Claims:We claim:
1. A BMS (102) for an Electric Vehicle (EV), to establish CAN communication during ground shift errors, said EV comprises a drive battery pack (104) to power a drive motor (124), and an auxiliary battery (128) for powering a Vehicle Control Unit (VCU) (120), and said BMS (102) comprises a controller (110) and a pre-charge circuit (108), each of said controller (110) and said VCU (120) are connected with respective CAN transceivers, namely a first transceiver (106) and a second transceiver (130), said first transceiver (106) is referenced to a negative terminal of said battery pack (104), and said second transceiver (130) is referenced to a negative terminal of said auxiliary battery (128), characterized in that BMS (102), said controller (110) configured to,
determine a failure of CAN communication between said VCU (120) and said BMS (102), based on an attempted first CAN based wake-up signal from said VCU (120), and
activate said pre-charge circuit (108) of said BMS (102) to equalize the ground potential at the negative terminals of said battery pack (104) and said auxiliary battery (128) and establish said CAN communication.

2. The BMS (102) as claimed in claim 1, wherein said failure is determined based on detection of only a dominant bit of any one selected from a group comprising said first CAN based wake-up signal and a following CAN based wake-up signal, before activation of said pre-charge circuit (108).

3. The BMS (102) as claimed in claim 1, wherein a difference of said ground potentials is compared with a threshold value and said CAN communication is established when said comparison is successful.

4. The BMS (102) as claimed in claim 1, wherein a time delay is configurable to prevent repeated activation of said pre-charge circuit (108).

5. The BMS (102) as claimed in claim 1, wherein said BMS (102) is independent of type of pre-charge circuit (108) used.

6. A method for establishing CAN communication by a BMS (102) during ground shift errors in an Electric Vehicle (EV), said EV comprises a drive battery pack (104) to power a drive motor (124), and an auxiliary battery (128) for powering a Vehicle Control Unit (VCU) (120), and said BMS (102) comprises a controller (110) and a pre-charge circuit (108), each of said controller (110) and said VCU (120) are connected with respective CAN transceivers, namely a first transceiver (106) and a second transceiver (130), said first transceiver (106) is referenced to a negative terminal of said battery pack (104), and said second transceiver (130) is referenced to a negative terminal of said auxiliary battery (128), characterized by, said method comprising the steps of:
determining, by said controller (110), a failure of CAN communication between said VCU (120) and said BMS (102) based on an attempted first CAN based wake-up signal from said VCU (120), and
activating said pre-charge circuit (108) to equalize the ground potential at the negative terminals of said battery pack (104) and said auxiliary battery (128) and establishing said CAN communication.

7. The method as claimed in claim 6, wherein determining said failure comprises detecting a dominant bit of any one selected from a group comprising said first CAN based wake-up signal and a following CAN based wake-up signal, before triggering activation of said pre-charge circuit (108).

8. The method as claimed in claim 6, comprises comparing a difference of said ground potentials with a threshold value and establishing said CAN communication when said comparison is successful.

9. The method as claimed in claim 6, configuring a time delay to prevent repeated activation of said pre-charge circuit (108).

10. The method as claimed in claim 6, is independent of type of pre-charge circuit (108) used in said BMS (102).
, Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed:

Field of the invention:
[0001] The present invention relates to a Battery Management System (BMS) and method to establish CAN communication during ground shift errors.

Background of the invention:
[0002] A majority of systems use isolated CAN transceivers to tackle the ground shift problem. In case it is a non CAN based system, hardwired wake up based on KL15 is used. An Opto-coupler maybe used in such systems to detect KL15 input. In some cases, a signal referenced to the battery may itself be toggled externally, this requires extra harness and pinouts in the connector. Some may use positive side switching to eliminate ground shift errors/issues.

