Method for discharging an energy storage module

Abstract

The invention relates to a method for discharging at least one energy storage module comprising a multi-level converter system, in which a multiplicity of energy storage modules and transistors are provided, wherein each energy storage module is able to be connected in parallel and / or in series with the respectively neighbouring energy storage module, the energy storage modules are monitored for an anomaly, and the energy storage modules, preferably the transistors, are switched such that at least one energy storage module is at least partially discharged when an anomaly is detected in a neighbouring energy storage module.

Description

[0001] Method for discharging an energy storage module

[0002] The invention relates to a method for discharging at least one energy storage module with a multilevel converter system in which a plurality of energy storage modules and transistors are provided, wherein each energy storage module can be connected in parallel and / or in series with the respectively adjacent energy storage module.

[0003] Current energy storage systems are typically loaded with direct current (DC). This is due to the design of conventional converter systems. The aim is to keep the alternating current components, i.e., harmonic oscillations, away from the energy storage devices.

[0004] Since many energy storage devices must be connected in series or parallel, a battery management system (BMS) is necessary. A DC link capacitor, for example, can be connected downstream of the energy storage devices. This serves to further smooth the three-phase currents of the converter and to keep high-frequency oscillations away from the energy storage devices. It also absorbs switching overshoots, as the inductance of the energy storage devices would drive the current further. The goal of this approach is to apply DC load to the energy storage devices, as this is assumed to contribute to the durability of the battery cell and reduce losses.

[0005] For example, in a conventional electric vehicle, the DC bus can house the converters that transfer the energy to the electric motor or, during braking energy recovery (recuperation), return it to the battery. Chargers that can operate with alternating current (AC) or direct current (DC) can also be connected to this bus. These converters are usually designed as two-level converters, e.g., as a B6 bridge in a three-phase version, or—especially in the field of solar systems—as three-level converters.

[0006] As an alternative to bridge circuits as converters, so-called multilevel converter systems are known.

[0007] Batteries, such as accumulators, can be used as energy storage devices or energy sources. The energy storage devices are not hard-wired together, but rather combined as individual submodules. This structure is required for each phase. Therefore, the energy storage devices are distributed across these phases and can be hard-wired in series or parallel, for example.

[0008] Batteries are chemical energy storage devices.

[0009] For example, lithium-ion cells are often used in electric vehicles.

[0010] In conventional batteries, the cells are statically connected to each other and typically operate at standardized voltages of 400 V or 800 V. In the event of thermal runaway in one cell, the generated heat can cause neighboring cells to also experience thermal runaway. This can lead to dangerous situations. For example, a chain reaction can occur, which in the worst case could cause the entire vehicle to burn down.

[0011] It is therefore an object of the invention to provide a method in which the risk of thermal runaway is reduced.

[0012] This object is achieved by the method having the features of claim 1. The method according to the invention is designed for discharging at least one energy storage module with a multilevel converter system and / or can be used for this purpose.

[0013] The energy storage module can be a storage device for a preferably frequency-dependent electrical source, for example a battery, e.g. an accumulator, a fuel cell, a solar cell and / or a (super)capacitor.

[0014] The process can be used, for example, in electric vehicles, e.g. electric cars, electric trucks and / or electric buses.

[0015] A variety of energy storage modules and transistors are provided.

[0016] A, preferably modular, multilevel converter system describes a type of arrangement or circuit of several energy storage modules or transistors.

[0017] Each energy storage module can have at least or exactly one battery, e.g. an accumulator, and / or at least or exactly one capacitor.

[0018] The transistors serve, for example, as switches that can be used to select current and / or voltage paths. This allows the energy storage modules to be integrated into or excluded from a desired configuration.

[0019] Preferably, each energy storage module is assigned at least or exactly two, three, four, five, six, seven, eight, nine, ten or more transistors.

[0020] 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.

[0021] 3V, 4V, 5V, 6V or 7V.

[0022] The transistor can be a lateral, planar, or trench transistor, for example. However, any design is conceivable.

[0023] The transistor is preferably designed as a MOSFET or comprises a MOSFET.

[0024] MOSFETs can be switched at high frequencies.

