Battery management system in a battery system

Abstract

The present invention relates to a battery management system (BMS) in a battery system (1) such as is used, inter alia, in a hybrid vehicle or electric vehicle. In order to improve a battery management system (BMS) in a battery system (1), said battery management system being provided for constantly monitoring currents, voltages and temperatures within modules (2) of the battery system (1) which are interconnected in parallel, according to the invention only one superordinate battery management system (NV-BMS-) is provided in the battery system (1) having a parallel circuit of modules (2), said superordinate battery management system being connected to one cell supervisory circuit (CSC+) per module (2), and each cell supervisory circuit (CSC+) being connected to a current-measurement shunt device and being expanded to control switches.

Description

[0001] Battery management system in a battery system

[0002] The present invention relates to a battery management system in a battery system for a low voltage level and in particular for a 48V voltage level, which is intended for the permanent monitoring of currents, voltages and temperatures within modules of the battery system connected in parallel, as is used, among other things, in a hybrid or electric vehicle.

[0003] It is known from the state of the art that every battery system is equipped with a battery management system, or BMS for short, for the permanent monitoring of currents, voltages and temperatures within modules of the associated battery system and their ongoing regulation. In order to enable the use of comparatively cheaper components, a 48V voltage level is generally selected at the busbar connections of the modules in order to maintain a sufficient distance from the 60V voltage level as the boundary to a high-voltage range with significantly increased safety requirements and higher component costs, etc. Battery systems of this type are used, among other things, for service and delivery vehicles in municipal use, autonomous small vehicles, e.g.in forestry and agriculture as well as in smaller construction and work machines or for maritime applications because, in addition to requiring less effort in terms of safety measures and electrical insulation than high-voltage systems, they also place lower demands on personnel and equipment in terms of service and maintenance. In a power range up to approx. 70kW, low-voltage systems offer cost and weight advantages over high-voltage systems, and generally available domestic and commercial power connections can be used for charging. At the 48V voltage level, battery management systems BMS are used in such a way that the cell voltage taps and temperature sensors of an associated battery module are evaluated directly in a cell monitoring circuit as part of a battery management system.In addition, switching units for connecting or disconnecting the battery module via MOSFETs are provided on a common circuit board, which can also integrate a current measuring device. This makes it possible for a module at the 48V voltage level to functionally combine all the components contained in a high-voltage distribution box (HVJB) in a high-voltage battery system on a single circuit board. This significantly reduces the costs of a battery management system at the 48V voltage level compared to other structures.

[0004] The increasing demand for ever greater electrical storage capacities is now leading to multiple low-voltage modules being interconnected to form increasingly larger battery systems. Using a classic BMS architecture familiar from the high-voltage sector, for example, multiple modules could be interconnected in parallel to form a battery system at the 48V level with a correspondingly greater electrical capacity. However, the state of the art described has disadvantages when it comes to parallelizing the described subsystems. With a large number of subsystems, the total costs for a battery system, in particular, increase essentially linearly with the number of subsystems.

[0005] The present invention has the object of creating an improved battery management system in a low-voltage battery system. This object is achieved according to the invention by the features of claim 1 in that in the low-voltage battery system, as a unit comprising a parallel connection of modules, only one higher-level battery management system BMS is provided, which is connected to an extended cell monitoring circuit CSC for each module, wherein each cell monitoring circuit CSC is additionally connected to a current measuring device and is designed to control switches.

[0006] The present invention is based on the approach of creating a cost-effective and scalable battery management system based on a division of tasks from known battery management systems. In particular, it has been recognized as sufficient to provide a control unit portion of a conventional battery management system only once within a low-voltage battery module whose performance can be scaled by connecting modules in parallel, whereby measuring and switching currents on a module-by-module basis is expedient. Arranged upstream of a parallel connection of the modules, comparatively low currents occur which can be switched reliably using inexpensive switches. Current measurement on a module basis is also expedient for the same reasons.In addition, the permissible currents at lower current intensities can be measured more reliably and accurately at module level and can therefore be monitored better than with a total current measurement of the modules connected in parallel. Processing of measurement signals and triggering of switching signals can be implemented more cheaply on a module basis using a functionally expanded cell monitoring circuit CSC than using a battery management system BMS provided separately in each module and connected to the cell monitoring circuit CSC. According to the invention, a control unit component from each module is outsourced to a single battery management system, which thus has a reduced structure compared to conventional battery management systems and is therefore also less expensive. Compared to known approaches, a solution according to the invention is distinguished from other systems in that it is less space- and cost-intensive.By means of a battery management system constructed according to the invention, it is possible to ensure that the total costs for a scalable battery system do not increase linearly with the number of sub-systems.

[0007] Advantageous developments of the invention are the subject of the dependent claims. Accordingly, for the lower currents within the modules, a semiconductor switch is advantageously provided as a switch in extended cell monitoring circuits for switching the respective module on and off, in particular a switch in the form of a MOSFET. Semiconductor switches are generally much smaller than mechanical switches, are generally faster, and have a longer service life while consuming less power. This also makes it possible to integrate the switches into the extended cell monitoring circuit as a common semiconductor component.

