Lithium titanate battery system of tramcar

Abstract

The invention discloses a tramcar lithium titanate battery system which comprises a battery box, an electrical box and a liquid cooling system, a positive electrode and a negative electrode of the battery box are connected to a B + connector X11 and a B-connector X12 of the electrical box through a B + connector X1 and a B-connector X2 respectively, the B + connector X11 enters the electrical box and then is directly divided into two positive electrode branches with pre-charging, and the B + connector X12 is directly divided into two negative electrode branches with pre-charging. The DC1 + connector X5 and the DC2 + connector X6 are respectively connected to the electrical cabinet; after entering the electrical box, the B-connector X12 passes through the main negative fuse FU3 and the main negative contactor KM2 and then is divided into two negative branches through the copper bar to reach the DC1-connector X7 and the DC2-connector X8; a DC1 + connector X5 and a DC1-connector X7 form a first group of output and are connected with a traction box DCU1; a DC < 2 + > connector X6 and a DC < 2-> connector X8 form a second group of output and are connected with a traction box DCU2; the whole vehicle CAN bus of the traction box DCU1 and the whole vehicle CAN bus of the traction box DCU2 are jointly connected to a whole vehicle communication X13 and finally connected with a battery management system BMS in the battery box and a connector X19 of the liquid cooling unit. The battery system is high in integration level, small in size and low in cost.

Description

Technical Field

[0001] The invention relates to rail transit technology, and in particular to a lithium titanate battery system for a tram. Background Art

[0002] The traditional power battery system and traction system have a one-to-one relationship. That is, for a tram with two traction systems at the front and rear of the train, four independent battery systems are generally configured, and there is a one-to-one relationship between the battery and the traction system. This configuration control strategy is simple, but it also has the following disadvantages:

[0003] The total volume of the battery system is large: the number of battery modules, box materials, wiring harness components, battery management system components, connectors, and liquid cooling components increase exponentially.

[0004] The total cost of the battery system is high: due to the large number of components and low integration. Summary of the invention

[0005] The purpose of the present invention is to provide a lithium titanate battery system for trams, in which one group of power batteries corresponds to two groups of traction systems.

[0006] The technical solution to achieve the purpose of the present invention is: a tram lithium titanate battery system, including a battery box, an electrical box and a liquid cooling system, wherein: the positive and negative electrodes of the battery box are connected to the B+ connector X11 and the B- connector X12 of the electrical box through the B+ connector X1 and the B- connector X2 respectively; after the B+ connector X11 enters the electrical box, it is directly divided into two positive branches with pre-charge, which are respectively connected to the DC1+ connector X5 and the DC2+ connector X6 of the electrical box; after the B- connector X12 enters the electrical box, it is connected to the DC1+ connector X5 and the DC2+ connector X6 of the electrical box through the main negative fuse FU3 After connecting to the main negative contactor KM2, it is divided into two negative branches through the copper bus to the DC1-connector X7 and DC2-connector X8; DC1+connector X5 and DC1-connector X7 are the first group of outputs, connected to the traction box DCU1; DC2+connector X6 and DC2-connector X8 are the second group of outputs, connected to the traction box DCU2; the vehicle CAN bus of the traction box DCU1 and the traction box DCU2 are connected to the vehicle communication X13, and finally connected to the battery management system BMS in the battery box and the connector X19 of the liquid cooling unit.

[0007] Furthermore, the battery box is provided with 8 lithium titanate battery modules, a 24V isolated power supply, a 4G module, a total Hall sensor TA1 and a battery management system BMS. The battery management system BMS includes a BMU master control module and BSU slave control modules 1 to 8, wherein:

[0008] Among the 8 lithium titanate battery modules, the positive electrode B1+ of battery module 1 is connected to the 1st pin of the manual maintenance switch MSD of the battery box, the 2nd pin of the manual maintenance switch MSD is connected to the 1st pin of the B+ connector X1 and the connector X14, the 2nd pin of the connector X14 is connected to the connector X2, the negative electrode B28- of battery module 1 is connected to the positive electrode of battery module 2, the negative electrode B56- of battery module 2 is connected to the positive electrode of battery module 3, and so on, the negative electrode of battery module 7 is connected to the positive electrode B196- of battery module 8, and the negative electrode B224- of battery module 8 is connected to the B- connector X2;

[0009] The input of the 24V isolated power supply is connected to pins 3 and 5 of connector X3. The output 24V_1 of the 24V isolated power supply is connected to the 4G module and the BMU main control module. The 1-pin KL15_1 signal, 2-pin KL15_2 signal, 7-pin KL30_1, and 8-pin KL30_2 of connector X3 are all connected to the BMU main control module in the BMS system.

[0010] The BMU main control module outputs control signals of five groups of contactors KM1, KM2, KM3, KM4, and KM5, which are connected to pins 9 to 18 of the battery box connector X3 respectively. Each contactor control signal is a positive signal and a negative signal.

[0011] The BMU main control module outputs 5V power to the Hall sensor TA2, and then collects the current of the branch where the fuse FU2 in the electrical box is located through the two signal lines of the Hall sensor TA2. The two signal lines of the Hall sensor TA2 and the two 5V power lines are connected to the BMU main control module through the 19th, 20th, 21st and 22nd pins of the connector X3 respectively;

[0012] The vehicle CAN bus of the BMU main control module is connected to pins 23, 24, and 25 of connector X3, and the CAN2 bus of the BMU main control module is connected to the CAN communication line of the 4G module accordingly;

[0013] The 26th pin HV_TC1+ and the 27th pin HV_TC2+ of the connector X3 are connected to the BMU main control module. The BMU main control module collects the voltage signals of HV_TC1+ and HV_TC2+ to determine whether the battery pre-charging is completed;

[0014] The CAN0 bus of the BMU master control module is connected to the CAN interface of the BSU slave control module 1 to the BSU slave control module 8; the BMU master control module outputs 24V_2 to power the BSU slave control module 1 to the BSU slave control module; each slave control module collects 28 cell voltages and 1 module temperature of 1 module;

[0015] The BMU main control module outputs 5V power to the Hall sensor TA1, and then collects the total current of the battery box through the two signal lines of the Hall sensor TA1;

[0016] The antenna of the 4G module passes through the through hole X17 of the battery box and is pasted on the outer wall of the battery box.

[0017] Furthermore, the electrical box is provided with fuse FU1, contactor KM1, contactor KM3, pre-charging resistor R1, fuse FU2, contactor KM4, contactor KM5, pre-charging resistor R2, current sensor TA2, current sensor TA3, current sensor TA4, fuse FU3, contactor KM2, copper bus and connector, wherein:

[0018] The B+ connector X11 of the electrical box is the total positive input of the battery box, which is divided into two branches through copper busbars 1 and 2, where: the B+ connector X11 is connected to pin 1 of fuse FU1 through copper busbar 1, and pin 2 of fuse FU1 is connected to pin 1 of contactor KM1 and pin 1 of pre-charging resistor R1 through copper busbar 3, and pin 2 of pre-charging resistor R1 is connected to pin 1 of contactor KM3, and pin 2 of contactor KM3 and pin 2 of contactor KM1 are connected to connector X5 through copper busbar 5, and a TA3 Hall sensor is mounted on copper busbar 5; the B+ connector X11 is connected to fuse FU2 through copper busbar 2 Pin 1 of fuse FU2, pin 2 of fuse FU2 is connected to pin 1 of contactor KM4 and pin 1 of pre-charging resistor R2 through copper bus 4, Hall sensor TA2 is sleeved on copper bus 4, pin 2 of pre-charging resistor R2 is connected to pin 1 of contactor KM5, pin 2 of contactor KM5 and pin 2 of contactor KM4 are connected to connector X6 through copper bus 6, Hall sensor TA4 is sleeved on copper bus 6, Hall sensor TA3 signal is connected to traction box DCU1 through connector X22 of electrical box, Hall sensor TA4 signal is connected to traction box DCU2 through connector X23 of electrical box;

[0019] The B-connector X12 of the electrical box is the total negative output of the battery box, the negative branch: pin 1 of fuse FU3 is connected to B-connector X12, pin 2 of fuse FU3 is connected to pin 1 of contactor KM2, pin 2 of contactor KM2 is connected to DC1-connector X7 through copper bus 8, and connector X7 is then connected to DC2-connector X8 through copper bus 9; the control signals of the five contactors KM1, KM2, KM3, KM4, and KM5 in the electrical box are connected to connector X10; the signal of connector X10 is then connected to the vehicle communication connector X13 together with the train signal and traction signal; connector X13 and connector X3 are connected through a wiring harness.

