CORRECTED BATTERIAL TERMINAL VOLTAGE

Description

TECHNICAL FIELD

[0001] Various examples concern techniques for determining a corrected terminal voltage for batteries coupled to a load via a DC / AC converter. This can be used, for example, to correct for noise currents in an inverter, particularly for an open-circuit scenario. BACKGROUND

[0002] Rechargeable batteries are used in a variety of application scenarios. Examples include traction batteries in electric vehicles and stationary energy storage systems, for example, to cushion peak loads in a power grid.

[0003] In various application scenarios, it is typically helpful to determine battery condition values ​​with particular precision. For example, it is desirable to determine the state of charge—that is, the available capacity compared to the capacity in a fully charged state.

[0004] Document DE 10 2019 115705 A1 discloses an estimation of the battery state of an electrical system using the electrode transient model. The electrical system includes a battery pack, sensors, and a controller. The configured sensors output measured state signals indicating an actual state of the battery backside, including a corresponding actual voltage, current, and temperature of each of the plurality of battery cells. The controller executes a method to generate, in response to the measured state signals, an estimated state of the plurality of battery cells using a respective open-circuit voltage and a low-frequency transient voltage of each of the plurality of battery cells.The controller estimates the low-frequency transient voltages using a porous electrode transient (PET) model as part of a model set. The PET model includes open-circuit voltage elements that represent an uneven charge distribution within a cell electrode. The battery pack's state of charge (SOC) is estimated based on the estimated voltages. An operating state of the electrical system is controlled in real time in response to the estimated SOC.

[0005] Document EP 3 267 551 A1 discloses a battery control device capable of obtaining a charge / discharge current with high accuracy. The battery control device includes a timing setting unit that calculates a voltage difference obtained by subtracting a calculated open-circuit voltage from a measured rest voltage, and sets first and second timings at which an absolute value of the voltage difference becomes equal to or less than a predetermined value and an absolute value of a difference in the open-circuit voltage becomes equal to or less than a predetermined value.The battery control device further includes the current integral amount calculation unit for obtaining the current integral amount, which is an integral amount with time of the current flowing through the cell from the first time point to the second time point, the current correction amount calculation unit calculating the current error included in a detection signal output from the current detection unit and setting the current error as the current correction amount based on the current integral amount and a time from the first time point to the second time point, and the current correction unit correcting the detection signal using the current correction amount.

[0006] US 2018 / 059190 A1 discloses a state estimation of an energy system. A number of variations may include products and methods for estimating the state of an energy system. At least one sensor may monitor a voltage and current of the energy storage system. An electronic control unit may be communicatively coupled to the energy storage system and receive inputs from the sensor. A circuit may be representative of the energy storage system and may be defined accordingly in the electronic control unit. The circuit may estimate a state of the energy storage system from a measured voltage and current.

[0007] Document EP 2 857 854 A1 discloses a battery control device that calculates at least an allowable current and an allowable power during charging / discharging of a battery from an open circuit voltage and an internal resistance of the battery and corrects the open circuit voltage and / or the internal resistance according to the charging / discharging situations of the battery. SUMMARY OF THE INVENTION

[0008] Therefore, there is a need for techniques to determine one or more battery condition values ​​with particular accuracy.

[0009] This problem is solved by the features of the independent patent claims. The features of the dependent patent claims define embodiments.

[0010] According to various examples, it is possible to determine one or more battery condition values ​​based on a corrected value for a battery terminal voltage. Examples of condition values ​​include the aging state or the state of charge.

[0011] The terminal voltage correction can be based on a correction term determined taking into account a DC / AC converter through which the battery is connected to a load. For example, different correction terms can be used for different types of DC / AC converters. It is also conceivable, in particular, for the correction term to be determined based on one or more operating parameters of the DC / AC converter.

[0012] A method includes obtaining a measured value for a terminal voltage of a battery. The battery is coupled to a load via a DC / AC converter. The method also includes determining a corrected value of the terminal voltage based on the measured value of the terminal voltage and a correction term. The correction term depends on one or more operating parameters of the DC / AC converter. The method also includes determining a battery health value based on the corrected value of the terminal voltage.

