Emc Study of an Automotive Application

Electromagnetic compatibility (EMC) has become an important area of electrical engineering in automotive industry. Testing standards and regulations imposed by governments and other agencies have forced companies to pay close attention to the electromagnetic properties of their products. Nedap Specials Automotive has developed and produced Sunroof Control Units (SCU) for more than 10 years. The SCU is assembled to build a sunroof system with a low-cost DC (Direct Current) motor and a sunroof structure, which are purchased from other suppliers. EMC is one of the most important concerns in the designing of SCU, because automotive products meet tighter EMC regulation, especially in the limitation for transient noise. On the other hand, with the adopting of Pulse Width Modulation (PWM) in a new product, additional electromagnetic interference (EMI) is gained, which even causes the EMI level of this product to go beyond the standard. To reach electromagnetic compatibility it is important to consider EMC in an early stage of design. That is, try to prevent a noise from occurring by optimizing crucial designable parameters. In this report, models of switch, relay, cable, motor and SCU are firstly developed in PSPICE so that the potential noise sources can be pointed out. Some models are validated by experiments. Our experience and the analysis and experiments described in this report show that the EMI is unwanted oscillatory current or voltage noise sources originated by transient. The transient may be opening and closure of switch, bouncing of relay, switching of MOSFET or commutation of motor, etc., and potential noise sources produced by transient will conduct and radiate interference to surrounding. Radiation models are constructed to find correlation between noise source and radiated emission. One model used in predicting radiated emission in low frequency has been presented and the condition for use is described. Experiences from former designs show that many designable parameters can determine how severely a transient causes EMI. Base on these validated models, the evaluation of designable parameters becomes feasibly. Unfortunately, changing some parameters makes benefit and disadvantage simultaneously in suppressing EMI which generated by different causes. Therefore, a compromise has to be found, and some configuration parameters that do not significantly affect EMI behavior can be discarded. Synthesis is done at last to get optimized configuration for designable parameters.