularly resilient nor have a particularly high storage capacity). In this context, it should be noted that in BEV applications, for example, the load capacity (performance) of the electrical energy storage device is not only relevant with regard to the required or desired electrical power when supplying power to the electric drive system, i.e. when discharging the energy storage device, but also with regard to the time required to (partially or fully) charge the energy storage device, i.e. the charging times or the fast charging capability. The fast charging capability is limited for high-energy cells (HEC). A design with high-performance cells (HPC) would remove this limitation, but would significantly reduce the maximum energy content of the energy storage device for its given weight or volume and thus the range of the vehicle.

Furthermore, it should be noted in this context that the load capacity (performance) in practice for a specific application must be defined in terms of a maximum permissible electrical power during operation, if necessary separately for discharging and charging the energy storage device (battery), taking into account that the aging or degeneration of battery cells and thus of the energy storage device is often associated with high currents or power during discharging and/or charging. In this respect, another conflict of objectives exists in that a higher permitted electrical power is generally associated with a shorter service life and/or cycle stability and, conversely, a longer service life and/or cycle stability is associated with a lower electrical load capacity. The cycle stability indicates how often a battery can be discharged and then recharged until its storage capacity falls below a certain value. In this respect, too, a compromise must be made when designing the energy storage device.

A known approach from the state of the art to solve the problems of electrical energy storage systems explained above is to use both high-energy cells (HEC) and high-performance cells (HPC) in an electrical energy storage system according to a "hybrid storage concept", to combine these different types of battery cells to combine their positive energy and performance characteristics.

An energy storage system of this type, which also forms the technical starting point of the present invention (hybrid storage concept), is known, for example, from the publication DE 10 2012 110 030 A1 and has an electrical energy storage device with a first storage unit made of high-energy cells (HEC) and a second storage unit made of high-current cells (HPC). When charging or discharging the energy storage device, the two storage units are normally connected in parallel via a controllable switch. This switch can be opened, for example, in order to be able to specifically charge or discharge only one of the two storage units. For this purpose, the system also has a connection device connected to connections of both storage units with two further controllable switches, via which the current flow can be directed accordingly when charging/discharging the energy storage device. The storage units can be charged and/or discharged with current pulses, in which case a charge equalization takes place between the two storage units in the pulse pauses.

A disadvantage of this known energy storage system is, for example, a potentially suboptimal distribution of energy or charge between the two storage units, depending on the application and operating situation. The type of "charge equalization" provided for this purpose, namely by connecting the two storage units in parallel, means that the voltages of both storage units are equalized. This results in a charge distribution that is not precisely known and cannot be influenced. As a result, the advantages of the hybrid storage concept cannot be optimally utilized, for example when it comes to combining high storage capacity as well as possible with high performance, including the ability of the energy storage system to quickly charge.

Another energy storage system according to the hybrid storage concept is known, for example, from DE 10 2015 007 405 A1 and has an electrical energy storage system with first storage modules and second Storage modules, the first storage modules each being made up of a high-energy cell (HEC) and a controllable bidirectional energy transfer unit and the second storage modules each being made up of a high-performance cell (HPC) and a controllable bidirectional energy transfer unit. The controllable energy transfer units (e.g. DC/AC converters) are connected in parallel on the output side and connected to a power supply network to be supplied by the energy storage system.

Another disadvantage of this known energy storage system is that, depending on the application and operating situation, the energy may not be distributed optimally between the two storage units. The publication only explicitly describes in this context that, for example, when discharging with a low power requirement, only the first storage modules (HEC) are discharged and, if a specified threshold value of the power is exceeded, the second storage modules (HPC) are also discharged in parallel. In this respect, this state of the art is not dedicated to further improving or optimizing the usability of the fundamental advantages of the hybrid storage concept in practice.

For example, in BEV applications, the arguments for such well-known versions of the hybrid storage concept have not yet been sufficient to achieve broad market penetration. Rather, concepts that many customers consider inconvenient dominate in this area, such as "opportunity charging" (small battery, short range and fast recharging at every opportunity) or "overnight charging" (large battery, long range and slow recharging overnight).

The combination of different battery cell types (HEC, HPC) according to a hybrid storage concept in an energy storage system brings more flexibility in the design of the electrical properties of the energy storage system. In practice, however, the specific designs of corresponding energy storage systems proposed so far often add up to a certain extent. also negative properties, which led to suboptimal solutions e.g. with regard to costs and/or weight of such systems.

It is therefore an object of the present invention to eliminate the above disadvantages of the prior art when storing energy and to enable an improved usability of the respective specific advantages of high-energy cells (HEC) and high-performance cells (HPC) in a hybrid storage concept and thus to enable an improvement in the usage properties of an energy storage system in practice.

As already explained, numerous physical parameters can be important for the performance characteristics of an energy storage system, depending on the application, in particular e.g.

- storage capacity or energy density,

- Load capacity or power density, whether in terms of discharging processes (e.g. high-performance power supply to an electrical consumer) and/or charging processes (e.g. rapid charging capability, whether in terms of partial or complete charging or recharging),

- Ageing behaviour, service life and cycle stability,

- Cost and weight.

According to a first aspect of the present invention, the above-mentioned object is achieved by an energy storage system according to claim 1. The energy storage system according to the invention comprises:

- an electrical energy storage device with a first storage unit made of high-performance cells (HPC) and a first connection for charging and discharging the high-performance cells, and with a second storage unit made of high-energy cells (HEC) and a second connection for charging and discharging the high-energy cells, a controllable bidirectional energy transfer unit which is connected on the one hand to the first connection and on the other hand to the second connection is connected to enable a transfer of energy between the first storage unit and the second storage unit,

- a connection device connected to the first connection for charging and discharging the electrical energy storage device,

- a detection device for detecting operating parameters of the electrical energy storage device, which comprise at least one state parameter of the high-performance cells and one state parameter of the high-energy cells,

- a control device for controlling the energy transfer unit according to a transmission algorithm which provides for controlling the energy transfer unit according to a transmission strategy depending on the detected operating parameters, wherein the transmission strategy provides for a specification of target values or target value ranges for a charge state of the high-performance cells and a charge state of the high-energy cells.

The energy storage system according to the invention advantageously enables an improved usability of the respective specific advantages of high-energy cells (HEC) and high-performance cells (HPC) and thus improved usage properties of the energy storage system.

The connection of the connection device used to charge/discharge the electrical energy storage device to the first connection, i.e. to the first storage unit, hereinafter also referred to as the HPC storage unit, advantageously enables a very direct and thus loss-free charging/discharging of the HPC storage unit with a comparatively high power. If additional power is required, the second storage unit, hereinafter also referred to as the HEC storage unit, can also be used by appropriately controlling the energy transfer unit. The energy transfer unit (power electronics) can advantageously be be dimensioned to match the load capacity (maximum power) of the HEC storage unit. An advantageous distribution of the energy or charge to the two storage units during operation of the energy storage system, or one that is optimized for the specific application, can be achieved by using the control device to execute a transmission algorithm that provides for controlling the energy transmission unit according to a transmission strategy depending on certain operating parameters recorded in the electrical energy storage device, whereby this transmission strategy provides for a specification of setpoint values or setpoint ranges for a charge level of the high-performance cells and a charge level of the high-energy cells (which should also include, for example, a setpoint value or setpoint range for a ratio of the two charge levels mentioned). The transmission algorithm or the transmission strategy implemented with it can, for example, be implemented program-controlled, for example by means of control software running in the control device.

