Patent Application
20160204480
The invention relates to a method and an apparatus for storing electric energy in electrochemical energy accumulators according to the generic part of claims 1 and 4.
For securing a sustainable energy supply, the amount of renewable energies rises due to the increasing amount of wind and solar power plants. Since the control of energy distribution networks for providing a constant grid voltage and grid frequency currently is effected by conventional power plants with rotating electric generators, which also remain connected with the energy distribution networks when the energy provided from wind and sun would be sufficient for the supply of the consumers connected to the energy distribution networks, the wind and solar power plants must be throttled down, so that the share to be contributed by the renewable energies in the energy supply is limited. To remove this limitation, a system for energy storage and grid control in electric energy distribution networks is required, which both can perform tasks of grid control and thereby allows a shutdown of conventional power plants, and feeds a sufficient amount of energy into an energy distribution network, when the energy provided from wind and sun is not sufficient for the supply of the consumers connected to the energy distribution networks.
For energy storage, electrochemical energy storage systems preferably are used in such a system because of the fast availability of electric power, which under electrotechnical aspects substantially differ by the C-rate, i.e. the ratio of power and energy. These differences chiefly result from different accumulator technologies with various electrode combinations, such as lead-acid accumulator, sodium-based high-temperature batteries, lithium-ion accumulators, redox-flow batteries, etc. However, due to differences in the design and manufacturing method of the individual manufacturers of electrochemical energy accumulators, considerable differences are obtained even with a similar cell chemistry. Furthermore, electrochemical energy storage systems differ in secondary features such as aging behavior, cycle stability, cycle depth, own consumption, self discharge, and other aspects.
A further essential electrotechnical aspect is the DC-voltage-side output voltage as well as the variance of the voltage between charged and discharged condition of the electrochemical energy storage systems. The electrotechnical features such as power, voltage and voltage variance require and provide for a multitude of topological possibilities for the connection of power electronic components such as DC/DC-converters and DC/AC-converters.
To optimally satisfy the electrotechnical requirements of a whole system, a combination of various electrochemical energy storage systems with different C-rates is desirable. However, this also results in a multitude of variants of topologies of power electronic components.
From DE 100 18 943 A1, for example, a photovoltaic off-grid system with a photovoltaic generator is known, which on the one hand is connected with a battery via a matching transformer and a bidirectional position controller and on the other hand provides an AC voltage on the output side via a stand-alone inverter. The energy management here is effected via a control and regulating means.
From EP 1 986 306 A1 an energy supply system is known, in which the energy produced by photovoltaic systems is stored in several storage battery units, downstream of which an inverter is provided for coupling the energy supply system to an AC voltage energy distribution network. By means of a control unit, the connection of the individual storage battery units to the energy distribution network is controlled.
From US 2011/029 16 06 A1 an energy storage system with a management system is known, which comprises two DC/DC-converters, an inverter, a control unit and a battery management system.
From AT 509 888 A4 a method for controlling electric energy accumulators is known, which consist of several battery units (cell stacks) each connected with a DC/DC converter with switching hysteresis. For optimizing the efficiency, the individual electric energy accumulators selectively are switched on and off, wherein different switching hystereses are achieved in that the switching hystereses of the DC/DC converters are parameterized with different switching points. There is furthermore provided a dynamic adaptation of the charging and discharging curves of the electric energy accumulators in dependence on the SOC (State of Charge) and SOH (State of Health) of individual energy accumulators or the entire system by a central control unit.
In an overall system composed of many electric energy accumulators and in particular in the case of an expansion of the system by including further, also spatially remote electric energy accumulators, the problem occurs that the central control unit must know the specific properties of each of the electric energy accumulators and consider the same in the control of the state of charge of the energy accumulator and the overall system, which leads to a considerable expenditure in the programming of the central control unit and to a significant susceptibility to failure of the overall system.
From the reference Atcitty, S. [et al.]: Summary of State-of-the-Art Power Conversion Systems for Energy Storage Applications (SANDIA REPORT SAND98-2019, September 1998) a compilation of a plurality of power electronic converter systems with inverters and DC/DC converters connected in series or in parallel is known, which are bidirectionally connected with a control unit and on the one hand are connected to an energy storage unit and on the other hand to an energy supply network or an AC voltage load.
