Method and apparatus to operate a battery unit

TECHNICAL FIELD

The present invention relates to a method and an apparatus to operate a battery unit, in particular for an electric vehicle. Furthermore, it relates to a battery system, an electrical vehicle, a computer program and a computer readable medium.

BACKGROUND

A high voltage battery pack of a battery electric vehicle or a plug-in hybrid electric vehicle is typically built by grouping battery cells in parallel and/or in series to compose battery cell modules. These modules are then electrically connected in series to provide a required high voltage on a DC link of the battery pack.

High-voltage batteries have their optimum efficiency within a certain temperature range. At very low temperatures, the internal resistances of a battery generally increase. This often leads to a corresponding reduction in an electric vehicle's range. For this reason, high-voltage batteries in electric vehicles are often subjected to temperature control before the electric vehicle is started.

Nowadays, a high-voltage heater is used to heat up the battery before operation, especially in cold conditions. For example, EP 2 853 001 B1 shows a power supply system of a hybrid electric vehicle, which includes a battery group and a battery heater mechanically connected to the battery group.

It is an object of the present invention to provide a method and an apparatus to operate a battery unit, in particular of an electric vehicle, which allows for improving efficiency of high-voltage batteries with reduced hardware costs.

SUMMARY

According to the present disclosure, the above-mentioned object is achieved by the features of the independent claims. Advantageous embodiments are given in the dependent claims. According to a first and second aspect, the present disclosure relates to a method and a corresponding apparatus for operating a battery unit, in particular of an electric vehicle. The method and the corresponding apparatus can also be used for a stationary battery unit.

An electric vehicle according to this disclosure is a vehicle which comprises an electric drive. So, an electric vehicle according to this disclosure is a pure electric vehicle, sometimes also called battery electric vehicle (“BEV”), or a hybrid electric vehicle (“HEV”), in particular a plug-in hybrid electric vehicle (“PHEV”). The battery unit may also be named battery pack.

The battery unit comprises at least one first string of battery modules electrically connected in series, each battery module comprises a plurality of battery cells electrically connected in parallel and/or in series. Each battery module of the at least one first string of battery modules comprises a power electronics unit and the battery modules of the at least one first string of battery modules are electrically connected in series via their respective power electronics unit. Each of the power electronics units comprises a DC/DC converter operable at least in buck mode, boost mode, bypass mode to bypass the respective battery module and path-through mode to connect a DC link circuit directly to the respective battery module.

This structure and configuration of the battery modules and DC/DC converters allows to operate the battery modules in a very flexible manner. This flexibility can be used for heating the battery unit but also independent from the heating aspect for voltage and/or state of charge balancing of the battery modules and for optimizing in view of provided energy or power. Different battery modules can be selected dependent on, for example, age, chemistry, manufacture, and size of the cells of the battery modules.

The method comprises the following steps: When the at least one first string of battery modules is disconnected from a power net, in particular a board net of the electric vehicle, measurement values which are representative for a temperature of at least one battery module are received and for heating the battery unit a first group of power electronics units is controlled dependent on the received measurement values such that each of the DC/DC converters of the first group of power electronics units operates in one of the following modes: buck mode, boost mode, bypass mode and path-through mode. Furthermore, the first group of power electronics units is controlled such that the DC/DC converters of the first group operate in at least two different modes and there is an energy transfer between at least two battery modules. The first group of power electronics units comprise some or all power electronics units of the at least one first string of battery modules.

In particular, for all battery modules the measurement values are received and the first group of power electronics units is controlled dependent on all received measurement values.

This advantageously allows a self-heating of the battery unit only with components of the battery unit which are also used when the battery unit is used as a power supply and/or when the battery is charged. Thus, self-heating of the battery without a dedicated heating device is possible.

In particular, the self-heating of the battery can be performed during stop time and/or before starting the vehicle.

Depending on the temperature of the battery unit the apparatus can adjust moving energy back and forth between the different battery modules and also through different strings. Moving the energy from some battery modules to other battery modules results in cell heating. Therefore, the heating may be performed until the temperature of the battery modules and cells, respectively, is in a pre-defined range that the electric vehicle can be driven or be charged from the charging station without harming the cells of the battery modules.

