WO2023144137A1

WO2023144137A1 - A control unit to manage group of battery packs in a system and method therefore

Info

Publication number: WO2023144137A1
Application number: PCT/EP2023/051668
Authority: WO
Inventors: Siva Prasad Reddy YETTELLA; Yatiraj Ramanujam; Anirudh Upadhyaya
Original assignee: Robert Bosch Gmbh; Bosch Limited
Priority date: 2022-01-31
Filing date: 2023-01-24
Publication date: 2023-08-03

Abstract

In a system (100) of group of battery packs (102), each of the battery pack (102) comprises a BMS controller (110), a BDU (104) and a pre-charge circuit (106), and each of the BMS controllers (110) communicates over a communication channel (108). The control unit (110) detects a wake-up signal, and the control unit (110) operatively controls the BMS controller (110), the BDU (104) and the pre-charge circuit (106) of the individual battery pack (102), and consequently determines connection scheme of the group of battery packs (102) in the system (100) without prior information on the connection scheme. The automatic detection of series/parallel connection without the need of an external control unit, as the BMS controller can take the role of a master/slave based on the algorithm.

Description

Title of the Invention: A CONTROL UNIT TO MANAGE GROUP OF BATTERY PACKS IN A SYSTEM AND METHOD THEREFORE

Field of the invention:

[0001] The present invention relates to a control unit to manage group of battery packs in a system and method therefore.

Background of the invention:

[0002] A patent literature CN104064720 discloses a lithium ion battery pack capable of outputting multiple voltages. The prior art relates to the technical field of a model ship battery, and in particular relates to a lithium ion battery pack capable of outputting multiple voltages. The lithium ion battery pack comprises cells, a printed circuit board assembly and a printed circuit board module, and is characterized in that plugs are embedded in the parts, corresponding to electrodes of the cells of the printed circuit board assembly; the battery pack is formed by sequentially connecting the cells, the printed circuit board assembly and the printed circuit board module; battery pack units with equal cells are connected with one another in series or in parallel by the printed circuit board module to form the battery pack capable of outputting different voltages. According to the lithium ion battery pack, the same number of cells with the same model are connected with one another in series or in parallel by the printed circuit board module to form the battery pack capable of outputting different voltages values, the varieties of the cells of the battery pack can be reduced, the structure is unified, sub materials needed by the battery pack can be shared to the utmost extent, and the production operation difficulty is lowered.

Brief description of the accompanying drawings: [0003] An embodiment of the disclosure is described with reference to the following accompanying drawing,

[0004] Fig. 1 illustrates a block diagram of a control unit to manage a group of battery packs in a system, according to an embodiment of the present invention;

[0005] Fig. 2 illustrates a block of charging station with the group of battery packs, according to an embodiment of the present invention, and

[0006] Fig. 3 illustrates a method for managing the group of battery packs in the system, according to the present invention.

Detailed description of the embodiments:

[0007] Fig. 1 illustrates a block diagram of a control unit to manage a group of battery packs in a system, according to an embodiment of the present invention. In the system 100 of group of battery packs 102, each of the battery pack 102 comprises a Battery Management System (BMS) controller, a Battery Disconnect Unit (BDU) 104 and a pre-charge circuit 106. Each of the BMS controller communicates over a communication channel 108. Further, the control unit 110 configured to detect a wake-up signal, characterized in that, the control unit 110 operatively controls the BMS controller, the BDU 104 and the pre-charge circuit 106 of the individual battery pack 102, and consequently determines connection scheme of the group of battery packs 102 in the system 100 without prior information on the connection scheme.

[0008] In accordance to the present invention, the control unit 110 comprises the memory element (not shown) such as Random Access Memory (RAM) and/or Read Only Memory (ROM), Analog-to-Digital Converter (ADC) and a Digital-to- Analog Convertor (DAC), clocks, timers and at least one processor (capable of implementing machine learning) connected with each other and to other components through communication bus channels. The memory element is prestored with logics or instructions or programs or applications or modules, which is/are accessed by the processor as per the defined routines. The internal components of the control unit 110 are not explained for being state of the art, and the same must not be understood in a limiting manner. The control unit 110 may also comprise communication units to communicate with the cloud server through wireless or wired means such as Global System for Mobile Communications (GSM), 3G, 4G, 5G, Wi-Fi, Bluetooth, Ethernet, serial networks, and the like.