The "operating parameters" of the electrical energy storage device to be recorded can, in the broadest sense, be any physical quantities, as long as they are suitable for characterizing a specific operating state of the energy storage device. According to the invention, at least one "state parameter" of the high-performance cells (HPC) and one state parameter of the high-energy cells (HEC) are recorded as operating parameters. Such a state parameter characterizes a specific property of the state of the battery cells in question (HPC or HEC) and thus of the storage unit formed from them.

In one embodiment of the invention, a "state of charge" of the relevant cells is provided as a state parameter of the high-performance cells (HPC) and/or the high-energy cells (HEC), which means a parameter that characterizes in a quantitative manner the extent to which the relevant battery cells (and thus the storage unit formed from them) are charged. Such a state of charge can thus be provided in particular, for example, the so-called "State of Charge" (SoC), ie a parameter that describes the currently stored electrical charge in relation to the nominal value of the maximum storable electrical charge (capacity of the battery). However, within the scope of the invention, the state of charge can also be provided as a parameter which characterizes the energy stored in the relevant cells instead of the electrical charge.

In one embodiment of the invention, a "performance parameter" is provided as a state parameter of the high-performance cells (HPC) and/or high-energy cells (HEC), which quantitatively characterizes the extent to which the battery cells in question (and thus the storage unit formed from them) are "loadable" with regard to charging and/or discharging. For this purpose, the so-called "State of Power" (SoP) can be provided in particular, i.e. a parameter that indicates a peak electrical power that can be maintained momentarily or for a certain short period of time (without violating predetermined specifications) in relation to a nominal power.

Alternatively or in addition to at least one such "performance parameter" (among the operating parameters to be taken into account by the transmission strategy), a state parameter of the high-performance cells (HPC) and/or the high-energy cells (HEC) can also be provided, in particular, for example, a parameter of the cells in question that quantifies another property characterizing their "performance state". For example, such a "performance state" (parameter) can be a parameter that characterizes a "current storage capacity" of the battery cells in question (and thus of the storage unit formed from them) with regard to degradation and aging processes. Such a performance state can be provided, for example, as the so-called "State of Health" (SoH), i.e. a parameter that indicates the maximum electrical charge that can be stored at the moment in relation to the nominal value of the maximum electrical charge that can be stored.

In one embodiment, a state parameter of the high-performance cells

(HPC) the state of charge (eg SoC) is provided. Alternatively or particularly Advantageously, however, a performance parameter (e.g. SoP) can also be provided as a state parameter of the high-performance cells.

In one embodiment, at least the state of charge (e.g. SoC) is provided as a state parameter of the high-energy cells (HEC).

In the context of the invention, "high-performance cells" (HPC) and "high-energy cells" (HEC) are battery cells of different types, whereby these terms are to be understood as being mutually related to one another, i.e. in particular, these terms are not intended to imply any restriction with regard to absolute values of a load capacity (maximum power or maximum current) or a storage capacity (energy or charge) of the battery cell or of a storage unit formed by an interconnection of such battery cells.

For the classification of the two different types of battery cells used, the so-called "C-factor" can be used, for example, defined as the quotient of the maximum discharge current and the nominal capacity (or the quotient of the maximum discharge power and the nominal energy capacity) of the battery cell or a storage unit in question. The C-factor can therefore also be viewed as the reciprocal of the time period within which a fully charged battery cell or storage unit is completely discharged with the maximum discharge current.

For the purposes of the invention, the cells with the larger C-factor then represent the high-performance cells (HPC) and the cells with the smaller C-factor represent the high-energy cells (HEC), whereby it should be noted that the terms "HPC" and "HEC" for the purposes of the invention are not intended to imply any restrictions with regard to absolute parameters relating to "power density" or "energy density" or their ratio (as quantifiable by the above C-value, for example), but merely express a corresponding relative (related to one another) difference between the properties of the two types of cells used. Two examples of the C value as defined above: For a storage unit with a nominal capacity of 20 Ah and a maximum discharge current of 200 A, the C factor is: (200 A) / (20 Ah) = 10 x (1/h). The storage unit can therefore be discharged in 0.1 h (=6 min). For a storage unit with a nominal capacity of 50 Ah and a maximum discharge current of 25 A, the C factor is (25 A) / (50 Ah) = 0.5 x (1/h). The storage unit can therefore be discharged in 2 h (=120 min).

In one embodiment of the invention, the high-performance cells (HPC) have a C value greater than 1 x (1/h), in particular greater than 2 x (1/h), and/or the high-energy cells (HEC) have a C value less than 1 x (1/h), in particular less than 0.5 x (1/h).

In one embodiment, the high performance cells (HPC) have a C value that is at least a factor of 2, in particular at least a factor of 5, greater than the C value of the high energy cells (HEC).

The cells can be electrochemical battery cells in particular. Examples of this include lithium-ion cells based on mixed transition metal oxides of lithium, whereby high-energy cells can be cells based on lithium nickel cobalt manganese oxide (NCM) and high-performance cells can be cells based on lithium titanate (LTO).

In an advantageous embodiment of the invention, the high-performance cells (HPC) are provided, for example, as ultracapacitors or as LTO type cells. Alternatively, cells of the LFP (lithium ferrophosphate) type can also be provided.

In an advantageous embodiment of the invention, the high-energy cells (HEC) are provided, for example, as cells of the LFP type or the NCM type. Alternatively, cells of the LNMO (lithium nickel manganese oxide) type can also be provided. The HEC storage unit and the HPC storage unit are preferably each formed from a plurality of identical battery cells connected in series and/or in parallel, in particular electrochemical battery cells.

In a preferred embodiment, the HEC storage unit and/or the HPC storage unit each provide for the cells to be interconnected to form a plurality of "modules", hereinafter also referred to as sub-units, wherein these sub-units have respective negative and positive connection contacts via which these sub-units can be supplied with current independently of one another, i.e. can be charged or discharged independently of one another. With regard to a specific embodiment of such an interconnection, it is advantageous to draw on the state of the art of electrical energy storage devices, from which such interconnections are known.

Within the scope of the invention, so-called "balancing" can be provided for the cells connected to form a module in order to equalize the charge states of these cells or at least to ensure that their charge states remain within a certain range (defined in the specific application). For the specific design of such battery cell balancing, it is advantageous to use state-of-the-art technology (e.g. "active" or "passive" balancing).

If, within the scope of the invention, such an interconnection to subunits is provided for the HEC storage unit and/or the HPC storage unit, the aforementioned negative and positive connection contacts are preferably connected to electrical connection contacts of the "connection" of the relevant storage unit, which in turn is connected to the controllable bidirectional energy transfer unit.

The term "connection" in the terms "first connection" (of the HPC storage unit) and "second connection" (of the HEC storage unit) is to be understood broadly and not limited to the simplest case of a two-pole connection (a negative pole and a positive pole of the storage unit). Rather, the "connection" of each storage unit can also have a corresponding plurality of electrical connection contacts with regard to the interconnection to several sub-units within the HPC storage unit and/or the HEC storage unit explained above.

