Energy storage device and method for operating an energy storage device

Abstract

Energy storage device (1), with: a plurality of parallel-connected power supply branches (Z), each coupled between an output terminal (1a, 1b, 1c) and a reference potential rail (4), wherein each of the power supply branches (Z) has a plurality of series-connected energy storage modules (3), each comprising: an energy storage cell module (5) which has at least one energy storage cell (5a, 5k), a coupling device (7) with coupling elements (7a, 7d; 7b, 7c) which are designed to selectively connect the energy storage cell module (5) to the respective energy supply branch (Z) or to bypass it in the respective energy supply branch (Z), and a current sensor device (8, 9a, 9b) which is connected in series to the at least one energy storage cell (5a, 5k) and which is designed to measure a current through the energy storage cell module (5) and to output it as a module current measurement signal; and a control unit (6) which is coupled to each of the current sensor devices (8, 9a, 9b) and which is designed to process the module current measurement signals of the current sensor devices (8, 9a, 9b), wherein the control unit (6) is further designed to control the coupling devices (7) of the energy storage modules (3) either in pulse-width modulated operation or in continuous current operation, and to average only the module current measurement signals of the current sensor devices (8, 9a, 9b) of those energy storage modules (3) which are controlled in continuous current operation to form a branch current measurement signal.

Description

[0001] The invention relates to an energy storage device and a method for operating an energy storage device, in particular a modular battery direct converter. State of the art

[0002] It is becoming apparent that in the future, electronic systems that combine new energy storage technologies with electric drive technology will increasingly be used both in stationary applications, such as wind turbines or solar systems, and in vehicles, such as hybrid or electric vehicles.

[0003] The feeding of multiphase power into an electrical machine is typically accomplished by a converter in the form of a pulse-controlled inverter. This involves converting a DC voltage provided by a DC link into a multiphase AC voltage, such as a three-phase AC voltage. The DC link is supplied by a string of battery modules connected in series. To meet the power and energy requirements of a specific application, several battery modules are often connected in series in a traction battery.

[0004] Connecting multiple battery modules in series poses the problem that the entire string fails if a single battery module fails. Such a failure of the power supply string can lead to a failure of the entire system. Furthermore, temporary or permanent performance reductions in a single battery module can lead to performance reductions in the entire power supply string.

[0005] US Pat. No. 5,642,275 A describes a battery system with an integrated inverter function. Systems of this type are known as multilevel cascaded inverters or battery direct inverters (BDIs). Such systems comprise direct current sources in multiple energy storage module strings, which can be connected directly to an electrical machine or an electrical grid. Single-phase or multi-phase supply voltages can be generated. The energy storage module strings comprise a plurality of energy storage modules connected in series, with each energy storage module having at least one battery cell and an associated controllable coupling unit, which allows the respective associated battery cell to be bypassed or the respective associated battery cell to be connected into the respective energy storage module string depending on control signals.The coupling unit can be designed in such a way that it also allows the respective assigned battery cell to be connected with inverse polarity into the respective energy storage module string, or even to interrupt the respective energy storage module string. By appropriately controlling the coupling units, e.g., using pulse-width modulation, suitable phase signals can also be provided to control the phase output voltage, thus eliminating the need for a separate pulse-width inverter. The pulse-width inverter required to control the phase output voltage is thus, in a sense, integrated into the BDI.

[0006] Compared to conventional systems, BDIs typically exhibit higher efficiency, greater reliability, and significantly lower harmonic content in their output voltage. This reliability is ensured, among other things, by the ability to bridge defective, failed, or not fully performing battery cells by appropriately controlling the coupling units assigned to them in the power supply strings. The phase output voltage of an energy storage module string can be varied and, in particular, adjusted in stages by appropriately controlling the coupling units. The output voltage gradation results from the voltage of an individual energy storage module, with the maximum possible phase output voltage being determined by the sum of the voltages of all energy storage modules in an energy storage module string.

[0007] The documents DE 10 2010 027 857 A1 and DE 10 2010 027 861 A1, for example, disclose battery direct inverters with several battery module strings which can be connected directly to an electrical machine.