[0003] A 48V lithium-ion battery typically has a BMS which usually have CAN to communicate with the other nodes (electronic control units) in the system (vehicle). The CAN is usually implemented as per ISO 11898 in the BMS. It is differential form of communication. Even though it is differential, the CAN transceiver operates within a limited common mode voltage range. If the potential is exceeded, the CAN communication does not work, even though the CAN transceiver may not be damaged. The ISO11898-2 standard requires transceivers to be functional over a common mode voltage range of -2V to +7V, which is far lower than the shift of around 48V. The ISO standards are mentioned for reference and easy understanding only, this must not be understood in limiting manner. The 48V systems have no isolation requirements and isolation may or may not implemented for cost reasons. In these cases, the BMS and all systems/components therein are referenced to the negative of a battery pack. These also employ solid state (MOSFETs, SSRs, etc.) based Battery Disconnect Unit (BDU) for packaging and cost considerations. As a result, negative side switching is employed to reduce complexity and cost. In battery packs that employ a negative side switching the ground shift voltage is higher than permissible when the MOSFETs are open, which hinders CAN communication. The systems that employ CAN based wake up hence does not work.

[0004] The traditional solutions, like using an optical isolator do not work with CAN. One way to work around this problem, is to use an isolated CAN transceiver, but this is expensive. Alternately positive side switching can be used, but this leads to additional complexity in circuitry and increase in Printed Circuit Board (PCB) footprint along with increasing cost. Alternately hardwired wake up could be implemented which could lead to additional wires and other components and additional pins in the connector.

[0005] The 48V Li-ion batteries usually have the BMS with one of its function being to disconnect the battery pack from the load. This is usually done in two ways, either using an electromechanical relay or using a semiconductor-based switch (e.g.: MOSFET). Owing to cost and packaging advantages, more and more battery packs are employing a semiconductor-based switching. Additionally, the switch is usually placed in the negative terminal of the battery pack, due to advantages in implementation compared to switching on the positive terminal. A controller in the BMS is referenced to the negative terminal of the lowest cell. The battery packs that use CAN based wake up are woken by an external node which is usually the vehicle control unit (VCU) in the vehicle. The VCU is referenced to the 12V auxiliary battery. When the MOSFETs are in the cut-off region (or OFF), a voltage comparable to the battery pack voltage is dropped across them, thus creating a large difference in the ground potential of the BMS and the VCU. The on-board CAN transceiver on the BMS is unable to drive CANH (CAN high) and CANL (CAN low) lines beyond this common mode voltage in order to transmit messages, thus hindering the wake up of battery pack.

[0006] A patent literature US5216674 discloses a method of and device for bringing a network interface out of a sleep mode into a wake-up state. An activation device for bringing a network interface of a computer network for a motor vehicle, with at least two bus lines, out of a sleep mode into a wake-up mode. The activation device includes a signal flank change detection circuit, which is coupled to the bus lines and a reference voltage. In the event of an interruption or in the event of a short-circuit of one of the bus lines to ground or to a supply voltage of the computer network, the circuit evaluates a signal arriving on the other, intact bus line and emits a wake-up signal for the activation of the network interface. The flank change detection circuit has two comparators, which are connected to the bus lines (U-, U+) and via a voltage divider to a reference voltage (Vcc/2). A voltage offset is produced by the voltage divider, by which offset the network interface can be brought into wake-up mode in the event of a short-circuit of the bus lines between each other, even if it was in sleep mode when the fault occurred.

Brief description of the accompanying drawings:
[0007] An embodiment of the disclosure is described with reference to the following accompanying drawing,
[0008] Fig. 1 illustrates a block diagram of a system of an Electric Vehicle (EV), according to an embodiment of the present invention;
[0009] Fig. 2 illustrates a conventional pre-charge circuit used in the BMS, according to an embodiment of the present invention;
[0010] Fig. 3 illustrates modified pre-charge circuits used in the BMS, according to an embodiment of the present invention, and
[0011] Fig. 4 illustrates a method for establishing CAN communication by a BMS during ground shift errors in the Electric Vehicle (EV), according to the present invention.