When composing an overall system of a plurality of individual converter systems or when expanding such overall system by including additional converter systems, however, there also occurs the problem that to maintain a specified state of charge of the overall system and the capacity of the individual energy accumulators, the control units of the individual converter systems must be connected with a central control unit which must know the specific properties of the converter systems and consider the same in the control of the state of charge of the energy storage systems and the overall system, which increases the programming expenditure and the susceptibility to failure of the overall system and leads to limitations of the useful life of the energy accumulators.
It is the object underlying the present invention to provide a method and an apparatus for storing electric energy in electrochemical energy accumulators and for exchanging electric energy with an electric energy distribution network as mentioned above, which ensures the use of different electrochemical energy accumulators with uniform communication interfaces and provides for the use of different topologies of power electronic components and electrochemical energy accumulators independent of the respectively employed technology of the electrochemical energy accumulators and the topology of the power electronic components in a hybrid power plant.
According to the invention, this object is solved by a method with the features of claim 1.
The solution according to the invention provides a method for storing electric energy in electrochemical energy accumulators and for exchanging electric energy with an electric energy distribution network, which ensures the use of different electrochemical energy accumulators with uniform communication interfaces and provides for the use of different topologies of power electronic components and electrochemical energy accumulators independent of the respectively employed technology of the electrochemical energy accumulators by abstraction of the topology- and accumulator-specific properties, so that a hybrid power plant can be composed of differently configured, but identically behaving storage units or modules at a point of common coupling of the electric energy supply network and at the communication interfaces to form a superordinate battery power plant management system.
By transferring the specific data and features of the electrochemical energy accumulators and the topology of the power electronic system into data and features specific for the electric energy supply network
Preferably, the specific data and features of the electrochemical energy accumulators and the topology of the power electronic system are combined in an abstract AC battery and transferred into the data and features of the electric energy distribution network, wherein the AC battery is controlled, monitored and regulated by means of an AC battery management.
The AC battery depicts the quantities characteristic for the respectively used battery technology, such as charging and discharging current, capacity, state of charge and the like, in quantities relevant for the electric energy distribution network, such as currently available and maximally providable power and currently absorbable and releasable energy by transformation of the quantities characterizing the battery technology.
With the provision of a base module designated as AC battery in contrast to a DC battery an interface uniform in terms of control is provided to a whole system, which creates the prerequisites for a use of different topologies of power electronic components and electrochemical energy accumulators with different technology.
The abstracting function of the AC battery management or the division into a battery-specific functionality creates an optimized operation on the basis of abstract battery models in conjunction with a battery power plant management. The AC batteries with a uniform energy-related behavior provide for the design of a power plant management which with different battery technologies can fulfill its task for example as hybrid power plant without technology-specific adaptations.
The definition of AC batteries, which contain identical or different topologies of power electronic systems such as inverters, converters and DC/DC converters, and DC batteries including fuel cells, which have the same or different chemical and/or physical properties, and which at their points of common coupling and with respect to their communication interfaces with a superordinate battery power plant management system show an identical behavior, provides for a simple control of an overall system composed of many AC batteries, a minimization of the susceptibility to failure of the overall system due to a defined control and detection of the state of charge (SOC) and state of health (SOH) of each individual AC battery, and an easy expansion of the overall system by including identical AC batteries, even when the same are arranged remote from each other, as well as an arbitrary exchange of individual AC batteries, without a change occurring at the point(s) of common coupling.
An apparatus for storing electric energy in electrochemical energy accumulators and for exchanging electric energy with an electric energy distribution network via a power electronic system connecting the electrochemical energy accumulators with the electric energy distribution network is characterized by at least one base module (AC batteries) comprising
Via a generic model of the battery-typical operating limits and phenomena, the AC battery as functional element of an energy distribution network thus realizes a uniform depiction of the DC source for an energy application, in particular
An AC battery consists of at least one DC/AC-converter and further power electronic components and battery units connected thereto on the DC voltage side and conceptionally serves as decoupling plane between a management system for the whole system for taking up, storing and releasing electric energy to an electric energy distribution network and the battery-technology-specific combination of power electronic components, DC batteries and, depending on the design variant, a transformer and forms the equivalent to a DC battery from the point of view of the electric energy technology.
In principle, the AC battery consists of
The aforementioned components of an AC battery represent placeholders for partial components more complex in terms of design, so that depending on the respective battery technology different topologies for inverters and DC batteries result from different marginal conditions such as for example the voltage swing of DC batteries dependent on the state of charge or the necessary intermediate circuit voltage for the output voltage of the inverters.