[0008] In such modularly configured battery systems, it is important to know the electrical operating parameters of the individual modules at all times during operation and throughout the entire operating cycle to ensure optimal performance. Current sensors are typically used for this purpose. These current sensors monitor the currents in each energy storage module or string for each energy storage module. The functionality, measurement deviations, and any linearity errors of these current sensors are crucial for selecting an optimal operating strategy tailored to the overall battery system.

[0009] There is therefore a need for a modular energy storage device and a method for operating a modular energy storage device with which current sensors that monitor the current consumption or input of energy storage cells of the energy storage device can be checked for functionality, measurement deviations and / or linearity errors and, if necessary, calibrated.

[0010] The document CN 1 03 901 257 A discloses a device and a method for measuring the current direction in a bridge arm of a modularized multi-stage power converter.

[0011] The document F. Khoucha et al., A 7-level single DC source cascaded H-bridge multilevel inverters control using hybrid modulation, The XIX International Conference on Electrical Machines - ICEM 2010, 2010 discloses a 7-level single DC source cascaded H-bridge multilevel inverter with hybrid modulation for use in electric and hybrid vehicles. Disclosure of the invention

[0012] According to a first aspect, the present invention provides an energy storage device having a plurality of parallel-connected energy supply branches, each coupled between an output terminal and a reference potential rail, wherein each of the energy supply branches has a plurality of series-connected energy storage modules. The energy storage modules each comprise an energy storage cell module having at least one energy storage cell, a coupling device having coupling elements designed to selectively connect the energy storage cell module to the respective energy supply branch or to bypass it in the respective energy supply branch, and a current sensor device connected in series to the at least one energy storage cell and designed to measure a current through the energy storage cell module and output it as a module current measurement signal.The energy storage device further comprises a control unit coupled to each of the current sensor devices and configured to process the module current measurement signals from the current sensor devices. The control unit is further configured to control the coupling devices of the energy storage modules either in pulse-width modulated operation or in continuous current operation, and to average only the module current measurement signals from the current sensor devices of those energy storage modules controlled in continuous current operation to form a branch current measurement signal.

[0013] According to a further aspect, the present invention provides an electric drive system comprising an energy storage device according to the first aspect of the invention and a multi-phase electric machine having a plurality of phase lines, each of which is coupled to one of the output terminals of the energy storage device.

[0014] According to a further aspect, the present invention provides a method for operating an energy storage device according to the first aspect of the invention, comprising the steps of selecting a first number of energy storage modules of a power supply branch of the energy storage device, the coupling devices of which are controlled in a pulse-width modulated operation, selecting a second number of energy storage modules of the power supply branch of the energy storage device, the coupling devices of which are controlled in a continuous current operation, measuring the current flowing through the energy storage modules of the first number of energy storage modules to generate first current measurement signals, and calculating a branch current measurement signal by averaging only the first current measurement signals. Advantages of the invention

[0015] One idea of ​​the present invention is to perform the calibration of current sensor devices in a modular energy storage device centrally in a coordinating control unit. This control unit can coordinate the calibration specifically in those energy storage modules that are particularly suitable for measuring currents due to their functional operating state in generating output voltages of the energy storage device.

[0016] According to one embodiment of the energy storage device according to the invention, the coupling devices can comprise coupling elements in a full-bridge circuit or a half-bridge circuit.

[0017] According to a further embodiment of the energy storage device according to the invention, the current sensor devices can each have a shunt resistor or a Hall sensor for current measurement.

[0018] According to one embodiment of the energy storage device according to the invention, the control unit can further be designed to calculate a plurality of measurement differences of the module current measurement signals from the averaged branch current measurement signal, and to calibrate the current sensor devices of the energy storage modules on the basis of an associated measurement difference of the calculated plurality of measurement differences.

[0019] According to one embodiment of the method according to the invention, the method may further comprise the steps of calculating a plurality of measurement differences of the first current measurement signals to the averaged branch current measurement signal, and calibrating the current sensor devices of the first number of energy storage modules on the basis of an associated measurement difference of the calculated plurality of measurement differences.