[0008] Building on this, in a further development a functionally expanded cell monitoring circuit with two semiconductor switches and a current measuring shunt resistor is arranged as a unit on a common circuit board, which is provided once for each module. Thus, in addition to measuring cell voltages and cell temperatures, the cell monitoring circuit is also responsible for current measurement and is designed to control the switches. The cell monitoring circuit has therefore been functionally expanded or made more intelligent compared to known devices. Advantageously, devices for monitoring the cell monitoring circuits of all modules connected in parallel and controlling the respective switches are arranged in the form of a microcontroller with the battery management system on a common circuit board.Thus, a battery management system according to the invention comprises at least two circuit boards at the 48V voltage level of the modules: One circuit board is designed with a microcontroller and software for implementing functional safety, which monitors and controls at least one slave. At least one second circuit board is designed as a slave for connecting or disconnecting a branch current or current through the respective at least one module, as well as for measuring current, cell voltages, and cell temperatures in conjunction with the cell monitoring circuit, and is arranged in the respective module.

[0009] In a further development of the invention, the at least one second circuit board is connected at module level via a bus to the first circuit board with the battery management system, which is essentially reduced to a control unit component, with a microcontroller.

[0010] In a preferred embodiment of the invention, the low-voltage BMS is provided on a circuit board with galvanic isolation of two individual AS ICs for the evaluation of the electrical voltages on up to 24 elementary memory cells as well as for their monitoring and control and is designed to execute BMS software, by means of which two modules with 12 elementary memory cells each in parallel connection can be read out.

[0011] The above describes a fundamentally freely scalable architecture of a battery management system that essentially requires only one circuit board with a microcontroller and software for connecting several similar systems or 48V modules in parallel. Compared to a battery system with a microcontroller for each of the parallel-connected modules, this results in significant savings in material and hardware, as well as in subsequent effort, such as checking and, if necessary, updating the software for the battery management system.

[0012] Further features and advantages of an embodiment of the invention are explained in more detail below with reference to exemplary embodiments based on the drawings. In this drawing, a schematic representation shows:

[0013] Figure 1: a block diagram of a battery system with an embodiment of a battery management system;

[0014] Figure 2 : a block diagram of a particular embodiment of a battery system and

[0015] Figure 3: a block diagram of a battery system according to the prior art in a representation according to Figure 1.

[0016] The same reference numerals are used for the same elements or method steps throughout the various figures. Without limiting the invention, only one use of exemplary embodiments of the invention using round cell battery modules is shown and described below against the background of use in an electrically powered land vehicle. However, it is obvious to a person skilled in the art that adaptation to mixed forms, such as hybrid vehicles, electrically powered aircraft or ships, and on the other hand also to stationary applications for power supply is possible. In the following, only a 48V level is considered as the low voltage level without limitation.

[0017] Figure 3 shows a block diagram of a battery system 1 which is basically known from the prior art. The battery system 1 is designed for a 48 V low voltage level and, in the example shown, comprises a unit formed from three identically constructed modules 2 by a parallel connection of busbars 3. Inside, the modules 2 each consist, in a manner not further shown in the drawing, of 576 elementary cylindrical storage cells connected to one another in series and / or in parallel, in which 12 cell clusters connected to one another in series are provided, each cell cluster consisting of 48 storage cells connected in parallel. This results in a 12 s48p connection for supplying a 48 V voltage to busbars 3 running to the outside.Each round cell module 2 has its own battery management system BMS and its own cell monitoring circuit CSC, so that the respective cell voltage and temperature of the storage cells can be monitored via the cell monitoring circuit CSC. Due to a direct coupling with the battery management system BMS, the cell monitoring circuit CSC can also be designed as an internal part of the battery management system BMS. In addition, the battery management system BMS has semiconductor switches in the form of MOSFETs at the 48 V voltage level for switching a partial current i through the module 2 and for measuring a value of this partial current i via its own current measuring shunt resistor for the respective module 2 as a parallel branch within the battery system 1. Simply adding the partial currents i for each module 2 results in a total current I of the battery system 1 of 3* i.As indicated in Figure 3, several identical units of the module 2 described above can be connected in parallel; here, there are three modules 2 . The individual battery management systems (BMS) of the modules 2 are connected to one another via a data bus 4 in the form of an isoSPI bus system in a master-slave circuit. From one of the battery management systems (BMS) as the master, a bus 5, here in the form of a CAN bus, then forms a data and control connection to a higher-level vehicle control system (VCU).

