u003cpu003eu003cpu003eCurrently, the installation method of the power battery of pure electric bus usually adopts multiple parallel battery modules installed in the battery box, and then the multiple battery boxes are fixed in the battery compartment of the bus, and the battery boxes pass outside the box. The positive and negative poles are connected in series. Since a considerable part of the power batteries used in pure electric buses use direct charging, that is, all battery modules on the vehicle are charged in series . At the same time, due to the capacity and internal resistance of different battery modules in the same vehicle There are differences in such aspects. Therefore, as the number of charge and discharge increases, the imbalance of different battery modules in terms of voltage, SOC, etc. will become more and more obvious , causing some battery modules to be dissatisfied and unable to discharge, while some battery modules will Cause overcharge or overdischarge. A certain pure electric city bus has 9 battery boxes. Each battery box is composed of 20 battery modules in series. Each battery module is composed of 32 12.5 Ah/3.2V lithium iron phosphate single cells in parallel. Therefore, the rated capacity of each battery module is 400 Ah, and the nominal voltage is 3.2 V; the total rated capacity of the vehicle battery is 400 Ah, and the nominal voltage is 576 V. The rated power of the AC asynchronous motor is 100 kW, the rated voltage is 576 V, the lowest operating voltage is 450 V, and the highest operating voltage is 700 V. The circuit design to prevent battery overcharge or overdischarge uses an EV200 relay connected in series between the 10th and 11th battery modules in each box, with a rated current of 200 A and a control current of 100 mA. The 20 battery modules are equally divided into two parts, and the 10 battery modules in each part are directly connected in series. At the same time, an EV200 relay is connected in series between the positive and negative electrodes of each battery box. During normal charging and discharging, the relay connected in series between the battery modules is closed, and the relay connected in series between the positive and negative electrodes of the battery box is disconnected to ensure that the battery modules of the box can be charged and discharged normally. During charging, when a battery module of a box is charged to the highest voltage, the relay connected in series between the battery modules of the battery box is disconnected, and the relay connected in series between the positive and negative electrodes of the battery box is closed. The battery pack
of this box stops charging, and the battery modules of other battery boxes are guaranteed to be charged normally; when the last box of batteries is fully charged, the charger automatically shuts down. When discharging, when a battery module of a box drops to the lowest voltage, the relay connected in series between the battery modules of the box is disconnected, and the relay connected in series between the positive and negative electrodes of the box is closed at the same time, and the battery of the box will stop discharging. At this time, the motor will limit the power and have related alarm measures to remind the driver to charge and maintain the battery nearby. Therefore, it can be avoided that the relays between the modules of two or more battery boxes are disconnected at the same time, and the voltage drop will not be too low to make the motor not work normally. Figure 1 is a schematic diagram of the circuit connection of the whole vehicle battery box; Figure 2 is a schematic diagram of the connection of the battery modules and relays in the battery box. u003c/pu003eu003c/pu003eu003cpu003eu003c/pu003eu003c/pu003e
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