[0020] Furthermore, the liquid cooling system is composed of a liquid cooling unit, a stainless steel water pipe, a hose, a joint, a coolant, a water cooling plate, and an expansion kettle, wherein:

[0021] The coolant is injected from the filling port of the expansion kettle, flows into the liquid cooling unit through the stainless steel water pipe and joint, the liquid cooling outlet X21 of the liquid cooling unit is connected to the battery water inlet X15 of the battery box, the battery water inlet X15 is connected to the water cooling plate on the battery module through a stainless steel water pipe, the water outlet of the water cooling plate of the battery module is connected to another stainless steel water pipe in the battery box that serves as a return water, and the coolant then flows back to the liquid cooling return water port X20 of the liquid cooling unit through the battery water outlet X16 of the battery box and the stainless steel water pipe;

[0022] Pins 1 and 2 of the liquid cooling unit connector X18 are connected to pins 1 and 2 of the battery box connector X14, respectively, to provide high-voltage power input to the water cooling unit; pins 1 and 2 of the liquid cooling unit connector X19 are connected to pins 4 and 6 of the connector X13, and pins 3, 4, and 5 of the connector X19 are connected to pins 23, 24, and 25 of the connector X13.

[0023] Furthermore, when the battery temperature is greater than or equal to 28°C, the BMU main control module in the battery box sends a cooling command to the liquid cooling unit through the vehicle CAN communication bus, and the air-conditioning compressor of the liquid cooling unit starts working; at this time, the temperature of the coolant at the outlet of the liquid cooling unit is gradually controlled to a preset value of about 10°C, and the heat generated by the battery is transferred to the coolant through the water cooling plate. After heating, the coolant flows back to the liquid cooling unit through the liquid cooling return port, and the heat is transferred to the air under the action of the refrigeration system in the liquid cooling unit, thereby reducing the temperature of each battery cell in the battery module; when the average battery temperature is lower than 24°C, the BMU main control module in the battery box sends a self-circulation command to the liquid cooling unit through the vehicle CAN communication bus to stop cooling, and the coolant is maintained in circulation in the pipeline through self-circulation driven by the water pump in the liquid cooling unit, so that the battery temperature of each module remains relatively consistent.

[0024] Further, DC1+connector X5, Hall sensor TA3, contactor KM1, contactor KM3, pre-charging resistor R1, fuse FU1, electrical box B+connector X11, battery box B+connector X1, manual maintenance switch MSD, battery modules 1-8, Hall sensor TA1, battery box B-connector X2, electrical box B-connector X12, fuse FU3, contactor KM2 and DC1-connector X7 constitute virtual battery 1;

[0025] DC2+connector X6, Hall sensor TA4, contactor KM5, contactor KM4, pre-charging resistor R2, Hall sensor TA2, fuse FU2, electrical box B+connector X11, battery box B+connector X1, manual maintenance switch MSD, battery modules 1-8, Hall sensor TA1, battery box B-connector X2, electrical box B-connector X12, fuse FU3, contactor KM2 and DC2-connector X8 constitute virtual battery 2;

[0026] The train equipment provides four sets of signals to the connector X13, the KL15_1 signal is connected to pin 1 of the connector X13, the KL15_2 signal is connected to pin 2 of the connector X13, the train 24V+ input is connected to pins 3 and 4 of the connector X13, and the train 24V- input is connected to pins 5 and 6 of the connector X13;

[0027] The train equipment provides train 24V signals and train network signals to traction boxes DCU1 and DCU2;

[0028] The traction box outputs three groups of signals to the connector X13. The traction box DCU1 outputs the KL30_1 signal to the 7th pin of the connector X13. The traction box DCU2 outputs the KL30_2 signal to the 8th pin of the connector X13. The vehicle CAN communication of the traction box DCU1 and the traction box DCU2 are short-circuited and connected to the 23rd, 24th and 25th pins of the connector X13.

[0029] In connector X10, the control signal of contactor KM1 is connected to pins 9 and 10 of connector X13, the control signal of contactor KM2 is connected to pins 11 and 12 of connector X13, the control signal of contactor KM3 is connected to pins 13 and 14 of connector X13, the control signal of contactor KM4 is connected to pins 15 and 16 of connector X13, the control signal of contactor KM5 is connected to pins 17 and 18 of connector X13, HV_TC1+ of connector X10 is connected to pin 26 of connector X13, and HV_TC2+ of connector X10 is connected to pin 27 of connector X13.

[0030] Further, the working process is:

[0031] The train starts, outputs 24V, and the traction box DCU1, traction box DCU2 and liquid cooling unit are powered on at low voltage; at the same time, the 24V isolated power supply in the battery box works, outputs 24V_1 signal, the BMU main control module in the battery box wakes up, and outputs 24V_2 signal to the BSU slave control module; after the BSU slave control module is powered on, it collects the 28 single cell voltages and 1 module temperature information managed by this module, and sends the module's single cell voltage and single cell temperature to the BMU main control module through the CAN0 bus; the BMU main control module performs calculations on the CAN data sent by the BSU slave control module, and calculates the highest single cell voltage and Number, lowest cell voltage and number, highest cell temperature and number, lowest cell temperature and number, the difference between the highest cell temperature and the lowest cell temperature, the difference between the highest cell voltage and the lowest cell voltage. At the same time, the BMU main control module collects and calculates the current values ​​of the two main positive branches, the total voltage value of the battery pack, and the insulation resistance value of the battery pack, and sends them to the vehicle CAN bus; the BMU main control module sends the fault status of the battery system to the vehicle CAN according to the protection threshold of the battery; when there is no fault, the fault flag bit sends 0, and when there is a fault, the flag bit sends 1; the traction DCU corresponding to the virtual battery reporting the fault will not send the input command, and the train will display the battery fault repair;

[0032] The train outputs the wake-up hard-wire signal KL15_1=24V. After the BMU main control module collects this signal as 24V, the BMU main control module outputs the working status flag bit of the virtual battery 1 as 1000;

[0033] The train outputs the wake-up hard-wire signal KL15_2 = 24V. When the BMU main control module collects this signal as 24V, the BMU main control module outputs the working status flag of the virtual battery 2 as 1000;

[0034] After the traction box DCU1 self-checks and finds no fault, it outputs the hard-wire signal KL30_1=24V indicating that traction 1 is fault-free, and the BMU main control module switches the state of virtual battery 1 to 0100. When the traction box DCU1 self-checks and finds fault, it outputs the traction box DCU1 fault signal KL30_1=0V, and sends the vehicle CAN network signal indicating that the traction box DCU1 is faulty to the train, waiting for maintenance;

[0035] After the traction box DCU2 self-checks and finds no fault, it outputs the hard-wire signal KL30_2=24V indicating that traction 2 is fault-free, and the BMU main control module switches the state of virtual battery 2 to 0100. When the traction box DCU2 self-checks and finds fault, it outputs the traction box DCU2 fault signal KL30_2=0V, and sends the vehicle CAN network signal indicating that traction DCU2 is faulty to the train, waiting for maintenance;

[0036] After the traction box DCU1 has no fault and receives the virtual battery 1 has no fault, it sends the virtual battery 1 input command, the BMU main control module controls the contactor KM3 to close and the contactor KM2 to close, the contactor KM1 is disconnected, the contactors KM4 and KM5 remain in the original state, and the state of the virtual battery 1 sent is 0010; at this time, the virtual battery 1 pre-charges the DCU1, and the current path is: B+connector X1→B+connector X11→fuse FU1→pre-charge resistor R1→contactor KM3→Hall sensor TA3→DC1+connector X5→traction DCU1→DC1-connector X7→contactor KM2→fuse FU3→B-connector X12→box B-connector X2;

