Device and method for preventing overcharging of a two-part battery

Abstract

Device for preventing overcharging of a battery comprising a master battery (1) and a slave battery (2), the device comprising: a master battery management system (BMS) (3) designed to determine whether the master battery (1) is overloaded and to switch off a main relay (SW1, SW2) connecting or disconnecting the battery and a motor (6) of a vehicle when the master battery (1) is overloaded as a result of the determination; and a slave BMS (4) designed to determine whether the slave battery (2) is overcharged, and to switch off a charging relay (SW3, SW4) connecting or disconnecting the battery from a charger (7) provided outside the vehicle when the slave battery (2) is overcharged as a result of the determination, where, when the master battery (1) is overcharged, the master BMS (3) generates a first overcharge signal and transmits the first overcharge signal to the slave BMS (4), then, when the slave battery (2) is overcharged, the slave BMS (4) generates a second overcharge signal and transmits the second overcharge signal to the master BMS (3), The slave BMS (4) switches off the charging relay (SW3, SW4) in response to the first overload signal, and The master BMS (3) switches off the main relay (SW1, SW2) in response to the second overload signal, where, if the master battery (1) is overloaded, both the main relay (SW1, SW2) and the charging relay (SW3, SW4) are switched off.

Description

TECHNICAL AREA

[0001] The present invention relates to a technique for preventing overcharging of a two-part battery, applicable to a device that uses electrical energy. In particular, the present invention relates to a technique for preventing overcharging of a high-voltage battery used in a hybrid vehicle, a plug-in hybrid vehicle, and an electric vehicle. STATE OF THE ART

[0002] Recently, various devices have emerged, such as industrial machines, household appliances and vehicles, that use a high-voltage battery, and in particular, high-voltage batteries have been used more actively in the field of automotive engineering.

[0003] A vehicle using an internal combustion engine that primarily uses fossil fuels, such as gasoline or heavy fuel oil, contributes significantly to pollution, including air pollution. Therefore, numerous efforts have recently been made to reduce pollution by developing electric vehicles (EVs) and hybrid vehicles.

[0004] The electric vehicle (EF) is a vehicle that uses neither oil fuel nor an internal combustion engine, but rather an electric battery and an electric motor. This means that an EF, where the vehicle is powered by rotating a motor using electricity stored in a battery, was developed before a gasoline-powered vehicle. However, due to problems such as the weight of the battery and charging time, the EF was not commercially available. But as energy and environmental issues have become increasingly serious in recent years, research into the commercialization of the EF has been underway since the 1990s.

[0005] Since battery technology has been significantly advanced recently, an electric vehicle (EF) and a hybrid electric vehicle (HEF) have now been commercialized, which adaptively use fossil fuel and electrical energy.

[0006] Since the HEF uses both gasoline and electricity as energy sources, the HEV receives positive assessments regarding improved fuel efficiency and reduced emissions. In the case of the HEF, the challenge lies in bridging the price gap between the HEF and a gasoline-powered vehicle, as the number of secondary batteries can be reduced to one-third of that of the EF. Therefore, the HEF is expected to play a transitional role in the development of a fully electric vehicle.

[0007] The HEF and the EF, which use electrical energy, employ a battery in which a plurality of rechargeable / dischargeable secondary cells are designed as a battery pack as the main power source, so that the HEF and the EF have the advantage that no exhaust fumes and very little noise pollution are produced.

[0008] As described above, in a vehicle that uses electrical energy, the battery power directly affects the vehicle's performance, so a battery management system (BMS) is required that can efficiently manage the charging / discharging of each battery cell by measuring the voltage of each battery cell and the voltage, current, and the like of the entire battery, and that is able to stably control a corresponding cell by monitoring the state of an integrated cell detection circuit that detects each battery cell.

[0009] The BMS (Battery Management System) has since been modified to accommodate the battery's structure. Unlike a standard HEV (Heavy Electric Vehicle), a plug-in HEV (Plug-in HEV) incorporates a high-voltage charging system as well as a high-voltage battery system, thus limiting the available battery mounting space. Consequently, in a PHEV, the battery cells are divided into a master battery and a slave battery, mounted in different positions within the vehicle. The BMS can consist of a master BMS, which controls the master battery, and a slave BMS, which controls the slave battery.

[0010] In a master BMS and slave BMS setup, the master BMS controls the charging / discharging state of the master battery and switches a main relay on / off that connects the battery to the vehicle's motor. The slave BMS, on the other hand, controls the charging / discharging state of the slave battery and switches a charging relay on / off that connects the battery to a charger. This means the master BMS and the slave BMS operate independently of each other.