[0020] According to one embodiment of the method according to the invention, the method may further comprise the steps of determining critical measurement differences which are above a predetermined measurement difference threshold, determining that current sensor devices of the first number of energy storage modules associated with the critical measurement differences are defective, and deactivating the defective current sensor devices and / or outputting a warning signal for detecting the defective current sensor devices.

[0021] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings. Short description of the drawings

[0022] They show: Fig. 1 is a schematic representation of a system with an energy storage device according to an embodiment of the invention; Fig. 2 is a schematic representation of an energy storage module of an energy storage device according to a further embodiment of the invention; and Fig. 3 a schematic representation of an energy storage module of an energy storage device according to a further embodiment of the invention.

[0023] Fig. Figure 1 shows a schematic representation of an electric drive system 100 with an energy storage device 1 for converting DC voltage provided in energy storage modules 3 into an n-phase AC voltage. The energy storage device 1 comprises a plurality of energy supply branches Z, of which Fig. 1 shows three energy storage modules which are suitable for generating a three-phase alternating voltage, for example for a three-phase electrical machine 2. However, it is clear that any other number of energy supply branches Z may also be possible. The energy supply branches Z may comprise a plurality of energy storage modules 3 which are connected in series in the energy supply branches Z. By way of example, in Fig. 1 shows three energy storage modules 3 per energy supply branch Z, although any other number of energy storage modules 3 may also be possible.

[0024] The energy storage device 1 has an output terminal 1a, 1b, 1c on each of the energy supply branches Z. The output terminals 1a, 1b, 1c of the energy storage device 1 are connected to phase lines 2a, 2b, and 2c, respectively, of the electrical machine 2. The electrical machine 2 can be, for example, a transverse flux machine, a switched reluctance machine, a synchronous machine, or an asynchronous machine, which, for example, has inductors connected to a star point.

[0025] The output terminals of the power supply branches Z that are not connected to the output terminals 1a, 1b, 1c are galvanically connected to one another to form a star point and together form a reference potential rail 4 of the power supply device 1. The reference potential 4 of this reference potential rail can, for example, be a ground potential. Even without further connection to a reference potential located outside the power supply device 1, the potential of the ends of the power supply branches Z that are connected to a star point can be defined as reference potential 4 by definition. The star point of the machine 2 can optionally be connected to the reference potential rail 4 of the power supply device via another line, the so-called star point line.

[0026] The electric drive system 100 may further comprise a control device 6 which is connected to the energy storage device 1 and by means of which the energy storage device 1 can be controlled in order to provide the desired output voltages at the respective output terminals 1a, 1b, 1c.

[0027] The energy storage modules 3 each have two output terminals 3a and 3b, via which an output voltage of the energy storage modules 3 can be provided. Since the energy storage modules 3 are primarily connected in series, the output voltages of the energy storage modules 3 add up to a total output voltage, which can be provided at the respective output terminals 1a, 1b, and 1c of the energy storage device 1.

[0028] Examples of designs of the energy storage modules 3 are shown in the Fig. 2 and Fig. 3 in greater detail. The energy storage modules 3 each comprise a coupling device 7 with a plurality of coupling elements 7a, 7c, and optionally 7b and 7d. The energy storage modules 3 further each comprise an energy storage cell module 5 with one or more series-connected energy storage cells 5a to 5k.

[0029] The energy storage cell module 5 can, for example, comprise series-connected energy storage cells 5a to 5k, for example lithium-ion cells. The number of energy storage cells 5a to 5k in the Fig. 2 and Fig. 3, two energy storage modules 3 are shown as an example, although any other number of energy storage cells 5a to 5k is also possible.

[0030] The energy storage cell modules 5 are connected via connecting lines to input terminals of the associated coupling device 7. The coupling device 7 is in Fig. 2 is designed, for example, as a full-bridge circuit with two coupling elements 7a, 7c and two coupling elements 7b, 7d. The coupling elements 7a, 7b, 7c, 7d can each have an active switching element, for example a semiconductor switch, and a freewheeling diode connected in parallel. It can be provided that the coupling elements 7a, 7b, 7c, 7d are designed as MOSFET switches, which already have an intrinsic diode, or IGBT switches. Alternatively, it is possible to design only two coupling elements 7a, 7d with an active switching element, so that - as in Fig. 3 as an example - an asymmetric half-bridge circuit is realized.

