As an emergency power supply device for energy storage in rail transit vehicles, on-board batteries are mainly used to supply power to urgent loads during vehicle wake-up, sleep, and emergency working conditions. The safety, reliability, and continuity of its power supply are the guarantee of emergency power supply for vehicles, and the outstanding operation status of the vehicle is directly related to whether the vehicle can operate safely and reliably. However, in practical use, problems with on-board batteries (such as leakage, short circuits, and even explosions) often occur, posing a threat to the safe and reliable operation of rail vehicles. In order to facilitate real-time understanding of the operation status of the battery during vehicle operation and prevent the serious negative impact of the battery on vehicle operation, more and more rail vehicles are equipped with on-board battery management systems. This system measures and analyzes the voltage of the battery cell or module, the voltage of the battery pack, the charging and discharging current, and the temperature relief of the battery module or box, providing comprehensive monitoring and health assessment of the battery. Abnormal situations of the battery can be sent to the TCMS system, which can provide early warning of abnormal situations and reduce or prevent the occurrence of battery problems. The batteries commonly used in rail vehicles may generate hydrogen gas during the charging process. To prevent hydrogen gas from igniting, electrical components that may cause electric sparks should be prevented from being placed inside the battery box. At the same time, in order to meet the requirements of lightweight vehicles, the structure of the battery box should comply with the lightweight requirements. Based on the premise that battery safety and monitoring equipment devices do not affect the space of the battery box, a vehicle mounted battery management system based on wired measurement and transmission is selected, which includes battery pack voltage collection, battery module voltage collection, battery module temperature collection, and environmental temperature collection inside the battery box. The collection signals are transmitted directly through cables from the battery to the main controller.

Introduction to System Plan 2

2.1 System composition

The vehicle battery management system mainly consists of one main controller, one current sensor, several temperature sensors, several voltage collection lines, cables, and conversion connectors. The main controller is mainly composed of power module, temperature collection module, voltage collection module, data processing and storage module, communication module, etc. This system is applicable to lead-acid batteries and nickel chromium batteries.

Figure 1 Composition diagram of battery handling system

2.2 System Function

During normal train operation, the battery handling system can measure and record the total voltage and current of the battery pack, battery module voltage, and battery in real-time online

Based on the collected data, module temperature and battery box temperature can be analyzed and calculated to distinguish overcharging, overdischarging, abnormal temperature, etc. of the battery, estimate the remaining capacity of the battery pack, and provide warnings and predictive prompts for the health status of the battery pack. The real-time data and alarm information of the battery pack can be transmitted to TCMS through MVB or Ethernet, and the historical data of the battery pack can be transmitted to the vehicle through protected Ethernet. Users can timely understand the health status of the battery based on the uploaded data, which facilitates better maintenance and protection of the battery.

Figure 2 Functional Block Diagram of Battery Handling System

2.2.1 Total voltage inspection of battery

The main controller uses integrated circuits internally to monitor the total voltage of the battery pack. The main controller's total voltage collection port is connected to the positive and negative poles of the battery pack through cables to measure the voltage of the battery pack. Monitoring data is used to distinguish overcharging and overdischarging of battery packs.

2.2.2 Voltage detection of battery module

The main controller uses integrated circuits to collect the voltage of battery modules. Each battery pack is divided into several battery modules, which are units composed of one or more individual cells. The voltage collection port of the main controller module is connected to the corresponding positive pole of the battery module through a cable, and the cable is connected to the pole of each battery module through a terminal device to monitor the voltage of each battery module. Monitoring data is used to identify abnormal battery modules in the battery pack.

2.2.3 Battery pack current detection

Use Hall current sensors to detect the charging and discharging currents of the battery pack. Each battery pack is equipped with an electric Hall current sensor, which is connected to the main controller and its operating power is provided by the main controller. The current sensor can accurately measure the charging and discharging current of the battery pack. Determine the condition of the battery based on the change in current passing through the main line of the battery pack, such as uniform charging, float charging, or discharging, and participate in the calculation of the remaining capacity of the battery pack.