From the different marginal conditions the following variants result, for example:
In a first variant, the AC batteries include several electrochemical energy storage modules connected in parallel with DC batteries having the same chemical and/or physical properties and with a battery management system associated to each electrochemical energy storage module, which controls and monitors the electrochemical energy storage module.
In a second variant, the AC batteries include several electrochemical energy storage modules connected in parallel in groups with DC batteries having the same chemical and/or physical properties and with a battery management system associated to each electrochemical energy storage module, which controls and monitors each electrochemical energy storage module, wherein the electrochemical energy storage modules connected in parallel in groups are connected with an inverter via a DC/DC-converter associated to each group.
Alternatively, the AC batteries include several electrochemical energy storage modules connected in parallel with DC batteries having different chemical and/or physical properties and with a battery management system associated to each electrochemical energy storage module, which controls and monitors the electrochemical energy storage module.
In this embodiment, different types of DC batteries can be combined in groups in an AC battery, wherein the data of the respective DC battery groups are input into the AC battery management or are retrieved from the AC battery management by the battery management systems, so that the AC battery management is able to correspondingly control and monitor the different DC battery groups.
The power electronic modules can consist of an inverter, which on the DC side is connected to the electrochemical energy storage modules and on the AC side is connected to a power bus bar or an inverter connected to a point of common coupling directly as medium-voltage inverter or via a medium-voltage transformer and a medium-voltage power switch, or of at least one DC/DC converter connected to the electrochemical energy storage modules and of an inverter which on the DC side is connected to the DC/DC converter(s) and on the AC side is connected to a power bus bar directly or via a medium-voltage transformer and a medium-voltage power switch.
For providing a specified DC voltage, the electrochemical energy storage modules can include several series-connected DC batteries with the same chemical and/or physical properties.
AC batteries can be used both as low-voltage and as medium-voltage batteries in conjunction with different topologies of power electronic components.
Unless the inverter is designed as medium-voltage inverter, AC batteries formed as medium-voltage batteries contain a medium-voltage transformer connected with the output of a power electronic module, which via a medium-voltage power switch is connected with a power bus bar or a point of common coupling. The AC batteries contain two electrochemical energy storage modules with DC batteries having the same chemical and/or physical properties, which are connected with one inverter each, which are connected to the primary windings of a three-winding transformer which on the secondary side is connected with the power bus bar or a point of common coupling.
In this embodiment, the AC battery is formed as low-voltage battery in which the DC batteries are connected to an inverter directly or via a DC/DC-converter, wherein the AC battery is connected to a power bus bar or a point of common coupling via a transformer and a power switch.
Alternatively, the AC battery can be formed as medium-voltage battery in which the DC batteries are connected to an inverter directly or via a DC/DC-converter, but which includes the possibly realized medium-voltage transformer and the medium-voltage power switch, so that it can directly be connected with the power bus bar or the point of common coupling.
A system consisting of several AC batteries with one point of common coupling is referred to as battery power plant whose control must be designed such that assured grid-side system services are ensured, in that the distribution of applications and tasks to the different AC batteries is optimized, in order to ensure a reliable and durable functionality of the battery power plant.
In use in a grid-forming battery power plant, i.e. in off-grid operation, the AC battery for example fulfills a realization of the features
In use of the AC battery in a grid-following battery power plant or control power plant, the AC battery for example provides
For each application, the AC battery fulfills a
As in use in a grid-forming battery power plant (off-grid operation) the AC batteries operated in parallel work as parallel voltage sources which divide the load produced at the point of common coupling between themselves, the load component of each individual AC battery is obtained by the battery power plant management system via the parametrization of the operating statics for active and reactive power via the interface. Among other things, this also provides for the asymmetric operation of the individual AC battery, in order to for example perform a calibration of the state-of-charge measurement.
A battery power plant formed as grid-forming power plant controls the power bus bar voltage and power bus bar frequency and provides short-circuit currents for triggering overcurrent protection mechanisms.
In operation as grid-following battery power plant (e.g. control power plant), the AC batteries operated in parallel work as parallel power sources which together provide the power required at the point of common coupling—e.g. in dependence on the grid frequency according to a required control static. The load component of each individual AC battery can be parametrized by the battery power plant management system via the uniform interface. Among other things, this also provides for the asymmetric operation of the individual AC battery, in order to for example perform a calibration of the state-of-charge measurement.
