Research On Optimizing Chaotic Modulation Signals To Reduce EMI Of SMPS

In this thesis, the effect on reducing the level of EMI of SMPS is discussed from different aspects. The results supply references to the optimization of chaotic sources that generate chaotic switching modulation signals. The main work of this thesis is presented as follows:1. Based on simply introducing traditional methods of improving EMC and reducing EMI, the characteristics of random switching modulation technique are summarized and the research development of applying chaotic theory to reducing EMI of SMPS is reviewed. The train of thought of study is provided.2. The effect of chaotic switching modulation signals of different chaotic characters on reducing the level of EMI is analyzed. Using a fourth-order capacitance circuit which can generate chaotic, sub-hyperchaotic and hyperchaotic signals as signal source, the power spectrums of the input current and the output voltage of Boost DC/DC converter controlled by chaotic switching modulation signals is compared with those controlled by classical PWM. Simulation results demonstrate that any character of chaotic modulation signal or any chaotic modulation scheme can reduce the level of EMI of Boost DC/DC converter, and different chaotic modulation schemes or different characters of chaos sequences have different effects on reducing EMI. The higher the chaotic level of chaos signal is, the better the effect on reducing the level of EMI.3. The effect on reducing EMI of SMPS controlled by chaotic switching modulation signals of different chaotic sources is also analyzed. Using Chua's circuit, Lorenz system, Rossler system and the fourth-order capacitance circuit as chaotic signal sources, the effects of different chaotic sources on reducing EMI are compared. The power spectrums of the input current and the output voltage of the normalized chaotic series modulated by different chaotic sources under the same switching modulation scheme is analyzed. Simulation results demonstrate: the chaotic modulation signals generated from the four kinds of chaotic sources can all reduce the peak level of the input current and the output voltage spectrums. Different chaotic signals have different effects. As far as chaotic sources are concerned, theeffect of Lorenz system on reducing the level of EMI is better than the others. 4. The effect of the value of Lyapunov exponents with the same chaotic character on reducing the level of EMI is discussed. Methods for computing the positive Lyapunov exponents are introduced first. The computation program is written, and the results of Chua's circuit, Lorenz system, Rossler system and the fourth-order capacitance circuit are listed. Then, the effect of the value of Lyapunov exponents on reducing the level of EMI is analyzed in two aspects. One aspect is analyzing the effect of the value of Lyapunov exponents of different chaotic signal sources. The other is analyzing the effect of Lyapunov exponents of the same chaotic signal. Study results demonstrate that the larger the positive Lyapunov exponent of the chaotic system is, the better the effect on reducing the level of EMI of SMPS controlled by chaotic modulation signal.