Pulse discharge method

Abstract

The invention relates to a method for pulse-discharging at least one energy storage module, in particular an energy storage module of an electric vehicle, comprising a multi-level converter system, in which a plurality of energy storage modules and transistors are provided, wherein each energy storage module can be connected in parallel or in series to a respective adjacent energy storage module, and the energy storage modules, preferably the transistors, are connected in such a way that at least one energy storage module is pulse-discharged to provide an energy-consuming device with energy.

Description

[0001] Pulse discharge method

[0002] The invention relates to a method for pulse discharge of at least one energy storage module.

[0003] So far, only pulsed charging is known, which can significantly shorten the charging time of an energy storage module and / or reduce heat generation. For example, due to the uniform thermal distribution, charging can be up to three times faster without excessively accelerating aging and thus reducing the lifespan. This is possible because the charging speed can be adjusted as a degree of freedom. The main limiting factor here is the charging infrastructure.

[0004] Pulsed discharge of an energy storage module, such as in an electric vehicle, is not yet known. This is because, in a conventional setup, the current that the energy storage modules must supply is determined by the driver. The driver essentially dictates the torque via the accelerator pedal. This torque is proportional to the current, leaving no degree of freedom.

[0005] It is therefore an object of the invention to create a method by which an energy storage module can be discharged quickly and / or in an optimized manner.

[0006] According to the invention, the method serves for pulse discharge of at least one energy storage module and / or can be used for this purpose.

[0007] The energy storage module can be a storage device for an electrical source, preferably frequency-dependent, such as a battery, accumulator, fuel cell, solar cell, and / or (super)capacitor. The method can be used, for example, in electric vehicles, such as electric cars, electric trucks, and / or electric buses. Furthermore, it can be applied to stationary energy storage systems and / or other inverter systems that are connected to the power grid and / or operated by an AC motor.

[0008] The method according to the invention uses a, preferably modular, multi-level converter system (MMC system).

[0009] A multilevel converter system is a type of arrangement or circuit of multiple energy storage modules or transistors.

[0010] According to the invention, a large number of energy storage modules and transistors are provided.

[0011] Each energy storage module can contain at least or exactly one battery, e.g. an accumulator, and / or at least or exactly one capacitor.

[0012] The transistors serve, for example, as switches by which current and / or voltage paths can be selected. This allows the energy storage modules to be integrated into a desired configuration or excluded from it.

[0013] Preferably, each energy storage module is assigned at least or exactly two, three, four, five, six, seven, eight, nine, ten or more transistors.

[0014] The transistor can be designed, for example, for a voltage of less than 500 V, 400 V, 300 V, 200 V, 100 V, 50 V, 40 V, 30 V, 20 V, or 10 V. Preferably, the transistor can be designed for a voltage between 2 V and 8 V, e.g.

[0015] The modules can be designed for 3 V, 4 V, 5 V, 6 V, or 7 V. Each energy storage module can be connected in parallel or in series with any adjacent energy storage module. Preferably, each energy storage module can be connected in series with its adjacent energy storage module. The possibility of parallel connection is advantageous but not necessary.

[0016] Preferably, the adjacent energy storage modules are connected to each other via two current and / or voltage paths. Each path can be assigned a transistor.

[0017] For example, three transistors are provided between two adjacent energy storage modules. This allows the energy storage modules to be connected in parallel or in series, for example.

[0018] Multilevel converter systems are significantly more versatile than two-level converters. This allows for the creation of virtually any configuration. For example, the energy storage modules can be connected to each other in any configuration, such as in parallel or in series. Individual energy storage modules can also be integrated into or excluded from a desired configuration.

[0019] Regarding a possible design of a multilevel converter system and / or a method for operating the multilevel converter system, reference is made to DE 10 2022 110 426 A1, the content of which is fully incorporated into this application.

[0020] The energy storage modules, preferably the transistors, are connected in such a way that at least one energy storage module is pulsedly discharged to provide energy to a consumer.