[0013] A computer program or a computer program product or a computer-readable storage medium comprises program code. This program code can be loaded and executed by a processor. When the processor executes the program code, a method is performed. The method comprises obtaining a measured value for a terminal voltage of a battery. The battery is coupled to a load via a DC / AC converter. The method also comprises determining a corrected value of the terminal voltage based on the measured value for the terminal voltage and further based on a correction term. The correction term depends on one or more operating parameters of the DC / AC converter. The method also comprises determining a condition value of the battery based on the corrected value of the terminal voltage.

[0014] A device comprises a processor and a memory. The processor can load program code from the memory and execute it in the program code. This causes the processor to obtain a measured value for a terminal voltage of a battery. The battery is coupled to a load via a DC / AC converter. The processor also determines a corrected value for the terminal voltage. This is based on the measured value for the terminal voltage and a further correction term. The correction term depends on one or more operating parameters of the DC / AC converter. The processor also determines a health value for the battery based on the corrected value for the terminal voltage.

[0015] The features set forth above and features described below may be used not only in the corresponding explicitly set forth combinations, but also in further combinations or in isolation, without departing from the scope of the present invention, which is defined by the appended claims. SHORT DESCRIPTION OF THE CHARACTERS

[0016] FIG. 1 schematically illustrates a system comprising several batteries and a server according to various examples. FIG. 2 illustrates details of a battery according to various examples. FIG. 3 illustrates details of a server according to various examples. FIG. 4 schematically illustrates a system comprising a battery, a DC / AC converter and a load according to various examples. FIG. 5 is a flowchart of an example method. FIG. 6schematically illustrates an equivalent circuit for a battery according to various examples. DETAILED DESCRIPTION OF EMBODIMENTS

[0017] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0018] The present invention is explained in more detail below using preferred embodiments with reference to the drawings. In the figures, identical reference numerals designate identical or similar elements. The figures are schematic representations of various embodiments of the invention. Elements shown in the figures are not necessarily drawn to scale. Rather, the various elements shown in the figures are depicted in such a way that their function and general purpose will be understood by those skilled in the art. Connections and couplings between functional units and elements shown in the figures can also be implemented as an indirect connection or coupling. A connection or coupling can be implemented wired or wirelessly. Functional units can be implemented as hardware, software, or a combination of hardware and software.

[0019] Techniques related to the characterization of rechargeable batteries are described below. The techniques described herein can be used in conjunction with a wide variety of battery types, for example, lithium-ion-based batteries such as lithium nickel manganese cobalt oxide batteries or lithium manganese oxide batteries.

[0020] The batteries described herein can be used for batteries in various application scenarios, for example, for batteries used in devices such as motor vehicles or drones or portable electronic devices such as mobile devices, such as traction batteries. It would also be conceivable to use the batteries described herein in the form of stationary energy storage devices. Indoor or outdoor applications are conceivable, which differ primarily in terms of temperature ranges. Application scenarios include: stationary energy storage in a micro-grid; energy storage for mobile applications; low-load energy storage; energy storage for light electric vehicles such as bicycles or scooters; energy storage for electric passenger cars; indoor applications; and outdoor applications.

[0021] Various examples of the invention relate to techniques for determining a battery's state value. Examples of state values ​​that can be determined based on the terminal voltage include: state of charge, state of aging, or performance. Further examples of state values ​​are battery capacity and impedance.

[0022] When determining the condition value, the battery terminal voltage can be taken into account according to various examples. In particular, a corrected value of the battery terminal voltage can be considered. The corrected value compensates for or reduces distortions in the terminal voltage due to interference currents or other influences.