Beside the provision of active power, the parallel AC batteries also can be used for voltage maintenance at the point of common coupling (provision of reactive power in connection with a voltage control at the power bus bar).
Via communication interfaces, the AC battery management system preferably is connected with a battery power plant management system which actuates the medium-voltage power switches and a power switch connecting the point of common coupling with the energy distribution network.
As an alternative to the provision of grid system services or as grid-forming power plant, the battery power plant can be operated as hybrid power plant in conjunction with renewable energy sources and for example in load-following operation ensure the maintenance of feed-in limitations at the common feed-in point (“peak-shaving”), control a specified power at the point of common coupling of the energy distribution network in dependence on the grid frequency, a load sequence or the like.
With reference to several exemplary embodiments illustrated in the drawing the idea underlying the invention will be explained in detail. In the drawing:
Electrochemical energy accumulators or batteries are DC systems in construction, which depending on the battery technology show a different characteristic electrical behavior at an electrical interface.
Lithium-ion batteries with their very high ratio of power to energy (c-rate of 1 and higher) are particularly useful as short-term accumulators and for the compensation of large short-term fluctuations by the provision of control power.
Sodium-sulfur batteries, on the other hand, have a very high storage capacity with a c-rate of 1/6. Hence, these high-temperature batteries are particularly suitable for the compensation of daily fluctuations of wind and solar energy.
Accumulators on the basis of vanadium redox flow have almost no self discharge, so that they are excellently suitable for example as seasonal accumulators. Because the energy source of vanadium redox flow batteries does not age or wear, they have an almost unlimited durability with little maintenance effort and depending on requirement, power and energy can be separated and be scaled flexibly.
In
Both qualitatively represented characteristic curves of lithium-ion batteries among other things show a different capacity depending on the discharging current, beside a typical cell voltage dependent on the state of charge. In addition, cell aging and hence also the remaining cell capacity depends on different influencing factors such as e.g. the history of the charging and discharging currents, the prevailing state of charge, and the temperature conditions.
Larger DC batteries consist of a suitable interconnection of individual cells to modules and of several modules to batteries, but generally are not prepared for energy applications, because
As functional element of a battery power plant the AC battery thus fulfills the task of realizing a uniform depiction of the DC voltage source for an energy application via a generic model of the battery-typical operating limits and phenomena and among other things comprises
This encapsulation of battery-typical properties of an electrochemical energy accumulator or a DC battery as well as the requirements of an AC battery uniform in terms of energy provide for the design of a power plant management which with different battery technologies without technology-specific adaptations can fulfill its function for example as hybrid power plant.
When determining the state of charge of battery systems it is assumed that the state-of-charge measurements of battery systems generally are based on the formation of an energy balance by taking account of models for the current cell behavior. All models assume that with increasing operating period the state-of-charge measurement is subject to a more or less pronounced drift, so that the state-of-charge measurement of a battery system involves an indefiniteness which greatly increases with time. Therefore, all battery systems regularly must approach defined states of charge, for example a full charge, in order to calibrate the determination of the state of charge, wherein for carrying out the calibration the battery system employs a fixed operating regime.
As an example,
To enable a battery power plant management superordinate to the AC battery management system to secure the influence of the calibration of the state of charge on the point of common coupling, the AC battery offers an estimate of the calibration schedule, i.e. of the course of the charging power over time, by indicating the desire for a calibration. This is shown in
Properties deviating therefrom are applicable for sodium-sulfur batteries and accumulators on the basis of vanadium redox flow. Since the exact requirements for an accumulator vary depending on the case of application and in part also on a project-specific basis, which concerns many properties, but especially the ratio of power and energy, which both in lithium-ion and in sodium-sulfur batteries is specified by the basic structure of the cells, different technologies are combined in a hybrid battery, if necessary, so that the advantages of the different technologies can be utilized.
The battery management systems 20.1 to 20.M monitor the DC batteries and provide a communication interface to the AC battery management.
The first AC battery 1.1 includes a DC/DC-converter 3.1 connected with the DC battery groups 2.1 connected in parallel, which is connected with an inverter 4.1 to which a first transformer 7.1 is connected.
Further AC batteries have a power electronic topology like the first AC battery 1.1 or are constructed corresponding to the M-th AC battery 1.M, in which the DC batteries 2.M connected in parallel are directly connected with an inverter 4.M which is connected to a transformer 7.M. The different topology of the individual AC batteries 1.1 or 1.M for example is based on a different battery technology and/or a different number of series-connected DC batteries of the individual DC battery groups 2.1 or 2.M.