[0025] At least one transistor, preferably all transistors, may, for example, have a switching frequency of at least 1 Hz, 2 Hz, 3 Hz, 4 Hz, 5 Hz, 6 Hz, 7 Hz, 8 Hz, 9 Hz, 10 Hz, 15 Hz, 20 Hz, 30 Hz, 40 Hz, 50 Hz or 100 Hz.

[0026] Switching can preferably be done using pulse width modulation (PWM).

[0027] The semiconductor material may be, for example, silicon, gallium nitride, gallium arsenide and / or silicon carbide.

[0028] Each energy storage module can be connected in parallel and / or in series with its adjacent energy storage module. Preferably, each energy storage module can be connected in series with its adjacent energy storage module. The option of parallel connection is advantageous but not necessary.

[0029] Preferably, the adjacent energy storage modules are each connected to each other via two current and / or voltage paths. A transistor can be assigned to each path. For example, three transistors are provided between two adjacent energy storage modules. The energy storage modules can thus be connected in parallel or in series, for example.

[0030] Each energy storage module has at least one energy storage cell.

[0031] For example, the energy storage module can have exactly one energy storage cell. However, each energy storage module preferably has multiple energy storage cells, e.g., at least 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100. For example, at least 100 energy storage cells, e.g., 140, can be provided in one energy storage module.

[0032] The energy storage cells of an energy storage module can preferably be connected in parallel. The energy storage cells of an energy storage module are preferably selected such that the same charge is present as in the mains, e.g., 230 V.

[0033] Multilevel converter systems are significantly more versatile than bridge circuits. This allows for virtually any configuration to be created. For example, the energy storage modules can be connected to each other in any way, e.g., parallel or series. Individual energy storage modules can also be included in or excluded from a desired configuration.

[0034] The energy storage modules are monitored for anomalies, preferably permanently.

[0035] The anomaly can, for example, be a deviation of a measured value from an expected and / or statistically calculated reference value, such as a thermal outlier and / or a "plasma cutter." The risk of thermal runaway can be detected early, for example, if an energy storage module develops a defect. The defect can, for example, occur gradually as an aging process. Furthermore, an energy storage module can be damaged suddenly in an accident, for example, if a foreign object, such as a guardrail, strikes the energy storage modules. In both cases, the method detects the anomaly, preferably instantly.

[0036] The energy storage modules, preferably the transistors, are switched such that at least one energy storage module is at least partially discharged if an anomaly is detected in a neighboring energy storage module.

[0037] The multilevel converter system enables the charging and / or discharging of each individual energy storage module. For example, if an anomaly, such as thermal runaway, is detected in energy storage module X, the neighboring energy storage modules, such as energy storage module X+1 and energy storage module X-1, are immediately discharged as much as possible to reduce the state of charge (SOC) of these energy storage modules. A lower state of charge helps delay or even prevent the effects of thermal runaway.

[0038] Even if the chemical energy of an energy storage module is usually several times (e.g., 4 to 7 times) higher than the electrical energy, reducing the electrical energy can be sufficient for this. Alternatively or additionally, the thermal insulation design, i.e., the precautions designed to prevent thermal runaway of neighboring energy storage modules, can be made less stringent using the method according to the invention.

[0039] For example, it is known that halving the state of charge results in a thermal runaway propagation rate slowing by 8.5 times. Preferably, the energy storage module is discharged by at least 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%.

[0040] The stronger the discharge, the more the risk of thermal runaway is reduced.

[0041] It was surprising that a multilevel converter system is capable of detecting anomalies and / or reacting to them, preventing thermal runaway from spreading to neighboring energy storage modules. Because a chain reaction is prevented or at least delayed, safety for vehicle occupants is significantly increased. This can prevent or at least delay a vehicle burnout.

[0042] Preferably, the vehicle occupant can be warned, e.g., visually and / or acoustically, when an anomaly is detected. This lets the vehicle occupant know that they must leave the vehicle.

[0043] In detail:

[0044] If an anomaly, such as thermal runaway, is detected, the system can enter a fail-safe state. Once the discharge voltage falls below a certain cut-off voltage, there is no way back to a fully functional system. In the safe state, attempts are made to prevent and slow the spread of thermal runaway, if possible. In the safe state, neighboring energy storage modules can be discharged in a specific sequence to slow the spread of thermal runaway.