[0023] Various examples of the invention are based on the realization that batteries are typically connected to a load via a power electronics circuit. The load can be, for example, the drive of an electric vehicle or an energy grid, such as a micro-grid, in a stationary battery storage system. Motors require alternating current, and the power electronics circuit can convert the battery's direct current into alternating current (DC / AC converter). Inverter circuits are typically used to convert the battery's direct current into alternating current. A typical inverter circuit provides a three-phase current flow with a specific frequency on the AC side.

[0024] It has been observed that the DC / AC converter can cause interference currents that distort the terminal voltage measurement. This is especially true in an open-circuit scenario. The terminal voltage is measured without any load from the consumer (open-circuit scenario). This means that the electrical power output by the inverter circuit is low.

[0025] To determine the terminal voltage, a corresponding measured value of the battery voltage can be obtained, for example, from a battery management system. Various examples are based on the finding that the open-circuit state (but also other states) in typical inverter circuits is associated with significant interference currents.

[0026] This is due to the switching processes of switching elements. Rapid changes in current flow cause interference currents. For example, typical inverter circuits may include switching elements that can be switched in phase, particularly in the idle state. In an inverter circuit with an IGBT switching topology, all half-bridges switch simultaneously. The interference level on the DC side of the inverter circuit in the idle state is correspondingly high. This affects both current flows in common mode and in differential mode with the switching cycle of the switching elements.

[0027] Accordingly, according to various examples described herein, it is possible to obtain a measured value for the terminal voltage of the battery, wherein the battery is coupled to a load via the DC / AC converter. A corrected value of the terminal voltage can then be determined based on this measured value of the terminal voltage, as well as a correction term. Furthermore, the method also includes determining a state value of the battery based on the corrected value of the terminal voltage.

[0028] The correction term can therefore account for electromagnetic interference caused by the DC / AC converter. In particular, the electromagnetic interference can include current flows induced, for example, by magnetic fields or other transient effects caused by the switching of the DC / AC converter's switching elements.

[0029] The correction term can depend on one or more operating parameters of the DC / AC converter. By taking one or more operating parameters of the DC / AC converter into account, the correction term can be determined dynamically, depending on the DC / AC converter's operating conditions. This allows the correction term to be determined with particular precision.

[0030] Various examples are based on the realization that the size of the correction term may depend on a switching voltage of the switching elements of the DC / AC converter, a switching frequency of the switching elements of the DC / AC converter and / or a total impedance of the system comprising battery and DC / AC converter.

[0031] For example, it has been observed that common-mode interference in a car inverter with a noise level of 140 dBµV corresponds to an interference voltage of 10 V, caused by common-mode currents, which arise, for example, from parasitic capacitances of the switching elements with respect to the heat sink housing ground. Common-mode interference currents with a switching frequency of approximately 8 A have also been observed in a stationary battery system coupled to a grid.

[0032] The induced common-mode or differential-mode interference currents are fed from the battery as an energy source. This means that even without electrical power being delivered to the load—i.e., in the idle scenario—energy is drawn from the battery. This means that the battery is effectively loaded, and accordingly, the measured value for the battery terminal voltage is distorted compared to the nominal terminal voltage. This distortion can be accounted for by the correction term.

[0033] Different techniques are conceivable for determining the correction term in the various variants. Some variants are shown below in Table 1. TABLE 1: Different operating parameters of the DC / AC converter that can be considered when determining the correction term. Short description Example implementation I Switching voltage and / or switching frequency For example, it would be possible for the correction term to be determined as a function of the switching voltage and / or the switching frequency of a driver of the switching elements of the DC / AC converter. For example, it would be conceivable for corresponding operating parameters to be measured or transmitted. For example, corresponding operating parameters could be tapped in a digital domain of the driver and provided to the unit that determines the correction term. II Measurement of interference currents The interference currents can also be measured. For this purpose, current measuring sensors can be provided, for example, on the DC side of the DC / AC converter. For example, the alternating currents could be measured inductively.

[0034] For example, it would be conceivable that the correction term—for example, depending on the operating parameters listed in Table 1—is looked up in a lookup table. It would also be possible to have a pre-parameterized model that provides the correction term depending on the measurement parameters.