In many conventional electrical energy storage systems that follow a modular approach, typically around 8-18 cells are combined to form a (separately powered) sub-unit (module) and then 6-40 such sub-units are connected to form a serial string. This more specific concept can also be advantageously provided for the connection of the cells in the HPC and HEC storage units of the energy storage system according to the invention.

Here is an example: Assuming a storage unit has 40 serially connected sub-units (each of which is made up of an associated part (e.g. 8 pieces) of the relevant cells), 41 connection contacts can be provided on this storage unit in order to be able to operate the 40 sub-units separately from one another (charge and discharge). In this case, the "connection" of the storage unit can therefore have a corresponding number of 41 electrical connection contacts that are connected to the controllable bidirectional energy transfer unit (generally: "n+1" connection contacts in the case of "n" serially connected sub-units).

This has the advantage that when transferring energy between the HPC storage unit and the HEC storage unit, an individually determined removal or supply of energy (for each individual sub-unit) is possible for the multiple sub-units.

In a further development of this embodiment, it is provided that during the transfer of energy between the HPC storage unit and the HEC storage unit, a "sub-unit balancing" is carried out on the relevant storage unit(s) (which have sub-units). Advantageously, this makes it possible to equalize the charge states of the sub-units (modules) forming a storage unit (HPC or HEC storage unit) and/or at least to ensure that these charge states remain within certain ranges defined in the specific application.

If an interconnection of the high-performance cells (HPC) and/or high-energy cells (HEC) to form subunits is provided, the operating parameters recorded within the scope of the invention and to be taken into account by the transmission strategy, in particular "state parameters" of the high-performance cells (HPC) and/or high-energy cells (HEC), such as SoC, SoP, SoH, etc., can be recorded individually for each subunit and taken into account by the transmission strategy when controlling the energy transfer.

The bidirectional energy transfer unit is used to transfer energy between the HPC storage unit and the HEC storage unit and is controlled accordingly by the control device for this purpose (according to the transfer strategy). The energy transfer unit can, for example, have one or more DC/DC converters. In the preferred case of interconnecting the cells in the HPC storage unit and/or the HEC storage unit to form separately operable sub-units, the energy transfer unit can have a DC/DC converter arrangement (e.g. comprising several DC/DC converters) which is designed to, on the one hand, discharge or supply a respective "partial energy" via the respective connection contacts of the sub-units and, on the other hand, to supply or discharge the "sum of the partial energies" via the connection of the other storage unit to the other storage unit (whereby the supply or discharge can again be provided divided into partial energies for respective sub-units of the other storage unit). In particular, the above-mentioned "sub-unit balancing" can be implemented in this way.

In one embodiment of the invention, the number of subunits of the HPC storage unit is equal to the number of subunits of the HEC storage unit. Deviating from this, the respective numbers of subunits, i.e. on the one hand the HPC storage unit and the HEC storage unit, on the other hand, may also be different from each other.

In this context, it should be noted that the respective nominal voltages ("terminal voltages") of the HPC and HEC storage units, which can be present, for example, between the ends of a serial string formed from many sub-units of the storage unit, can be provided at least approximately the same. However, within the scope of the invention, very different nominal voltages can also be provided for the HPC and HEC storage units. Such different nominal voltages between the HPC and HEC sides may (depending on the circuit concept of the energy transfer unit) be taken into account accordingly in the specific design of the energy transfer unit.

Different nominal voltages (e.g. different from each other by at least a factor of 2, in particular at least a factor of 5) of the HPC and HEC storage units are actually advantageous in many cases. Here is an example: Depending on the application, it can bring various advantages to provide a "modular" structure for the energy storage system in the sense that the HPC storage unit, the HEC storage unit and the energy transfer unit are not all structurally combined into one unit (e.g. in a common housing). In this case, the energy storage system therefore consists of several spatially separate modules that are to be connected to one another via an electrical cable arrangement. A lower (or higher) voltage level of a storage unit and thus also in the area of an associated cable connection can then be used, for example, to meet corresponding requirements regarding insulation (or

cable cross-section) can be advantageously reduced.

In a particularly advantageous embodiment of the invention, the energy transmission unit can be controlled by means of the control device for a transmission of energy, in which a time-modulated current flows via the second connection for charging and/or discharging the high-energy cells. As already mentioned, the comparatively high storage capacity or energy density of the high-energy cells (HEC) also means that the HEC storage unit tends to have a lower load capacity or power density. The use of the HEC storage unit as envisaged in the invention is therefore problematic in that it limits the load capacity of the entire system (energy storage system), both when discharging and when charging the energy storage device. In particular, this limits the fast charging capability, for example.

However, with the embodiment in which a time-modulated current flows through the second terminal for charging and/or discharging the high-energy cells, the limitation of the load capacity of the energy storage system can be advantageously mitigated, since it has been found that, depending on the specific type of battery cell, a significant increase in the load capacity can be achieved by using a time-modulated (variable) current for charging or discharging the battery cells (compared to charging/discharging using a constant current).

In practice, this embodiment can therefore be used advantageously to increase the load capacity of the energy storage system during charging and/or discharging. Alternatively or additionally, however, the benefit of this embodiment can also lie in extending the service life of the storage unit in question.

In any case, this embodiment contributes very advantageously to improving the performance characteristics of the energy storage system, since it defuses the conflicting objectives explained at the beginning (e.g. regarding storage capacity, load capacity, in particular e.g. with regard to fast charging capability and charging times, and aging behavior, etc.).

In a further development of this embodiment, it is provided that the transmission strategy further provides for a specification of one or more modulation parameters for the time-modulated current. Such a "modulation parameter" can in particular represent, for example, a quantitative measure of a certain property of the time-modulated current, such as a frequency in the case of a periodic time course of the current.

In particular, the specification of the modulation parameter(s) can be provided depending on the recorded operating parameters (and/or "external operating parameters or control commands" described below), for example in order to optimize the benefit of the temporal modulation of the current operating situation (be it the energy storage unit or a device representing its installation environment, such as a vehicle). Each such modulation parameter can be modified and adapted inline, for example adaptively, in accordance with suitable cell criteria determined by the electrochemistry of the cells. In this way, the quick charging time of the high-energy cells (HEC) can be extended. Overall, this can advantageously shorten the charging time of the HEC storage unit (in relation to the high-energy cells) even further.

In a further development, it is provided that the time-modulated current has a pulse current component and/or a ripple current component.

The term "pulse current component" can refer to a sequence of more or less pronounced and clearly distinguishable pulses in the time course of the current, whereby a fluctuation level (amplitude) of this sequence of pulses corresponds at least approximately to a fluctuation level of the time course of the current.

The pulses can be rectangular or sinusoidal pulses. Triangular pulses can also be provided. In the case of identical pulses that are equidistant in time, the pulse current component represents a periodic current component of the time-modulated current. However, the pulse current component can also be formed by pulses whose time interval and/or whose pulse shape (e.g. a pulse-pause ratio) varies systematically over the time course of the current.