Detailed description of the embodiments:
[0012] Fig. 1 illustrates a block diagram of a system of an Electric Vehicle (EV), according to an embodiment of the present invention. The system 100 comprises a battery pack 104 having the BMS 102, an On-Board Charger (OBC) 114, a Body Control Unit (BCU) 116, a Cluster Control Unit (CCU) or a Human Machine Interface (HMI) 118, a Vehicle Control Unit (VCU) 120, a Motor Control Unit (MCU) 122 and a drive motor 124. The system 100 also comprises a non-isolated DC-DC converter 126 connected between the battery pack 104 and an auxiliary battery 128. Further, the battery pack 104 is of 48V, and the auxiliary battery 128 is of 12V. The specific voltage is for explanation and must not be understood in limiting manner. The positive terminal (B+) and negative terminal (B-) of the battery pack 104 is marked for clarity. Further, all the aforesaid control units are connected with each other through the CAN network formed by CAN high (CANH) 132 and CAN low (CANL) 134. Also, the OBC 114 and the MCU 122 are connected across the battery pack 104, whereas the remaining control units are coupled across the auxiliary battery 128. The OBC 114 is connectable to an external supply 112 for charging purpose. The system 100 describes the basic architecture of control units communicating with each other through CAN network (or CAN bus).

[0013] In accordance to an embodiment of the present invention, the BMS 102 is provided for an Electric Vehicle (EV) to establish CAN communication during ground shift errors. The EV comprises the drive battery pack 104 to power the drive motor 124, and the auxiliary battery 128 for powering the VCU 120. The BMS 102 comprises a controller 110 and a pre-charge circuit 108. Each of the controller 110 and the VCU 120 are connected with respective CAN transceivers, namely a first transceiver 106 and a second transceiver 130, respectively. The first transceiver 106 is referenced to a negative terminal of the battery pack 104, and the second transceiver 130 is referenced to a negative terminal of the auxiliary battery 128, characterized in that BMS 102, the controller 110 configured to, determine a failure of CAN communication between the VCU 120 and the BMS 102, based on an attempted first CAN based wake-up signal from the VCU 120, and activate the pre-charge circuit 108 of the BMS 102 to equalize the ground potential at the negative terminals of the battery pack 104 and the auxiliary battery 128, and establish CAN communication. The controller 110 is able to establish the CAN communication because the ground shift error is eliminated due to potential equalization.

[0014] The failure is determined based on detection of only a dominant bit of any one selected from a group comprising the first CAN based wake-up signal and a following CAN based wake-up signal (next or second), before activation of the pre-charge circuit 108. Alternatively, the absence of CAN communication between the VCU 120 and the controller 110 of the BMS 102 for a specific set time threshold results in determination of failure. The controller 110 calculates a difference of the ground potentials and compares with a threshold value. The CAN communication is established when the comparison is successful. The controller 110 is able to configure a time delay to prevent repeated activation of the pre-charge circuit 108. The time delay is provided to check if the equalization of the potential is achieved in set time threshold or not. Further, the BMS 102 is independent of type of pre-charge circuit 108 used such as resistor based or current controlled based or any other type of pre-charge circuit 108.

[0015] The controller 110 comprises memory element (not shown) such as Random Access Memory (RAM) and/or Read Only Memory (ROM), Analog-to-Digital Converter (ADC) and vice-versa Digital-to-Analog Convertor (DAC), clocks, timers and at least one processor (capable of implementing machine learning) connected with the each other and to other components through communication bus channels. The memory element is pre-stored with logics or instructions or programs or applications and/or threshold values, which is/are accessed by the processor as per the defined routines. The internal components of the controller 110 are not explained for being state of the art, and the same must not be understood in a limiting manner. The controller 110 may also comprise communication units to communicate with a server or cloud (not shown) 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. In accordance to an embodiment of the present invention, the controller 110 is the Battery Control Unit inside the BMS 102 or a separate control unit interfaced with the Battery Control Unit.