[0037] After the traction box DCU2 has no fault and receives the virtual battery 2 has no fault, it sends the virtual battery 2 input command, the BMU main control module controls the contactor KM5 to close and the contactor KM2 to close, the contactor KM4 to disconnect, the contactor KM1 and the contactor KM3 to keep the original state, and the state of the virtual battery 2 sent is 0010. At this time, the battery pre-charges the DCU2, and the current path is: B+connector X1→B+connector X11→fuse FU2→Hall sensor TA2→pre-charge resistor R2→contactor KM5→Hall sensor TA4→DC2+connector X6→traction DCU2→DC2-connector X8→contactor KM2→fuse FU3→electrical box B-connector X12→B-connector X2;

[0038] After the virtual battery 1 is pre-charged, the BMU main control module controls contactors KM1 and KM2 to close, contactor KM3 to open, contactors KM4 and KM5 to keep their original states, and sends the state of battery 1 as 0001. At this time, the battery supplies power to DCU1, and the current path is: B+ connector X1→B+ connector X11→fuse FU1→contactor KM1→Hall sensor TA3→DC1+ connector X5→traction DCU1→DC1- connector X7→contactor KM2→fuse FU3→B- connector X12→B- connector X2;

[0039] After the virtual battery 2 is pre-charged, the BMU main control module controls the contactors KM4 and KM2 to close, the contactor KM5 to open, the contactors KM1 and KM3 to keep the original status, and sends the status of the virtual battery 2 as 0001. At this time, the battery supplies power to DCU2, and the current path is: B+ connector X1→B+ connector X11→fuse FU2→Hall sensor TA2→contactor KM4→Hall sensor TA4→DC2+ connector X6→traction DCU2→DC2- connector X8→contactor KM2→fuse FU3→B- connector X12→B- connector X2;

[0040] The train power-off command is sent to the traction box DCU1, which sends the battery 1 disconnection command. The BMU master disconnects the contactor KM1, and the other contactors remain in their original state.

[0041] The train power-off command is sent to the traction box DCU2, which sends the battery 2 disconnection command. The BMU master disconnects the contactor KM4, and the other contactors remain in their original state.

[0042] When both traction box DCU1 and traction box DCU2 issue the battery disconnection command, the BMU master disconnects the KM2 contactor. At this time, all five contactors in the electrical box are in the disconnected state.

[0043] The 4G module is responsible for sending the cell voltage information, cell temperature information, SOC, insulation resistance, battery branch 1 current, battery branch 2 current, total voltage, contactor status of battery branch 1, virtual battery 1 status, virtual battery 2 status, water cooler status, traction box DCU1 command, traction box DCU2 command sent by the BMU main control module through the CAN2 bus to the 4G cloud platform. By logging into the 4G cloud platform interface, you can view the real-time or historical information of the battery system.

[0044] Furthermore, when the voltage of HV_TC1+ collected by the BMU main control module is greater than or equal to 95% of HV+, the pre-charging of virtual battery 1 is completed; when the voltage of HV_TC2+ collected by the BMU main control module is greater than or equal to 95% of HV+, the pre-charging of virtual battery 2 is completed.

[0045] Furthermore, the SOC estimation method is:

[0046] The BMU main control module collects the total current once every 10mS and accumulates the SOC once, as shown in Formula 1;

[0047] SOC 新 =SOC 旧 +[(m*I*10 / 3600000) / n]*100%-----Formula 1,

[0048] Where I is the real-time current value, which is collected by the main Hall sensor TA1 and sent to the BMU main control module, SOC 新 Represents the SOC value at the current moment; SOC 旧 is the last SOC value; m is the SOC calibration factor; n is the nominal capacity of the battery pack.

[0049] Furthermore, the SOC calibration strategy includes:

[0050] SOC calibration strategy 1 is:

[0051] According to the data table of cell voltage and SOC corresponding to the cell voltage after constant current charging for 30s at 25℃, the SOC calibration function is performed at the cell voltage point corresponding to SOC of 84%. If the current SOC is lower than 84%, the value of m in Formula 1 is 1.1, so that the SOC increases rapidly to 85%. When the train receives an SOC of 85% from the BMU main control, charging stops. If the current SOC is equal to 84%, and the highest cell voltage is lower than the value in the table, the SOC stops increasing until the highest cell voltage is greater than or equal to the value in the table. The SOC increases normally until the SOC accumulates to 85%. When the train receives an SOC of 85% from the BMU main control, charging stops.

[0052] SOC calibration strategy 2:

[0053] The SOC is calibrated within 45 minutes when the train returns to the depot for rest every day. During the rest period, the battery system is not charged or discharged and is in a static state. After the battery has been stationary for 30 minutes and the state is basically stable, a rough OCV calibration is performed using the relationship curve between the lithium titanate battery voltage and SOC. The current new SOC value is estimated based on the corresponding relationship between the current average cell voltage value and SOC. If the estimated SOC is more than 10% lower than the current SOC of the BMS, the current SOC will be lowered by 10%. Otherwise, no calibration is performed.

[0054] Compared with the prior art, the present invention has the following significant advantages: high battery system integration, small size, low cost, and the use of a customized SOC algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is the electrical schematic diagram of the battery box and liquid cooling unit.

[0056] Figure 2 It is the electrical schematic diagram of the electrical box.

[0057] Figure 3 It is a timing diagram of the battery system working status.

[0058] Figure 4 It is the charging current waveform.

[0059] Figure 5 Schematic diagram of the water circuit of the battery liquid cooling system.

[0060] Figure 6 This is a schematic diagram of the copper busbar position in the electrical box. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0062] A lithium titanate battery system for trams, comprising a battery box, an electrical box and a liquid cooling system, wherein: the battery positive electrode B+ connector X1 and the negative electrode B- connector X2 of the battery box are respectively connected to the B+ connector X11 and the B- connector X12 of the electrical box; after the B+ connector X11 enters the electrical box, it is directly divided into two positive electrode branches with pre-charge, which are respectively connected to the DC1+ connector X5 and the DC2+ connector X6 of the electrical box; after the B- connector X12 enters the electrical box, it is connected to the DC1+ connector X5 and the DC2+ connector X6 of the electrical box through the main negative fuse FU3 and the main negative contactor K After M2, it is divided into two negative branches through the copper bus to DC1-connector X7 and DC2-connector X8; DC1+connector X5 and DC1-connector X7 are the first group of outputs, connected to the traction box DCU1; DC2+connector X6 and DC2-connector X8 are the second group of outputs, connected to the traction box DCU2; the vehicle CAN bus of the traction box DCU1 and the traction box DCU2 are connected to the vehicle communication X13, and finally connected to the battery management system BMS in the battery box and the connector X19 of the liquid cooling unit.

