[0020] The present invention will be further described below in conjunction with the drawings.
[0021] Such as figure 1 , figure 2 The shown low-temperature charging and heating system for the power battery of a pure electric vehicle includes a vehicle control unit 1, an on-board charger 2, a battery management system 4, a power battery 5, a DC/DC converter 6, a thermal management system 7, and PTC heating An insulation detection circuit 10 is connected in parallel with the vehicle charger 2 and the fan module 9 is composed of a fan and a fan relay that controls the fan to turn on the power. The vehicle control unit 1 communicates with the vehicle charger 2, the battery management system 4, the DC/DC converter 6, the thermal management system 7, and coordinates the vehicle charger 2, the battery management system 4, and the DC/DC converter 6 , The work of the thermal management system 7; the on-board charger 2 is connected with the external power cabinet 3, the PTC heater 8, the power battery 5, and the DC/DC converter 6 to convert the 220V AC in the external power cabinet 3 into 330V DC. Supply power to the PTC heater 8, DC/DC converter 6 and charge the power battery 5. The external power cabinet 3 can provide power greater than 6kw. The vehicle charger 2 and PTC heater 8 are both 6kw, making the whole set The system can be optimized; the battery management system 4 communicates with the on-board charger 2, sends charging demand information to the on-board charger 2, and obtains relevant charging information. The battery management system 4 is connected to the power battery 5, and the power battery 5 Various parameters are managed. The battery management system 4 is connected to the fan module 9, and the fan relay is controlled to be disconnected or connected, so that the fan does not work or work. When the fan is working, the heat generated by the PTC heater is blown into the battery pack. Power battery heating; the thermal management system 7 is connected to the PTC heater 8 to control the working power of the PTC heater 8; the DC/DC converter 6 is connected to the power battery 5 to convert high-voltage direct current to low-voltage direct current to the vehicle control unit 1 , Battery management system 4, thermal management system 7 supply power.
[0022] Such as figure 2 As shown, during the low-temperature charging and heating process, the total positive and total negative relays on the power battery circuit are both closed, and the on-board charger 2 works in constant current mode to supply power to the PTC heater 8 and the DC/DC converter 6 , And charge the power battery 5 at the same time.
[0023] According to the analysis of the circuit principle,
[0024] I 1 = I 2 +I 3 +I 4 (1)
[0025] In formula (1), I 1 Is the output current of the vehicle charger 2 in A; I 2 Is the input current of the DC/DC converter 6, unit A; I 3 Is the input current of PTC heater 8, unit A; I 4 It is the allowable input charging current of the power battery 5, in A.
[0026] When the temperature T of the power battery 5 is less than or equal to 5°C, it enters the low-temperature charging and heating mode. The battery management system 4 controls the power battery not to charge or low current charging under the instruction of the vehicle control unit 1. The thermal management system is in the vehicle control unit Under the command of 1, the PTC heater 8 is controlled to heat, the battery management system 4 controls the fan relay in the fan module 9 to turn on, the fan works, and the heat generated by the PTC heater 8 is blown into the battery pack. The target limit of the power battery 5 is not charged or charged with a small current:
[0027] I 4 = 0 , T ≤ 0 0.1 C , 0 T ≤ 5 - - - ( 2 )
[0028] In formula (2), T is the temperature of the power battery, in °C; C is the battery capacity.
[0029] The vehicle control unit 1 controls the output current of the on-board charger 2 and the current supplied to the PTC heater 8 according to the above-mentioned target limit.
[0030] The power balance relationship of each component during low temperature charging and heating is:
[0031] P 1 =P 2 +P 3 +P 4 (3)
[0032] In formula (3), P 1 Is the maximum allowable charging power sent by the vehicle control unit 1 to the on-board charger 2, in W; P 2 Is the power value actually consumed by the DC/DC converter 6, in W; P 3 PTC heater 8 actual maximum available power value, unit W; P 4 It is the control target value of the charging power of the power battery 5, in W.
[0033] PTC heater 8 heating process, its maximum available power P 3 It is related to the maximum allowable charging power that the vehicle control unit 1 sends to the thermal management system 7, and the maximum available power of the PTC heater 8 is controlled by the vehicle control unit 1. The PTC heater power sent by the thermal management system 7 is calculated based on the current water temperature, flow rate and the power demand sent by the vehicle control unit 1, which will cause some fluctuations in the power of the PTC heater, in order to avoid some large PTC heating The power of the power supply fluctuates, which brings current impact to the power battery, causing the negative electrode material of the power battery to crystallize. Therefore, the charging power of the power battery needs to be limited. Control target value P of charging power of power battery 4 As shown in formula (4),
[0034] P 4 = 0 , T ≤ 0 0.1 C * U , 0 T ≤ 5 - - - ( 4 )
[0035] In formula (4), U is the DC bus voltage of the power battery in V.
