Method for directly heating at least one energy storage module

Abstract

The invention relates to a method for directly heating at least one energy storage module with 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 series or in parallel to a respective neighbouring 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 heated, wherein at least one transistor has a switching frequency of at least 1 Hz.

Description

[0001] Method for directly heating at least one energy storage module

[0002] The invention relates to a method for directly heating at least one energy storage module, in which a plurality of energy storage modules and transistors are provided.

[0003] Current energy storage systems are usually 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 otherwise 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 converters that transfer energy to the electric motor or, during braking, return it to the battery. This bus can also be used to connect chargers that operate with alternating current (AC) or direct current (DC).

[0006] These converters are usually designed as two-point converters, e.g. as a B6 bridge in a three-phase version, or - especially in the area of ​​solar systems - as three-point converters.

[0007] As an alternative to bridge circuits as converters, so-called multilevel converter systems (MMC systems) are known.

[0008] Batteries, such as accumulators, capacitors, fuel cells, and / or solar panels, 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.

[0009] Batteries are chemical energy storage devices that behave according to the so-called Arrhenius equation. The reaction rate increases with every 10°C temperature difference. Therefore, raising the temperature of the batteries is advantageous for fast charging. It is also advantageous to raise the temperature of the energy storage modules, for example, in winter, to avoid unnecessary damage to the batteries.

[0010] So far, this has been solved by installing external, e.g. electrical, heating elements in the area of ​​the energy storage or by generating additional losses in the motor or a central converter.

[0011] However, this entails additional costs. Furthermore, the energy storage modules are only heated indirectly, leading to heat losses due to transport and / or radiation.

[0012] It is therefore an object of the invention to provide a method for directly heating at least one energy storage module which has a high efficiency.

[0013] This problem is solved by the method having the features of claim 1 .

[0014] According to the invention, the method is designed for directly heating at least one energy storage module with a multilevel converter system or can be used for this purpose.

[0015] At least one energy storage module is heated directly, i.e., internally, directly, or integrated. Therefore, no external heating elements, such as electrical ones, are necessary.

[0016] The energy storage module can be a storage device for a preferably frequency-dependent electrical source, such as a battery, e.g., an accumulator, a fuel cell, a solar cell, and / or a (super)capacitor. The method can be used, for example, in electric vehicles, e.g., electric cars, electric trucks, and / or electric buses. Use in hydrogen vehicles is also conceivable. Furthermore, this can be applied to stationary energy storage devices and / or other converter systems that are used in the power grid and / or driven by an AC motor.

[0017] A variety of energy storage modules and transistors are provided.

[0018] A, preferably modular, multilevel converter system describes a type of arrangement or circuit of several energy storage modules or transistors.

[0019] Each energy storage module can have at least or exactly one battery, e.g. an accumulator, and / or at least or exactly one capacitor.

[0020] 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.

[0021] Preferably, each energy storage module is assigned at least or exactly two, three, four, five, six, seven, eight, nine, ten or more transistors.

[0022] The transistor can, for example, be designed 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., 3 V, 4 V, 5 V, 6 V, or 7 V.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The energy storage modules, preferably the transistors, are switched in such a way that at least one energy storage module is heated.

[0027] Preferably, losses are artificially increased. These losses generate heat, which is released directly into the energy storage area.

[0028] Switching can preferably be done using pulse width modulation (PWM).

[0029] At least one transistor, preferably all transistors, has / 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.

[0030] Multilevel converter systems, which are primarily used as variable DC voltage or battery management systems, are typically switched relatively slowly or infrequently, e.g., less than once per second. This is because such systems are performance-optimized and losses, such as switching losses, should be minimized. The intermediate circuit voltage also needs to be changed slowly, since the requirements for the intermediate circuit voltage change only slowly.

[0031] According to the invention, however, contrary to the normal procedure of keeping losses as small as possible, losses are to be artificially increased in order to generate heat.