Via a communication line 16 the AC battery management 5.1 or 5.M of the AC batteries 1.1 to 1.M is connected with a power electronic controller 40.1 or 40.M, which with respect to the first AC battery 1.1 is connected with the inverter 4.1 via a communication line 17 and with the DC/DC-converter 3.1 via a communication line 18 or with respect to the M-th AC battery 1.1. via a communication line 17 with the inverter 4.M. Furthermore, the AC battery management 5.1 or 5.M is connected with the battery management systems 20.1 or 20.M of the DC batteries 2.1 to 2.M via a communication line 15.
A battery power plant management 6 associated to all AC batteries 1.1 to 1.M is connected with the AC battery management 5.1 to 5.M of the AC batteries 1.1 to 1.M via communication lines 12, and via a communication line 13 is connected with the power switches 8.1 to 8.M associated to the individual AC batteries 1.1 to 1.M and via a communication line 14 with the PCC power switch 9.
The AC battery management 5.1-5.N optimizes the use of the partial components of the AC batteries 1.1-1.N and thus for example provides for a maintenance of the partial components in ongoing operation, whereas the battery power plant management 6 controls the cooperation of the AC batteries 1.1-1.N on the AC side, calibrates the AC batteries 1.1-1.N and distributes the requirements for the battery power plant to individual AC batteries 1.1-1.N such that a homogeneous battery system is visible to the outside. As will be explained in detail below, both AC batteries 1.1-1.N with different power electronic topology and DC batteries with different battery technology or of a different type can be combined and their common use can be optimized.
In a third embodiment of a battery power plant BKW shown in
In this embodiment, individual or all AC batteries 1.1-1.N can contain DC batteries 21.1-21.M each with the same or a different battery technology. For example, the AC battery 1.1 can include DC batteries 21.1 with the same battery technology, whereas the AC battery 1.N includes DC batteries 211.M, 212.N connected in parallel in groups, whose groups 211.M and 212.N each have the same battery technology or are of the same battery type, but which are formed differently from group to group.
In this configuration of an AC battery 1.N the AC battery management 5.M performs the control and monitoring of the groups 211.M, 212.N with different battery technology, after the corresponding data were input into the AC battery management 5.M or after the battery management systems 22.M provided in a group have output corresponding identification data to the AC battery management 5.M.
A fourth embodiment is schematically shown in
Analogous to the embodiment according to
The embodiments according to
In all exemplary embodiments shown in
The form of the parametrization of the total behavior depends on the respective case of application of the battery power plant. Whereas in off-grid operation schedules concerning the expected power band for a planning horizon are communicated on the part of an energy management system together with the desired control behavior around the operating points obtained and thus the battery power plant management 6 is allowed to make an optimization due to schedules, the requirements in use of a battery power plant for system services in the control power plant application result from a “grid code” and the current grid frequency.
An example for the superordinate operating tasks of the battery power plant management 6 to secure the fulfillment of external requirements at the point of common coupling 10 such as the specification of an expected power band and a power static by taking account of the internal requirements by the individual AC batteries 1.1 to 1.N is a calibration of the state of charge SOC of the AC battery 1.N according to
Due to specifications A at the point of common coupling 10, the battery power plant management 6 determines adapted operating points for the remaining batteries 1.1 to 1.M, in order to meet the specifications A at the point of common coupling 10, or it must dismiss the state-of-charge calibration possibly by assessment of the still rising indefiniteness of the state of charge of the battery power plant for the duration of the schedule. The specifications A at the point of common coupling 10 must be in correspondence with possible operating points calculated by the battery power plant management 6 and the internal requirements of the AC battery 1.N such as the planning of a state-of-charge calibration SOC for the AC battery 1.N, which in the form of the estimated power schedule for the duration of the calibration represent constraints for the operation of the AC battery 1.N.
Further requirements for the battery power plant management 6 can consist in the
The battery power plant BKW need not necessarily be installed at one place, but also can be composed of many AC batteries or units arranged spatially remote from each other. An example for this is shown in
In modification of the battery power plant schematically shown in
Analogous to the configuration of a battery power plant BKW according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 211 951.8 | Jun 2013 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/063281 | 6/24/2014 | WO | 00 |
