麦慧敏

摘 要：某电动汽车车载充电机在充电过程中出现自动中断充电故障，反复验证3次均复现故障，每次充电时间10-30min不等。通过调查，发现充电机内部导热胶在温度上升后对滤波薄膜电容引脚产生应力，拉脱其引脚，使滤波电路失效产生EMI干扰，导致BMS采样精度紊乱（采集到充电电流超过阈值）发出停止充电指令。随后，通过增加引脚塑封、增大散热量的措施，可以有效解决该问题。

关键词：充电中断 热胀冷缩 EMI

Analysis and Optimization of the Automatic Interruption of Charging of a Vehicle-Mounted Charger

Mai Huimin

Abstract：An electric vehicle on-board charger has an automatic interruption of charging failure during the charging process. It has been repeatedly verified that the automatic interruption occurs 3 times， and the charging time varies from 10 to 30 minutes. Through investigation， it is found that the thermal conductive glue inside the charger will stress the pin of the filter film capacitor after the temperature rises， the pin is pulled off， the filter circuit failure is made and EMI interference is caused， resulting in disorder of BMS sampling accuracy （collected charging current exceeds the threshold）， which send the stop-charging command. Subsequently， the problem can be effectively solved by increasing the plastic encapsulation of the pins and increasing the amount of heat dissipation.

Key words：charging interruption， thermal expansion and contraction， EMI

1 引言

车载充电机（OBC）是固定安装在电动汽车上用于控制和调整蓄电池充电的电能转换装置，由于大功率充放产生巨大的发热量。为降低对内部元器件寿命和性能的影响，要求高热量的电子器件/芯片/MOSFET等必须与五金铸模的壳体内壁接触，以有效实现热传递。国内企业早期采用壳体内部灌满导热胶的方案来实现热传递，该方式除了能快速导热外还起到各带电元器件间的绝缘防护作用。但由于导热胶的热胀冷缩，对内部元器件引脚的拉扯应力长期存在，从而破坏其引脚使功能失效。某车型的车载充电机曾出现过该失效模式，我们通过台架试验，对比出问题原因和措施效果，使问题得到改进。

2 问题描述

某车型车载充电机不能充电，装车复测3次，均出现自动中断充电，充电时间10min-30min不等。分别监控充电机、BMS的报文，充电机报文显示充电电流约为25A（与实际充电电流相符），但BMS报文显示约为65A。当在充电机输出线束上加上磁环时，BMS报文充电电流回归正常，充电机恢复充电功能，取消磁环后，故障复现。……