[0032] For example, a converter string can have 100 stages. The entire converter string can therefore have 100 times the frequency. For example, the maximum switching frequency of a transistor and / or the entire converter train can be at least 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz, 100 kHz, 150 kHz, 200 kHz, 250 kHz, 300 kHz, 400 kHz, 500 kHz, 600 kHz, 700 kHz, 800 kHz, 900 kHz, 1 MHz, 1.1 MHz, 1.2 MHz, 1.3 MHz, 1.4 MHz, 1.5 MHz, 2 MHz, 5 MHz, 10 MHz, 20 MHz, 30 MHz, 40 MHz, 50 MHz, 80 MHz, 100 MHz or 120 MHz.

[0033] Such high switching frequencies are not achieved in multilevel converter systems used as variable DC voltage or battery management systems.

[0034] By means of the method according to the invention, at least one energy storage module can be heated directly with high efficiency.

[0035] An additional, external heater is not necessary. The heat is generated directly at the point where it is needed, heating the energy storage modules directly.

[0036] There are no heat transfer losses and no additional components are required.

[0037] Further developments of the invention can also be found in the dependent claims, the description and the accompanying drawings.

[0038] According to one embodiment, the transistor is designed as a MOSFET or IGBT or comprises a MOSFET or IGBT.

[0039] Metal-oxide-semiconductor field-effect transistors (MOSFETs) or insulated-gate bipolar transistors (IGBTs) can be switched at high frequencies.

[0040] The semiconductor material could be silicon, gallium nitride, gallium arsenide, and / or silicon carbide, for example. Organic semiconductors are also conceivable.

[0041] For example, preconditioning and / or optimum operating settings for MOSFETs are possible.

[0042] According to a further embodiment, at least one energy storage module is short-circuited for heating. During normal operation, short circuits should generally be avoided, as they can lead to damage to the energy storage modules.

[0043] To heat an energy storage module, however, short circuits can be deliberately created. The resulting short circuit creates a current flow, which in turn generates heat, which directly heats the energy storage module.

[0044] According to a further embodiment, the energy storage module is short-circuited for a maximum of 1 ms, preferably 1 ps, preferably 1 ns.

[0045] Such short short-circuit times are mainly possible in multilevel converter systems.

[0046] The very short short-circuit times prevent damage to the energy storage modules, as the current never reaches very high levels. The current increases over time. The inductances in the circuit effectively slow the increase.

[0047] According to a further embodiment, switching is pulse width modulated.

[0048] A maximum short-circuit current corresponds to the quotient of the voltage of the energy storage module and the sum of the resistances of the energy storage module and the transistor(s).

[0049] For example, the short-circuit current for an energy storage module voltage of 4 V, an internal resistance of the energy storage module of 10 mQ and two transistors with a resistance of 1 mQ each results in a value of 333.3 A. In the event of a short circuit, this results in a heat loss P = U * I of 1333 W.

[0050] However, such high heat loss is not necessary and may not be beneficial to battery health.

[0051] A limit of, for example, 10 C is advantageous, where one C corresponds to the discharge of the energy storage module in one hour. For example, this corresponds to a maximum short-circuit current of an energy storage module (with 3 Ah) of l = 10 * 3 A = 30 A. Therefore, it is advantageous to switch the short circuit using pulse-width modulation (PWM) depending on the desired heating output.

[0052] Depending on the topology, the short circuit is possible on different transistors and can preferably be evenly distributed.

[0053] In principle, any transistor can create a short circuit.

[0054] If several different short-circuit possibilities exist, it is advantageous to use them evenly. This ensures homogeneous heating of the transistors and the energy storage module.

[0055] The majority of losses occur in the energy storage module, while heat input from the transistors plays a minor role. However, this also has a positive aspect. In this type of converter, the power electronics are often mounted on the energy storage module, and the heat is transferred into the energy storage module via the contacts. The transistor, for example, is directly connected to the energy storage module via a metal material, such as copper.

[0056] A short circuit can occur, for example, while a vehicle is moving. The voltage is not available to the converter at the moment of the short circuit. However, due to the short short-circuit times, this is not a problem. The converter arm or current path is preferably not interrupted during this time, thus preventing load interruption and / or voltage dips.