[0036] When the temperature of the power battery 5 is heated to above 5°C, the vehicle control unit 1 instructs the thermal management system 7 to turn off the PTC heater 8 to stop heating the battery pack, and instructs the battery management system 4 to control the fan relay in the fan module 9 to turn off Turn on, the fan stops working, exits the low temperature heating mode, and enters the normal charging mode (the charging method of the normal charging mode is the same as the existing charging method).
[0037] Such as image 3 As shown, the method for low-temperature charging and heating of a pure electric vehicle power battery using the above-mentioned low-temperature charging and heating system includes:
[0038] Step 1: Insert the charging gun of the on-board charger 2 into the external power cabinet 3 for connection.
[0039] Step 2: Vehicle control unit 1, vehicle charger 2, battery management system 4, DC/DC converter 6 and thermal management system 7 are powered on at low voltage, vehicle control unit 1 instructs battery management system 4 to connect the power battery line The total positive and total negative relays are connected to complete high-voltage power-on.
[0040] Step 3: After the vehicle control unit 1 detects the charging signal from the battery management system 4, it enters the charging mode, closes the AC charging relay of the on-board charger 2, and the power battery completes precharging.
[0041] Step 4: The vehicle control unit 1 obtains the temperature T of the power battery 5 from the battery management system 4, and determines whether the temperature T is less than or equal to 5°C; if not, enter the normal charging mode; if so, then the battery management system 4 Send low-temperature heating demand 1 to the vehicle control unit 1. The vehicle control unit 1 starts timing when it receives the low-temperature heating demand 1, and detects the fault that affects charging within t seconds. If there is a fault, it will enter the power-off process. If there is no fault, it will enter the low temperature charging and heating mode.
[0042] Step 5: In the low-temperature charging and heating mode, the battery management system 4 sends the AC charging demand voltage, the AC charging demand current and the high-voltage output enable signal 1 to the on-board charger 2 and calculates the maximum allowable charging power; the vehicle control unit 1 judges The current temperature T. If the temperature T is less than or equal to 0°C, the vehicle control unit 1 instructs the battery management system 4 to control the charging current of the power battery to 0, instructs the thermal management system 7 to control the PTC heater for heating, and instructs the battery management system 4 to control The fan relay in the fan module 9 is turned on, the fan works, and blows the heat generated by the PTC heater into the battery pack; if the temperature T is greater than 0°C and less than or equal to 5°C, the vehicle control unit 1 instructs the battery management system 4 to control the power battery Charge the small current with a current of 0.1C, instruct the thermal management system 7 to adjust the power of the PTC heater 8 for heating, and instruct the battery management system 4 to control the fan relay in the fan module 9 to turn on, the fan works, and the PTC heater 8 is generated In the process, the battery management system 4 always detects whether the charging current exceeds the limit of 0.1C. If the current exceeds 0.1C and continues for 2S, it will report a charging overcurrent level three fault and enter the power-off Process.
[0043] Step 6: The battery management system 4 always detects the temperature T of the power battery 5. If it detects that the temperature T of the power battery 5 is less than or equal to 5°C, repeat step 5; if it detects that the temperature T of the power battery is greater than 5°C, send a low temperature The heating demand 0 is sent to the vehicle control unit 1, and the vehicle control unit 1 sends the maximum allowable charging power of 0W to the on-board charger 2 and exits the low-temperature charging heating mode command 1, and instructs the thermal management system 7 to control the PTC heater to disconnect and stop For heating, the battery management system 4 is instructed to control the fan relay in the fan module 9 to disconnect, and the fan stops working. At the same time, the power management system 4 sends the on-board charger 2 AC charging demand voltage 0V, AC charging demand current 0A, high voltage output enable Signal 0 and maximum allowable charging power 0W, exit the low temperature heating mode, and enter the normal charging mode.
[0044] In the normal charging mode, if the vehicle control unit 1 detects that the temperature T of the power battery is less than or equal to 5°C, it re-enters the low-temperature charging and heating process.