[0021] The consumer could be, for example, an electric motor, such as in an electric vehicle. In principle, all electrically powered devices, such as machines, are conceivable as consumers. In the case of feeding power back into the grid (e.g., with a bidirectional charger), the grid itself can be the consumer.

[0022] The pulse can be, for example, between 1 kHz and 2 kHz, preferably between

[0023] The frequency range is between 1.2 kHz and 1.8 kHz. This depends, for example, on the state of charge (SoC), the maximum available battery capacity (SoH), the temperature, the cell dimensions, and / or the chemical composition.

[0024] It was surprising that the use of a multilevel converter system also makes pulsed discharge of an energy storage module possible.

[0025] This is due, for example, to the fact that the electricity can be distributed differently among the energy storage modules.

[0026] The energy storage module can therefore be discharged quickly and / or in an optimized manner.

[0027] Furthermore, pulsed discharge can help to prevent or remove dendrites.

[0028] Repeated charging can lead to the formation of dendrites, or deposits. These can reduce the performance of the energy storage modules and / or cause a short circuit.

[0029] Pulsed discharge can prevent dendrites from depositing or allow them to be removed.

[0030] Further developments of the invention can also be found in the dependent claims, the description, and the accompanying drawings. According to one embodiment, an individual frequency is applied to the energy storage module.

[0031] Preferably, each energy storage module receives an individual frequency that is not visible from the outside, as it is balanced out in the overall signal from other energy storage modules.

[0032] For example, the multilevel converter system can apply a frequency to individual energy storage modules, but this frequency is not visible to the overall system at the output. This can lead to internal frequency loading.

[0033] According to another embodiment, an optimal frequency and / or pulse shape is selected based on specific properties of the energy storage module.

[0034] The pulse shape determines, for example, how long the energy storage module is on or off, how high the current and / or voltage is, and / or whether negative components are present.

[0035] The specific property could be, for example, the temperature, the state of charge, the aging, the size and / or the chemical composition.

[0036] In another embodiment, the energy storage module to be discharged is integrated into a configuration.

[0037] For example, an energy storage module might initially be excluded from a configuration for discharge. It can then be integrated into a configuration and, for instance, connected in series with at least one other energy storage module. This results in a current flow from 0 A to > 0 A, during which the voltage response is measured. The ratio of voltage to current yields the complex impedance. Based on the known frequencies, the equivalent circuit can then be populated with data.

[0038] Connecting the energy storage modules in series is sufficient for discharging. Parallel connection is therefore not necessary, but is theoretically possible if the energy storage modules have corresponding pathways. Furthermore, this increases the degrees of freedom.

[0039] In this way, for example, the frequency response can be determined, which is also fundamentally possible with a (single) series connection.

[0040] According to another embodiment, the configuration is varied.

[0041] The reconfigurable energy storage modules are preferably interconnected in such a way that the resulting harmonics can be adjusted for each energy storage module independently of the external load. Any desired voltage can be generated by connecting the cells in series, or in certain embodiments, in parallel. If a sine wave is approximated, a 4 V energy storage module 1, 2, or 3 can be used in a given voltage stage. This switching of the energy storage modules allows the load profile of each individual module to be adjusted. The aim is, for example, to achieve the spectrum with the lowest losses.

[0042] For example, if a user presses the accelerator pedal, the electricity can be supplied from different energy storage modules.

[0043] In another embodiment, the energy storage module to be discharged is integrated into the configuration in such a way that losses during discharge are minimized. This increases discharge efficiency.

[0044] According to another embodiment, the energy storage module to be discharged is integrated into the configuration in such a way that the discharge time is minimal.

[0045] This means that a large amount of energy can be provided within a short time.

[0046] Depending on the application, optimization can focus on minimal losses and / or minimal discharge time. A compromise between comparatively low losses and a comparatively short discharge time is also possible.

[0047] In another embodiment, it is iteratively determined in which configuration the losses and / or the discharge time are minimal.

[0048] This allows the intersection point of the real part and the imaginary part of the AC resistance to be determined.