[0057] In principle, only one energy storage module can be short-circuited. Alternatively, multiple energy storage modules can be short-circuited simultaneously.

[0058] For example, in the case of a short circuit that contributes to the output voltage, two energy storage modules are always short-circuited at the same time.

[0059] According to a further embodiment, the switching frequency for heating is increased.

[0060] Preferably, the switching frequency is increased compared to the switching frequency required for normal, power-optimized operation. Increasing the switching frequency increases switching losses. These deliberately generated losses lead to heat loss, which is dissipated directly in the energy storage area.

[0061] As with the variant with the artificially generated short circuit, effects are also used here which are intended to be prevented and / or avoided in normal, performance-optimized operation.

[0062] It was surprising that these effects can be used to specifically heat an energy storage module.

[0063] According to a further embodiment, at least two energy storage modules are connected in parallel for heating.

[0064] For example, the compensating current, e.g. charging and / or discharging losses, can be used in parallel connected state to heat the energy storage modules.

[0065] According to a further embodiment, the energy storage modules connected in parallel have different charge states.

[0066] For example, energy storage modules with different charge states can be used to create a charge balance between them by connecting them in parallel.

[0067] For example, a cell can be discharged and then connected in parallel to a fuller cell. This results in small increments of cell voltage, meaning the cell voltage itself is, in a sense, divided. Preferably, the cells are not completely discharged. They are simply given a different history. Thus, a different voltage remains at the same state of charge.

[0068] The different charge states can occur during normal operation. Alternatively, they can also be deliberately created.

[0069] For example, energy storage modules can be connected in series without connecting other energy storage modules in parallel. This causes them to discharge more rapidly during operation than other energy storage modules. This principle can be reversed during charging. For example, energy storage modules that require less charging can be connected in parallel more often.

[0070] The charge differences should preferably not be too large to avoid damage to the energy storage modules. Compensation can be achieved using power electronics, such as PWM. This can take into account aging effects and / or frequency dependencies of the energy storage modules.

[0071] If the charge differences are known, the charge distribution can preferably be uniform.

[0072] For example, the following voltage distribution may exist:

[0073] 1. Energy storage module: 3.5 V

[0074] 2. Energy storage module: 4.2 V

[0075] 3. Energy storage module: 4.2 V

[0076] 4. Energy storage module: 4.2 V

[0077] 5. Energy storage module: 3.5 V

[0078] 6. Energy storage module: 4.2 V

[0079] 7. Energy storage module: 4.2 V

[0080] 8. Energy storage module: 4.2 V

[0081] 9. Energy storage module: 3.5 V

[0082] The 1st, 5th and 9th energy storage modules are more heavily discharged.

[0083] In order to heat the energy storage modules, for example, energy storage module 1 is connected in parallel to energy storage module 2 and energy storage module 5 to energy storage module 6, and at the same time energy storage module 8 is connected to energy storage module 9. If the losses are too high, PWM can be used.

[0084] This triggers a compensating current of l = AU / R. In the example, four transistors are connected in parallel in the compensating loop.

[0085] This leads (neglecting dynamic effects such as braking effects due to the inductance) to: I = (U [energy storage module U] - U [energy storage module 2) / (4 * R [transistor] + 2 * R [energy storage module]) flowing as a compensating current. Using the same example in the variant described above, this means that an energy storage module and the transistors lead to a compensating current of I = 0.7 V / (4 * 1 mQ + 2 * 10 mQ) = 30 A. The energy storage modules are heated on the one hand by the heat p = I 2 * R = (30 A) 2 * 10 mQ = 8.75 W heated, but also by the losses occurring at the transistors.

[0086] After this first step, energy storage modules 1 and 2, 5 and 6, and 8 and 9, have equalized their voltages. The equilibrium voltage in this case is 3.85 V:

[0087] 1. Energy storage module: 3.85 V

[0088] 2. Energy storage module: 3.85 V

[0089] 3. Energy storage module: 4.2 V

[0090] 4. Energy storage module: 4.2 V

[0091] 5. Energy storage module: 3.85 V

[0092] 6. Energy storage module: 3.85 V

[0093] 7. Energy storage module: 4.2 V

[0094] 8. Energy storage module: 3.85 V

[0095] 9. Energy storage module: 3.85 V

[0096] In the next step, energy storage module 2 is connected in parallel to energy storage module 3, also 5 to 4 and 7 to 8.