[0011] Accordingly, if the master battery is overcharged during charging, the master BMS can shut off the main relay to prevent an overcurrent from flowing into the vehicle's engine; however, the master BMS cannot control the charging relay, so there is a problem in that it is not possible to prevent the master battery from being continuously overcharged.

[0012] Examples of such previously known designs can be found in US 2009 / 0 146 610 A1, DE 21 2010 000 081 U1, US 2014 / 0 079 960 A1, US 2014 / 0 365 792 A1 and US 2014 / 0 252 847 A1. PRESENTATION OF THE INVENTION

[0013] The present invention aims to provide a device and a method for preventing overcharging, wherein an overcharging signal is transmitted between a master battery management system (BMS) and a slave BMS when the master BMS and the slave BMS are overcharged.

[0014] This problem is solved by a device according to the features of independent claim 1 and / or by a method with the features of independent claims 8 or 9. Further embodiments are described in the dependent claims.

[0015] An exemplary embodiment of the present invention provides a device to prevent a battery from being overcharged, comprising a master battery and a slave battery, wherein the device includes: a master battery management system (BMS) that determines whether the master battery is overcharged, and a main relay that connects or disconnects the battery and a vehicle engine, switching off as a result of the determination when the master battery is overcharged;and a slave BMS that determines whether the slave battery is overcharged and, as a result of the determination, switches off a charging relay that connects or disconnects the battery and a charger provided outside the vehicle if the slave battery is overcharged, wherein if either of the master battery and slave battery is overcharged during the charging of the battery, either of the master BMS and slave BMS transmits an overcharge signal to the other BMS indicating that either of the master battery and slave battery is overcharged, and wherein, upon receiving the overcharge signal, either of the master BMS and slave BMS switches off the main relay or the charging relay, respectively, wherein if the master battery is overcharged, both the main relay and the charging relay are switched off.

[0016] In the exemplary embodiment, if the voltage of a battery cell contained in the master battery is higher than an overcharge reference voltage, the master BMS can determine that the master battery is overcharged.

[0017] In the exemplary embodiment, if the master battery is overcharged during charging, the master BMS can transmit the first overcharge signal to the slave BMS, indicating the overcharging of the master battery, and when the slave BMS receives the first overcharge signal, the slave BMS can switch off the charging relay.

[0018] In the exemplary embodiment, if it is determined that the slave battery is overcharged or the first overcharge signal has been received from the master BMS, the slave BMS can switch off the charging relay.

[0019] In the exemplary embodiment, if the voltage of a battery cell contained in the slave battery is higher than an overcharge reference voltage, the slave BMS can determine that the slave battery is overcharged.

[0020] In the exemplary embodiment, if the slave battery is overcharged during battery charging, the slave BMS can transmit the second overcharge signal to the master BMS, indicating the overcharge of the slave battery, and when the master BMS receives the second overcharge signal, the master BMS can switch off the main relay.

[0021] In the exemplary embodiment, if it is determined that the master battery is overloaded or the second overload signal has been received from the slave BMS, the master BMS can switch off the main relay.

[0022] Another exemplary embodiment of the present invention provides a method for preventing overcharging of a battery comprising a master battery and a slave battery, wherein the method comprises: detecting an overcharge, wherein an overcharged battery is identified from the master battery and slave battery during battery charging; switching off a main relay, wherein, when the master battery is overcharged as a result of the detection during overcharge detection, a master BMS connects the battery to a vehicle engine or disconnects the battery from the vehicle engine; transmitting a first overcharge signal, wherein the master BMS transmits a first overcharge signal to a slave BMS indicating an overcharge of the master battery;and switching off a charging relay, wherein, when the first overload signal is received during the transmission of the first overload signal, the battery is connected to a charger provided outside the vehicle or the battery is disconnected from the charger, wherein, if the master battery is overloaded, both the main relay and the charging relay are switched off.

[0023] A further exemplary embodiment of the present invention provides a method for preventing overcharging of a battery with a master battery and a slave battery, wherein the method comprises: detecting an overcharge, wherein an overcharged battery is detected from the master battery and slave battery during the charging of the battery; switching off a charging relay, wherein, if the slave battery is overcharged, as a result of the detection during the overcharge detection, a slave BMS connects the battery to a charger of a vehicle provided outside the vehicle, or disconnects the battery from the charger; transmitting a second overcharge signal, wherein the slave BMS transmits a second overcharge signal to a master BMS indicating an overcharge of the slave battery;and switching off a main relay, wherein, when the second overload signal is received during the transmission of the second overload signal, the battery is connected to a vehicle engine or the battery is disconnected from the vehicle engine, wherein, if the master battery is overloaded, both the main relay and the charging relay are switched off.