[0049] One attempts (at least as a first approximation) to operate each energy storage module at the frequency where its frequency intersects the real axis. However, at approximately 1 kHz, this is highly dependent on the specific energy storage module. Furthermore, other factors play a role in fast charging and discharging. Ultimately, it is best to validate experimentally the frequency at which the most energy can be input into the energy storage module or at which optimal discharge can occur. It is also important to note that the on and off times make a significant difference. For example, a high pulse, e.g., at 33 C, followed by a longer pause can be advantageous.

[0050] For example, one can start at a minimum value in a Nyquist diagram and then gradually approach the optimum. Alternatively or additionally, previous data can be used.

[0051] According to another embodiment, the configuration is determined with regard to several, preferably all, energy storage modules.

[0052] For example, two, three, four, five or more energy storage modules can be optimized with regard to certain discharge characteristics.

[0053] Preferably, the optimization is performed with regard to all energy storage modules.

[0054] This leads to a reduction in overall losses and / or a reduction in overall unloading time.

[0055] Software can be used to find one or more configurations that optimize the total loss or discharge time of several or all energy storage modules.

[0056] For example, the software can work using neural networks, Kalman filters, and / or artificial intelligence. This allows the process to be continuously improved using recorded data.

[0057] In another embodiment, several energy storage modules are discharged simultaneously.

[0058] This allows the energy storage modules to be loaded evenly. It also enables a large amount of energy to be made available within a short time.

[0059] According to another embodiment, the energy storage modules are discharged differently. For example, one energy storage module can be discharged more deeply than another energy storage module, and vice versa.

[0060] The degree to which an individual energy storage module is discharged depends, for example, on the properties of the respective energy storage module, such as its state of charge, temperature and / or design.

[0061] The invention also relates to a multilevel converter system, preferably a modular multilevel battery system, for carrying out the method according to the invention with a plurality of energy storage modules and transistors, wherein each energy storage module is connected in parallel to or in series with a respective adjacent energy storage module.

[0062] The system includes a control device designed to switch the energy storage modules, preferably the transistors, such that at least one energy storage module is pulsedly discharged to provide energy to a consumer.

[0063] At least one transistor has a switching frequency of at least 1 Hz.

[0064] An optimized frequency can preferably be between 1 kHz and 4 kHz, e.g. at 1.2 kHz or 1.5 kHz.

[0065] All embodiments and components of the multilevel converter system described herein are preferably designed to be operated, for example, by means of a control device, according to the method described herein. Furthermore, all embodiments of the device and all embodiments of the method described herein can be combined with one another, preferably also independently of the specific configuration in which they are mentioned. It should be noted that terms such as "a" or "an" do not necessarily mean "exactly one" or "exactly one," although this is also possible. The terms "a" or "an" can therefore be understood as "at least one" or "exactly one." The use of the singular preferably includes the plural existence of the components, and vice versa.

[0066] It is noted that "vorzugsweise" and "bevorzugt" can be translated as "preferably" in English. A feature introduced by "vorzugsweise" or "bevorzugt" is purely optional, can be omitted, and does not constitute a limitation, for example, of claims.

[0067] The invention can also be characterized by the following aspects:

[0068] 1. Method for pulse discharge of at least one energy storage module (10, 12, 14, 16), preferably of an electric vehicle, with a multilevel converter system in which a plurality of energy storage modules (10, 12, 14, 16) and transistors (18) are provided, wherein each energy storage module (10, 12, 14, 16) can be connected in parallel and / or in series to the respective adjacent energy storage module (10, 12, 14, 16), and the energy storage modules (10, 12, 14, 16), preferably the transistors (18), are connected such that at least one energy storage module (10, 12, 14, 16) is pulse discharged to provide energy to a consumer.

[0069] 2. Method according to aspect 1, characterized in that an individual frequency is applied to the energy storage module (10, 12, 14, 16).