[0063] (1) Battery box

[0064] like Figure 1As shown, the battery box is equipped with 8 1P28S 70Ah lithium titanate battery modules, 24V isolated power supply, 4G module, main Hall sensor TA1 and BMU master control module and BSU slave control module 1 to BSU slave control module 8 of the battery management system BMS. In the battery box, pins 3 and 5 of connector X3 are connected to the input of the 24V isolated power supply, and the output 24V_1 of the 24V isolated power supply is connected to the 4G module and the BMU master control module. The 1-pin KL15_1 signal, 2-pin KL15_2 signal, 7-pin KL30_1, and 8-pin KL30_2 of connector X3 are all connected to the BMU master control module in the BMS system. The BMU master control module outputs five groups of contactor control signals: KM1, KM2, KM3, KM4, and KM5, which are connected to pins 9 to 18 of the battery box connector X3 respectively. Each contactor control signal is two signals, one positive and one negative. The BMU main control module outputs 5V power to the Hall sensor TA2, and then collects the current of the branch where FU2 in the electrical box is located through the two signal lines of the Hall sensor TA2. The two signal lines of the Hall sensor TA2 and the two 5V power lines are connected to the BMU main control module through the 19th, 20th, 21st and 22nd pins of X3 respectively. The vehicle CAN bus of the BMU main control module is connected to the 23rd, 24th and 25th pins of X3. The CAN2 bus of the BMU main control module is connected to the CAN communication line of the 4G module accordingly. The 26th pin HV_TC1+ and the 27th pin HV_TC2+ of the connector X3 are both connected to the BMU main control module. The BMU main control module collects these two voltage signals for the judgment basis of the completion of battery pre-charging. The CAN0 bus of the BMU main control module is connected to the CAN interface of the BSU slave control module 1 to the BSU slave control module 8. The BMU main control module outputs 24V_2 to power the BSU slave control module 1 to the BSU slave control module. The BMU main control module outputs 5V power to the Hall sensor TA1, and then collects the total current of the battery box through the two signal lines of the Hall sensor TA1. The positive pole B1+ (HV+) of battery module 1 is connected to the 1st pin of the manual maintenance switch MSD of the battery box, and the 2nd pin of the manual maintenance switch MSD is connected to the 1st pin of the connector X1 and the connector X14, and the 2nd pin of the connector X14 is connected to the connector X2. The negative pole B28- of battery module 1 is connected to the positive pole of battery module 2, and the negative pole B56- of battery module 2 is connected to the positive pole of battery module 3. By analogy, the negative pole of battery module 7 is connected to the positive pole B196- of battery module 8, and the negative pole B56- of battery module 2 is connected to the positive pole of battery module 3. The negative pole B224 of the battery module 8 is connected to the connector X2. Each slave control module collects 28 cell voltages and 1 module temperature of 1 module, that is: BSU slave control module 1 collects 28 cell voltages B1~B28 and 1 module temperature T1 of battery module 1; BSU slave control module 2 collects 28 cell voltages B29~B56 and 1 module temperature T2 of battery module 2. The antenna of the 4G module passes through the through hole X17 of the battery box and is pasted on the outer wall of the battery box.X15 of the battery box is the battery water inlet, and X16 of the battery box is the battery water outlet.

[0065] The lithium titanate battery used in this solution has the characteristics of high charge and discharge rate (continuous 8C ~ 15C), good low-temperature performance (-40 ~ 55℃), long cycle life (more than 12,000 times), and high safety. One set of lithium titanate batteries can meet the traction and braking power requirements of two traction systems.

[0066] (2) Electrical box

[0067] like Figure 2 , Figure 6 As shown, the electrical box is provided with fuse FU1, contactor KM1, pre-charge contactor KM3, pre-charge resistor R1, fuse FU2, main positive contactor KM4, pre-charge contactor KM5, pre-charge resistor R2, Hall sensor TA2, Hall sensor TA3, Hall sensor TA4, main negative fuse FU3, main negative contactor KM2, copper bus, connectors X10, X11, X12, X5, X6, X7, X8, X22, X23, among which:

[0068] The B+ connector X11 of the electrical box is the total positive input of the battery box, which is divided into two branches through copper busbars 1 and 2, where: connector X11 is connected to pin 1 of fuse FU1 through copper busbar 1, and pin 2 of fuse FU1 is connected to pin 1 of contactor KM1 and pin 1 of pre-charging resistor R1 through copper busbar 3, and pin 2 of pre-charging resistor R1 is connected to pin 1 of contactor KM3, and pin 2 of contactor KM3 and pin 2 of contactor KM1 are connected to connector X5 through copper busbar 5, and TA3 Hall sensor is mounted on copper busbar 5; connector X11 is connected to pin 1 of fuse FU2 through copper busbar 2. Pin 2 of fuse FU2 is connected to pin 1 of contactor KM4 and pin 1 of pre-charging resistor R2 through copper bus 4, Hall sensor TA2 is sleeved on copper bus 4, pin 2 of pre-charging resistor R2 is connected to pin 1 of contactor KM5, pin 2 of contactor KM5 and pin 2 of contactor KM4 are connected to connector X6 through copper bus 6, Hall sensor TA4 is sleeved on copper bus 6, Hall sensor TA3 signal is connected to traction box DCU1 through connector X22 of electrical box, Hall sensor TA4 signal is connected to traction box DCU2 through connector X23 of electrical box;

[0069] The B-connector X12 of the electrical box is the total negative output of the battery box. The negative branch: the 1st pin of the fuse FU3 is connected to the connector X12, the 2nd pin of the fuse FU3 is connected to the 1st pin of KM2, and the 2nd pin of KM2 is connected to the DC1-connector X7 and the DC2-connector X8. The control signals of the five contactors KM1, KM2, KM3, KM4, and KM5 in the electrical box are connected to the connector X10. The signal of the connector X10 is then connected to the X13 vehicle communication connector together with the train signal and the traction signal. The connector X13 is connected to the connector X3 through a wiring harness.

[0070] (3) Liquid cooling system

[0071] The liquid cooling system consists of a liquid cooling unit, stainless steel water pipes, hoses, joints, coolant, water cooling plate, expansion kettle, etc. The coolant is injected from the filling port of the expansion kettle, flows into the liquid cooling unit through the stainless steel water pipes and joints, and the X21 liquid cooling outlet of the liquid cooling unit is connected to the X15 battery water inlet of the battery box. The battery water inlet is connected to the water cooling plate on the battery module through a stainless steel water pipe. The outlet of the water cooling plate of the battery module is connected to another stainless steel water pipe in the battery box that serves as a return water. The coolant then flows back to the X20 liquid cooling return port of the liquid cooling unit through the stainless steel water pipe via the X16 battery outlet of the battery box. Pins 1 and 2 of the X18 connector of the liquid cooling unit are connected to pins 1 and 2 of the X14 connector of the battery box, respectively, to provide high-voltage power input to the water cooling unit. Pins 1 and 2 of connector X19 of the liquid cooling unit are connected to pins 4 and 6 of connector X13, and pins 3, 4, and 5 of connector X19 are connected to pins 23, 24, and 25 of connector X13. When the battery temperature is greater than or equal to 28°C, the BMU main control module in the battery box sends a cooling command to the liquid cooling unit through the vehicle CAN communication bus, and the air conditioning compressor of the liquid cooling unit works. At this time, the temperature of the coolant at the outlet of the liquid cooling unit is gradually controlled to a preset value of about 10°C. The heat generated by the battery is transferred to the coolant through the water cooling plate. After heating, the coolant flows back to the liquid cooling unit through the liquid cooling return port, and the heat is transferred to the air under the action of the refrigeration system in the liquid cooling unit, thereby reducing the temperature of each battery cell in the battery module. When the average battery temperature is lower than 24°C, the BMU main control module in the battery box sends a self-circulation command to the liquid cooling unit through the vehicle's CAN communication bus to stop cooling. Driven by the water pump in the liquid cooling unit, the coolant is maintained in circulation in the pipeline through self-circulation, so that the battery temperature of each module remains relatively consistent.

[0072] The rated cooling power of the liquid cooling unit is 9kW, the voltage operating range is 400-750VDC, and the water pump performance is 200kpa@30L / min. The liquid cooling unit has a low-voltage wake-up function, built-in fuse and pre-charging circuit to ensure that the instantaneous impact current of the contactor closing or disconnecting is less than 10A. The system has its own diagnostic function, and the diagnostic information is sent to the BMU main control module and 4G module through the CAN bus. The liquid cooling unit receives the control instructions of the BMU main control module in the battery box and enters four working states: standby, cooling, heating, and self-circulation. The BMU main control sends corresponding instructions to the liquid cooling unit according to the average temperature T of the battery module (T=(T1+T2+T3+T4+T5+T6+T7+T8) / 8) to ensure that the battery operates within the optimal temperature range of 20-30℃.

[0073] (4) Control part

[0074] The battery management system BMS consists of 1 BMU master control module and 8 BSU slave control modules. Each BSU slave control module independently manages 1 lithium titanate battery module. The BMU master control module is connected to each BSU slave control module using the CAN0 bus. The power supply 24V_2 of the BSU slave control module is provided by the BMU master control module. The BMU master control module manages two virtual batteries at the same time, communicates with two traction DCUs, and collects signals from two trains.