[0016] In accordance to an embodiment of the present invention, the vehicle is preferably a two-wheeler such as a motorcycle, a scooter, a moped, etc. However, the controller 110 is equally adaptable to be used for three-wheelers such as auto-rickshaws, four wheelers such as cars and the other existing and new vehicles (even snow mobiles) where the cruise control features has been in use and possible to be used.

[0017] Fig. 2 illustrates a conventional pre-charge circuit used in the BMS, according to an embodiment of the present invention. A first circuit 200 represents, by approximation, a circuit internal to/inside the battery pack 104. The first circuit 200 comprises cells 202, the conventional pre-charge circuit 108 which is conventional current limiter based circuit and Battery Disconnect Unit (BDU) 204. The BDU 204 is not discussed due to being state of the art. The elements denoted by Q are MOSFETs, and which are denoted by R are resistors. Also, the acronym “cv” denotes the signals from the controller 110. The elements Q1, Q2, are transistors and Rg and Rs (“s” in Rs denotes “sense”) are resistors, all of which shows a typical implementation of a current limiter based pre-charge circuit 108. Further, a capacitor Czk refers to the total system capacitance (including motor controller, DC/DC, etc.) that is to be pre-charged. The resistor Rg is the gate resistance that is added to prevent ringing and limit the current into the gate when Q1 is turned ON/OFF.

[0018] When the BMS 102 receives the pre-charge request, the controller 110 (or another control unit in communication with the controller 110) charges the gate of Q1, through Rg, to turn it ON. As the current flows, the drop across Rs rises. The gate of Q2 is connected across Rs, and hence Q2 starts conducting as well. This reduces the gate voltage at Q1, thereby limiting the current through Q1. This forms a negative feedback network, that limits the current through Q1 to a maximum value based on the value of Rs and characteristics of Q1 and Q2.

[0019] Fig. 3 illustrates modified pre-charge circuits used in the BMS, according to an embodiment of the present invention. Similar to the Fig. 2, a second circuit 310 and a third circuit 320 are shown, which are in fact the first pre-charge circuit 108 but with two added group of components, a first group 302 and a second group 304, respectively. Also, a BMS ground 206 and system ground 208 are shown for simplicity. In an embodiment of the present invention, the current limiter based pre-charge circuit 108 comprises the at least one group 302, 304, used in a specific manner, to increase the negative feedback which will reduce the gate–source voltage across the pre-charge MOSFET. This reduces the current during the equalization while also being a safe high impedance path. If a normal pre-charge is required, these group of elements is made inactive.

[0020] In accordance to an embodiment of the present invention, and with respect to a second circuit 310 comprising the first group 302, the Q3 and R2 are employed to further reduce the gate voltage at Q1. The element Q3 is turned ON by the controller 110 on the BMS 102 when it is desired to equalize the ground potentials through a small, safe current. This presents R2, which in conjunction with Rg, creates a voltage divider which reduces the gate voltage at Q1. The resistor R2 is selected such that the current through Q2 (dictated by feedback caused by Rs) and R2 are comparable so as to prevent creating a low resistance path through Q2 which could otherwise render R2 ineffective. The element Q3 can be a low power, small signal transistor and R2 can be a low power resistor. When it is desired to perform pre-charge, Q3 is turned OFF and the pre-charge circuit 108 functions as described earlier.

[0021] Alternatively, in accordance to an embodiment and with respect to the third circuit 320 comprising the second group 304, the elements Q4 and R1 are employed to implement the same function. When it is desired to perform potential equalization, Q4 is turned OFF, and Q1 is turned ON. The resistor R1 has a larger value such that the drop across R1 and Rs is greater, thereby increasing the amount of negative feedback. This limits the current through Q1 to a small and safe value. When it is desired to perform pre-charge, Q4 is turned ON, thereby providing a low impedance path across R1, and the circuit functions as described earlier. The elements Q4 and R1 must be rated for similar power ratings as Q1 and Rs. The embodiments using first group 302 and the second group 304 are optional and at least one is implementable with the pre-charge circuit 108. The first group 302 and the second group 304 achieve above function in different ways. Further, alternate implementations could include a resistor based pre-charge scheme where a higher resistance is selected to limit the equalization current, and a lower resistor is selected to perform pre-charge with a higher current.

