| Electromagnetic interference has been always a concern in electronic systems, in particular at the point of the power supply. It is known that DC/DC converters are the principle culprits in generating conducted noise interference due to the switching action of their MOSFET which is the main element of the DC to DC conversion that use Pulse Width Modulation techniques (PWM) to step-up or to step-down the input voltage to the desired output level. Passive filters have been a straightforward solution to overcome typical conducted electromagnetic interference (EMI) problems at the expense of space, weight and power losses that can be reflected in the final product. The objective of this project is to find an EMI filtering method which does not depend on the input parameters of the power supply such as current and voltage which have direct effect on the size and the weight of the product.; To overcome these constraints, an active EMI filter is proposed. The active EMI filter is based on the image of the noise current phase shifted by 180 degrees and injected back to the DC bus to cancel out the incident noise. However, the combination of the active and the passive filters shows a substantial attenuation of the conducted EMI emissions as compared to the passive filter only. Also, this combination contributes to an important reduction of the size and weight of the passive filter. A complete circuit including the DC/DC converter has been designed and tested. Experimental results to demonstrate the performance and the effectiveness of the active EMI filter in DC/DC converters are presented. |