[0024] The present invention enables an overcharge signal to be transmitted between the master BMS and the slave BMS via the master BMS, even if one of the master batteries and the slave battery is overcharged during charging.

[0025] Accordingly, even if one of the master battery and slave battery is overcharged during charging, the master BMS and the slave BMS will switch off both the main relay and the charging relay.

[0026] One effect is therefore to reduce the risk of a certain accident, such as a vehicle fire or explosion, due to battery overcharging.

[0027] The preceding summary is intended only as an illustration and is in no way limiting. In addition to the aspects, embodiments, and features described above, further aspects, embodiments, and features will become clearer with reference to the drawings and the subsequent, more detailed description. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a configuration diagram with a master BMS and a slave BMS. Fig. Figure 2 is a block diagram illustrating a device for preventing overloading according to an exemplary embodiment of the present invention. Fig. Figure 3 is a flowchart illustrating a method for preventing overcharging via a device for preventing overcharging when a master battery is overcharged, according to an exemplary embodiment of the present invention. Fig. Figure 4 is a flowchart illustrating a method for preventing overcharging via a device for preventing overcharging when a slave battery is overcharged, according to an exemplary embodiment of the present invention.

[0028] It should be understood that the accompanying drawings are not necessarily to scale and represent a somewhat simplified depiction of various features that illustrate the basic principles of the invention. The specific design features of the present invention, as disclosed herein, including, for example, certain dimensions, orientations, positions, and shapes, are partly determined by specific applications and the operating environment.

[0029] In the figures, the reference numerals in all figures of the drawing refer to identical or equivalent parts of the invention. DETAILED DESCRIPTION

[0030] Exemplary embodiments of the present invention are described in more detail below with reference to the accompanying drawings.

[0031] The following describes a device for preventing overloading according to an exemplary embodiment of the present invention by means of Fig. 1 and Fig. 2 described.

[0032] Fig. Figure 1 is a configuration diagram with a master battery management system (BMS) and a slave BMS. Based on Fig. Figure 1 illustrates a connection arrangement between a master battery 1, a slave battery 2, a master BMS 3, a slave BMS 4, an inverter 5, a motor 6 and a charger 7.

[0033] Master battery 1 and slave battery 2 can contain a high-voltage battery installed in a hybrid or electric vehicle. Specifically, master battery 1 and slave battery 2 can contain a high-voltage battery installed in a plug-in hybrid electric vehicle (PHEV). Here, master battery 1 and slave battery 2 represent concepts for subdivided positions in which the batteries are mounted, and the structure and characteristics of master battery 1 and slave battery 2 can be identical.

[0034] For example, if 96 battery cells are required to operate the PHEV, 48 of these cells could be mounted in the spare tire position at the bottom of the vehicle's trunk, and the remaining 48 cells could be mounted behind a rear seat. The battery located in the spare tire position at the bottom of the trunk could be designated as master battery 1, and the battery mounted behind the rear seat could be designated as slave battery 2. Alternatively, the battery located in the spare tire position at the bottom of the trunk could be designated as slave battery 2, and the battery mounted behind the rear seat could be designated as master battery 1.

[0035] In the exemplary embodiment, when the main relays SW1 and SW2 are switched on, the master battery 1 and the slave battery 2 can supply current to the motor 6 via the inverter 5. In the exemplary embodiment, when the main relays SW1 and SW2 are switched on, the master battery 1 and the slave battery 2 can draw current from the motor 6 via the inverter 5. The inverter 5 can be used to convert direct current (DC) and alternating current (AC).

[0036] When charging relays SW3 and SW4 are switched on, master battery 1 and slave battery 2 can draw power and be charged via charger 7. Charger 7 can draw power from a power source located outside the vehicle.

[0037] In the exemplary embodiment, the master BMS 3 can determine whether the master battery 1 is overcharged. Specifically, if the voltage of a battery cell contained in the master battery 1 is higher than an overcharge reference voltage, the master BMS 3 can determine that the master battery 1 is overcharged. This means that if the master battery 1 contains 48 battery cells and the voltage of just one of these 48 battery cells is higher than the overcharge reference voltage, then the master BMS 3 can determine that the master battery 1 is overcharged.