[0075] For the convenience of the following description:

[0076] The DC1+connector X5 of the electrical box, the Hall sensor TA3, the contactor KM1, the contactor KM3, the pre-charging resistor R1, the fuse FU1, the electrical box B+connector X11, the battery box B+connector X1, the manual maintenance switch MSD, the battery modules 1 to 8, the Hall sensor TA1, the battery box B-connector X2, the electrical box B-connector X12, the fuse FU3, the contactor KM2, the DC1-connector X7, the above components and circuits constitute a virtual battery 1;

[0077] The DC2+connector X6 of the electrical box, the Hall sensor TA4, the contactor KM5, the contactor KM4, the pre-charging resistor R2, the Hall sensor TA2, the fuse FU2, the electrical box B+connector X11, the battery box B+connector X1, the manual maintenance switch MSD, the battery modules 1 to 8, the Hall sensor TA1, the battery box B-connector X2, the electrical box B-connector X12, the fuse FU3, the contactor KM2, the DC2-connector X8, the above components and circuits constitute the virtual battery 2;

[0078] The train equipment provides four sets of signals to connector X13: the KL15_1 signal is connected to pin 1 of connector X13, the KL15_2 signal is connected to pin 2 of connector X13, the train 24V+ input is connected to pins 3 and 4 of connector X13, and the train 24V- input is connected to pins 5 and 6 of connector X13.

[0079] The train equipment provides train 24V signals and train network signals to traction boxes DCU1 and DCU2.

[0080] The traction box outputs three sets of signals to connector X13: traction box DCU1 outputs KL30_1 signal to pin 7 of connector X13, traction box DCU2 outputs KL30_2 signal to pin 8 of connector X13, and the vehicle CAN communication of traction boxes DCU1 and DCU2 are short-circuited and connected to pins 23, 24, and 25 of connector X13.

[0081] The KM1 control (one positive and one negative) of connector X10 of the electrical box is connected to pin 9 (control positive) and pin 10 (control negative) of connector X13, the KM2 control of connector X10 is connected to pin 11 and pin 12 of connector X13, the KM3 control of connector X10 is connected to pin 13 and pin 14 of connector X13, the KM4 control of connector X10 is connected to pin 15 and pin 16 of connector X13, the KM5 control of connector X10 is connected to pin 17 and pin 18 of connector X13, the HV_TC1+ of connector X10 is connected to pin 26 of connector X13, and the HV_TC2+ of connector X10 is connected to pin 27 of connector X13.

[0082] Working process:

[0083] 1. The train starts, outputs 24V, and the traction box DCU1, traction box DCU2 and liquid cooling unit are powered on at low voltage; at the same time, the 24V isolated power supply in the battery box works, outputs 24V_1 signal, the BMU main control module in the battery box wakes up, and outputs 24V_2 signal to the BSU slave control module. After the BSU slave control module is powered on, it collects the 28 cell voltages and 1 module temperature information managed by this module, and sends the cell voltage and cell temperature of the module to the BMU main control module through the CAN0 bus. The BMU main control module performs calculations on the CAN data sent by the BSU slave control module, calculates the highest cell voltage and number, the lowest cell voltage and number, the highest cell temperature and number, the lowest cell temperature and number, the difference between the highest cell temperature and the lowest cell temperature, and the difference between the highest cell voltage and the lowest cell voltage among the 8 modules in the battery box. At the same time, the BMU main control module collects and calculates the current values ​​of the two main positive branches, the total voltage value of the battery pack, and the insulation resistance value of the battery pack, and sends them to the vehicle CAN bus. The BMU main control module sends the fault status of the battery system to the vehicle CAN according to the battery protection threshold. When there is no fault, the fault flag is 0, and when there is a fault, the flag is 1. The traction DCU corresponding to the virtual battery reporting the fault will not send the input command, and the train will display the battery fault repair report.

[0084] 2. The train outputs the wake-up hard-wire signal KL15_1=24V. After the BMU main control module detects that this signal is 24V, the BMU main control module outputs the working status flag of the virtual battery 1 as 1000 (init_1 initialization status=1, Standby_1 standby status=0, Precharge_1 pre-charging status=0, Operational_1 working status=0).

[0085] 3. The train outputs the wake-up hard-wire signal KL15_2=24V. When the BMU main control module detects that this signal is 24V, the BMU main control module outputs the working status flag of the virtual battery 2 as 1000 (init_2 initialization status=1, Standby_2 standby status=0, Precharge_2 pre-charging status=0, Operational_2 working status=0).

[0086] 4. After the traction box DCU1 self-checks and finds no fault, it outputs the hard-wire signal KL30_1=24V indicating that traction 1 is fault-free, and the BMU main control module switches the state of virtual battery 1 to 0100 (init_1 initialization state=0, Standby_1 standby state=1, Precharge_1 pre-charge state=0, Operational_1 working state=0). When the traction box DCU1 self-checks and finds a fault, it outputs the traction box DCU1 fault signal KL30_1=0V, and sends the vehicle CAN network signal indicating that the traction box DCU1 is faulty to the train, waiting for maintenance.

[0087] 5. After the traction box DCU2 self-checks and finds no fault, it outputs the hard-wire signal KL30_2=24V indicating that traction 2 is fault-free, and the BMU main control module switches the state of virtual battery 2 to 0100 (init_2 initialization state=0, Standby_2 standby state=1, Precharge_2 pre-charge state=0; Operational_2 working state=0). When the traction box DCU2 self-checks and finds fault, it outputs the traction box DCU2 fault signal KL30_2=0V, and sends the vehicle CAN network signal indicating that traction DCU2 is faulty to the train, waiting for maintenance.

[0088] 6. After the traction box DCU1 has no faults and receives the virtual battery 1 has no faults, it sends the virtual battery 1 input command, the BMU main control module controls KM3 to close and KM2 to close, KM1 to disconnect, KM4 and KM5 to keep the original status, and sends the virtual battery 1 status as 0010 (init_1 initialization status = 0, Standby_1 standby status = 0, Precharge_1 precharge status = 1; Operational_1 working status = 0). At this time, the virtual battery 1 precharges the DCU1, and the current path is: battery box B + connector X1 → electrical box B + connector X11 → fuse FU1 → precharge resistor R1 → contactor KM3 → Hall sensor TA3 → DC1 + connector X5 → traction DCU1 → DC1-connector X7 → contactor KM2 → fuse FU3 → electrical box B-connector X12 → battery box B-connector X2.

[0089] 7. After the traction box DCU2 has no faults and receives the virtual battery 2 has no faults, it sends the virtual battery 2 input command, the BMU main control module controls KM5 and KM2 to close, KM4 to disconnect, KM1 and KM3 to keep the original state, and sends the virtual battery 2 state as 0010 (init_2 initialization state = 0, Standby_2 standby state = 0, Precharge_2 precharge state = 1; Operational_2 working state = 0). At this time, the battery precharges DCU2, and the current path is: battery box B + connector X1 → electrical box B + connector X11 → fuse FU2 → Hall sensor TA2 → precharge resistor R2 → contactor KM5 → Hall sensor TA4 → DC2 + connector X6 → traction DCU2 → DC2-connector X8 → contactor KM2 → fuse FU3 → electrical box B-connector X12 → battery box B-connector X2.

[0090] 8. After the virtual battery 1 is pre-charged, the BMU main control module controls KM1 and KM2 to close, KM3 to disconnect, KM4 and KM5 to keep the original status, and sends the status of battery 1 as 0001 (init_1 initialization status = 0, Standby_1 standby status = 0, Precharge_1 pre-charging status = 0; Operational_1 working status = 1). At this time, the battery supplies power to DCU1, and the current path is: battery box B + connector X1 → electrical box B + connector X11 → fuse FU1 → contactor KM1 → Hall sensor TA3 → DC1 + connector X5 → traction DCU1 → DC1-connector X7 → contactor KM2 → fuse FU3 → electrical box B-connector X12 → battery box B-connector X2

[0091] 9. After the virtual battery 2 is pre-charged, the BMU main control module controls KM4 and KM2 to close, KM5 to disconnect, KM1 and KM3 to keep the original status, and sends the battery 2 status as 0001 (init_2 initialization status = 0, Standby_2 standby status = 0, Precharge_2 pre-charge status = 0; Operational_2 working status = 1). At this time, the battery supplies power to DCU2, and the current path is: battery box B + connector X1 → electrical box B + connector X11 → fuse FU2 → Hall sensor TA2 → contactor KM4 → Hall sensor TA4 → DC2 + connector X6 → traction DCU2 → DC2-connector X8 → contactor KM2 → fuse FU3 → electrical box B-connector X12 → battery box B-connector X2

[0092] 10. The train power-off command is sent to the traction box DCU1, and DCU1 sends the battery 1 disconnection command. The BMU main control disconnects the KM1 contactor, and the other contactors remain in their original state;

[0093] 11. The train power-off command is sent to the traction box DCU2, and DCU2 sends the battery 2 disconnection command. The BMU main control disconnects the KM4 contactor, and the other contactors remain in their original state;

[0094] 12. When both traction box DCU1 and traction box DCU2 send battery disconnection instructions, the BMU master control disconnects the KM2 contactor. At this time, the five contactors in the electrical box are in the disconnected state.