2.2.4 Battery temperature detection

Select a digital temperature sensor sealed in copper terminals with adhesive to detect temperature. The battery pack is divided into several battery modules, each module is equipped with a temperature sensor and installed on the negative pole of each battery module to monitor the temperature of the module's pole. Identify abnormal battery modules based on temperature detection data. Set up a temperature sensor to detect the temperature of the battery box and identify abnormal environmental temperatures in the battery box.

2.2.5 Remaining Capacity Calculation of Batteries

Use the deeply optimized ampere hour integral method to calculate SOC.

Basic principle of Anshi integral method accounting:

Accumulate the discharge capacity of the battery at different currents as the discharge capacity of the battery.

Accounting formula: SOC=SOC0-

During this period, SOC0 is the initial SOC value; CN is the additional capacity of the battery; K is the calibration coefficient for fitting temperature, current, aging degree, etc; η is the charging and discharging power; I is the current value; Dt is the integral of time.

2.2.6 Data Transmission

The system uses MVB or Ethernet to exchange data with TCMS, completing real-time data collection and transmission of fault information.

Connected to the on-board Ethernet switch via Ethernet protection interface, it completes functions such as long-distance protection, software updates, and offline history download.

2.2.7 Data Storage

Data storage: Data storage is divided into real-time data storage and fault data storage.

Real time data storage: The data monitored by the system is stored by the main controller, and the system monitoring data is stored once at a certain time interval (such as 1 minute), with a storage time not less than a certain number of days (such as 15 days). The specific timing can be adjusted as needed.

Fault data storage: Whenever a new fault alarm occurs, the real-time data of the system at that time is stored once, and the fault data storage is not less than a certain time (such as 6 months).

2.2.8 Fault alarm

Determine the upper limit alarm for charging voltage and the lower limit alarm for discharging voltage of the battery pack based on the total voltage of the battery.

Based on the voltage of the battery module, determine the upper limit alarm for charging voltage, lower limit alarm for discharging voltage, and alarm for excessive voltage difference in the battery module.

Determine the upper limit alarm of battery charging current and the lower limit alarm of discharging current based on the battery charging and discharging current.

Based on the temperature sensor detecting the battery temperature, determine the upper limit alarm for battery temperature and the alarm for excessive temperature difference. Battery box temperature online alarm.

Determine the SOC lower limit alarm based on the remaining capacity (SOC) of the battery.

2.2.3 Capacity (SOC) accounting and correction

SOC is the actual amount of electricity that a battery can release at that time, measured as a percentage of its capacity. SOC is closely related to parameters such as battery voltage, current, and temperature. In this plan, the ampere hour integration method is used to calculate SOC, and the cumulative discharge amount of the battery at different currents is used as the discharge amount of the battery. The calculation formula is as follows:

SOC=SOC0-

During this period, SOC0 is the initial SOC value; CN is the additional capacity of the battery; K is the calibration parameter for temperature, current, aging degree, etc; η is the charging and discharging power; I is the current value.

After integrating the current and time, the temperature of the box is converted into a compensation coefficient and introduced into the estimation of SOC. At the same time, the discharge curve of the battery pack is compared and corrected to obtain the remaining capacity value.

3 Conclusions

This vehicle mounted battery handling system, under the premise of not affecting battery safety and monitoring equipment not affecting the space of the battery box, detects the total voltage, total current, battery module voltage, battery module temperature, and box temperature of the battery. After analyzing and calculating the detected data, real-time information such as the total voltage, charging and discharging current, battery module voltage, battery module temperature, and capacity of the battery pack can be obtained in a timely manner. Based on the threshold values set for each parameter, the corresponding condition of the battery can be determined. When a parameter exceeds the set threshold, TCMS will issue a warning and alarm prompt. Protective personnel can inspect and protect the battery based on the prompt information to prevent abnormal situations from deteriorating and accidents from occurring, and to improve the reliability of vehicle operation.