[0097] At a compensating current of I = 0.35 V / (4*1 mQ + 2*10 mQ) = 15 A, a heat loss of P = I 2 * R = (15 A) 2 * 10 mQ = 2.25 W.

[0098] In the final step, the heat can now be distributed equally across all energy storage modules. There are different methods possible to distribute the losses across all energy storage modules. The procedure shown here only represents the simplest distribution. For example, it is conceivable to repeatedly interrupt the charging processes quickly and never achieve complete equalization, but rather to distribute them in small partial steps. Likewise, different starting temperatures and / or connections to the cooling circuit can be taken into account. Alternatively or additionally, any differences due to aging could be compensated for. This procedure can, for example, be used while the converter is in operation. For this purpose, the energy storage modules are bridged to the outside, for example, and a short circuit can, for example, be generated only internally.

[0099] For example, a vehicle can be brought up to operating temperature and / or to the optimal charging temperature before charging without any loss for the customer.

[0100] Bridging to the outside is possible because the upper transistors of the energy storage modules have to be closed anyway when connected in parallel.

[0101] Energy storage modules with different states of charge can be heated by connecting them in parallel, resulting in charging and discharging losses. The charging and discharging power varies for most energy storage modules. For example, the charging power, e.g., 10 C, may be lower than the discharging power, e.g., 3 C. The charging power is the limiting variable here to avoid damage to the energy storage module.

[0102] The energy storage modules to be heated can be used to generate the output voltage. This can involve a superposition of a load current, which depends, for example, on the motor or power grid operating point.

[0103] Alternatively, the energy storage modules to be heated are not used to generate the output voltage. This allows the compensating current to be determined very precisely.

[0104] According to a further embodiment, the configuration of the integrated energy storage modules changes over time.

[0105] By selecting different configurations, the temperature can be regulated, for example, while driving. For example, if energy storage modules are too cold, a configuration with high losses can be selected.

[0106] Preferably, the configuration can change at each stage. Alternatively or additionally, the configuration can be changed within a stage. The energy storage modules can be included in or excluded from a desired configuration.

[0107] Exclusion can be achieved, for example, by closing a switch, e.g. the upper one, so that no current flows through the corresponding energy storage module.

[0108] According to a further embodiment, an energy storage module for heating is connected alone or in series with at least one other energy storage module.

[0109] Losses of the energy storage modules are calculated according to P = I 2 * R [Energy storage module]. Losses depend on the number of energy storage modules connected in parallel.

[0110] If only half the number of energy storage modules is integrated into the configuration, the losses double.

[0111] For selective heating, for example, configurations can be chosen in which energy storage modules are connected in series alone, without parallel energy storage modules to reduce the current.

[0112] Heating can be carried out while driving, for example. The load current can be distributed by interconnecting the energy storage modules so that the energy storage modules heat up to their maximum.

[0113] Heating can also occur when the vehicle is stationary. To generate a load current, a current can be generated by raising the neutral point of an electric motor. This allows charging back and forth between the individual phases.

[0114] For example, in a three-phase setup with U1 = 100 V, U2 = 50 V, and U3 = 100 V, phase 2 can be charged from phase 3 and phase 1. If these are connected purely in series, without utilizing the parallel connection option, losses can be maximized. Alternatively or additionally, when generating this load current, all energy storage modules can be connected in parallel to heat them all simultaneously. This offset can be generated, for example, while driving, when the maximum output voltage is not yet required at the motor.

[0115] The method according to the invention does not require any additional components such as heating elements or supply lines.

[0116] Furthermore, no monitoring of the heat distribution is necessary, since the temperature is generated directly at the energy storage modules.

[0117] Individual heating of the energy storage modules is possible, so that there is no risk of uneven heating and / or inhomogeneities in the system can be compensated.

