Research On The Electromagnetic Interference Testing Methods For Automotive Generator

With the rapid development of electronic technology and automotive industry, more and more electronic equipments are used in vehicles. They have greatly improved comfort and security in the vehicle, but at the same time the electromagnetic compatibility problem in the vehicle's electrical system is also becoming increasingly prominent. As an important part of the vehicle's power system, the generator provides power to other equipments, and its electromagnetic compatibility has direct and important influence on their normal operation. Therefore, study on electromagnetic compatibility of vehicles has quite significant theoretical and engineering value. Sponsored by Project 097------Key Technology Study on Electromagnetic Compatibility in Cars(NO:10111613)of China South Industries Group Corporation, this paper discusses the formation mechanism and testing techniques of electromagnetic interference in automotive generators. The contents are as follows:First, through literature research and study on domestic and foreign documents, the main content, methods, and current foreign research level of automotive electromagnetic compatibility are discussed. On this basis, there is a focused discussion on the significance and the main contents of electromagnetic compatibility research in automotive generators.Second, the working principle of the automotive generator and sources of electromagnetic interference have been studied. It is pointed out that electromagnetic interference forms during the automotive generator's rectification, voltage regulating, and load dumping process; the generator rectifier commutation process generates a lot of DC interference; moreover, as the alternator adjuster's power adjustment is transient, self-induced electromotive force of varied frequency and peak value forms in the coil. In addition, intentional or unintentional disconnection with the battery due to cable corrosion, bad connection, or normal engine operation causes a transient load-dump phenomenon of output voltage increase in the generator.Third, electromagnetic interference of the generator has significant influence on the normal performance of sensitive equipments and systems in the vehicle. It also has a significant impact on the passing of laws pertaining to vehicle electromagnetic compatibility. Therefore, by analyzing the formation mechanism of electromagnetic interference in generator-rectifier system, it is pointed out that the electromagnetic interference in the DC rectifier mainly forms when there is a voltage jump caused by silicon diode switching during the commutation process; and a formula to calculate electromagnetic conduction and radiation is derived.Fourth, taking into account factors such as changes in engine speed and electrical load, the complex electromagnetic environment inside the vehicle etc., it is unlikely to accurately test the generator's electromagnetic disturbance characteristics in vehicles. Moreover, the generator test bench is usually dragged by electric motors. During operation they form a strong electromagnetic interference which needs to be shielded, and yet this shielding is quite difficult to realize. For the above reasons, generator test bench dragged and adjusted by air motor is designed. Generator's electromagnetic interference conduction and radiation has been tested. Generator's transient voltage during load dump has been tested and analyzed.