Xin Geng with adviser P.T. Krein
Standard pulse-width modulation (PWM) provides the internal actuation for most control schemes for both dc-dc and dc-ac converters. Switching signals generated by standard PWM techniques are rich in harmonics, which may cause detrimental effects to the converter’s working environment. The concept of modifying harmonic characteristics of PWM signals to meet various design objectives is referred to as “spectrum management” (Figure 26). In this project, a few attempts were made to address basic challenges in this area.
First, double Fourier integral analysis was used as the main tool for design and analysis of spectrum-management techniques. The concept of modifying function was introduced to characterize the mathematical nature of spectrum management. In particular, explicit designs were obtained for the purpose of selective harmonic elimination and electromagnetic interference suppression. Then, a new scheme called predistorted PWM was proposed. It has the capability to provide high-quality switching signals with guaranteed performance in both time and frequency domains. Finally, a simple mathematical framework for frequency-modulated PWM (FM-PWM) was proposed using the concept of phase-modulating function. Connection between the modifying function in the double Fourier integral and the phase-modulating function in FM-PWM was established such that a solid basis for the design of modulation profiles for different spectrum-shaping tasks was provided. Otherwise one has to rely on empirical observations and experiments.
The ultimate goal of spectrum-management technology is to provide the designer the ability to specify a desired harmonic spectrum and then to realize it using a proper modulation scheme. The work brings us closer to understanding how to execute this challenging but important procedure.