[0038] In the exemplary embodiment, if the master battery 1 is overcharged, the master BMS 3 can switch off the main relays SW1 and SW2. This prevents an overcurrent from flowing into the motor 6. However, when the master battery 1 and the slave battery 2 are being charged, the charging relays SW3 and SW4 remain switched on. Therefore, a problem arises in that it is not possible to resolve an overcharge situation of the master battery 1 solely by switching off the main relays SW1 and SW2.

[0039] In the exemplary embodiment, the slave BMS 4 can determine whether the slave battery 2 is overcharged. Specifically, if the voltage of a battery cell in the slave battery 2 is equal to or higher than the overcharge reference voltage, the slave BMS 4 can determine that the slave battery 2 is overcharged. This means that if the slave battery 2 contains 48 battery cells and the voltage of just one of these 48 battery cells is higher than the overcharge reference voltage, the slave BMS 4 can determine that the slave battery 2 is overcharged.

[0040] In the exemplary embodiment, the slave BMS 4 can switch off the charging relays SW3 and SW4 if the slave battery 2 is overcharged. This prevents the slave battery 2 from being overcharged. However, the main relays SW1 and SW4 remain switched on, creating a problem in that an overcurrent can flow into the motor 6 if only the charging relays SW3 and SW4 are switched off.

[0041] To solve the aforementioned problems, it is necessary that an overcharge information from the master battery 1 or the slave battery 2 is shared between master BMS 3 and slave BMS 4.

[0042] Fig. Figure 2 is a block diagram illustrating a device for preventing overloading according to an exemplary embodiment of the present invention.

[0043] Referring to Fig. 2. The device for preventing overloading according to the exemplary embodiment of the present invention can comprise the master BMS 3 and the slave BMS 4.

[0044] The master BMS 3 can include an overload detection unit 11, a debouncing circuit 12, an OR gate 13, an internal signal output unit 14, a common signal output unit 15, an external signal output unit 16 and a microcomputer 17.

[0045] Overcharge detection unit 11 can determine whether master battery 1 is overcharged. If it is determined that master battery 1 is overcharged, overcharge detection unit 11 can transmit an initial overcharge signal to OR gate 13 and internal signal output unit 14. This initial overcharge signal indicates that master battery 1 is overcharged.

[0046] The debouncing circuit 12 can determine whether a signal transmitted from the slave BMS 4 to the master BMS 3 is noise. Specifically, if the signal transmitted from the slave BMS 4 to the master BMS 3 is received in less than a predetermined time, the debouncing circuit 12 can determine that the transmitted signal is noise and block it. Conversely, if the signal transmitted from the slave BMS 4 to the master BMS 3 is received for the predetermined time or longer, the debouncing circuit 12 can determine that the transmitted signal is a second overload signal and transmit it to the OR gate 13 and to the external signal output unit 16.

[0047] When the first overload signal is transmitted from the overload detection unit 11 or the second overload signal is transmitted from the debouncing circuit 12, the OR gate 13 can transmit the transmitted signal to the common signal output unit 15.

[0048] When the first overload signal is transmitted from unit 11 for overload detection, the internal signal output unit 14 can transmit the first overload signal to the slave BMS 4 via the microcomputer 17 and a low-side switch (LSW) 18. Accordingly, even if the master battery 1 is overloaded, information about the overload state of the master battery 1 itself can be communicated to the slave BMS 4.

[0049] When the first overload signal is received by the OR gate 13, the common signal output unit 15 can transmit the first overload signal to the microcomputer 17 and the main relays SW1 and SW2. Accordingly, the main relays SW1 and SW2 can be switched off.

[0050] When the second overload signal is received by the debouncing circuit 12, the common signal output unit 15 can transmit the second overload signal to the microcomputer 17.

[0051] If the first overload signal is received only by the internal signal output unit 14, the microcomputer 17 can detect that the main relays SW1 and SW2 are switched off via the master BMS 3. Conversely, if the second overload signal is received only by the external signal output unit 16, the microcomputer 17 can detect that the main relays SW1 and SW2 are switched off via the slave BMS 4. Accordingly, the microcomputer 17 can confirm whether the slave battery 2 is overloaded and also whether the master battery 1 is overloaded.

[0052] The slave BMS 4 can include an overload detection unit 21, a debouncing circuit 22, an OR gate 23, an internal signal output unit 24, a common signal output unit 25, an external signal output unit 26 and a microcomputer 27.