[0045] For example, the multilevel converter system can monitor the state of charge and assess the charge level of each energy storage module separately. Therefore, future thermal runaway can be predicted. If an energy storage module is at a critical state of charge, the system can completely isolate the energy storage module to prevent the system from entering a safe state, thus avoiding an irreversible system condition and preventing thermal runaway.

[0046] Further developments of the invention can also be found in the dependent claims, the description and the accompanying drawings.

[0047] According to one embodiment, a comparison is made between a measured value and a reference value for monitoring purposes.

[0048] For example, it can be monitored whether a measured value exceeds or falls below a specified threshold.

[0049] According to a further embodiment, an anomaly is detected when there is a deviation of at least 5%, preferably of at least 10%.

[0050] Normally, the state of an energy storage module changes very slowly over time, e.g. due to wear and / or normal aging processes.

[0051] However, if large and / or sudden changes occur, for example of at least 5% or at least 10%, e.g. within a maximum period of 10 minutes, 5 minutes, 2 minutes, 60 s, 30 s, 25 s, 20 s, 15 s, 10 s, 9 s, 8 s, 7 s, 6 s, 5 s, 4 s, 3 s, 2 s, 1 s, 0.5 s, 0.25 s, 0.2 s or 0.1 s, this is a sign that an anomaly is present.

[0052] Alternatively, it is also possible that no major and / or sudden changes occur, even though an anomaly is present. In this case, a deviation that is only noticeable during dynamic operation, for example, can be detected using a KL or other data-driven method. According to another embodiment, the anomaly is monitored using a voltage measurement.

[0053] Preferably, each energy storage module has its own voltage sensor.

[0054] This variant is particularly cost-effective, as each energy storage module is preferably equipped with a voltage sensor anyway. This can now also be used to detect anomalies.

[0055] Alternatively, an additional voltage sensor can be provided.

[0056] According to another embodiment, the anomaly is monitored using a current measurement.

[0057] Preferably, each energy storage module has its own current sensor.

[0058] According to a further embodiment, the anomaly is monitored by means of a charge measurement and / or a resistance measurement.

[0059] Preferably, each energy storage module has its own charge sensor and / or resistance sensor.

[0060] The resistance sensor can, for example, detect whether there is a sudden change in the (internal) resistance.

[0061] If the resistance becomes very low or very high, for example, this is an indication of an anomaly. This can be seen alternatively or additionally by the changing voltage and / or current.

[0062] According to a further embodiment, the anomaly is monitored using a temperature measurement and / or pressure measurement. Preferably, each energy storage module has its own temperature sensor and / or pressure sensor.

[0063] A high or rising temperature, for example, is an indication of an anomaly.

[0064] According to a further embodiment, the anomaly is monitored using an ultrasound measurement.

[0065] Preferably, each energy storage module has its own ultrasonic sensor.

[0066] Various methods can be implemented for monitoring, including sensor technologies such as voltage, current, charge, resistance, temperature, pressure and / or ultrasonic sensors or other suitable sensors.

[0067] Preferably, these sensors continuously monitor the condition of the energy storage modules and detect potential anomalies indicating thermal runaway. Once such a condition is detected, the system preferably automatically initiates the necessary measures to control and / or minimize the spread of the thermal runaway.

[0068] Overall, the proposed mechanism offers an innovative solution to improve the safety and reliability of battery systems.

[0069] According to a further embodiment, the charge of the energy storage module is distributed to other energy storage modules during discharging.

[0070] Preferably, the energy storage modules are discharged in the vicinity of the anomaly. The charge can then be transferred preferentially to energy storage modules located as far away from the anomaly as possible.

[0071] According to a further embodiment, during discharging, the charge of the energy storage module is transferred to a motor, e.g. motor coils, an air conditioning system, a battery cooling system and / or a heater of a vehicle.

[0072] For example, the air conditioning and / or heating can be operated at maximum capacity.

[0073] Preferably, the energy storage modules are discharged in the vicinity of the anomaly by discharging energy to any load, such as the headlights. Possible loads include various vehicle devices and / or the generation of reactive power. Whether the vehicle devices are damaged is of secondary importance, as the primary goal is to prevent the vehicle from burning out.

