The Research To Reduce EMI Level Of Switched-mode Power Supply By Controlling Chaos

To reduce EMI level of switched-mode power supply by controlling chaos is studied in this thesis. With investigating how EMI occur in the switched-mode power supply circuits and what the chaos characteristic is of nonlinear system, three kinds of methods to reduce EMI level of switched-mode power supply based on chaos are presented. The following is the main work of this thesis:1. We take the peak current controlled DC/DC boost converter as an example. We compare and analyze power spectrum of input inductance current quantitatively of chaotic operation and periodic operation of converter. The computer simulation results demonstrate that power spectrum of input current has lower peak of power spectrum of chaotic operation than it of periodic operation, and then EMI level is reduced.2. On the base of chaos inherent in the switched-mode power supply the idea is present to uses controlling parameters to change the state of the circuit to reduce EMI level. We take current-controlled DC/DC Boost converter with feedback as a computer simulation example and explain the mechanism; the simulation results demonstrate that by making use of chaos inherent in DC/DC Boost converter and controlling parameters we can reduce EMI level of the switched-mode power supply without any additional circuits being involved.3. We add simple minimal input current controlling circuit to traditional peak current controlled DC/DC boost converter to make the converter with the minimal and maximal input current controlled at the same time. With comparing and analyzing the input current and output voltage oftraditional and the new converter circuits, we draw a conclusion that thenew converter could be used to reduce peak in low power spectrum scope under the switch frequency and reduce EMI level also. 4. From the conclusion that the switched-mode power supply of chaotic operation could be used to reduce EMI, we use the famous OGY method to control the DC/DC boost converter and adjust it to operate on chaos state with output voltage demanded; and then EMI level is reduced.