According to at least one embodiment of the first and second aspect, the battery unit comprises at least one circulation line that circulates a fluid coolant to absorb heat generated by the cells of at least some of the battery modules and/or by the power electronic units of at least some the battery modules when the respective battery modules receive and/or transmit energy from or to one or more other battery modules, respectively, and to transfer the absorbed heat at least partly to other battery modules.

The circulation line may be arranged in a heat sink which is attached to housings of the battery modules of the at least one first string.

According to at least one embodiment of the first and second aspect, the circulation line is thermally coupled with one or more other thermal cycles, in particular with one or more thermal cycles of the electric vehicle, outside the battery unit for heat transfer. In particular, the circulation line may be thermally coupled with a thermal cycle used for heating a cabinet of the electric vehicle.

According to at least one embodiment of the first and second aspect, the circulation line is configured as serial cooling cycle. In particular, the battery modules are arranged side by side and the circulation line may be arranged along a serpentine line such that it passes along one battery module after the other and that it respectively passes along all the cells and the power electronics of the battery modules.

According to at least one embodiment of the first and second aspect, the circulation line is configured as parallel cooling cycle. In particular, the circulation line may be arranged that the respective parallel line sections pass along the cells and the power electronics of the battery modules, which are arranged side by side.

According to at least one embodiment of the first and second aspect, the battery unit comprise one or more second strings of second battery modules, wherein the second battery modules of the one or more second strings are electrically connected in series and each second battery module comprises a plurality of battery cells electrically connected in parallel and/or in series. When the at least one first string of battery modules is used for heating the battery unit the second string is charged, for example by a charging station or another vehicle or used to drive the electric vehicle. The battery modules of the at least one first string and the second battery modules of the at least one second string may be configured in the same way or may be configured differently. The second string may be electrically connected to power net, in particular to the board net, of the electric vehicle.

This advantageously allows, for example that also during driving the electric vehicle the self-heating of the battery unit can be used for heating the cabinet of the electric vehicle.

According to at least one embodiment of the first and second aspect, further measurement values which are representative for a voltage and/or state of charge of at least one battery module are received and the first group of power electronics units are in addition controlled dependent on the received further measurement values. This advantageously allows that cells are not overcharged or undercharged during self-heating. In particular, the second measurement values are received for all battery modules and dependent on all received second measurement values the first group of power electronics units is controlled.

According to a third aspect, the present disclosure relates to a battery system comprising a battery unit, in particular for an electric vehicle, and an apparatus according to the second aspect. The battery unit comprises at least one first string of battery modules electrically connected in series. Each battery module comprises a plurality of battery cells electrically connected in parallel and/or in series and each battery module of the at least one first string of battery modules comprise a power electronics unit and the battery modules of the at least one first string of battery modules are electrically connected in series via their respective power electronics unit, each of the power electronics units comprises a DC/DC converter operable at least in buck mode, boost mode, bypass mode to bypass the respective battery module and path-through mode to connect a DC link circuit directly to the respective battery module.

According to a fourth aspect, the present disclosure relates to an electric vehicle comprising a battery system according to the third aspect.

Advantageous embodiments of the first and second aspect are also valid for the third aspect and fourth aspect.

According to a fifth aspect, the present disclosure relates to a computer program which, when executed by a processor of a battery management apparatus, causes the battery management apparatus to perform the method according to the first aspect or an advantageous embodiment of the first aspect.

The computer program may be implemented as computer readable instruction code in any suitable programming language such as JAVA, C++, etc. The computer program may be stored on a computer-readable storage medium (CD-Rom, DVD, Blu-ray disc, removable drive, volatile or non-volatile memory, built-in memory/processor, etc.). The instruction code may program a computer or other programmable device, such as, in particular, a control unit for a battery of an electric vehicle, such that the desired functions are performed. Further, the computer program may be provided on a network, such as the Internet, from which it may be downloaded by a user or automatically, as needed. According to a sixth aspect, the present disclosure relates to a computer readable medium comprising a computer program which, when the program is executed by a processor of a battery management apparatus, causes the battery management apparatus to perform the method according to the first aspect or an advantageous embodiment of the first aspect.

The invention may be implemented both by means of a computer program, i.e., software, and by means of one or more special electrical circuits, i.e., hardware, or in any hybrid form, i.e., by means of software components and hardware components.