[0095] 13. The 4G module is responsible for sending the cell voltage information, cell temperature information, SOC, insulation resistance, battery branch 1 current, battery branch 2 current, total voltage, contactor status of battery branch 1, virtual battery 1 status, virtual battery 2 status, water cooler status, traction box DCU1 command, traction box DCU2 command sent by the BMU main control module through the CAN2 bus to the 4G cloud platform. By logging into the 4G cloud platform interface, you can view the real-time or historical information of the battery system, which greatly facilitates the diagnosis and maintenance of the battery system.

[0096] The specific method for judging the completion of pre-charging is as follows:

[0097] When the voltage of HV_TC1+ collected by the BMU main control module is greater than or equal to 95% of HV+, the pre-charging of virtual battery 1 is completed;

[0098] When the voltage of HV_TC2+ collected by the BMU main control module is greater than or equal to 95% of HV+, the pre-charging of virtual battery 2 is completed;

[0099] The battery charging path is as follows:

[0100] When the train pantograph is raised for charging, the current path is: power grid → train pantograph + → traction box DCU1 / 2 → contactor KM1 / KM4 → fuse FU1 / FU2 → electrical box B + connector X11 → battery box B + connector X1 → battery modules 1~8 → battery box B-connector X2 → electrical box B-connector X12 → fuse FU3 → contactor KM2 → traction box DCU1 / 2 → train pantograph - → power grid.

[0101] SOC estimation method:

[0102] The basic algorithm is ampere-hour integration. The BMU main control module collects the total current once every 10mS and accumulates the SOC once, as shown in Formula 1. I in the formula is the real-time current value, which is collected by the total Hall sensor TA1 and sent to the BMU main control module.

[0103] SOC 新 =SOC 旧 +[(m*I*10 / 3600000) / n]*100%-----Formula 1,

[0104] SOC 新 Represents the SOC value at the current moment; SOC 旧 is the SOC value before the last time (10ms); m is the calibration coefficient of SOC, which is normally 1; 10 / 3600000 is the conversion of ms to h; n is the nominal capacity of the battery pack, in Ah.

[0105] SOC calibration strategy 1:

[0106] According to the data table of cell voltage and SOC corresponding to the cell under 25°C condition and constant current charging for 30s, the SOC calibration function starts at the cell voltage point corresponding to 84% SOC.

[0107] If the current SOC is lower than 84%, the value of m in Formula 1 is 1.1, so that the SOC increases quickly to 85%. When the train receives the SOC of 85% from the BMU main control, charging stops.

[0108] If the current SOC is equal to 84% and the highest cell voltage is lower than the value in the table, the SOC stops increasing until the highest cell voltage is greater than or equal to the value in the table. The SOC increases normally until the SOC accumulates to 85%. When the train receives an SOC of 85% from the BMU main control, charging stops.

[0109] Table 1 Correspondence between voltage and SOC of a 70Ah lithium titanate battery cell at 25℃

[0110] Charging current(A) 70 140 210 280 350 Single cell voltage (mV) 2440 2480 2520 2560 2600 SOC reference value 84％ 84％ 84％ 84％ 84％

[0111] SOC calibration strategy 2:

[0112] Because trams use the short time when passengers get on and off the bus to charge, the charging time at each station is uncertain, roughly between 19 and 50 seconds. Therefore, the conditions of SOC calibration strategy 1 are sometimes not met. Then we can adopt the second SOC calibration strategy as a supplement, as follows:

[0113] The SOC is calibrated within 45 minutes of the train's daily rest period. During the rest period, the battery system is not charged or discharged and is in a static state. After 30 minutes of rest, when the battery is basically stable, a rough OCV calibration is performed using the voltage and SOC relationship curve of the lithium titanate battery. According to the corresponding relationship between the current average voltage value of the single cell and the SOC, the current new SOC value is estimated. If the estimated SOC is more than 10% lower than the current SOC of the BMS, the current SOC is lowered by 10%, otherwise, no calibration is performed. The purpose of this calibration is to prevent the SOC from being too high. The discharge rate of a battery with a falsely high SOC is higher than the discharge rate when the SOC is normal, which will accelerate battery aging and reduce the battery life. SOC calibration during the rest period is a supplement to the SOC charging calibration in the station.

[0114] In summary, the present invention realizes the use of two groups of lithium titanate battery systems as the traction power of the 2M3T five-car train, realizes a tram battery system solution with one group of batteries and two groups of traction, and customizes the SOC estimation method according to the working conditions of the tram.

[0115] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0116] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A tram lithium titanate battery system, characterized in that: It includes a battery box, an electrical box and a liquid cooling system, wherein: the positive and negative electrodes of the battery box are connected to the B+ connector X11 and B- connector X12 of the electrical box through the B+ connector X1 and B- connector X2 respectively; after the B+ connector X11 enters the electrical box, it is directly divided into two positive branches with pre-charge, which are respectively connected to the DC1+ connector X5 and DC2+ connector X6 of the electrical box; after the B- connector X12 enters the electrical box, it passes through the main negative fuse FU3 and the main negative contactor KM2 and then is divided through the copper busbar Two negative branches are formed to DC1-connector X7 and DC2-connector X8; DC1+connector X5 and DC1-connector X7 are the first group of outputs, connected to traction box DCU1; DC2+connector X6 and DC2-connector X8 are the second group of outputs, connected to traction box DCU2; the vehicle CAN bus of traction box DCU1 and traction box DCU2 are connected to the vehicle communication X13 together, and finally connected to the battery management system BMS in the battery box and the connector X19 of the liquid cooling unit.

2. The lithium titanate battery system for trams according to claim 1, characterized in that: The battery box is equipped with 8 lithium titanate battery modules, 24V isolated power supply, 4G module, main Hall sensor TA1 and battery management system BMS. The battery management system BMS includes BMU master control module and BSU slave control modules 1 to 8, among which: Among the 8 lithium titanate battery modules, the positive electrode B1+ of battery module 1 is connected to the 1st pin of the manual maintenance switch MSD of the battery box, the 2nd pin of the manual maintenance switch MSD is connected to the 1st pin of the B+ connector X1 and the connector X14, the 2nd pin of the connector X14 is connected to the connector X2, the negative electrode B28- of battery module 1 is connected to the positive electrode of battery module 2, the negative electrode B56- of battery module 2 is connected to the positive electrode of battery module 3, and so on, the negative electrode of battery module 7 is connected to the positive electrode B196- of battery module 8, and the negative electrode B224- of battery module 8 is connected to the B- connector X2; The input of the 24V isolated power supply is connected to pins 3 and 5 of connector X3. The output 24V_1 of the 24V isolated power supply is connected to the 4G module and the BMU main control module. The 1-pin KL15_1 signal, 2-pin KL15_2 signal, 7-pin KL30_1, and 8-pin KL30_2 of connector X3 are all connected to the BMU main control module in the BMS system. The BMU main control module outputs control signals of five groups of contactors KM1, KM2, KM3, KM4, and KM5, which are connected to pins 9 to 18 of the battery box connector X3 respectively. Each contactor control signal is a positive signal and a negative signal. The BMU main control module outputs 5V power to the Hall sensor TA2, and then collects the current of the branch where the fuse FU2 in the electrical box is located through the two signal lines of the Hall sensor TA2. The two signal lines of the Hall sensor TA2 and the two 5V power lines are connected to the BMU main control module through the 19th, 20th, 21st and 22nd pins of the connector X3 respectively; The vehicle CAN bus of the BMU main control module is connected to pins 23, 24, and 25 of the connector X3, and the CAN2 bus of the BMU main control module is connected to the CAN communication line of the 4G module accordingly; The 26th pin HV_TC1+ and the 27th pin HV_TC2+ of the connector X3 are connected to the BMU main control module. The BMU main control module collects the voltage signals of HV_TC1+ and HV_TC2+ to determine whether the battery pre-charging is completed; The CAN0 bus of the BMU master control module is connected to the CAN interface of the BSU slave control module 1 to the BSU slave control module 8; the BMU master control module outputs 24V_2 to power the BSU slave control module 1 to the BSU slave control module; each slave control module collects 28 cell voltages and 1 module temperature of 1 module; The BMU main control module outputs 5V power to the Hall sensor TA1, and then collects the total current of the battery box through the two signal lines of the Hall sensor TA1; The antenna of the 4G module passes through the through hole X17 of the battery box and is pasted on the outer wall of the battery box.

