Study On Restraint Method On Electromagnetic Interference Of Electric Turn-Table System

With the development of science and technology, more and more electronic equipments are used in industrial production and common living, at the same time, the problems of Electromagnetic Compatibility (EMC) stand out plainly. In order to ensure the equipment and system not to produce harmful interference to other equipments, and ensure the electronic equipments could get the Electromagnetic Compatibility certificate for going to the market, people must analyze, forecast and restrain the electromagnetic interference.In this thesis, aimed at an electrical turn table system, measurements and analysis of its electromagnetic interference are presented, and conclusion is that the main interference source is the Pulse Width Modulate (PWM) inverter which is employed in the turn table system. The structure of the table and the circuit of the PWM inverter were analyzed, and the principle of the PWM inverter was illustrated, then the causes of its interference were found out: The differential mode (DM) EMI is due to the pulsating current from the fast switch and the common mode (CM) EMI is due to the high dv/dt charging and discharging the parasitic capacitor. The DM lumped equivalent circuit model is analyzed. A simple equivalent circuit is proposed to study the CM EMI. The parameters of passive element are measured by experiment. Time-domain and frequency- domain analysis are conducted to obtain CM current waveforms and noise spectra in 10 KHz~30MHz frequency range. The CM current is a decaying oscillatory waveform. The simulated CM EMI waveforms are compared with the actual experiments to verify the validity of the proposed model.In allusion to the conducted interference of the turn table system, firstly, effects of the noise source and the load impedances of the EMI filter on the insertion loss are discussed. Then noise source impedance is estimated by insertion loss method based on experiments. A method of designing EMI filter is proposed, which simplifies the design of EMI filter. Practical design examples including CM and DM EMI filter indicate that the EMI filter design method is simple and effective.According to the radiated interference of a turn table system, methods based...