BRIEF DESCRIPTION OF THE DRAWINGS

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary and are intended to provide an overview or framework to understand the nature and character of the claims. The accompanying drawings are included to provide a further understanding of the invention. The drawings illustrate one or more embodiments, and together with the description serve to explain principles and operation of the various embodiments.

The same elements in different figures of the drawings are denoted by the same reference signs.

The drawings are not necessarily drawn to scale but are configured to clearly illustrate the disclosure.

Figure 1 shows an exemplary embodiment of a battery system for an electric vehicle,

Figure 2 shows an exemplary embodiment of a battery unit with battery modules operating in different modes,

Figure 3 shows an exemplary embodiment of a battery module,

Figure 4a shows an exemplary embodiment of a cooling cycle of the battery unit, Figure 4b shows a further exemplary embodiment of a cooling cycle of the battery unit, and

Figure 5 shows an exemplary embodiment of a flow chart for a program.

DETAILED DESCRIPTION OF EMBODIMENTS

The present disclosure is described in greater detail hereinafter with reference to the accompanying drawings showing embodiments of the disclosure.

Figure 1 shows an exemplary battery system 1 , in particular for an electric vehicle. The battery system 1 comprises a battery unit 10 and an apparatus 11 for operating the battery unit 10. The apparatus 11 for operating the battery unit 10 may also be named battery management system. The apparatus 11 for operating the battery unit 10 comprise, for example, a battery management controller with a microprocessor or microcontroller.

The apparatus 11 for operating the battery unit 10 is for example configured to communicate with a vehicle control unit 12.

The battery unit 10 comprises a plurality of battery modules 2. The battery modules 2 are electrically connected in series to form a first string 3. In the embodiment shown in Figure 1 , the battery comprises only one first string 3. Alternatively, the battery may comprise more than one first string 3 of battery modules 2. The first string 3 of battery modules 2 provides a DC link voltage between main connectors 7, 9 of the battery unit 10. A nominal voltage of each battery module 2 is for example 48 V.

The battery modules 2 comprise multiple battery cells 4, which are electrically connected in series and/or parallel to form a battery module 2.

In addition, the battery modules 2 each comprise a power electronics unit 14. The battery modules 2 are electrically connected in series via their power electronics units 14, which is indicated by connection 19 in Figure 1.

Each power electronics unit 14 comprises a DC/DC converter. For instance, the DC/DC converters are configured to set the output voltage of the respective battery module 2 to a predetermined value. Furthermore, the DC/DC converters may be controlled to bypass certain modules 2 if necessary. To achieve this, the DC/DC converters of the power electronics units 14 are operable in buck mode, boost mode and also in path-through mode and in bypass mode.

The DC/DC converters each have two input terminals and two output terminals. The input terminals are electrically connected to the battery cells 4 of the respective battery module 2 and the output terminals are electrically connected in series to the next, i.e. the subsequent and the preceding, battery modules 2 of the first string 3. Thus, the battery modules 2 are electrically connected in series via their power electronics unit 14.

In particular, the power electronics units 14 comprise switches operable by a control unit for switching the respective battery module 2 into a bypass mode or a path-through mode. In Figure 2 the different modes are shown. In the bypass mode, the DC link bypasses the respective module, i.e. the respective module does not contribute to the DC link voltage. In pass-through mode, the connection is routed through to the battery module 2 without the DC/DC converter affecting an output voltage. Thus, the DC link circuit is electrically connected directly to the respective battery module 2.

This battery system 1 with battery modules 2 each having a power electronics unit 14 has the advantage, that, when driving the electric vehicle the current drawn from each of the battery modules 2 can be optimised to ensure an even load of the battery modules 2. Furthermore, it is possible to charge the battery either from a 400V or 800V charging station. Because of the DC/DC converters, the voltage can be boosted on the DC-link side to a higher value. Performance can be maintained even in the case of a low state of charge of some modules by adding more modules in series.

