Authors: Kuang Xiaojun, Tang Xiangjiao, Li Hongbo, Wang Yong, Chang Sheng
1. Introduction to Power Management Systems
The automotive power management system can monitor the state of the battery and manage the load to calculate and evaluate the starting performance of the battery, thereby determining the current state of the battery and predicting the time the vehicle can be parked. Due to the high cost of automotive power management systems, they are generally equipped only in high-end models.
Figure 1 shows the composition of the power management system for a certain model. It can control the distribution of electrical energy in the vehicle, thereby enhancing the performance of the battery, optimizing the output power of the generator, and improving the overall performance of the vehicle through monitoring the battery state and managing the load.
2. Function Description of the Power Management System
The power management system mainly controls the battery management, vehicle static current management, and vehicle dynamic power management in three aspects.
The power management system includes the following functions.
1. Monitor the charging state of the battery, including the battery voltage, output current, and other information.
2. In extreme electrical conditions of the vehicle, limit and cut off the electrical load consumption.
3. Adjust the voltage of the generator to maintain optimal output voltage.
The battery sensor monitors the battery’s voltage, current, and temperature in real-time and sends the data to the controller for calculation, determining the current charging state and power of the battery, and predicting subsequent states.
The battery management system provides the power management system with the current real-time state of the battery and the predicted electrical performance information. It not only better meets the power demands of electrical equipment but also improves the economy of the vehicle’s electrical system.
The battery management system provides relevant parameters of the battery, such as state of charge, state of health, and state of function. It predicts how the battery will respond to pre-defined loading conditions, such as whether the engine can start under the current state of the battery. Using model-based algorithms, complex software algorithms can calculate the monitored battery current, voltage, and temperature signals to obtain the above battery parameters.
2.2 Static Power Management of the Vehicle (Engine Not Running)
Static power management of the vehicle refers to reducing the overall current consumption of the vehicle during the parking period when the engine is not running. In the case of the ignition switch being turned off, it controls the current supply to various controllers. Based on monitoring the remaining battery charge state and voltage, it will gradually turn off certain electrical devices to avoid over-discharging the battery, thereby ensuring the starting performance of the vehicle and extending the battery’s lifespan.
By conducting hierarchical management of the vehicle’s electrical load, the battery sensor monitors the state of the battery in real-time, sequentially shutting down the power supply to the vehicle’s electrical load under different battery states to reduce current consumption and ensure the vehicle’s starting capability. When the engine is not running, if the battery voltage is detected to be below a certain value, some non-essential electrical devices will be turned off to reduce further consumption of the battery’s charge. At the same time, a signal will be sent to the instrument panel to alert the driver of the low battery voltage, generally limiting or canceling comfort-related functions or functions that do not affect vehicle operation, while functions related to vehicle operation cannot be canceled.
Due to the different characteristics of batteries from different manufacturers, the specific low voltage threshold for the battery needs to be determined based on the type and supplier of the battery, but it must ensure that the battery voltage can still start the engine when it reaches the low voltage threshold.
2.3 Dynamic Power Management System (Engine Running)
During vehicle operation, dynamic power management distributes the current generated by the generator to different electrical devices according to their load demands. When the output current of the generator exceeds the consumption demand of the vehicle load, it will adjust the generator’s output voltage to supply power to the battery, ensuring it reaches optimal charging status.
When the engine is idling for an extended period, if the load current consumption is large enough to cause the battery voltage to drop below a certain voltage U1, the battery sensor will send an idle speed increase signal to the EMS, requesting the engine to raise the idle speed to a certain value, thereby increasing the generator’s output current to meet the current consumption of electrical loads and the charging needs of the battery.
With the help of relevant battery parameters, the power management system can optimize the charging voltage and take measures to reduce the load of the vehicle’s electrical system or increase the generator’s output power (such as raising the engine’s idle speed) when the battery performance degrades, or adopt both measures simultaneously.
After taking the corresponding measures, if the battery’s performance state is still below the specified threshold, the power management system will send relevant alarm information to the instrument panel for display, prompting the driver to take appropriate actions.
3. Overview of Common Power Management Solutions in Domestic Models
As the degree of electrification in vehicles increases and the number of electrical loads equipped in vehicles grows, some mid-to-high-end models have begun to be equipped with power management systems. Common power management solutions are as follows.
3.1 Without Battery Sensors
This solution manages the load solely by detecting the battery voltage, where the controller monitors the battery voltage state to manage the load. When the battery voltage is too high or too low, related functions are limited or turned off. As shown in Figure 2.
Figure 2 Managing Load by Monitoring Battery Voltage
The advantage of this solution is the full utilization of existing resources in the vehicle without increasing hardware costs, allowing for load management to avoid over-discharging the battery. However, due to the absence of battery sensors to monitor the battery state, it cannot accurately determine the battery’s charge level.
3.2 Independent Power Management Module
This solution consists of a battery state monitoring sensor and a power management module, connected via a LIN bus. The power management module communicates with other nodes on the bus via a CAN bus. As shown in Figure 3.
Figure 3 Independent Power Management Module
This solution allows for precise and efficient management of the battery due to the presence of an independent battery state monitoring sensor and controller. However, this solution incurs higher costs due to the addition of controllers and sensors.
3.3 BCM Integrated Power Management Module
This solution consists of a BCM and battery sensor, integrating the power management module within the body control module. The BCM and battery sensor are connected via a LIN bus, with the BCM communicating with other control modules on the bus via a CAN bus.
Figure 4 BCM Integrated Power Management Module
This solution has lower costs due to the absence of an independent power management module. However, it requires higher development capabilities from the body control module manufacturer and higher system integration capabilities from the OEM.
Each of the three solutions has its advantages and disadvantages, and the choice should be made based on the vehicle’s positioning, cost budget, and the development capabilities of the OEM and suppliers.