[0053] The overcharge detection unit 21 can determine whether slave battery 2 is overcharged. If it is determined that slave battery 2 is overcharged, the overcharge detection unit 21 can transmit a second overcharge signal to the OR gate 23 and to the internal signal output unit 24. This second overcharge signal indicates that slave battery 2 is overcharged.

[0054] The debouncing circuit 22 can determine whether a signal transmitted from the master BMS 3 to the slave BMS 4 is noise. Specifically, if the signal transmitted from the master BMS 3 to the slave BMS 4 is transmitted for a shorter time than a predetermined duration, the debouncing circuit 22 can determine that the transmitted signal is noise and block it. Conversely, if the signal transmitted from the master BMS 3 to the slave BMS 4 is transmitted for the predetermined duration or longer, the debouncing circuit 22 can determine whether the transmitted signal is the first overload signal and transmit the signal to the OR gate 23 and the external signal output unit 26.

[0055] If the second overload signal is transmitted from the unit 21 for detecting overload, or if the first overload signal is transmitted from the debouncing circuit 22, the debouncing circuit 22 can transmit the transmitted signal to the common signal output unit 25.

[0056] When the second overcharge signal is received by unit 21 for overcharge detection, the debouncing circuit 22 can transmit the second overcharge signal to the master BMS 3 via the microcomputer 27 and a low-side switch (LSW) 28. Accordingly, even if slave battery 2 is overcharged, information about the overcharge state of slave battery 2 can be transmitted to the master BMS 3.

[0057] When the second overload signal is received by the OR gate 23, the debouncing circuit 22 can transmit the second overload signal to the microcomputer 27 and the charging relays SW3 and SW4. Accordingly, the charging relays SW3 and SW4 can be switched off.

[0058] When the first overload signal is received by the debouncing circuit 22, the external signal output unit 26 can transmit the first overload signal to the microcomputer 27.

[0059] If the second overload signal is received only by the internal signal output unit 24, the microcomputer 27 can detect that the charging relays SW3 and SW4 are switched off via the slave BMS 4. Conversely, if the first overload signal is received only by the external signal output unit 26, the microcomputer 27 can detect that the charging relays SW3 and SW4 are switched off via the master BMS 3. Accordingly, the microcomputer 27 can also confirm whether the master battery 3 is overloaded and also whether the slave battery 2 is overloaded.

[0060] Accordingly, the BMS according to the exemplary embodiment of the present invention can be implemented such that even if one of the master battery 1 and slave battery 2 is overcharged during charging, the overcharge signal is transmitted between the master BMS 3 and the slave BMS 4. Accordingly, even if one of the master battery 1 and slave battery 2 is overcharged during charging, all of the main relays SW1 and SW2 and charging relays SW3 and SW4 can be switched off. Consequently, one benefit is to reduce the risk of a serious accident, such as a vehicle fire or explosion, due to battery overcharging.

[0061] The following describes a method for preventing overloading according to an exemplary embodiment of the present invention, based on Fig. 3 and Fig. 4 described. Repetitions in the description of the parts are explained using the following: Fig. 1 and Fig. 2 omitted.

[0062] Fig. Figure 3 is a flowchart illustrating a method for preventing overcharging with the device for preventing overcharging when the master battery is overcharged, according to an exemplary embodiment of the present invention.

[0063] Referring to Fig. 3. The master BMS 3 can first determine whether the master battery 1 is overloaded (S301).

[0064] If the master battery 1 is overloaded as a result of the determination in step S301, then the master BMS 3 can switch off the main relays SW1 and SW2 to connect or disconnect between the battery and the engine 6 of a vehicle (S303).

[0065] Then the master BMS 3 can transmit an initial overload signal, which reports the overload of the master battery 1 to the slave BMS 4 (S305).

[0066] When the first overload signal is received by the master BMS 3, the slave BMS 40 can switch off the charging relays SW3 and SW4 to connect or disconnect the battery and the charger 7 provided outside the vehicle (S307).

[0067] Fig. Figure 4 is a flowchart illustrating a method for preventing overcharging with the device for preventing overcharging when the slave battery is overcharged, according to an exemplary embodiment of the present invention.

[0068] Referring to Fig. 4 The slave BMS 4 can first determine whether the slave battery 2 is overloaded (S401).

[0069] If the slave battery 2 is overloaded as a result of the determination in step S401, then the slave BMS 4 can switch off the charging relays SW3 and SW4 (S403).

[0070] The slave BMS 4 can then transmit a second overload signal, which reports the overload of the slave battery 2 to the master BMS 3 (S405).