[0009] According to an embodiment of the present invention, to determine the connection scheme, the control unit 110 configured to, identify a total number (n) of battery packs 102 based on number of new messages received over the communication channel 108 having unique identities of respective battery pack 102. The control unit 110 then performs pre-charging by one of the battery pack 102 which has highest voltage and isolates remaining battery packs 102. Further, while the pre-charge is being performed, the control unit 110 receives link voltages reported by all BMS controllers and determines number of battery packs 102 connected in parallel (y). The control unit 110 then determines number of battery packs 102 connected in series (x) based on total number (n) of battery packs 102 and number of battery packs 102 determined to be connected in parallel (y), i.e. y=n/x.

[0010] According to an embodiment of the present invention, while the precharging is performed, the control unit 110 is configured to measure at least one parameter selected from a group comprising a duration of a voltage across a link capacitor and a current drawn during the pre-charging. The control unit 110 then compares the at least one parameter with respective threshold to determine number of series connected battery pack 102 is one or more than one. Further, while the link voltages are being reported, the control unit 110 is configured to determine number of battery packs 102 connected in parallel (y) based on number of battery packs 102 which reports link voltages in proximity to the battery pack 102 performing precharge. The control unit 110 configured to coordinate closing of the BDUs 104 of all battery packs 102 based on the voltage and pre-charge requirement. [0011] According to an embodiment of the present invention, the control unit 110 is at least one selected from a group comprising an external controller and the BMS controller itself which is part of one of the battery pack 102 from the group of battery packs 102. The external controller is for example, a Vehicle Control Unit (VCU) or other controllers which are interfaced with the VCU or directly connected with the group of battery packs 102 or a cloud computer. If the control unit 110 is the BMS controller of one of the battery pack 102, then the first BMS controller which respond to the wake-up signal is designated as master and remaining BMS controllers 110 are designated as slaves. The master the plays the role of the control unit 110, i.e. determines the connection scheme of the group of battery packs 102.

[0012] According to the present invention, a working of the control unit 110 is envisaged without limiting to the same. Consider the control unit 110 is the BMS controller as shown in the Fig. 1. The system 100 is part of a vehicle such as an electric scooter, where multiple of battery packs 102 are needed. The battery packs 102 are connected in a required configuration based on the system voltage inside a battery compartment of the vehicle. The connection scheme or configuration is unknown. Suppose there are ‘n’ battery packs 102 with ‘x’ in series and ‘y’ in parallel as connection scheme. The connection scheme may or may not be known during the assembly, but the control unit 110 is not preset with the information. The individual battery pack 102 in the system 100 each have the BMS controller, with Controller Area Network (CAN) communication channel 108, and equipped with the pre-charge circuit 106. Upon system 100 wake-up, each of the battery pack 102 communicates respective status, battery identification (ID) and other information on CAN. The first BMS controller to successfully transmit the CAN message is assigned as the master. Every successive BMS controller then communicates after a pseudo random interval. Each of the BMS controller successively use different message IDs based on availability. The master then determine the number of battery packs ‘n’ in the system 100 based on the transmitted CAN messages. Upon request from the higher-level system to make the power available, the master follows the below sequence of operation, post start-up diagnosis and checks. First, the master instructs the battery pack 102 with highest voltage to perform pre-charge. In case the pre-charge operation fails i.e. no current is drawn from the battery pack 102, the master infer i.e. number of battery packs 102 connected in series are greater than one, i.e. x>l. In the event the pre-charge is successful, the master infers that the number of battery packs 102 in series is one, i.e. x = 1. The number of battery packs 102 that measure a voltage equal to (or within an acceptable range of) the voltage of the battery pack 102 in pre-charge state is ‘y’. Finally, the number of battery pack 102 in series is calculated as x = n/y. The master then co-ordinates the closing of the remaining BDUs 104 based on the voltage and pre-charge requirement.

[0013] In brief, once the system 100 is switched ON, i.e. a driver inserts a key (not required for keyless type vehicle) and turns ON the vehicle, a wake up request is triggered by the VCU to the group of battery packs 102. Alternatively, a higher level system or an ignition system itself or a Master/Motor Control Unit MCU may as well be a wakeup source and not limited to what is disclosed in the present invention. Consider the BMS controller of the battery pack 102 (Bn) responds first to the wake-up request, then Bn is designated as the master and the BMS controllers of the remaining battery packs 102 are designated as slaves. The master then determines the configuration scheme of the battery packs 102 in the battery compartment, which is then used for charging, discharging the battery packs 102 as a whole.