[0118] The heat is generated where it's needed and doesn't have to be conducted through the housing and / or all the windings of the energy storage modules. This increases the efficiency of the energy storage modules from the start of operation, and minimizes the thermal stress on the overall structure.

[0119] Preferably, the heat output is continuously adjustable, since, for example, the heating can be adjusted to any desired level using pulse width modulation.

[0120] According to a further embodiment, conduction losses, voltage, current and / or frequency for heating are changed.

[0121] A corresponding change preferably corresponds to a switching of the energy storage modules in the sense of the invention.

[0122] For example, it is possible to change the frequency so that it lies in the inductive and / or capacitive ranges. Normally, these ranges would be avoided. However, these frequency ranges are suitable for heating. The loads can be adjusted via the frequencies, for example. If switching occurs very quickly, there is no exchange of charge carriers. For example, the frequency can be changed to the resonant frequency. This may even make it possible to repair defective batteries.

[0123] Alternatively or in addition to the frequency, conduction losses and / or the voltage and / or current can be changed.

[0124] The voltage of individual cells depends on the charge state and the (chemical) history of the cells. For example, a voltage difference can be created. The cells can then be connected in parallel so that the voltages balance each other. Unlike a charge difference, this has the advantage of allowing the maximum charge to be utilized.

[0125] For example, the internal resistance of some transistor types, such as MOSFETs, depends on the voltage applied to the gate. However, for other transistor types, the current can be crucial.

[0126] The gate terminal is the control terminal of the component. A MOSFET has a source, drain, and gate. The voltage at the gate can be used to determine the resistance between drain and source. For example, the voltage at the gate can be changed so that the MOSFET is not fully switched on, i.e., it assumes a state between on and off. In this way, the internal resistance of the switch and thus the losses can be adjusted. For example, if the voltage is halved, the resistance doubles.

[0127] Preferably, due to the relationship P = I 2 * R the heating of the semiconductor can be adjusted.

[0128] If the transistor heats up significantly, this heat can be dissipated into the battery via the already existing electrically conductive connections, since the electrically conductive connections also transfer heat. This does not increase losses in the battery, but does increase losses in the transistor. This allows heating directly at the battery's active material, since the cathode and anode extend through the entire battery. The heat therefore does not have to first pass from the outside through the casing and the battery windings.

[0129] Each layer has an internal thermal resistance that counteracts or slows down the heating process. This can have a significant impact on battery life in a vehicle that is started from cold. Lithium-ion batteries, in particular, age more rapidly at subzero temperatures.

[0130] This can be prevented by the method according to the invention.

[0131] The invention also relates to a multilevel converter 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 and / or in series to the respectively adjacent energy storage module.

[0132] The system comprises a control device which is designed to switch the energy storage modules, preferably the transistors, in such a way that at least one energy storage module is heated.

[0133] At least one transistor has a switching frequency of at least 1 Hz.

[0134] All embodiments and components of the multilevel converter system described here are preferably designed to be operated according to the method described here, e.g., by means of a control device. Furthermore, all embodiments of the device described here, as well as all embodiments of the method described here, can be combined with one another, preferably independently of the specific embodiment in whose context they are mentioned. For example, two or more of the heating processes can also be carried out simultaneously or sequentially, as required.

[0135] 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

[0136] MMC system,

[0137] Fig. 2 shows a curve of the output voltage of a PWM system according to the state of the art,

[0138] Fig. 3 shows a curve of the output voltage of an embodiment of an MMC system according to the invention,

[0139] Fig. 4 shows a (loss) power optimized configuration of an MMC-

[0140] State-of-the-art systems,

[0141] Fig. 5 shows a configuration of an embodiment of an MMC system according to the invention for heating energy storage modules, and

[0142] Fig. 6 shows a configuration of another embodiment of an MMC system according to the invention for heating energy storage modules.

[0143] 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.

[0144] 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.

[0145] Fig. 1 shows a multilevel converter system for directly heating at least one energy storage module 10, 12, 14, 16. Neighboring energy storage modules 10, 12, 14, 16 are each connected to each other via several paths.

[0146] In each path there is a switch designed as transistor 18.