[0035] There are, in turn, different variants for filling a corresponding lookup table or parameterizing such a model. For example, it would be conceivable for the correction term to be determined empirically in a laboratory setup, perhaps as a function of the operating parameters of the DC / AC converter. For example, an EMC measurement of the power electronics could be performed, for example, according to the CISPR 25:2016 c standard. It is then possible to use the correction table to approximate the true terminal voltage using the corrected value.

[0036] FIG. 1illustrates aspects related to a system 80. The system 80 includes a server 81 connected to a database 82. Furthermore, the system 80 includes communication links 49 between the server 81 and each of a plurality of batteries 91-96. The communication links 49 could be implemented, for example, via a cellular network. For example, the batteries 91-96 may form an ensemble, i.e., all be of the same type.

[0037] In FIG. 1 It is illustrated by way of example that the batteries 91-96 can send measurement data 41 to the server 81 via the communication connections 49. For example, it would be possible for the measurement data 41 to be indicative of one or more measured values ​​of state variables of the respective battery 91-96, e.g., state of charge, current flow, voltage, temperature, etc.

[0038] In FIG. 1It is also illustrated by way of example that the server 81 can send control data 42 to the batteries 91-96 via the communication connections 49. For example, it would be possible for the control data 42 to indicate one or more operating limits for the future operation of the respective battery 91-96. For example, the control data could indicate one or more control parameters for thermal management of the respective battery 91-96 and / or charge management of the respective battery 91-96. By using the control data 42, the server 81 can therefore influence or control the operation of the batteries 91-96. This could, for example, be based on an aging value that is determined by the server 81 for the respective battery.

[0039] In FIG. 1In addition, a state value 99 is schematically illustrated for each of the batteries 91-96. Examples of state values ​​are, for example, state of charge (SOC), aging state, etc. Techniques are described below for determining such a state value 99 with particular accuracy.

[0040] FIG. 2 illustrates aspects related to batteries 91-96. Batteries 91-96 are coupled to a respective device 69. This device—e.g., an electric motor—is powered by electrical energy from the respective battery 91-96. It therefore represents an electrical load.

[0041] The batteries 91-96 comprise or are associated with one or more management systems 61, e.g., a BMS or other control logic such as an on-board unit in the case of a vehicle. The management system 61 can be implemented, for example, by software on a CPU. Alternatively or additionally, an application-specific integrated circuit (ASIC) or a field-programmable gated array (FPGA) could be used, for example. The batteries 91-96 could communicate with the management system 61, for example, via a bus system. The batteries 91-96 also comprise a communication interface 62. The management system 61 can establish a communication connection 49 with the server 81 via the communication interface 62.

[0042] While in FIG. 2 While the management system 61 is drawn separately from the batteries 91-96, in other examples it would also be possible for the management system 61 to be part of the batteries 91-96.

[0043] In addition, the batteries 91-96 comprise one or more battery blocks 63. Each battery block 63 typically comprises a number of battery cells connected in parallel and / or in series. Electrical energy can be stored there.

[0044] Typically, the management system 61 can access one or more sensors in the one or more battery blocks 63. The sensors can, for example, measure state variables of the respective battery and provide corresponding measured values, such as the current flow and / or the voltage in at least some of the battery cells. Alternatively or additionally, the sensors can also measure other state variables associated with at least some of the battery cells, such as temperature, volume, pressure, etc. The management system 61 can then be configured to send one or more such measured values ​​from sensors in the form of measurement data 41 to the server 81.

[0045] The measured values ​​can be preprocessed to a greater or lesser extent by the management system 61 before being sent as the measured data 41. For example, compression would be conceivable, such as in the form of a load spectrum. Measured values ​​could also be filtered, for example, based on events.

[0046] FIG. 3 Illustrates aspects related to server 81. Server 81 includes a processor 51 and a memory 52. ​​Memory 52 may include a volatile storage element and / or a non-volatile storage element. Furthermore, server 81 also includes a communications interface 53. Processor 51 may establish a communications link 49 with each of batteries 91-96 and database 82 via communications interface 53.