[0014] In the above example, consider the control unit 110 is the VCU of the vehicle. The VCU sends the wake-circuit and is the master, whereas the BMS controllers of all the battery packs 102 are slaves. The master then coordinates with the slaves and determines the connection scheme of the group of battery packs 102 in the battery compartment.

[0015] According to an embodiment of the present invention, the battery pack 102 with the control unit 110 is provided as a single unit. The similar battery packs 102 if used together enables the determination of the connection scheme. In an alternative embodiment, the VCU is the control unit 110, which coordinates the determination of the connection scheme of the group of battery packs 102 in the system 100. Further, the battery pack 102 is a low voltage battery pack 102 without limiting to the same. For example, 12V battery pack, 24V battery pack, 48 V battery pack and the like. The battery pack 102 is possible to be of high voltage as well.

[0016] According to an embodiment of the present invention, the connection scheme corresponds to interconnection of the individual battery packs 102 with each other, for example 6 batteries are connected in 3 series, 2 parallel. Further, the system 100 is part of vehicles such as a two-wheeler such as motorcycle, scooter, a three-wheelers such as auto-rickshaws, a four-wheeler such as cars, multi-wheel vehicles such as Buses, trucks, logistic vehicles such as electric-karts, electrictrolleys, e-beds, and other vehicles such as snowmobiles and water sports vehicles, which require battery packs 102. The system 100 is also possible to be part of different domain such as power tools, charging station 202 (shown in Fig. 2), bulk chargers and those areas where ecosystem of multiple battery packs 102 are used either permanently or in swappable manner.

[0017] According to an embodiment of the present invention, the control unit 110 is able to determine the connection scheme of group of battery packs 102 which are arranged in the form of a matrix.

[0018] According to an embodiment of the present invention, a group of battery packs 102 is provided. Each of the group of battery packs 102 are equipped with the BMS controller which are capable of determining the connection scheme in which they are connected in the system 100. The group of battery pack 102 comprises at least two battery packs 102 and any one of the group of battery pack 102 is able to become the master or slave based on the first response transmitted on receiving the wake-up signal in the system 100. [0019] Fig. 2 illustrates a block of charging station with the group of battery packs, according to an embodiment of the present invention. The charging station 202 comprises necessary circuits such as current control unit, an AC -DC converter, and a DC-DC converter to enable charging of the battery pack 102. Further, the charging station 202 is connected with source of electrical energy such as AC supply from grid, or renewable source of energy such as Solar, Wind, Hydro, etc., or diesel generator sets, etc. The charging station 202 comprises swapping based charging based on the need or type of the vehicle. The circuit shown in Fig. 2 is for understanding and must not be understood in limiting manner.

[0020] According to an embodiment of the present invention, the control unit 110 is used in the charging station 202 or bulk chargers, which allows multiple battery packs 102 to connect in series/ parallel configurations during charging. If connected in series, the overall current in the DC line in the charger station 202 maybe lowered, hence saving space and cost. In an embodiment, no changes is done to the charging station 202. The charging station 202 communicates with only one control unit 110 which is the master, of the multiple battery packs 102 kept in the slots, hence making the control simpler and thus there is potential to reduce the number of CAN channels on the charging station 202 as well. In an alternative embodiment, the control unit 110 is provided in the charging station 202 which then coordinates with the battery packs 102 placed in the slots for charging. The control unit 110 determines the connection scheme and in turn the slot location, which is then used to improve or optimize charging and discharging accordingly based on the requirement.

[0021] Consider a scenario where the x is 3 and y is 3 and n is 9. The battery packs 102 are equipped with the BMS controllers which functions as the control unit 110 described above. When the battery packs 102 are assembled in the group in the system 100, and the wake-up signal is generated, say B21 responds first and therefore becomes the master. Once all the battery packs have performed respective initial communication over the communication channel 108 the master is able to determine n as 9. The slaves also performs checks for error or malfunction before reporting the respective status on the communication channel 108. The master then initiates pre-charging through the battery pack which reported highest voltage say B32 as the first pre-charging battery pack 102. The battery packs B31, B32 and B33 are connected in parallel, hence even through the BDU 104 of B31 and B33 is open, the link voltage is same as that of B32 which is being used for pre-charging. The master also determines that B31, B32 and B33 are three battery packs 102 connected in parallel (y) and is the first string. At the same time, the link voltages of remaining battery packs Bn, B12, B13, B21, B22 and B23 are either zero or less than a threshold voltage. The master is able to determine the connection scheme based on n and y.