[0147] The adjacent energy storage modules 10, 12, 14, 16 can thus be connected in series or parallel. Individual energy storage modules 10, 12, 14, 16 can also be bridged if necessary, e.g., by closing the upper switch 18, and thus excluded from a configuration.

[0148] Fig. 2 shows the voltage curve U over time t of a PWM modulation.

[0149] For a three-phase DC / AC system coupling, six switches are required.

[0150] In a B6 bridge or a two-level converter, the DC voltage is switched on synchronously via several or one switch, so that an AC voltage is only generated on average over time.

[0151] The sinusoidal target voltage 20 is therefore only rudimentarily simulated by the output voltage 22 of the PWM system.

[0152] Fig. 3 shows the voltage curve U in volts over time t in seconds of an MMC system.

[0153] The sinusoidal target voltage 20 is simulated by the construction of individual stages 24. The output voltage 24 therefore simulates the sinusoidal target voltage 20 much better.

[0154] Fig. 4 shows a power loss-optimized configuration of an MMC system. The voltage U is shown in volts over time t in seconds.

[0155] An example shows how the first three voltage levels can be formed by connecting the energy storage modules 10, 12, 14, and 16 in parallel. To optimize performance and achieve the best efficiency, all energy storage modules 10, 12, 14, and 16 are always integrated into the configuration at each level.

[0156] Fig. 5, however, shows a configuration in which all energy storage modules 10, 12, 14, and 16 are connected in series. This results in maximum heating power.

[0157] In this example, energy storage module 10 is heated the most and energy storage module 16 is heated the least.

[0158] Fig. 6 shows a configuration in which the energy storage module 10 experiences the maximum heating power, since it is always alone in the current path.

[0159] In the first stage, the energy storage module 10 is connected alone and in the further stages in series with at least one of the other energy storage modules 12, 14, 16.

[0160] The configurations shown in Figs. 5 and 6 are purely exemplary. Depending on which energy storage module(s) 10, 12, 14, 16 are to be heated, other configurations are also conceivable.

[0161] Since each energy storage module 10, 12, 14, 16 can be controlled separately, even the smallest differences can be compensated. For example, a vehicle's cooling system may have coolant temperature inequalities, which can be actively compensated. Furthermore, it is possible to dynamically increase the temperature of individual energy storage modules 10, 12, 14, 16 for specific load cases.

[0162] List of reference symbols

[0163] 10, 12, 14, 16 energy storage module

[0164] 18 Transistor 20 Target voltage

[0165] 22 Output voltage PWM system

[0166] 24 stage, output voltage MMC system

[0167] U voltage t time

Claims

Claims for a method for directly heating 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 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 heated, wherein at least one transistor (18) has a switching frequency of at least 1 Hz. The method according to claim 1, characterized in that the transistor (18) is configured as a MOSFET or IGBT or comprises a MOSFET or IGBT. Method according to claim 1 or 2, characterized in that at least one energy storage module (10, 12, 14, 16) is short-circuited for heating.A method according to claim 3, characterized in that the energy storage module (10, 12, 14, 16) is short-circuited for a maximum of 1 ms, preferably 1 ps, preferably 1 ns. A method according to any of the preceding claims, characterized in that the switching is pulse-width modulated.

6. Method according to one of the preceding claims, characterized in that the switching frequency for heating is increased.

7. Method according to one of the preceding claims, characterized in that at least two energy storage modules (10, 12, 14, 16) are connected in parallel for heating.

8. Method according to claim 7, characterized in that the parallel connected energy storage modules (10, 12, 14, 16) have different charge states.

9. Method according to one of the preceding claims, characterized in that the configuration of the integrated energy storage modules (10, 12, 14, 16) changes over time.

10. Method according to claim 9, characterized in that an energy storage module (10) is connected in series for heating alone or with at least one other energy storage module (12, 14, 16).

11. Method according to one of the preceding claims, characterized in that the transmission losses for heating are modified.

12. Method according to one of the preceding claims, characterized in that the voltage and / or the current is changed for heating.

13. Method according to one of the preceding claims, characterized in that the frequency for heating is changed.

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