Insulation monitoring method of high-voltage system
of new energy vehicles
In vehicle-mounted systems, insulation monitoring is usually carried out by methods such as electrical monitoring, physical monitoring, and low-frequency signal injection. That is, through sensors and monitoring modules installed at key nodes, insulation resistance and leakage current are detected in real time or periodically. Once the relevant parameters are detected to be lower than the threshold, the system will immediately trigger a warning or even cut off the high-voltage power supply to protect the safety of the vehicle and occupants. Several conventional monitoring methods are introduced as follows:
1. Leakage current monitoring
The principle is to monitor the current between the high-voltage system and the ground (vehicle body). Any unexpected current flow (i.e., leakage current) indicates that there may be poor insulation. Under normal circumstances, the leakage current of the high-voltage system to the ground should be very small. When the leakage current exceeds the set threshold, it is considered that there is a problem with the insulation.
In the actual implementation process, a current sensor is integrated into the BMS or other high-voltage control unit. By real-time monitoring of the current in the high-voltage circuit, especially the current flowing to the ground, the software analyzes these data through an algorithm and compares them with the preset safety standards to determine whether there is an abnormality.
2. Insulation resistance monitoring
The insulation resistance value of the key parts of the high-voltage system is measured regularly or under specific conditions to evaluate the insulation performance.
3. Low-frequency signal injection method monitoring
This detection method is an efficient high-voltage insulation monitoring technology. Its working principle is to inject a low-frequency AC signal of tens of hertz to hundreds of hertz into one end of the high-voltage circuit (such as the positive or negative electrode of the high-voltage battery), and set a monitoring point at the other end (such as the chassis or ground). When the injected low-frequency signal passes through the high-voltage circuit, if the insulation performance of this circuit is good, the attenuation of this signal is very small, but if there is an insulation defect or leakage path in the circuit, the signal will leak to the ground along this path, resulting in a weakened signal strength reaching the monitoring point. During the process, the magnitude of the insulation impedance can be calculated by measuring the amplitude, phase change or frequency response of the signal in the loop, and by comparing the preset safety threshold of the system, when the detected signal attenuation or the calculated insulation impedance is lower than this threshold, the system will trigger an alarm to indicate the existence of an insulation fault.
Based on the above principle, the specific implementation process can be to use a dedicated signal generator to generate a low-frequency AC signal, and inject it into the high-voltage system through an isolation coupler, and set a high-precision current or voltage sensor at the other end of the loop to collect the signal, and optimize the signal quality through the signal conditioning circuit for subsequent analysis, and then convert the analog signal into a digital signal through an A/D converter, and digitally process it by an MCU or an application-specific integrated circuit (ASIC), to calculate parameters such as signal attenuation and phase shift, and then estimate the insulation impedance. Finally, the insulation state is judged by comparing the analysis results with the preset standards. If a problem is found, the corresponding safety strategy is implemented.
In addition to the conventional insulation monitoring methods mentioned above, driven by intelligence, in order to better monitor insulation safety, in some more advanced systems, temperature sensors and humidity sensors are also used to monitor the surrounding environment of the high-voltage system (because environmental factors may affect insulation performance, such as high temperature or high humidity environments. The performance of insulation materials will decrease). By combining this parameter, a more detailed assessment of the insulation condition of the high-voltage system can be further performed.
