Reducing Electromagnetic Interference in DC-DC Converters with Chaos Control

Electromagnetic Interference (EMI) resulting from high rates of changes of voltage and current, impairing other devices’ performance and harming human being’s health, has become a major concern in designing direct current (DC-DC) converters for a long time due to the increasingly wide applications of various electrical and electronic devices in industry and daily life. Thus, the question of how to reduce the annoying, harmful EMI has to be faced by scientists and engineers. Normally, EMI is handled by appending a properly tuned filter to reduce it within low frequency bands, referring to conducted EMI, or dealt with by electromagnetic shielding when it is within high frequency bands, referring to radiated EMI. However, as a filter is restricted in a narrow frequency band, it is not applicable to a much broader EMI frequency band alone. Therefore, multiple filters should be employed, increasing the difficulty of design. In addition, the affixed filter circuits not only increase cost, but also imply an increase of size and weight, rendering a product to lack portability. Electromagnetic shielding is the process of limiting the penetration of electromagnetic fields into a space, by blocking them with a barrier made of conductive material. Typically, it is applied to enclosures, separating electrical devices from the ‘outside world ́, and to cables, separating wires from the environment, through which the cables run. Shielding is an effective but expensive solution for EMI suppression. Moreover, in practice there are many leak sources on the enclosures. Therefore, both approaches are not perfect solutions of EMI suppression. Due to the pseudo-random and continuous spectrum characteristics of chaos, more recently the EMI problem has been tackled by the spread spectrum approach employing chaos control. However, there exist two prominent problems still unsolved: one is that the ripples of the output waveforms are much bigger than those with periodically running DC-DC converters, degrading DC power supplies; and the other one is that the parameter design of DC-DC converters becomes difficult due to the variational frequency under chaos control. Trying to fight these two problems, this dissertation is to improve the conventional chaos control approaches and to propose some new strategies of chaos control for EMI suppression. Two kinds of control approaches will be proposed in this dissertation. One is a novel chaotic peak current mode control via parameter modulation, which cannot only reduce EMI but also suppress output ripples easily; the other one is to combine chaos control with the most important and common control method in DC-DC converter, i.e., pulse width modulation (PWM) control, to form a novel chaos-based PWM control, named chaotic PWM control. This chaotic PWM control has the advantages of being easy to design, of applicability in various DC-DC converters, and of flexibility to reach a trade-off between output ripple and EMI. Therein, the chaotic carrier plays a key rôle in generating chaotic signals, which is designed both in digital and analogue ways, providing two alternative choices for different applications in practice. Moreover, a chaotic soft switching PWM control is put forward, which combines soft switching with chaotic PWM due to the fact that the soft switching technique is to switch on and off at zero current or zero voltage to alleviate the high rates of changes of voltage and current, to reach a better effect for EMI reduction and to reduce the power loss as well. Furthermore, the proposed EMI control approaches are simulated and implemented in hardware. The experiments are of great significance to verify the theoretical results and simulations, especially for future marketing. To this end, some theoretical concerns about the calculation of the invariant density of a chaotic mapping in a peak current mode boost converter, parameter estimation, ripple estimation, and about stability analysis in a chaotic PWM DC-DC converter are also addressed in this dissertation, providing theoretical explanation and verification for the simulation and experimental results, and a guideline for systems design. Finally, one of the modern spectral estimation method, viz., the Prony method, is employed to replace the conventional fast Fourier transform in estimating the spectra of chaotic signals, providing more accurate results. Di sse r a tio n H ng Li