Power battery system: introduction of insulation monitoring principle and detection method
The power battery system is a vehicle-mounted high-voltage electrical system that provides energy absorption, storage and supply for electric vehicles. Safety problems may occur during the start, operation and stop of electric vehicles. To ensure the safe operation of the power battery system, Active monitoring and protection of the battery system is required. Commercial Elevator,Commercial Elevators,Building Passenger Elevator,Golden Commercial Elevators APSL ELEVATOR TECHNOLOGY(SUZHOU) CO.,LTD. , https://www.fujiapsl.com
(I) Insulation monitoring function principle <br> Under normal operating conditions, the electric vehicle power system is an independent system that is completely insulated from the vehicle housing, but does not rule out the insulation caused by aging or damp of high voltage lines after long-term vehicle operation. The vehicle body is charged and the vehicle operating conditions are complicated, and the vibration, temperature and humidity are drastically changed, and the acid and alkali gas corrosion causes damage of the insulating layer, so that the insulation performance is degraded. Monitoring the insulation performance in real time is of great significance to ensure the personal safety of the personnel and the safe operation of the vehicle.
GB/T 18384.3-2015 personnel electric shock protection defines the maximum working voltage is less than or equal to 60V power components for the A-level voltage level, the maximum operating voltage is greater than 60V power components for the B-level voltage level, for the B-class power components must meet enough Insulation resistance (Ri ≥ (Vb * 500 Ω / V)). In the GB/T 18384.1-2015 vehicle-mounted rechargeable energy storage system, it is stipulated that the BMS needs to perform insulation detection under the condition that all components of the power battery system are integrated, and the insulation resistance value is used to measure the insulation state. The insulation resistance can be divided into total positive ground and total negative ground. The system insulation state Ri is generally taken as the minimum between the two.
　
Figure 1. Principle of Insulation Resistance Measurement <br> At present, BMS mainly adopts the measurement method recommended by the national standard, as shown in Figure 1. Rx is the HV+ ground resistance, Ry is the HV-to-ground resistance, and R1 and R2 are the standard resistances for the known resistance values. The measurement method is as follows:
Step 1: Close S1, disconnect S2, collect U1 point voltage and total pressure U;
Step 2: Close S2, disconnect S1, collect U2 point voltage and total pressure U;
The equation Rx=(U*R2-(R1+R2)*(U1+U2))/U1; Ry=(U*R2-(R1+R2)*(U1+U2))/U2 can be obtained and substituted into U1. U2, R1, R2, and total pressure U can solve Rx and Ry through the equation. The insulation resistance of the power battery system takes a small value between Rx and Ry.
(2) Detection factor <br> The size of the insulation resistance is changed by the form of series resistor. When the insulation resistance is less than the standard value, it can detect whether the BMS can measure the insulation fault. When the insulation resistance is greater than the standard value, it is detected whether the BMS is insulated. False alarm of the fault.
(III) Detection method <br> The detection principle of insulation monitoring is shown in Figure 2. The detection method is as follows:
1. Connect a 420kΩ resistor between HV+ and ground. The battery system switches to the operating state. The BMS does not recognize the insulation fault. The insulation resistance between HV+ and ground = 420kΩ 5%. Between HV- and ground. The resistance value is 2500KΩ. The battery system switches to the standby state.
2. Connect a second resistor between HV- and ground, with a resistance of 380 kΩ. The battery system switches to the operating state. The BMS recognizes the insulation fault. The insulation resistance between HV+ and ground = 420kΩ 5%. HV- and ground. The insulation resistance value between = 380kΩ 5%.