The different modes of operation of the DC/DC converters, i.e. in particular the bypass mode and the path-through mode, have the advantage that individual battery modules 2 can be switched on and off to either contribute to the voltage supply and/or self-heating of the battery unit 10 or not to contribute. This makes it possible to use the battery unit 10 very flexibly and to supply different voltage levels. This fully switchable battery allows e.g. to replace the separate low voltage supply of the electric vehicle by supplying 48 V or 12 V from individual battery modules 2 of the battery unit 10. Furthermore, a low voltage supplied by only one or only a few battery modules 2 can be used to pre-charge a DC link capacitor. Hence, the battery unit 10 can be used very flexibly to replace other components of the vehicle.

The special architecture of the battery unit 10 and battery modules 2 also allows a very flexible self-heating of the battery unit 10.

Each battery module 2 comprises for example a cell supervision circuit 13 which is configured to supervise respective temperatures of the cells 4 of the battery module 2 (see Figure 1 ). For example, for the temperature measurement of the battery modules two or three temperature sensors are used with each battery module. A hot spot of each cell may be estimated based on a pre-defined function.

The cell supervision circuits 13 may be configured to communicate with the apparatus 11 of the battery system 1 to transmit recorded temperature measurements to the apparatus 11 .

Figure 2 shows two first strings 3 of battery modules 2, wherein the DC/DC converters of the battery modules 2 operate in different modes.

Figure 3 shows an exemplary embodiment of a battery module 2 of the battery unit 10 shown in Figure 1 and its power electronics unit 14. The power electronics unit 14 comprises the DC/DC converter and additional switches to control different modes of operation of the power electronics unit 14. In a buck/boost mode, switch S3 and S4 are on and switches S1 and S2 are switching. In the buck/boost mode, the voltage drop between terminals 20 and 21 can be set to a predetermined voltage according to a state of charge of the battery module 2 and according to a demand from the vehicle control unit 12.

In a bypass mode, switches S1 , S2 and S4 are on and switch S3 is off, so that the battery module 2 is bypassed. This mode can be chosen, when a specific battery module 2 is not required to contribute to the self-heating of the battery unit 10 or when a certain battery module 2 is defective. In particular, the bypass mode can be chosen when only some battery modules 2 shall contribute e.g. to self-heating of the battery unit 10. Hence, the number of modules 2 which should contribute at a certain time is fully flexible.

If the required voltage on the DC-link side is equal to the cell voltages, the DC/DC operates in path-through mode. In a path-through mode, switches S1 , S3 and S4 are on and switch S2 is off. In this mode, the battery module 2 is operated in a conventional mode without adjusting the output voltage.

Furthermore, the power electronics unit 14 can be operated in a standby mode, where switches S1 and S2 are off and switches S3 and S4 are on, and in an open circuit mode, in which all switches are off and no high voltage is present.

The switches S1 , S2, S3 and S4 are controlled by the apparatus 11 for operating the battery unit 10.

Figures 4a and 4b each show a further exemplary embodiment of a battery unit 10. The battery unit 10 comprises multiple, in particular two, first strings 3 of battery modules 2. Each first string 3 of battery modules 2 comprises multiple, in particular six, battery modules. But also, different numbers of first strings 3 or cells 4 per battery module 2 are possible. The battery modules 2 are arranged side by side and are electrically connected in series.

The battery unit 10 comprises at least one circulation line 23 that circulates a fluid coolant to absorb heat generated by the cells 4 of at least some of the battery modules 2 and/or by the power electronic units 14 of at least some the battery modules 2 when the respective battery modules 2 receive or transmit energy from/to one or more other battery modules 2, and to transfer the absorbed heat at least partly to other battery modules 2.

For example, the battery unit 10 comprises for each string of battery modules of the battery unit 10 a circulation line 23.

Each of the circulation lines 23 is, for example, arranged in a heat sink which is attached to housings of the battery modules 2.

Preferably, the battery modules 2 of one first string 3 are arranged side by side.

For instance, as shown in Figure 4a the circulation line 23 is configured as serial cooling cycle. The circulation line 23 is, for example, arranged along a serpentine line such that it passes along one battery module 2 after the other and that it passes along all the cells 4 and the power electronics unit 14 of the respective battery module 2. Alternatively, as shown in Figure 4b the circulation line 23 may be configured as parallel cooling cycle. In particular, the circulation line 23 may be arranged that the respective parallel line sections pass along the cells 4 and the power electronics unit 14 of a respective the battery module 2, which are arranged side by side.