With the convention of designating the polarity (current direction) of the current as "positive" which causes the desired transfer of energy, i.e. from the HPC storage unit to the HEC storage unit or vice versa, an average value of the temporally modulated current must be positive. However, this does not exclude the possibility of negative values being assumed over the course of the current. Such "negative current flow phases", preferably relatively short in duration and/or associated with small absolute values of the current intensity, can even be advantageous depending on the specific battery cell type (e.g. to avoid the formation of dendrites in lithium-ion cells by depolarization of the electrode).

The fluctuation level (amplitude) of the sequence of pulses or thus of the pulse current component can be defined by predetermined lower and upper limits (of the current intensity), whereby according to the above, the upper limit must be positive, but the lower limit can also be negative if negative current flow phases are provided.

With regard to characterizing the pulse current component, at least one of the following properties can be quantified by the modulation parameter(s): frequency of the pulse train, amplitude of the pulses, lower limit, upper limit, pulse-pause ratio. Alternatively or additionally, it can be provided, for example, to specify a certain pulse geometry using the modulation parameter(s) (e.g. rectangular, sine or triangular pulses).

The term "ripple current component" is intended to describe a sequence of fluctuations (alternating current component) that is present in the course of the current over time, which can be superimposed on a direct current, for example, whereby the fluctuation height (amplitude) of the sequence of fluctuations is significantly smaller (for example by at least a factor of 5, in particular at least a factor of 10) than the current strength of the direct current. Alternatively, the sequence of fluctuations can be superimposed on a current that varies over time (for example a "pulse current component"), whereby in this case Case the fluctuation height (amplitude) of the sequence of fluctuations is substantially smaller (eg by at least a factor of 5, in particular at least a factor of 10) than a fluctuation height of the said time-varying current and a frequency or fundamental frequency of the fluctuations is substantially larger (eg by at least a factor of 5, in particular at least a factor of 10) than a corresponding frequency or fundamental frequency of the said time-varying current.

The fluctuations representing the ripple current component can be, for example, rectangular or sinusoidal or triangular fluctuations. In particular, the ripple current component can represent a periodic current component of the time-modulated current. However, the ripple current component can also be formed by non-periodic fluctuations.

With regard to characterizing the ripple current component, the modulation parameter(s) can quantify at least one of the following properties: frequency of the fluctuations (ripples), amplitude of the fluctuations.

If the high-performance cells (HPC) and/or high-energy cells (HEC), as already explained above, are advantageously connected to respective sub-units (modules) of the relevant storage unit(s) and the operating parameters recorded and to be taken into account by the transfer strategy include one or more "state parameters" (such as SoC, SoP, SoH, etc.) recorded individually for each sub-unit of the relevant storage unit(s), the transfer strategy can also provide for individual specification of modulation parameters for these sub-units in the case of controlling the energy transfer "with time-modulated current". This means that the individual "current profiles" of the currents flowing during such an energy transfer (from HPC to HEC or vice versa) when discharging or charging sub-units are specified individually (for each sub-unit). In a particularly advantageous embodiment of the invention, the energy storage system further comprises a data interface via which the following can be supplied to the control device from an external device:

- control commands, whereby the transmission strategy is modified depending on the control commands supplied, and/or

- external operating parameters, whereby the transmission strategy further provides for the control of the energy transmission unit depending on supplied external operating parameters.

The "external device" can in particular be, for example, a device that is communicatively connected (e.g. wired, e.g. via a digital data transmission bus) to the energy storage system or its control device in the usage situation, which represents a component of an installation environment of the energy storage system. If the energy storage system is installed on board a vehicle, for example to supply electrical energy to an electrical drive system of the vehicle, the external device can in particular be, for example, a central control device (e.g. program-controlled computer device) or another vehicle-specific control device.

The external device can advantageously be a device in which data is available (e.g. stored and/or calculated from stored data) which contains information about current and/or expected future use of the energy storage system. Such data as such, or data calculated from such data by further processing on the vehicle side, can advantageously be fed to the control device of the energy storage system as external operating parameters.

In the example of use for the electric drive system of a

Vehicle, the data or elements thereof may e.g. one or more of the represent the following "external operating parameters": current accelerator pedal position, current drive power (including negative drive power during recuperation), current current strength of a current with which the electrical energy storage device is currently being discharged/charged. Alternatively or additionally, the data or elements thereof can represent, for example, the same operating parameters as stated above, but not as current values but rather values expected or forecast for the future.

Future-related data on board the vehicle could, for example, originate from a navigation system, perhaps representing properties of a current route determined by the navigation system (e.g. incline, decline, curves, traffic lights, etc.) and/or the properties of a route defined by the user of the vehicle in the navigation system (e.g. altitude above sea level along the route and/or at the start and/or destination, etc.).

In another embodiment, the "external device" is, for example, a server device that is communicatively connected to the vehicle via a mobile network, so that the transmission strategy in the energy storage system of the vehicle can be modified by control commands supplied via the mobile network (in order to achieve an optimization of the transmission strategy). The generation of such control commands can in this case be based in particular, for example, on data from a

Fleet management of a large number of vehicles can be realized, each of which is also equipped with an energy storage system of the type described here.

In one embodiment, the external operating parameters include a current power requirement and/or a future forecast power requirement.

The transmission strategy implemented by means of the control device can advantageously take into account the data supplied by the external device when controlling the energy transmission unit in such a way that which further improves or optimizes the operation of the energy storage system. For example, it can be provided that the specification of the setpoint values or setpoint ranges for the charge level of the high-performance cells and/or the charge level of the high-energy cells is modified depending on the data received.

In one embodiment, it is provided that the HPC storage unit and/or the HEC storage unit each have a plurality of sub-units that can be operated separately from one another, each of which is formed from an associated part of the high-performance cells or high-energy cells of the storage unit in question, and that the controllable bidirectional energy transfer unit in conjunction with the first connections (on the HPC storage unit) and the second connections (on the HEC storage unit) is designed to enable a respective partial energy to be removed or supplied to the plurality of sub-units in a manner determined individually by the control device when energy is transferred between the HPC storage unit and the HEC storage unit.

In one embodiment, the electrical energy storage device has an energy storage capacity of at least 20 kWh, in particular at least 40 kWh.

In an embodiment that is advantageous for many applications, the second storage unit (HEC) has an energy storage capacity that is greater than the energy storage capacity of the first storage unit (HPC). This is preferably at least a factor of 2, in particular at least a factor of 5.

According to a further aspect of the invention, the object mentioned at the outset is achieved by a method for operating an energy storage system of the type described here, comprising the steps:

Detecting operating parameters of an electrical energy storage device of the energy storage system, comprising at least one state parameter of high-performance cells (HPC) of a first storage unit (HPC storage unit) of the electrical energy storage device and a state parameter of high-energy cells (HEC) of a second storage unit (HEC storage unit) of the electrical energy storage device, and

- Executing a transfer algorithm which provides for a transfer of energy between the HPC storage unit and the HEC storage unit according to a transfer strategy depending on the detected operating parameters, wherein the transfer strategy provides for a specification of setpoint values or setpoint ranges for a state of charge of the high-performance cells and a state of charge of the high-energy cells.