[0031] The coupling elements 7a, 7b, 7c, 7d can be controlled in such a way, for example, with the aid of the Fig. 1, that the respective energy storage cell module 5 is selectively connected between the output terminals 3a and 3b or that the energy storage cell module 5 is bridged or bypassed. With reference to Fig. 2, the energy storage cell module 5 can be connected, for example, in the forward direction between the output terminals 3a and 3b by placing the active switching element of the coupling element 7d and the active switching element of the coupling element 7a in a closed state, while placing the two remaining active switching elements of the coupling elements 7b and 7c in an open state. A bridging state or bypass state can be set, for example, by placing the two active switching elements of the coupling elements 7a and 7b in a closed state, while keeping the two active switching elements of the coupling elements 7c and 7d in an open state. A second bridging state orThe bypass state can be set by keeping the two active switching elements of the coupling elements 7a and 7b in the open state, while the two active switching elements of the coupling elements 7c and 7d are closed. Finally, the energy storage cell module 5 can be connected, for example, in the reverse direction between the output terminals 3a and 3b by placing the active switching element of the coupling element 7b and the active switching element of the coupling element 7c in a closed state, while the two remaining active switching elements of the coupling elements 7a and 7d are open. Analogous considerations can be made for the asymmetric half-bridge circuit in . Fig. 3. By appropriately controlling the coupling devices 7, individual energy storage cell modules 5 of the energy storage modules 3 can be integrated into the series circuit of a power supply branch in a targeted manner and with any polarity.

[0032] The electric drive system 100 in Fig. 1 for supplying an electrical machine 2 in an electrically powered vehicle. However, it can also be provided that the energy storage device 1 is used to generate electrical power for a power grid 2.

[0033] To generate a phase voltage between the output terminals 1a, 1b, 1c on the one hand and the reference potential rail 4 on the other hand, usually only a portion of the energy storage cell modules 5 of the energy storage modules 3 are required. Their coupling devices 7 can be controlled such that the total output voltage of a power supply branch Z can be adjusted in stages within a rectangular voltage / current adjustment range between the negative voltage of an individual energy storage cell module 5 multiplied by the number of energy storage modules 3 and the positive voltage of an individual energy storage cell module 5 multiplied by the number of energy storage modules 3 on the one hand, and the negative and positive nominal current through an individual energy storage module 3 on the other.

[0034] For intermediate values ​​between the discrete steps of the rectangular voltage / current adjustment range, individual energy storage modules 3 can be controlled using a pulse-width modulated (PWM) control method, i.e., the coupling elements 7a to 7d of the coupling devices 7 of the respective energy storage modules 3 are switched intermittently in order to switch the energy storage cell module 5 into the energy supply branch Z for a specific (short) period of time during a PWM cycle and to bypass it again in the energy supply branch Z for a specific subsequent (short) period of time. The ratio of these time periods characterizes the average voltage contribution that the respective energy storage cell module 5 contributes to the total voltage of the energy supply branch Z.

[0035] In order to set a defined output voltage on the power supply branch Z at a specific time, a first number of energy storage modules 3 of a power supply branch Z are selected, whose coupling devices 7 are controlled in pulse-width modulated operation. These first energy storage modules 3, usually only one, serve to fine-tune the total output voltage of the respective power supply branch Z. By changing the pulse width of the PWM control signals, the total output voltage of the respective power supply branch Z can be varied almost continuously.

[0036] The basic base of the total output voltage of the respective energy supply branch Z is provided by the selection of a second number of energy storage modules 3 of the energy supply branch Z, the coupling devices 7 of which are controlled in a continuous current operation, i.e. the coupling devices 7 are controlled in such a way that their energy storage cell modules 5 are permanently coupled into the energy supply branch Z and contribute to the total output voltage of the respective energy supply branch Z with the full module voltage.

