Research To Reduce EMI Of SMPS Based On Chaotic Switching Modulation Technique

In this thesis ,based on chaotic switching signal modulation ,we study the effect on reducing EMI of SMPS. The work of this thesis is presented as follows:1. The idiographic measure which can improve EMC of SMPS have been summarized. Passive measure include :filter ,fielding , earthing ,bypass, decoupling etc. Positive measure have resonant switching modulation (include soft switching modulation), random switching modulation and chaotic switching modulation which be studied in this thesis.2. The characteristics of stochastic and chaotic signals have been studied. Taking Chua's circuit as signal source , all kinds chaotic signal sequence can be obtained in computer. Correlation characteristic of chaotic sequences have been studied. It demonstrate that chaotic sequences have the same characteristics as chaotic signal .Replaced the random signals with chaotic signals,all kinds chaotic switching modulation mode can be obtained.3. Chaotic switching signal obtained from Chua's circuit was used to control Buck DC/DC converter. By compared the power spectrum of input current between chaotic modulations and classical PWM, it demonstrate that chaotic switching modulations have good effect on spreading power spectrum , which can be used to reduce the level of EMI and to improve EMC of SMPS. Chaotic switching modulations introduce low-frequency harmonic spectrum of output voltage as random switching modulation .In some case , low-frequency noise ripple offset the effect chaotic switching modulations reduce the level of EMI .It indicates that the CCFMFD integrates the advantages of spreading harmonic power at the multiples of the switching frequency and not introducing significant noise ripple at low-frequency range .Among all chaotic switching modulations, the CCFMFD is considered as the best choice in applying to DC/DC converter.4. Chaotic switching modulation signals generated from different chaos sequences have been used to control SMPS .The effect of reducing the level of EMI be compared .Simulation results demonstrate : in the CPWM and CPPM ,chaos sequences generated from Henon map is superior to the one generated from Chua's circuit at lower multiples of switching frequency on reducing the level ofEMI; in the CCFMFD, it has contrary results ;in the CCFMVD ,chaos sequences generated from Chua's circuit is superior to the one generated from Henon map. Chaotic switching modulations generated from different chaos sequences introduce low-frequency output noise ripple: in the CPWM,CPPM and CCFMVD ,the output noise ripple introduced by Henon map chaos sequences is smaller than Chua's circuit chaos sequences; in the CCFMFD, Chua's circuit chaos sequences introduced smaller noise ripple .This clue to us that it is important to choose chaos sequences in applying chaotic modulation to DC/DC converters.