High speed trains have become an important means of transportation for people's travel, and the design of train operation safety and passenger comfort is increasingly becoming an important factor in the manufacturing process of high-speed trains. As the energy system of high-speed trains, the battery can continuously provide DC110V DC power to important low-voltage components during train operation to ensure emergency power supply in case of unexpected high-voltage power outages. But if the battery power supply is excessive, it will cause insufficient voltage and result in power loss, so the voltage it provides cannot meet the normal operation of important components of the train. The key research topic of this article is to design a system that can monitor the battery voltage in real time and automatically shut down when the voltage is lower than the set value, in order to achieve low-voltage protection for the battery.

Keywords: high-speed train; Battery; Electricity deficit; low voltage protection

In recent years, the domestic high-speed rail industry has developed rapidly, bringing great convenience to people's travel. To ensure the safety of train operation, it is necessary to have a comprehensive emergency power supply and control system to ensure the continuous operation of important low-voltage electrical appliances on the train. To prevent excessive use of the train battery system, this control system can issue an alarm when the battery voltage drops to DC96V and automatically disconnect the battery power supply circuit after 15 minutes of continued use, thus achieving the two purposes of early train preparation and protecting the battery body.

Design analysis

1.1 EMU battery power supply system

The high-speed train adopts redundant design in the battery power supply system, that is, each standard train is designed with two independent batteries and corresponding battery chargers to supply power to the train's DC110V bus. The design of this power supply method ensures that in the event of a failure in one group of batteries and chargers, the other group can provide power to the low-voltage bus. The overall power supply system of the train battery is shown in Figure 1.

Figure 1 Redundant power supply system for train battery

The design of the battery depletion protection system can prevent the occurrence of unexpected battery depletion and undervoltage, which can lead to the failure of the high-speed train to operate. If a battery depletion occurs, it will cause the charger to be unable to start the charging program normally and can only rely on the ground power supply for forced direct charging, resulting in damage to the battery body.

1.2 Principles and Analysis of Control Circuit Design

To design a low voltage protection control system for batteries on high-speed trains that have already been put into operation, it is necessary to activate the internal backup line of the corresponding model's electrical cabinet, and add time relays, status relays, and action relays. This system adopts a modular design, with relays installed side by side at the bottom of the electrical cabinet, allowing for a more intuitive view of their working status. The overall control circuit design is shown in Figure 2.

Figure 2 Overall design diagram of control circuit

This designed battery voltage monitoring system can monitor the overall voltage of the high-speed train battery in real time. When the voltage U<DC96V and the train is in a parked and prepared state, the low voltage monitoring relay=32-K22 will transmit a low voltage feedback signal to the train KLIP station, and the time relay=32-K21 coil will be powered. If the battery voltage U<DC96V lasts for 15 minutes, the normally open contact of the time relay will close, and the low voltage control relay=32-K23 coil of the battery will be energized, causing the normally open contact to close. This will then switch the battery power supply switch from the ON position to the 0 position, cutting off the battery power supply line and achieving the purpose of protecting the battery system under low voltage conditions.

1.3 Selection of Control Circuit Components

To ensure the stability and continuous operation of the control system, Siemens 3RA2813-2AW10 power on delay time relay is selected. This type of relay can set the action time according to the actual situation. When the coil of this type of relay is powered on, the contact cannot immediately act. When the coil is powered on for a preset time, the contact immediately closes, allowing other relays in the control circuit to work.

The Siemens 3GU4 monitoring relay is selected for low voltage monitoring of batteries. This type of relay can adjust the monitored voltage value according to actual needs to adapt to the different low-voltage protection standards of high-speed train batteries produced on different platforms and meet the different needs of customers.

Function verification and fault handling of control circuit 2

Design and build a low-voltage control circuit for the battery car of the CRH3 high-speed train undergoing Level 5 maintenance at the host factory, unplug the battery power plug, and simulate battery power supply using a ground DC110V power supply. Adjust the minimum monitoring voltage of the battery low voltage monitoring relay to DC96V, set the contact action time of the time relay to 22-K21 for 15 minutes, and adjust the power supply voltage to below DC96V.

After 15 minutes of low voltage state, the time relay=32-K21 contact closes, the battery power supply line is cut off, and the low voltage protection function of the designed circuit is realized.

3 Conclusion

By simulating and testing the low-voltage protection system after installation, it can effectively extend the service life of the battery, reduce the maintenance cost of high-speed trains, and provide important guidance for the study of the full life cycle of key components of trains, in order to meet the protection of the battery under low voltage conditions when the train is in a parked and prepared state.