Understanding Common BMS Wake-Up Signals for EVs Batteries
(Last Updated On: 06/02/2024)
Understanding Common BMS Wake-Up Signals for EVs Batteries
The Battery Management System (BMS) serves as a control system ensuring the safe use of power batteries in EVs. It monitors the real-time status and various parameters of the battery, implementing necessary measures such as balanced discharge to maintain consistency among module parameters within the battery pack. This guarantees the safe use of EVs. BMS controllers operate in two modes: Normal and Sleep. To transition from Sleep to Normal, one or more wake-up signals are required. This article summarizes common internal and external wake-up signals for BMS controllers.
1. Constant Power (KL30):
The power supply and wake-up signals for the BMS are illustrated in the diagram below. KL30 provides constant power, and the BMS has multiple wake-up sources, which can originate from both internal and external factors. The wake-up signals can be of various types, such as level wake-up, edge wake-up, resistance wake-up, bus wake-up, and more. The awakened device could be a power chip or a microcontroller, and the specific choice depends on the requirements of the system design.
2. KL15 Ignition Signal:
KL15, found on the ON position of the car key, is connected on one end to the vehicle’s +12V power supply and on the other end to the BMS controller. Before ignition, the KL15 switch is open, resulting in no signal input, and the BMS controller remains inactive. After ignition, the KL15 switch closes, enabling the +12V power supply, activating the power management chip, and subsequently waking up the BMS controller.
3. VCU Hardwire Wake-Up Signal:
In some scenarios, the BMS is awakened after entering a sleep mode through the Vehicle Control Unit (VCU). In one situation, when KL15 is powered, the VCU is initially awakened, and then the VCU, in turn, uses a hardwired signal to wake up the BMS. In another scenario, after the BMS has entered sleep mode, if the VCU detects certain faults within the vehicle, it uses a hardwired signal to wake up the BMS. Subsequently, the system follows predefined processing procedures to address the detected issues.
4. AC Charging PP Wake-Up:
PP wake-up, also known as plug-in wake-up, is a confirmation signal for AC charging, as shown below. PP is a resistance signal. When the specified resistance value is detected, it indicates that the charging circuit is successfully connected and ready for charging. If the PP detection circuit is integrated into the BMS, PP wake-up functionality needs to be reserved.
5. OBC Hardwire Wake-Up:
OBC hardwire wake-up is also relevant in AC charging scenarios. In this situation, the CC detection circuit is integrated into the On-Board Charger (OBC) device. Once the charging gun is connected, the OBC is awakened. Subsequently, the OBC outputs a signal to wake up the BMS, initiating the entire vehicle into the AC charging process.
6. DC Charging CC2 Wake-Up:
Similar to AC charging, DC charging also involves plug-in wake-up, known as CC2 wake-up, which, like the CC signal, is a resistance signal. When the equipment detects the specified resistance value, it indicates that the charging circuit is successfully connected and ready for charging. Typically, this detection circuit is placed in the BMS controller. Additionally, the DC charging port has an auxiliary power source, A+, which is a +12V DC power supply. In practical usage, some manufacturers may use this signal to wake up the BMS.
7. CAN Bus Wake-Up:
To reduce system power consumption, BMS may enter a low-power mode under appropriate conditions. In this mode, the entire controller, except for the minimum circuit of the CAN transceiver monitoring data on the CAN bus, remains inactive, significantly lowering system power consumption.
When the BMS controller is in sleep mode, it can be awakened via the CAN bus to transition into normal operating mode. In such cases, the BMS requires constant power, and the CAN transceiver chip in the BMS controller must have bus wake-up functionality. Several chip suppliers, such as NXP, TI, Infineon, have developed chips with bus wake-up capabilities.
In instances where the system requires collaboration with the BMS to perform other functions, CAN nodes like the VCU may send specific wake-up messages to the bus. The BMS’s CAN transceiver, upon monitoring the wake-up message, outputs a voltage signal to enable the power management chip. The power management chip then initiates internal circuits, providing power to the microcontroller and other circuits, and the BMS enters normal operating mode. This mode’s advantage lies in utilizing the existing CAN bus for wake-up functionality, reducing the number of harnesses between system nodes, and facilitating wiring.
8. Sampling Board Fault Wake-Up:
Due to the potential for significant safety incidents if issues arise with the power battery, even when the entire vehicle is powered off and the BMS enters a sleep state, there is a requirement for the sampling board to periodically monitor the parameters of the power battery. In the event of detecting a fault, the sampling board outputs a signal to wake up the BMS controller. Subsequently, the system initiates the corresponding processing procedures to minimize the impact of the fault and ensure the safety of the vehicle.
9. RTC Wake-Up:
BMS controllers typically incorporate a real-time clock to keep track of the operational time of the power battery. When the accumulated time exceeds a set value, the real-time clock circuit outputs an alarm wake-up signal. This signal serves to awaken the BMS, initiating self-check procedures to maximize the safety of the power battery.
In conclusion, this article delves into the critical aspect of unlocking efficiency in Battery Management Systems (BMS) by understanding common wake-up signals. The BMS plays a pivotal role in ensuring the safe and efficient operation of power batteries in electric vehicles. By monitoring real-time status and various parameters, the BMS employs measures like balanced discharge to maintain consistency within battery packs, thereby guaranteeing the safe use of EVs.
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