[0070] 3. A method according to aspect 1 or 2, characterized in that an optimal frequency and / or pulse shape is selected based on specific properties of the energy storage module (10, 12, 14, 16). A method according to any of the preceding aspects, characterized in that the energy storage module (10, 12, 14, 16) to be discharged is integrated into a configuration, preferably wherein the configuration is varied. A method according to aspect 4, characterized in that the energy storage module (10, 12, 14, 16) to be discharged is integrated into the configuration such that the losses during discharge are minimal. A method according to aspect 4 or 5, characterized in that the energy storage module (10, 12, 14, 16) to be discharged is integrated into the configuration such that the discharge time is minimal. A method according to any one of aspects 4 to 6, characterized in that the configuration in which the losses and / or the discharge time are minimal is determined iteratively.Method according to aspect 7, characterized in that the configuration is determined with respect to several, preferably all, energy storage modules (10, 12, 14, 16). Method according to one of the preceding aspects, characterized in that several energy storage modules (10, 12, 14, 16) are discharged simultaneously.

[0071] 10. Method according to aspect 9, characterized in that the energy storage modules (10, 12, 14, 16) are discharged differently.

[0072] The invention is described below by way of example with reference to the drawings. The drawings show:

[0073] Fig. 1 shows an embodiment of a device according to the invention.

[0074] MMC system,

[0075] Fig. 2 shows the output voltage curve of a 2-level system according to the prior art.

[0076] Fig. 3 shows the output voltage curve of an embodiment of an MMC system according to the invention,

[0077] Fig. 4 shows an optimized configuration of a device according to the invention.

[0078] MMC Systems,

[0079] Fig. 5 shows another optimized configuration of an MMC system according to the invention,

[0080] Fig. 6 shows a Nyquist diagram of an electrochemical

[0081] Impedance spectroscopy

[0082] Fig. 7 shows a diagram of the current load over time for parallel connected energy storage modules, and Fig. 8 shows a diagram of the frequency components.

[0083] It should first be noted that the embodiments shown are purely exemplary. Individual features can be implemented not only in the combination shown, but also individually or in other technically feasible combinations. For example, the features of one embodiment can be combined with features of another embodiment in any way. The configuration and / or number of energy storage modules, paths, and transistors shown is purely exemplary and, in principle, arbitrary.

[0084] If a figure contains a reference numeral that is not explained in the immediately associated descriptive text, reference is made to the corresponding preceding or subsequent explanations in the figure description. Thus, the same reference numerals are used for identical or comparable components in the figures and are not explained again.

[0085] Fig. 1 shows a multilevel converter system for pulse discharge of at least one energy storage module 10, 12, 14, 16.

[0086] Adjacent energy storage modules 10, 12, 14, 16 are each connected to each other via several paths.

[0087] Each path includes a switch designed as a transistor 18.

[0088] The adjacent energy storage modules 10, 12, 14, 16 can thus be connected in series or in parallel. Individual energy storage modules 10, 12, 14, 16 can also be bypassed if necessary, e.g., by closing the upper switch 18, and thus excluded from a configuration.

[0089] Traditionally, a DC link capacitor would be required to absorb the current before the energy storage modules and / or buffer the frequencies. Such a DC link capacitor is not necessary with a multilevel converter system.

[0090] Fig. 2 shows the voltage profile U over time t of a PWM modulation.

[0091] Six switches are required for a three-phase DC / AC system coupling.

[0092] In a B6 bridge or a two-point converter, the DC voltage is switched on synchronously via several or one switch, so that only an AC voltage is present on average over time.

[0093] The sinusoidal target voltage 20 is therefore only rudimentarily simulated by the output voltage 22 of the PWM system.

[0094] Fig. 3 shows the voltage curve U in volts over time t in seconds of an MMC system.

[0095] The sinusoidal target voltage 20 is simulated by the arrangement of individual stages 24. The output voltage 24 therefore replicates the sinusoidal target voltage 20 much more accurately.

[0096] Figure 4 shows a possible switching configuration of an MMC system to generate a sine wave. The voltage U is shown in volts over time t in seconds.

[0097] An example shows how the first three voltage levels can be formed by connecting the energy storage modules 10, 12, 14, 16 in parallel.

[0098] To optimize the discharge process, all energy storage modules 10, 12, 14, 16 can be integrated into the configuration at each stage. If multiple energy storage modules 10, 12, 14, 16 are connected in parallel, the current is divided.