3. The tram lithium titanate battery system according to claim 2, characterized in that: The electrical box is equipped with fuse FU1, contactor KM1, contactor KM3, pre-charging resistor R1, fuse FU2, contactor KM4, contactor KM5, pre-charging resistor R2, current sensor TA2, current sensor TA3, current sensor TA4, fuse FU3, contactor KM2, copper bus and connectors, among which: The B+ connector X11 of the electrical box is the total positive input of the battery box, which is divided into two branches through copper busbars 1 and 2, where: the B+ connector X11 is connected to pin 1 of fuse FU1 through copper busbar 1, and pin 2 of fuse FU1 is connected to pin 1 of contactor KM1 and pin 1 of pre-charging resistor R1 through copper busbar 3, and pin 2 of pre-charging resistor R1 is connected to pin 1 of contactor KM3, and pin 2 of contactor KM3 and pin 2 of contactor KM1 are connected to connector X5 through copper busbar 5, and a TA3 Hall sensor is mounted on copper busbar 5; the B+ connector X11 is connected to fuse FU2 through copper busbar 2 Pin 1 of fuse FU2, pin 2 of fuse FU2 is connected to pin 1 of contactor KM4 and pin 1 of pre-charging resistor R2 through copper bus 4, Hall sensor TA2 is sleeved on copper bus 4, pin 2 of pre-charging resistor R2 is connected to pin 1 of contactor KM5, pin 2 of contactor KM5 and pin 2 of contactor KM4 are connected to connector X6 through copper bus 6, Hall sensor TA4 is sleeved on copper bus 6, Hall sensor TA3 signal is connected to traction box DCU1 through connector X22 of electrical box, Hall sensor TA4 signal is connected to traction box DCU2 through connector X23 of electrical box; The B-connector X12 of the electrical box is the total negative output of the battery box, the negative branch: pin 1 of fuse FU3 is connected to B-connector X12, pin 2 of fuse FU3 is connected to pin 1 of contactor KM2, pin 2 of contactor KM2 is connected to DC1-connector X7 through copper bus 8, and connector X7 is then connected to DC2-connector X8 through copper bus 9; the control signals of the five contactors KM1, KM2, KM3, KM4, and KM5 in the electrical box are connected to connector X10; the signal of connector X10 is then connected to the vehicle communication connector X13 together with the train signal and traction signal; connector X13 and connector X3 are connected through a wiring harness.

4. The lithium titanate battery system for trams according to claim 3, characterized in that: The liquid cooling system consists of a liquid cooling unit, stainless steel water pipes, hoses, joints, coolant, water cooling plates, and expansion kettles, including: The coolant is injected from the filling port of the expansion kettle, flows into the liquid cooling unit through the stainless steel water pipe and joint, the liquid cooling outlet X21 of the liquid cooling unit is connected to the battery water inlet X15 of the battery box, the battery water inlet X15 is connected to the water cooling plate on the battery module through a stainless steel water pipe, the water outlet of the water cooling plate of the battery module is connected to another stainless steel water pipe in the battery box that serves as a return water, and the coolant then flows back to the liquid cooling return water port X20 of the liquid cooling unit through the battery water outlet X16 of the battery box and the stainless steel water pipe; Pin 1 and Pin 2 of connector X18 of the liquid cooling unit are respectively connected to Pin 1 and Pin 2 of connector X14 of the battery box, providing high voltage power input to the water cooling unit; Pin 1 and Pin 2 of connector X19 of the liquid cooling unit are connected to Pin 4 and Pin 6 of connector X13, and Pin 3, Pin 4, and Pin 5 of connector X19 are connected to Pin 23, Pin 24, and Pin 25 of connector X13.

5. The lithium titanate battery system for trams according to claim 4, characterized in that: When the battery temperature is greater than or equal to 28°C, the BMU main control module in the battery box sends a cooling command to the liquid cooling unit through the vehicle CAN communication bus, and the air conditioning compressor of the liquid cooling unit starts working; At this time, the temperature of the coolant at the outlet of the liquid cooling unit is gradually controlled to a preset value of about 10°C. The heat generated by the battery is transferred to the coolant through the water cooling plate. After heating, the coolant flows back to the liquid cooling unit through the liquid cooling return port, and the heat is transferred to the air under the action of the refrigeration system in the liquid cooling unit, thereby reducing the temperature of each battery cell in the battery module; when the average battery temperature is lower than 24°C, the BMU main control module in the battery box sends a self-circulation command to the liquid cooling unit through the vehicle CAN communication bus to stop cooling. Driven by the water pump in the liquid cooling unit, the coolant is maintained in circulation in the pipeline through self-circulation, so that the battery temperature of each module remains relatively consistent.

6. The lithium titanate battery system for trams according to claim 4, characterized in that: DC1+connector X5, Hall sensor TA3, contactor KM1, contactor KM3, pre-charging resistor R1, fuse FU1, electrical box B+connector X11, battery box B+connector X1, manual maintenance switch MSD, battery modules 1-8, Hall sensor TA1, battery box B-connector X2, electrical box B-connector X12, fuse FU3, contactor KM2 and DC1-connector X7 constitute virtual battery 1; DC2+connector X6, Hall sensor TA4, contactor KM5, contactor KM4, pre-charging resistor R2, Hall sensor TA2, fuse FU2, electrical box B+connector X11, battery box B+connector X1, manual maintenance switch MSD, battery modules 1-8, Hall sensor TA1, battery box B-connector X2, electrical box B-connector X12, fuse FU3, contactor KM2 and DC2-connector X8 constitute virtual battery 2; The train equipment provides four sets of signals to the connector X13, the KL15_1 signal is connected to pin 1 of the connector X13, the KL15_2 signal is connected to pin 2 of the connector X13, the train 24V+ input is connected to pins 3 and 4 of the connector X13, and the train 24V- input is connected to pins 5 and 6 of the connector X13; The train equipment provides train 24V signals and train network signals to traction boxes DCU1 and DCU2; The traction box outputs three groups of signals to the connector X13. The traction box DCU1 outputs the KL30_1 signal to the 7th pin of the connector X13. The traction box DCU2 outputs the KL30_2 signal to the 8th pin of the connector X13. The vehicle CAN communication of the traction box DCU1 and the traction box DCU2 are short-circuited and connected to the 23rd, 24th and 25th pins of the connector X13. In connector X10, the control signal of contactor KM1 is connected to pins 9 and 10 of connector X13, the control signal of contactor KM2 is connected to pins 11 and 12 of connector X13, the control signal of contactor KM3 is connected to pins 13 and 14 of connector X13, the control signal of contactor KM4 is connected to pins 15 and 16 of connector X13, the control signal of contactor KM5 is connected to pins 17 and 18 of connector X13, HV_TC1+ of connector X10 is connected to pin 26 of connector X13, and HV_TC2+ of connector X10 is connected to pin 27 of connector X13.