[0047] For example, program code may be stored in memory 52 and loaded by processor 51. Processor 51 may then execute the program code. Executing the program code causes processor 51 to perform one or more of the following processes, as described in detail in connection with the various examples herein: characterizing batteries 91-96; determining a corrected value for the terminal voltage of a battery; determining a battery condition value based on the corrected value of the terminal voltage; etc.

[0048] FIG. 4 schematically illustrates a system 200 comprising a battery 201, a DC-AC converter 202, and a load 203. The battery 201 may be one of the batteries 91-96 from FIG. 1 implement. Accordingly, the load 203 may correspond to the device 69. The DC / AC converter 202 may, for example, use a half-bridge architecture or a full-bridge architecture.

[0049] During operation of the system 200, interference currents 250 may occur, which distort the measurement of the terminal voltage of the battery 201.

[0050] To correct such effects, status data 210 relating to one or more operating parameters of the DC / AC converter 202 can be provided. For this purpose, a corresponding interface 204 of the DC / AC converter 202 can be provided, which provides the status data 210. For example, the interface 204 could be implemented by a microcontroller that controls a driver circuit for switching elements of the DC / AC converter 202. For example, it would be conceivable for the status data 210 to be transmitted to the server 81, e.g., as part of the measurement data 41 (see FIG. FIG. 1 ).

[0051] Based on the status data 210, a corrected value of the terminal voltage can then be determined. This can serve as the basis for determining a status value 99 of the battery 201.

[0052] A corresponding correction term can be determined, for example, on the server 81; however, it would also be conceivable that the correction term is already determined by the management system of the battery 201 (see FIG. 2 : Management system 61); in such a case, the status data 210 can be transferred to the management system.

[0053] FIG. 5 is a flowchart of an exemplary method. The method of FIG. 5 can be executed, for example, by server 81. It would also be conceivable that the procedure FIG. 5 at least partly carried out by a management system of one of the batteries 91-96 (see FIG. 1 ). In FIG. 5 Optional blocks are shown with dashed lines.

[0054] First, a measured value for the battery terminal voltage is obtained in block 3005. The terminal voltage is defined between the positive and negative poles of the battery. This can be done, for example, in the form of measurement data 41.

[0055] In some examples, the measured value for the terminal voltage can be obtained in a nominal idle state of the battery 91-96. The nominal idle state can, for example, be caused by a rest state of the respective consumer (see FIG. 2 : Device 69; and FIG. 4 : Load 203). Then the measured value for the terminal voltage describes an open-circuit voltage of the battery.

[0056] Then, optional block 3010 can be used to obtain a measured value for one or more operating parameters of the DC / AC converter (see FIG. 4: Status data 210). It is not necessary in all implementations to obtain a current measured value for the operating parameters of the DC / AC converter. Rather, in some examples, it would also be conceivable for one or more operating parameters of the DC / AC converter to be fixed, meaning they do not have to be determined dynamically based on measured values.

[0057] Depending on the implementation of the one or more operating parameters, different measured values ​​can be obtained in block 3010. In one example, it would be conceivable, for example, that a measured value for a switching voltage and / or a switching frequency of one or more switching elements (e.g., field-effect transistors or other transistors) of the DC / AC converter is obtained.

[0058] In another example, it would be conceivable that a measured value for a current flow in the DC / AC converter - for example a common-mode current flow and / or a differential-mode current flow - is obtained.

[0059] It is then optionally possible to determine a correction value for the measured terminal voltage in block 3015. This is based on the measured value for one or more operating parameters from block 3010. In some examples, it would also be conceivable for the correction value to be fixed.

[0060] The correction value could be determined, for example, by looking up a lookup table. For example, the lookup table could contain different correction values, for example, for different switching voltages and / or switching frequencies of the switching elements of the DC / AC converter. It would also be conceivable to use a parameterized model instead of a lookup table, which receives one or more operating parameters of the DC / AC converter as input and provides the correction value as output. Such a model could, for example, be parameterized based on laboratory measurements.