The embodiments and special configurations described here for the energy storage system according to the invention can, individually or in any combination, also be provided in an analogous manner as embodiments or special configurations of the method according to the invention, and vice versa.

In one embodiment of the method, the operating parameters to be recorded further comprise a current intensity of a current flowing through a connection device of the energy storage system when charging or discharging the electrical energy storage device. Alternatively or additionally, information about this current intensity could also be received, for example, as one of the external operating parameters mentioned above.

In one embodiment, a transfer of energy can be controlled according to the transfer algorithm, in which a time-modulated current flows through a connection of the HEC storage unit for charging and/or discharging the high-energy cells (HEC). Depending on the specific implementation of the energy transfer (eg by means of a DC/DC converter arrangement), a correspondingly time-modulated current can also flow from the energy transfer unit to a connection of the HEC storage unit. However, it is also conceivable that the latter current flows "smoothed" (direct current) from the energy transfer unit to the connection of the HEC storage unit.

In one embodiment, the method further comprises receiving control commands for modifying the transmission strategy depending on received control commands, and/or external operating parameters for controlling the transmission of the energy further depending on received external operating parameters.

According to yet another aspect of the invention, a use of an energy storage system of the type described here and/or a method of the type described here for supplying electrical energy to an electric drive system of a vehicle is proposed.

Advantageously, it can also be used, for example, to supply electrical energy to a power supply network for consumers that can be connected to it, for example in connection with the feeding of electrical energy from renewable energy sources into such a power supply network.

The invention is described in more detail below using exemplary embodiments with reference to the accompanying drawings. They each show schematically:

Fig. 1 is a block diagram of an energy storage system including installation environment (drive system of a BEV) according to an embodiment,

Fig. 2 to 6 various exemplary time courses of a time-modulated current used for charging and discharging high energy cells (HEC) of the energy storage system, and

Fig. 7 is a flow chart of an operating method carried out by a control device of the energy storage system. Fig. 1 shows an energy storage system 10 having an electrical energy storage device (rechargeable battery) with a first storage unit 20 and a second storage unit 30.

The first storage unit 20 ("HPC storage unit") is formed from high-performance cells 22 and has a first connection 24 for charging and discharging the high-performance cells 22. The second storage unit 30 ("HEC storage unit") is formed from high-energy cells 32 and has a second connection 34 for charging and discharging the high-energy cells 32.

In the example shown, the high-performance cells are 22 cells based on lithium titanate (LTO) and the high-energy cells are 32 cells based on lithium nickel manganese cobalt oxide (NCM).

In both storage units 20, 30, the battery cells 22, 32 are each connected in series and in parallel in such a way that sub-units (not shown in the figure) that can be supplied with current separately (independently of one another) are formed in each storage unit.

In the example, it is assumed that in each of the two storage units 20, 30 the respective high-performance cells 22 and 33 are each made up of a corresponding part of the high-performance cells 22 and 33.

The sub-units formed by high-energy cells 32 are connected in series, so that a respective "voltage of the storage unit" 20 or 30 results from the sum of partial voltages of the respective individual sub-units and is applied to the connection contacts of the respective connection 24 or 34 shown in Fig. 1.

The energy storage system 10 further comprises a controllable bidirectional energy transmission unit 40, which is connected on the one hand to the first connection 24 and on the other hand to the second connection 34, in order to enable a transmission of energy in the direction from the first storage unit 20 to the second storage unit 30 or vice versa.

For charging and discharging the electrical energy storage device 20, 30, a connection device 50 connected to the first connection 24 is provided.

The energy storage system 10 further comprises a control device 70 which generates the aforementioned control signal ct and by means of which, during operation of the energy storage system 10, the energy transmission unit 40 is controlled according to a transmission algorithm which, in the example, is defined by a control program running in the control device 70 designed as a program-controlled computer device.

The control of the energy transfer unit 40 takes place according to a transmission strategy depending on certain operating parameters, which include a current state of charge "soc-p" of the high-performance cells 22 and a current state of charge "soc-e" of the high-energy cells 32. According to an advantageous development, these operating parameters also include a current power state (e.g. so-called state of power, "SoP") at least for the high-performance cells 22 (HPC storage unit).

The charge states soc-p and soc-e can each be defined as a so-called "State of Charge" (SoC), i.e. as a parameter that indicates the currently stored charge in relation to the nominal value of the maximum storable charge (capacity of the battery).

To record the current charge states soc-p, soc-e, the two storage units 20, 30 are each equipped with a battery monitoring sensor 60 or 62. Such a battery monitoring sensor is known as such from the state of the art. For the specific design of the sensor 60, 62, this state of the art can therefore be used, for example. In the example, the recorded operating parameters soc-p, soc-e are Input variables of the transmission algorithm are fed to the control device 70.

Within the scope of the invention, however, the term "state of charge" is to be understood broadly as any parameter suitable for quantifying the charge in question. Deviating from the example shown, this parameter could therefore also refer to the "load" of electrical energy stored in the storage unit in question instead of the electrical charge.

In the example, the energy storage system 10 also has a sensor or current measuring device 64 for measuring a load current IL currently flowing at the connection device 50 of the energy storage system 10. The current measuring device 64 outputs a sensor signal il representative of the current IL, which, as shown in Fig. 1, is also fed to the control device 70, e.g. as a further operating parameter to be taken into account in the context of the transmission strategy.

If the currents flowing through the first and second terminals 24, 34 of the two storage units 20, 30 are designated as IP and IE as shown in Fig. 1, the following applies: IL = IP + IE, i.e. the load current IL corresponds to the sum of the currents at the two storage units 20, 30, whereby a convention is assumed here according to which positive currents each mean a discharge and negative currents each mean a charge of the energy storage system 10 or the respective storage unit 20 or 30.

According to the transmission strategy for controlling the energy transfer unit 40 already mentioned above, setpoint values or setpoint ranges are provided for the state of charge soc-p of the high-performance cells 22 and the state of charge soc-e of the high-energy cells 32.

It should be noted that the load current IL (discharge or charge current of the energy storage system 10) in the respective application situation is "externally" is specified, so that a corresponding reduction or increase in the total charge of the energy storage system 10 (sum of the charges of the storage units 20, 30) is already determined by this load current IL in the example shown. The transmission strategy and the control of the energy transmission unit 40 based thereon can, however, advantageously influence how such a reduction or increase in the total charge is "distributed between the two storage units 20, 30".

The specification of target values or target value ranges for the charge states, in the example the parameters soc-p, soc-e, means that the control device 70 attempts, as far as possible, to always change the values of these parameters soc-p and soc-e, or e.g. the corresponding stored electrical charges (or practically equivalently: stored electrical energies) of the two storage units 20, 30 by controlling the energy transfer unit 40 in a way by which the actual values, i.e. "actual values", are changed in the direction of the target values or target value ranges.

If and as long as the relevant actual values recorded as operating parameters or resulting therefrom assume setpoint values specified by the transmission strategy or lie within setpoint ranges specified by the transmission strategy, the control device 70 causes the energy transmission unit 40 to be deactivated by means of the control signal ct.