[0037] To ensure that the load is distributed as evenly as possible across all energy storage cells 5a to 5k of the various energy storage modules 3 of a power supply branch Z, for example, to achieve uniform discharge, thermal stress, and aging of all energy storage cells 5a to 5k, balancing control mechanisms (so-called "cell balancing" methods) are used to ensure that the performance of the energy storage device 1 is as long-lasting and consistently high as possible. Due to manufacturing processes, there are fluctuations in the internal resistance and capacity of energy storage cells 5a to 5k. For example, energy storage cells that are deeply discharged age more quickly, which can lead to capacity losses and an increase in cell drift.On the other hand, even with energy storage cells with different charge states, the total sum of all capacities cannot be fully utilized, since the total capacity is determined by the weakest energy storage cell in each case.

[0038] Current sensor devices are therefore installed in the energy storage modules 3. These devices are connected in series to the energy storage cells 5a to 5k and are designed to measure a current through the energy storage cell module 5 and output it as a module current measurement signal. For this purpose, the current sensor devices can, for example, comprise a current sensor 8, such as a shunt resistor or a Hall sensor, which measures the current through the energy storage cell module 5. A microcontroller 9b is fed via the voltage drop across a shunt resistor 8, which is routed via an operational amplifier 9a, and outputs the module current measurement signal to a communication bus K, such as a CAN bus. The microcontroller 9b can also receive trigger signals via a trigger bus T, which can, for example, request a measurement and subsequent output of module current measurement signals.

[0039] The trigger bus T and the communication bus K can interconnect all of the current sensor devices in the energy storage modules 3. As shown in Fig. As shown by way of example in Figure 1, the trigger bus T and the communication bus K can be jointly connected to the control unit 6. This enables the control unit 6 to monitor and specifically control the current sensor devices of the individual energy storage modules 3. The control unit 6 therefore serves not only to adjust the branch voltages of the power supply branches Z via the control of the coupling devices 7, but also to coordinate and monitor the current sensor devices of the energy storage modules 3.

[0040] In addition, the control unit 6 can also receive current measurement information via a branch current sensor 6a, such as a shunt resistor, which transmits a measurement signal directly to the control unit 6 via an operational amplifier 6b. For reasons of clarity, only one branch current sensor 6a with an operational amplifier 6b is shown in Fig. 1, but such a branch current sensor can be arranged in each of the power supply branches Z and electrically connected to the control unit 6.

[0041] In order to specifically check individual current sensor devices of the energy storage modules 3, the control unit 6 can measure the currents flowing through the energy storage modules 3 for those energy storage modules 3 that are currently operating in continuous mode. The constant current of the entire power supply branch Z always flows in these energy storage modules 3. The energy storage modules 3 that are currently operating in pulse-width modulated mode are temporarily disregarded when measuring the module current measurement signals, since the currents flowing through these energy storage modules 3 are subject to (desired) fluctuations.

[0042] From the current measurement signals flowing through the energy storage modules 3 of the first number of energy storage modules 3, i.e., the energy storage modules 3 in continuous operation, a branch current measurement signal can be determined by averaging in the control unit 6. The branch current measurement signal corresponds to the current flowing through the entire power supply branch Z. Under ideal conditions, the averaged branch current measurement signal should exactly correspond to the individual current measurement signals.

[0043] Due to linearity errors, inaccuracies, and manufacturing tolerances of the current sensors used, deviations of the individual current measurement signals from the averaged branch current measurement signal occur in reality. For this purpose, the control unit 6 can calculate a plurality of measurement differences between the module current measurement signals and the averaged branch current measurement signal in order to calibrate the current sensor devices of the energy storage modules 3 based on the measurement differences. Each of the current sensor devices involved in the averaging can be assigned an associated measurement difference from the calculated plurality of measurement differences, which allows suitable calibration measures, for example, by setting a measurement offset in the operational amplifiers 9a or digitally in the microcontrollers 9b.