Optionally, the circulation lines 23 are thermally coupled with one or more other thermal cycles of the electric vehicle outside the battery unit 10 for heat transfer. In particular, the circulation line 23 may be thermally coupled with a thermal cycle used for heating a cabinet of the electric vehicle.

Figure 5 shows an exemplary embodiment of a flow chart of a program for operating a battery unit 10, in particular of an electric vehicle.

The program may run on a processor of the apparatus 11 for operating the battery unit 10. The apparatus 11 for operating the battery unit 10 may comprise a distributed hardware and/or software architecture. Thus, the processor may be arranged in the electrical vehicle or outside of the vehicle.

In a step S01 , the program is started. Furthermore, in step S01 , for example, program variables are initialized.

The start of the program may be caused by a trigger signal. The trigger signal is, for example, generated in response to a request of a driver for heating a cabinet of the vehicle during a stop or in response to a request of starting or charging the electric vehicle. The trigger signal may be sent by the vehicle control unit 12.

In a step S03, it is checked, whether the vehicle’s board net is electrically disconnected from the battery unit or from the at least one first string 3 of battery modules 2 of the battery unit 10. If the board net is already disconnected the program continuous in step S05. If the board net is not yet disconnected, an output signal is provided to control a respective switch setting of at least on switch provided for connecting/disconnection the board net form the at least one first string 3, such that the disconnection of the board net and the at least one first string 3 is achieved.

In step S05, measurement values which are representative for a temperature of at least one battery module 2, are received. Preferably, the measurement values for all battery modules 2 of the batter unit 10 are received. For example, the cell supervision circuit 13 periodically provides the measurement values. Alternatively, first a request to provide the measurement values may be sent to the cell supervision circuit 13.

Optionally in step S05 additionally second measurement values which are representative for an output voltage and/or state of charge of the respective battery modules 2, are received.

In step S07, after receiving the measurement values, for heating the battery unit 10 a first group of power electronics units 14 is controlled depending on the received temperature measurement values and optionally dependent on the second measurement values, such that each of the DC/DC converters of the first group of power electronics units 14 operates in one of the following modes: buck mode, boost mode, bypass mode and path-through mode, and that the DC/DC converters of the first group operate in at least two different modes and there is an energy transfer between at least two battery modules 2.

Thus, the controlling causes an active battery module charge and discharge, which causes a heating of the battery cells 4 of the involved battery modules 2.

In particular, in step S07 at least one output signal is provided to control a respective switch setting of the switches S1 , S2, S3, S4 or the power electronics units 14.

This controlling for self-heating of the battery unit 10 may continue until the cell temperature of the cells 4 of the battery modules 2 is in a predefined range such that they can be used to drive the electric vehicle or can be charged from a charging station without damaging the cells 4 or reducing performance.

In step S09 the program is terminated.

For controlling the heating of the battery unit 10, a duration for the self-heating may be predefined and/or a percentage of the involved battery modules 2 or first strings 3 may be predefined.

Also the selection of battery modules 2 or first strings 3 which are involved in the self-heating may depend on different factors, for example age, size etc. of the cells 4 of the battery modules 2 or specific characteristics of the battery modules 2 or first strings 3. Thus, apparatus 11 for operating the battery unit 10 is configured, for example during vehicle stop time, when the battery is not electrically conductive connected to the board net of the electric vehicle, to control the battery unit 10 such that energy is moved from one or more battery modules 2 to other first string/strings 3. When the DC/DC converters start to operate in buck or boost mode, they generate losses that heat up the fluid coolant that passes by also the battery cells 4. Depending on the temperature of the battery unit 10, the apparatus 11 for operating the battery unit 10 is configured to adjust the moving energy back and forth through the different first strings 3. In addition, moving the energy from some battery modules 2 to other battery modules 2 results in cell heating.

REFERENCE SIGNS

1 battery system

2 battery module

3 string of battery modules

4 battery cell

7,9 main connector

10 battery unit

11 apparatus for operating a battery unit

12 vehicle control unit

13 cell supervision circuit

14 power electronics unit

19 connection

20,21 terminals

23 circulation line

S01 , S09 program steps