[0022] The pre-charging using the B32 is incomplete as the series connected battery pack 102 is yet to be found to form a closed circuit with an external link capacitor. The master checks for the battery pack with next higher voltage apart from the first string. Consider the master selects B13 as the next battery pack 102 for pre-charge. The same steps are repeated as done when B32 was considered for pre-charge. The master determines that Bn and B12 are measuring the same link voltages as B13, and identifies them to be connected in parallel in a second string. The master finally checks the next higher voltage for pre-charge from the remaining battery packs 102, say B22 is selected. Again, the same steps of pre-charge is repeated as above and the master determines the B21, B22 and B23 are connected in parallel as the third string. After all the three strings are found, the pre-charge is completed as a closed loop circuit is formed with an external link capacitor using the three battery packs 102 which are B13, B22, and B32. The pre-charging of remaining battery packs 102 is completed which is fast in comparison to the first pre-charging.

[0023] According to the present invention, the working example provided in Fig. 2 is applicable for Fig. 1 as well and is explained once to avoid repetition. Further, a detailed explanation is provided in the method flow diagrams in Fig. 3 and Fig. 4. [0024] Fig. 3 illustrates a method for managing the group of battery packs in the system, according to the present invention. Each of the battery pack 102 comprises the Battery Management System (BMS) controller, the Battery Disconnect Unit (BDU) 104 and the pre-charge circuit 106, and each of the BMS controllers communicate over the communication channel 108. The method comprises multiple steps of which, a step 302 comprises detecting a wake-up signal of the system 100. The method is characterized by a step 304 which comprises determining the connection scheme of the group of battery packs 102 in the system 100 by operatively controlling the BMS controller, the BDU 104 and the pre-charge circuit 106 of individual battery pack 102. The method is performed executed by the control unit 110.

[0025] The step 304 of determining connection scheme comprises further steps, of which a step 306 comprises identifying the total number (n) of battery packs 102 based on number of new messages received over the communication channel 108 having unique identities of respective battery pack 102. A step 308 comprises precharging by one of the battery pack 102 which has highest voltage and isolating remaining battery packs 102. A step 310 comprises, while the pre-charging is being performed, receiving link voltages reported by the BMS controllers and determining number of battery packs 102 connected in parallel (y). A step 312 comprises determining number of battery packs 102 connected in series (x) based on the total number (n) of battery packs 102 and the number of battery packs 102 determined to be connected in parallel (y).

[0026] The step 310 of determining ‘y’, comprises a step 314 of measuring at least one parameter selected from the group comprising the duration of the voltage across the link capacitor and the current drawn during the pre-charging. A step 316 comprises comparing the at least one parameter with respective threshold for determining number of series connected battery pack 102 is one or more than one. Further, in the step 310, while the link voltages are being reported, a step 318 comprises determining number of battery packs 102 connected in parallel based on number of battery packs 102 which reports link voltages in proximity to the battery pack 102 performing pre-charge.

[0027] According to the present invention, the control unit 110 is at least one selected from the group comprising the external controller and the BMS controller of one of the battery pack 102 from of the group of battery packs 102 and the cloud computer connected to the battery packs 102.