[0074] All aspects, embodiments, and features of the invention described here can be combined with each other, preferably independently of the specific embodiment in which they are mentioned. Preferably, all subject matter of the dependent claims can be combined with each other and with the subject matter of the independent claim.

[0075] The invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 shows an embodiment of a

[0076] MMC system, and

[0077] Fig. 2 to 4 a schematic representation of an embodiment of the method according to the invention.

[0078] First, it should be noted that the illustrated embodiments are purely exemplary in nature. 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 arbitrarily with features of another embodiment. The configuration and / or number of energy storage modules, paths, and transistors shown are purely exemplary and fundamentally arbitrary.

[0079] If a figure contains a reference symbol that is not explained in the immediately corresponding description, reference is made to the corresponding preceding or following explanations in the figure description. Thus, the same reference symbols are used for identical or comparable components in the figures and these are not explained again.

[0080] Fig. 1 shows a multilevel converter system for discharging at least one energy storage module 10, 12, 14, 16.

[0081] Neighboring energy storage modules 10, 12, 14, 16 are each connected to each other via several paths.

[0082] In each path there is a switch designed as transistor 18.

[0083] The adjacent energy storage modules 10, 12, 14, 16 can thus be connected in series or parallel to one another. Furthermore, individual energy storage modules 10, 12, 14, 16 can be bridged if necessary, e.g., by closing the upper switch 18, and thus excluded from a configuration.

[0084] Each energy storage module 10, 12, 14, 16 may have a sensor 20, e.g. a voltage sensor.

[0085] If an anomaly is detected, the adjacent energy storage modules 10, 12, 14, 16 can be discharged to prevent thermal runaway.

[0086] Fig. 2 to 4 show several energy storage modules 10, 12, 14, 16.

[0087] If an anomaly is detected, as shown in Fig. 2 (the corresponding energy storage module is marked with an X), the neighboring energy storage modules, such as the (lighter shown) energy storage modules X+1 and X-1 (e.g. energy storage modules 14, 16), are immediately discharged as much as possible (see Fig. 3).

[0088] This delays the spread of thermal conduction.

[0089] As shown in Fig. 4, in a further step, the energy storage modules (e.g. energy storage module 12) adjacent to the energy storage modules X+1 and X-1 (shown in lighter color) can be discharged.

[0090] The propagation of thermal conduction can be further delayed in this way.

[0091] It is noted that "vorzugsweise" can be translated into English as "preferably." A feature introduced by "vorzugsweise" is purely optional, can be omitted, and does not constitute a limitation, for example, of the claims.

[0092] 10, 12, 14, 16 energy storage module

[0093] 18 Transistor 20 Sensor

Claims

Claims 1. A method for discharging at least one energy storage module (10, 12, 14, 16) 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 with the respectively adjacent energy storage module (10, 12, 14, 16), the energy storage modules (10, 12, 14, 16) are monitored for an anomaly, and the energy storage modules (10, 12, 14, 16), preferably the transistors (18), are connected in such a way that at least one energy storage module (10, 12, 14, 16) is at least partially discharged when an adjacent energy storage module (10, 12, 14, 16) an anomaly is detected.

2. Method according to claim 1, characterized in that a comparison is made between a measured value and a reference value for monitoring purposes.

3. Method according to claim 1 or 2, characterized in that an anomaly is detected when there is a deviation of at least 5%, preferably of at least 10%.

4. Method according to one of the preceding claims, characterized in that the anomaly is monitored by means of a voltage measurement.

5. Method according to one of the preceding claims, characterized in that the anomaly is monitored by means of a current measurement.

6. Method according to one of the preceding claims, characterized in that the anomaly is monitored by means of a charge measurement and / or a resistance measurement.

7. Method according to one of the preceding claims, characterized in that the anomaly is monitored by means of a temperature measurement and / or pressure measurement.

8. Method according to one of the preceding claims, characterized in that the anomaly is monitored by means of an ultrasound measurement.

9. Method according to one of the preceding claims, characterized in that during discharging the charge of the energy storage module (10, 12, 14, 16) is distributed to further energy storage modules (10, 12, 14, 16).

10. Method according to one of the preceding claims, characterized in that during discharging the charge of the energy storage module (10, 12, 14, 16) is transferred to an engine, an air conditioning system, a battery cooling system and / or a heating system of a vehicle.

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