In Fig. 1, the first and second connections 24, 34 of the two storage units 20, 30 and their line connections to the energy transfer unit 40 are each shown in a simplified two-pole manner, ie with only two connection contacts and connection lines. In view of the above-mentioned design of the storage units 20, 30 with serially connected subunits, the connections 24, 34 can actually each have a corresponding plurality of connection contacts, which are connected to the energy transfer unit 40 via a corresponding plurality of connection lines. The controllable bidirectional energy transfer unit 40 can be designed in conjunction with the first and second connections 24, 34 to implement a respective partial energy discharge or supply determined individually by the control device 70 for the multiple sub-units during the transfer or exchange of energy between the first and second storage units 20, 30. This advantageously enables balancing to be implemented with regard to the respective sub-units during the energy transfer between the storage units 20, 30. In this case, for example, when energy is transferred from the first storage unit 20 to the second storage unit 30, the energy to be transferred is preferably taken from "relatively well charged" sub-units of the storage unit 20 and/or preferably transferred to "relatively poorly charged" sub-units of the storage unit 30 (or vice versa, i.e. energy is preferably taken from "relatively well charged" sub-units of the storage unit 30 and/or preferably transferred to "relatively poorly charged" sub-units of the storage unit 20).

Information required for such balancing of the subunits within the storage units 20, 30 can be provided in the example by the battery monitoring (sensors 60, 62) and thus transmitted to the control device 70, for example by means of the signals soc-p, soc-e. Independently of this, the battery monitoring can also be designed to implement balancing relating to individual battery cells within each of the subunits within the storage units.

As an example of a particularly advantageous application of the invention, Fig. 1 shows a use of the energy storage system 10 for supplying electrical energy to an electric drive system 1 of a vehicle.

The electric drive system 1 has an inverter 2 connected to the connection device 50 of the energy storage system 10 for supplying current to an electric drive machine 4. The electric drive machine 4 represents a drive component in a drive train of the vehicle, symbolized by dashed lines in Fig. 1, for driving vehicle wheels 5. In the example, the vehicle is a pure electric vehicle (BEV), but could also be, for example, a hybrid vehicle additionally having an internal combustion engine.

The electric drive system 1 further comprises a control device 3, by means of which the inverter 2 is controlled during operation of the vehicle. For this purpose, the control device 3 generates a control signal ci to be supplied to the inverter 2 based on a current power requirement supplied to the control device 3 (e.g. based on an accelerator pedal position, etc.).

The current power requirement can, for example, represent a requirement for a specific electrical power, or a specific torque or a specific speed, etc. when driving the vehicle. The control device 3 meets such a power requirement by causing the drive machine 4 to be energized with a corresponding electrical power, which is provided by a corresponding discharge of the energy storage system 10 via the connection device 50 and the inverter 2.

To enable recuperation operation of the drive motor 4 (when braking the vehicle), the inverter 2 can be operated bidirectionally and can be controlled accordingly by the control signal ci. The control device 3 can therefore also meet "negative" power requirements in which the drive motor 4, operated as a generator, generates electrical power that can be used via the inverter 2 and the connection device 50 as a charging power for charging the energy storage system 10.

In addition, the energy storage system 10 can also be charged at a charging station when the vehicle is parked. For this purpose, the vehicle has a charging connection 6 (e.g. charging socket) which is connected to a charging electronics (e.g.

rectifier) is also connected to the connection device 50. The electrical connections between energy storage system 10, inverter 2 and charging connection 6 are shown in Fig. 1 in a somewhat simplified manner without the isolating devices typically provided in practice in this area (e.g. relays, contactors, etc.), by means of which individual components of these can be electrically decoupled from the rest of the system as required (and e.g. also in the event of detected faults or defects).

The control device 3 shown in Fig. 1 can also be designed to control such separating devices and represent a component (possibly a functional component) of a more comprehensive vehicle electronics system, which consists of a plurality of components (not shown in Fig. 1) that are designed separately but are communicatively connected to one another, e.g. via a digital data bus system (e.g. CAN bus, LIN bus, etc.).

In the example shown, a particularly advantageous feature of the energy storage system 10 is that the energy transfer unit 40 can be controlled by means of the control device 70 for a transfer of energy, in which a time-modulated current IE flows via the second connection 34 for charging and/or discharging the high-energy cells 32. This increases the load capacity of the high-energy cells 32 and thus ultimately of the energy storage system 10 during charging and discharging and extends the service life of the high-energy cells 32.

In order to optimize these advantageous effects, the transmission strategy in the example further provides for a specification of one or more modulation parameters for the time-modulated current IE, which depends on the recorded operating parameters, here e.g. at least on the parameter soc-e.

The time-modulated current IE can have a pulse current component and/or a ripple current component, whereby in each specific operating situation the following can be determined by modulation parameters encoded in the control signal ct: - presence of a pulse current component or its intensity and, if applicable, other properties of the pulse current component, and

- Presence of a ripple current component or its intensity and, if applicable, other properties of the ripple current component.

Fig. 2 to 6 illustrate the terms "pulse current component" and "ripple current component" using some exemplary time profiles of a current IE used for charging and discharging the second storage unit (HEC) (as a function of time t).

Fig. 2 and 3 each show a current IE that has only a "pulse current component" and is formed by a sequence of periodic rectangular pulses, whereby a fluctuation level (amplitude) of this pulse sequence corresponds to a fluctuation level of the time profile of the current IE. In the example in Fig. 2, the pulses are rectangular and in Fig. 2 a pulse period Tp as well as pulse times T1 and pulse pause times T2 of this current profile are shown.

In the example of Fig. 2, the current intensity IE is greater than or equal to zero at any time, whereas in the example of Fig. 3, the current IE also assumes negative values in certain temporal phases or, in other words, the fluctuation height (amplitude) of the pulse sequence extends into the negative value range (IE < 0).

Fig. 4 shows a current IE that has a "ripple current component" that is formed by a sequence of rather small amplitude fluctuations (alternating current component) that are present over time and that are superimposed on a specific direct current in this example. In the example in Fig. 4, the fluctuations (ripples) are periodic and in this example have the form of rectangular pulses with a pulse period tp and pulse times t1 and pulse pause times t2. As far as the fluctuation level (amplitude) of the "ripple current component" superimposed on a direct current is concerned, this can, within the scope of the invention, be at least 1%, in particular at least 5% of the current intensity of the direct current. On the other hand, it is often advantageous if the fluctuation level of the ripple current component is a maximum of 40%, in particular a maximum of 30%, of the current intensity of the direct current.

Fig. 5 and 6 each show a current IE that has both a "pulse current component" and a "ripple current component", whereby in the example of Fig. 5 it is provided that the current intensity of the current IE is positive at all times, whereas in the example of Fig. 6 the current IE also assumes negative values in certain temporal phases. For the sake of better representation, a width of the pulses of the pulse current component corresponding to the pulse period Tp is shown larger in Fig. 5 and 6 than in Fig. 2 to 4. In the examples of Fig. 5 and 6 the fluctuations (ripples) are also periodic and have the form of rectangular pulses with a pulse period tp and pulse times t1 and pulse pause times t2.

