Design Of Active EMI Filter For DC Power Supplies

To solve the problem of electromagnetic interference (EMI) from the DC powersupply in electrical and electronic systems, this thesis studies in the working principle,design, simulation and experimental measurement of active EMI filter. With the newlyproposed interference cancellation principle, several active EMI filters applied in DCpower supply system are designed, manufactured and tested. The experimental resultsreveal that, compared with the existing method, these filters are more advantageous inlow-frequency noise attenuation.This thesis is divided into the following three parts:The first part introduces the research background, significance, domestic andinternational research progress, and also studies the classification of EMI filter, thesource and form of interference. The insertion loss of filter is analyzed and calculatedwith the network theory.The second part analyses four kinds of topologies of the EMI active filter for theDC power supply, and then advances the selecting principle of filter structures.According to the principle, the topology of current detection and compensation isselected to design the filter. With simulations, the filters are designed and analyzed. Thesimulation result and theoretical design are also compared in this part.In the third part, the frequency responses of the filter elements as well as theinfluence of the load impedances are investigated with the methods of theoreticalanalysis and simulation. Through the test of each transformer, the detecting modules aredesigned. Besides, this part studies the testing methods of active EMI filter for DCpower supplying system, which has also been applied to test the designed filters in theexperiments of this thesis. The experimental results show that the proposed filters aresuperior in inhibitory effect on noise in the low frequency band.