[0022] Fig. 4 illustrates a method for establishing CAN communication by a BMS during ground shift errors in the Electric Vehicle (EV), according to the present invention. The EV comprises the drive battery pack 104 to power the drive motor 124, and the auxiliary battery 128 for powering the Vehicle Control Unit (VCU) 120. The BMS 102 comprises the controller 110 and the pre-charge circuit 108. Each of the controller 110 and the VCU 120 are connected with respective CAN transceivers, namely the first transceiver 106 and the second transceiver 130, respectively. The first transceiver 106 is referenced to the negative terminal of the battery pack 104, and the second transceiver 130 is referenced to the negative terminal of the auxiliary battery 128. The method is characterized by, a step 402 which comprises determining, by the controller 110, the failure of CAN communication between the VCU 120 and the BMS 102, based on the attempted first CAN based wake-up signal from the VCU 120. A step 404 comprises, activating the pre-charge circuit 108 to equalize the ground potential at the negative terminals of the battery pack 104 and the auxiliary battery 128 and establishing the CAN communication. The controller 110 is able to establish the CAN communication because the ground shift error is eliminated due to potential equalization.

[0023] The step 402 of determining the failure comprises detecting the dominant bit of any one selected from a group comprising the first CAN based wake-up signal and the following CAN based wake-up signal, before triggering activation of the pre-charge circuit 108. The detection of dominant bit is also referred to as detecting CAN activity. Alternatively, the absence of CAN communication between the VCU 120 and the controller 110 of the BMS 102 for the set time threshold determines the failure. The method after step 404 further comprises a decision step 406 where the difference of the ground potentials is compared with the threshold value. If the decision is No, then the step 404 is executed in a loop. However, if the decision is Yes, i.e. when the comparison is successful (less than the threshold value), then a step 408 is performed which comprises establishing the CAN communication. A step 410 comprises continuing the wake-up sequence with other control units of the electric vehicle, such as vehicle start-up sequence. Further, in between the steps 404 and the decision step 406, the time delay is added, which is optional. The time delay ensures that the step 404 of equalizing the potential is achieved within a set time threshold. If not, then the method is aborted and the next CAN based wake up signal is awaited, to start the method afresh. The time delay also prevents repeated activation of the pre-charge circuit 108.

[0024] Further, the BMS 102 is independent of type of pre-charge circuit 108 used such as resistor based or current limiter/controlled based or any other type of pre-charge circuit 108, as described in Fig. 2 and Fig. 3.

[0025] In accordance to the present invention, the BMS 102 and the method to equalize ground potentials in 48V (or higher voltage) systems is disclosed. The present invention relates to system architecture in BMS 102, which commands Li-ion battery communication wake-up, and power-up. In conventional solution, the vehicle system interfaces and architectures sometimes drive expensive changes to battery controllers, which utilize internal switching circuits to make power available. However, in the present invention, the BMS 102 and the method discloses a low-cost option to make bus power available faster and a potential functional add-on of pre-charge through this process to equalize power in the bus. The first transceiver 106 on the BMS 102, when idle (i.e., listening), is able to detect activity on the CAN bus and may also be able to read the messages sent on it, but is not able to transmit because of the ground shift. In the present invention, the controller 110 of the BMS 102, detects if there is a CAN activity, which is done by looking at a sudden change in the voltage between CANH 132 and CANL 134. Once the CAN activity is detected by the controller 110, the potential equalization is performed immediately, with low currents, so that the ground potentials are equalized. Once the equalization is completed, the first transceiver 106 starts transmitting messages (or CAN communication is established).

[0026] 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.