In Fig. 2 to 6, the "pulse current component" is shown as a square wave signal by way of example only. In contrast to this, another pulse shape can also be provided within the scope of the invention, whether permanently or temporarily (e.g. depending on a modulation parameter specification of the control device 70). The same applies to the selection of the pulse period Tp shown in the figures as well as the pulse times T1 and pulse pause times T2. These can also be specified or varied within a wide range within the scope of the invention. In many applications, however, it can be advantageous if T1 > T2 applies. In particular, T1 can be provided to be larger than T2 by a factor of at least 2, for example.

As far as the pulse period Tp in the "pulse current component" is concerned, this can be specified within the scope of the invention, for example, in a range from 0.1 ms to 10 s, corresponding to a frequency in the range from 0.1 Hz to 10 kHz, whether fixed or variable during operation of the energy storage system (depending from a modulation parameter specification of the control device). In an embodiment that is advantageous in many cases, Tp is in a range from 0.1 ms to 0.1 s.

In Fig. 3, a fluctuation level (amplitude) of the pulse current component is shown as extending largely in the positive value range. As an alternative, within the scope of the invention, it can also be provided that this fluctuation level extends largely in the negative value range. If a current IE is provided with a fluctuation level extending into the negative value range (as is the case in Fig. 3, for example), it is usually advantageous if, viewed on average over time, a "positive" power, corresponding to the areas (integrals) of the sections running in the positive value range, is significantly greater than a "negative" power corresponding to the areas of the sections running in the positive range. In particular, such a positive power can be provided to be greater than the negative power by a factor of at least 2, in particular at least 5. In other words, the ratio T 1 /T2 should be selected to be greater the further the "negative current peaks" extend into the negative value range. In an exemplary embodiment, T1 > 100 x T2 applies.

As far as the fluctuation level (amplitude) of the "ripple current component" superimposed on a pulse current is concerned, within the scope of the invention this can be, for example, at least 1%, in particular at least 5% of the (overall) fluctuation level of the current IE. On the other hand, it is often advantageous if the fluctuation level of the ripple current component is a maximum of 40%, in particular a maximum of 30% of the fluctuation level of the current IE.

Returning to Fig. 1 and the already mentioned specification of one or more modulation parameters, a dependency of each such modulation parameter on one or more of the detected operating parameters (such as state of charge soc-e, etc.) programmed for this purpose in the control device 70 can be based in particular on the results of tests carried out beforehand on the relevant type of high-energy cells. In the example shown, a further particularly advantageous feature is that the energy storage system 10 has a data interface via which, during operation of the energy storage system 10, the control device 70 can be supplied with control commands cs and/or external operating parameters pe from an external device, in the example the vehicle-side control device 3.

Such control commands cs cause the transmission strategy to be modified depending on the specific control command supplied (i.e., for example, certain parameters of a transmission algorithm defined by parameters are changed), whereas external operating parameters pe can be used as further input variables of the transmission algorithm, i.e. the transmission strategy provides that the energy transmission unit 40 is additionally controlled depending on supplied external operating parameters pe.

In the example, the external operating parameters pe include, for example, a current power requirement as well as a power requirement predicted for the future, e.g. based on data obtained from a navigation system of the vehicle, including information about a current route (e.g. incline, decline, curves, traffic lights, etc.) that has an impact on the energy or power requirements of the vehicle and/or comparable (but relevant further into the future) information about properties of a route defined in the navigation system.

In particular in the present application for supplying electrical energy to an electric drive system of a vehicle, it is usually advantageous if an energy storage capacity of the second storage unit 30 (HEC storage unit) is significantly greater than an energy storage capacity of the first storage unit 20 (HPC storage unit). These capacities can differ from one another, for example, by at least a factor of 5, in particular by at least a factor of 10. Fig. 7 shows a schematic flow diagram of the operating method carried out by means of the control device 70 of the energy storage system 10.

In a step S1, the charge states (e.g. "SoC") soc-p, soc-e of the high-performance cells (HPC) 22 and high-energy cells (HEC) 32 are recorded by means of the sensors 60, 62 in the storage units 20, 30 of the electrical energy storage device and communicated to the control device 70 of the energy storage system 10. In an advantageous embodiment, the power state (e.g. "SoP") of at least the high-energy cells 32 (HPC) is also recorded and communicated to the control device 70 as yet another operating parameter of the electrical energy storage device (20, 30).

In steps S2 and S3 carried out by the control device 70 in parallel to step S1, in step S2 (optionally) one or more control commands cs are received if such control commands cs are output from the external control device 3 of the vehicle to the energy storage system 10, and in step S3 one or more external operating parameters pe are received which are output from the external control device 3 of the vehicle to the control device 70.

In a step S4, the control device 70 executes a transmission algorithm implemented by software stored therein in order to transmit energy as required between the first storage unit 20 and the second storage unit 30 according to a transmission strategy depending on at least the detected charge states soc-p, soc-e (and e.g. additional performance state of at least the high-performance cells 22, possibly also high-energy cells 32) and the received external operating parameter(s), for which the control device 70 generates a suitable control signal ct based on a corresponding specification of setpoint ranges for the charge states soc-p, soc-e and communicates it to the energy transmission unit 40.

If a control command cs was received in step S2, it is used in step

S4 modifies the transmission strategy accordingly, in particular, for example, modified dependence of the energy transfer or setpoint ranges on the recorded operating parameters and the operating parameters (transmitted externally) are used.

In a step S5, the energy transfer between the storage units 20, 30 is carried out by the energy transfer unit 40 as a function of the control signal ct. Preferably, in step S5, it is provided that a time-modulated current IE flows via the connection 34 of the second storage unit 30 for charging or discharging the high-energy cells 32 by appropriately controlling the energy transfer unit 40.

The processing then returns to the parallel steps S1 to S3.

In step S2, for example, a control command can be received which commands the transfer of a specific electrical charge (or electrical energy) from one of the storage units 20, 30 to the other of these storage units 20, 30. Such a command can be generated by a vehicle electronics device (e.g. program-controlled central control unit), for example based on a forecast of a future (more or less imminent) power requirement. The forecast can be based, for example, on an evaluation of data obtained from a navigation system of the vehicle, be it, for example, relating to a current route and/or, for example, relating to a route specified in the navigation system by a user. Deviating from this example, an evaluation of external operating parameters (e.g. data from the navigation system) could also be carried out internally, i.e. by the control device 70 of the energy storage system 10, and the transmission strategy could provide for the evaluation result to be taken into account accordingly. Another example of a control command is a command for permanent modification of the transmission strategy (comparable to an "update" of the software running in the control unit 70), e.g. based on data from a fleet management of a large number of vehicles. In step S3, a speed of the vehicle can be transmitted to the control device as an external operating parameter, for example, and then in step S4, a specification of target values or target value ranges for the charge states dependent on this speed can be provided. An example of this: As long as the vehicle is stationary (e.g. in a traffic jam) or is driving very slowly, there is no significant possibility of recuperating braking energy. In this operating state of the vehicle, it can therefore be expedient to tend to increase the proportion of total energy stored in the HPC storage unit (e.g. in comparison to an operating state with a vehicle speed in a medium range). The supply of the external operating parameter "vehicle speed" and/or other external operating parameters characterizing the operating state of the vehicle advantageously allows the control device 70 to optimize the transmission strategy in this way. In this context, it should be noted that, in contrast to this example, an evaluation of an external operating parameter (e.g. vehicle speed) could also be carried out externally, e.g. by the vehicle electronics mentioned, and based on this, control commands cs could be generated and transmitted (in step S2).