[0071] When the second overload signal is received by the slave BMS 4, the master BMS 30 can switch off the main relays SW1 and SW2 (S407).

Claims

[1] Device for preventing overcharging of a battery comprising a master battery (1) and a slave battery (2), the device comprising: a master battery management system (BMS) (3) designed to determine whether the master battery (1) is overloaded and to switch off a main relay (SW1, SW2) connecting or disconnecting the battery and a motor (6) of a vehicle when the master battery (1) is overloaded as a result of the determination; and a slave BMS (4) designed to determine whether the slave battery (2) is overcharged, and to switch off a charging relay (SW3, SW4) connecting or disconnecting the battery from a charger (7) provided outside the vehicle when the slave battery (2) is overcharged as a result of the determination, where, when the master battery (1) is overcharged, the master BMS (3) generates a first overcharge signal and transmits the first overcharge signal to the slave BMS (4), then, when the slave battery (2) is overcharged, the slave BMS (4) generates a second overcharge signal and transmits the second overcharge signal to the master BMS (3), The slave BMS (4) switches off the charging relay (SW3, SW4) in response to the first overload signal, and The master BMS (3) switches off the main relay (SW1, SW2) in response to the second overload signal, where, if the master battery (1) is overloaded, both the main relay (SW1, SW2) and the charging relay (SW3, SW4) are switched off. [2] Device according to claim 1, wherein when a voltage of a battery cell contained in the master battery (1) is higher than an overcharge reference voltage, the master BMS (3) determines that the master battery (1) is overcharged. [3] Device according to claim 1 or 2, wherein, when the master battery (1) is overcharged during battery charging, the master BMS (3) transmits the first overcharge signal indicating the overcharge of the master battery (1) to the slave BMS (4), and when the slave BMS (4) receives the first overload signal, the slave BMS (4) switches off the charging relay (SW3, SW4). [4] Device according to claim 3, wherein when it is determined that the slave battery (2) is overcharged or the first overcharge signal is received by the master BMS (3), the slave BMS (4) switches off the charging relay (SW3, SW4). [5] Device according to one of the preceding claims, wherein when a voltage of a battery cell contained in the slave battery (2) is higher than an overcharge reference voltage, the slave BMS (4) determines that the slave battery (2) is overcharged. [6] Device according to one of the preceding claims, wherein, when the slave battery (2) is overcharged during the charging of the battery, the slave BMS (4) transmits the second overcharge signal indicating the overcharge of the slave battery (2) to the master BMS (3), and then, when the master BMS (3) receives the second overload signal, the master BMS (3) switches off the main relay (SW1, SW2). [7] Device according to claim 6, wherein when it is determined that the master battery (1) is overloaded or the second overload signal is received by the slave BMS (4), the slave BMS (4) switches off the main relay (SW1, SW2). [8] Method for preventing overcharging of a battery comprising a master battery (1) and a slave battery (2), the method comprising: Detecting an overcharge, whereby an overcharged battery is identified from master battery (1) and slave battery (2) during the charging of the battery; Switching off a main relay (SW1, SW2) connecting or disconnecting between the battery and a motor (6) of a vehicle when the master battery (1) is overcharged as a result of the overcharge detection; Transmission of an initial overload signal, wherein a master BMS (3) transmits an initial overload signal indicating an overload of the master battery (1) to a slave BMS (4); and Switching off a charging relay (SW3, SW4) connecting or disconnecting between a battery and a charger (7) provided outside the vehicle when the first overcharge signal is transmitted, where, if the master battery (1) is overloaded, both the main relay (SW1, SW2) and the charging relay (SW3, SW4) are switched off. [9] Method for preventing an overcharging of a battery comprising a master battery (1) and a slave battery (2), the method comprising: Detecting an overcharge, whereby an overcharged battery is identified from master battery (1) and slave battery (2) during the charging of the battery; Switching off a charging relay (SW3, SW4) connecting or disconnecting between the battery and a charger (7) provided outside a vehicle when the slave battery (2) is overcharged as a result of the overcharging detection; Transmission of a second overload signal, wherein a slave BMS (4) transmits a second overload signal, indicating an overload of the slave battery (2), to a master BMS (3); and Switching off a main relay (SW1, SW2), wherein, when the second overload signal is received during the transmission of the second overload signal, the battery is connected to a motor (6) of a vehicle or the battery is disconnected from the motor (6) of the vehicle, where, if the master battery (1) is overloaded, both the main relay (SW1, SW2) and the charging relay (SW3, SW4) are switched off.

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