[0099] Fig. 5, however, shows a configuration in which all energy storage modules 10, 12, 14, 16 are connected in series.

[0100] Depending on the application or characteristics of the energy storage modules 10, 12, 14, 16, such a configuration can also optimize the discharge process.

[0101] By including the energy storage module 10 alone in the configuration in the first stage and in the second stage connected in series with another energy storage module 12, in the third stage with two further energy storage modules 12, 14 and in the fourth stage with three further energy storage modules 12, 14,16, the behavior in different frequency ranges can be determined, for example.

[0102] Fig. 6 shows a Nyquist diagram of an electrochemical impedance spectroscopy (EIS) using the example of a lithium-ion battery as an energy storage module 10, 12, 14, 16.

[0103] This approach is applicable to other storage technologies as well.

[0104] The energy efficiency factor (EIS) of battery cells varies considerably depending on the manufacturer, but even cells from the same manufacturer can differ significantly due to variations in protection circuitry, cathode and anode materials, and / or electrolytes. It is particularly interesting that the EIS can differ even between cells of the same type and manufacturer. However, the basic curve is the same for all types of energy storage devices. The x-axis represents the real part of the impedance, i.e., the complex AC resistance in Q. This corresponds to the actual losses of the battery at the respective operating points.

[0105] Furthermore, the y-axis shows the imaginary part of the impedance in Q at the respective operating points.

[0106] The different operating points result from the different voltage frequencies applied to the battery. The frequencies in the upper right area are low frequencies (LF) and are strongly influenced by diffusion. The losses in the lower left area correspond to losses at high frequencies (HF) and are strongly influenced by inductive behavior.

[0107] The Nyquist diagram does not allow for the direct reading of exact frequency values. These must be displayed separately.

[0108] However, it can be seen in the Nyquist diagram that the point of least loss (P = I) 2 * Re(Z)) depends on the x-axis and is the point that is furthest to the left, since only the ohmic losses occur here.

[0109] A conventional DC load is located in the Nyquist diagram at the low frequencies LF and thus at the maximum losses.

[0110] Measurements were also carried out with different charge levels (not shown). These resulted in different curve shapes.

[0111] Battery losses depend not only on frequency and current, but also on the battery's state of charge. Adjusting these losses for different battery states would therefore be advantageous. Temperature and / or the battery's age also affect its frequency response and losses.

[0112] It is desirable to operate the battery at a point where the discharge rate and / or the losses during discharge are low.

[0113] Fig. 7 shows the waveform of the current I with which an M2B module is loaded during a sine wave (measurement with eight M2B modules and an additional capacitor module equipped with 860 pF), over the time t.

[0114] An M2B module is a so-called Modular Multilevel Battery Converter, essentially a subtype of an MMC system.

[0115] The waveform resembles a rectified sine wave. The differences from the envelope of a rectified sine signal result from the parallel connection of the energy storage modules 10, 12, 14, 16. Jumps in current load occur when previously parallel-connected energy storage modules 10, 12, 14, 16 are switched to series operation.

[0116] This current can be applied to the energy storage modules 10, 12, 14, 16. The current does not need to be sinusoidal. If the energy storage module 10, 12, 14, 16 is repeatedly switched on and off, virtually any frequency is possible.

[0117] Fig. 8 shows the frequency components of the current waveform depicted in Fig. 7 in percent. As expected with a rectified sine wave, the frequencies f = 0 Hz and f = 100 Hz dominate. Other frequency components such as 50 Hz, 150 Hz, etc., are significantly lower and have an amplitude of less than 15% of the DC component.

[0118] Low frequencies, especially up to approximately 300 Hz, have a high relative impact. Using an MMC system, or more specifically an M2B system, on the European power grid (50 Hz) results in a 100 Hz load on the batteries. This is twice the normal value, as both the positive and negative half-waves of a sine wave pass through the batteries.

[0119] When the inverter is used with a three-phase motor, the frequency load therefore depends on the electrical speed of the motor and corresponds to twice this speed in the inverter modules.

[0120] If the losses in this example battery are lowest at 2 kHz, then the losses can be reduced by using an MMC system operating at an output frequency of 1 kHz.