[0028] Fig. 4 illustrates a detailed method flow diagram of managing the group of battery packs, according to the present invention. Assuming that in the system 100, ‘n’ battery packs 102 are present, connected in an ‘x’ series, ‘y’ parallel scheme or configuration depending on the requirement and/or application. The method enables determination of the ‘n’, ‘x’ and ‘y’. Further, in the method the BMS controller is considered to be the control unit 110. A step 402 comprises detecting/receiving a wake-up request. In a step 404 each BMS controller waits for a pseudo-random interval before sending a response to any wake-up signal based on a unique hardware (HW) ID flashed onto the respective BMS controller during production or manufacturing. For example, based on message transmission time, baud rate, etc., the pseudo-random interval could be any duration between 10-30ms (example only). In step 406, the first BMS controller to successfully transmit a CAN message over the communication channel 108 is designated as the master. The master uses the first set of message IDs in a set of message IDs reserved for the battery system. In brief, the master is allocated by the BMS controller itself or by the VCU. In step 408, every other BMS controller sends messages after waiting for pseudo random intervals based on the respective unique HW ID. The BMS controllers adopts successive message IDs in the set based on availability at time of communication or set reserved for the battery system for transmission. In brief, the slave IDs are allocated. A step 410 comprises checking if any new messages received within a set duration to ensure all the battery packs 102 are accounted. If Yes, then the allocation of slave IDs are continued, otherwise the master and the slave are identified. In other words, if no new messages are received for more than a defined time interval (e.g. 500ms), all battery packs 102 in the system 100 have performed initial communication. The master determines the number of battery packs 102 connected in the system 100 based on number of message IDs used/received. In step 412, the master instructs all the BMS controllers to perform the start-up checks. If errors are detected, then the respective battery pack 102 is permanently isolated through the BDU 104. If any BMS controller reports a fault in the BDU 104, the battery pack 102 remains in the safe state and all the remaining battery pack 102 are isolated through respective BDUs until reset.

[0029] In step 414, all the BMS controllers report back the volage, State of Charge (SOC), State of Health (SOH), temperature and other characteristics of respective battery pack 102 to the master. The master instructs the battery pack 102 with the highest voltage to perform pre-charge. When pre-charge is in process, all the other battery packs 102 are disconnected. In step 416, the master measures the duration of the pre-charge or the current drawn. If the link voltage rises almost instantly, then load capacitance is not present across the terminals of the batter pack 102 which is performing the pre-charge, i.e. a closed path is not formed, and thus ‘x’ is greater than one. If voltage rises after some significant interval (example 50ms), then load capacitance is present across the terminal of the battery pack 102 performing the pre-charge and ‘x’ is equal to 1 . In step 418, all the slaves measure the link voltage, (despite being disconnected), and report to master. The number of slaves that measure the respective link voltage within a preset proximal range of the voltage of the battery pack 102 performing pre-charge, is equal to the number of battery packs 102 connected in parallel, i.e. ‘y’. The master then determines the number of battery pack 102 connected in series as x=n/y.

[0030] In step 420, the master then commands the battery pack 102 with the next highest voltage which does not measure respective voltage (or zero link voltage) in the previous step, to close the respective BDU 104 through the pre-charge circuits 106. The master determines which battery packs 102 are paralleled based on which new battery pack 102 read the voltage in pre-charge state. This is repeated until all the slaves that have their BDU 104 open, measure respective link voltage. The precharge is also completed in this step. In step 422, the master instructs all the slaves that have respective BDUs 104 open to close if estimated equalization current is within an acceptable limit. In step 422, the master communicates combined current/power limits and SoC, SoH of the system 100 to other nodes and is now active for further requirements in the system 100. Although, the control unit 110 and the system 100 in Fig. 1 and Fig. 2 and the method in Fig. 3 and Fig. 4 are explained independently, but they complement each other. The method is carried out in the system 100 by the control unit 110.

[0031] According to the present invention, the control unit 110 and the method helps saving time and cost for system 100 integration (including software development, variant development) by automatic detection of series/ parallel combination to suit various system applications from 12V kick scooters to 24-36 V trolleys to 48V traction two-wheelers. The method uses a master/slave concept and communicates charging/ discharging current limits based on SOC, SOH and temperature. This control unit 110 and method helps standardize a low voltage battery packs 102 to be used across different applications in a series or parallel combination. There is no need for an additional control unit, as every battery pack 102 comes equipped with the BMS controller which takes the role of a master or slave based on the algorithm. The present invention ensures that components and systems 100 from different suppliers can be integrated easily without needing additional development to manage a multi-battery system 100. For example, a two 12V battery pack 102 connected in series in a 24V kick scooter can operate jointly to communicate with the VCU for vehicle operation. The present invention is also applicable and extendible to High Voltage systems.

[0032] According to an embodiment of the present invention, auto-detection of configuration of group of battery packs 102 by the control unit 110 is disclosed. The control unit 110 is possible to be BMS controller of the battery pack 102 itself. An approach to design BMS controller with an architecture which seamlessly works for multiple low voltage applications (for example 12V through 48V) with intelligence to adapt to series parallel combinations. In the system 100, each battery pack 102 is equipped with the BMS controller and the master designation is provided based on strategy. The master works with the VCU or a charger controller to intelligently simplify controls, nodes and improve functional robustness of battery state initiation and charging.