7. The lithium titanate battery system for trams according to claim 6, characterized in that: The working process is: The train starts, outputs 24V, and the traction box DCU1, traction box DCU2 and liquid cooling unit are powered on at low voltage; at the same time, the 24V isolated power supply in the battery box works, outputs 24V_1 signal, the BMU main control module in the battery box wakes up, and outputs 24V_2 signal to the BSU slave control module; after the BSU slave control module is powered on, it collects the 28 single cell voltages and 1 module temperature information managed by this module, and sends the module's single cell voltage and single cell temperature to the BMU main control module through the CAN0 bus; the BMU main control module performs calculations on the CAN data sent by the BSU slave control module, and calculates the highest single cell voltage and Number, lowest cell voltage and number, highest cell temperature and number, lowest cell temperature and number, the difference between the highest cell temperature and the lowest cell temperature, the difference between the highest cell voltage and the lowest cell voltage. At the same time, the BMU main control module collects and calculates the current values ​​of the two main positive branches, the total voltage value of the battery pack, and the insulation resistance value of the battery pack, and sends them to the vehicle CAN bus; the BMU main control module sends the fault status of the battery system to the vehicle CAN according to the protection threshold of the battery; when there is no fault, the fault flag bit sends 0, and when there is a fault, the flag bit sends 1; the traction DCU corresponding to the virtual battery reporting the fault will not send the input command, and the train will display the battery fault repair; The train outputs the wake-up hard-wire signal KL15_1=24V. After the BMU main control module collects this signal as 24V, the BMU main control module outputs the working status flag bit of the virtual battery 1 as 1000; The train outputs the wake-up hard-wire signal KL15_2 = 24V. When the BMU main control module collects this signal as 24V, the BMU main control module outputs the working status flag of the virtual battery 2 as 1000; After the traction box DCU1 self-checks and finds no fault, it outputs the hard-wire signal KL30_1=24V indicating that traction 1 is fault-free, and the BMU main control module switches the state of virtual battery 1 to 0100. When the traction box DCU1 self-checks and finds fault, it outputs the traction box DCU1 fault signal KL30_1=0V, and sends the vehicle CAN network signal indicating that the traction box DCU1 is faulty to the train, waiting for maintenance; After the traction box DCU2 self-checks and finds no fault, it outputs the hard-wire signal KL30_2=24V indicating that traction 2 is fault-free, and the BMU main control module switches the state of virtual battery 2 to 0100. When the traction box DCU2 self-checks and finds fault, it outputs the traction box DCU2 fault signal KL30_2=0V, and sends the vehicle CAN network signal indicating that traction DCU2 is faulty to the train, waiting for maintenance; After the traction box DCU1 has no fault and receives the virtual battery 1 has no fault, it sends the virtual battery 1 input command, the BMU main control module controls the contactor KM3 to close and the contactor KM2 to close, the contactor KM1 is disconnected, the contactors KM4 and KM5 remain in the original state, and the state of the virtual battery 1 sent is 0010; at this time, the virtual battery 1 pre-charges the DCU1, and the current path is: B+connector X1→B+connector X11→fuse FU1→pre-charge resistor R1→contactor KM3→Hall sensor TA3→DC1+connector X5→traction DCU1→DC1-connector X7→contactor KM2→fuse FU3→B-connector X12→box B-connector X2; After the traction box DCU2 has no fault and receives the virtual battery 2 has no fault, it sends the virtual battery 2 input command, the BMU main control module controls the contactor KM5 to close and the contactor KM2 to close, the contactor KM4 to disconnect, the contactor KM1 and the contactor KM3 to keep the original state, and the state of the virtual battery 2 sent is 0010. At this time, the battery pre-charges the DCU2, and the current path is: B+connector X1→B+connector X11→fuse FU2→Hall sensor TA2→pre-charge resistor R2→contactor KM5→Hall sensor TA4→DC2+connector X6→traction DCU2→DC2-connector X8→contactor KM2→fuse FU3→electrical box B-connector X12→B-connector X2; After the virtual battery 1 is pre-charged, the BMU main control module controls contactors KM1 and KM2 to close, contactor KM3 to open, contactors KM4 and KM5 to keep their original states, and sends the state of battery 1 as 0001. At this time, the battery supplies power to DCU1, and the current path is: B+ connector X1→B+ connector X11→fuse FU1→contactor KM1→Hall sensor TA3→DC1+ connector X5→traction DCU1→DC1- connector X7→contactor KM2→fuse FU3→B- connector X12→B- connector X2; After the virtual battery 2 is pre-charged, the BMU main control module controls the contactors KM4 and KM2 to close, the contactor KM5 to open, the contactors KM1 and KM3 to keep the original status, and sends the status of the virtual battery 2 as 0001. At this time, the battery supplies power to DCU2, and the current path is: B+ connector X1→B+ connector X11→fuse FU2→Hall sensor TA2→contactor KM4→Hall sensor TA4→DC2+ connector X6→traction DCU2→DC2- connector X8→contactor KM2→fuse FU3→B- connector X12→B- connector X2; The train power-off command is sent to the traction box DCU1, which sends the battery 1 disconnection command. The BMU master disconnects the contactor KM1, and the other contactors remain in their original state. The train power-off command is sent to the traction box DCU2, which sends the battery 2 disconnection command. The BMU master disconnects the contactor KM4, and the other contactors remain in their original state. When both traction box DCU1 and traction box DCU2 issue the battery disconnection command, the BMU master disconnects the KM2 contactor. At this time, all five contactors in the electrical box are in the disconnected state. The 4G module is responsible for sending the cell voltage information, cell temperature information, SOC, insulation resistance, battery branch 1 current, battery branch 2 current, total voltage, contactor status of battery branch 1, virtual battery 1 status, virtual battery 2 status, water cooler status, traction box DCU1 command, traction box DCU2 command sent by the BMU main control module through the CAN2 bus to the 4G cloud platform. By logging into the 4G cloud platform interface, you can view the real-time or historical information of the battery system.

8. The lithium titanate battery system for trams according to claim 7, characterized in that: When the voltage of HV_TC1+ collected by the BMU main control module is greater than or equal to 95% of HV+, the pre-charging of virtual battery 1 is completed; when the voltage of HV_TC2+ collected by the BMU main control module is greater than or equal to 95% of HV+, the pre-charging of virtual battery 2 is completed.

9. The lithium titanate battery system for trams according to claim 7, characterized in that: The SOC estimation method is: The BMU main control module collects the total current once every 10mS and accumulates the SOC once, as shown in Formula 1; SOC 新 = SOC 旧 + [(m * I * 10 / 3600000) / n] * 100% ----- Formula 1, Where I is the real-time current value, which is collected by the main Hall sensor TA1 and sent to the BMU main control module, SOC 新 Represents the SOC value at the current moment; SOC 旧 is the last SOC value; m is the SOC calibration factor; n is the nominal capacity of the battery pack.

10. The lithium titanate battery system for trams according to claim 9, characterized in that: SOC calibration strategies include: SOC calibration strategy 1 is: According to the data table of cell voltage and SOC corresponding to the cell voltage after constant current charging for 30s at 25℃, the SOC calibration function is performed at the cell voltage point corresponding to SOC of 84%. If the current SOC is lower than 84%, the value of m in Formula 1 is 1.1, so that the SOC increases rapidly to 85%. When the train receives an SOC of 85% from the BMU main control, charging stops. If the current SOC is equal to 84%, and the highest cell voltage is lower than the value in the table, the SOC stops increasing until the highest cell voltage is greater than or equal to the value in the table. The SOC increases normally until the SOC accumulates to 85%. When the train receives an SOC of 85% from the BMU main control, charging stops. SOC calibration strategy 2: The SOC is calibrated within 45 minutes when the train returns to the depot for rest every day. During the rest period, the battery system is not charged or discharged and is in a static state. After the battery has been stationary for 30 minutes and the state is basically stable, a rough OCV calibration is performed using the relationship curve between the lithium titanate battery voltage and SOC. The current new SOC value is estimated based on the corresponding relationship between the current average cell voltage value and SOC. If the estimated SOC is more than 10% lower than the current SOC of the BMS, the current SOC will be lowered by 10%. Otherwise, no calibration is performed.

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