Effective EMI Suppression Procedure Using RL Snubbers for Automotive Brush Motor Systems

In automotive brush motor systems, there are two types of noise that cause electromagnetic interference (EMI) problems: brush noise from the brush motor and switching noise from the electronic control unit (ECU). Brush noise can be mitigated by installing an EMI filter into the brush motor. However, another EMI issue related to switching noise may arise due to LC resonance between the X capacitor of the EMI filter and the equivalent series inductance (ESL) of the power cables. The RL snubber is promising for resonance suppression because its components can be easily mounted on the ECU board, thus reducing EMI without necessitating many design process revisions. Furthermore, our proposed optimal design method for RL snubbers, based on circuit simulations, is applicable. This is because an automotive brush motor system equipped with an RL snubber can be represented by a simple equivalent circuit characterized by a third-order characteristic equation, meeting the requirements of our optimal design method. In this study, we introduced an implementation procedure for an RL snubber based on the optimal design method and tested it within the automotive brush motor system. The experimental results confirmed that the proposed implementation procedure is effective in designing RL snubbers that significantly suppress EMI in practical applications.