In step S4, the transmission strategy can not only determine (within the scope of the target value or target range specification of the charge states soc-p, soc-e) whether or when a transfer of electrical charge (or energy) should take place from one of the storage units 20, 30 to the other. In an advantageous embodiment, it is rather provided that the transmission strategy also determines, by specifying the modulation parameters explained above, with which "current profile" (properties of the time-modulated current IE) the energy transfer is accomplished. All parameters that can be used here to influence the target value/range specification can alternatively or additionally be used to specify or change one or more modulation parameters within the scope of the transmission strategy. An example of this: If it can be found out from data from a fleet management of a large number of vehicles (e.g. by Kl) that the performance and/or service life of the energy storage system (or the individual storage units 20, 30) depends on a specific setting or change of the modulation parameters, possibly also on operating parameters (internal and/or external), a corresponding command for modifying the transmission strategy can be transmitted to the control unit 70.

List of reference symbols

1 electric drive system

2 inverters

3 Control device (of the vehicle)

4 electric drive machine

5 vehicle wheels

6 Charging port

7 Charging electronics

10 Energy storage system

20 first storage unit (HPC)

22 high-performance cells

24 first connection

30 second storage unit (HEC)

32 high-energy cells

34 second connection

40 Energy transfer unit

50 Connection device

60 Sensors (for first storage unit)

62 Sensors (for second storage unit)

64 Sensors (current measurement)

70 Control device

IP charge/discharge current (first storage unit)

IE charge/discharge current (second storage unit) t time

T1 Pulse time (for pulse current component)

T2 Pulse pause time (for pulse current component)

Tp Period (for pulse current component) t1 Pulse time (for ripple current component) t2 Pulse pause time (for ripple current component) tp Period (for ripple current component)

IL charging/discharging current (load current of the energy storage device)

11 Measured value for charging/discharging current soc-p Measured value for state of charge (first storage unit) soc-e Measured value for state of charge (second storage unit) ci Control signal (for inverter) ct Control signal (for energy transfer unit) cs Control signal (for control device) pe Control signal (data concerning external operating parameters)

Claims

Patent claims

1. Energy storage system (10), comprising

- an electrical energy storage device (20, 30) with a first storage unit (20) made of high-performance cells (22) and a first connection (24) for charging and discharging the high-performance cells (22), and with a second storage unit (30) made of high-energy cells (32) and a second connection (34) for charging and discharging the high-energy cells (32),

- a controllable bidirectional energy transfer unit (40) which is connected on the one hand to the first connection (24) and on the other hand to the second connection (34) in order to enable a transfer of energy between the first storage unit (20) and the second storage unit (30),

- a connection device (50) connected to the first connection (24) for charging and discharging the electrical energy storage device (20, 30),

- a detection device (60, 62, 64) for detecting operating parameters (soc-p, soc-e, il) of the electrical energy storage device (20, 30), which comprise at least one state parameter (soc-p) of the high-performance cells (22) and one state parameter (soc-e) of the high-energy cells (32),

- a control device (70) for controlling the energy transfer unit (40) according to a transmission algorithm which provides for controlling the energy transfer unit (40) according to a transmission strategy depending on the detected operating parameters (soc-p, soc-e, il), wherein the transmission strategy provides for a specification of target values or target value ranges for a state of charge (soc-p) of the high-performance cells (22) and a state of charge (soc-e) of the high-energy cells (32).

2. Energy storage system (10) according to claim 1, wherein the energy transfer unit (40) can be controlled by means of the control device (70) for a transfer of energy, in which a time-modulated current (IE) flows via the second connection (34) for charging and/or discharging the high-energy cells (32).

3. Energy storage system (10) according to claim 2, wherein the transmission strategy further provides for a specification of one or more modulation parameters for the time-modulated current (IE), in particular wherein this specification of the modulation parameters is provided as a function of the detected operating parameters (soc-p, soc-e, il).

4. Energy storage system (10) according to claim 2 or 3, wherein the time-modulated current (IE) has a pulse current component and/or a ripple current component.

5. Energy storage system (10) according to one of the preceding claims, further comprising a data interface via which the control device (70) can be supplied from an external device:

- control commands (cs), whereby the transmission strategy is modified depending on the control commands supplied, and/or

- external operating parameters (pe), wherein the transmission strategy further provides for the control of the energy transmission unit (40) as a function of supplied external operating parameters (pe).

6. Energy storage system (10) according to claim 5, wherein the external operating parameters (pe) comprise a current power requirement and/or a power requirement predicted for the future.

7. Energy storage system (10) according to one of the preceding claims, wherein - the first storage unit (20) and/or the second storage unit (30) each have a plurality of separately operable sub-units, each of which is formed from an associated part of the high-performance cells (22) or high-energy cells (32) of the relevant storage unit (20, 30), and

- the controllable bidirectional energy transmission unit (40) in connection with the first and second connections is designed to enable a respective partial energy to be removed or supplied as individually determined by the control device (70) for the plurality of partial units during the transmission of energy between the first storage unit (20) and the second storage unit (30).

8. Energy storage system (10) according to one of the preceding claims, wherein the electrical energy storage device (20, 30) has an energy storage capacity of at least 20 kWh, in particular at least 40 kWh.

9. A method for operating an energy storage system (10) according to one of the preceding claims, comprising the steps:

- detecting operating parameters (soc-p, soc-e, il) of an electrical energy storage device (20, 30) of the energy storage system (10), wherein these operating parameters (soc-p, soc-e, il) comprise at least:

- a state parameter (soc-p) of high-performance cells (22) of a first storage unit (20) of the electrical energy storage device (20, 30), and a state parameter (soc-e) of high-energy cells (32) of a second storage unit (30) of the electrical energy storage device (20, 30). - Executing a transfer algorithm which provides for a transfer of energy between the first storage unit (20) and the second storage unit (30) according to a transfer strategy depending on the detected operating parameters (soc-p, soc-e, il), wherein the transfer strategy provides for a specification of target values or target value ranges for a state of charge (soc-p) of the high-performance cells (22) and a state of charge (soc-e) of the high-energy cells (32).

10. The method according to claim 9, wherein a transfer of energy can be controlled according to the transfer algorithm, in which a time-modulated current (IE) flows via a terminal (34) of the second storage unit (30) for charging and/or discharging the high-energy cells (32).

11. The method of claim 9 or 10, further comprising receiving

- control commands (cs) for modifying the transmission strategy depending on received control commands, and/or

- external operating parameters (pe) for controlling the transmission of energy further depending on received external operating parameters (pe).

12. Use of an energy storage system (10) according to one of claims 1 to 8 and/or a method according to one of claims 9 to 11 for supplying electrical energy to an electric drive system of a vehicle.

13. Use of an energy storage system (10) according to one of claims 1 to 8 and/or a method according to one of claims 9 to 11 for supplying electrical energy to a power supply network for consumers that can be connected thereto.