[0033] The automatic detection of series/parallel connection without the need of an external control unit (can be used in any system 100 without needing additional development). Useful when the same battery pack 102 are sold as a unit and multiple units are used in series as well as parallel for a wide variety of applications. Example, a 12V battery can be used y in parallel, x in series. The system 100 uses Controller Area Network (CAN) communication, pre-charge circuit 106, a master slave concept and link voltage measurement to automatically detect the configuration. Also, as an example, Lithium-ion battery packs 102 which can be serially or parallelly integrated can be auto used with BMS controllers which can automatically detect the configuration. This reduces complexity and multi BMS requirement. The battery packs 102 are possible to be modularized.

[0034] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.

Claims

We claim:

1. A control unit (110) to manage a group of battery packs (102) in a system (100), each of said battery pack (102) comprises a Battery Management System (BMS) controller, a Battery Disconnect Unit (BDU) (104) and a precharge circuit (106), and each of said BMS controllers communicates over a communication channel (108), said control unit (110) configured to detect a wake-up signal, characterized in that, determine connection scheme of said group of battery packs (102) in said system (100) by operative control of said BMS controller, said BDU (104) and said pre-charge circuit (106) of individual battery pack (102).

2. The control unit (110) as claimed in claim 1, wherein to determine said connection scheme, said control unit (110) configured to, identify a total number (n) of battery packs (102) based on number of new messages received over said communication channel (108) having unique identities of individual battery pack (102); perform pre-charging by one of said battery pack (102) which has highest voltage and isolate remaining battery packs (102); while said pre-charge is being performed, receive link voltages reported by all BMS controllers and determine number of battery packs (102) connected in parallel (y), and determine number of battery packs (102) connected in series (x) based on total number (n) of battery packs (102) and number of battery packs (102) determined to be connected in parallel (y). The control unit (110) as claimed in claim 2, wherein while said pre-charging is performed, said control unit (110) configured to measure at least one parameter selected from a group comprising a duration of a voltage across a link capacitor and a current drawn during said precharging, and compare said at least one parameter with respective threshold to determine number of series connected battery pack (102). The control unit (110) as claimed in claim 2, wherein while said link voltages are being reported, said control unit (110) configured to determine number of battery packs (102) connected in parallel based on number of battery packs (102) which reports link voltages in proximity to said battery pack (102) performing pre-charge. The control unit (110) as claimed in claim 1 is any one selected from a group comprising an external controller and said BMS controller of one of said battery pack (102) from of said group of battery packs (102). A method of managing a group of battery packs (102) in a system (100), each of the battery pack (102) comprises a Battery Management System (BMS) controller, a Battery Disconnect Unit (BDU) (104) and a pre-charge circuit (106), and each of said BMS controllers communicate over a communication channel (108), said method comprises a step of detecting, by a control unit (110), a wake-up signal, characterized by, determining connection scheme of said group of battery packs (102) in said system (100) by operatively controlling said BMS controller, said BDU (104) and said pre-charge circuit (106) of individual battery pack (102). The method as claimed in claim 6, wherein said step of determining connection scheme comprises the steps of, identifying a total number (n) of battery packs (102) based on number of new messages received over said communication channel (108) having unique identities of respective battery pack (102); pre-charging by one of said battery pack (102) which has highest voltage, and isolating remaining battery packs (102); while said pre-charging is being performed, receiving link voltages reported by BMS controllers and determining number of battery packs (102) connected in parallel (y), and determining number of battery packs (102) connected in series (x) based on said total number (n) of battery packs (102) and said number of battery packs (102) determined to be connected in parallel (y). The method as claimed in claim 7, wherein while said pre-charging is performed, said control unit (110) comprises the steps of measuring at least one parameter selected from a group comprising a duration of a voltage across a link capacitor and a current drawn during said precharging, and comparing said at least one parameter with respective threshold for determining number of series connected battery packs (102). The method as claimed in claim 7, wherein while said link voltages is being reported, said control unit (110) comprises a step of determining number of battery packs (102) connected in parallel based on number of battery packs (102) which reports link voltages in proximity to said battery pack (102) performing pre-charge. The method as claimed in claim 7, wherein said control unit (110) is at least one selected from a group comprising an external controller and said BMS controller of one of said battery pack (102) from of said group of battery packs (102).