[0121] The variable battery configuration of MMC systems allows for free control of the frequency range in which the energy storage modules 10, 12, 14, 16 are loaded. This is also necessary because the optimal operating point during discharge depends on various parameters and changes, for example, over the lifetime of an energy storage module 10, 12, 14, 16 (and possibly the other energy storage modules 10, 12, 14, 16).

[0122] This can be achieved, for example, through software and / or software updates.

[0123] For example, dependencies on the temperature of the energy storage modules 10, 12, 14, 16 can also be compensated.

[0124] Accordingly, a dependency on the number of cycles (lifespan) of the energy storage modules 10, 12, 14, 16 can be compensated.

[0125] The spectrum can be adjusted to charge or discharge as quickly as possible. For example, this can minimize heat generation. (List of reference symbols)

[0126] 10, 12, 14, 16 Energy storage module

[0127] 18 transistors

[0128] 20 Target voltage

[0129] 22 Output voltage PWM system

[0130] 24-stage, output voltage M MC system

[0131] U voltage t time

[0132] Re(Z) Real part of the complex resistance lm(Z) Imaginary part of the complex resistance

[0133] NF low frequencies

[0134] RF high frequencies

[0135] Current f Frequency

Claims

Claims 1. Method for pulse-discharging at least one energy storage module (10, 12, 14, 16), preferably one energy storage module (10, 12, 14, 16) of an electric vehicle, with a multilevel converter system in which a plurality of energy storage modules (10, 12, 14, 16) and transistors (18) are provided, wherein each energy storage module (10, 12, 14, 16) can be connected in parallel to or in series with a neighboring energy storage module (10, 12, 14, 16), and the energy storage modules (10, 12, 14, 16), preferably the transistors (18), are connected such that at least one energy storage module (10, 12, 14, 16) is pulse-discharged to provide energy to a consumer.

2. Method according to claim 1, characterized in that an individual frequency is applied to the energy storage module (10, 12, 14, 16).

3. Method according to claim 1 or 2, characterized in that an optimal frequency and / or pulse shape is selected based on specific properties of the energy storage module (10, 12, 14, 16).

4. Method according to one of the preceding claims, characterized in that the energy storage module (10, 12, 14, 16) to be discharged is integrated into a configuration, preferably wherein the configuration is varied.

5. Method according to claim 4, characterized in that the energy storage module (10, 12, 14, 16) to be discharged is integrated into the configuration in such a way that the losses during discharge are minimal.

6. Method according to claim 4 or 5, characterized in that the energy storage module (10, 12, 14, 16) to be discharged is integrated into the configuration in such a way that the discharge time is minimal.

7. Method according to one of claims 4 to 6, characterized in that it is iteratively determined in which configuration the losses and / or the discharge time are minimal.

8. Method according to claim 7, characterized in that the determination of the configuration is carried out with respect to several, preferably all, energy storage modules (10, 12, 14, 16).

9. Method according to one of the preceding claims, characterized in that several energy storage modules (10, 12, 14, 16) are discharged simultaneously.

10. Method according to claim 9, characterized in that the energy storage modules (10, 12, 14, 16) are discharged differently.

11. Method according to any of the preceding claims, characterized in that the consumer is an electric motor of an electric vehicle.

12. Method according to one of the preceding claims, characterized in that the pulse is between 1 kHz and 2 kHz, preferably between 1.2 kHz and 1.8 kHz.

13. Multilevel converter system for carrying out a method according to one of the preceding claims with a plurality of energy storage modules (10, 12, 14, 16) and transistors (18), wherein each energy storage module (10, 12, 14, 16) is or can be connected in parallel to or in series with a respective adjacent energy storage module (10, 12, 14, 16).

14. Multilevel converter system according to the previous claim, characterized in that the system comprises a control device configured to switch the energy storage modules (10, 12, 14, 16) such that at least one energy storage module (10, 12, 14, 16) is pulsedly discharged to provide energy to a consumer.

15. Electric vehicle comprising a multilevel converter system according to claim 13 or 14.

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