[0044] With the determined measurement differences, it is also advantageously possible to improve compensation control mechanisms, since the accuracy of the current measurements is improved. Furthermore, it can also be provided, for example, to determine those critical measurement differences which lie above a predetermined measurement difference threshold value, for example a maximum permissible deviation from the branch current measurement signal. For the current sensor devices for which critical measurement differences have been determined, it can be determined that these current sensor devices are defective. As a result, the current sensor devices identified as defective can, for example, be deactivated. Additionally or alternatively, a warning signal can also be output by the control unit 6, for example to the on-board electronics of an electrically powered vehicle which uses the electric drive system 100, so that the driver can recognize that an error is present.the on-board electronics can activate an emergency program.

Claims

[1] Energy storage device (1), comprising: a plurality of parallel-connected power supply branches (Z), each coupled between an output terminal (1a, 1b, 1c) and a reference potential rail (4), wherein each of the power supply branches (Z) has a plurality of series-connected energy storage modules (3), each comprising: an energy storage cell module (5) which has at least one energy storage cell (5a, 5k), a coupling device (7) with coupling elements (7a, 7d; 7b, 7c) which are designed to selectively connect the energy storage cell module (5) to the respective energy supply branch (Z) or to bypass it in the respective energy supply branch (Z), and a current sensor device (8, 9a, 9b) which is connected in series to the at least one energy storage cell (5a, 5k) and which is designed to measure a current through the energy storage cell module (5) and to output it as a module current measurement signal; and a control unit (6) which is coupled to each of the current sensor devices (8, 9a, 9b) and which is designed to process the module current measurement signals of the current sensor devices (8, 9a, 9b), wherein the control unit (6) is further designed to control the coupling devices (7) of the energy storage modules (3) either in pulse-width modulated operation or in continuous current operation, and to average only the module current measurement signals of the current sensor devices (8, 9a, 9b) of those energy storage modules (3) which are controlled in continuous current operation to form a branch current measurement signal. [2] Energy storage device (1) according to claim 1, wherein the coupling devices (7) comprise coupling elements (7a, 7d; 7b, 7c) in a full-bridge circuit. [3] Energy storage device (1) according to claim 1, wherein the coupling devices (7) comprise coupling elements (7a, 7d; 7b, 7c) in a half-bridge circuit. [4] Energy storage device (1) according to one of claims 1 to 3, wherein the current sensor devices (8, 9a, 9b) each have a shunt resistor (8) or a Hall sensor for current measurement. [5] Energy storage device (1) according to one of claims 1 to 4, wherein the control unit (6) is further configured to calculate a plurality of measurement differences of the module current measurement signals to the averaged branch current measurement signal, and to calibrate the current sensor devices (8, 9a, 9b) of the energy storage modules (3) on the basis of an associated measurement difference of the calculated plurality of measurement differences. [6] Electric drive system (100), with: an energy storage device (1) according to one of claims 1 to 5; and a multi-phase electrical machine (2) having a plurality of phase lines (2a, 2b, 2c), each of which is coupled to one of the output terminals (1a, 1b, 1c) of the energy storage device (1). [7] Method for operating an energy storage device (1) according to one of claims 1 to 5, comprising the steps: Selecting a first number of energy storage modules (3) of a power supply branch (Z) of the energy storage device (1), the coupling devices (7) of which are controlled in a pulse-width modulated operation; Selecting a second number of energy storage modules (3) of the energy supply branch (Z) of the energy storage device (1), the coupling devices (7) of which are controlled in a continuous current operation; Measuring the current flowing through the energy storage modules (3) of the first number of energy storage modules (3) to generate first current measurement signals; and Calculating a branch current measurement signal by averaging only the first current measurement signals. [8] The method of claim 7, further comprising the steps of: Calculating a plurality of measurement differences of the first current measurement signals to the averaged branch current measurement signal; and Calibrating the current sensor devices (8, 9a, 9b) of the first number of energy storage modules (3) on the basis of an associated measurement difference of the calculated plurality of measurement differences. [9] The method of claim 8, further comprising the steps of: Determining critical measurement differences that are above a predetermined measurement difference threshold; Determining that current sensor devices (8, 9a, 9b) of the first number of energy storage modules (3) associated with the critical measurement differences are defective; and Deactivating the defective current sensor devices (8, 9a, 9b) and / or issuing a warning signal to detect the defective current sensor devices (8, 9a, 9b).

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