[0018] A growing need for ever greater electrical storage capacities is now leading, even in low-voltage applications, to multiple battery modules 2 being interconnected to form increasingly larger battery systems 1. As can be seen from the above illustration and description of Figure 3, the overall costs for a battery system 1 with modules 2 connected in parallel increase essentially linearly with the number of sub-systems or modules 2. Figure 1 shows an exemplary embodiment of an improved battery management system in a battery system 1 as a solution with savings potential, particularly in the case of extensive parallel connections. Here, in a battery system 1 with three modules 2 connected in parallel, only one higher-level battery management system NV-BMS- designed for this low-voltage application is provided.The NV-BMS battery management system is connected to an extended cell monitoring circuit CSC+ for each module 2. Unlike a known cell monitoring circuit CSC, which only includes sensors and signal evaluations for cell voltage and temperature monitoring, each cell monitoring circuit CSC+ is connected to a current measuring device in the form of a current measuring shunt resistor for determining the size of a partial current i through the respective module 2 and is expanded to control semiconductor switches for switching the flow of this partial current i on and off.

[0019] The measures described above protect a battery system 1 with several modules 2 by means of a single modified battery management system NV-BMS-, which here is reduced to a pure control unit for safety monitoring of cell voltages, partial currents i and cell temperatures, whereby this monitoring is carried out for all connected modules 2 via an isoSPI bus 4. The battery management system NV-BMS- essentially only comprises one microprocessor on a first separate circuit board. This circuit board is connected to an extended cell monitoring circuit CSC+ as a second circuit board for data exchange for each module 2. Even with n modules 2 connected in parallel, only one battery management system BMS with a single microprocessor and corresponding software for the monitoring tasks is provided in a battery system 1 instead of n microprocessors.With the fundamentally free scalability of a battery system 1, in a circuit according to Figure 1, the circuitry effort as well as the software maintenance effort have been significantly reduced in this exemplary embodiment compared to a known approach according to Figure 3.

[0020] The illustration in Figure 2 shows a block diagram of a special embodiment of a low-voltage battery system 1 which makes use of an existing battery management system module. This module is characterized as a circuit board by the galvanic isolation of two individual AS ICs A1, A2 for evaluating the cell voltages as well as BMS software which, in the case of a 48V or NV BMS, can also read two modules 2 with 12 cells each if these modules 2 are connected in parallel. This means that with this NV BMS on one circuit board with the associated cell monitoring circuits CSC+, two battery modules 2 connected in parallel can be monitored in a single battery management system. In this way, larger systems with higher capacity and lower hardware costs can be achieved by saving on hardware in the form of a complete second 48V or low-voltage battery management system.By adapting the software of this battery management system, it is possible to select whether 24 elementary cells are used either in a single module 2 in series or divided into two modules 2 in parallel connection, as indicated by the arrows of the AS ICs A1, A2 in Figure 2. The hardware costs of a low-voltage battery system according to Figure 2 are significantly reduced compared to one according to Figure 3.

[0021] Reference number list

[0022] 1 battery system

[0023] 2 round cell modules / modules

[0024] 3 busbar

[0025] 4 Bus / isoSPI

[0026] 5 Bus / CAN

[0027] Al , A2 Application-specific integrated circuits (AS IC )

[0028] BMS Battery Management System

[0029] CSC cell monitoring circuit

[0030] CSC+ functionally extended cell monitoring circuit i partial current per module 2

[0031] I Total current of battery system 1

[0032] NV-BMS - functionally reduced low-voltage battery management system

[0033] VCU central vehicle control

Claims

Claims Battery Management System (BMS) in a battery system (1) for a low-voltage level and in particular for a 48V voltage level, which is provided for the permanent monitoring of currents, voltages, and temperatures within modules (2) of the battery system (1) connected in parallel, characterized in that in the battery system (1) with a parallel connection of modules (2), only one higher-level battery management system (NV-BMS-) is provided, which is connected to one cell monitoring circuit (CSC+) per module (2), wherein each cell monitoring circuit (CSC+) is connected to a current measuring device and is designed to control switches. Battery management system (BMS) according to the preceding claim, characterized in that each switch in extended cell monitoring circuits (CSC+) of the modules (2) is designed as a semiconductor switch, in particular in the form of a MOSFET.Battery management system (BMS) according to one of the preceding claims, characterized in that each module. (2) a functionally extended cell monitoring circuit (CSC+) with two semiconductor switches and a current measuring shunt resistor is arranged as a unit on a common circuit board. Battery management system (BMS) according to one of the preceding claims, characterized in that Devices for monitoring the cell monitoring circuits (CSC+) of all modules (2) connected in parallel and controlling the respective switches in the form of a microcontroller are arranged with the battery management system (NV- BMS-) on a first common circuit board. Battery management system (BMS) according to the preceding claim, characterized in that at least one second circuit board with devices for monitoring the cell monitoring circuits (CSC+) is connected to the first circuit board via a bus (4). Battery management system (BMS) according to one of the preceding claims, characterized in that the battery management system (BMS) is connected to a higher-level vehicle control system (VCU) via a bus (5).Battery management system (BMS) according to one of the preceding claims, characterized in that the low-voltage battery management system (NV-BMS-) is provided on a circuit board with galvanic isolation of two individual ASICs (A1, A2) for the evaluation of 24 cell voltages for monitoring and control, and is designed to execute BMS software, by means of which two modules (2) each with 12 elementary cells in parallel connection can also be read out.

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