[0061] Subsequently, in block 3020, the corrected value of the terminal voltage is determined based on the measured value from block 3005 and a correction value, such as the correction value determined in block 3015. As a general rule, there are different ways to determine the corrected value of the terminal voltage. One possibility would be to consider corresponding voltage sources for the control voltage and terminal voltage in a battery equivalent circuit. One such example is shown in FIG. 6 shown. In FIG. 6 A battery equivalent circuit is shown. This has a series of resistors 405, in particular a DC resistor and AC resistors. In this respect, the battery equivalent circuit is impedance-based. FIG. 6It is also evident that a series connection of a voltage source 401 – which has a voltage corresponding to the corrected value of the terminal voltage – and another voltage source 402 – which has a voltage corresponding to the correction term – is used. The sum of the voltages of the voltage sources 401, 402 corresponds to the measured value for the terminal voltage.

[0062] Then, in block 3025, a battery state value 99 can be determined based on the corrected terminal voltage value from block 3020, i.e., voltage source 401. For example, a current state of charge (SOC) could be determined, or battery aging could also occur.

[0063] Of course, the features of the previously described embodiments and aspects of the invention can be combined with one another. In particular, the features can be used not only in the described combinations, but also in other combinations or on their own, without departing from the scope of the invention, which is defined by the appended claims.

Claims

1. Method, which comprises: - obtaining a measured value for a terminal voltage of a battery (91-96, 201), which is coupled with a load (69, 203) via a DC / AC inverter (202), - determining a corrected value of the terminal voltage based on the measured value for the terminal voltage and furthermore based on a correction term which depends on one or more operating parameters of the DC / AC inverter (202), and - determining a state value (99) of the battery (91-96, 201) based on the corrected value of the terminal voltage, characterized in that the method further comprises: - obtaining a measured value for a switching voltage and / or a switching frequency of one or more switching elements of the DC / AC inverter (202), wherein the one or more operating parameters of the DC / AC inverter (202) include the switching voltage and / or the switching frequency.

2. Method according to Claim 1, wherein the method furthermore comprises: - obtaining a measured value for a current flow in the DC / AC inverter (202), wherein the one or more operating parameters of the DC / AC inverter (202) include current flow in the DC / AC inverter (202).

3. Method according to Claim 2, wherein the current flow comprises at least one of a common-mode current flow and a differential-mode current flow.

4. Method according to one of the preceding claims, wherein the method furthermore comprises: - determining the correction term based on the one or more operating parameters of the DC / AC inverter (202) by means of a lookup in a lookup table.

5. Method according to one of the preceding claims, wherein the method furthermore comprises: - parametrizing an impedance-based replacement circuit (400) of the battery (91-96, 201) based on the corrected value of the terminal voltage.

6. Method according to one of the preceding claims, wherein the measured value for the terminal voltage describes an open-circuit voltage of the battery (91-96, 201).

7. Method according to one of the preceding claims, wherein the method furthermore comprises: - receiving state data (210) which are indicative for the one or the plurality of operating parameters of the DC / AC inverter (202).

8. Device (61, 81) having a processor which is set up for executing the following steps: - obtaining a measured value for a terminal voltage of a battery (91-96, 201), which is coupled with a load (69, 203) via a DC / AC inverter (202), - determining a corrected value of the terminal voltage based on the measured value for the terminal voltage and furthermore based on a correction term which depends on one or more operating parameters of the DC / AC inverter (202), and - determining a state value (99) of the battery (91-96, 201) based on the corrected value of the terminal voltage, characterized in that the processor is furthermore set up for executing the following steps: - obtaining a measured value for a switching voltage and / or a switching frequency of one or more switching elements of the DC / AC inverter (202), wherein the one or more operating parameters of the DC / AC inverter (202) include the switching voltage and / or the switching frequency.

9. Device according to Claim 8, wherein the processor is furthermore set up for executing the method according to one of Claims 1 to 7.